119295694
Remarks on possible local parity violation in heavy ion collisions
In this Rapid Communication we discuss some observations concerning the possible local parity violation in heavy ion collisions recently announced by the STAR Collaboration. Our results can be summarized as follows (i) the measured correlations for same-charge pairs are mainly in-plane and not out of plane, (ii) if there is a parity-violating component it is large and surprisingly of the same magnitude as the background, and (iii) the observed dependence of the signal on the transverse momentum (${p}_{t}$) is consistent with a soft boost in ${p}_{t}$ and thus in line with expectations from the proposed chiral magnetic effect.
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.
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.
73681368
Charge-dependent azimuthal correlations from AuAu to UU collisions
Abstract We study the charge-dependent azimuthal correlations in relativistic heavy ion collisions, as motivated by the search for the Chiral Magnetic Effect (CME) and the investigation of related background contributions. In particular we aim to understand how these correlations induced by various proposed effects evolve from collisions with AuAu system to that with UU system. To do that, we quantify the generation of magnetic field in UU collisions at RHIC energy and its azimuthal correlation with the matter geometry using event-by-event simulations. Taking the experimental data for charge-dependent azimuthal correlations from AuAu collisions and extrapolating to UU with reasonable assumptions, we examine the resulting correlations to be expected in UU collisions and compare them with recent STAR measurements. Based on such analysis we discuss the viability for explaining the data with a combination of the CME-like and flow-induced contributions.
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.
54841531
Partial Quark-Lepton Universality and Neutrino CP Violation
We study a model with partial quark-lepton universality that can naturally arise in grand unified theories. We find that constraints on the model can be reduced to a single condition on the Dirac CP phase in the neutrino sector. Using our current knowledge of the CKM and PMNS mixing matrices, we predict at .
118470936
Texture and cofactor zeros of the neutrino mass matrix
A bstractWe study Majorana neutrino mass matrices that have two texture zeros, or two cofactor zeros, or one texture zero and one cofactor zero. The two texture/cofactor zero conditions give four constraints, which in conjunction with the five measured oscillation parameters completely determine the nine independent real parameters of the neutrino mass matrix. We also study the implications that future measurements of neutrinoless double beta decay and the Dirac CP phase will have on these cases.
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.
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.