The ATLAS experiment has observed 1995 Z boson candidates in data corresponding to 0.15 inverse nb of integrated luminosity obtained in the 2011 LHC Pb+Pb run at sqrt(s_NN)=2.76 TeV. The Z bosons are reconstructed via di-electron and di-muon decay channels, with a background contamination of less than 3%. Results from the two channels are consistent and are combined. Within the statistical and systematic uncertainties, the per-event Z boson yield is proportional to the number of binary collisions estimated by the Glauber model. The elliptic anisotropy of the azimuthal distribution of the Z boson with respect to the event plane is found to be consistent with zero.
The corrected per-event rapidity distribution of Z bosons over the centrality region 0-80%.
The corrected per-event transverse momentum distribution of Z bosons in the centrality region 0-5%.
The corrected per-event transverse momentum distribution of Z bosons in the centrality region 5-10%.
Measurements of the centrality and rapidity dependence of inclusive jet production in $\sqrt{s_\mathrm{NN}} = 5.02$ TeV proton--lead ($p$+Pb) collisions and the jet cross-section in $\sqrt{s} = 2.76$ TeV proton--proton collisions are presented. These quantities are measured in datasets corresponding to an integrated luminosity of 27.8 nb$^{-1}$ and 4.0 pb$^{-1}$, respectively, recorded with the ATLAS detector at the Large Hadron Collider in 2013. The $p$+Pb collision centrality was characterised using the total transverse energy measured in the pseudorapidity interval $-4.9 < \eta < -3.2$ in the direction of the lead beam. Results are presented for the double-differential per-collision yields as a function of jet rapidity and transverse momentum ($p_\mathrm{T}$) for minimum-bias and centrality-selected $p$+Pb collisions, and are compared to the jet rate from the geometric expectation. The total jet yield in minimum-bias events is slightly enhanced above the expectation in a $p_\mathrm{T}$-dependent manner but is consistent with the expectation within uncertainties. The ratios of jet spectra from different centrality selections show a strong modification of jet production at all $p_\mathrm{T}$ at forward rapidities and for large $p_\mathrm{T}$ at mid-rapidity, which manifests as a suppression of the jet yield in central events and an enhancement in peripheral events. These effects imply that the factorisation between hard and soft processes is violated at an unexpected level in proton-nucleus collisions. Furthermore, the modifications at forward rapidities are found to be a function of the total jet energy only, implying that the violations may have a simple dependence on the hard parton-parton kinematics.
The $R_{\mathrm{coll}}$ and $T_{p\mathrm{A}}$ values and their uncertainties in each centrality bin.
Per-event jet yields in 0-90% p+Pb collisions, within the centre of mass rapidity -2.1 to -1.2 (positive denotes downstream proton direction).
Per-event jet yields in 0-90% p+Pb collisions, within the centre of mass rapidity -1.2 to -0.8 (positive denotes downstream proton direction).
This paper presents measurements of charged-hadron spectra obtained in $pp$, $p$+Pb, and Pb+Pb collisions at $\sqrt{s}$ or $\sqrt{s_{_\text{NN}}}=5.02$ TeV, and in Xe+Xe collisions at $\sqrt{s_{_\text{NN}}}=5.44$ TeV. The data recorded by the ATLAS detector at the LHC have total integrated luminosities of 25 pb${}^{-1}$, 28 nb${}^{-1}$, 0.50 nb${}^{-1}$, and 3 $\mu$b${}^{-1}$, respectively. The nuclear modification factors $R_{p\text{Pb}}$ and $R_\text{AA}$ are obtained by comparing the spectra in heavy-ion and $pp$ collisions in a wide range of charged-particle transverse momenta and pseudorapidity. The nuclear modification factor $R_{p\text{Pb}}$ shows a moderate enhancement above unity with a maximum at $p_{\mathrm{T}} \approx 3$ GeV; the enhancement is stronger in the Pb-going direction. The nuclear modification factors in both Pb+Pb and Xe+Xe collisions feature a significant, centrality-dependent suppression. They show a similar distinct $p_{\mathrm{T}}$-dependence with a local maximum at $p_{\mathrm{T}} \approx 2$ GeV and a local minimum at $p_{\mathrm{T}} \approx 7$ GeV. This dependence is more distinguishable in more central collisions. No significant $|\eta|$-dependence is found. A comprehensive comparison with several theoretical predictions is also provided. They typically describe $R_\text{AA}$ better in central collisions and in the $p_{\mathrm{T}}$ range from about 10 to 100 GeV.
- - - - - - - - - - - - - - - - - - - - <br><b>charged-hadron spectra:</b> <br><i>pp reference:</i> <a href="?version=1&table=Table1">for p+Pb</a> <a href="?version=1&table=Table10">for Pb+Pb</a> <a href="?version=1&table=Table19">for Xe+Xe</a> <br><i>p+Pb:</i> <a href="?version=1&table=Table2">0-5%</a> <a href="?version=1&table=Table3">5-10%</a> <a href="?version=1&table=Table4">10-20%</a> <a href="?version=1&table=Table5">20-30%</a> <a href="?version=1&table=Table6">30-40%</a> <a href="?version=1&table=Table7">40-60%</a> <a href="?version=1&table=Table8">60-90%</a> <a href="?version=1&table=Table9">0-90%</a> <br><i>Pb+Pb:</i> <a href="?version=1&table=Table11">0-5%</a> <a href="?version=1&table=Table12">5-10%</a> <a href="?version=1&table=Table13">10-20%</a> <a href="?version=1&table=Table14">20-30%</a> <a href="?version=1&table=Table15">30-40%</a> <a href="?version=1&table=Table16">40-50%</a> <a href="?version=1&table=Table17">50-60%</a> <a href="?version=1&table=Table18">60-80%</a> <br><i>Xe+Xe:</i> <a href="?version=1&table=Table20">0-5%</a> <a href="?version=1&table=Table21">5-10%</a> <a href="?version=1&table=Table22">10-20%</a> <a href="?version=1&table=Table23">20-30%</a> <a href="?version=1&table=Table24">30-40%</a> <a href="?version=1&table=Table25">40-50%</a> <a href="?version=1&table=Table26">50-60%</a> <a href="?version=1&table=Table27">60-80%</a> </br>- - - - - - - - - - - - - - - - - - - - <br><b>nuclear modification factors (p<sub>T</sub>):</b> <br><i>R<sub>pPb</sub>:</i> <a href="?version=1&table=Table28">0-5%</a> <a href="?version=1&table=Table29">5-10%</a> <a href="?version=1&table=Table30">10-20%</a> <a href="?version=1&table=Table31">20-30%</a> <a href="?version=1&table=Table32">30-40%</a> <a href="?version=1&table=Table33">40-60%</a> <a href="?version=1&table=Table34">60-90%</a> <a href="?version=1&table=Table35">0-90%</a> <br><i>R<sub>AA</sub> (Pb+Pb):</i> <a href="?version=1&table=Table36">0-5%</a> <a href="?version=1&table=Table37">5-10%</a> <a href="?version=1&table=Table38">10-20%</a> <a href="?version=1&table=Table39">20-30%</a> <a href="?version=1&table=Table40">30-40%</a> <a href="?version=1&table=Table41">40-50%</a> <a href="?version=1&table=Table42">50-60%</a> <a href="?version=1&table=Table43">60-80%</a> <br><i>R<sub>AA</sub> (Xe+Xe):</i> <a href="?version=1&table=Table44">0-5%</a> <a href="?version=1&table=Table45">5-10%</a> <a href="?version=1&table=Table46">10-20%</a> <a href="?version=1&table=Table47">20-30%</a> <a href="?version=1&table=Table48">30-40%</a> <a href="?version=1&table=Table49">40-50%</a> <a href="?version=1&table=Table50">50-60%</a> <a href="?version=1&table=Table51">60-80%</a> </br>- - - - - - - - - - - - - - - - - - - - <br><b>nuclear modification factors (y*/eta):</b> <br><i>R<sub>pPb</sub>:</i> <br> 0-5%: <a href="?version=1&table=Table52">0.66-0.755GeV</a> <a href="?version=1&table=Table53">2.95-3.35GeV</a> <a href="?version=1&table=Table54">7.65-8.8GeV</a> <a href="?version=1&table=Table55">15.1-17.3GeV</a> <br> 5-10%: <a href="?version=1&table=Table56">0.66-0.755GeV</a> <a href="?version=1&table=Table57">2.95-3.35GeV</a> <a href="?version=1&table=Table58">7.65-8.8GeV</a> <a href="?version=1&table=Table59">15.1-17.3GeV</a> <br> 10-20%: <a href="?version=1&table=Table60">0.66-0.755GeV</a> <a href="?version=1&table=Table61">2.95-3.35GeV</a> <a href="?version=1&table=Table62">7.65-8.8GeV</a> <a href="?version=1&table=Table63">15.1-17.3GeV</a> <br> 20-30%: <a href="?version=1&table=Table64">0.66-0.755GeV</a> <a href="?version=1&table=Table65">2.95-3.35GeV</a> <a href="?version=1&table=Table66">7.65-8.8GeV</a> <a href="?version=1&table=Table67">15.1-17.3GeV</a> <br> 30-40%: <a href="?version=1&table=Table68">0.66-0.755GeV</a> <a href="?version=1&table=Table69">2.95-3.35GeV</a> <a href="?version=1&table=Table70">7.65-8.8GeV</a> <a href="?version=1&table=Table71">15.1-17.3GeV</a> <br> 40-60%: <a href="?version=1&table=Table72">0.66-0.755GeV</a> <a href="?version=1&table=Table73">2.95-3.35GeV</a> <a href="?version=1&table=Table74">7.65-8.8GeV</a> <a href="?version=1&table=Table75">15.1-17.3GeV</a> <br> 60-90%: <a href="?version=1&table=Table76">0.66-0.755GeV</a> <a href="?version=1&table=Table77">2.95-3.35GeV</a> <a href="?version=1&table=Table78">7.65-8.8GeV</a> <a href="?version=1&table=Table79">15.1-17.3GeV</a> <br> 0-90%: <a href="?version=1&table=Table80">0.66-0.755GeV</a> <a href="?version=1&table=Table81">2.95-3.35GeV</a> <a href="?version=1&table=Table82">7.65-8.8GeV</a> <a href="?version=1&table=Table83">15.1-17.3GeV</a> <br><i>R<sub>AA</sub> (Pb+Pb):</i> <br> 0-5%: <a href="?version=1&table=Table84">1.7-1.95GeV</a> <a href="?version=1&table=Table85">6.7-7.65GeV</a> <a href="?version=1&table=Table86">20-23GeV</a> <a href="?version=1&table=Table87">60-95GeV</a> <br> 5-10%: <a href="?version=1&table=Table88">1.7-1.95GeV</a> <a href="?version=1&table=Table89">6.7-7.65GeV</a> <a href="?version=1&table=Table90">20-23GeV</a> <a href="?version=1&table=Table91">60-95GeV</a> <br> 10-20%: <a href="?version=1&table=Table92">1.7-1.95GeV</a> <a href="?version=1&table=Table93">6.7-7.65GeV</a> <a href="?version=1&table=Table94">20-23GeV</a> <a href="?version=1&table=Table95">60-95GeV</a> <br> 20-30%: <a href="?version=1&table=Table96">1.7-1.95GeV</a> <a href="?version=1&table=Table97">6.7-7.65GeV</a> <a href="?version=1&table=Table98">20-23GeV</a> <a href="?version=1&table=Table99">60-95GeV</a> <br> 30-40%: <a href="?version=1&table=Table100">1.7-1.95GeV</a> <a href="?version=1&table=Table101">6.7-7.65GeV</a> <a href="?version=1&table=Table102">20-23GeV</a> <a href="?version=1&table=Table103">60-95GeV</a> <br> 40-50%: <a href="?version=1&table=Table104">1.7-1.95GeV</a> <a href="?version=1&table=Table105">6.7-7.65GeV</a> <a href="?version=1&table=Table106">20-23GeV</a> <a href="?version=1&table=Table107">60-95GeV</a> <br> 50-60%: <a href="?version=1&table=Table108">1.7-1.95GeV</a> <a href="?version=1&table=Table109">6.7-7.65GeV</a> <a href="?version=1&table=Table110">20-23GeV</a> <a href="?version=1&table=Table111">60-95GeV</a> <br> 60-80%: <a href="?version=1&table=Table112">1.7-1.95GeV</a> <a href="?version=1&table=Table113">6.7-7.65GeV</a> <a href="?version=1&table=Table114">20-23GeV</a> <a href="?version=1&table=Table115">60-95GeV</a> <br><i>R<sub>AA</sub> (Xe+Xe):</i> <br> 0-5%: <a href="?version=1&table=Table116">1.7-1.95GeV</a> <a href="?version=1&table=Table117">6.7-7.65GeV</a> <a href="?version=1&table=Table118">20-23GeV</a> <br> 5-10%: <a href="?version=1&table=Table119">1.7-1.95GeV</a> <a href="?version=1&table=Table120">6.7-7.65GeV</a> <a href="?version=1&table=Table121">20-23GeV</a> <br> 10-20%: <a href="?version=1&table=Table122">1.7-1.95GeV</a> <a href="?version=1&table=Table123">6.7-7.65GeV</a> <a href="?version=1&table=Table124">20-23GeV</a> <br> 20-30%: <a href="?version=1&table=Table125">1.7-1.95GeV</a> <a href="?version=1&table=Table126">6.7-7.65GeV</a> <a href="?version=1&table=Table127">20-23GeV</a> <br> 30-40%: <a href="?version=1&table=Table128">1.7-1.95GeV</a> <a href="?version=1&table=Table129">6.7-7.65GeV</a> <a href="?version=1&table=Table130">20-23GeV</a> <br> 40-50%: <a href="?version=1&table=Table131">1.7-1.95GeV</a> <a href="?version=1&table=Table132">6.7-7.65GeV</a> <a href="?version=1&table=Table133">20-23GeV</a> <br> 50-60%: <a href="?version=1&table=Table134">1.7-1.95GeV</a> <a href="?version=1&table=Table135">6.7-7.65GeV</a> <a href="?version=1&table=Table136">20-23GeV</a> <br> 60-80%: <a href="?version=1&table=Table137">1.7-1.95GeV</a> <a href="?version=1&table=Table138">6.7-7.65GeV</a> <a href="?version=1&table=Table139">20-23GeV</a> <br>- - - - - - - - - - - - - - - - - - - -
Charged-hadron cross-section in pp collisions. The systematic uncertainties are described in the section 7 of the paper. The total systematic uncertainties are determined by adding the contributions from all relevant sources in quadrature.
Charged-hadron spectrum in the centrality interval 0-5% for p+Pb, divided by 〈TPPB〉. The systematic uncertainties are described in the section 7 of the paper. The total systematic uncertainties are determined by adding the contributions from all relevant sources in quadrature.
Measurements of the yield and nuclear modification factor, $R_\mathrm{ AA}$, for inclusive jet production are performed using 0.49 nb$^{-1}$ of Pb+Pb data at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV and 25 pb$^{-1}$ of $pp$ data at $\sqrt{s}=5.02$ TeV with the ATLAS detector at the LHC. Jets are reconstructed with the anti-$k_t$ algorithm with radius parameter $R=0.4$ and are measured over the transverse momentum range of 40-1000 GeV in six rapidity intervals covering $|y|<2.8$. The magnitude of $R_\mathrm{ AA}$ increases with increasing jet transverse momentum, reaching a value of approximately 0.6 at 1 TeV in the most central collisions. The magnitude of $R_\mathrm{ AA}$ also increases towards peripheral collisions. The value of $R_\mathrm{ AA}$ is independent of rapidity at low jet transverse momenta, but it is observed to decrease with increasing rapidity at high transverse momenta.
The ⟨TAA⟩ and ⟨Npart⟩ values and their uncertainties in each centrality bin.
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In this paper Au+Au collisions at 11.6A GeV/c are characterized by two global observables: the energy measured near zero degrees (EZCAL) and the total event multiplicity. Particle spectra are measured for different event classes that are defined in a two-dimensional grid of both global observables. For moderately central events (σ/σint<12%) the proton dN/dy distributions do not depend on EZCAL but only on the event multiplicity. In contrast the shape of the proton transverse spectra shows little dependence on the event multiplicity. The change in the proton dN/dy distributions suggests that different conditions are formed in the collision for different event classes. These event classes are studied for signals of new physics by measuring pion and kaon spectra and yields. In the event classes doubly selected on EZCAL and multiplicity there is no indication of any unusual pion or kaon yields, spectra, or K/π ratio even in the events with extreme multiplicity.
Table for event classification (from CLASS1 to CLASS8) where ZCAL energy solely used for event selection. Number of Projectile Participants Npp=197*(1-E(P=3)/EKIN(P=1)).
CLASS1 (see Table for event classification).
CLASS1 (see Table for event classification).
Momentum spectra of charged pions over nearly full rapidity coverage from target to beam rapidity have been measured in the 0-5% most central Au+Au collisions in the beam energy range from 2 to 8 AGeV by the E895 Experiment. Using a thermal parameterization to fit the transverse mass spectra, rapidity density distributions are extracted. The observed spectra are compared with predictions from the RQMD v2.3 cascade model and also to a thermal model including longitudinal flow. The total 4$\pi$ yields of the charged pions are used to infer an initial state entropy produced in the collisions.
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Rapidity distributions of protons from central $^{197}$Au + $^{197}$Au collisions measured by the E895 Collaboration in the energy range from 2 to 8 AGeV at the Brookhaven AGS are presented. Longitudinal flow parameters derived using a thermal model including collective longitudinal expansion are extracted from these distributions. The results show an approximately linear increase in the longitudinal flow velocity, $<\beta\gamma>_{L}$, as a function of the logarithm of beam energy.
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K − /K + and p ¯ / p ratios measured in 158 A·GeV Pb+Pb collisions are shown as a function of transverse momentum P T and centrality in top 8.5% central region. Little centrality dependence of the K − / K + and p ¯ / p ratios is observed. The transverse mass m T distribution and dN/dy of K + , K − , p and p ¯ around mid-rapidity are obtained. The temperature T ch and the chemical potentials for both light and strange quarks (μ q , μ s ) at chemical freeze-out are determined by applying simple thermodynamical model to the present data. The resultant μ q , μ s and T ch are compared with those obtained from similar analysis of SPS S+A and AGS Si+A data. The chemical freeze-out temperature T ch at CERN energies is higher than thermal freeze-out temperature T fo which is extracted from m T distribution of charged hadrons. At AGS energies T ch is close to T fo .
Data obtained from the fit of MT spectra.
Data obtained from the fit of MT spectra.