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.
118672243
Topology and criticality in the resonating Affleck-Kennedy-Lieb-Tasaki loop spin liquid states
We exploit a natural Projected Entangled-Pair State (PEPS) representation for the resonating Affleck-Kennedy-Lieb-Tasaki loop (RAL) state. By taking advantage of PEPS-based analytical and numerical methods, we characterize the RAL states on various two-dimensional lattices. On square and honeycomb lattices, these states are critical since the dimer-dimer correlations decay as a power law. On kagome lattice, the RAL state has exponentially decaying correlation functions, supporting the scenario of a gapped spin liquid. We provide further evidence that the RAL state on the kagome lattice is a $\mathbb{Z}_2$ spin liquid, by identifying the four topological sectors and computing the topological entropy. Furthermore, we construct a one-parameter family of PEPS states interpolating between the RAL state and a short-range Resonating Valence Bond state and find a critical point, consistent with the fact that the two states belong to two different phases. We also perform a variational study of the spin-1 kagome Heisenberg model using this one-parameter PEPS.
118857728
Dynamical chiral symmetry breaking in QED{sub 3} at finite density and impurity potential
We study the effects of finite chemical potential and impurity scattering on dynamical fermion mass generation in (2+1)-dimensional quantum electrodynamics. In any realistic systems, these effects usually cannot be neglected. The longitudinal component of the gauge field develops a finite static length produced by chemical potential and impurity scattering, while the transverse component remains long-ranged because of the gauge invariance. Another important consequence of impurity scattering is that the fermions have a finite damping rate, which reduces their lifetime. By solving the Dyson-Schwinger equation for the fermion mass function, it is found that these effects lead to strong suppression of the critical fermion flavor N{sub c} and the dynamical fermion mass in the symmetry broken phase.
119096204
Two-particle angular correlations in p+p and Cu+Cu collisions at PHOBOS
We present results on two-particle angular correlations in p+p and Cu+Cu collisions over a broad range of (η, ). The PHOBOS detector has a uniquely large angular coverage for inclusive charged particles. This allows for the study of correlations on both long- and short-range pseudorapidity scales. A complex two-dimensional correlation structure emerges which is interpreted in the context of a cluster model. The cluster size and its decay width are extracted from the two-particle pseudorapidity correlation function. Relative to p+p collisions, Cu+Cu reactions show a non-trivial decrease of cluster size with increasing centrality. These results may provide insight into the hadronization stage of the hot and dense medium created in heavy-ion collisions.
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.
119292700
Matter fields near quantum critical point in (2+1)-dimensional U(1) gauge theory
We study chiral phase transition and confinement of matter fields in (2+1)-dimensional U(1) gauge theory of massless Dirac fermions and scalar bosons. The vanishing scalar boson mass, r = 0, defines a quantum critical point between the Higgs phase and the Coulomb phase. We consider only the critical point r = 0 and the Coulomb phase with r > 0. The Dirac fermion acquires a dynamical mass when its flavor is less than certain critical value N c f , which depends quantitatively on the flavor Nb and the scalar boson mass r. When Nf < N c f , the matter fields carrying internal gauge charge are all confined if r 6 0 but are deconfined at the quantum critical point r = 0. The system has distinct low-energy elementary excitations at the critical point r = 0 and in the Coulomb phase with r 6 0. We calculate the specific heat and susceptibility of the system at r = 0 and r 6 0, which can help to detect the quantum critical point and to judge whether dynamical fermion mass generation takes place.
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.
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}.
118600692
The extraordinary glow
Abstract In this contribution I discuss some recent progress in understanding the evolution of the pre-thermal quark–gluon matter, known as the glasma, during the early stage in heavy ion collisions, and the implication for early time photon and dilepton emissions.
118438096
A study of the correlations between jet quenching observables at RHIC
Focusing on four types of correlation plots, RAA vs. v2, RAA vs. IAA, IAA vs. v IAA 2 and v2 vs. vAA 2 , we demonstrate how the centrality dependence of correlations between multiple jet quenching observables provide valuable insight into the energy loss mechanism in a quark-gluon plasma. In particular we find that a qualitative energy loss model gives a good description of RAA vs. v2 only when we take ∆E ∼ l and a medium geometry generated by a model of the Color Glass Condensate. This same ∆E ∼ l model also qualitatively describes the trigger pT dependence of RAA vs. IAA data and makes novel predictions for the centrality dependence for this RAA vs. IAA correlation. Current data suggests, albeit with extremely large uncertainty, that vAA 2 ≫ v2, a correlation that is difficult to reproduce in current energy loss models.
118419318
Azimuthally fluctuating magnetic field and its impacts on observables in heavy-ion collisions
Article history: The heavy-ion collisions can produce extremely strong transient magnetic and electric fields. We study the azimuthal fluctuation of these fields and their correlations with the also fluctuating matter geometry (characterized by the participant plane harmonics) using event-by-event simulations. A sizable suppression of the angular correlations between the magnetic field and the 2nd and 4th harmonic participant planes is found in very central and very peripheral collisions, while the magnitudes of these correlations peak around impact parameter b ∼ 8-10 fm for RHIC collisions. This can lead to notable impacts on a number of observables related to various magnetic field induced effects, and our finding suggests that the optimal event class for measuring them should be that corresponding to b ∼ 8-10 fm. © 2012 Elsevier B.V. All rights reserved.