High-momentum two-particle correlations are a useful tool for studying jet-quenching effects in the quark-gluon plasma. Angular correlations between neutral-pion triggers and charged hadrons with transverse momenta in the range 4–12 GeV/c and 0.5–7 GeV/c, respectively, have been measured by the PHENIX experiment in 2014 for Au+Au collisions at √(s__NN)=200 GeV. Suppression is observed in the yield of high-momentum jet fragments opposite the trigger particle, which indicates jet suppression stemming from in-medium partonic energy loss, while enhancement is observed for low-momentum particles. The ratio and differences between the yield in Au+Au collisions and p+p collisions, I_AA and Δ_AA, as a function of the trigger-hadron azimuthal separation, Δϕ, are measured for the first time at the Relativistic Heavy Ion Collider. These results better quantify how the yield of low-p_T associated hadrons is enhanced at wide angle, which is crucial for studying energy loss as well as medium-response effects.

The PHENIX experiment measured the centrality dependence of two-pion Bose-Einstein correlation functions in root sNN = 200 GeV Au + Au collisions at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. The data are well represented by Levy-stable source distributions. The extracted source parameters are the correlation-strength parameter lambda, the Levy index of stability a, and the Levy-scale parameter R as a function of transverse mass m(T) and centrality. The lambda(m(T)) parameter is constant at larger values of m(T), but decreases as m(T) decreases. The Levy-scale parameter R(m(T)) decreases with mT and exhibits proportionality to the length scale of the nuclear overlap region. The Levy exponent alpha(m(T)) is independent of m(T) within uncertainties in each investigated centrality bin, but shows a clear centrality dependence. At all centralities, the Levy exponent a is significantly different from that of Gaussian ( alpha= 2) or Cauchy ( alpha = 1) source distributions. Comparisons to the predictions of Monte-Carlo simulations of resonance-decay chains show that, in all but the most peripheral centrality class (50%-60%), the obtained results are inconsistent with the measurements, unless a significant reduction of the in-medium mass of the eta meson is included. In each centrality class, the best value of the in-medium eta mass is compared to the mass of the. meson, as well as to several theoretical predictions that consider restoration of U-A(1) symmetry in hot hadronic matter.

High-momentum two-particle correlations are a useful tool for studying jet-quenching effects in the quarkgluon plasma. Angular correlations between neutral-pion triggers and charged hadrons with transverse momenta in the range 4-12 GeV/c and 0.5-7 GeV/c, respectively, have been measured by the PHENIX experiment in 2014 for Au + Au collisions at root sNN = 200 GeV. Suppression is observed in the yield of high-momentum jet fragments opposite the trigger particle, which indicates jet suppression stemming from in-medium partonic energy loss, while enhancement is observed for low-momentum particles. The ratio and differences between the yield in Au + Au collisions and p + p collisions, I-AA and Delta(AA), as a function of the trigger-hadron azimuthal separation, Delta phi, are measured for the first time at the BNL Relativistic Heavy Ion Collider. These results better quantify how the yield of low-pT associated hadrons is enhanced at wide angle, which is crucial for studying energy loss as well as medium-response effects.

A. Adare,12 C. Aidala,39,45 N. N. Ajitanand,63,* Y. Akiba,57,58,† R. Akimoto,11 J. Alexander,63 M. Alfred,24 H. Al-Ta’ani,52 A. Angerami,13 K. Aoki,32,57 N. Apadula,29,64 Y. Aramaki,11,57 H. Asano,35,57 E. C. Aschenauer,7 E. T. Atomssa,64 T. C. Awes,54 B. Azmoun,7 V. Babintsev,25 A. Bagoly,17 M. Bai,6 B. Bannier,64 K. N. Barish,8 B. Bassalleck,51 S. Bathe,5,58 V. Baublis,56 S. Baumgart,57 A. Bazilevsky,7 R. Belmont,12,69 A. Berdnikov,60 Y. Berdnikov,60 D. S. Blau,34,50 M. Boer,39 J. S. Bok,51,52,72 K. Boyle,58 M. L. Brooks,39 J. Bryslawskyj,5,8 H. Buesching,7 V. Bumazhnov,25 S. Butsyk,51 S. Campbell,13,64 V. Canoa Roman,64 P. Castera,64 C.-H. Chen,58,64 C. Y. Chi,13 M. Chiu,7 I. J. Choi,26 J. B. Choi,10,* S. Choi,62 R. K. Choudhury,4 P. Christiansen,41 T. Chujo,68 O. Chvala,8 V. Cianciolo,54 Z. Citron,64,70 B. A. Cole,13 M. Connors,21,58,64 M. Csanád,17 T. Csörgő,18,71 S. Dairaku,35,57 T. W. Danley,53 A. Datta,44 M. S. Daugherity,1 G. David,7,64 K. DeBlasio,51 K. Dehmelt,64 A. Denisov,25 A. Deshpande,58,64 E. J. Desmond,7 K. V. Dharmawardane,52 O. Dietzsch,61 L. Ding,29 A. Dion,29,64 J. H. Do,72 M. Donadelli,61 L. D’Orazio,43 O. Drapier,36 A. Drees,64 K. A. Drees,6 J. M. Durham,39,64 A. Durum,25 S. Edwards,6 Y. V. Efremenko,54 T. Engelmore,13 A. Enokizono,54,57,59 S. Esumi,68 K. O. Eyser,7,8 B. Fadem,46 W. Fan,64 N. Feege,64 D. E. Fields,51 M. Finger,9 M. Finger, Jr.,9 F. Fleuret,36 S. L. Fokin,34 J. E. Frantz,53 A. Franz,7 A. D. Frawley,20 Y. Fukao,57 Y. Fukuda,68 T. Fusayasu,48 K. Gainey,1 C. Gal,64 P. Gallus,14 P. Garg,3,64 A. Garishvili,66 I. Garishvili,38 H. Ge,64 A. Glenn,38 X. Gong,63 M. Gonin,36 Y. Goto,57,58 R. Granier de Cassagnac,36 N. Grau,2 S. V. Greene,69 M. Grosse Perdekamp,26 T. Gunji,11 L. Guo,39 H.-Å. Gustafsson,41,* T. Hachiya,57,58 J. S. Haggerty,7 K. I. Hahn,19 H. Hamagaki,11 S. Y. Han,19 J. Hanks,13,64 S. Hasegawa,30 T. O. S. Haseler,21 K. Hashimoto,57,59 E. Haslum,41 R. Hayano,11 X. He,21 T. K. Hemmick,64 T. Hester,8 J. C. Hill,29 K. Hill,12 A. Hodges,21 R. S. Hollis,8 K. Homma,23 B. Hong,33 T. Horaguchi,68 Y. Hori,11 T. Hoshino,23 N. Hotvedt,29 J. Huang,7 S. Huang,69 T. Ichihara,57,58 H. Iinuma,32 Y. Ikeda,57,68 J. Imrek,16 M. Inaba,68 A. Iordanova,8 D. Isenhower,1 M. Issah,69 D. Ivanishchev,56 B. V. Jacak,64 M. Javani,21 Z. Ji,64 J. Jia,7,63 X. Jiang,39 B. M. Johnson,7,21 K. S. Joo,47 V. Jorjadze,64 D. Jouan,55 D. S. Jumper,26 J. Kamin,64 S. Kaneti,64 B. H. Kang,22 J. H. Kang,72 J. S. Kang,22 J. Kapustinsky,39 K. Karatsu,35,57 S. Karthas,64 M. Kasai,57,59 G. Kasza,17,18 D. Kawall,44,58 A. V. Kazantsev,34 T. Kempel,29 V. Khachatryan,64 A. Khanzadeev,56 K. M. Kijima,23 B. I. Kim,33 C. Kim,8,33 D. J. Kim,31 E.-J. Kim,10 H. J. Kim,72 K.-B. Kim,10 M. Kim,62 M. H. Kim,33 Y.-J. Kim,26 Y. K. Kim,22 D. Kincses,17 E. Kinney,12 Á. Kiss,17 E. Kistenev,7 J. Klatsky,20 D. Kleinjan,8 P. Kline,64 T. Koblesky,12 Y. Komatsu,11,32 B. Komkov,56 J. Koster,26 D. Kotchetkov,53 D. Kotov,56,60 A. Král,14 F. Krizek,31 S. Kudo,68 G. J. Kunde,39 B. Kurgyis,17 K. Kurita,57,59 M. Kurosawa,57,58 Y. Kwon,72 G. S. Kyle,52 R. Lacey,63 Y. S. Lai,13 J. G. Lajoie,29 A. Lebedev,29 B. Lee,22 D. M. Lee,39 J. Lee,19,65 K. B. Lee,33 K. S. Lee,33 S. H. Lee,29,64 S. R. Lee,10 M. J. Leitch,39 M. A. L. Leite,61 M. Leitgab,26 Y. H. Leung,64 B. Lewis,64 N. A. Lewis,45 X. Li,39 S. H. Lim,39,72 L. A. Linden Levy,12 M. X. Liu,39 S. Lökös,17,18 B. Love,69 D. Lynch,7 C. F. Maguire,69 Y. I. Makdisi,6 M. Makek,70,73 A. Manion,64 V. I. Manko,34 E. Mannel,7,13 H. Masuda,59 S. Masumoto,11,32 M. McCumber,12,39 P. L. McGaughey,39 D. McGlinchey,12,20,39 C. McKinney,26 M. Mendoza,8 B. Meredith,26 W. J. Metzger,18 Y. Miake,68 T. Mibe,32 A. C. Mignerey,43 D. E. Mihalik,64 A. Milov,70 D. K. Mishra,4 J. T. Mitchell,7 G. Mitsuka,58 Y. Miyachi,57,67 S. Miyasaka,57,67 A. K. Mohanty,4 S. Mohapatra,63 H. J. Moon,47 T. Moon,72 D. P. Morrison,7 S. I. Morrow,69 S. Motschwiller,46 T. V. Moukhanova,34 T. Murakami,35,57 J. Murata,57,59 A. Mwai,63 T. Nagae,35 K. Nagai,67 S. Nagamiya,32,57 K. Nagashima,23 J. L. Nagle,12 M. I. Nagy,17,71 I. Nakagawa,57,58 H. Nakagomi,57,68 Y. Nakamiya,23 K. R. Nakamura,35,57 T. Nakamura,57 K. Nakano,57,67 C. Nattrass,66 A. Nederlof,46 M. Nihashi,23,57 R. Nouicer,7,58 T. Novák,18,71 N. Novitzky,31,64 A. S. Nyanin,34 E. O’Brien,7 C. A. Ogilvie,29 K. Okada,58 J. D. Orjuela Koop,12 J. D. Osborn,45 A. Oskarsson,41 M. Ouchida,23,57 K. Ozawa,11,32,68 R. Pak,7 V. Pantuev,27 V. Papavassiliou,52 B. H. Park,22 I. H. Park,19,65 J. S. Park,62 S. Park,57,62,64 S. K. Park,33 S. F. Pate,52 L. Patel,21 M. Patel,29 H. Pei,29 J.-C. Peng,26 W. Peng,69 H. Pereira,15 D. V. Perepelitsa,7,12,13 G. D. N. Perera,52 D.Yu. Peressounko,34 C. E. PerezLara,64 R. Petti,7,64 C. Pinkenburg,7 R. P. Pisani,7 M. Proissl,64 A. Pun,53 M. L. Purschke,7 H. Qu,1 P. V. Radzevich,60 J. Rak,31 I. Ravinovich,70 K. F. Read,54,66 D. Reynolds,63 V. Riabov,50,56 Y. Riabov,56,60 E. Richardson,43 D. Richford,5 T. Rinn,29 D. Roach,69 G. Roche,40,* S. D. Rolnick,8 M. Rosati,29 Z. Rowan,5 J. Runchey,29 B. Sahlmueller,64 N. Saito,32 T. Sakaguchi,7 H. Sako,30 V. Samsonov,50,56 M. Sano,68 M. Sarsour,21 K. Sato,68 S. Sato,30 S. Sawada,32 B. K. Schmoll,66 K. Sedgwick,8 R. Seidl,57,58 A. Sen,21,29,66 R. Seto,8 A. Sexton,43 D. Sharma,64,70 I. Shein,25 T.-A. Shibata,57,67 K. Shigaki,23 M. Shimomura,29,49,68 K. Shoji,35,57 P. Shukla,4 A. Sickles,7,26 C. L. Silva,29,39 D. Silvermyr,41,54 K. S. Sim,33 B. K. Singh,3 C. P. Singh,3 V. Singh,3 M. J. Skoby,45 M. Slunečka,9 R. A. Soltz,38 W. E. Sondheim,39 S. P. Sorensen,66 I. V. Sourikova,7 P. W. Stankus,54 E. Stenlund,41 M. Stepanov,44,* A. Ster,71 S. P. Stoll,7 T. Sugitate,23 A. Sukhanov,7 J. Sun,64 J. Sziklai,71 E. M. Takagui,61 A. Takahara,11 A Takeda,49 A. Taketani,57,58 Y. Tanaka,48 S. Taneja,64 K. Tanida,30,58,62 M. J. Tannenbaum,7 S. Tarafdar,3,69 A. Taranenko,50,63 G. Tarnai,16 E. Tennant,52 H. Themann,64 R. Tieulent,42 A. Timilsina,29 T. Todoroki,57,68 L. Tomášek,28 M. Tomášek,14,28 H. Torii,23 C. L. Towell,1 R. S. Towell,1 I. Tserruya,70 Y. Tsuchimoto,11 T. Tsuji,11 Y. Ueda,23 B. Ujvari,16 C. Vale,7 H. W. van Hecke,39 M. Vargyas,17,71 S. Vazquez-Carson,12 E. Vazquez-Zambrano,13 A. Veicht,13 J. Velkovska,69 R. Vértesi,71 M. Virius,14 A. Vossen,26 V. Vrba,14,28 E. Vznuzdaev,56 X. R. Wang,52,58 Z. Wang,5 D. Watanabe,23 K. Watanabe,68 Y. Watanabe,57,58 Y. S. Watanabe,11 F. Wei,29,52 R. Wei,63 S. N. White,7 D. Winter,13 S. Wolin,26 C. L. Woody,7 M. Wysocki,12,54 B. Xia,53 C. Xu,52 Q. Xu,69

Received 2 October 2023DOI:https://doi.org/10.1103/PhysRevC.108.049905©2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasParticle correlations & fluctuationsQuark-gluon plasmaRelativistic heavy-ion collisionsPhysical SystemsBose-Einstein condensatesPionsNuclear Physics

The measurement of direct photons from Au$+$Au collisions at $\sqrt{s_{_{NN}}}=39$ and 62.4 GeV in the transverse-momentum range $0.4<p_T<3$ Gev/$c$ is presented by the PHENIX collaboration at the Relativistic Heavy Ion Collider. A significant direct-photon yield is observed in both collision systems. A universal scaling is observed when the direct-photon $p_T$ spectra for different center-of-mass energies and for different centrality selections at $\sqrt{s_{_{NN}}}=62.4$ GeV is scaled with $(dN_{\rm ch}/d\eta)^{\alpha}$ for $\alpha=1.21{\pm}0.04$. This scaling also holds true for direct-photon spectra from Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV measured earlier by PHENIX, as well as the spectra from Pb$+$Pb at $\sqrt{s_{_{NN}}}=2760$ GeV published by ALICE. The scaling power $\alpha$ seems to be independent of $p_T$, center of mass energy, and collision centrality. The spectra from different collision energies have a similar shape up to $p_T$ of 2 GeV/$c$. The spectra have a local inverse slope $T_{\rm eff}$ increasing with $p_T$ of $0.174\pm0.018$ GeV/$c$ in the range $0.4<p_T<1.3$ GeV/$c$ and increasing to $0.289\pm0.024$ GeV/$c$ for $0.9<p_T<2.1$ GeV/$c$. The observed similarity of low-$p_T$ direct-photon production from $\sqrt{s_{_{NN}}}= 39$ to 2760 GeV suggests a common source of direct photons for the different collision energies and event centrality selections, and suggests a comparable space-time evolution of direct-photon emission.

The measurement of direct photons from Au+Au collisions at √sNN=39 and 62.4 GeV in the transverse-momentum range 0.4

The PHENIX collaboration presents a systematic study of $\pi^0$ production from $p$$+$$p$, $p$$+$Al, $p$$+$Au, $d$$+$Au, and $^{3}$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV. Measurements were performed with different centrality selections as well as the total inelastic, 0%--100%, selection for all collision systems. For 0%--100% collisions, the nuclear modification factors, $R_{xA}$, are consistent with unity for $p_T$ above 8 GeV/$c$, but exhibit an enhancement in peripheral collisions and a suppression in central collisions. The enhancement and suppression characteristics are similar for all systems for the same centrality class. It is shown that for high-$p_T$-$\pi^0$ production, the nucleons in the $d$ and $^3$He interact mostly independently with the Au nucleus and that the counter intuitive centrality dependence is likely due to a physical correlation between multiplicity and the presence of a hard scattering process. These observations disfavor models where parton energy loss has a significant contribution to nuclear modifications in small systems. Nuclear modifications at lower $p_T$ resemble the Cronin effect -- an increase followed by a peak in central or inelastic collisions and a plateau in peripheral collisions. The peak height has a characteristic ordering by system size as $p$$+$Au $>$ $d$$+$Au $>$ $^{3}$He$+$Au $>$ $p$$+$Al. For collisions with Au ions, current calculations based on initial state cold nuclear matter effects result in the opposite order, suggesting the presence of other contributions to nuclear modifications, in particular at lower $p_T$.

A. Adare, C. Aidala, 41 N.N. Ajitanand, Y. Akiba, 53 R. Akimoto, H. Al-Ta’ani, J. Alexander, A. Angerami, K. Aoki, N. Apadula, Y. Aramaki, 52 H. Asano, 52 E.C. Aschenauer, E.T. Atomssa, T.C. Awes, B. Azmoun, V. Babintsev, M. Bai, B. Bannier, K.N. Barish, B. Bassalleck, S. Bathe, 53 V. Baublis, S. Baumgart, A. Bazilevsky, R. Belmont, A. Berdnikov, Y. Berdnikov, X. Bing, D.S. Blau, J.S. Bok, K. Boyle, M.L. Brooks, H. Buesching, V. Bumazhnov, S. Butsyk, S. Campbell, P. Castera, C.-H. Chen, C.Y. Chi, M. Chiu, I.J. Choi, J.B. Choi, S. Choi, R.K. Choudhury, P. Christiansen, T. Chujo, O. Chvala, V. Cianciolo, Z. Citron, B.A. Cole, M. Connors, M. Csanád, T. Csörgő, S. Dairaku, 52 A. Datta, M.S. Daugherity, G. David, A. Denisov, A. Deshpande, 59 E.J. Desmond, K.V. Dharmawardane, O. Dietzsch, L. Ding, A. Dion, 59 M. Donadelli, O. Drapier, A. Drees, K.A. Drees, J.M. Durham, 59 A. Durum, L. D’Orazio, S. Edwards, Y.V. Efremenko, T. Engelmore, A. Enokizono, S. Esumi, K.O. Eyser, B. Fadem, D.E. Fields, M. Finger, M. Finger, Jr., F. Fleuret, S.L. Fokin, J.E. Frantz, A. Franz, A.D. Frawley, Y. Fukao, T. Fusayasu, K. Gainey, C. Gal, A. Garishvili, I. Garishvili, A. Glenn, X. Gong, M. Gonin, Y. Goto, 53 R. Granier de Cassagnac, N. Grau, S.V. Greene, M. Grosse Perdekamp, T. Gunji, L. Guo, H.-Å. Gustafsson, ∗ T. Hachiya, J.S. Haggerty, K.I. Hahn, H. Hamagaki, J. Hanks, K. Hashimoto, 54 E. Haslum, R. Hayano, X. He, T.K. Hemmick, T. Hester, J.C. Hill, R.S. Hollis, K. Homma, B. Hong, T. Horaguchi, Y. Hori, S. Huang, T. Ichihara, 53 H. Iinuma, Y. Ikeda, 62 J. Imrek, M. Inaba, A. Iordanova, D. Isenhower, M. Issah, D. Ivanishchev, B.V. Jacak, M. Javani, J. Jia, 58 X. Jiang, B.M. Johnson, K.S. Joo, D. Jouan, D.S. Jumper, J. Kamin, S. Kaneti, B.H. Kang, J.H. Kang, J.S. Kang, J. Kapustinsky, K. Karatsu, 52 M. Kasai, 54 D. Kawall, 53 A.V. Kazantsev, T. Kempel, A. Khanzadeev, K.M. Kijima, B.I. Kim, C. Kim, D.J. Kim, E.-J. Kim, H.J. Kim, K.-B. Kim, Y.-J. Kim, Y.K. Kim, E. Kinney, Á. Kiss, E. Kistenev, J. Klatsky, D. Kleinjan, P. Kline, Y. Komatsu, B. Komkov, J. Koster, D. Kotchetkov, D. Kotov, 55 A. Král, F. Krizek, G.J. Kunde, K. Kurita, 54 M. Kurosawa, Y. Kwon, G.S. Kyle, R. Lacey, Y.S. Lai, J.G. Lajoie, A. Lebedev, B. Lee, D.M. Lee, J. Lee, K.B. Lee, K.S. Lee, S.H. Lee, S.R. Lee, M.J. Leitch, M.A.L. Leite, M. Leitgab, B. Lewis, S.H. Lim, L.A. Linden Levy, M.X. Liu, B. Love, C.F. Maguire, Y.I. Makdisi, M. Makek, 67 A. Manion, V.I. Manko, E. Mannel, S. Masumoto, M. McCumber, P.L. McGaughey, D. McGlinchey, 19 C. McKinney, M. Mendoza, B. Meredith, Y. Miake, T. Mibe, A.C. Mignerey, A. Milov, D.K. Mishra, J.T. Mitchell, Y. Miyachi, 61 S. Miyasaka, 61 A.K. Mohanty, H.J. Moon, D.P. Morrison, † S. Motschwiller, T.V. Moukhanova, T. Murakami, 52 J. Murata, 54 T. Nagae, S. Nagamiya, 52 J.L. Nagle, ‡ M.I. Nagy, I. Nakagawa, 53 Y. Nakamiya, K.R. Nakamura, 52 T. Nakamura, K. Nakano, 61 C. Nattrass, A. Nederlof, M. Nihashi, 52 R. Nouicer, 53 N. Novitzky, A.S. Nyanin, E. O’Brien, C.A. Ogilvie, K. Okada, A. Oskarsson, M. Ouchida, 52 K. Ozawa, R. Pak, V. Pantuev, V. Papavassiliou, B.H. Park, I.H. Park, S.K. Park, S.F. Pate, L. Patel, H. Pei, J.-C. Peng, H. Pereira, D.Yu. Peressounko, R. Petti, 59 C. Pinkenburg, R.P. Pisani, M. Proissl, M.L. Purschke, H. Qu, J. Rak, I. Ravinovich, K.F. Read, 60 D. Reynolds, V. Riabov, Y. Riabov, E. Richardson, N. Riveli, D. Roach, G. Roche, ∗ S.D. Rolnick, M. Rosati, B. Sahlmueller, N. Saito, T. Sakaguchi, V. Samsonov, 51 M. Sano, M. Sarsour, S. Sawada, K. Sedgwick, R. Seidl, 53 A. Sen, R. Seto, D. Sharma, I. Shein, T.-A. Shibata, 61 K. Shigaki, M. Shimomura, K. Shoji, 52 P. Shukla, A. Sickles, C.L. Silva, D. Silvermyr, K.S. Sim, B.K. Singh, C.P. Singh, V. Singh, M. Slunečka, R.A. Soltz, W.E. Sondheim, S.P. Sorensen, M. Soumya, I.V. Sourikova, P.W. Stankus, E. Stenlund, M. Stepanov, A. Ster, S.P. Stoll, T. Sugitate, A. Sukhanov, J. Sun, J. Sziklai, E.M. Takagui, A. Takahara, A. Taketani, 53 Y. Tanaka, S. Taneja, K. Tanida, 57 M.J. Tannenbaum, S. Tarafdar, A. Taranenko, 58 E. Tennant, H. Themann, T. Todoroki, 62 L. Tomášek, M. Tomášek, H. Torii, R.S. Towell, I. Tserruya, Y. Tsuchimoto, T. Tsuji, C. Vale, H.W. van Hecke, M. Vargyas, E. Vazquez-Zambrano, A. Veicht, J. Velkovska, R. Vértesi, M. Virius, A. Vossen, V. Vrba, 26 E. Vznuzdaev, X.R. Wang, D. Watanabe, K. Watanabe, Y. Watanabe, 53 Y.S. Watanabe, F. Wei, R. Wei, S. Whitaker, S.N. White, D. Winter, S. Wolin, C.L. Woody, M. Wysocki, Y.L. Yamaguchi, 52 R. Yang, A. Yanovich, J. Ying, S. Yokkaichi, 53 Z. You, I. Younus, 46 I.E. Yushmanov, W.A. Zajc, and A. Zelenski

We present direct photon-hadron correlations in 200 GeV/A Au + Au, d + Au, and p + p collisions, for direct photon p(T) from 5-12 GeV/c, collected by the PHENIX Collaboration in the years from 2006 to 2011. We observe no significant modification of jet fragmentation in d + Au collisions, indicating that cold nuclear matter effects are small or absent. Hadrons carrying a large fraction of the quark's momentum are suppressed in Au + Au compared to p + p and d + Au. As the momentum fraction decreases, the yield of hadrons in Au + Au increases to an excess over the yield in p + p collisions. The excess is at large angles and at low hadron p(T) and is most pronounced for hadrons associated with lower momentum direct photons. Comparison to theoretical calculations suggests that the hadron excess arises from medium response to energy deposited by jets.

This corrects the article DOI: 10.1103/PhysRevLett.109.152301.

As a colorless probe, direct photons balance the p_T of the away-side jet at leading order. Direct photon-hadron correlations are thus an excellent probe for nuclear structure and QCD effects, including parton energy loss in the Quark-Gluon Plasma. PHENIX has measured π^0 and direct photon-triggered two-particle azimuthal correlations in a variety of collision systems ranging from p+p to Au+Au at 200 GeV. In p+Au and d+Au collisions, no modification of the per-trigger jet yield or away-side correlation width compared to p+p collisions is observed for direct photon triggered correlations while an increase in the away-side width for π^0 triggered correlations in p+Au has been measured. In Au+Au collisions, direct photons have been identified statistically as well as using an isolation cut. Combining data sets from different collision systems allows us to quantify the transition from suppression at high z_T (p_T,h/p_T,γ) to the enhancement of low z_T particles relative to p+p, and to study this transition as a function of trigger p_T.

Experimental results at RHIC and at the LHC show a similar strong suppression for light and heavy quark probes at high pT, and a possible quark mass dependence of suppression at low pT. More high precision measurements of separated charm and bottom are needed to quantify the dependence of medium effects on the quark mass. The PHENIX experiment measured separated electrons from bottom and charm decays using displaced vertex distributions at mid-rapidity |y|<0.35. Azimuthal anisotropy of electrons from separated charm and bottom decays are obtained from high statistics Au+Au data taken in 2014. PHENIX also measures muons from heavy quark decays in d+Au collisions at forward rapidity to study collective effects on heavy flavor production in small systems. These proceedings report the azimuthal anisotropy of charm and bottom at mid-rapidity in minimum bias Au+Au collisions and the anisotropy of single muons from heavy quark decays in d+Au collisions.

Using the extraordinary versatility of RHIC in selecting different colliding species, the PHENIX experiment has collected data in p+Al, p+Au, d+Au, and He-3+Au collisions at 200 GeV center-of-mass energy and conducted a comprehensive set of anisotropic flow measurements. These geometry-controlled experiments provide a unique testing ground for theoretical models that produce azimuthal particle correlations based on initial- and/or final-state effects. A complete set of triangular anisotropies of inclusive charged particles and final results on identified pion and proton v(2)(p(T)) are shown. The mass-ordered splitting in v(2)(p(T)) provides information about the role of early-stage collective flow and late-stage hadronic rescattering. Detailed model comparisons with all observables are discussed.

We present measurements of azimuthal correlations of charged hadron pairs in sNN=200 GeV Au+Au collisions for the trigger and associated particle transverse-momentum ranges of 14GeV/c) correlations is suppressed compared with that of correlations measured in p+p collisions. At the lowest associated particle pT(0.5

The versatility of RHIC allowed the PHENIX collaboration to measure low momentum direct photons from small systems, such as p+p, p+A, d+Au at sNN=200GeV as well as from large A+A systems, such as Au+Au and Cu+Cu at 200GeV and Au+Au at 62.4GeV and 39GeV. In these measurements PHENIX has discovered a large excess over the scaled p+p yield of direct photons in A+A collisions, and a non-zero excess over the scaled p+p yield in central p+A collisions. Another PHENIX discovery is that at low-pT the integrated yield of direct photons, dNγ/dy, from large systems follows a universal scaling as a function of the charged-particle multiplicity, (dNch/dη)α, with α = 1.25. The observed scaling properties of direct photons from these systems show that the photon production yield increases faster than the charged-particle multiplicity.