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.
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.
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.
118833743
Formation Region and Amplitude of Colour Superconductivity in an Instanton—Induced Model
Colour superconductivity is investigated in the frame of a two flavour instanton-induced model.The ratio of diquark to quark-antiquark coupling constants is restricted to be c/(Nc-1) with 1≤c≤2.87 and controls the formation region and amplitude of colour superconductivity.While the finite current quark mass changer the chiral transition significantly,it does not considerably change the colour superconductivity.
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.
118439777
Charge-Dependent Correlations in Relativistic Heavy Ion Collisions and the Chiral Magnetic Effect
We provide a phenomenological analysis of present experimental searches for local parity violation manifested through the Chiral Magnetic Effect. We introduce and discuss the relevant correlation functions used for the measurements. Our analysis of the available data from both RHIC and LHC shows that the present experimental evidence for the Chiral Magnetic Effect is rather ambiguous. We further discuss in some detail various background contributions due to conventional physics, which need to be understood quantitatively in order to draw a definitive conclusion about the existence of local parity violation in heavy ion collisions.
118692088
Seesaw mechanism with four texture zeros in the neutrino Yukawa matrix
With the recent observation of nonzero \theta_{13}, five neutrino oscillation parameters are now known. By imposing four zeros in the Yukawa coupling matrix of the type I seesaw model, the number of parameters in the neutrino mass matrix is reduced to seven, and we are able to make predictions for the lightest neutrino mass, Dirac CP phase, and neutrinoless double beta decay. Four texture zeros in the Yukawa coupling matrix is equivalent to either a single texture zero or a single cofactor zero for an off-diagonal element of the light neutrino mass matrix. We find strong similarities between single texture zero models with one mass ordering and single cofactor zero models with the opposite mass ordering. In the context of a specific class of single-flavor leptogenesis models, we find additional constraints on the parameter space.
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 .
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}.
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.
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.