2010 Vol. 34, No. 9
One of the most fascinating challenges facing modern strong interaction physics is to understand the origin of the spin of the nucleon in terms of the spin and orbital angular momentum of the quarks and gluons. We review recent progress on this problem as well as some of the uncertainties associated with state of the art lattice QCD simulations. In particular, we explain the importance of the corrections associated with chiral extrapolation and finite volume corrections, especially for the term B(0) extracted from the appropriate low moment of the deeply virtual Compton scattering amplitude.
In the last years many states in the charmonium mass region were discovery by BABAR, Belle and CDF collaborations. I discuss some of these discoveries, and how the QCD Sum Rule approach can be used to understand the structure of these states.
Isospin violation is driven through the light quark mass difference and electromagnetic effects. I review recent progress in extracting the light quark mass difference and tests of the chiral dynamics of Quantum Chromodynamics in various reactions involving light as well
as heavy quarks.
Coupled-channel KN dynamics near threshold and its repercussions in few-body K-nuclear systems are briefly reviewed, highlighting studies of a K－pp quasibound state. In heavier nuclei, the extension of mean-field calculations to multi-K nuclear and hypernuclear quasibound states is discussed. It is concluded that strangeness in finite self-bound systems is realized through hyperons, with no room for kaon condensation.
Employing an approach based on the Green functions of Landau-gauge QCD, some selected results from a calculation of meson and baryon properties are presented. A rainbow-ladder truncation to the quark Dyson-Schwinger equation is used to arrive at a unified description of mesons and baryons by solving Bethe-Salpeter and covariant Faddeev equations, respectively.
We report the progress on understanding some of those existing puzzles in charmonium decays. We show that the intermediate meson loops (IML) as a long-distance transition mechanism will provide novel insights into these issues. In particular, we show that the
IML mechanism would be essentially important for understanding the ψ(3770) non- DD decays. We also comment that such a mechanism is correlated with the Okubo-Zweig-Iizuka (OZI) rule evasions in charmonium hadronic decays.
We discuss a possible interpretation of the open charm mesons Ds0*(2317), Ds1(2460) and the hidden charm mesons X(3872), Y(3940) and Y(4140) as hadron molecules. Using a phenomenological Lagrangian approach we review the strong and radiative decays of the Ds0*(2317) and Ds1(2460) states. The X(3872) is assumed to consist dominantly of molecular hadronic components with an additional small admixture of a charmonium configuration. Determing the radiative (γJ/ψ and γψ(2s)) and strong (J/ψ 2π and J/ψ 3π) decay modes we show that the present experimental observation is consistent with the molecular structure assumption of the X(3872). Finally, we give evidence for molecular interpretations of the Y(3940) and Y(4140) related to the observed strong decay modes J/ψ+ω or J/ψ+φ, respectively.
I discuss several recent highly accurate theoretical predictions for masses of baryons containing the b quark, especially Ωb (ssb) very recently reported by CDF. I also point out an approximate effective supersymmetry between heavy quark baryons and mesons and provide predictions for the magnetic moments of Λc and Λb. Proper treatment of the color-magnetic hyperfine interaction in QCD is crucial for obtaining these results.
We review the recent experimental results on hadron spectroscopy from B-factories focusing on the exotic charmonium-like states. Among them we discuss the X(3872), Y(3940), Z(4430)+, Z(4050)+, Z(4250)+ and Y(4140) states found in B-meson decays, the X(3940) and X(4160) states produced in double charmonium production, the Y(4260), Y(4325), Y(4660) and X(4630) states produced with initial-state radiation in e+e－ annihilation and the X(3915), Y(4350) states observed in two-photon collisions.
While several experiments based on the Drell-Yan process have revealed the presence
of light antiquarks in the proton, the experimental signatures for strange quark components remain consistent with 0. Phenomenological studies of meson photoproduction on nucleons with hadronic models indicate that the underprediction of the NΔ transition strengths by the three quark model may be attributed to the missing ``meson cloud" contributions. If qqqqq configurations are included in the baryon wave functions the conclusions that emerge are that (a) a combination of at least three different qqqqq configurations are required for a satisfactory description of the nucleon properties and (b) that the vanishing of the axial form factor of the N(1535) resonance is a natural consequence of the cancellation of the contributions of the qqq and qqqqq configurations.
Production and properties of φ-meson under the extreme hot dense matter which is formed in Au+Au collisions at RHIC energy have been briefly reviewed. The issues are focused on transverse momentum (pT) spectra of φ, elliptic flow of φ, nuclear modification factor of φ, the ratio of Ω(pT)φ(pT) versus pT, the ratio of Ω(pT/3)/φ(pT/2) versus pT/nq, spin alignment of φ and the enhancement of φ etc. These observables give the significant information of the strange quark dynamics in hot dense matter under the extreme condition.
We overview two interconnected topics: possible effective restoration of chiral symmetry in highly excited hadrons and possible existence of confined but chirally symmetric matter at low temperatures and high densities.
The η meson can be bound to atomic nuclei. Experimental search is discussed in the form of final state interaction for the reactions dp→3Heη and dd→4Heη. For the latter case tensor polarized deuterons were used in order to extract the s-wave strength. For both reactions complex scattering lengths are deduced: a3Heη=[±(10.7±0.8－0.5 +0.1)+i.(1.5±2.6－0.9+1.0)] fm and a4Heη=[±(3.1±0.5)+i.(0±0.5)] fm. In a two-nucleon transfer reaction under quasi-free conditions, p27Al→^3HeX, was investigated. The system X can be the bound 25Mg⊙η at rest. When a possible decay of an intermediate N*(1535) is required, a highly significant bump shows up in the missing mass spectrum. The data give for a bound state a binding energy of 13.3±1.6 MeV and a width of σ=4.4±1.3 MeV.
Studying nucleon-nucleon (NN) correlated pairs will teach us a great deal about the high momentum part of the nuclear wave function, the short range part of the NN interaction, and the nature of cold dense nuclear matter. These correlations are similar in all nuclei, differing only in magnitude. High momentum nucleons, p > pfermi, all have a correlated partner with approximately equal and opposite momentum. At pair relative momenta of 300 < prel < 500 MeV/c, these correlated pairs are dominated by tensor correlations. This is shown by the dominance of pn over pp pairs at pair total momentum and by the parity of pn to pp pairs at large pair total momentum.
The combination of Anti-de Sitter space (AdS) methods with light-front holography leads to a semi-classical first approximation to the spectrum and wavefunctions of meson and baryon light-quark bound states. Starting from the bound-state Hamiltonian equation of motion in QCD, we derive relativistic light-front wave equations in terms of an invariant impact variable ζ which measures the separation of the quark and gluonic constituents within the hadron at equal light-front time. These equations of motion in physical space-time are equivalent to the equations of motion which describe the propagation of spin-J modes in anti—de Sitter (AdS) space. Its eigenvalues give the hadronic spectrum, and its eigenmodes represent the probability distributions of the hadronic constituents at a given scale. Applications to the light meson and baryon spectra are presented. The predicted meson spectrum has a string-theory Regge form M2 = 4κ2(n+L+S/2 ); i.e., the square of the eigenmass is linear in both L and n, where n counts the number of nodes of the wavefunction in the radial variable ζ. The space-like pion and nucleon form factors are also well reproduced. One thus obtains a remarkable connection between the description of hadronic modes in AdS space and the Hamiltonian formulation of QCD in physical space-time quantized on the light-front at fixed light-front time τ. The model can be systematically improved by using its complete orthonormal solutions to diagonalize the full QCD light-front Hamiltonian or by applying the Lippmann-Schwinger method in order to systematically include the QCD interaction terms.
We report on new attempt to investigate baryon-baryon interactions in lattice QCD. From the Bethe-Salpeter (BS) wave function, we have successfully extracted the nucleon-nucleon (NN) potentials in quenched QCD simulations, which reproduce qualitative features of modern NN potentials. The method has been extended to obtain the tensor potential as well as the central potential and also applied to the hyperon-nucleon (YN) interactions, in both quenched and full QCD.
The mass pattern of nucleon and Δ resonances is compared with predictions based on quark models, the Skyrme model, AdS/QCD, and the conjecture of chiral symmetry restoration.
Results are presented from the HERMES experiment which uses semi-inclusive deep inelastic lepton scattering to study the flavor structure of the nucleon. Data have been accumulated for pion and kaon double spin asymmetries, single-spin azimuthal asymmetries for meson electroproduction, deep virtual Compton scattering (DVCS), and meson multiplicities. These results provide information on the properties of the strange sea in the proton, constraints on transverse momentum dependent quark parton distributions, and demonstrate the promise of DVCS for isolating the total angular momentum carried by the quarks in the proton.
After the end of data taking in 2007, the experiments H1 and ZEUS have entered into an intense phase of data analysis. Recent results of this effort on neutral (NC) and charged current (CC) cross sections at high Q2, the longitudinal structure function FL, inclusive diffraction, heavy flavour production and on searches for glueballs are presented. Also shown are results of a combined analysis on inclusive NC and CC cross sections performed by H1 and ZEUS using HERA-I data.
We have held an inauguration ceremony of the Japan Proton Accelerator Research Complex (J-PARC) on July 6, 2009, celebrating the completion of its construction. Now, the beam commissioning of the 50 GeV main proton synchrotron is in progress to improve the beam intensity and quality. A lot of important experimental programs in Nuclear Physics are waiting for the beam. In this report, I introduce some examples.
Selected results from experiments at COSY-Julich are presented: an attempt to measure the mass of the η meson with high precision (ANKE facility), first steps towards the detection of rare η decays (WASA), and several measurements of KK-pair production (ANKE, COSY-11, MOMO).
The Compass experiment at CERN is studying the nucleon spin structure with a 160 GeV polarized muon beam and polarized targets as well as hadron structure with 190 GeV pion, kaon and proton beams. The paper gives an overview of the results for the helicity and transverse spin structure of the nucleon. A first result from the spectroscopy experiments, the observation of a resonance with exotic JPC=1－+ quantum numbers at 1660 MeV is also presented. The paper ends with an outlook to future measurements.
Photoproduction of baryons with strangeness, such as the Ε (1385), Λ(1520) and possibly the Θ+, are described from measurements at the LEPS/SPring-8 facility in Japan. Linearly polarized photons in the energy range of 1.5—2.4 GeV, along with the forward-angle kinematics at LEPS, provide unique data to learn about these baryons, which are non-perturbative solutions of QCD.
Theoretical and computational advances have enabled not only the masses of the ground states, but also some of the low-lying excited states to be calculated using Lattice Gauge Theory. In this talk, I look at recent progress aimed at understanding the spectrum of baryon excited states, including both baryons composed of the light u and d quarks, and of the heavier quarks. I then describe recent work aimed at understanding the radiative transitions between baryons, and in particular the N-Roper transition. I conclude with the prospects for future calculations.
In this talk, I discuss our recent studies of three-hadron systems and the resonances found therein. The studies consist of solving Faddeev equations with the input two body interactions obtained from the chiral Lagrangians. The systems which we study are either
made of two mesons and a baryon or of three mesons. The motivation for these studies comes from the data on many baryon resonances, especially the ones with Jπ= 1/2+, which show a large branching ratio to the two meson-one baryon decay channels. In addition to this, several new studies at BES, BELLE, BABAR etc., claim the existence of new meson resonances which seem to couple strongly to three-meson systems, where mostly two out of the three mesons appear as a known resonance. Hitherto, we have studied two meson-one baryon systems with strangeness = －1, 0 and 1 and three-meson systems made of two-pseudoscalars and a vector meson.As we will show in this manuscript, we find many resonances which couple to three-hadrons.
We study charmonium (ccnn), bottomonium (bbnn) and exotic (ccnn and bbnn) four-quark states by means of a standard non-relativistic quark potential model. We look for possible bound states. Among them we are able to distinguish between meson-meson molecules and compact four-quark states.
We argue that the heavy quark spin symmetry can lead to important consequences for heavy flavor hadronic molecules. It can be used to predict new heavy flavor hadronic molecules and hence provides a method to identify the nature of some newly observed exotic hadrons. For example, if the Y(4660) were an S-wave ψ′f0(980) shallow bound state, then the mass, width and line shape of its spin partner are predicted.
If the number of colors Nc is taken large, baryons and their excitations can be considered in a mean-field approach. We argue that the mean field in baryons breaks spontaneously the spherical and SU(3) flavor symmetries, but retains the SU(2) symmetry of simultaneous rotations in space and isospace. The one-quark and quark-hole excitations in the mean field, together with the SU(3) rotational bands about them determine the spectrum of baryon resonances, which turns out to be in good accordance with reality when one puts Nc=3. A by-product of this scheme is a confirmation of the light pentaquark Θ+ baryon uudds as a typical Gamov—Teller resonance long known in nuclear physics. An extension of the same large-Nc logic to charmed baryons leads to a prediction of a anti-decapenta (15)-plet of charmed pentaquarks, two of which, B++c=cuuds and B+c= cudds, may be light and stable with respect to strong decays.
Light hadron spectroscopy is a powerful tool in hadronic physics. Several recent BES results on hadron spectroscopy are reported in this proceeding, including the confirmation of the enhancement in pp invariant mass in radiative J/ψ decays, the observation of a charged κ± decaying to K±π0 and the measurement of exclusive decays of the χc0 and χc2 to π0π0 and ηη.
We review some recent progress in our understanding of the lowest-lying spin-1/2 and spin-3/2 baryon magnetic moments (MMs) in terms of Chiral Perturbation Theory (ChPT). In particular, we show that at next-to-leading-order ChPT can describe the MMs of the octet
baryons quite well. We also make predictions for the decuplet MMs at the same chiral order. Among them, the MMs of the Δ++ and Δ+ are found to agree well with data within the experimental uncertainties.
The prevailing theoretical quark and gluon momentum, orbital angular momentum and spin operators, satisfy either gauge invariance or the corresponding canonical commutation relation, but one never has these operators which satisfy both except the quark spin. The
conflicts between gauge invariance and the canonical quantization requirement of these operators are discussed. A new set of quark and gluon momentum, orbital angular momentum and spin operators, which satisfy both gauge invariance and canonical momentum and angular momentum commutation relation, are proposed. To achieve such a proper decomposition the key point is to separate the gauge field into the pure gauge and the gauge covariant parts. The same conflicts also exist in QED and quantum mechanics, and have been solved in the same manner. The impacts of this new decomposition to the nucleon internal structure are discussed.
The positive parity scalar Ds0*(2317) and axial-vector Ds1*(2460) charmed strange mesons are gene-rated by coupled-channel dynamics through the s-wave scattering of Goldstone bosons off the pseudoscalar and vector D(Ds)-meson ground states. The specific masses of these states are obtained as a consequence of the attraction arising from the Weinberg-Tomozawa interaction in the chiral Lagrangian. Chiral corrections to order Qχ2 are calculated and found to be small. The Ds0*(2317) and Ds1*(2460) mesons decay either strongly into the isospin-violating π0Ds and π0Ds* channels or electromagnetically. We show that the π0-η and (K0D+-K+D0) mixings act constructively to generate strong widths of the order of 140 keV and emphasize the sensitivity of this value to the KD component of the states. The one-loop contribution to the radiative decay amplitudes of scalar and axial-vector states is calculated using the electromagnetic Lagrangian to chiral order Qχ2. We show the importance of taking into account processes involving light vector mesons explicitly in the dynamics of electromagnetic decays. The radiative width are sensitive to both ηDs and KD components, hence providing information complementary to the strong widths on the positive parity Ds-meson structure.
In this paper we calculate the equation of state (EOS) of QCD at zero temperature and finite chemical potential by using several models of quark propagators including the Dyson-Schwinger equations (DSEs) model, the hard-dense-loop (HDL) approximation and the quasi-particle model. The results are analyzed and compared with the known results in the
Any description of gluons requires a well-defined gauge. This is complicated non-perturbatively by Gribov copies. A possible method-independent gauge definition to resolve this problem is presented and afterwards used to study the properties of gluons at any temperature. It is found that only chromo-electric properties reflect the phase transition. From these the gauge-invariant phase transition temperature is determined for SU(2) and SU(3) Yang-Mills theory independently.
Quarks are proposed to be grouped together to make quark-clusters due to the strong interaction in cold quark matter at a few nuclear densities, because a weakly coupling treatment of the interaction between quarks there would be inadequate. Cold quark matter is then conjectured to be in solid state (i.e., forming a crystal structure) if the inter-cluster potential is deep enough to localize clusters in lattice. Such a solid state of cold quark matter would be very necessary for us to understand different manifestations of pulsar-like compact stars, and could not be ruled by first principles.
We study the properties of charmed hadrons in dense matter within a coupled-channel approach which accounts for Pauli blocking effects and meson self-energies in a self-consistent manner. We analyze the behaviour in this dense environment of dynamically-generated baryonic resonances as well as the open-charm meson spectral functions. We discuss the implications of the in-medium properties of open-charm mesons on the Ds0(2317) and the predicted X(3700) scalar resonances.
A short overview over the ABC phenomenon is given, which is known since 50 years without any satisfactory explanation. On the basis of new exclusive and kinematically complete data obtained with the WASA detector at COSY we show that this phenomenon is linked with a resonant energy dependence in the total cross section of isoscalar double-pionic fusion processes. This resonance structure is connected with the baryon-baryon system, in particular with the pn and ΔΔ systems, however, has a mass, which is 90 MeV below the nominal ΔΔ threshold and a width of only 70 MeV, i.e., five times smaller than expected from a conventional t-channel ΔΔ scenario.
The role of Poincare covariant space-time translations is investigated in the case of a relativistic quantum mechanics approach to the pion charge form factor. It is shown that the related constraints are generally inconsistent with the assumption of a single-particle current, which is most often referred to. The only exception is the front-form approach with q+=0. How accounting for the related constraints, as well as restoring the equivalence of different RQM approaches in estimating form factors, is discussed. Some extensions of this work and, in particular, the relationship with a dispersion-relation approach, are presented. Conclusions relative to the underlying dynamics are given.
The effect of the two-photon exchange on the deuteron electromagnetic form factors is estimated based on an effective Lagrangian approach. A numerical estimate calculation of the effect is discussed. In particular, the effect on the polarization observables is analyzed.
The two highest precision determinations of αs(MZ2), that based on the analysis of short-distance-sensitive lattice observables, and that based on an analysis of hadronic τ decay data, have, until very recently, given results which are not in good agreement. I review new versions of these analyses which bring the two determinations into excellent agreement, and discuss prospects for additional future improvements.
Applying the AdS/CFT correspondence, the expansion of the heavy-quark potential of N=4 supersymmetric Yang-Mills theory at large Nc is carried out to the next-leading term in the large 't Hooft coupling at zero temperature. The strong coupling corresponds to the semi-classical expansion of the string-sigma model, the gravity dual of the Wilson loop operator, with the next-leading term expressed in terms of functional determinants of fluctuations. The singularities of these determinants are examined and their contributions are evaluated numerically. We find the next-leading order correction is negative and suppressed by minus square root of the 't Hooft coupling relative to the leading order.
One of the first measurements that will be made at the LHC by ATLAS deals with the
properties of inelastic collisions, namely the central charged particle density and transverse momentum distributions. Current predictions of these distributions have large uncertainties in the LHC energy range. We describe the ATLAS minimum bias triggers, designed to select all kind of inelastic interactions, and the performance of the track reconstruction software which was adapted to soft particle track reconstruction. The precision with which the minimum bias distributions can be measured with early data is presented and the uncertainties on the inelastic distributions due to trigger bias is discussed.
We study the semileptonic decays of the lowest-lying bc baryons to the lowest-lying cc baryons (Ξbc(′*)→Ξcc(*) and Ωbc(′*)→Ωcc(*)) , in the limit mb, mc>>ΛQCD and close to the zero recoil point. The separate heavy quark spin symmetries make it possible to describe all these decays using a single form factor. We also show how these constraints can be used to test the validity of different quark model calculations. bb to bc baryon decays are also discussed.
Recently, we have derived a two--nucleon potential and consistent nuclear electromagnetic currents in chiral effective field theory with pions and nucleons as explicit degrees of freedom. The calculation of the currents has been carried out to include N3LO corrections, consisting of two--pion exchange and contact contributions. The latter involve unknown low-energy constants (LECs), some of which have been fixed by fitting the np S- and P-wave phase shifts up to 100 MeV lab energies. The remaining LECs entering the current operator are determined so as to reproduce the experimental deuteron and trinucleon magnetic moments, as well as the np cross section. This electromagnetic current operator is utilized to study the nd and n3He radiative captures at thermal neutron energies. Here we discuss our results stressing on the important role played by the LECs in reproducing the experimental data.
Low-energy scattering of D*+ and D01 meson is studied using quenched lattice QCD with improved lattice actions on anisotropic lattices. The threshold scattering parameters, namely the scattering length a0 and the effective range r0, for the s-wave scattering in JP=0－ channel are extracted: a0=2.52(47) fm and r0=0.7(1) fm. It is argued that, albeit the interaction between the two charmed mesons being attractive, it is unlikely that they can form a shallow bound state in this channel. Our calculation provides some useful information on the nature of the newly discovered resonance-like structure Z+(4430) by the Belle Collaboration.
The fixed target COMPASS experiment at CERN offers the opportunity to search for exotic mesons and glueball candidates in the light quark sector with unprecedented statistics. Preliminary results from the 2008 data taken with an incoming negative hadron beam (190 GeV/c, mainly pions) on a liquid hydrogen target are presented. New detectors dedicated to hadron beam measurements have been added. These give access to rare neutral and kaonic channels. An amplitude analysis which will allow to fit simultaneously diffractively and/or centrally produced resonances will be described and compared with those used in the CERN WA102 and BNL E852 experiments.
The KLOE collaboration has recently published new results concerning scalar and pseudoscalar mesons. Here the φ→a0(980)γ→ηπ0γ decay analysis and the search for the φ→K0K0γ decay are discussed, together with the η→π+π－e+e－ decay measurements annd the new results for the pseudoscalar mixing angle and gluonium content of the η' meson.
ALICE, A Large Ion Collider Experiment, is dedicated to study the QCD matter at extreme high temperature and density to understand the Quark Gluon Plasma (QGP) and phase transition. High-transverse-momentum photons and neutral mesons from the initial hard scattering of partons can be measured with ALICE calorimeters, PHOS (PHOton Spectrometer) and EMCAL (ElectroMagnetic CALorimeter). Combing the additional central tracking detectors, the γ-jet and π0-jet measurements thus can be accessed. These measurements offer us a sensitive tomography probe of the hot-dense medium generated in the heavy ion collisions. In this paper, high pT and photon physics is discussed and the ALICE calorimeters capabilities of high-transverse-momentum neutral mesons and γ-jet measurements are presented.
The spectrum of Ds mesons is systematically studied in a semi-classic mass loaded flux tube model. Ds in D-wave multiplets is predicted to have lower masses in comparison with most theoretical predictions. DsJ(2632)+, Ds1(2700)±, D*sJ(2860)+ and DsJ(3040)+ are interpreted in the constituent quark model.
An understanding of the confinement mechanism in QCD requires a detailed mapping of the spectrum of hybrid mesons. Understanding confinement means understanding the role of
gluons and it is in hybrid mesons that the gluonic degrees of freedom are manifest. High statistics searches for such states with π and p beams have resulted in some tantalizing signals. There is good reason to expect beams of photons to yield hybrid mesons with JPC quantum numbers not possible within the conventional picture of mesons as qq bound states. Meager data currently exist on the photoproduction of light quark mesons. This talk represents an overview of the available data and what has been learned. In looking toward the future, the GlueX experiment at Jefferson Laboratory represents a new initiative that will perform detailed spectroscopy of the light-quark meson spectrum. This experiment and its capabilities will be reviewed.
Chiral effective field theory describes the interaction of nucleons and pions in the low-energy regime of QCD. This theory offers a consistent picture of nuclear forces and nuclear current operators. We study the electromagnetic processes based on ChEFT dynamical picture and compare our predictions to results obtained in the conventional framework. In particular, we consider low energy photo-disintegration of the deuteron at different orders of the chiral expansion. We investigate a role of different ingredients in the two-nucleon current operator. For the first time calculations involve consistent contributions from long-range two-pion exchange currents which appear at next-to-leading order of the chiral expansion. We present novel results for cross sections and various polarization observables.
The phenomenological non-relativistic quark model has been employed to obtain the ground state masses of light vector mesons and their radially excited states and their decay widths. The full hamiltonian used in the investigation has kinetic energy, the confinement potential and the one-gluon-exchange potential. A good agreement is obtained with the experimental masses and their leptonic decay widths.
We report here the mass spectrum and magnetic moments of ccq(q∈u,d,s) systems in the potential model framework by assuming the inter-quark potential as the colour coulomb plus power form with power index ν varying between 0.1 to 2.0. Here the two charm quarks are considered for the diquark states. The conventional one gluon exchange interaction has been employed to get the hyperfine and the fine structure between different states. We have predicted many low-lying states whose experimental verification can exclusively support the quark-diquark structure of the baryons.
We propose one possible mechanism, i.e., the vector meson (VV) rescattering effects, to interpret the near threshold narrow enhancement observed in J/ψ→γpp. The estimate indicates that these effects can give sizeable contributions to this channel, and a destructive interference between different rescattering amplitudes is required to reproduce the line shape of the data.
In my talk, we present the dynamical study of Y(4140) and Y(3930) under the Ds*Ds* and D*D* molecular assignments respectively. The importance to theoretically and experimentally study their open-charm decay, hidden-charm decay, radiative decay and double-photon decay is proposed combing with the theoretical calculation of the decay behavior of Y(4140) and Y(3930). According to the recent new experimental progress made by Belle, we further indicate the reasonability of molecular explanation to Y(4140). Another event cluster around 4270 MeV in the J/ψφ invariant mass spectrum of B→K J/ψφ can provide us more hints to reveal the creation mechanism of molecular structure in B meson decay, which will be helpful to clarify the underlying structure of Y(4140) and Y(3930).
We calculate the Ds1(2536)+ decays into D*K channels, including the decay Ds1(2536)+\→ D+π－K+ through a virtual D*0 in a constituent quark model. Widths and S/D amplitudes ratio are in agreement with the recent Belle and BABAR data, being the results sensitive to 1P1 and 3P1 mixture.
The di-gamma and di-gluon decay widths of P-wave cc mesons are computed in nonrelativistic phenomenological quark-antiquark potential of the type V(r)=－4/3αs/r+Arν with different choices of ν using spectroscopic parameters. The numerically obtained radial solutions are employed to obtain the di-gamma and di-gluon decay widths. The computed decay widths are consistent with other model predictions as well as with the known experimental values in the range of potential index 0.7≤ν≤1.1.
The difference between the strange and antistrange quark distributions, δs(x)=s(x)－s(x), and the combination of light quark sea and strange quark sea, Δ(x)=d(x)+u(x)－s(x)－s(x), are originated from non-perturbative processes and can be calculated using non-perturbative models of the nucleon. We report calculations of δs(x) and Δ(x) using the meson cloud model. Combining our calculations of Δ(x) with relatively well known light antiquark distributions obtained from global analysis of available experimental data, we estimate the total strange sea distributions of the nucleon.
A new and simple statistical approach is performed to calculate the parton distribution functions (PDFs) of the nucleon in terms of light-front kinematic variables. Analytic expressions of x-dependent PDFs are obtained in the whole x region. And thereafter, we treat the temperature T as a parameter of the atomic number A to explain the nuclear EMC ef\/fect in the region x∈[0.2, 0.7]. We give the predictions of PDF ratios, and they are very different from those by other models, thus experiments aiming at measuring PDF ratios are suggested to provide a discrimination of different models.
We apply an AdS/CFT-inspired color-dipole model which contains only three free parameters to describe the HERA data for the inclusive structure function F2 at small Bjorken-x and virtuality. We found that the saturation scale in our AdS/CFT-based parameterization varies in the range of 1÷3 GeV becoming independent of energy/Bjorken-x at very small x. This leads to the prediction of x-independence of the structure functions at very small x. With the fitted parameters in our model, the predictions for F2, longitudinal structure function, charm structure function and total photo-production cross-sections in the kinematic regions of future experiments can be given.
The polarization effect on the spin symmetry for anti-Lambda spectrum in 16O+Λ system has been studied in relativistic mean-field theory. The PK1 effective interaction is used for nucleon-meson couplings and G-parity symmetry with a reduction factor ξ=0.3 is adopted for anti-Lambda-meson couplings. The energy differences between spin doublets in the anti-Lambda spectrum are around 0.10-0.73 MeV for pΛ state. The dominant components of the Dirac spinor for the anti-Lambda spin doublets are found to be near identical. It indicates that the spin symmetry is still well-conserved against the polarization effect from the valence anti-Lambda hyperon, which leads to a highly compressed cold nucleus with the central density up to 2－3 times of saturated density.
A chiral quark-model approach is employed to study the KN scattering at low energies. The processes of K－p→Σ0π0, Λπ0 and K0n at PK≤800 MeV/c (i.e. the center mass energy W≤1.7 GeV) are investigated. The analysis shows that the Λ(1405)S01 dominates the processes K－p→Σ0π0, K0n in the energy region considered here. Around PK=400 MeV/c, the Λ(1520)D03 is responsible for a strong resonant peak in the cross section of K－p→Σ0π0 and K0n. To reproduce the data, an unexpectedly large coupling for Λ(1520)D03 to KN is needed. In contrast, the coupling for Λ(1670)S01 to KN appears to be weak, which could be due to configuration mixings between Λ(1405)S01 and Λ(1670)S01. By analyzing K－p→Λπ0, evidences for two low mass S-wave states, Σ(1480)S11 and Σ(1560)S11, seem to be available. With these two states, the reaction K－p→K0n can also be described well. However, it is difficult to understand the low masses of Σ(1480)S11 and Σ(1560)S11. The s-channel amplitudes for K－p→Λπ0 are also larger than the naive quark model expectations. The non-resonant background contributions, i.e. t-channel and/or u-channel, also play important roles in the explanation of the angular distributions due to amplitude interferences.
The rapidity dependence of the elliptic flow of direct photons in Au+Au collisions at √s NN=200 GeV are predicted, based on a three-dimensional ideal hydrodynamic description of the hot and dense matter. The rapidity dependence of the elliptic flow v2(y) of direct photons (mainly thermal photons) is very sensitive to the initial energy density distribution along longitudinal direction, which provides a useful tool to extract the realistic initial condition from measurements.
In this paper, we present the centrality, transverse momentum region and rapidity window size dependence of charged particle fluctuation from Relativistic Quantum Molecular Dynamics (RQMD) model. DQ, ΓQ and ΦQ all depend on the rapidity windows we chosen. ν+－,dyn is a promising observable in experiments, it weakly depends on the acceptance. The beam energy dependence of ν+－,dyn has been studied to present baseline prediction for net charge fluctuations in experiments.
In the chiral symmetry breaking phase described by the NJL model at quark level, along with the chiral symmetry restoration the ratio of shear viscosity to entropy density η/s drops down monotonously and reaches the minimum at the critical point, while the ratio of
bulk viscosity to entropy density ζ/s behaves oppositely.
STAR's measurement of directed flow for pions, kaons(KS0), protons and anti-protons, for Au+Au collisions at 200 GeV obtained in Run7 are presented, as well as elliptic flow for identified particles measured in Au+Au(Run7) and Cu+Cu(Run5) collisions. It is found that the slope of proton v1(y) at midrapidity is extremely small. Elliptic flow results are compared to Hydro calculation and the discrepancy is discussed.
In color superconductor the gluon condensate drops down at moderate density but goes up at high density and can even exceed its vacuum value when the density is high enough.
Jet quenching has been proposed as a probe of the properties of the strongly interacting quark-gluon-plasma in high energy heavy ion collisions. At the meantime, it is also important to study the excitation of medium by propagating jets. Based on Boltzmann equation, a Monte Carlo was constructed to simulate the elastic collisions with thermal partons by energetic jets. Medium modification due to jet-medium interaction has been studied within
this model in a uniform medium.
We review our main results concerning the transport coefficients of a light meson gas, in particular we focus on the case of a massive pion gas. Leading order results according to the chiral power-counting are presented for the DC electrical conductivity, thermal conductivity, shear viscosity, and bulk viscosity. We also comment on the possible correlation between the bulk viscosity and the trace anomaly in QCD, as well as the relation between unitarity and a minimum of the quotient η/s near the phase transition.
With a multi-phase transport (AMPT) model, a γ-jet with known production point and momentum is triggered to search for the origin of double-peak structure in di-hadron azimuthal correlation in central Au+Au collisions at RHIC energy. The different configurations of triggered γ-jet produce different shapes of medium responses. The key of the double-peak structure is found to be a strong shadowing effect of dense core, which is related to transverse expansion and radial flow of partonic matter.
At quark level, we study the effect of ideal mixing of singlet σ0 and octet σ8 scalar mesons on baryon-baryon interaction in the chiral SU(3) quark model. We solve the resonating group method equation for scattering process and bound state. The results show that the binding energy of deuteron and nucleon-nucleon and hyperon-nucleon scattering data can be reasonably described for ideal mixing. Taking the same parameters we used in the scattering calculation, we further investigate the possible dibaryons and find the binding energy of (ΩΩ)ST=00 and (Ξ*Ω)ST=0 1/2 can be reduced a lot for ideal mixing.
We describe the production of ΛΛ in pp collisions using a constituent quark model which has been successfully applied to the NN system.
The measurement of parity-violating (PV) observables in few-nucleon system can shed light on our current understanding of the weak interaction between nucleons. Theoretical models describe the nucleon-nucleon weak interaction at low energies use a series of undetermined parameters. Two parity violating measurements have been considered: the capture of polarized slow neutrons on hydrogen (n+p→d+γ) at Los Alamos National Laboratory for first phase and Oka Ridge National Laboratory for second phase and the helicity dependence of the deuteron photodisintegration cross section using circularly polarized photons (\γ+d→n+p) at Shanghai Institute of Applied Physics. The goal of both experiments is to constraint the weak meson-nucleon couplings to a precision of 1×10－8. The introduction of both experiments is presented.
The cross sections of the fragments produced in the projectile fragmentation reactions of the even calcium isotopes from A=36 to A=52 are calculated using the statistical abrasion ablation model. The neutron skin thickness are studied by investigating the fragments isotopic cross section distributions. The neutron-skin thicknesses of the calcium isotopes have a good linear correlation to the peak positions of their fragment isotopic cross section distributions. The correlation between the neutron skin thickness and the neutron density distributions of 48Ca is investigated by introducing a parameter to adjust the diffuseness parameter in the fermi-type density distribution.
The exclusive electroproduction of pseudoscalar and vector mesons was studied with the HERMES spectrometer at the DESY laboratory by scattering 27.6 GeV positron and electron beams off a transversely polarized hydrogen target. The results are compared to calculations based on generalized parton distributions, some of which are sensitive to the contribution of the total angular momentum of the quarks to the proton spin.
Generalized Parton Distributions (GPDs) provide a way to access total angular momenta of partons and give a multidimensional picture of the nucleon structure. Deeply Virtual Compton Scattering (DVCS) is the most direct exclusive process to study GPDs. Different azimuthal cross-section asymmetries with respect to beam helicity, beam charge, and target
polarization have been measured in the HERMES experiment. A recoil detector was installed at HERMES to directly detect the recoil proton.
In this paper we present the non-singlet QCD analysis to determine valence quark distribution up to four loop. We obtain the fractional difference between the 4-loop and the 1-, 2- and 3-loop presentations of xuv(x,Q2) and xdv(x,Q2).
We clarify the difference among potential models so far proposed to explain mass spectra of heavy-light mesons via transformations of the vacuum. Applying our idea to QQ quarkonium, we obtain the extra term, 1/r2 with positive coefficient, other than non-relativistic potential terms expected for quarkonium.
We determine the strong coupling constant αs up to 4-loop in perturbative QCD. Testing QCD requires the measurement of αs over ranges of energy scales. In this analysis, the value of αs is determined from the unpolarized structure functions data points by minimizing the χ2 function between the theory result and experimental data. Using perturbative QCD calculations from threshold corrections, we obtain αs(MZ2)=0.1139±0.0020 at N3LO which is in good agreement with the very recently results from the inclusive jet cross section in pp collisions at √s=1.96 TeV.
We analyze the effects of hyperfine mixing in b→c semileptonic decays of doubly heavy baryons. We qualitatively confirm the results by W. Roberts and M. Pervin in Int. J. Mod. Phys. A, 2009, 24: 2401—2413, finding that mixing has a great impact on those transitions. However, predictions without mixing differ by a factor of 2 and this discrepancy translates to the mixed case where large differences in decay widths are observed between the two calculations.
γ+jet events provide a tomographic measurement of the medium formed in heavy ion collisions at LHC energies. Tagging events with a well identified high pT direct photon and measuring the correlation distribution of hadrons emitted oppositely to the photon in ALICE, allows us to determine, with a good approximation, both the jet fragmentation function and the back-to-back azimuthal alignment of the direct photon and the jet. Comparing these two observables measured in pp collisions with the ones measured in AA collisions will reveal the modifications of the jet structure induced by the medium formed in AA collisions and consequently will infer the medium properties.
The HERMES measured azimuthal amplitudes of cross sections and their transverse target single spin asymmetries for hadron productions in semi-inclusive deep inelastic scattering.
From the extracted amplitudes, novel parton distribution functions can be studied. The recent results related to Sivers and Boer-Mulders distribution functions are discussed.
The decay properties of the D and Ds mesons are computed in a nonrelativistic phenomenological quark-antiquark potential of the type V(r)=－4/3αs/r+Arν with different choices of ν. Numerical method to solve the Schrodinger equation has been used to obtain the spectroscopy of qQ mesons. The numerically obtained radial solutions are employed to obtain the decay constant and leptonic decay widths. It has been observed that predictions of the ground state masses and the decay widths are consistent with other model predictions as well as with the known experimental values.
We investigate masses of light mesons from a coupled system of Dyson—Schwinger (DSE) and Bethe—Salpeter equations (BSE), taking into account dominant non-Abelian, sub-leading Abelian, and dominant pion cloud contributions to the dressed quark-gluon vertex. The axial-vector Ward-Takahashi identity preserving Bethe-Salpeter kernel is constructed and the spectrum of light mesons calculated. Our model goes significantly beyond the rainbow-ladder. We find that sub-leading Abelian corrections are further dynamically suppressed, and that our results supersede early qualitative predictions from simple truncation schemes.
Based on a data sample of 384 million BB pairs collected with the BABAR detector at the PEP-Ⅱ asymmetric e+e－ storage ring, we measure branching fractions, direct CP, isospin and lepton-flavor asymmetries for the rare decays B→K(*)l+l－ in two di-lepton mass bins above and below the J/ψ resonance. For the B→K*l+l－ decay, we also measure the K* longitudinal polarization fraction and the di-lepton forward-backward asymmetry.
A new particle Σ* with JP=1/2－ was predicted by unquenched quark models with its mass around the well established Σ(1385) with JP=3/2+. Here we re-examine some old data of the K－p→Λπ+π－ reaction. Firstly we re-fit the data for kaon beam momenta in the range of 1.0－1.8 GeV. Secondly we study the reaction at the energies around Λ*(1520) peak. Both studies show evidence for the existence of Σ* with JP=1/2－ around 1380 MeV. Higher statistic data on relevant reactions are needed to clarify the situation.
We discuss recent progress in extracting the excited meson spectrum and radiative transition form factors from lattice QCD. We mention results in the charmonium sector, including the first lattice QCD calculation of radiative transition rates involving excited charmonium states, highlighting results for high spin and exotic states. We present recent results on a highly excited isovector meson spectrum from dynamical anisotropic lattices. Using carefully constructed operators we show how the continuum spin of extracted states can be reliably identified and confidently extract excited states, states with exotic quantum numbers and states of high spin. This spectrum includes the first spin-four state extracted from lattice QCD. We conclude with some comments on future prospects.
We investigate the AdS/QCD duality for the two-point correlation functions of the lowest dimension scalar meson and scalar glueball operators, in the case of the Soft Wall holographic model of QCD. Masses and decay constants as well as gluon condensates are
compared to their QCD estimates. In particular, the role of the boundary conditions for the bulk-to-boundary propagators is emphasized.
We review a recent work on masses of mesons and nucleons within a hard wall model of holographic QCD in a unified approach. In order to treat meson and nucleon properties on the same footing, we introduced the same infrared (IR) cut for both sectors. In framework of present approach, the best fit to the experimental data is achieved introducing the anomalous dimension for baryons.
The scheme-scale ambiguity that has plagued perturbative analysis in QCD remains on obstacle to making precise tests of the theory. Many attempts have been done to resolve the scale ambiguity. In this regard the BLM, EC, PMS and CORGI approaches are more distinct. We try to employ these methods to fix the scale ambiguity at NLO, NNLO and even in more higher order approximations. By optimizing the renormalization scale, there will be a possibility to predicate higher order terms. We present general results for predicted terms at any order, using different optimization methods. Some observable as specific examples will be used to indicate the validity of scale fixing to predicate the higher order terms.
The weak-coupling expansion for thermodynamic quantities in thermal field theories is poorly convergent unless the coupling constant is tiny. We discuss the calculation of the free energy for a hot gas of electrons and photons to three-loop order using hard-thermal-loop perturbation theory (HTLpt). We show that the hard-thermal-loop perturbation reorganization improves the convergence of the successive approximations to the QED free energy at large coupling, e~2. The reorganization is gauge invariant by construction, and due to the cancellations among various contributions, we obtain a completely analytic result for the resummed thermodynamic potential at three loops.
As early physics programs with the ATLAS detector, we present J/ψ and Υ production cross section and spin alignment measurements, and the strategy for the jet energy calibration.
We use the constituent quark model to extract polarized parton distributions and finally polarized nucleon structure function. Due to limited experimental data which do not cover whole (x,Q2) plane and to increase the reliability of the fitting, we employ the Jacobi orthogonal polynomials expansion. It will be possible to extract the polarized structure functions for Helium, using the convolution of the nucleon polarized structure functions with the light cone moment distribution. The results are in good agreement with available
experimental data and some theoretical models.
We present the performance of the ALICE muon spectrometer for measuring the charm and beauty inclusive pt differential production cross sections via single muons and unlike-sign dimuons in proton-proton collisions at √s=14 TeV.
- A SCOAP3 participating journal - free Open Access publication for qualifying articles
- Average 24 days to first decision
- Fast-track publication for selected articles
- Subscriptions at over 3000 institutions worldwide
- Free English editing on all accepted articles
- The Most Influential Paper Award of Chinese Physics Society in 2020
- CPC authorship won the âIOP Publishing awards top cited Chinese authorsâ
- Notification to our authors â Delay in the production process
- The 2020 summer holiday-Office closure
- Impact factor of Chinese Physics C is 2.463 in 2019