54998219
Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC
A search for the Standard Model Higgs boson in proton–proton collisions with the ATLAS detector at the LHC is presented. The datasets used correspond to integrated luminosities of approximately 4.8 fb−1 collected at View the MathML source in 2011 and 5.8 fb−1 at View the MathML source in 2012. Individual searches in the channels H→ZZ(⁎)→4l, H→γγ and H→WW(⁎)→eνμν in the 8 TeV data are combined with previously published results of searches for H→ZZ(⁎), WW(⁎), View the MathML source and τ+τ− in the 7 TeV data and results from improved analyses of the H→ZZ(⁎)→4l and H→γγ channels in the 7 TeV data. Clear evidence for the production of a neutral boson with a measured mass of View the MathML source is presented. This observation, which has a significance of 5.9 standard deviations, corresponding to a background fluctuation probability of 1.7×10−9, is compatible with the production and decay of the Standard Model Higgs boson.
21554167
Measurement of the muon reconstruction performance of the ATLAS detector using 2011 and 2012 LHC proton–proton collision data
This paper presents the performance of the ATLAS muon reconstruction during the LHC run with $$pp$$pp collisions at $$\sqrt{s}=7$$s=7–8 TeV in 2011–2012, focusing mainly on data collected in 2012. Measurements of the reconstruction efficiency and of the momentum scale and resolution, based on large reference samples of $${J/\psi \rightarrow \mu \mu }$$J/ψ→μμ, $$Z \rightarrow \mu \mu $$Z→μμ and $${\Upsilon \rightarrow \mu \mu }$$Υ→μμ decays, are presented and compared to Monte Carlo simulations. Corrections to the simulation, to be used in physics analysis, are provided. Over most of the covered phase space (muon $$|\eta |<2.7$$|η|<2.7 and $$5 \lesssim p_{\mathrm{T}}\lesssim 100$$5≲pT≲100 GeV) the efficiency is above $$99\,\%$$99% and is measured with per-mille precision. The momentum resolution ranges from $$1.7\,\%$$1.7% at central rapidity and for transverse momentum $$p_{\mathrm{T}}\simeq 10$$pT≃10 GeV, to $$4\,\%$$4% at large rapidity and $$p_{\mathrm{T}}\simeq 100$$pT≃100 GeV. The momentum scale is known with an uncertainty of $$0.05\,\%$$0.05% to $$0.2\,\%$$0.2% depending on rapidity. A method for the recovery of final state radiation from the muons is also presented.
11562016
Evidence for the spin-0 nature of the Higgs boson using ATLAS data
Studies of the spin and parity quantum numbers of the Higgs boson are presented, based on protonproton collision data collected by the ATLAS experiment at the LHC. The Standard Model spin-parity J( ...
118525905
Yield correlations and $p_T$ dependence of charm hadrons in Pb + Pb collisions at $\sqrt{s_{NN}}= 2.76$ TeV
Recently the ALICE Collaboration has published a few data of charm hadrons in Pb + Pb collisions at the CERN Large Hadron Collider (LHC). We extend the quark combination to the charm sector and point out that the measurement of charm hadron yields can provide important insights into charm quark hadronization mechanism and properties of the hot and dense matter produced in high energy reactions. We propose several types of yield ratios, e.g. $D^{*+}/D^0$, $D_s^+/D^+$ and $\Lambda_c^+/D_s^+$, to measure various properties of low $p_T$ charm quark hadronization. We argue that ratios $D_s^+/D^0$ and $2D_s^+/(D^0+D^+)$ as the function of transverse momentum can serve as good probes for the dynamics of charm quark hadronization. We further make predictions for the yields and $p_T$ spectra of identified charm hadrons in central Pb + Pb collisions at $\sqrt{s_{NN}}= 2.76$ TeV.
119294887
Self-gravitational interaction in $z=$4 Horava-Lifshitz gravity
Motivated by recent works [1,2], the influences of self-gravitational interaction on the Hawking radiation are studied both for (3 + 1) and (4 + 1) dimensional black holes in $z = 4$ Ho\u{r}ava-Lifshitz gravity. It is found that the tunneling entropies $S_{B(3 + 1)}$ and $S_{B(4 + 1)}$ independent on particle's mass are consistent with the thermodynamical entropies $S_{BH(3 + 1)}$ and $S_{BH(4 + 1)}$, respectively. There is a very visible degree of uniformity between thermodynamics and quantum tunneling in $z = 4$ Ho\u{r}ava-Lifshitz gravity. It suggests that the entropies contained corrected terms could be explained well by the self-gravitational interaction of Hawking radiation. The study of tunneling process may shed light on understanding the Ho\u{r}ava-Lifshitz gravity.
119629879
Study of a prototype water Cherenkov detector for the Daya Bay neutrino experiment
The Daya Bay reactor neutrino experiment is designed to precisely measure the neutrino mixing angle theta(13). The anti-neutrino detectors are shielded by highly purified water against radioactivity and spallation neutrons from surrounding rocks. The water also serves as a Cherenkov detector to tag cosmic-ray muons, which induce main backgrounds. In order to study water purification and details of the detector response, a prototype water Cherenkov detector is constructed at the Institute of High Energy Physics (IHEP), Beijing. The detector is divided by Tyvek into two sections and viewed by two 8 in. photomultipliers. Cosmic-ray muons are used for detector response studies and a Monte Carlo simulation based on the Geant4 package shows good agreement with the experimental data. (C) 2012 Elsevier B.V. All rights reserved.
118644726
Hadron yield correlation and constituent quark degree of freedom in heavy ion collisions
Based on the assumption of the production of deconfined quark matter, we use a quark combination model to systematically investigate hadron yields in heavy ion collisions from RHIC $\sqrt{s_{NN}}=200, 130, 62.4$ GeV to SPS $E_{beam}=158, 80, 40, 30, 20 $ AGeV. We find that as the collision energy is greater than or equal to 30 AGeV the yields of various hadrons, their correlations, in particular, the observables $A=\frac{\bar{\Lambda} k^{-} p}{\Lambda k^{+} \bar{p}}$ and $B=\frac{\Lambda k^{-}\bar{\Xi}^{+}}{\bar{\Lambda} k^{+}\Xi^{-}}$, are all reproduced; however, as the collision energy drops to 20 AGeV quark combination fails. This indicates that the constituent quark degrees of freedom represent a decisive factor in thermal hadron production above 30 AGeV and seem to be invalid at 20 AGeV. In addition, hadron yields as well as particle ratios at midrapidity in the most central Pb+Pb collisions at $\sqrt{s_{NN}}=5.5$ TeV are predicted.