Physical Sciences and Mathematics Commons^™

Harmonic Decomposition Of Three-Particle Azimuthal Correlations At Energies Available At The Bnl Relativistic Heavy Ion Collider, L. Adamczyk, James K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, N. N. Ajitanand, I. Alekseev, D. M. Anderson, R. Aoyama, A. Aparin, D. Arkhipkin, E. C. Aschenauer, M. U. Ashraf, A. Attri, G. S. Averichev, X. Bai, V. Bairathi, A. Behera, R. Bellwied, A. Bhasin, A. K. Bhati, P. Bhattarai, J. Bielcik, J. Bielcikova, L. C. Bland, I. G. Bordyuzhin, J. Bouchet, J. D. Brandenburg, A. V. Brandin, D. Brown, Renee H. Fatemi, Suvarna Ramachandran

Physics and Astronomy Faculty Publications

We present measurements of three-particle correlations for various harmonics in Au+Au collisions at energies ranging from √s_NN = 7.7 to 200 GeV using the STAR detector. The quantity ⟨cos(mϕ₁ + nϕ₂ − (m + n)ϕ₃)⟩, with ϕ being the azimuthal angles of the particles is evaluated as a function of √s_NN, collision centrality, transverse momentum, p_T, pseudorapidity difference, Δη, and harmonics (m and n). These data provide detailed information on global event properties such as the three-dimensional structure of the initial …

Low-PT E+ E- Pair Production In Au + Au Collisions At √SNn = 193 Gev And U + U Collisions At √SNn = 193 Gev At Star, J. Adam, L. Adamczyk, J. R. Adams, James K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, N. N. Ajitanand, I. Alekseev, D. M. Anderson, R. Aoyama, A. Aparin, D. Arkhipkin, E. C. Aschenauer, M. U. Ashraf, F. Atetalla, A. Attri, G. S. Averichev, X. Bai, 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, Renee H. Fatemi, Suvarna Ramachandran

Physics and Astronomy Faculty Publications

We report first measurements of e⁺e⁻ pair production in the mass region 0.4 < M_ee < 2.6  GeV/c² at low transverse momentum (p_T < 0.15  GeV/c) in noncentral Au+Au collisions at √s_NN = 200  GeV and U+U collisions at √s_NN = 193  GeV. Significant enhancement factors, expressed as ratios of data over known hadronic contributions, are observed in the 40%–80% centrality of these collisions. The excess yields peak distinctly at low p_T with a width (√⟨p²_T⟩) between 40 and 60  MeV/c. The absolute cross section of …

Azimuthal Anisotropy In Cu+Au Collisions At √SNn = 200 Gev, L. Adamczyk, J. R. Adams, James K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, N. N. Ajitanand, I. Alekseev, D. M. Anderson, R. Aoyama, A. Aparin, D. Arkhipkin, E. C. Aschenauer, M. U. Ashraf, A. Attri, G. S. Averichev, X. Bai, V. Bairathi, K. Barish, A. Behera, R. Bellwied, A. Bhasin, A. K. Bhati, P. Bhattarai, J. Bielcik, J. Bielcikova, L. C. Bland, I. G. Bordyuzhin, J. Bouchet, J. D. Brandenburg, Renee H. Fatemi, Suvarna Ramachandran

Physics and Astronomy Faculty Publications

The azimuthal anisotropic flow of identified and unidentified charged particles has been systematically studied in Cu+Au collisions at √s_NN = 200 GeV for harmonics n = 1–4 in the pseudorapidity range |η| < 1. The directed flow in Cu+Au collisions is compared with the rapidity-odd and, for the first time, the rapidity-even components of charged particle directed flow in Au+Au collisions at √s_NN = 20 GeV. The slope of the directed flow pseudorapidity dependence in Cu+Au collisions is found to be similar to that in Au+Au collisions, with the intercept shifted toward positive pseudorapidity values, i.e., the Cu-going direction. The mean transverse momentum projected onto the spectator plane ⟨p_x⟩ in Cu+Au collision also exhibits approximately linear dependence on pseudorapidity with the intercept …

Globalization Polarization Of Λ Hyperons In Au + Au Collisions At √SNn = 200 Gev, J. Adam, L. Adamczyk, J. R. Adams, James K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, N. N. Ajitanand, I. Alekseev, D. M. Anderson, R. Aoyama, A. Aparin, D. Arkhipkin, E. C. Aschenauer, M. U. Ashraf, F. Atetalla, A. Attri, G. S. Averichev, X. Bai, 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, Renee H. Fatemi, Suvarna Ramachandran

Physics and Astronomy Faculty Publications

Global polarization of Λ hyperons has been measured to be of the order of a few tenths of a percentage in Au+Au collisions at √s_NN = 200 GeV, with no significant difference between Λ and Λ ̄. These new results reveal the collision energy dependence of the global polarization together with the results previously observed at √s_NN = 7.7–62.4 GeV and indicate noticeable vorticity of the medium created in noncentral heavy-ion collisions at the highest Relativistic Heavy Ion Collider collision energy. The signal is in rough quantitative agreement with the theoretical predictions from a hydrodynamic model …

Beam Energy Dependence Of Jet-Quenching Effects In Au + Au Collisions At √SNn = 7.7, 11.5, 14.5, 19.6, 27, 39, And 62.4 Gev, L. Adamczyk, J. R. Adams, J. Kevin Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, N. N. Ajitanand, I. Alekseev, D. M. Anderson, R. Aoyama, A. Aparin, D. Arkhipkin, E. C. Aschenauer, M. U. Ashraf, A. Attri, G. S. Averichev, X. Bai, V. Bairathi, K. Barish, A. Behera, R. Bellwied, A. Bhasin, A. K. Bhati, P. Bhattarai, J. Bielcikova, J. Bielcikova, L. C. Bland, I. G. Bordyuzhin, J. Bouchet, J. D. Brandenburg, Renee H. Fatemi, Suvarna Ramachandran

Physics and Astronomy Faculty Publications

We report measurements of the nuclear modification factor RCP for charged hadrons as well as identified π⁺⁽⁻⁾, K⁺⁽⁻⁾, and p^(p¯) for Au + Au collision energies of √s_NN = 7.7, 11.5, 14.5, 19.6, 27, 39, and 62.4 GeV. We observe a clear high-pT net suppression in central collisions at 62.4 GeV for charged hadrons which evolves smoothly to a large net enhancement at lower energies. This trend is driven by the evolution of the pion spectra but is also very similar for the kaon spectra. While the magnitude of the proton R_{CP …}

Measurement Of The 3ΛH Lifetime In Au+Au Collisions At The Bnl Relativistic Heavy Ion Collider, L. Adamczyk, J. R. Adams, James K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, N. N. Ajitanand, I. Alekseev, J. Alford, D. M. Anderson, R. Aoyama, A. Aparin, D. Arkhipkin, E. C. Aschenauer, M. U. Ashraf, A. Attri, G. S. Averichev, X. Bai, V. Bairathi, K. Barish, A. Behera, R. Bellwied, A. Bhasin, A. K. Bhati, P. Bhattarai, J. Bielcik, J. Bielcikova, L. C. Bland, I. G. Bordyuzhin, J. Bouchet, Renee H. Fatemi, Suvarna Ramachandran

Physics and Astronomy Faculty Publications

An improved measurement of the ³_ΛH lifetime is presented. In this paper, the mesonic decay modes ³_ΛH → ³He + π⁻ and ³_ΛH → d + p + π⁻ are used to reconstruct the ³_ΛH from Au+Au collision data collected by the STAR collaboration at Relativistic Heavy Ion Collider (RHIC). A minimum χ² estimation is used to determine the lifetime of τ = 142⁺²⁴₋₂₁(stat.) ± 29(syst.) ps. This lifetime is about 50% shorter than the lifetime τ = 263 ± 2 ps of a free …

Beam-Energy Dependence Of Directed Flow Of Λ, Λ¯, K±, K0S, And Φ In Au + Au Collisions, L. Adamczyk, J. R. Adams, James K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, N. N. Ajitanand, I. Alekseev, D. M. Anderson, R. Aoyama, A. Aparin, D. Arkhipkin, E. C. Aschenauer, M. U. Ashraf, A. Attri, G. S. Averichev, X. Bai, V. Bairathi, K. Barish, A. Behera, R. Bellwied, A. Bhasin, A. K. Bhati, P. Bhattarai, J. Bielcik, J. Bielcikova, L. C. Bland, I. G. Bordyuzhin, J. Bouchet, J. D. Brandenburg, Renee H. Fatemi, Suvarna Ramachandran

Physics and Astronomy Faculty Publications

Rapidity-odd directed-flow measurements at midrapidity are presented for Λ, Λ¯, K^±, K⁰_s, and ϕ at √s_NN = 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV in Au + Au collisions recorded by the Solenoidal Tracker detector at the Relativistic Heavy Ion Collider. These measurements greatly expand the scope of data available to constrain models with differing prescriptions for the equation of state of quantum chromodynamics. Results show good sensitivity for testing a picture where flow is assumed to be imposed before hadron formation and the observed particles are assumed to form …

Coherent Diffractive Photoproduction Of Ρ0 Mesons On Gold Nuclei At 200 Gev/Nucleon-Pair At The Relativistic Heavy Ion Collider, L. Adamczyk, James K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, N. N. Ajitanand, I. Alekseev, D. M. Anderson, R. Aoyama, A. Aparin, D. Arkhipkin, E. C. Aschenauer, M. U. Ashraf, A. Attri, G. S. Averichev, X. Bai, V. Bairathi, A. Behera, R. Bellwied, A. Bhasin, A. K. Bhati, P. Bhattarai, J. Bielcik, J. Bielcikova, L. C. Bland, I. G. Bordyuzhin, J. Bouchet, J. D. Brandenburg, A. V. Brandin, D. Brown, Renee H. Fatemi, Suvarna Ramachandran

Physics and Astronomy Faculty Publications

The STAR Collaboration reports on the photoproduction of π⁺π⁻ pairs in gold-gold collisions at a center-of-mass energy of 200 GeV/nucleon-pair. These pion pairs are produced when a nearly real photon emitted by one ion scatters from the other ion.

We fit the π⁺π⁻ invariant-mass spectrum with a combination of ρ⁰ and ω resonances and a direct π⁺π⁻ continuum. This is the first observation of the ω in ultraperipheral collisions, and the first measurement of ρ−ω interference at energies where photoproduction is dominated by Pomeron exchange. The ω amplitude is consistent …

Bulk Properties Of The Medium Produced In Relativistic Heavy-Ion Collisions From The Beam Energy Scan Program, L. Adamczyk, James K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, N. N. Ajitanand, I. Alekseev, D. M. Anderson, R. Aoyama, A. Aparin, D. Arkhipkin, E. C. Aschenauer, M. U. Ashraf, A. Attri, G. S. Averichev, X. Bai, V. Bairathi, A. Behera, R. Bellwied, A. Bhasin, A. K. Bhati, P. Bhattarai, J. Bielcik, J. Bielcikova, L. C. Bland, I. G. Bordyuzhin, J. Bouchet, J. D. Brandenburg, A. V. Brandin, D. Brown, Renee H. Fatemi, Suvarna Ramachandran

Physics and Astronomy Faculty Publications

We present measurements of bulk properties of the matter produced in Au+Au collisions at √S_NN = 7.7, 11.5, 19.6, 27, and 39 GeV using identified hadrons (π^±, K^±, p, and p¯) from the STAR experiment in the Beam Energy Scan (BES) Program at the Relativistic Heavy Ion Collider (RHIC). Midrapidity (|y| < 0.1) results for multiplicity densities dN/dy, average transverse momenta ⟨p_T⟩, and particle ratios are presented. The chemical and kinetic freeze-out dynamics at these energies are discussed and presented as a function of collision centrality and energy. These results constitute the systematic …

Measurement Of Jet Quenching With Semi-Inclusive Hadron+Jet Distributions In Au + Au Collisions At √SNn = 200 Gev, L. Adamczyk, James K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, N. N. Ajitanand, I. Alekseev, D. M. Anderson, R. Aoyama, A. Aparin, D. Arkhipkin, E. C. Aschenauer, M. U. Ashraf, A. Attri, G. S. Averichev, X. Bai, V. Bairathi, A. Behera, R. Bellwied, A. Bhasin, A. K. Bhati, P. Bhattarai, J. Bielcik, J. Bielcikova, L. C. Bland, I. G. Bordyuzhin, J. Bouchet, J. D. Brandenburg, A. V. Brandin, D. Brown, Renee H. Fatemi, Suvarna Ramachandran

Physics and Astronomy Faculty Publications

The STAR Collaboration reports the measurement of semi-inclusive distributions of charged-particle jets recoiling from a high transverse momentum hadron trigger, in central and peripheral Au + Au collisions at √^s_NN = 200 GeV. Charged jets are reconstructed with the anti-k_T algorithm for jet radii R between 0.2 and 0.5 and with low infrared cutoff of track constituents (p_T > 0.2 GeV/c). A novel mixed-event technique is used to correct the large uncorrelated background present in heavy ion collisions. Corrected recoil jet distributions are reported at midrapidity, for charged-jet transverse momentum p^ch_T,jet < GeV/c. Comparison is made to similar measurements for Pb + Pb collisions at √s = …

Dijet Imbalance Measurements In Au + Au And Pp Collisions At √SNn = 200 Gev At Star, L. Adamczyk, James K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, I. Alekseev, D. M. Anderson, R. Aoyama, A. Aparin, D. Arkhipkin, E. C. Aschenauer, M. U. Ashraf, A. Attri, G. S. Averichev, X. Bai, V. Bairathi, R. Bellwied, A. Bhasin, A. K. Bhati, P. Bhattarai, J. Bielcik, J. Bielcikova, L. C. Bland, I. G. Bordyuzhin, J. Bouchet, J. D. Brandenburg, A. V. Brandin, D. Brown, I. Bunzarov, J. Butterworth, Renee H. Fatemi, Suvarna Ramachandran

Physics and Astronomy Faculty Publications

We report the first dijet transverse momentum asymmetry measurements from Au + Au and pp collisions at RHIC. The two highest-energy back-to-back jets reconstructed from fragments with transverse momenta above 2  GeV/c display a significantly higher momentum imbalance in heavy-ion collisions than in the pp reference. When reexamined with correlated soft particles included, we observe that these dijets then exhibit a unique new feature—momentum balance is restored to that observed in pp for a jet resolution parameter of R = 0.4, while rebalancing is not attained with a smaller value of R = 0.2.

Measurement Of D0 Azimuthal Anisotropy At Midrapidity In Au + Au Collisions At √SNn = 200 Gev, L. Adamczyk, James K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, N. N. Ajitanand, I. Alekseev, D. M. Anderson, R. Aoyama, A. Aparin, D. Arkhipkin, E. C. Aschenauer, M. U. Ashraf, A. Attri, G. S. Averichev, X. Bai, V. Bairathi, A. Behera, R. Bellwied, A. Bhasin, A. K. Bhati, P. Bhattarai, J. Bielcik, J. Bielcikova, L. C. Bland, I. G. Bordyuzhin, J. Bouchet, J. D. Brandenburg, A. V. Brandin, D. Brown, Renee H. Fatemi, Suvarna Ramachandran

Physics and Astronomy Faculty Publications

We report the first measurement of the elliptic anisotropy (v²) of the charm meson D0 at midrapidity (|y| < 1) in Au+Au collisions at √s_NN = 200  GeV. The measurement was conducted by the STAR experiment at RHIC utilizing a new high-resolution silicon tracker. The measured D⁰ v₂ in 0%–80% centrality Au + Au collisions can be described by a viscous hydrodynamic calculation for a transverse momentum (p_T) of less than 4  GeV/c. The D⁰ v₂ as a function of transverse kinetic energy (m_T − m₀, where m …

Elliptic Flow Of Electrons From Heavy-Flavor Hadron Decays In Au + Au Collisions At √SNn = 200, 62.4, And 39 Gev, L. Adamczyk, J. Kevin Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, N. N. Ajitanand, I. Alekseev, D. M. Anderson, R. Aoyama, A. Aparin, D. Arkhipkin, E. C. Aschenauer, M. U. Ashraf, A. Attri, G. S. Averichev, X. Bai, V. Bairathi, A. Behera, R. Bellwied, A. Bhasin, A. K. Bhati, P. Bhattarai, J. Bielcik, J. Bielcikova, L. C. Bland, I. G. Bordyuzhin, J. Bouchet, J. D. Brandenburg, A. V. Brandin, D. Brown, Renee H. Fatemi, Suvarna Ramachandran

Physics and Astronomy Faculty Publications

We present measurements of elliptic flow (ν₂) of electrons from the decays of heavy-flavor hadrons (e_HF) by the STAR experiment. For Au+Au collisions at √s_NN = 200 GeV we report v₂, for transverse momentum (p_T) between 0.2 and 7 GeV/c, using three methods: the event plane method (v₂{EP}), two-particle correlations (v₂{2}), and four-particle correlations (v₂{4}). For Au+Au collisions at √s_NN = 62.4 and 39 GeV we report v₂{2} for p_T < 2 GeV/c …