Transverse momentum ($p_{\rm T}$) spectra of charged particles at mid-pseudorapidity in Xe-Xe collisions at $\sqrt{s_{\rm NN}}$ = 5.44 TeV measured with the ALICE apparatus at the Large Hadron Collider are reported. The kinematic range $0.15 < p_{\rm T} < 50$ GeV/$c$ and $|\eta| < 0.8$ is covered. Results are presented in nine classes of collision centrality in the 0-80% range. For comparison, a pp reference at the collision energy of $\sqrt{s}$ = 5.44 TeV is obtained by interpolating between existing \pp measurements at $\sqrt{s}$ = 5.02 and 7 TeV. The nuclear modification factors in central Xe-Xe collisions and Pb-Pb collisions at a similar center-of-mass energy of $\sqrt{s_{\rm NN}}$ = 5.02 TeV, and in addition at 2.76 TeV, at analogous ranges of charged particle multiplicity density $\left\langle\rm{d}N_{\rm ch}/\rm{d}\eta\right\rangle$ show a remarkable similarity at $p_{\rm T}> 10$ GeV/$c$. The comparison of the measured $R_{\rm AA}$ values in the two colliding systems could provide insight on the path length dependence of medium-induced parton energy loss. The centrality dependence of the ratio of the average transverse momentum $\left\langle p_{\rm{T}}\right\rangle$ in Xe-Xe collisions over Pb-Pb collision at $\sqrt{s}$ = 5.02 TeV is compared to hydrodynamical model calculations.
Transverse momentum spectra of charged particles in XeXe collisions in nine centrality classes.
Interpolated pp reference spectrum and invariant cross section.
Nuclear modification factor for XeXe. Additional systematic error: 0-5 pct data: +6.1 pct -6.1 pct 5-10 pct data: +6.6 pct -6.6 pct 10-20 pct data: +7.4 pct -7.4 pct 20-30 pct data: +9.8 pct -9.8 pct 30-40 pct data: +11.5 pct -11.5 pct 40-50 pct data: +12.9 pct -12.9 pct 50-60 pct data: +13.8 pct -13.8 pct 60-70 pct data: +14.0 pct -14.0 pct 70-80 pct data: +12.9 pct -12.9 pct
A measurement of $J/\psi$ and $\psi(2\mathrm{S})$ production is presented. It is based on a data sample from Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV and $pp$ collisions at $\sqrt{s}$ = 5.02 TeV recorded by the ATLAS detector at the LHC in 2015, corresponding to an integrated luminosity of $0.42\mathrm{nb}^{-1}$ and $25\mathrm{pb}^{-1}$ in Pb+Pb and $pp$, respectively. The measurements of per-event yields, nuclear modification factors, and non-prompt fractions are performed in the dimuon decay channel for $9 < p_{T}^{\mu\mu} < 40$ GeV in dimuon transverse momentum, and $-2.0 < y_{\mu\mu} < 2.0$ in rapidity. Strong suppression is found in Pb+Pb collisions for both prompt and non-prompt $J/\psi$, as well as for prompt and non-prompt $\psi(2\mathrm{S})$, increasing with event centrality. The suppression of prompt $\psi(2\mathrm{S})$ is observed to be stronger than that of $J/\psi$, while the suppression of non-prompt $\psi(2\mathrm{S})$ is equal to that of the non-prompt $J/\psi$ within uncertainties, consistent with the expectation that both arise from \textit{b}-quarks propagating through the medium. Despite prompt and non-prompt $J/\psi$ arising from different mechanisms, the dependence of their nuclear modification factors on centrality is found to be quite similar.
Per-event-yield of prompt jpsi production in 5.02 TeV PbPb collision data as a function of pT for three different centrality slices in the rapidity range |y| < 2.
Per-event-yield of non-prompt jpsi production in 5.02 TeV PbPb collision data as a function of pT for three different centrality slices in the rapidity range |y| < 2.
Non-prompt fraction of jpsi production in 5.02 TeV PbPb collision data as a function of pT for three different centrality slices in the rapidity range |y| < 2.
The PHENIX collaboration presents first measurements of low-momentum ($0.4<p_T<3$ GeV/$c$) direct-photon yields from Au$+$Au collisions at $\sqrt{s_{_{NN}}}$=39 and 62.4 GeV. For both beam energies the direct-photon yields are substantially enhanced with respect to expectations from prompt processes, similar to the yields observed in Au$+$Au collisions at $\sqrt{s_{_{NN}}}$=200. Analyzing the photon yield as a function of the experimental observable $dN_{\rm ch}/d\eta$ reveals that the low-momentum ($>$1\,GeV/$c$) direct-photon yield $dN_{\gamma}^{\rm dir}/d\eta$ is a smooth function of $dN_{\rm ch}/d\eta$ and can be well described as proportional to $(dN_{\rm ch}/d\eta)^\alpha$ with $\alpha{\sim}$1.25. This new scaling behavior holds for a wide range of beam energies at the Relativistic Heavy Ion Collider and Large Hadron Collider, for centrality selected samples, as well as for different, $A$$+$$A$ collision systems. At a given beam energy the scaling also holds for high $p_T$ ($>5$\,GeV/$c$) but when results from different collision energies are compared, an additional $\sqrt{s_{_{NN}}}$-dependent multiplicative factor is needed to describe the integrated-direct-photon yield.
Direct photon spectra(Physical Review C87, 054907 (2013)) normalized by $(dN_{ch}/d\eta)^{1.25}$ for in p+p at $\sqrt{s_{NN}}$= 200 GeV.
Direct photon spectra(Physics Letters B94, 106 (1980)) normalized by $(dN_{ch}/d\eta)^{1.25}$ for in p+p at $\sqrt{s_{NN}}$= 62.4 GeV.
Direct photon spectra(Nucl. Part. Phys. 23, A1 (1997) and Sov. J. Nucl. Phys. 51, 836 (1990)) normalized by $(dN_{ch}/d\eta)^{1.25}$ for in p+p at $\sqrt{s_{NN}}$= 63 GeV.
We have measured direct photons for $p_T<5~$GeV/$c$ in minimum bias and 0\%--40\% most central events at midrapidity for Cu$+$Cu collisions at $\sqrt{s_{_{NN}}}=200$ GeV. The $e^{+}e^{-}$ contribution from quasi-real direct virtual photons has been determined as an excess over the known hadronic contributions in the $e^{+}e^{-}$ mass distribution. A clear enhancement of photons over the binary scaled $p$$+$$p$ fit is observed for $p_T<4$ GeV/$c$ in Cu$+$Cu data. The $p_T$ spectra are consistent with the Au$+$Au data covering a similar number of participants. The inverse slopes of the exponential fits to the excess after subtraction of the $p$$+$$p$ baseline are 285$\pm$53(stat)$\pm$57(syst)~MeV/$c$ and 333$\pm$72(stat)$\pm$45(syst)~MeV/$c$ for minimum bias and 0\%--40\% most central events, respectively. The rapidity density, $dN/dy$, of photons demonstrates the same power law as a function of $dN_{\rm ch}/d\eta$ observed in Au$+$Au at the same collision energy.
Direct photon fraction measured with the virtual photon method for different systems in $\sqrt{s_{NN}}$ = 200 GeV Cu+Cu collisions.
The direct photon spectra for Minimum Bias and 0-40% centrality in $\sqrt{s_{NN}}$ = 200 GeV Cu+Cu collisions.
We present a measurement of inclusive $J/\psi$ production at mid-rapidity ($|y|<1$) in $p+p$ collisions at a center-of-mass energy of $\sqrt{s}$ = 200 GeV with the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The differential production cross section for $J/\psi$ as a function of transverse momentum ($p_T$) for $0
Top$:$ J/$\psi$ cross section times branching ratio as a function of pT in p+p collisions at $\sqrt{s_{NN}}$ = 200 GeV. Solid circles are from this analysis for |y| < 1; open circles and blue squares are the published results for |y| < 1 from STAR; triangles are the published results for |y| < 0.35 from PHENIX. Bars and boxes are statistical and systematic uncertainties, respectively. The curves are CEM (green), NLO NRQCD A (orange) [4], CGC + NRQCD (blue) , and NLO NRQCD B (magenta) theoretical calculations, respectively. Bottom$:$ ratios of these results with respect to the central value from this analysis.
The corrected $n_{ch}$ distributions at mid-rapidity (|$\eta$| < 1) for MB events (open circles) and J/$\psi$ events with J/$\psi$ $p_{T}$ greater than 0 (purple circles), 1.5 (blue squares), and 4 GeV/c (red triangles) in p+p collisions at $\sqrt{s}$ = 200 GeV. The fit function is a negative binomial function. Bars and boxes are statistical and systematic uncertainties, respectively.
The multiplicity dependence of J/$\psi$ production in p+p collisions at $\sqrt{s}$ = 200 GeV. Purple circles, blue squares, and red triangles represent the results for J/$\psi$ with $p_{T}$ greater than 0, 1.5, and 4 GeV/c, respectively. Bars and open boxes are statistical and systematic uncertainties, respectively. The ALICE result is shown in the left panel. The purple, blue and red bands in the middle panel are generated from PYTHIA8 for J/$\psi$ with $p_{T}$ greater than 0, 1.5, and 4 GeV/c, respectively. The blue and red bands in the right panel are from EPOS3 model calculations for D$^{0}$ with 2 < $p_{T}$ < 4 and 4 < $p_{T}$ < 8 GeV/c, respectively, while the green curve is from the Percolation model for J/$\psi$ with $p_{T}$ > 0 GeV/c.
The experimental study of the collisions of heavy nuclei at relativistic energies has established the properties of the quark-gluon plasma (QGP), a state of hot, dense nuclear matter in which quarks and gluons are not bound into hadrons. In this state, matter behaves as a nearly inviscid fluid that efficiently translates initial spatial anisotropies into correlated momentum anisotropies among the produced particles, producing a common velocity field pattern known as collective flow. In recent years, comparable momentum anisotropies have been measured in small-system proton-proton ($p$$+$$p$) and proton-nucleus ($p$$+$$A$) collisions, despite expectations that the volume and lifetime of the medium produced would be too small to form a QGP. Here, we report on the observation of elliptic and triangular flow patterns of charged particles produced in proton-gold ($p$$+$Au), deuteron-gold ($d$$+$Au), and helium-gold ($^3$He$+$Au) collisions at a nucleon-nucleon center-of-mass energy $\sqrt{s_{_{NN}}}$~=~200 GeV. The unique combination of three distinct initial geometries and two flow patterns provides unprecedented model discrimination. Hydrodynamical models, which include the formation of a short-lived QGP droplet, provide a simultaneous description of these measurements.
$v_2$for 0-5% central p+Au collisions
$v_2$for 0-5% central d+Au collisions
$v_2$for 0-5% central $^3$He+Au collisions
Dihadron and isolated direct photon-hadron angular correlations are measured in $p$$+$$p$ collisions at $\sqrt{s}=200$ GeV. The correlations are sensitive to nonperturbative initial-state and final-state transverse momentum $k_T$ and $j_T$ in the azimuthal nearly back-to-back region $\Delta\phi\sim\pi$. In this region, transverse-momentum-dependent evolution can be studied when several different hard scales are measured. To have sensitivity to small transverse momentum scales, nonperturbative momentum widths of $p_{\rm out}$, the out-of-plane transverse momentum component perpendicular to the trigger particle, are measured. These widths are used to investigate possible effects from transverse-momentum-dependent factorization breaking. When accounting for the longitudinal momentum fraction of the away-side hadron with respect to the near-side trigger particle, the widths are found to increase with the hard scale; this is qualitatively similar to the observed behavior in Drell-Yan and semi-inclusive deep-inelastic scattering interactions. The momentum widths are also studied as a function of center-of-mass energy by comparing to previous measurements at $\sqrt{s}=510$ GeV. The nonperturbative jet widths also appear to increase with $\sqrt{s}$ at a similar $x_T$, which is qualitatively consistent to similar measurements in Drell-Yan interactions. To quantify the magnitude of any transverse-momentum-dependent factorization breaking effects, calculations will need to be performed to compare to these measurements.
The per-trigger yields are shown as a function of $\Delta\phi$ in several $p_T^{trig}$ $\otimes$ $p_T^{assoc}$ bins.
The per-trigger yields are shown as a function of $\Delta\phi$ in several $p_T^{trig}$ $\otimes$ $p_T^{assoc}$ bins.
The per-trigger yields are shown as a function of $\Delta\phi$ in several $p_T^{trig}$ $\otimes$ $p_T^{assoc}$ bins.
PHENIX reports differential cross sections of $\mu\mu$ pairs from semileptonic heavy-flavor decays and the Drell-Yan production mechanism measured in $p$$+$$p$ collisions at $\sqrt{s}=200$ GeV at forward and backward rapidity ($1.2<|\eta|<2.2$). The $\mu\mu$ pairs from $c\bar{c}$, $b\bar{b}$, and Drell-Yan are separated using a simultaneous fit to unlike- and like-sign muon pair spectra in mass and $p_T$. The azimuthal opening angle correlation between the muons from $c\bar{c}$ and $b\bar{b}$ decays and the pair-$p_T$ distributions are compared to distributions generated using {\sc pythia} and {\sc powheg} models, which both include next-to-leading order processes. The measured distributions for pairs from $c\bar{c}$ are consistent with {\sc pythia} calculations. The $c\bar{c}$ data presents narrower azimuthal correlations and softer $p_T$ distributions compared to distributions generated from {\sc powheg}. The $b\bar{b}$ data are well described by both models. The extrapolated total cross section for bottom production is $3.75{\pm}0.24({\rm stat}){\pm}^{0.35}_{0.50}({\rm syst}){\pm}0.45({\rm global})$[$\mu$b], which is consistent with previous measurements at the Relativistic Heavy Ion Collider in the same system at the same collision energy, and is approximately a factor of two higher than the central value calculated with theoretical models. The measured Drell-Yan cross section is in good agreement with next-to-leading-order quantum-chromodynamics calculations.
Inclusive $\mu^+ \mu^-$ pair mass distributions from $p$+$p$ collisions at $\sqrt{s}$ = 200 GeV over the mass range from 0 to 15 GeV/$c^2$. Results are shown separately for the south and north muon arms. The data are compared to the cocktail of expected sources.
Inclusive like-sign $\mu \mu$ pair yield from $p$+$p$ collisions as a function of mass for the south and north muon arms and the ratio of data to expected sources.
Inclusive unlike-sign $\mu \mu$ pair yield from $p$+$p$ collisions at $\sqrt{s}$ = 200 GeV as a function of mass in different $p_T$ slices for the south and north muon arms and the ratio of data to expected sources.
Measurements of prompt $\psi$(2S) meson production cross sections in proton-lead (pPb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of $\sqrt{s_{_\mathrm{NN}}}=$ 5.02 TeV are reported. The results are based on pPb and pp data collected by the CMS experiment at the LHC, corresponding to integrated luminosities of 34.6 nb$^{-1}$ and 28.0 pb$^{-1}$, respectively. The nuclear modification factor $R_\mathrm{pPb}$ is measured for prompt $\psi$(2S) in the transverse momentum range 4 $<$ p$_\mathrm{T}$ $<$ 30 GeV$/c$ and the center-of-mass rapidity range $-$2.4 $< y_\mathrm{cm} <$ 1.93. The results on $\psi$(2S) $R_\mathrm{pPb}$ are compared to the corresponding modification factor for prompt J$/\psi$ mesons and are found to be more suppressed than the J$/\psi$ states over the entire kinematic range studied.
Differential cross section (multiplied by the dimuon branching fraction) of prompt $\psi$(2S) mesons in pPb collisions at $\sqrt(s_{\textrm{NN}})=5.02 $ TeV, as a function of $p_{\textrm{T}}$, for four backward $y_{\mathrm{CM}}$ regions. The fully correlated luminosity uncertainty of 3.5% is not inlcuded in the point-by-point uncertainty.
Differential cross section (multiplied by the dimuon branching fraction) of prompt $\psi$(2S) mesons in pPb collisions at $\sqrt(s_{\textrm{NN}})=5.02 $ TeV, as a function of $p_{\textrm{T}}$, for four backward $y_{\mathrm{CM}}$ regions. The fully correlated luminosity uncertainty of 3.5% is not included in the point-by-point uncertainty. NOTE- The cross section unit is nb (nano barn); the y-axes of the figures in the publication show pb (pico barn) by mistake.
Differential cross section (multiplied by the dimuon branching fraction) of prompt $\psi$(2S) mesons in pPb collisions at $\sqrt(s_{\textrm{NN}})=5.02 $ TeV, as a function of $p_{\textrm{T}}$, for three forward $y_{\mathrm{CM}}$ regions. The fully correlated luminosity uncertainty of 3.5% is not inlcuded in the point-by-point uncertainty.
A search for supersymmetric partners of top quarks decaying as $\tilde{t}_1\to c\tilde\chi^0_1$ and supersymmetric partners of charm quarks decaying as $\tilde{c}_1\to c\tilde\chi^0_1$, where $\tilde\chi^0_1$ is the lightest neutralino, is presented. The search uses 36.1 ${\rm fb}^{-1}$ $pp$ collision data at a centre-of-mass energy of 13 TeV collected by the ATLAS experiment at the Large Hadron Collider and is performed in final states with jets identified as containing charm hadrons. Assuming a 100% branching ratio to $c\tilde\chi^0_1$, top and charm squarks with masses up to 850 GeV are excluded at 95% confidence level for a massless lightest neutralino. For $m_{\tilde{t}_1,\tilde{c}_1}-m_{\tilde\chi^0_1}
Acceptance for best expected CLS SR in the $\tilde{t}_1/\tilde{c}_1-\tilde{\chi}_1^0$ mass plane.
Acceptance for SR1 in the $\tilde{t}_1/\tilde{c}_1-\tilde{\chi}_1^0$ mass plane.
Acceptance for SR1 in the $\tilde{t}_1/\tilde{c}_1-\tilde{\chi}_1^0$ mass plane.
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