arXiv subjects

Bin Zhang

Publications and source records attributed to Bin Zhang.

At least 307 records · Page 17Linked to original sources

arXiv2006

Signatures for Majorana neutrinos at hadron colliders

The Majorana nature of neutrinos may only be experimentally verified via lepton-number violating processes involving charged leptons. We explore the $ΔL=2$ like-sign dilepton production at hadron colliders to search for signals of Majorana neutrinos. We find significant sensitivity for resonant production of a Majorana neutrino in the mass range of 10-80 GeV at the current run of the Tevatron with 2 fb$^{-1}$ integrated luminosity, and in the range of 10-400 GeV at the LHC with 100 fb$^{-1}$.

hep-ph↗

arXiv2006

J/psi production from charm coalescence in relativistic heavy ion collisions

J/psi production and collective flow is studied with a coalescence model based on phase space distribution of charm quarks from a multi-phase transport model simulation of relativistic heavy ion collisions. Both the yield and the flow of J/psi particles are sensitive to charm quark final state interactions. As the charm quark rescattering cross section increases from 3 mb to 10 mb, J/psi elliptic flow increases faster than corresponding light hadron elliptic flows. The v_2(p_t) of J/psi crosses that of D mesons to reach a value that is about the peak value of the D meson flow but at a higher p_t. As J/psi elliptic flow has only contributions from charm quarks, it complements D meson elliptic flow in reflecting charm properties in the Quark-Gluon Plasma.

nucl-th↗

arXiv2005

A Multi-Phase Transport Model for Relativistic Heavy Ion Collisions

We describe in detail how the different components of a multi-phase transport (AMPT) model, that uses the Heavy Ion Jet Interaction Generator (HIJING) for generating the initial conditions, Zhang's Parton Cascade (ZPC) for modeling partonic scatterings, the Lund string fragmentation model or a quark coalescence model for hadronization, and A Relativistic Transport (ART) model for treating hadronic scatterings, are improved and combined to give a coherent description of the dynamics of relativistic heavy ion collisions. We also explain the way parameters in the model are determined, and discuss the sensitivity of predicted results to physical input in the model. Comparisons of these results to experimental data, mainly from heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC), are then made in order to extract information on the properties of the hot dense matter formed in these collisions.

nucl-th↗

arXiv2005

Anomalous gauge couplings of the Higgs boson at high energy photon colliders

We study the sensitivity of testing the anomalous gauge couplings $g_{HVV}$'s of the Higgs boson in the formulation of linearly realized gauge symmetry via the processes $γγ\to ZZ$ and $γγ\to WWWW$ at polarized and unpolarized photon colliders based on $e^+e^-$ linear colliders of c.m.~energies 500 GeV, 1 TeV, and 3 TeV. Signals beyond the standard model (SM) and SM backgrounds are carefully studied. We propose certain kinematic cuts to suppress the standard model backgrounds. For an integrated luminosity of 1 ab$^{-1}$, we show that (a) $γγ\to ZZ$ can provide a test of $g_{Hγγ}$ to the $3σ$ sensitivity of $O(10^{-3}-10^{-2})$ TeV$^{-1}$ at a 500 GeV ILC, and $O(10^{-3})$ TeV$^{-1}$ at a 1 TeV ILC and a 3 TeV CLIC, and (b) $γγ\to WWWW$ at a 3 TeV CLIC can test all the anomalous couplings $g_{HVV}$'s to the $3σ$ sensitivity of $O(10^{-3}-10^{-2})$ TeV$^{-1}$.

hep-ph↗

arXiv2005

Charm elliptic flow in Au+Au collisions at RHIC

Using the perturbative method for the simulation of charmed particles, the dynamical origin of charm quark elliptic flow is studied in the framework of a multi-phase transport (AMPT) model. Besides the expected ordering relative to that of light quarks according to quark masses, charm quark elliptic flow is seen to be sensitive to the parton scattering cross section. To describe the observed large elliptic flow of electrons from the decay of charmed mesons, a charm quark elastic scattering cross section much larger than that estimated from the perturbative QCD is required.

nucl-th↗

arXiv2005

Charm elliptic flow at RHIC

Charm elliptic flow in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) is studied in a multiphase transport model. Assuming that the cross section for charm quark scattering with other light quarks is the same as that between light quarks, we find that both charm and light quark elliptic flows are sensitive to the value of the cross section. Compared to that of light quarks, the elliptic flow of charm quarks is smaller at low transverse momentum but approaches comparable values at high transverse momentum. Similar features are seen in the elliptic flow of charmed mesons as well as that of the electrons from their semileptonic decays when the charmed mesons are produced from quark coalescence during hadronization of the partonic matter. To describe the large electron elliptic flow observed in available experimental data requires a charm quark scattering cross section that is much larger than that given by the perturbative QCD.

nucl-th↗

arXiv2004

Distinguishing technicolor models via tt-bar productions at polarized photon colliders

We study top quark pair productions at a polarized photon collider from an e(+)e(-) linear collider (LC) in various improved technicolor model, namely, the one-family walking technicolor model, the top-color-assisted technicolor model, and the top-color-assisted multiscale technicolor model. Recent constraint on the top-pion mass from the precision data of R(b) is considered. It is shown that, considering only the statistical errors, a polarized photon collider from a 500 GeV LC with an integrated luminosity of 500 inverse fb is sufficient for distinguishing the three improved technicolor models experimentally.

hep-ph↗

arXiv2004

J/psi production in a gluon plasma produced in Au-Au collisions at the Relativistic Heavy Ion Collider

Centrality dependence of J/psi production in Au-Au collisions at 200 GeV nucleon-nucleon center of mass energy is studied using the Glauber model plus the kinetic formation model. Initial J/psi production and destruction by incoming nucleons are described by the Glauber model. J/psi-charm equilibration in the gluon plasma is described by the kinetic formation model. We explore the possibility of J/psi suppression suggested by the recent PHENIX data. We show that the J/psi yield monotonically decreases with increasing centrality in the kinetic formation model when the charm mass is smaller than a critical mass. The final J/psi yield is between the value after the Glauber suppression and the dynamical equilibrium value. This underscores the importance of both J/psi production from d-Au collisions, which is essential in determining the Glauber suppression, and high statistics Au-Au data, which can further constrain final state J/psi-charm equilibration.

nucl-th↗

arXiv2003

K-twisted K-theory for SU(N)

We present a version of twisted equivariant $K$-theory-$K$-twisted equivariant $K$-theory, and use Grothendieck differentials to compute the $K$ -twisted equivariant $K$-theory of simple simply connected Lie groups. We did the calculation explicitly for SU(N) explicitly. The basic idea is to interpret an equivariant gerbe as an element of equivariant $K$-theory of degree 1.

math.KT↗

arXiv2003

Equivariant Todd Classes for Toric Varieties

For a complete toric variety, we obtain an explicit formula for the localized equivariant Todd class in terms of the combinatorial data -- the fan. This is based on the equivariant Riemann-Roch theorem and the computation of the equivariant cohomology and equivariant homology of toric varieties.

math.AG↗

arXiv2003

Nuclear profile dependence of elliptic flow from a parton cascade

The transverse profile dependence of elliptic flow is studied in a parton cascade model. We compare results from the binary scaling profile to results from the wounded nucleon scaling profile. The impact parameter dependence of elliptic flow is shown to depend sensitively on the transverse profile of initial particles, however, if elliptic flow is plotted as a function of the relative multiplicity, the nuclear profile dependence disappears. The insensitivity was found previously in a hydrodynamical calculation. Our calculations indicate that the insensitivity is also valid with additional viscous corrections. In addition, the minimum bias differential elliptic flow is demonstrated to be insensitive to the nuclear profile of the system.

nucl-th↗

arXiv2003

Testing anomalous gauge couplings of the Higgs boson via weak-boson scatterings at the LHC

We propose a sensitive way to test the anomalous HVV couplings (V=W(+/-),Z(0)) of the Higgs boson (H), which can arise from either the dimension-3 effective operator in a nonlinearly realized Higgs sector or the dimension-6 effective operators in a linearly realized Higgs sector, via studying the VV scattering processes at the CERN LHC. The gold-plated pure leptonic decay modes of the final state weak bosons in the processes pp->VVjj are studied. For comparison, we also analyze the constraints from the precision electroweak data, the expected precision of the measurements of the Higgs boson production rate, decay width and branching ratios at the Tevatron run-2 and the CERN LHC, and the requirement of unitarity of the S-matrix. We show that, with an integrated luminosity of 300 inverse fb and sufficient kinematical cuts for suppressing the backgrounds, studying the process pp->w(+)+W(+)+j+j->l(+)+nu+l(+)+nu+j+j can probe the anomalous HWW couplings at a few tens of percent level for the nonlinearly realized Higgs sector, and at the level of 0.01-0.08 inverse TeV for the linearly realized effective Lagrangian.

hep-ph↗

arXiv2003

Equivariant gerbes over compact simple Lie groups

Using groupoid $S^1$-central extensions, we present, for a compact simple Lie group $G$, an infinite dimensional model of $S^1$-gerbe over the differential stack $G/G$ whose Dixmier-Douady class corresponds to the canonical generator of the equivariant cohomology $H_G^3 (G, Z)$.

math.SG↗

arXiv2002

Anomalous Gauge Interactions of the Higgs Boson: Precision Constraints and Weak Boson Scatterings

Interaction of Higgs scalar (H) with weak gauge bosons (V=W,Z) is the {\it key} to understand electroweak symmetry breaking (EWSB) mechanism. New physics effects in the HVV interactions, as predicted by models of compositeness, supersymmetry and extra dimensions, can be formulated as anomalous couplings via a generic effective Lagrangian. We first show that the existing electroweak precision data already impose nontrivial indirect constraints on the anomalous HVV couplings. Then, we systematically study VV --> VV scatterings in the TeV region, via Gold-plated pure leptonic decay modes of the weak bosons. We demonstrate that, even for a light Higgs boson in the mass range 115GeV < m_H < 300GeV, this process can directly probe the anomalous HVV interactions at the LHC with an integrated luminosity of 300fb^{-1}, which further supports the ``No-Lose'' theorem for the LHC to uncover the EWSB mechanism. Comparisons with the constraints from measuring the cross section of VH associate production and the Higgs boson decay width are also given.

hep-ph↗

arXiv2002

Nuclear modification of heavy quark fragmentation function and J/psi production in ultrarelativistic heavy ion collisions

In ultrarelativistic heavy ion collisions, charm quark fragmentation is modified due to the melting of strings inside the high density partonic matter. D mesons produced in hadronization can further produce J/psi particles. Using a multiphase transport model, we investigate the effect on the rapidity distribution of the produced J/psi particles with two different charm quark fragmentation functions. It is shown that the J/psi rapidity distribution is sensitive to the nuclear modification of charm quark fragmentation and thus is a good indicator of the onset of string melting and the production of deconfined partonic matter.

nucl-th↗

arXiv2002

J/psi production in relativistic heavy ion collisions from a multi-phase transport model

Using A Multi-Phase Transport (AMPT) model, we study J/psi production from interactions between charm and anti-charm quarks in initial parton phase and between D and Dbar mesons in final hadron phase of relativistic heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC). Including also the inverse reactions of J/psi absorption by gluons and light mesons, we find that the net number of J/psi from the parton and hadron phases is smaller than that expected from the superposition of initial nucleon-nucleon collisions, contrary to the J/psi enhancement predicted by the kinetic formation model. The production of J/psi is further suppressed if one includes the color screening effect in the parton phase. We have also studied the dependence of J/psi production on the charm quark mass and the effective charm meson mass.

nucl-th↗

arXiv2001

Detailed Balance and Sea-Quark Flavor Asymmetry of Proton

In this study, the proton is taken as an ensemble of quark-gluon Fock states. Using the principle of detailed balance, the probabilities of finding every Fock states of the proton are obtained without any parameter. A new origin of the light flavor sea quark asymmetry, i.e., $\bar{u} \not= \bar{d}$, is given as a pure statistical effect. It is found that $\bar{d}-\bar{u} \approx 0.124$, which is in surprisingly agreement with the experimental observation.

hep-ph↗

arXiv2001

Probing Mechanical and Chemical Instabilities in Neutron-Rich Matter

The isospin-dependence of mechanical and chemical instabilities is investigated within a thermal and nuclear transport model using a Skyrme-type phenomenological equation of state for neutron-rich matter. Respective roles of the nuclear mean field and the 2-body stochastic scattering on the evolution of density and isospin fluctuations in either mechanically or chemically unstable regions of neutron-rich matter are investigated. It is found that the mean field dominates overwhelmingly the fast growth of both fluctuations, while the 2-body scattering influences significantly the later growth of the isospin fluctuation only. The magnitude of both fluctuations decreases with the increasing isospin asymmetry because of the larger reduction of the attractive isoscalar mean field by the stronger repuslive neutron symmetry potential in the more neutron-rich matter. Moreover, it is shown that the isospin fractionation happens later, but grows faster in the more neutron-rich matter. Implications of these results to current experiments exploring properties of neutron-rich matter are discussed.

nucl-th↗