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.
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.
56455253
Facets of the QCD Phase-Diagram
In this contribution we will discuss two aspects of the matter created in ultra-relativistic heavy ion collisions. First we will attempt to define a universal measure for the fluidity of a substance, which will allow a correct comparison between the fluidity of a Quark Gluon Plasma and any well known substance. Second we will discuss current measurements of particle correlations and their implication for possible local parity violation.
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.
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.
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).