53358558
The Chrial Magnetic Wave and Strong Field Effects in Heavy Ion Collisions
A number of recent progresses in the study of strong field effects in heavy ion collisions are discussed here: 1) the Chiral Magnetic Wave (CMW) and its experimental manifestation via splitting of positive/negative pions' elliptic flow; 2) the event-by-event azimuthal fluctuations of strong EM fields and its correlations with matter geometry; 3) a new mechanism for generating axial current in external electric field, the Chiral Electric Separation Effect (CESE).
118643861
Glasma evolution and Bose-Einstein condensation with elastic and inelastic collisions
In this paper we investigate the role of inelastic collisions in the kinetic evolution of a highly overpopulated gluon system starting from Glasma-type initial condition. Using the Gunion-Bertsch formula we derive the inelastic collision kernel under the collinear and small angle approximations. With both numerics and analytic analysis, we show that the inelastic process has two effects: globally changing (mostly reducing) the total particle number, while locally at small momentum regime always filling up the infrared modes extremely quickly. This latter effect is found to significantly speed up the emergence of a local thermal distribution in the infrared regime with vanishing local "chemical potential" and thus catalyze the onset of dynamical Bose-Einstein Condensation to occur faster (as compared with the purely elastic case) in the overpopulated Glasma.
119181141
Anomalous transport effects and possible environmental symmetry ‘violation’ in heavy-ion collisions
The heavy-ion collision provides a unique many-body environment where local domains of strongly interacting chiral medium may occur and in a sense allow environmental symmetry ‘violation’ phenomena. For example, certain anomalous transport processes, forbidden in usual medium, become possible in such domains. We briefly review recent progress in both the theoretical understanding and experimental search of various anomalous transport effects (such as the chiral magnetic effect, chiral separation effect, chiral electric separation effect, chiral electric /magnetic waves, etc.) in the hot QCD fluid formed by such collisions.
18691426
On the Fluidity and Super-Criticality of the QCD matter at RHIC
In this paper we discuss the fluidity of the hot and dense QCD matter created in ultrarelativistic heavy ion collisions in comparison with various other fluids, and in particular suggest its possible super-criticality. After examining the proper way to compare non-relativistic and relativistic fluids from both thermodynamic and hydrodynamic perspectives, we propose a new fluidity measure which shows certain universality for a remarkable diversity of critical fluids. We then demonstrate that a fluid in its super-critical regime has its fluidity considerably enhanced. Finally we discuss a possible relationship between the seemingly good fluidity of the QCD matter produced in heavy ion collisions at center of mass energy of √ s = 200 AGeV and the super-criticality of this matter with respect to the Critical-End-Point of the QCD phase diagram. Implications on the matter fluidity from SPS to LHC energies and potential signals for the search of the QCD Critical-End-Point via a beam energy scan are discussed as well.
118483879
Enhancement of jet quenching around phase transition: result from the dynamical holographic model
The phase transition and jet quenching parameter (q) over cap are investigated in the framework of the dynamical holographic QCD model. We find that both the trace anomaly and the ratio of the jet quenching parameter over cubic temperature (q) over cap /T-3 show a peak around the critical temperature T-c, and the ratio of the jet quenching parameter over entropy density (q) over cap / s sharply rises at T-c. This indicates that the jet quenching parameter can characterize the phase transition. The effect of the jet quenching parameter enhancement around the phase transition on the nuclear modification factor R-AA and elliptic flow upsilon(2) are also analyzed, and we find that the temperature-dependent jet quenching parameter from the dynamical holographic QCD model can considerably improve the description of jet quenching azimuthal anisotropy as compared with the conformal case.
119285694
Conserved charge fluctuations and susceptibilities in strongly interacting matter
A bstractWe study the conserved charge fluctuations, as quantified by the corresponding susceptibilities, in strongly interacting matter as motived by the quark-gluon plasma. Using the gauge-gravity correspondence approach, we study the patterns of conserved charge fluctuations in two types of holographic models for QCD, the D4/D8 and the D3/D7 models. We compute and compare the quark number susceptibilities in both models and find an interesting common feature of the two: at very strong coupling higher order susceptibilities are suppressed and the conserved charge fluctuations become purely Guassian. In light of the state-of-the-art lattice QCD results we also discuss what we can learn from these susceptibilities about the underlying degrees of freedom in the 1 ~ 2Tc quark-gluon plasma and examine the viability of different ideas such as holography, quasi-particles, as well as bound states. From analyzes of second order susceptibilities we conclude that the bound states exist and are important in the 1 ~ 2Tc region. We further construct and make predictions for several ratios of fourth-order susceptibilities that can sensitively reveal such bound states.
118598318
One diagonal texture or cofactor zero of the neutrino mass matrix
In view of the recent measurement of nonzero $\theta_{13}$, we carry out a systematic study of a simple class of neutrino models that has one diagonal texture or cofactor zero in the mass matrix. There are seven free parameters in the model and five of them are already measured by neutrino oscillation experiments; some cases for the normal or inverted hierarchy are excluded and for the rest we obtain the preferred values for the lightest neutrino mass and Dirac CP phase. We find that there are strong similarities between one diagonal texture zero models with one mass hierarchy and one diagonal cofactor zero models with the opposite mass hierarchy. We also make predictions for neutrinoless double beta decay for these models. For the one cofactor zero models, we present a simple realization based on a new U(1) gauge symmetry.
209836136
First Measurement of the Cross Section for Top-Quark Pair Production in Proton-Proton Collisions at sqrt(s)=7 TeV
The first measurement of the cross section for top-quark pair production in pp collisions at the LHC at center-of-mass energy sqrt(s)= 7 TeV has been performed using 3.1 {pm} 0.3 inverse pb of data recorded by the CMS detector. This result utilizes the final state with two isolated, highly energetic charged leptons, large missing transverse energy, and two or more jets. Backgrounds from Drell-Yan and non-W/Z boson production are estimated from data. Eleven events are observed in the data with 2.1 {pm} 1.0 events expected from background. The measured cross section is 194 {pm} 72 (stat.) {pm} 24 (syst.) {pm} 21 (lumi.) pb, consistent with next-to-leading order predictions.
122553437
Constraints on texture zero and cofactor zero models for neutrino mass
Imposing a texture or cofactor zero on the neutrino mass matrix reduces the number of independent parameters from nine to seven. Since five parameters have been measured, only two independent parameters would remain in such models. We find the allowed regions for single texture zero and single cofactor zero models. We also find strong similarities between single texture zero models with one mass hierarchy and single cofactor zero models with the opposite mass hierarchy. We show that this correspondence can be generalized to texture-zero and cofactor-zero models with the same homogeneous costraints on the elements and cofactors.
119282241
Perturbations to $\mu-\tau$ symmetry in neutrino mixing
Many neutrino mixing scenarios that have \mu-\tau symmetry with \theta_{13}=0 are in disagreement with recent experimental results that indicate a nonzero value for \theta_{13}. We investigate the effect of small perturbations on Majorana mass matrices with \mu-\tau symmetry and derive analytic formulae for the corrections to the mixing angles. We find that since m_1 and m_2 are nearly degenerate, \mu-\tau symmetry mixing scenarios are able to explain the experimental data with about the same size perturbation for most values of \theta_{12}. This suggests that the underlying unperturbed mixing need not have \theta_{12} close to the experimentally preferred value. One consequence of this is that a new class of models with \mu-\tau symmetry is possible, with unperturbed \theta_{12} equal to zero or 90 degrees for arbitrary unperturbed \theta_{13}.
202110088
Search for resonances in the dijet mass spectrum from 7 TeV pp collisions at CMS
A search for narrow resonances with a mass of at least 1 TeV in the dijet mass spectrum is performed using pp collisions at root s = 7 TeV corresponding to an integrated luminosity of 1 fb(-1), collected by the CMS experiment at the LHC. No resonances are observed. Upper limits at the 95% confidence level are presented on the product of the resonance cross section, branching fraction into dijets, and acceptance, separately for decays into quark-quark, quark-gluon, and gluon-gluon pairs. The data exclude new particles predicted in the following models at the 95% confidence level: string resonances with mass less than 4.00 TeV, E-6 diquarks with mass less than 3.52 TeV, excited quarks with mass less than 2.49 TeV, axigluons and colorons with mass less than 2.47 TeV, and W' bosons with mass less than 1.51 TeV. These results extend previous exclusions from the dijet mass search technique. (C) 2011 CERN. Published by Elsevier B.V. All rights reserved.