2017 Vol. 41, No. 5
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2017, 41(5): 051001. doi: 10.1088/1674-1137/41/5/051001
Abstract:
Analogous to the quarkyonic matter at high baryon density in which the quark Fermi seas and the baryonic excitations coexist, it is argued that a “quarksonic matter” phase appears at high isospin density where the quark (antiquark) Fermi seas and the mesonic excitations coexist. We explore this phase in detail in both large Nc and asymptotically free limits. In the large N_c limit, we sketch a phase diagram for the quarksonic matter. In the asymptotically free limit, we study the pion superfluidity and thermodynamics of the quarksonic matter by using both perturbative calculations and an effective model.
Analogous to the quarkyonic matter at high baryon density in which the quark Fermi seas and the baryonic excitations coexist, it is argued that a “quarksonic matter” phase appears at high isospin density where the quark (antiquark) Fermi seas and the mesonic excitations coexist. We explore this phase in detail in both large Nc and asymptotically free limits. In the large N_c limit, we sketch a phase diagram for the quarksonic matter. In the asymptotically free limit, we study the pion superfluidity and thermodynamics of the quarksonic matter by using both perturbative calculations and an effective model.
2017, 41(5): 053001. doi: 10.1088/1674-1137/41/5/053001
Abstract:
In the past few decades, numerous searches have been made for the neutrinoless double-beta decay (0vββ) process, aiming to establish whether neutrinos are their own antiparticles (Majorana neutrinos), but no 0vββ decay signal has yet been observed. A number of new experiments are proposed but they ultimately suffer from a common problem: the sensitivity may not increase indefinitely with the target mass. We have performed a detailed analysis of the physics potential by using the Jiangmen Underground Neutrino Observatory (JUNO) to improve the sensitivity to 0vββ up to a few meV, a major step forward with respect to the experiments currently being planned. JUNO is a 20 kton low-background liquid scintillator (LS) detector with 3%E(MeV) energy resolution, now under construction. It is feasible to build a balloon filled with enriched xenon gas (with 136Xe up to 80%) dissolved in LS, inserted into the central region of the JUNO LS. The energy resolution is ～1.9% at the Q-value of 136Xe 0vββ decay. Ultra-low background is the key for 0vββ decay searches. Detailed studies of background rates from intrinsic 2vββ and 8B solar neutrinos, natural radioactivity, and cosmogenic radionuclides (including light isotopes and 137Xe) were performed and several muon veto schemes were developed. We find that JUNO has the potential to reach a sensitivity (at 90% C. L.) to T1/20vββ of 1.8×1028 yr (5.6×1027 yr) with ～50 tons (5 tons) of fiducial 136Xe and 5 years exposure, while in the 50-ton case the corresponding sensitivity to the effective neutrino mass, mββ, could reach (5-12) meV, covering completely the allowed region of inverted neutrino mass ordering.
In the past few decades, numerous searches have been made for the neutrinoless double-beta decay (0vββ) process, aiming to establish whether neutrinos are their own antiparticles (Majorana neutrinos), but no 0vββ decay signal has yet been observed. A number of new experiments are proposed but they ultimately suffer from a common problem: the sensitivity may not increase indefinitely with the target mass. We have performed a detailed analysis of the physics potential by using the Jiangmen Underground Neutrino Observatory (JUNO) to improve the sensitivity to 0vββ up to a few meV, a major step forward with respect to the experiments currently being planned. JUNO is a 20 kton low-background liquid scintillator (LS) detector with 3%E(MeV) energy resolution, now under construction. It is feasible to build a balloon filled with enriched xenon gas (with 136Xe up to 80%) dissolved in LS, inserted into the central region of the JUNO LS. The energy resolution is ～1.9% at the Q-value of 136Xe 0vββ decay. Ultra-low background is the key for 0vββ decay searches. Detailed studies of background rates from intrinsic 2vββ and 8B solar neutrinos, natural radioactivity, and cosmogenic radionuclides (including light isotopes and 137Xe) were performed and several muon veto schemes were developed. We find that JUNO has the potential to reach a sensitivity (at 90% C. L.) to T1/20vββ of 1.8×1028 yr (5.6×1027 yr) with ～50 tons (5 tons) of fiducial 136Xe and 5 years exposure, while in the 50-ton case the corresponding sensitivity to the effective neutrino mass, mββ, could reach (5-12) meV, covering completely the allowed region of inverted neutrino mass ordering.
2017, 41(5): 053101. doi: 10.1088/1674-1137/41/5/053101
Abstract:
We introduce the 2D dimensional double space with the coordinates ZM= (xμ, yμ), whose components are the coordinates of initial space xμ and its T-dual yμ. We shall show that in this extended space the T-duality transformations can be realized simply by exchanging the places of some coordinates xa, along which we want to perform T-duality, and the corresponding dual coordinates y_a. In such an approach it is evident that T-duality leads to the physically equivalent theory and that a complete set of T-duality transformations forms a subgroup of the 2D permutation group. So, in double space we are able to represent the backgrounds of all T-dual theories in a unified manner.
We introduce the 2D dimensional double space with the coordinates ZM= (xμ, yμ), whose components are the coordinates of initial space xμ and its T-dual yμ. We shall show that in this extended space the T-duality transformations can be realized simply by exchanging the places of some coordinates xa, along which we want to perform T-duality, and the corresponding dual coordinates y_a. In such an approach it is evident that T-duality leads to the physically equivalent theory and that a complete set of T-duality transformations forms a subgroup of the 2D permutation group. So, in double space we are able to represent the backgrounds of all T-dual theories in a unified manner.
2017, 41(5): 053102. doi: 10.1088/1674-1137/41/5/053102
Abstract:
From the overlap lattice quark propagator calculated in the Landau gauge, we determine the quark chiral condensate by fitting operator product expansion formulas to the lattice data. The quark propagators are computed on domain wall fermion configurations generated by the RBC-UKQCD Collaborations with Nf=2+1 flavors. Three ensembles with different light sea quark masses are used at one lattice spacing 1/a=1.75(4) GeV. We obtain <ψψ>MS(2 GeV)=(-304(15)(20) MeV)3 in the SU(2) chiral limit.
From the overlap lattice quark propagator calculated in the Landau gauge, we determine the quark chiral condensate by fitting operator product expansion formulas to the lattice data. The quark propagators are computed on domain wall fermion configurations generated by the RBC-UKQCD Collaborations with Nf=2+1 flavors. Three ensembles with different light sea quark masses are used at one lattice spacing 1/a=1.75(4) GeV. We obtain <ψψ>MS(2 GeV)=(-304(15)(20) MeV)3 in the SU(2) chiral limit.
2017, 41(5): 053103. doi: 10.1088/1674-1137/41/5/053103
Abstract:
Determination of proton parton distribution functions is presented under the dynamical parton model assumption by applying DGLAP equations with GLR-MQ-ZRS corrections. We provide two data sets, referred to as IMParton16, which are from two different nonperturbative inputs. One is the naive input of three valence quarks and the other is the input of three valence quarks with flavor-asymmetric sea components. Basically, both data sets are compatible with the experimental measurements at high scale (Q2 >2 GeV2). Furthermore, our analysis shows that the input with flavor-asymmetric sea components better reproduces the structure functions at high Q2. Generally, the parton distribution functions obtained, especially the gluon distribution function, are good options for inputs to simulations of high energy scattering processes. The analysis is performed under the fixed-flavor number scheme for nf= 3, 4, 5. Both data sets start from very low scales, around 0.07 GeV2, where the nonperturbative input is directly connected to the simple picture of the quark model. These results may shed some lights on the origin of the parton distributions observed at high Q2.
Determination of proton parton distribution functions is presented under the dynamical parton model assumption by applying DGLAP equations with GLR-MQ-ZRS corrections. We provide two data sets, referred to as IMParton16, which are from two different nonperturbative inputs. One is the naive input of three valence quarks and the other is the input of three valence quarks with flavor-asymmetric sea components. Basically, both data sets are compatible with the experimental measurements at high scale (Q2 >2 GeV2). Furthermore, our analysis shows that the input with flavor-asymmetric sea components better reproduces the structure functions at high Q2. Generally, the parton distribution functions obtained, especially the gluon distribution function, are good options for inputs to simulations of high energy scattering processes. The analysis is performed under the fixed-flavor number scheme for nf= 3, 4, 5. Both data sets start from very low scales, around 0.07 GeV2, where the nonperturbative input is directly connected to the simple picture of the quark model. These results may shed some lights on the origin of the parton distributions observed at high Q2.
2017, 41(5): 053104. doi: 10.1088/1674-1137/41/5/053104
Abstract:
Recent experimental signals have led to a revival of tetraquarks, the hypothetical q2q2 hadronic states proposed by Jaffe in 1976 to explain the light scalar mesons. Mesonic structures with exotic quantum numbers have indeed been observed recently, though a controversy persists as to whether these are true resonances and not merely kinematical threshold enhancements, or otherwise states not of a true q2q2 nature. Moreover, puzzling non-exotic mesons are also often claimed to have a tetraquark configuration. However, the corresponding model calculations are practically always carried out in pure and static bound-state approaches, ignoring completely the coupling to asymptotic two-meson states and unitarity, especially the dynamical effects thereof. In this short paper we argue that these static predictions of real tetraquark masses are highly unreliable and provide little evidence of the very existence of such states.
Recent experimental signals have led to a revival of tetraquarks, the hypothetical q2q2 hadronic states proposed by Jaffe in 1976 to explain the light scalar mesons. Mesonic structures with exotic quantum numbers have indeed been observed recently, though a controversy persists as to whether these are true resonances and not merely kinematical threshold enhancements, or otherwise states not of a true q2q2 nature. Moreover, puzzling non-exotic mesons are also often claimed to have a tetraquark configuration. However, the corresponding model calculations are practically always carried out in pure and static bound-state approaches, ignoring completely the coupling to asymptotic two-meson states and unitarity, especially the dynamical effects thereof. In this short paper we argue that these static predictions of real tetraquark masses are highly unreliable and provide little evidence of the very existence of such states.
2017, 41(5): 053105. doi: 10.1088/1674-1137/41/5/053105
Abstract:
We perform a systematical study of possible molecular states composed of the S wave heavy light mesons, where the S-D mixing and η-η' mixing are explicitly included. Our calculation indicates that the observed X(3872) could be a loosely shallow molecular state composed of DD* +h.c, while neither Zc(3900)/Zc(4020) nor Zb(10610)/Zb(10650) is supported to be a molecule. Some observed possible molecular states are predicted, which could be searched for by further experimental measurements.
We perform a systematical study of possible molecular states composed of the S wave heavy light mesons, where the S-D mixing and η-η' mixing are explicitly included. Our calculation indicates that the observed X(3872) could be a loosely shallow molecular state composed of DD* +h.c, while neither Zc(3900)/Zc(4020) nor Zb(10610)/Zb(10650) is supported to be a molecule. Some observed possible molecular states are predicted, which could be searched for by further experimental measurements.
2017, 41(5): 053106. doi: 10.1088/1674-1137/41/5/053106
Abstract:
The extremely small branching ratio of the b→ssd decay in the Standard Model makes it a suitable channel to explore new-physics signals. We study this ΔS = 2 process in Randall-Sundrum models, including the custodially protected and the bulk-Higgs Randall-Sundrum models. Exploring the experimentally favored parameter spaces of these models suggests a possible enhancement of the decay rate, compared to the Standard Model result, by at most two orders of magnitude.
The extremely small branching ratio of the b→ssd decay in the Standard Model makes it a suitable channel to explore new-physics signals. We study this ΔS = 2 process in Randall-Sundrum models, including the custodially protected and the bulk-Higgs Randall-Sundrum models. Exploring the experimentally favored parameter spaces of these models suggests a possible enhancement of the decay rate, compared to the Standard Model result, by at most two orders of magnitude.
2017, 41(5): 053107. doi: 10.1088/1674-1137/41/5/053107
Abstract:
Generic axiomatic-nonextensive statistics introduces two asymptotic properties, to each of which a scaling function is assigned. The first and second scaling properties are characterized by the exponents c and d, respectively. In the thermodynamic limit, a grand-canonical ensemble can be formulated. The thermodynamic properties of a relativistic ideal gas of hadron resonances are studied, analytically. It is found that this generic statistics satisfies the requirements of the equilibrium thermodynamics. Essential aspects of the thermodynamic self-consistency are clarified. Analytical expressions are proposed for the statistical fits of various transverse momentum distributions measured in most-central collisions at different collision energies and colliding systems. Estimations for the freezeout temperature (Tch) and the baryon chemical potential (μb) and the exponents c and d are determined. The earlier are found compatible with the parameters deduced from Boltzmann-Gibbs (BG) statistics (extensive), while the latter refer to generic nonextensivities. The resulting equivalence class (c,d) is associated with stretched exponentials, where Lambert function reaches its asymptotic stability. In some measurements, the resulting nonextensive entropy is linearly composed on extensive entropies. Apart from power-scaling, the particle ratios and yields are excellent quantities to highlighting whether the particle production takes place (non)extensively. Various particle ratios and yields measured by the STAR experiment in central collisions at 200, 62.4 and 7.7 GeV are fitted with this novel approach. We found that both c and d<1, i.e. referring to neither BG- nor Tsallis-type statistics, but to (c,d)-entropy, where Lambert functions exponentially rise. The freezeout temperature and baryon chemical potential are found comparable with the ones deduced from BG statistics (extensive). We conclude that the particle production at STAR energies is likely a nonextensive process but not necessarily BG or Tsallis type.
Generic axiomatic-nonextensive statistics introduces two asymptotic properties, to each of which a scaling function is assigned. The first and second scaling properties are characterized by the exponents c and d, respectively. In the thermodynamic limit, a grand-canonical ensemble can be formulated. The thermodynamic properties of a relativistic ideal gas of hadron resonances are studied, analytically. It is found that this generic statistics satisfies the requirements of the equilibrium thermodynamics. Essential aspects of the thermodynamic self-consistency are clarified. Analytical expressions are proposed for the statistical fits of various transverse momentum distributions measured in most-central collisions at different collision energies and colliding systems. Estimations for the freezeout temperature (Tch) and the baryon chemical potential (μb) and the exponents c and d are determined. The earlier are found compatible with the parameters deduced from Boltzmann-Gibbs (BG) statistics (extensive), while the latter refer to generic nonextensivities. The resulting equivalence class (c,d) is associated with stretched exponentials, where Lambert function reaches its asymptotic stability. In some measurements, the resulting nonextensive entropy is linearly composed on extensive entropies. Apart from power-scaling, the particle ratios and yields are excellent quantities to highlighting whether the particle production takes place (non)extensively. Various particle ratios and yields measured by the STAR experiment in central collisions at 200, 62.4 and 7.7 GeV are fitted with this novel approach. We found that both c and d<1, i.e. referring to neither BG- nor Tsallis-type statistics, but to (c,d)-entropy, where Lambert functions exponentially rise. The freezeout temperature and baryon chemical potential are found comparable with the ones deduced from BG statistics (extensive). We conclude that the particle production at STAR energies is likely a nonextensive process but not necessarily BG or Tsallis type.
2017, 41(5): 053108. doi: 10.1088/1674-1137/41/5/053108
Abstract:
At high energy, the cross section at finite scattering angle of a hard exclusive process falls off as a power of the Manderstam variable s. If all involved quark-gluon compositions undergo hard momentum transfers, the fall-off scaling is determined by the underlying valence structures of the initial and final hadrons, known as the constituent counting rule. In spite of the complication due to helicity conservation, it has been argued that when applied to exclusive process with exotic multiquark states, the counting rule is a powerful way to determine the valence degrees of freedom inside hadron exotics. In this work, we demonstrate that for hadrons with hidden flavors, the naive application of the constituent counting rule is problematic, since it is not mandatory for all components to participate in hard scattering at the scale \sqrts. We illustrate the problems in the viewpoint based on effective field theory. We clarify the misleading results that may be obtained from the constituent counting rule in exclusive processes with exotic candidates such as Zc±(ccud/ccdu), Zb±(bbud/bbdu), X(3872), etc.
At high energy, the cross section at finite scattering angle of a hard exclusive process falls off as a power of the Manderstam variable s. If all involved quark-gluon compositions undergo hard momentum transfers, the fall-off scaling is determined by the underlying valence structures of the initial and final hadrons, known as the constituent counting rule. In spite of the complication due to helicity conservation, it has been argued that when applied to exclusive process with exotic multiquark states, the counting rule is a powerful way to determine the valence degrees of freedom inside hadron exotics. In this work, we demonstrate that for hadrons with hidden flavors, the naive application of the constituent counting rule is problematic, since it is not mandatory for all components to participate in hard scattering at the scale \sqrts. We illustrate the problems in the viewpoint based on effective field theory. We clarify the misleading results that may be obtained from the constituent counting rule in exclusive processes with exotic candidates such as Zc±(ccud/ccdu), Zb±(bbud/bbdu), X(3872), etc.
2017, 41(5): 054001. doi: 10.1088/1674-1137/41/5/054001
Abstract:
This work presents the basic characteristics of singly, doubly and heavily charged projectile fragments (PFs) emitted in inelastic interactions of 32S ions with photo-emulsion nuclei at Dubna energy (3.7 A GeV). Our experimental data are compared with the corresponding data for other projectiles at the same incident energy. The study of mean multiplicities of different charged PFs against the projectile mass shows a power-law relationship. The multiplicity distributions of singly and doubly charged PFs have been fitted well with a Gaussian distribution function. The yields of PFs broken up from the interactions of 32S projectile nuclei with different target nuclei are studied. The beam energy dependence in terms of the various order moments is studied as well.
This work presents the basic characteristics of singly, doubly and heavily charged projectile fragments (PFs) emitted in inelastic interactions of 32S ions with photo-emulsion nuclei at Dubna energy (3.7 A GeV). Our experimental data are compared with the corresponding data for other projectiles at the same incident energy. The study of mean multiplicities of different charged PFs against the projectile mass shows a power-law relationship. The multiplicity distributions of singly and doubly charged PFs have been fitted well with a Gaussian distribution function. The yields of PFs broken up from the interactions of 32S projectile nuclei with different target nuclei are studied. The beam energy dependence in terms of the various order moments is studied as well.
2017, 41(5): 054002. doi: 10.1088/1674-1137/41/5/054002
Abstract:
The deuterium depth distribution for a 20 keV/D D3+ beam implanted into ytterbium (Yb) at a temperature between 300 and 340 K was studied using the D(d,p)T reaction. By analyzing the proton yields, the deuterium depth distribution from the front surface to 500 nm depth was found. The results indicate that an equilibrium deuterium distribution region from the front surface to a depth approximately equal to the mean range of implanted deuterons was formed in Yb during the implantation. The deduced deuterium concentration in the equilibrium deuterium distribution region was D/Yb = 22%.
The deuterium depth distribution for a 20 keV/D D3+ beam implanted into ytterbium (Yb) at a temperature between 300 and 340 K was studied using the D(d,p)T reaction. By analyzing the proton yields, the deuterium depth distribution from the front surface to 500 nm depth was found. The results indicate that an equilibrium deuterium distribution region from the front surface to a depth approximately equal to the mean range of implanted deuterons was formed in Yb during the implantation. The deduced deuterium concentration in the equilibrium deuterium distribution region was D/Yb = 22%.
2017, 41(5): 054101. doi: 10.1088/1674-1137/41/5/054101
Abstract:
In this paper, the nuclear longitudinal form factors are systematically studied from the intrinsic charge multipoles. For axially deformed nuclei, two different types of density profiles are used to describe their charge distributions. For the same charge distributions expanded with different basis functions, the corresponding longitudinal form factors are derived and compared with each other. Results show the multipoles Cλ of longitudinal form factors are independent of the basis functions of charge distributions. Further numerical calculations of longitudinal form factors of 12C indicates that the C0 multipole reflects the contributions of spherical components of all nonorthogonal basis functions. For deformed nuclei, their charge RMS radii can also be determined accurately by the C0 measurement. The studies in this paper examine the model-independent properties of electron scattering, which are useful for interpreting electron scattering experiments on exotic deformed nuclei.
In this paper, the nuclear longitudinal form factors are systematically studied from the intrinsic charge multipoles. For axially deformed nuclei, two different types of density profiles are used to describe their charge distributions. For the same charge distributions expanded with different basis functions, the corresponding longitudinal form factors are derived and compared with each other. Results show the multipoles Cλ of longitudinal form factors are independent of the basis functions of charge distributions. Further numerical calculations of longitudinal form factors of 12C indicates that the C0 multipole reflects the contributions of spherical components of all nonorthogonal basis functions. For deformed nuclei, their charge RMS radii can also be determined accurately by the C0 measurement. The studies in this paper examine the model-independent properties of electron scattering, which are useful for interpreting electron scattering experiments on exotic deformed nuclei.
2017, 41(5): 054102. doi: 10.1088/1674-1137/41/5/054102
Abstract:
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2017, 41(5): 054103. doi: 10.1088/1674-1137/41/5/054103
Abstract:
In this work, β+/EC decays of some medium-mass nuclei are investigated within the extended quasiparticle random-phase approximation (QRPA), where neutron-neutron, proton-proton and neutron-proton (np) pairing correlations are taken into consideration in the specialized Hartree-Fock-Bogoliubov (HFB) transformation. In addition to the pairing interaction, the Brückner G-matrix obtained with the charge-dependent Bonn nucleon-nucleon force is used for the residual particle-particle and particle-hole interactions. Calculations are performed for even-even proton-rich isotopes ranging from Z =24 to Z =34. It is found that the np pairing interaction plays a significant role in β-decay for some nuclei far from stability. Compared with other theoretical calculations, our calculations show good agreement with the available experimental data. Predictions of β-decay half-lives for some very neutron-deficient nuclei are made for reference.
In this work, β+/EC decays of some medium-mass nuclei are investigated within the extended quasiparticle random-phase approximation (QRPA), where neutron-neutron, proton-proton and neutron-proton (np) pairing correlations are taken into consideration in the specialized Hartree-Fock-Bogoliubov (HFB) transformation. In addition to the pairing interaction, the Brückner G-matrix obtained with the charge-dependent Bonn nucleon-nucleon force is used for the residual particle-particle and particle-hole interactions. Calculations are performed for even-even proton-rich isotopes ranging from Z =24 to Z =34. It is found that the np pairing interaction plays a significant role in β-decay for some nuclei far from stability. Compared with other theoretical calculations, our calculations show good agreement with the available experimental data. Predictions of β-decay half-lives for some very neutron-deficient nuclei are made for reference.
2017, 41(5): 054104. doi: 10.1088/1674-1137/41/5/054104
Abstract:
The quenching factors of one-neutron spectroscopic factors, which are ratios of theoretical to experimental one-neutron removal cross sections, are studied for the carbon isotopes 15-19C, with 12C and 9Be targets within incident energies from around 50 to 900 MeV/nucleon. The resulting values of quenching factors do not show strong energy dependence within such an energy range. The average values of the these quenching factors agree well with the systematics in [J.A. Tostevin and A. Gade, Phys. Rev. C, 90 057602 (2014)], which was established for a large set of radioactive nuclei with different masses below 305 MeV/nucleon.
The quenching factors of one-neutron spectroscopic factors, which are ratios of theoretical to experimental one-neutron removal cross sections, are studied for the carbon isotopes 15-19C, with 12C and 9Be targets within incident energies from around 50 to 900 MeV/nucleon. The resulting values of quenching factors do not show strong energy dependence within such an energy range. The average values of the these quenching factors agree well with the systematics in [J.A. Tostevin and A. Gade, Phys. Rev. C, 90 057602 (2014)], which was established for a large set of radioactive nuclei with different masses below 305 MeV/nucleon.
2017, 41(5): 055101. doi: 10.1088/1674-1137/41/5/055101
Abstract:
We compare six models (including the baryonic model, two dark matter models, two modified Newtonian dynamics models and one modified gravity model) in accounting for galaxy rotation curves. For the dark matter models, we assume NFW profile and core-modified profile for the dark halo, respectively. For the modified Newtonian dynamics models, we discuss Milgrom's MOND theory with two different interpolation functions, the standard and the simple interpolation functions. For the modified gravity, we focus on Moffat's MSTG theory. We fit these models to the observed rotation curves of 9 high-surface brightness and 9 low-surface brightness galaxies. We apply the Bayesian Information Criterion and the Akaike Information Criterion to test the goodness-of-fit of each model. It is found that none of the six models can fit all the galaxy rotation curves well. Two galaxies can be best fitted by the baryonic model without involving nonluminous dark matter. MOND can fit the largest number of galaxies, and only one galaxy can be best fitted by the MSTG model. Core-modified model fits about half the LSB galaxies well, but no HSB galaxies, while the NFW model fits only a small fraction of HSB galaxies but no LSB galaxies. This may imply that the oversimplified NFW and core-modified profiles cannot model the postulated dark matter haloes well.
We compare six models (including the baryonic model, two dark matter models, two modified Newtonian dynamics models and one modified gravity model) in accounting for galaxy rotation curves. For the dark matter models, we assume NFW profile and core-modified profile for the dark halo, respectively. For the modified Newtonian dynamics models, we discuss Milgrom's MOND theory with two different interpolation functions, the standard and the simple interpolation functions. For the modified gravity, we focus on Moffat's MSTG theory. We fit these models to the observed rotation curves of 9 high-surface brightness and 9 low-surface brightness galaxies. We apply the Bayesian Information Criterion and the Akaike Information Criterion to test the goodness-of-fit of each model. It is found that none of the six models can fit all the galaxy rotation curves well. Two galaxies can be best fitted by the baryonic model without involving nonluminous dark matter. MOND can fit the largest number of galaxies, and only one galaxy can be best fitted by the MSTG model. Core-modified model fits about half the LSB galaxies well, but no HSB galaxies, while the NFW model fits only a small fraction of HSB galaxies but no LSB galaxies. This may imply that the oversimplified NFW and core-modified profiles cannot model the postulated dark matter haloes well.
2017, 41(5): 055102. doi: 10.1088/1674-1137/41/5/055102
Abstract:
The purpose of this work is to demonstrate how an arbitrarily chosen background of the Universe can be made a solution of a simple geometric sigma model. Geometric sigma models are purely geometric theories in which spacetime coordinates are seen as scalar fields coupled to gravity. Although they look like ordinary sigma models, they have the peculiarity that their complete matter content can be gauged away. The remaining geometric theory possesses a background solution that is predefined in the process of constructing the theory. The fact that background configuration is specified in advance is another peculiarity of geometric sigma models. In this paper, I construct geometric sigma models based on different background geometries of the Universe. Whatever background geometry is chosen, the dynamics of its small perturbations is shown to have a generic classical stability. This way, any freely chosen background metric is made a stable solution of a simple model. Three particular models of the Universe are considered as examples of how this is done in practice.
The purpose of this work is to demonstrate how an arbitrarily chosen background of the Universe can be made a solution of a simple geometric sigma model. Geometric sigma models are purely geometric theories in which spacetime coordinates are seen as scalar fields coupled to gravity. Although they look like ordinary sigma models, they have the peculiarity that their complete matter content can be gauged away. The remaining geometric theory possesses a background solution that is predefined in the process of constructing the theory. The fact that background configuration is specified in advance is another peculiarity of geometric sigma models. In this paper, I construct geometric sigma models based on different background geometries of the Universe. Whatever background geometry is chosen, the dynamics of its small perturbations is shown to have a generic classical stability. This way, any freely chosen background metric is made a stable solution of a simple model. Three particular models of the Universe are considered as examples of how this is done in practice.
2017, 41(5): 056001. doi: 10.1088/1674-1137/41/5/056001
Abstract:
The Alpha Magnetic Spectrometer (AMS-02), which is installed on the International Space Station (ISS), has been collecting data successfully since May 2011. The main goals of AMS-02 are the search for cosmic anti-matter, dark matter and the precise measurement of the relative abundance of elements and isotopes in galactic cosmic rays. In order to identify particle properties, AMS-02 includes several specialized sub-detectors. Among these, the AMS-02 Ring Imaging Cherenkov detector (RICH) is designed to provide a very precise measurement of the velocity and electric charge of particles. We describe a method to reject the dominant electron background in antiproton identification with the use of the AMS-02 RICH detector as a veto for rigidities below 3 GV. A ray tracing integration method is used to maximize the statistics of p with the lowest possible e- background, providing 4 times rejection power gain for e- background with respect to only 3% of p signal efficiency loss. By using the collected cosmic-ray data, e- contamination can be well suppressed within 3% with β ≈ 1, while keeping 76% efficiency for p below the threshold.
The Alpha Magnetic Spectrometer (AMS-02), which is installed on the International Space Station (ISS), has been collecting data successfully since May 2011. The main goals of AMS-02 are the search for cosmic anti-matter, dark matter and the precise measurement of the relative abundance of elements and isotopes in galactic cosmic rays. In order to identify particle properties, AMS-02 includes several specialized sub-detectors. Among these, the AMS-02 Ring Imaging Cherenkov detector (RICH) is designed to provide a very precise measurement of the velocity and electric charge of particles. We describe a method to reject the dominant electron background in antiproton identification with the use of the AMS-02 RICH detector as a veto for rigidities below 3 GV. A ray tracing integration method is used to maximize the statistics of p with the lowest possible e- background, providing 4 times rejection power gain for e- background with respect to only 3% of p signal efficiency loss. By using the collected cosmic-ray data, e- contamination can be well suppressed within 3% with β ≈ 1, while keeping 76% efficiency for p below the threshold.
2017, 41(5): 056002. doi: 10.1088/1674-1137/41/5/056002
Abstract:
A low background thermal neutron flux detection system has been designed to measure the ambient thermal neutron flux of the second phase of the China Jinping Underground Laboratory (CJPL-II), right after completion of the rock bolting work. A 3He proportional counter tube combined with an identical 4He proportional counter tube was employed as the thermal neutron detector, which has been optimised in energy resolution, wall effect and radioactivity of construction materials for low background performance. The readout electronics were specially designed for long-term stable operation and easy maintenance in an underground laboratory under construction. The system was installed in Lab Hall No. 3 of CJPL-II and accumulated data for about 80 days. The ambient thermal neutron flux was determined under the assumption that the neutron field is fully thermalized, uniform and isotropic at the measurement position.
A low background thermal neutron flux detection system has been designed to measure the ambient thermal neutron flux of the second phase of the China Jinping Underground Laboratory (CJPL-II), right after completion of the rock bolting work. A 3He proportional counter tube combined with an identical 4He proportional counter tube was employed as the thermal neutron detector, which has been optimised in energy resolution, wall effect and radioactivity of construction materials for low background performance. The readout electronics were specially designed for long-term stable operation and easy maintenance in an underground laboratory under construction. The system was installed in Lab Hall No. 3 of CJPL-II and accumulated data for about 80 days. The ambient thermal neutron flux was determined under the assumption that the neutron field is fully thermalized, uniform and isotropic at the measurement position.
2017, 41(5): 056003. doi: 10.1088/1674-1137/41/5/056003
Abstract:
A new concept for a hybrid structure gaseous detector module with ion backflow suppression for the time projection chamber in a future circular collider is presented. It is a hybrid structure cascaded Gas Electron Multiplier (GEM) with a Micromegas detector. Both Micromegas and GEM have the capability to naturally reduce most of the ions produced in the amplification region. The GEM also acts as the preamplifer device and increases gas gain together with the Micromegas. Feasibility tests of the hybrid detector are performed using an 55Fe X-ray source. The energy resolution is better than 27% for 5.9keV X-rays. It is demonstrated that a backflow ratio better than 0.2% can be reached in the hybrid readout structure at a gain of 5000.
A new concept for a hybrid structure gaseous detector module with ion backflow suppression for the time projection chamber in a future circular collider is presented. It is a hybrid structure cascaded Gas Electron Multiplier (GEM) with a Micromegas detector. Both Micromegas and GEM have the capability to naturally reduce most of the ions produced in the amplification region. The GEM also acts as the preamplifer device and increases gas gain together with the Micromegas. Feasibility tests of the hybrid detector are performed using an 55Fe X-ray source. The energy resolution is better than 27% for 5.9keV X-rays. It is demonstrated that a backflow ratio better than 0.2% can be reached in the hybrid readout structure at a gain of 5000.
2017, 41(5): 056101. doi: 10.1088/1674-1137/41/5/056101
Abstract:
The silicon-strip tracker of the China Seismo-Electromagnetic Satellite (CSES) consists of two double-sided silicon strip detectors (DSSDs) which provide incident particle tracking information. A low-noise analog ASIC VA140 was used in this study for DSSD signal readout. A beam test on the DSSD module was performed at the Beijing Test Beam Facility of the Beijing Electron Positron Collider (BEPC) using a 400-800 MeV/c proton beam. The pedestal analysis results, RMSE noise, gain correction, and intensity distribution of incident particles of the DSSD module are presented.
The silicon-strip tracker of the China Seismo-Electromagnetic Satellite (CSES) consists of two double-sided silicon strip detectors (DSSDs) which provide incident particle tracking information. A low-noise analog ASIC VA140 was used in this study for DSSD signal readout. A beam test on the DSSD module was performed at the Beijing Test Beam Facility of the Beijing Electron Positron Collider (BEPC) using a 400-800 MeV/c proton beam. The pedestal analysis results, RMSE noise, gain correction, and intensity distribution of incident particles of the DSSD module are presented.
2017, 41(5): 056201. doi: 10.1088/1674-1137/41/5/056201
Abstract:
A reconstruction algorithm for unfolding neutron energy spectra has been developed, based for the first time on the potential reduction interior point algorithm. This algorithm can be easily applied to neutron energy spectrum reconstruction in the recoil proton method. We transform the neutron energy spectrum unfolding problem into a typical nonnegative linear complementarity problem. The recoil proton energy spectrum and response matrix at angles of 0^o and 30^o are generated by the Geant4 simulation toolkit. Several different neutron energy test spectra are also employed. It is found that this unfolding algorithm is stable and provides efficient, accurate results.
A reconstruction algorithm for unfolding neutron energy spectra has been developed, based for the first time on the potential reduction interior point algorithm. This algorithm can be easily applied to neutron energy spectrum reconstruction in the recoil proton method. We transform the neutron energy spectrum unfolding problem into a typical nonnegative linear complementarity problem. The recoil proton energy spectrum and response matrix at angles of 0^o and 30^o are generated by the Geant4 simulation toolkit. Several different neutron energy test spectra are also employed. It is found that this unfolding algorithm is stable and provides efficient, accurate results.
2017, 41(5): 056202. doi: 10.1088/1674-1137/41/5/056202
Abstract:
A fast physics analysis framework has been developed based on SNiPER to process the increasingly large data sample collected by BESIII. In this framework, a reconstructed event data model with SmartRef is designed to improve the speed of Input/Output operations, and necessary physics analysis tools are migrated from BOSS to SNiPER. A real physics analysis e+e- +π+π-J/ψ is used to test the new framework, and achieves a factor of 10.3 improvement in Input/Output speed compared to BOSS. Further tests show that the improvement is mainly attributed to the new reconstructed event data model and the lazy-loading functionality provided by SmartRef.
A fast physics analysis framework has been developed based on SNiPER to process the increasingly large data sample collected by BESIII. In this framework, a reconstructed event data model with SmartRef is designed to improve the speed of Input/Output operations, and necessary physics analysis tools are migrated from BOSS to SNiPER. A real physics analysis e+e- +π+π-J/ψ is used to test the new framework, and achieves a factor of 10.3 improvement in Input/Output speed compared to BOSS. Further tests show that the improvement is mainly attributed to the new reconstructed event data model and the lazy-loading functionality provided by SmartRef.
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