2018 Vol. 42, No. 8
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2018, 42(8): 083001. doi: 10.1088/1674-1137/42/8/083001
Abstract:
We report new measurements of the cross sections for the production of DD final states at the ψ(3770) resonance. Our data sample consists of an integrated luminosity of 2.93 fb-1 of e+e- annihilation data produced by the BEPCⅡ collider and collected and analyzed with the BESⅢ detector. We exclusively reconstruct three D0 and six D+ hadronic decay modes and use the ratio of the yield of fully reconstructed DD events ("double tags") to the yield of all reconstructed D or mD mesons ("single tags") to determine the number of D0D0 and D+D- events, benefiting from the cancellation of many systematic uncertainties. Combining these yields with an independent determination of the integrated luminosity of the data sample, we find the cross sections to be σ(e+e- → D0D0)=(3.615±0.010±0.038) nb and σ(e+e- → D+D-)=(2.830±0.011±0.026) nb, where the uncertainties are statistical and systematic, respectively.
We report new measurements of the cross sections for the production of DD final states at the ψ(3770) resonance. Our data sample consists of an integrated luminosity of 2.93 fb-1 of e+e- annihilation data produced by the BEPCⅡ collider and collected and analyzed with the BESⅢ detector. We exclusively reconstruct three D0 and six D+ hadronic decay modes and use the ratio of the yield of fully reconstructed DD events ("double tags") to the yield of all reconstructed D or mD mesons ("single tags") to determine the number of D0D0 and D+D- events, benefiting from the cancellation of many systematic uncertainties. Combining these yields with an independent determination of the integrated luminosity of the data sample, we find the cross sections to be σ(e+e- → D0D0)=(3.615±0.010±0.038) nb and σ(e+e- → D+D-)=(2.830±0.011±0.026) nb, where the uncertainties are statistical and systematic, respectively.
2018, 42(8): 083101. doi: 10.1088/1674-1137/42/8/083101
Abstract:
The mass spectra of charmonium are investigated using a Coulomb plus linear (Cornell) potential. Gaussian wave functions in position space as well as in momentum space are employed to calculate the expectation values of potential and kinetic energy respectively. Various experimental states (X(4660)(53S1), X(3872)(23P1), X(3900)(21P1), X(3915)(23P0) and X(4274)(33P1) etc.) are assigned as charmonium states. We also study the Regge trajectories, pseudoscalar and vector decay constants, electric and magnetic dipole transition rates, and annihilation decay widths for charmonium states.
The mass spectra of charmonium are investigated using a Coulomb plus linear (Cornell) potential. Gaussian wave functions in position space as well as in momentum space are employed to calculate the expectation values of potential and kinetic energy respectively. Various experimental states (X(4660)(53S1), X(3872)(23P1), X(3900)(21P1), X(3915)(23P0) and X(4274)(33P1) etc.) are assigned as charmonium states. We also study the Regge trajectories, pseudoscalar and vector decay constants, electric and magnetic dipole transition rates, and annihilation decay widths for charmonium states.
2018, 42(8): 083102. doi: 10.1088/1674-1137/42/8/083102
Abstract:
We calculate the next-to-leading-order cross section for the inclusive production of Λb baryons in m pp collisions in the general-mass variable-flavor-number scheme. We use realistic evolved non-perturbative fragmentation functions obtained from fits to m B-meson production in e+e- annihilation and compare our results for transverse-momentum and rapidity distributions with recent experimental data from the CMS and the LHCb collaborations at the CERN LHC. We find satisfactory agreement in general, with some indication for the need to modify the available fragmentation functions at larger values of the scale variable.
We calculate the next-to-leading-order cross section for the inclusive production of Λb baryons in m pp collisions in the general-mass variable-flavor-number scheme. We use realistic evolved non-perturbative fragmentation functions obtained from fits to m B-meson production in e+e- annihilation and compare our results for transverse-momentum and rapidity distributions with recent experimental data from the CMS and the LHCb collaborations at the CERN LHC. We find satisfactory agreement in general, with some indication for the need to modify the available fragmentation functions at larger values of the scale variable.
2018, 42(8): 083103. doi: 10.1088/1674-1137/42/8/083103
Abstract:
The dissociation temperatures of quarkonium states in a thermal medium are obtained in the framework of the quark model with the help of the Gaussian Expansion Method (GEM). This is the first time this method has been applied to the dissociation problem of mesons. The temperature-dependent potential is obtained by fitting the lattice results. Solving the Schrödinger equation with the GEM, the binding energies and corresponding wave functions of the ground states and the excited states are obtained at the same time. The accuracy and efficiency of the GEM provide a great advantage for the dissociation problem of mesons. The results show that the ground states 11S0 and 13S1 have much higher dissociation temperatures than other states, and the spin-dependent interaction has a significant effect on the dissociation temperatures of 13S1 and 11S0. We also suggest using the radius of the bound state as a criterion of quarkonium dissociation. This can help to avoid the inaccuracy caused by the long tail of quarkonium binding energy dependence on temperature.
The dissociation temperatures of quarkonium states in a thermal medium are obtained in the framework of the quark model with the help of the Gaussian Expansion Method (GEM). This is the first time this method has been applied to the dissociation problem of mesons. The temperature-dependent potential is obtained by fitting the lattice results. Solving the Schrödinger equation with the GEM, the binding energies and corresponding wave functions of the ground states and the excited states are obtained at the same time. The accuracy and efficiency of the GEM provide a great advantage for the dissociation problem of mesons. The results show that the ground states 11S0 and 13S1 have much higher dissociation temperatures than other states, and the spin-dependent interaction has a significant effect on the dissociation temperatures of 13S1 and 11S0. We also suggest using the radius of the bound state as a criterion of quarkonium dissociation. This can help to avoid the inaccuracy caused by the long tail of quarkonium binding energy dependence on temperature.
2018, 42(8): 083104. doi: 10.1088/1674-1137/42/8/083104
Abstract:
The DArk Matter Particle Explorer (DAMPE) has observed a tentative peak at E～1.4 TeV in the cosmic-ray electron spectrum. In this paper, we interpret this excess in the scotogenic type-II seesaw model. This model extends the canonical type-II seesaw model with dark matter (DM) candidates and a loop-induced vacuum expectation value of the triplet scalars, v△, resulting in small neutrino masses naturally even for TeV scale triplet scalars. Assuming a nearby DM subhalo, the DAMPE excess can be explained by DM annihilating into a pair of triplet scalars which subsequently decay to charged lepton final states. Spectrum fitting of the DAMPE excess indicates it potentially favors the inverted neutrino mass hierarchy. We also discuss how to evade associated neutrino flux in our model.
The DArk Matter Particle Explorer (DAMPE) has observed a tentative peak at E～1.4 TeV in the cosmic-ray electron spectrum. In this paper, we interpret this excess in the scotogenic type-II seesaw model. This model extends the canonical type-II seesaw model with dark matter (DM) candidates and a loop-induced vacuum expectation value of the triplet scalars, v△, resulting in small neutrino masses naturally even for TeV scale triplet scalars. Assuming a nearby DM subhalo, the DAMPE excess can be explained by DM annihilating into a pair of triplet scalars which subsequently decay to charged lepton final states. Spectrum fitting of the DAMPE excess indicates it potentially favors the inverted neutrino mass hierarchy. We also discuss how to evade associated neutrino flux in our model.
2018, 42(8): 083105. doi: 10.1088/1674-1137/42/8/083105
Abstract:
We present a detailed study on the properties of the free energy density at high temperature by applying the principle of maximum conformality (PMC) scale-setting method within effective field theory. The PMC utilizes the renormalization group equation recursively to identify the occurrence and pattern of the non-conformal {βi}-terms, and determines the optimal renormalization scale at each order. Our analysis shows that a more accurate free energy density up to gs5-order level without renormalization scale dependence can be achieved by applying the PMC. We also observe that by using a smaller factorization scale around the effective parameter mE, the PMC prediction is consistent with the lattice QCD prediction derived at low temperature.
We present a detailed study on the properties of the free energy density at high temperature by applying the principle of maximum conformality (PMC) scale-setting method within effective field theory. The PMC utilizes the renormalization group equation recursively to identify the occurrence and pattern of the non-conformal {βi}-terms, and determines the optimal renormalization scale at each order. Our analysis shows that a more accurate free energy density up to gs5-order level without renormalization scale dependence can be achieved by applying the PMC. We also observe that by using a smaller factorization scale around the effective parameter mE, the PMC prediction is consistent with the lattice QCD prediction derived at low temperature.
2018, 42(8): 083106. doi: 10.1088/1674-1137/42/8/083106
Abstract:
Reconsideration of the T-duality of the open string allows us to introduce some geometric features in non-geometric theories. First, we have found what symmetry is T-dual to the local gauge transformations. It includes transformations of background fields but does not include transformations of the coordinates. According to this we have introduced a new, up to now missing term, with additional gauge field AiD (D denotes components with Dirichlet boundary conditions). It compensates non-fulfilment of the invariance under such transformations on the end-points of an open string, and the standard gauge field AaN (N denotes components with Neumann boundary conditions) compensates non-fulfilment of the gauge invariance. Using a generalized procedure we will perform T-duality of vector fields linear in coordinates. We show that gauge fields AaN and AiD are T-dual to ★ADa and ★ANi respectively. We introduce the field strength of T-dual non-geometric theories as derivatives of T-dual gauge fields along both T-dual variable yμ and its double ȳμ. This definition allows us to obtain gauge transformation of non-geometric theories which leaves the T-dual field strength invariant. Therefore, we introduce some new features of non-geometric theories where field strength has both antisymmetric and symmetric parts. This allows us to define new kinds of truly non-geometric theories.
Reconsideration of the T-duality of the open string allows us to introduce some geometric features in non-geometric theories. First, we have found what symmetry is T-dual to the local gauge transformations. It includes transformations of background fields but does not include transformations of the coordinates. According to this we have introduced a new, up to now missing term, with additional gauge field AiD (D denotes components with Dirichlet boundary conditions). It compensates non-fulfilment of the invariance under such transformations on the end-points of an open string, and the standard gauge field AaN (N denotes components with Neumann boundary conditions) compensates non-fulfilment of the gauge invariance. Using a generalized procedure we will perform T-duality of vector fields linear in coordinates. We show that gauge fields AaN and AiD are T-dual to ★ADa and ★ANi respectively. We introduce the field strength of T-dual non-geometric theories as derivatives of T-dual gauge fields along both T-dual variable yμ and its double ȳμ. This definition allows us to obtain gauge transformation of non-geometric theories which leaves the T-dual field strength invariant. Therefore, we introduce some new features of non-geometric theories where field strength has both antisymmetric and symmetric parts. This allows us to define new kinds of truly non-geometric theories.
2018, 42(8): 083107. doi: 10.1088/1674-1137/42/8/083107
Abstract:
Within the framework of the perturbative QCD approach, we calculate the time-like B_cm Bc(Bc*) form factors F(Q2) and A2(Q2). We include relativistic corrections and QCD corrections, either of which can give about 20% correction to the leading-order contribution, but there are cancellation effects between them. We calculate the cross sections of the e+e-→ Bc- Bc+(Bc*+) processes. The cross sections are enhanced at the Z pole to be σPP (Q=mZ)~1.3×10-5 pb and σPV (Q=mZ)~2.5×10-5 pb, which are still too small to be detected by proposed e+e- colliders such as the Circular Electron Positron Collider.
Within the framework of the perturbative QCD approach, we calculate the time-like B_cm Bc(Bc*) form factors F(Q2) and A2(Q2). We include relativistic corrections and QCD corrections, either of which can give about 20% correction to the leading-order contribution, but there are cancellation effects between them. We calculate the cross sections of the e+e-→ Bc- Bc+(Bc*+) processes. The cross sections are enhanced at the Z pole to be σPP (Q=mZ)~1.3×10-5 pb and σPV (Q=mZ)~2.5×10-5 pb, which are still too small to be detected by proposed e+e- colliders such as the Circular Electron Positron Collider.
2018, 42(8): 083108. doi: 10.1088/1674-1137/42/8/083108
Abstract:
We investigate the resonant production of color octet muons in order to explore the discovery potential of Future Circular Collider (FCC)-based μp colliders. It is shown that the search potentials of μp colliders essentially surpass the potential of the LHC and would exceed that of the FCC m pp collider.
We investigate the resonant production of color octet muons in order to explore the discovery potential of Future Circular Collider (FCC)-based μp colliders. It is shown that the search potentials of μp colliders essentially surpass the potential of the LHC and would exceed that of the FCC m pp collider.
2018, 42(8): 084101. doi: 10.1088/1674-1137/42/8/084101
Abstract:
We study the near-threshold pion-induced production of φ mesons off nuclei in the kinematical conditions of the HADES experiment, recently performed at GSI. The calculations have been performed within a collision model based on the nuclear spectral function. The model accounts for both the primary π- meson-proton π-p → φn and the secondary pion-nucleon πN → φN φ production processes as well as the effects of the nuclear φ and nucleon mean-field potentials. We find that the primary reaction channel π-p → φn dominates in the φ production off 12C and 184W target nuclei in the HADES acceptance window at incident pion momentum of 1.7 GeV/c. We calculate the momentum dependence of the absolute and relative (transparency ratio) φ meson yields from the above direct channel. The calculations have been performed for this initial pion momentum allowing for different options for the φN absorption cross section σφN and different scenarios for the in-medium mass shifts of the φ meson and secondary neutron, produced together with φ in this channel. We demonstrate that the transparency ratio for the φ mesons has, contrary to the absolute cross sections, an insignificant sensitivity to the φ meson and secondary neutron in-medium mass shifts at φ momenta studied in the HADES experiment. On the other hand, we show that there are measurable changes in the transparency ratio due to the φN absorption cross section, which means that such a relative observable can be useful to help determine this cross section from the data taken in the HADES experiment.
We study the near-threshold pion-induced production of φ mesons off nuclei in the kinematical conditions of the HADES experiment, recently performed at GSI. The calculations have been performed within a collision model based on the nuclear spectral function. The model accounts for both the primary π- meson-proton π-p → φn and the secondary pion-nucleon πN → φN φ production processes as well as the effects of the nuclear φ and nucleon mean-field potentials. We find that the primary reaction channel π-p → φn dominates in the φ production off 12C and 184W target nuclei in the HADES acceptance window at incident pion momentum of 1.7 GeV/c. We calculate the momentum dependence of the absolute and relative (transparency ratio) φ meson yields from the above direct channel. The calculations have been performed for this initial pion momentum allowing for different options for the φN absorption cross section σφN and different scenarios for the in-medium mass shifts of the φ meson and secondary neutron, produced together with φ in this channel. We demonstrate that the transparency ratio for the φ mesons has, contrary to the absolute cross sections, an insignificant sensitivity to the φ meson and secondary neutron in-medium mass shifts at φ momenta studied in the HADES experiment. On the other hand, we show that there are measurable changes in the transparency ratio due to the φN absorption cross section, which means that such a relative observable can be useful to help determine this cross section from the data taken in the HADES experiment.
2018, 42(8): 084102. doi: 10.1088/1674-1137/42/8/084102
Abstract:
We examine the structural properties and half-life decay of Ra isotopes within the axially deformed Relativistic Mean-Field (RMF) theory with NL3 force parameters. We work out the binding energy (BE), RMS radii, two-neutron separation energies (S2n), and some other observables. The results are in good agreement with the finite-range droplet model (FRDM) and experimental results. Considering the possibility of neutron magic number, the α-decay and cluster decay half-lives of Ra isotopes are calculated systematically using the Q-values obtained from the RMF formalism. These decay half-life calculations are carried out by taking three different empirical formulae. The calculated decay half-lives are found to be highly sensitive to the choice of Q-values. Possible shell or sub-shell closures are found at daughter nuclei with N=128 and N=126 when alpha and 8Be, 12C, 18O respectively are emitted from Ra isotopes. Though the cluster radioactivity is affected by the shell closure of parent and daughter, a long half-life indicates the stability of the parent, and a small parent half-life indicates that the shell stability of the daughter against decay.
We examine the structural properties and half-life decay of Ra isotopes within the axially deformed Relativistic Mean-Field (RMF) theory with NL3 force parameters. We work out the binding energy (BE), RMS radii, two-neutron separation energies (S2n), and some other observables. The results are in good agreement with the finite-range droplet model (FRDM) and experimental results. Considering the possibility of neutron magic number, the α-decay and cluster decay half-lives of Ra isotopes are calculated systematically using the Q-values obtained from the RMF formalism. These decay half-life calculations are carried out by taking three different empirical formulae. The calculated decay half-lives are found to be highly sensitive to the choice of Q-values. Possible shell or sub-shell closures are found at daughter nuclei with N=128 and N=126 when alpha and 8Be, 12C, 18O respectively are emitted from Ra isotopes. Though the cluster radioactivity is affected by the shell closure of parent and daughter, a long half-life indicates the stability of the parent, and a small parent half-life indicates that the shell stability of the daughter against decay.
2018, 42(8): 084103. doi: 10.1088/1674-1137/42/8/084103
Abstract:
We propose a novel method to search for the chiral magnetic effect (CME) in heavy ion collisions. We argue that the relative strength of the magnetic field (mainly from spectator protons and responsible for the CME) with respect to the reaction plane and the participant plane is opposite to that of the elliptic flow background arising from the fluctuating participant geometry. This opposite behavior in a single collision system, hence with small systematic uncertainties, can be exploited to extract the possible CME signal from the flow background. The method is applied to existing data from hic, and the outcome discussed.
We propose a novel method to search for the chiral magnetic effect (CME) in heavy ion collisions. We argue that the relative strength of the magnetic field (mainly from spectator protons and responsible for the CME) with respect to the reaction plane and the participant plane is opposite to that of the elliptic flow background arising from the fluctuating participant geometry. This opposite behavior in a single collision system, hence with small systematic uncertainties, can be exploited to extract the possible CME signal from the flow background. The method is applied to existing data from hic, and the outcome discussed.
2018, 42(8): 084104. doi: 10.1088/1674-1137/42/8/084104
Abstract:
Expressions of the spectroscopic factors (SFs) corresponding to one-particle transfer reactions have been established using a schematic definition. These expressions have been derived by taking into account the isovector neutron-proton (np) pairing correlations and a particle-number projection in the framework of the generalized Sharp-BCS (SBCS) method. Recently proposed expressions of the projected wave-functions of odd-mass nuclei have been used for this purpose. The formalism has first been tested using the single-particle energies of the schematic picket-fence model. It is shown that the np pairing and particle-number fluctuation effects are far from negligible and they depend on the pairing gap parameter values. Their behavior is not the same when the parent nuclei are even-even or odd. Predictions dealing with the SFs corresponding to one-proton stripping and one-neutron pick-up reactions in proton-rich nuclei have then been established within the framework of the realistic Woods-Saxon model. It is shown that the np pairing effect as well as the particle-number projection effect are important and thus have to be included in future calculations of the SF corresponding to these kinds of reactions.
Expressions of the spectroscopic factors (SFs) corresponding to one-particle transfer reactions have been established using a schematic definition. These expressions have been derived by taking into account the isovector neutron-proton (np) pairing correlations and a particle-number projection in the framework of the generalized Sharp-BCS (SBCS) method. Recently proposed expressions of the projected wave-functions of odd-mass nuclei have been used for this purpose. The formalism has first been tested using the single-particle energies of the schematic picket-fence model. It is shown that the np pairing and particle-number fluctuation effects are far from negligible and they depend on the pairing gap parameter values. Their behavior is not the same when the parent nuclei are even-even or odd. Predictions dealing with the SFs corresponding to one-proton stripping and one-neutron pick-up reactions in proton-rich nuclei have then been established within the framework of the realistic Woods-Saxon model. It is shown that the np pairing effect as well as the particle-number projection effect are important and thus have to be included in future calculations of the SF corresponding to these kinds of reactions.
2018, 42(8): 084105. doi: 10.1088/1674-1137/42/8/084105
Abstract:
The influence of σ* and φ on the proto-neutron star (PNS) PSR J0348+0432 is described by the relativistic mean field theory (RMFT) through choosing effective coupling constants. We use an entropy per baryon S=1 to describe the thermal effects on PSR J0348+0432 in this work and compare this PNS with and without σ*, φ. These effects include the particle number distribution, mass-radius relation, moment of inertia and surface gravitational redshift. The PNS PSR J0348+0432 with σ* and φ has more nucleons and will push forward the threshold for the appearance of the hyperons. The mass-radius relations are (2.010M⊙, 12.6520 km) with σ* and φ and (2.010M⊙, 12.6170 km) without σ* and φ. The moments of inertia corresponding to PNS PSR J0348+0432 are (2.010M⊙, 1.510×1045 g·cm2) and (2.010M⊙, 1.559×1045 g·cm2) respectively, and the surface gravitational redshifts are (2.010M⊙, 0.3747) and (2.010M⊙, 0.3701) respectively. With the help of these calculations, we study the restriction of σ* and φ on the interactions between baryons in the PNS core.
The influence of σ* and φ on the proto-neutron star (PNS) PSR J0348+0432 is described by the relativistic mean field theory (RMFT) through choosing effective coupling constants. We use an entropy per baryon S=1 to describe the thermal effects on PSR J0348+0432 in this work and compare this PNS with and without σ*, φ. These effects include the particle number distribution, mass-radius relation, moment of inertia and surface gravitational redshift. The PNS PSR J0348+0432 with σ* and φ has more nucleons and will push forward the threshold for the appearance of the hyperons. The mass-radius relations are (2.010M⊙, 12.6520 km) with σ* and φ and (2.010M⊙, 12.6170 km) without σ* and φ. The moments of inertia corresponding to PNS PSR J0348+0432 are (2.010M⊙, 1.510×1045 g·cm2) and (2.010M⊙, 1.559×1045 g·cm2) respectively, and the surface gravitational redshifts are (2.010M⊙, 0.3747) and (2.010M⊙, 0.3701) respectively. With the help of these calculations, we study the restriction of σ* and φ on the interactions between baryons in the PNS core.
2018, 42(8): 085101. doi: 10.1088/1674-1137/42/8/085101
Abstract:
Spherical gravitational collapse towards a black hole with non-zero tangential pressure is studied. Exact solutions corresponding to different equations of state are given. We find that when taking the tangential pressure into account, the exact solutions have three qualitatively different outcomes. For positive tangential pressure, the shell around a black hole may eventually collapse onto the black hole, or expand to infinity, or have a static but unstable solution, depending on the combination of black hole mass, mass of the shell and the pressure parameter. For vanishing or negative pressure, the shell will collapse onto the black hole. For all eventually collapsing solutions, the shell will cross the event horizon, instead of accumulating outside theeventhorizon, even if clocked by a distant stationary observer.
Spherical gravitational collapse towards a black hole with non-zero tangential pressure is studied. Exact solutions corresponding to different equations of state are given. We find that when taking the tangential pressure into account, the exact solutions have three qualitatively different outcomes. For positive tangential pressure, the shell around a black hole may eventually collapse onto the black hole, or expand to infinity, or have a static but unstable solution, depending on the combination of black hole mass, mass of the shell and the pressure parameter. For vanishing or negative pressure, the shell will collapse onto the black hole. For all eventually collapsing solutions, the shell will cross the event horizon, instead of accumulating outside theeventhorizon, even if clocked by a distant stationary observer.
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