119194069
Event-by-event azimuthal anisotropy of jet quenching in relativistic heavy ion collisions
Background: Strong jet quenching has been observed in heavy ion collisions at both the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) that can be understood through substantial jet energy loss in the created hot QCD matter. Yet the azimuthal anisotropy of jet quenching has not been thoroughly studied in the presence of strong fluctuations in the initial condition. Purpose: We present with full details a systematic quantification of the hard probe azimuthal response to the geometry and fluctuations of the hot QCD matter at both RHIC and LHC. We also examine the hard-soft dihadron correlation arising from the hard and soft sectors’ responses to the common fluctuating initial condition. Methods: An even-by-event MC simulation is employed. Different geometrical jet-quenching models are tested. The azimuthal anisotropy of jet quenching is extracted and decomposed as harmonic responses (for n=1-6) to the corresponding harmonics in the initial state. Results: We show that such jet response harmonics are sensitive to the jet quenching models as well as to the initial composition of bulk matter. Their centrality dependence puts a strong constraint on the path-length and medium-density dependence of jet energy loss. The computed hard-soft dihadron correlation shows a strong peak on the near side in RHIC central collisions. The triggered correlation in noncentral collisions is also presented. Conclusions: Only the jet-quenching model with near-Tc enhancement survives the secondharmonic test by the RHIC and LHC. Other harmonics in this model are consistent with the available data. We also demonstrate that the experimentally observed “hard ridge” can be explained in our calculation and that its trigger-azimuthal-angle and associate-pt dependence could also be qualitatively understood.
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.
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.
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.
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.
119297409
Jet Quenching and Its Azimuthal Anisotropy in AA and possibly High Multiplicity pA and dA Collisions
We report our calculation of jet quenching and its azimuthal anisotropy in the high energy AA and high multiplicity pA and dA collisions. The purpose of this study is twofold. First, we improve our previous event-by-event studies, by properly implementing $p_t$ dependence in the modeling. We show that, within the jet "monography" scenario featuring a strong near-Tc-enhancement of jet energy loss, the computed high-$p_t$ nuclear modification factor $R_{AA}$ and the harmonic coefficients in its azimuthal anisotropy $v_{2,\,3,\,4}$, agree well with the available data from both Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC). Second, in light of current discussions on possible final state collective behavior in the high-multiplicity pPb and dAu collisions, we examine the implication of final state jet attenuation in such collisions, by applying the same model used in AA collisions and quantifying the corresponding $R_{pA}$ and $R_{dA}$ and their azimuthal anisotropy. The high-$p_t$ $V_n$ provide a set of clean indicators of final state energy loss. In particular we find in the most central pPb (5.02 TeV) and dAu (200 GeV) collisions, $V_2$ is on the order of $0.01$ and $0.1$ respectively, measurable with current experimental accuracy. In addition, our high-$p_t$ $R_{dA}$ is around $0.6$ which is compatible with preliminary dAu results from RHIC.
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.
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 .
118477299
Dual models of the neutrino mass spectrum
We show that any model with a homogeneous relationship among elements of the neutrino mass matrix with one mass hierarchy yields predictions for the oscillation parameters and Majorana phases similar to those given by a model with the same homogeneous relationship among cofactors of the neutrino mass matrix with the opposite mass hierarchy, except when the lightest mass is of order 20 meV or less.
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.
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.