First Direct Measurement of Jets in $\sqrt{s_{NN}}=200$ GeV Heavy Ion Collisions by STAR
Sevil Salur
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Proceedings of the 3rd International Conference on Hard and Electro- Magnetic Probes of High-Energy Nuclear Collisions 8-14 June 2008, Illa da Toxa (Galicia-Spain)
We present the first measurement of reconstructed jets in ultra-relativistic heavy ion collisions. Utilizing the large coverage of the STAR Time Projection Chamber and Electromagnetic Calorimeter, we apply several modern jet reconstruction algorithms and background subtraction techniques and explore their systematic uncertainties in heavy ion events. The differential spectrum for inclusive jet production in central Au+Au collisions at $\sqrt {s_{NN}}= 200$ GeV is presented. In order to assess the jet reconstruction biases, this spectrum is compared with the jet cross section measured in $\sqrt{s}=200$ GeV p+p collisions scaled by the number of binary N-N collisions to account for nuclear geometric effects.
Measurements of strangeness production in jets help illuminate the QCD mechanisms in fragmentation. Furthermore, they provide a crucial baseline for heavy-ion studies where modifications in jet chemistry have recently been observed by the STAR experiment. We present new results on strange particle production in jets from p+p $\sqrt{s}$ = 200 GeV collisions measured by the STAR experiment. The fragmentation functions of the Λ, \barΛ and K0Short particles are obtained using various jet finding algorithms, and then compared to various models. Strange particle ratios in jets will be obtained and c…
Measurements of strangeness production in jets help illuminate the QCD mechanisms in fragmentation. Furthermore, they provide a crucial baseline for heavy-ion studies where modifications in jet chemistry have recently been predicted. We present new results on strange particle production in jets from p+p \sqrt{s} = 200 GeV collisions measured by the STAR experiment. The momentum distributions of the Λ, \barΛ and K0Short particles are obtained using various jet finding algorithms, and then compared to various models. Strange particle ratios in jets are obtained and compared to values obtained fr…
We analyze the relative azimuthal ($Δϕ$) distribution of same-charge and opposite-charge particle pairs. We then remove elliptic flow background using the ZYAM method. Comparisons between near angle $Δϕ$ peak widths are presented for various centralities.
We present the current status of the measurement of jets that contain a D meson (D-tagged jets) with ALICE. D-meson candidates, identified via their hadronic decay channels, were combined with the other charged tracks reconstructed with the central tracking system, using the anti-$k_{\rm T}$ jet-finding algorithm. The yield of D-tagged jets was extracted through an invariant mass analysis of the D-meson candidates. A Monte Carlo simulation was used to determine the detector performance and validate the signal extraction techniques.
We present an experimental study of full jet reconstruction in the high multiplicity environment of heavy ion collisions, utilizing 200 GeV p+p and central Au+Au data measured by STAR. Inclusive differential jet production cross sections and ratios are reported, as well as high-pT hadron-jet coincidences.
In this contribution we report $e^{+}e^{-}$ spectra with various invariant mass and p$_{T}$ differentials in Au$+$Au collisions at $\sqrt{s_{NN}}$=200 GeV and U$+$U collisions at $\sqrt{s_{NN}}$=193 GeV. The structure of the t ($t\approx p^2_{\mathrm{T}}$) distributions of these mass regions will be shown and compared with the same distributions in ultra-peripheral collisions. Additionally, this contribution discusses first measurements of $μ^{+}μ^{-}$ invariant mass spectra from STAR's recently installed Muon Telescope Detector (MTD) in p$+$p and Au$+$Au collisions at $\sqrt{s_{NN}}$ = 200 Ge…
We present STAR's measurement of the $e^{+}e^{-}$ continuum as a function of centrality, invariant mass, and transverse momentum for U+U collisions at $\sqrt{s_{NN}}$ = 193 GeV. Also reported are the acceptance-corrected $e^{+}e^{-}$ invariant mass spectra for minimum-bias Au+Au collisions at $\sqrt{s_{NN}}$ = 27, 39, and 62.4 GeV and U+U collisions at $\sqrt{s_{NN}}$ = 193 GeV. The connection between the integrated $e^{+}e^{-}$ excess yields normalized by charge particle multiplicity ($dN_{ch}/dy$) at mid-rapidity and the lifetime of the fireball is discussed.
Transverse Single-Spin Asymmetry for Inclusive and Diffractive Electromagnetic Jets at Forward Rapidity in $p^{\uparrow}$+p Collisions at $\sqrt{s} = 200$ GeV and $510$ GeV at STAR
We present recent results from Al(beam)+Au(target) collisions at $\sqrt{s_{NN}}=4.9$ GeV and Au+Au collisions at $\sqrt{s_{NN}}=4.5$\kern 0.16667em GeV from the STAR fixed-target (FXT) program. We report transverse mass spectra of protons, $K^0_S$ and $Λ$, rapidity density distributions of $π^\pm$, $K^0_S$ and $Λ$, directed flow of protons, $π^\pm$, $K^0_S$ and $Λ$, and elliptic flow of protons and $π^{\pm}$. These are the first measurements of pion directed and elliptic flow in this energy range at RHIC. Pion and proton elliptic flow show mass ordering. Measurements are compared with the publ…
Measurements of direct photon production in p+Pb and p+C collisions at $\sqrt{s_\mathrm{NN}} = 17.4\mathrm{GeV}$ are presented. Upper limits on the direct photon yield as a function of $p_\mathrm{T}$ are derived and compared to the results for Pb+Pb collisions at $\sqrt{s_\mathrm{NN}} = 17.3$ GeV. The production of the $η$ meson, which is an important input to the direct photon signal extraction, has been determined in the $η\rightarrow 2γ$ channel for p+C collisions at $\sqrt{s_\mathrm{NN}} = 17.4\mathrm{GeV}$.
The phase diagram of strongly interacting matter can be explored by analyzing data of heavy-ion collisions at different center of mass collision energies. For investigating the space-time structure of the hadron emission source, HBT correlation measurements are among the best tools. In this paper we present the latest results from the RHIC PHENIX experiment on such measurements in $\sqrt{s_{\rm NN}}=$ 39 GeV and 62 GeV Au+Au collisions.
In this paper we present the study of the azimuthal correlation function of non-photonic electrons with low-pT hadrons produced in Cu+Cu collision at sqrt(s_NN)=200 GeV measured by STAR experiment at RHIC. Possible modification of the awayside peak is observed.
Negatively charged hadron (h-) production in Au+Au collisions at BNL-RHIC is studied with the STAR experiment. Results are presented on h- multiplicity, pseudorapidity and transverse momentum distributions at sqrt(s_NN) = 130 GeV.
We report on the pT dependence of nuclear modification factors ($R_{CP}$) for Ks, Lambda, Xi and the Anti-Lambda/Ks ratios at mid-rapidity from Au+Au collisions at \sqrt{s_{NN}} = 39, 11.5 and 7.7 GeV. At \sqrt{s_{NN}} = 39 GeV, the $R_{CP}$ data shows a baryon/meson separation at intermediate pT and a suppression for Ks for pT up to 4.5 GeV/$c$; the Anti-Lambda/Ks shows baryon enhancement in the most central collisions. However, at \sqrt{s_{NN}} = 11.5 and 7.7 GeV, $R_{CP}$ shows much less baryon/meson separation and Anti-Lambda/Ks shows almost no baryon enhancement. These observations indica…
We investigate modification of the bottom quark production due to cold nuclear matter effects (CNM) at mid-rapidity in d+Au collisions at $\sqrt{s_{NN}} = 200$ GeV at RHIC. Our results indicate that bottom production is not suppressed due to CNM effects in those collisions. We also found that shadowing and initial $k_T$ breadboarding for charm quarks explains at low $p_T$ ($p_T < 3$ GeV/c) the enhancement of heavy flavor decay electron yield in d+Au collisions at $\sqrt{s_{NN}} = 200$ GeV compared to p+p.
Jet quenching in the hot and dense medium created in ultra-relativistic heavy ion collisions is a well-established experimental phenomenon at RHIC. It has long been anticipated that the LHC heavy ion program would substantially advance the study of jet quenching by providing access to highly energetic jets and by measuring fully-reconstructed jets. Immediately following turn-on of the LHC with lead beams, in November 2010, that expectation was fulfilled through the observation of large di-jet asymmetries that may indicate substantial jet quenching. We will present recent results from ATLAS aim…
We study the production of ${\rm K}_{\rm S}^{0}$ mesons and $Λ$ baryons in jets in p--Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV with ALICE at the LHC. The $p_{\rm T}$-differential density of the particles produced in jets is compared to the inclusive distributions and the $Λ/{\rm K}_{\rm S}^{0}$ ratio is reported in bins of multiplicity of the collisions. The hard scatterings are selected on an event-by-event basis using the anti-$k_{\rm T}$ clustering algorithm with resolution parameter $R=0.2,~0.3$ and $0.4$, reconstructed from charged particles with a minimum $p_{\rm T,jet}$ of $10$ (or…
The first results of single jet observables in Pb+Pb collisions at sqrt(s_NN)=2.76 TeV measured with the ATLAS detector at the LHC are presented. Full jets are reconstructed with the anti-kt algorithm with R= 0.2 and 0.4, using an event-by-event subtraction procedure to correct for the effects of the underlying event including elliptic flow. The geometrically-scaled ratio of jet yields in central and peripheral events,Rcp, indicates a clear suppression of jets with ET >100 GeV. The transverse and longitudinal distributions of jet fragments is also presented. We find little no substantial chang…
The production of $Λ$ baryons and ${\rm K}^{0}_{\rm S}$ mesons (${\rm V}^{0}$ particles) was measured in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV and pp collisions at $\sqrt{s} = 7$ TeV with ALICE at the LHC. The production of these strange particles is studied separately for particles associated with hard scatterings and the underlying event to shed light on the baryon-to-meson ratio enhancement observed at intermediate transverse momentum ($p_{\rm T}$) in high multiplicity pp and p-Pb collisions. Hard scatterings are selected on an event-by-event basis with jets reconstructed with t…
We investigate the squeezed back-to-back correlations (BBC) of $K^+$$K^-$, caused by the mass modification of the particle in the dense medium formed in d+Au collisions at $\sqrt{s_{NN}}=200$ GeV and Au+Au collisions at $\sqrt{s_{NN}}=62.4$ GeV. Considering some kaons may be not affected by the medium, we further study the BBC functions of $K^+$$K^-$ when parts of all kaons have a mass-shift. Our results indicate that the BBC functions of $K^+$$K^-$ can be observed when only about 10$\%$ of all kaons have a mass-shift in d+Au collisions at $\sqrt{s_{NN}}=200$ GeV and the peripheral collisions …
We report the first measurement of fully corrected semi-inclusive charged recoil jets for both direct-photon ($γ_{dir}$) and $π^{0}$ triggers, within two trigger transverse energy ranges between 9 GeV and 15 GeV, in central Au+Au collisions at $\sqrt {s_{\rm NN}}$ = 200 GeV using data with an integrated luminosity of 13 $\rm nb^{-1}$ collected by the STAR experiment. A comparison between $π^{0}$-triggered recoil jets in p+p collisions and PYTHIA is discussed. A comparison is also presented between the suppression of $γ_{dir}$- and $π^{0}$-triggered recoil jets in central Au+Au collisions with …
We present a measurement of b jet transverse momentum (pt) spectra in proton-lead (pPb) collisions using a dataset corresponding to about 35 inverse nanobarns collected with the CMS detector at the LHC. Jets from b quark fragmentation are found by exploiting the long lifetime of hadrons containing a b quark through tagging methods using distributions of the secondary vertex mass and displacement. Extracted cross sections for b jets are scaled by the effective number of nucleon-nucleon collisions and are compared to a reference obtained from PYTHIA simulations of pp collisions. The PYTHIA-based…
The quark-gluon plasma is studied via medium-induced changes to correlations between jets and charged particles in PbPb collisions compared to pp reference data. This analysis uses data sets from PbPb and pp collisions with integrated luminosities of 166 inverse microbarns and 5.3 inverse picobarns, respectively, collected at sqrt(s[NN]) = 2.76 TeV. The angular distributions of charged particles are studied as a function of relative pseudorapidity (Delta eta) and relative azimuthal angle (Delta phi) with respect to reconstructed jet directions. Charged particles are correlated with all jets wi…
This Letter presents measurements of correlated production of nearby jets in Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 2.76$ TeV using the ATLAS detector at the Large Hadron Collider. The measurement was performed using 0.14 ${\rm nb}^{-1}$ of data recorded in 2011. The production of correlated jet pairs was quantified using the rate, $R_{ΔR}$, of "neighbouring" jets that accompany "test" jets within a given range of angular distance, $ΔR$, in the pseudorapidity--azimuthal angle plane. The jets were measured in the ATLAS calorimeter and were reconstructed using the anti-$k_{t}$ algorithm w…
We report on the measurement of hadron composition in charged jets in pp at $\sqrt{s}=7$ TeV and show the first data on particle type dependent jet fragmentation at the LHC. Further, we present $(Λ+\barΛ)/2$K$^{0}_{\mathrm{S}}$ ratios measured in charged jets in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 2.76$ TeV and in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV. While the ratio of the inclusive $p_{\mathrm{T}}$ spectra of $Λ$ and K$^{0}_{\mathrm{S}}$ exhibits centrality dependent enhancement both in Pb-Pb and p-Pb system, the $(Λ+\barΛ)/2$K$^{0}_{\mathrm{S}}$ ratio measured in…
In this paper, results on the J/$ψ$ cross section and polarization measured via the dielectron decay channel at mid-rapidity in $p+p$ collisions at $\sqrt{s}$ = 200 and 500 GeV in the STAR experiment are discussed. The first measurement of $ψ(2S)$ to J/$ψ$ ratio at $\sqrt{s}$ = 500 GeV is also reported.
We predict the elliptic flow parameter v_2 in U+U collisions at sqrt{s_{NN}}=200 GeV and in Pb+Pb collisions at sqrt{s_{NN}} = 2.76 TeV using a hybrid model in which the evolution of the quark gluon plasma is described by ideal hydrodynamics with a state-of-the-art lattice QCD equation of state, and the subsequent hadronic stage by a hadron cascade model.
In hydrodynamical modeling of ultrarelativistic heavy-ion collisions, the freeze-out is typically assumed to take place at a surface of constant temperature or energy density. A more physical approach is to assume that freeze-out takes place at a surface of constant Knudsen number. We evaluate the Knudsen number as a ratio of the expansion rate of the system to the pion scattering rate, and apply the constant Knudsen number freeze-out criterion to ideal hydrodynamical description of heavy-ion collisions at RHIC ($\sqrt{s_\mathrm{NN}}=200$ GeV) and the LHC ($\sqrt{s_\mathrm{NN}}=2760$ GeV) ener…
