Bulk Properties of the System Formed in Au+Au Collisions at $\sqrt{s_{\mathrm{NN}}}$ = 14.5 GeV
STAR Collaboration, J. Adam, L. Adamczyk, J. R. Adams, J. K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, I. Alekseev, D. M. Anderson, R. Aoyama, A. Apari… 展开作者
STAR Collaboration, J. Adam, L. Adamczyk, J. R. Adams, J. K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, I. Alekseev, D. M. Anderson, R. Aoyama, A. Aparin, E. C. Aschenauer, M. U. Ashraf, F. G. Atetalla, A. Attri, G. S. Averichev, V. Bairathi, K. Barish, A. J. Bassill, A. Behera, R. Bellwied, A. Bhasin, A. K. Bhati, J. Bielcik, J. Bielcikova, L. C. Bland, I. G. Bordyuzhin, J. D. Brandenburg, A. V. Brandin, J. Bryslawskyj, I. Bunzarov, J. Butterworth, H. Caines, M. Calderón de la Barca Sánchez, D. Cebra, I. Chakaberia, P. Chaloupka, B. K. Chan, F-H. Chang, Z. Chang, N. Chankova-Bunzarova, A. Chatterjee, S. Chattopadhyay, J. H. Chen, X. Chen, J. Cheng, M. Cherney, W. Christie, H. J. Crawford, M. Csanád, S. Das, T. G. Dedovich, I. M. Deppner, A. A. Derevschikov, L. Didenko, C. Dilks, X. Dong, J. L. Drachenberg, J. C. Dunlop, T. Edmonds, N. Elsey, J. Engelage, G. Eppley, R. Esha, S. Esumi, O. Evdokimov, J. Ewigleben, O. Eyser, R. Fatemi, S. Fazio, P. Federic, J. Fedorisin, Y. Feng, P. Filip, E. Finch, Y. Fisyak, L. Fulek, C. A. Gagliardi, T. Galatyuk, F. Geurts, A. Gibson, K. Gopal, D. Grosnick, A. Gupta, W. Guryn, A. I. Hamad, A. Hamed, J. W. Harris, L. He, S. Heppelmann, S. Heppelmann, N. Herrmann, L. Holub, Y. Hong, S. Horvat, B. Huang, H. Z. Huang, S. L. Huang, T. Huang, X. Huang, T. J. Humanic, P. Huo, G. Igo, W. W. Jacobs, C. Jena, A. Jentsch, Y. JI, J. Jia, K. Jiang, S. Jowzaee, X. Ju, E. G. Judd, S. Kabana, S. Kagamaster, D. Kalinkin, K. Kang, D. Kapukchyan, K. Kauder, H. W. Ke, D. Keane, A. Kechechyan, M. Kelsey, Y. V. Khyzhniak, D. P. Kikoła, C. Kim, T. A. Kinghorn, I. Kisel, A. Kisiel, M. Kocan, L. Kochenda, L. K. Kosarzewski, L. Kramarik, P. Kravtsov, K. Krueger, N. Kulathunga Mudiyanselage, L. Kumar, R. Kunnawalkam Elayavalli, J. H. Kwasizur, R. Lacey, J. M. Landgraf, J. Lauret, A. Lebedev, R. Lednicky, J. H. Lee, C. Li, W. Li, W. Li, X. Li, Y. Li, Y. Liang, R. Licenik, T. Lin, A. Lipiec, M. A. Lisa, F. Liu, H. Liu, P. Liu, P. Liu, T. Liu, X. Liu, Y. Liu, Z. Liu, T. Ljubicic, W. J. Llope, M. Lomnitz, R. S. Longacre, S. Luo, X. Luo, G. L. Ma, L. Ma, R. Ma, Y. G. Ma, N. Magdy, R. Majka, D. Mallick, S. Margetis, C. Markert, H. S. Matis, O. Matonoha, J. A. Mazer, K. Meehan, J. C. Mei, N. G. Minaev, S. Mioduszewski, D. Mishra, B. Mohanty, M. M. Mondal, I. Mooney, Z. Moravcova, D. A. Morozov, Md. Nasim, K. Nayak, J. M. Nelson, D. B. Nemes, M. Nie, G. Nigmatkulov, T. Niida, L. V. Nogach, T. Nonaka, G. Odyniec, A. Ogawa, S. Oh, V. A. Okorokov, B. S. Page, R. Pak, Y. Panebratsev, B. Pawlik, D. Pawlowska, H. Pei, C. Perkins, R. L. Pintér, J. Pluta, J. Porter, M. Posik, N. K. Pruthi, M. Przybycien, J. Putschke, A. Quintero, S. K. Radhakrishnan, S. Ramachandran, R. L. Ray, R. Reed, H. G. Ritter, J. B. Roberts, O. V. Rogachevskiy, J. L. Romero, L. Ruan, J. Rusnak, O. Rusnakova, N. R. Sahoo, P. K. Sahu, S. Salur, J. Sandweiss, J. Schambach, W. B. Schmidke, N. Schmitz, B. R. Schweid, F. Seck, J. Seger, M. Sergeeva, R. Seto, P. Seyboth, N. Shah, E. Shahaliev, P. V. Shanmuganathan, M. Shao, F. Shen, W. Q. Shen, S. S. Shi, Q. Y. Shou, E. P. Sichtermann, S. Siejka, R. Sikora, M. Simko, J. Singh, S. Singha, D. Smirnov, N. Smirnov, W. Solyst, P. Sorensen, H. M. Spinka, B. Srivastava, T. D. S. Stanislaus, M. Stefaniak, D. J. Stewart, M. Strikhanov, B. Stringfellow, A. A. P. Suaide, T. Sugiura, M. Sumbera, B. Summa, X. M. Sun, Y. Sun, Y. Sun, B. Surrow, D. N. Svirida, P. Szymanski, A. H. Tang, Z. Tang, A. Taranenko, T. Tarnowsky, J. H. Thomas, A. R. Timmins, D. Tlusty, M. Tokarev, C. A. Tomkiel, S. Trentalange, R. E. Tribble, P. Tribedy, S. K. Tripathy, O. D. Tsai, B. Tu, Z. Tu, T. Ullrich, D. G. Underwood, I. Upsal, G. Van Buren, J. Vanek, A. N. Vasiliev, I. Vassiliev, F. Videbæk, S. Vokal, S. A. Voloshin, F. Wang, G. Wang, P. Wang, Y. Wang, Y. Wang, J. C. Webb, L. Wen, G. D. Westfall, H. Wieman, S. W. Wissink, R. Witt, Y. Wu, Z. G. Xiao, G. Xie, W. Xie, H. Xu, N. Xu, Q. H. Xu, Y. F. Xu, Z. Xu, C. Yang, Q. Yang, S. Yang, Y. Yang, Z. Yang, Z. Ye, Z. Ye, L. Yi, K. Yip, H. Zbroszczyk, W. Zha, D. Zhang, L. Zhang, S. Zhang, S. Zhang, X. P. Zhang, Y. Zhang, Z. Zhang, J. Zhao, C. Zhong, C. Zhou, X. Zhu, Z. Zhu, M. Zurek, M. Zyzak
We report systematic measurements of bulk properties of the system created in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 14.5 GeV recorded by the STAR detector at the Relativistic Heavy Ion Collider (RHIC).The transverse momentum spectra of $π^{\pm}$, $K^{\pm}$ and $p(\bar{p})$ are studied at mid-rapidity ($|y| < 0.1$) for nine centrality intervals. The centrality, transverse momentum ($p_T$),and pseudorapidity ($η$) dependence of inclusive charged particle elliptic flow ($v_2$), and rapidity-odd charged particles directed flow ($v_{1}$) results near mid-rapidity are also presented. These measurements are compared with the published results from Au+Au collisions at other energies, and from Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV. The results at $\sqrt{s_{\mathrm{NN}}}$ = 14.5 GeV show similar behavior as established at other energies and fit well in the energy dependence trend. These results are important as the 14.5 GeV energy fills the gap in $μ_B$, which is of the order of 100 MeV,between $\sqrt{s_{\mathrm{NN}}}$ =11.5 and 19.6 GeV. Comparisons of the data with UrQMD and AMPT models show poor agreement in general.
We present the elliptic flow $v_{2}$ of electrons from the semi-leptonic decays of heavy-flavour hadrons at mid-rapidity for semi-central ($20-40%$ centrality) Pb-Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 2.76 TeV measured with the ALICE detector. A positive $v_{2}$ is observed at low $p_\mathrm{T}$ in semi-central collisions. Comparisons with previous measurements obtained at lower collision energy at RHIC in Au-Au collisions at $\sqrt{s_\mathrm{NN}}$ = 0.2 TeV and with theoretical models are also presented.
An improved value for the lifetime of the (anti-)hypertriton has been obtained using the data sample of Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}} = $ 5.02 TeV collected by the ALICE experiment at the LHC. The (anti-)hypertriton has been reconstructed via its charged two-body mesonic decay channel and the lifetime has been determined from an exponential fit to the d$N$/d($ct$) spectrum. The measured value, $τ$ = 242$^{+34}_{-38}$ (stat.) $\pm$ 17 (syst.) ps, is compatible with all the available theoretical predictions, thus contributing to the solution of the longstanding hypertriton lifetime…
The self-normalised $ψ(2S)$ yields as a function of charged-particle multiplicity in pp collisions at $\sqrt{s}$ = 13 TeV and p--Pb collisions at $\sqrt{s_{\mathrm{NN}}}$= 8.16 TeV, using the ALICE detector at the CERN LHC, are reported in these proceedings. This measurement represents one of the main tools to understand the role of multiparton interactions and their influence on charmonium production in small systems, i.e pp and pA collisions. The ratio of $ψ(2S)$-over-J/$ψ$ as a function of charged-particle multiplicity is also presented for both pp and p--Pb collisions. The comparison to th…
Transverse momentum ($p_{\mathrm{T}}$) distributions of identified hadrons produced in p-Pb collisions at $\mathrm{\sqrt{s_{NN}} = 5.02\ TeV}$ have been measured at mid-rapidity (0 $< y_{\mathrm{CMS}} <$ 0.5) by ALICE. Particle tracks are reconstructed using the central barrel detectors. Particle identification is performed via specific energy loss, time-of-flight or their characteristic decay topology over a wide transverse momentum range (0 GeV/c up to 8 GeV/c). Spectral shapes and particle ratios are measured in six multiplicity classes. They are compared with several model calculations and…
The ALICE Collaboration has studied the inclusive J/$ψ$ and $ψ(\mathrm{2S})$ production in p-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV, at the CERN LHC. The J/$ψ$ measurement is performed in the $μ^{+}μ^{-}$ and in the $e^{+}e^{-}$ decay channels, down to zero $p_{\mathrm{T}}$. The results are in fair agreement with theoretical predictions. The $ψ(\mathrm{2S})$ measurement has also been performed. In particular, a smaller $ψ(\mathrm{2S})$ nuclear modification factor, with respect to the J$/ψ$ one, has been observed.
The STAR Collaboration reports measurements of back-to-back azimuthal correlations of di-$π^0$ produced at forward pseudorapidity ($2.6<η<4.0$) in $p+$$p$, $p+$$\mathrm{Al}$ and $p+$$\mathrm{Au}$ collisions at a center-of-mass energy per nucleon-nucleon pair of 200 GeV. A clear suppression of the correlated away-side yields is observed in $p+$$\mathrm{Au}$ and for the first time in $p+$$\mathrm{Al}$ collisions, compared with the $p$$+$$p$ data. The enhanced suppression found in $p+$$\mathrm{Au}$ with respect to $p+$$\mathrm{Al}$ collisions exhibits the saturation scale ($Q_s^2$) dependence on …
The pseudorapidity density of charged particles ($\mathrm{d}N_\mathrm{ch}/\mathrm{d}η$) at mid-rapidity in Pb-Pb collisions has been measured at a center-of-mass energy per nucleon pair of $\sqrt{s_{\rm NN}}$ = 5.02 TeV. It increases with centrality and reaches a value of $1943 \pm 54$ in $|η|<0.5$ for the 5% most central collisions. A rise in $\mathrm{d}N_\mathrm{ch}/\mathrm{d}η$ as a function of $\sqrt{s_{\rm NN}}$ for the most central collisions is observed, steeper than that observed in proton-proton collisions and following the trend established by measurements at lower energy. The centra…
Results on the production of $^{4}{\textrm{He}}$ and $^{4}\overline{\textrm{He}}$ nuclei in Pb-Pb collisions at $ \sqrt{s_{\mathrm{NN}}} = 2.76 $ TeV in the rapidity range $ \mid y \mid < 1$, using the ALICE detector, are presented in this paper. The rapidity densities corresponding to 0-10% central events are found to be $\mathrm{d}N/\mathrm{d}y _{^{4}\mathrm{He}} = (0.8 \pm 0.4 ~(\mathrm{stat}) \pm 0.3~(\mathrm{syst}))\times 10^{-6}$ and $\mathrm{d}N/\mathrm{d}y _{^{4}\mathrm{\overline{He}}} = (1.1 \pm 0.4~(\mathrm{stat}) \pm 0.2~(\mathrm{syst}))\times 10^{-6}$, respectively. This is in agre…
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…
The higher order harmonic flow observables $v_n$ ($n > 3$) and their non-linear responses to the initial state anisotropy have the strong potential to constrain shear and bulk viscosity to entropy ratios because of different sensitivities for various stages of heavy-ion collisions. The measurements of the flow coefficients and the non-linear coefficients up to the ninth and fifth harmonic, respectively, are presented in Pb-Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02\,\mathrm{TeV}$ for charged hadrons. In addition, the results of $p_\mathrm{T}$-differential non-linear flow modes for $π^\pm$, $\…
The ALICE Collaboration reports a search for jet quenching effects in pp collisions at $\sqrt{\mathrm{s}}$=13 TeV, in events selected on high multiplicity compared to the minimum bias population. The measurement is based on the semi-inclusive acoplanarity distribution of jets recoiling from a high-$p_\mathrm{T}$ trigger hadron. Significant broadening of the recoil jet acoplanarity distribution is observed in high multiplicity pp collisions, in both data and in simulations based on the PYTHIA model. Analysis is ongoing to elucidate the origin of this effect.
We investigate the dependence of elliptic flows $v_2$ on transverse momentum $P_T$ for charged hadrons produced in nucleus-nucleus collisions at high energy by using a multi-source ideal gas model which includes the interaction contribution of the emission sources. Our calculated results are approximately in agreement with the experimental data over a wider $P_T$ range from the STAR and ALICE Collaborations. It is found that the expansion factor increases linearly with the impact parameter from most central (0-5%) to mid-peripheral (35-40%) collisions.
Recent ALICE measurements of jet splittings in Pb--Pb and pp collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV are reported. These measurements scan the phase space of jet emissions in search of medium-induced signals which are expected to emerge at different scales. These include effects such as multiple soft-radiation, single hard emissions, and color coherence. The Lund plane diagram is shown, including projections onto distributions of the splitting scale $k_{\mathrm{T}}$ in intervals of the splitting angle $R_{\mathrm{g}}$. Soft Drop grooming is applied to access hard splittings within th…
Measurement of Z-boson production in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=8.16$ TeV and Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV is reported. It is performed in the dimuon decay channel, through the detection of muons with pseudorapidity $-4 < η_μ < -2.5$ and transverse momentum $p_{\rm T}^μ > 20$ GeV/$c$ in the laboratory frame. The invariant yield and nuclear modification factor are measured for opposite-sign dimuons with invariant mass $60 < m^{μμ} < 120$ GeV$c^2$ and rapidity $2.5 < y_{cms}^{μμ} < 4$. They are presented as a function of rapidity and, for the Pb-Pb collis…
We report jet substructure measurements in $\mathrm{p\kern-0.05em p}$ and $\mbox{Pb-Pb}$ collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with the ALICE detector. Charged-particle jets were reconstructed at midrapidity with the ALICE tracking detectors using the anti-$k_{\mathrm{T}}$ algorithm with resolution parameters $R=0.2$ and $R=0.4$. In $\mathrm{p\kern-0.05em p}$ collisions, the groomed jet momentum fraction, $z_{\mathrm{g}}$, and the groomed jet radius, $θ_{\mathrm{g}} \equiv R_{\mathrm{g}}/R$, are measured for the first time using the Dynamical Grooming method. Additionally, new system…
We present the semi-inclusive measurement of charged jets recoiling from direct-photon and $π^{0}$ triggers in central Au+Au collisions at $\sqrt{s_{\mathrm {NN}}}$ = 200 GeV, using a dataset with integrated luminosity 13 $\mathrm {nb^{-1}}$ recorded by the STAR experiment in 2014. The photon and $π^{0}$ triggers are selected within transverse energy ($\rm E_\mathrm{T}^\mathrm{trig}$) between 9 GeV and 20 GeV. Charged jets are reconstructed with the anti-$k_{\mathrm{T}}$ algorithm with resolution parameters R = 0.2 and 0.5. A Mixed-Event technique developed previously by STAR is used to correc…
Semi-inclusive charged jet spectra per trigger at STAR are presented binned by event activity (EA) as determined by the Beam Beam Counter (BBC) signal in the Au-going direction. The selected EA determination is motivated by correlations between the number of charged tracks in the Time Projection Chamber (TPC) ($|η|<1$) and EA ($η_\mathrm{EA}\in[-5,-2]$) which are also presented. The jet spectra per trigger at high EA are suppressed relative to the spectra at low EA. A PYTHIA investigation refutes that the suppression results from a trivial autocorrelation between jet kinematics and the accepta…
ATLAS measurements of two-particle correlations are presented for $\sqrt{s} = 5.02$ and $13$ TeV $pp$ collisions and for $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV $p$+Pb collisions at the LHC. The correlation functions are measured as a function of relative azimuthal angle $Δϕ$, and pseudorapidity separation $Δη$, using charged particles detected within the pseudorapidity interval $|η|{<}2.5$. Azimuthal modulation in the long-range component of the correlation function, with $|Δη|{>}2$, is studied using a template fitting procedure to remove a "back-to-back" contribution to the correlation function …
The cross sections for $Υ$(1S), $Υ$(2S), and $Υ$(3S) production in lead-lead (PbPb) and proton-proton (pp) collisions at $\sqrt{s_{_\mathrm{NN}}} =$ 5.02 TeV have been measured using the CMS detector at the LHC. The nuclear modification factors, R$_\mathrm{AA}$, derived from the PbPb-to-pp ratio of yields for each state, are studied as functions of meson rapidity and transverse momentum, as well as PbPb collision centrality. The yields of all three states are found to be significantly suppressed, and compatible with a sequential ordering of the suppression, R$_\mathrm{AA}$($Υ$(1S)) $>$ R$_\mat…
Heavy quarks are a powerful probe for investigating the properties of the Quark-Gluon Plasma created in heavy-ion collisions, since they are produced in initial hard scattering processes and experience all the stages of the medium evolution. ALICE has measured the production of $\mathrm{D}^0$, $\mathrm{D}^+$, $\mathrm{D}^{*+}$, and $\mathrm{D}_{\mathrm{s}}^+$ mesons at central rapidity in their hadronic decay channels in various collision systems and energies. We present recent results for D-meson production measured by the ALICE Collaboration in pp collisions at $\sqrt{s}=7$ and 2.76 TeV, Pb-…
Full jet reconstruction in heavy-ion collisions is a promising tool for quantitative study of properties of the dense medium produced at RHIC. Measurements of d+Au collisions are important to disentangle initial state nuclear effects from medium-induced $k_\mathrm{T}$ broadening and jet quenching. We report measurements of mid-rapidity ($|η_{jet}| < 0.4|$) di-jet correlations in d+Au using high-statistics run 8 RHIC data at $\sqrt{s_\mathrm{NN}} = 200 \mathrm{GeV}$.
The transverse momentum ($p_{\mathrm T}$) distribution of primary charged particles is measured in minimum bias (non-single-diffractive) p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with the ALICE detector at the LHC. The $p_{\mathrm T}$ spectra measured near central rapidity in the range $0.5<p_{\mathrm T}<20$ GeV/$c$ exhibit a weak pseudorapidity dependence. The nuclear modification factor $R_{\mathrm{pPb}}$ is consistent with unity for $p_{\mathrm T}$ above 2 GeV/$c$. This measurement indicates that the strong suppression of hadron production at high $p_{\mathrm T}$ observed in Pb-P…
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 B$_\mathrm{c}^+$ meson is observed for the first time in heavy ion collisions. Data from the CMS detector are used to study the production of the B$_\mathrm{c}^+$ meson in lead-lead (PbPb) and proton-proton (pp) collisions at a center-of-mass energy per nucleon pair of $\sqrt{s_{\mathrm{NN}}} =$ 5.02 TeV, via the B$_\mathrm{c}^+$ $\to$ (J/$ψ$ $\to$ $μ^+μ^-$)$μ^+ν_μ$ decay. The B$_\mathrm{c}^+$ nuclear modification factor, derived from the PbPb-to-pp ratio of production cross sections, is measured in two bins of the trimuon transverse momentum and of the PbPb collision centrality. The B$_\m…
The elliptic azimuthal anisotropy coefficient ($v_2$) is measured for charm (D$^0$) and strange (K$_\mathrm{S}^0$, $Λ$, $Ξ^-$, and $Ω^-$) hadrons, using a data sample of pPb collisions collected by the CMS experiment, at a nucleon-nucleon center-of-mass energy $\sqrt{s_{_\mathrm{NN}}} =$ 8.16 TeV. A significant positive $v_2$ signal from long-range azimuthal correlations is observed for all particle species in high-multiplicity pPb collisions. The measurement represents the first observation of possible long-range collectivity for open heavy flavor hadrons in small systems. The results suggest…
We present results of a search for two hypothetical strange dibaryon states, i.e. the H-dibaryon and the possible $\bar{Λ\mathrm{n}}$ bound state. The search is performed with the ALICE detector in central (0-10%) Pb-Pb collisions at $ \sqrt{s_{\rm{NN}}} = 2.76$ TeV, by invariant mass analysis in the decay modes $\bar{Λ\mathrm{n}} \rightarrow \bar{\mathrm{d}} π^{+} $ and H-dibaryon $\rightarrow Λ\mathrm{p} π^{-}$. No evidence for these bound states is observed. Upper limits are determined at 99% confidence level for a wide range of lifetimes and for the full range of branching ratios. The resu…
Azimuthal correlation studies of heavy-flavour particles with charged particles in p--Pb collisions can give an insight into the cold nuclear matter effects \cite{Andronic:2015wma} on heavy-quark production and hadronization into heavy-flavour jets. Multiplicity-dependent measurements of angular correlations of heavy-flavour particles with charged hadrons allow us to investigate the collective behavior of the system and the initial state effects on heavy flavour hadron production. In addition, they can reveal possible modifications of the heavy-quark fragmentation and hadronization at differen…
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 …
Neutral pions ($π^0$) in $\sqrt{s_\mathrm{NN}}$ = 200 GeV and 62.4 GeV Au+Au collisions were measured at RHIC-PHENIX Year-4 Run. In $\sqrt{s_\mathrm{NN}}$ = 200 GeV, $π^0$ specta are measured up to p$_\mathrm{T}$ = 20 GeV/$c$. %PHENIX extended the p$_\mathrm{T}$ region of A strong suppression by a factor of $\sim$ 5 is observed and stays almost constant up to 20 GeV/$c$.
The production cross section of prompt $\mathrm{Λ_{c}^{+}}$ charm baryons was measured with the ALICE detector at the LHC at midrapidity in proton-proton (pp) and proton-lead (p-Pb) collisions at a centre-of-mass energy per nucleon pair of $\sqrt{s_\mathrm{NN}} = 5.02$ TeV. The $\mathrm{Λ_{c}^{+}}$ and $\rm {\overlineΛ{}_c^-}$ baryons were reconstructed in the hadronic decay channels $\rm Λ_{c}^{+} \rightarrow p K^{-}π^{+}$ and $\rm Λ_{c}^{+}\to p K^{0}_{S}$ and respective charge conjugates. The measured differential cross sections as a function of transverse momentum ($p_{\rm T}$) and the $p_…
We report the elliptic flow ($v_{2}$) of $K_{s}^{0}$, $Λ$, $\barΛ$, $ϕ$, $Ξ^{-}$, and $\overlineΞ^{+}$ at mid-rapidity for Ru+Ru and Zr+Zr collisions at $\sqrt{s_{\mathrm {NN}}}$ = 200 GeV. The transverse momentum ($p_{T}$) and centrality dependence of $v_{2}$ have been studied. The number of constituent quark (NCQ) scaling for all the (multi-)strange hadrons has also been tested. The dependence in the ratio of average $v_{2}$ ($\langle$$v_{2}$$\rangle$) on centrality shows a deviation from unity indicating a difference in nuclear structure and deformation between the isobars. The results show…
We present a systematic analysis of two-pion interferometry in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV using the STAR detector at RHIC. We extract the HBT radii and study their multiplicity, transverse momentum, and azimuthal angle dependence. The Gaussianess of the correlation function is studied. Estimates of the geometrical and dynamical structure of the freeze-out source are extracted by fits with blast wave parameterizations. The expansion of the source and its relation with the initial energy density distribution is studied.
The first measurement of dielectron ($\mathrm{e}^{+}\mathrm{e}^{-}$) production in central (0$-$10$\%$) Pb-Pb collisions at $\mathbf{\sqrt{\textit{s}_{\mathrm{NN}}}}$ = 2.76 TeV at the LHC is presented. The dielectron invariant-mass spectrum is compared to the expected contributions from hadron decays in the invariant-mass range $0 < m_{\mathrm{ee}}<3.5\ \mathrm{GeV}/\textit{c}^{2}$. The ratio of data and the cocktail of hadronic contributions without vacuum $ρ^{0}$ is measured in the invariant-mass range $0.15 < m_{\mathrm{ee}}<0.7\ \mathrm{GeV}/\textit{c}^{2}$, where an excess of dielectrons…
Heavy quarks (charm and beauty) are produced in hard-scattering processes and the study of their production in proton--proton (pp) collisions is an important test for calculations based on perturbative Quantum Chromodynamics (pQCD). Heavy-flavor production as a function of charged-particle multiplicity provides insight into the processes occurring at the partonic level and the interplay between the hard and soft particle production mechanisms in pp collisions. In this contribution, measurements of open heavy-flavor production as a function of multiplicity, via the study of the $\mathrm{D}$-mes…
Charged-hadron and identified-hadron ($K^\mathrm{0}_\mathrm{S}$, $Λ$, $Ξ^\mathrm{-}$) yield measurements in photo-nuclear Pb+Pb and $p$+Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV with ATLAS
Heavy quarks, i.e. charm and beauty, are produced on a shorter time scale with respect to the strongly-interacting matter produced in high-energy heavy-ion collisions. Therefore, they are unique probes to study the mechanisms of parton energy loss, hadronisation and thermalization in the hot and dense state of matter. The nuclear modification factor ($R_{\rm AA}$) and the elliptic flow ($v_{2}$) are two of the main experimental observables that allow us to investigate the interaction strength of heavy quarks with the medium. The most recent results on heavy-flavour production and elliptic flow…
We report the transverse energy ($E_{\mathrm T}$) measured with ALICE at midrapidity in Pb-Pb collisions at ${\sqrt{s_{\mathrm {NN}}}}$ = 2.76 TeV as a function of centrality. The transverse energy was measured using identified single particle tracks. The measurement was cross checked using the electromagnetic calorimeters and the transverse momentum distributions of identified particles previously reported by ALICE. The results are compared to theoretical models as well as to results from other experiments. The mean $E_{\mathrm T}$ per unit pseudorapidity ($η$), $\langle $d$E_{\mathrm T}/$d$η…
Modifications of the properties of jets in PbPb collisions, relative to those in pp collisions, are studied at a nucleon-nucleon center-of-mass energy of $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV via correlations of charged particles with the jet axis in relative pseudorapidity ($Δη$), relative azimuth ($Δϕ$), and relative angular distance from the jet axis $Δ\mathrm{r} = \sqrt{{(Δη)^{2}+(Δϕ)^{2}}}$. This analysis uses data collected with the CMS detector at the LHC, corresponding to integrated luminosities of 404 $μ$b$^{-1}$ and 27.4 pb$^{-1}$ for PbPb and pp collisions, respectively. Charged particl…
Measurements of azimuthal angle and transverse momentum ($p_\mathrm{T}$) correlations of isolated photons and associated jets are reported for pp and PbPb collisions at $\sqrt{s_{_{\mathrm{NN}}}} =$ 5.02 TeV. The data were recorded with the CMS detector at the CERN LHC. For events containing a leading isolated photon with $p_\mathrm{T}^γ>$ 40 GeV$/c$ and an associated jet with $p_\mathrm{T}^\text{jet} >$ 30 GeV$/c$, the photon+jet azimuthal correlation and $p_\mathrm{T}$ imbalance in PbPb collisions are studied as functions of collision centrality and $p_\mathrm{T}^γ$. The results are compared…
Reconstruction of jets in high-energy heavy-ion collisions is challenging due to the large and fluctuating background coming from the underlying event. We report results on full jet reconstruction, obtained from data collected in 2011 by the ALICE detector at LHC for Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76~\mathrm{TeV}$. The analysis makes use of the tracking system and the electromagnetic calorimeter. Signal jets, which come from hard scattered partons, are reconstructed using the anti-$k_{\mathrm{T}}$ jet finder algorithm. The average background is subtracted on a jet-by-jet basis t…
Production cross sections of $Υ$(1S), $Υ$(2S), and $Υ$(3S) states decaying into $μ^+μ^-$ in proton-lead (pPb) collisions are reported using data collected by the CMS experiment at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV. A comparison is made with corresponding cross sections obtained with pp data measured at the same collision energy and scaled by the Pb nucleus mass number. The nuclear modification factor for $Υ$(1S) is found to be $R_\mathrm{pPb}(Υ(1S))$ = 0.806 $\pm$ 0.024 (stat) $\pm$ 0.059 (syst). Similar results for the excited states indicate a sequential suppression pattern, such that $R_\ma…
Measurements of prompt $ψ$(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 $ψ$(2S) in the transverse momentum range 4 $<$ p$_\mathrm{T}$ $<$ 30 GeV$/c$ and the center-of-mass rapidity range $-$2.4 $< y_\mathrm{…
The differential cross sections of $Λ_\mathrm{c}^+$ baryon production are measured via the exclusive decay channel $Λ_\mathrm{c}^+$ $\to$ pK$^-π^+$ using the CMS detector at the LHC. Spectra are measured as a function of transverse momentum ($p_\mathrm{T}$) in proton-proton (pp) and lead-lead (PbPb) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The measurement is performed within the $Λ_\mathrm{c}^+$ rapidity interval $|y|$ $<$ 1.0 in the $p_\mathrm{T}$ range of 5-20 GeV/$c$ in pp and 10-20 GeV/$c$ in PbPb collisions. The observed yields of $Λ_\mathrm{c}^+$ for $p_\mathrm{…
The transverse momentum ($p_{\mathrm T}$) distribution of primary charged particles is measured at midrapidity in minimum-bias p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with the ALICE detector at the LHC in the range $0.15<p_{\mathrm T}<50$ GeV/$c$. The spectra are compared to the expectation based on binary collision scaling of particle production in pp collisions, leading to a nuclear modification factor consistent with unity for $p_{\mathrm T}$ larger than 2 GeV/$c$, with a weak indication of a Cronin-like enhancement for $p_{\rm T}$ around 4 GeV/$c$. The measurement is compared …
Measurements of dijet $p_{\mathrm{T}}$ correlations in Pb+Pb and $pp$ collisions at a nucleon-nucleon centre-of-mass energy of $\sqrt{s_{\mathrm{NN}}}=2.76\textrm{ TeV}$ are presented. The measurements are performed with the ATLAS detector at the Large Hadron Collider using Pb+Pb and $pp$ data samples corresponding to integrated luminosities of 0.14 nb$^{-1}$ and 4.0 pb$^{-1}$, respectively. Jets are reconstructed using the anti-$k_t$ algorithm with radius parameter values $R=0.3$ and $R=0.4$. A background subtraction procedure is applied to correct the jets for the large underlying event pres…
A measurement of $\textit{W}$ boson production in lead-lead collisions at $\sqrt{s_{\mathrm{NN}}}=$2.76 TeV is presented. It is based on the analysis of data collected with the ATLAS detector at the LHC in 2011 corresponding to an integrated luminosity of 0.14 $\mathrm{nb}^{-1}$ and 0.15 $\mathrm{nb}^{-1}$ in the muon and electron decay channels, respectively. The differential production yields and lepton charge asymmetry are each measured as a function of the average number of participating nucleons $< N_{\mathrm{part}} >$ and absolute pseudorapidity of the charged lepton. The results are com…
The almost hermetic coverage of the CMS detector is used to measure the distribution of transverse energy, $E_\mathrm{T}$, over 13.2 units of pseudorapidity, $η$, for pPb collisions at a center-of-mass energy per nucleon pair of $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV. The huge angular acceptance exploits the fact that the CASTOR calorimeter at $-6.6$ $<$ $η$ $<$ $-5.2$ is effectively present on both sides of the colliding system because of a switch in the proton-going and lead-going beam directions. This wide acceptance enables the study of correlations between well-separated angular regions and ma…
The $p_\mathrm{T}$-differential production cross sections of prompt and non-prompt (produced in beauty-hadron decays) D mesons were measured by the ALICE experiment at midrapidity ($|y|<0.5$) in proton--proton collisions at $\sqrt{s}=5.02~\mathrm{TeV}$. The data sample used in the analysis corresponds to an integrated luminosity of $(19.3\pm0.4)~\mathrm{nb^{-1}}$. D mesons were reconstructed from their decays $\mathrm{D^0 \to K^-π^+}$, $\mathrm{D^+\to K^-π^+π^+}$, and $\mathrm{D_s^+\to ϕπ^+\to K^-K^+π^+}$ and their charge conjugates. Compared to previous measurements in the same rapidity regio…
The differential invariant yield as a function of transverse momentum ($p_\mathrm{T}$) of electrons from semileptonic heavy-flavour hadron decays was measured at midrapidity in central (0-10%), semi-central (30-50%) and peripheral (60-80%) lead-lead (Pb-Pb) collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\text{ TeV}$ in the $p_{\mathrm{T}}$ intervals 0.5-26 GeV/$c$ (0-10% and 30-50%) and 0.5-10 GeV/$c$ (60-80%). The production cross section in proton-proton (pp) collisions at $\sqrt{s}=5.02$ TeV was measured as well in $0.5<p_\mathrm{T}<10$ GeV/$c$ and it lies close to the upper band of perturbative…
The production of K$^{*}$(892)$^{0}$ and $ϕ$(1020) mesons has been measured in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV. K$^{*0}$ and $ϕ$ are reconstructed via their decay into charged hadrons with the ALICE detector in the rapidity range $-0.5 < y <0$. The transverse momentum spectra, measured as a function of the multiplicity, have p$_{\mathrm{T}}$ range from 0 to 15 GeV/$c$ for K$^{*0}$ and from 0.3 to 21 GeV/$c$ for $ϕ$. Integrated yields, mean transverse momenta and particle ratios are reported and compared with results in pp collisions at $\sqrt{s}$ = 7 TeV and Pb-Pb collis…
The prompt production of the charm baryon $\rm Λ_{c}^{+}$ and the $\rm Λ_{c}^{+}/\mathrm {D^0}$ production ratios were measured at midrapidity with the ALICE detector in pp and p-Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$TeV. These new measurements show a clear decrease of the $\rm Λ_{c}^{+}/\mathrm {D^0}$ ratio with increasing transverse momentum ($p_{\rm T}$) in both collision systems in the range $2<p_{\rm T}<12$ GeV/$c$, exhibiting similarities with the light-flavour baryon-to-meson ratios ${\rm p}/π$ and $Λ/\mathrm {K^0_S}$. At low $p_{\rm T}$, predictions that include additional colo…
ATLAS measurements of the production of muons from heavy-flavor decays in $\sqrt{s_{\mathrm{NN}}} = 2.76$ TeV Pb+Pb collisions and $\sqrt{s} = 2.76$ TeV $pp$ collisions at the LHC are presented. Integrated luminosities of 0.14 $\mathrm{nb}^{-1}$ and 570 $\mathrm{nb}^{-1}$ are used for the Pb+Pb and $pp$ measurements, respectively, which are performed over the muon transverse momentum range $4 < p_{\mathrm{T}} < 14$ GeV and for five Pb+Pb centrality intervals. Backgrounds arising from in-flight pion and kaon decays, hadronic showers, and mis-reconstructed muons are statistically removed using a…
Measurements of the azimuthal anisotropy in lead-lead collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV are presented using a data sample corresponding to 0.49 $\mathrm{nb}^{-1}$ integrated luminosity collected by the ATLAS experiment at the LHC in 2015. The recorded minimum-bias sample is enhanced by triggers for "ultra-central" collisions, providing an opportunity to perform detailed study of flow harmonics in the regime where the initial state is dominated by fluctuations. The anisotropy of the charged-particle azimuthal angle distributions is characterized by the Fourier coefficients, $v_{2}…
The Anomalous Viscous Fluid Dynamics model, AVFD, is used in concert with the charge-sensitive correlator $R_{Ψ_2}(ΔS)$ to investigate the scaling properties of background- and chiral-magnetically-driven (CME) charge separation ($ΔS$), characterized by the inverse variance $\mathrm{σ^{-2}_{R_{Ψ_2}}}$ of the $R_{Ψ_{2}}(ΔS)$ distributions obtained in collisions at $\sqrt s_{\mathrm{NN}}=200$ GeV. The $\mathrm{σ^{-2}_{R_{Ψ_2}}}$ values for the background are observed to be event-shape-independent. However, they scale with the reciprocal charged-particle multiplicity $(1/\left< N_{\rm ch} \right>)…
