ArticlePDF Available

Transverse momentum and centrality dependence of dihadron correlations in Au+Au collisions at √sNN=200 GeV: Jet quenching and the response of partonic matter

Authors:

Abstract and Figures

Azimuthal angle (Δϕ) correlations are presented for charged hadrons from dijets for 0.4<pT<10 GeV/c in Au+Au collisions at √sNN=200 GeV. With increasing pT, the away-side distribution evolves from a broad and relatively flat shape to a concave shape, then to a convex shape. Comparisons to p+p data suggest that the away-side can be divided into a partially suppressed “head” region centered at Δϕ~π and an enhanced “shoulder” region centered at Δϕ~π±1.1. The pT spectrum for the head region softens toward central collisions, consistent with the onset of jet quenching. The spectral slope for the shoulder region is independent of centrality and trigger pT, which offers constraints on energy transport mechanisms and suggests that it contains the medium response to energetic jets.
Content may be subject to copyright.
arXiv:0705.3238v1 [nucl-ex] 22 May 2007
Transverse momentum and centrality dependence of dihadron correlations in Au+Au
collisions at sNN = 200 GeV: Jet-quenching and the response of partonic matter
A. Adare,8S. Afanasiev,22 C. Aidala,9N.N. Ajitanand,49 Y. Akiba,43, 44 H. Al-Bataineh,38 J. Alexander,49
A. Al-Jamel,38 K. Aoki,28, 43 L. Aphecetche,51 R. Armendariz,38 S.H. Aronson,3J. Asai,44 E.T. Atomssa,29
R. Averbeck,50 T.C. Awes,39 B. Azmoun,3V. Babintsev,18 G. Baksay,14 L. Baksay,14 A. Baldisseri,11 K.N. Barish,4
P.D. Barnes,31 B. Bassalleck,37 S. Bathe,4S. Batsouli,9, 39 V. Baublis,42 F. Bauer,4A. Bazilevsky,3S. Belikov,3, 21
R. Bennett,50 Y. Berdnikov,46 A.A. Bickley,8M.T. Bjorndal,9J.G. Boissevain,31 H. Borel,11 K. Boyle,50
M.L. Brooks,31 D.S. Brown,38 D. Bucher,34 H. Buesching,3V. Bumazhnov,18 G. Bunce,3, 44 J.M. Burward-Hoy,31
S. Butsyk,31, 50 S. Campbell,50 J.-S. Chai,23 B.S. Chang,58 J.-L. Charvet,11 S. Chernichenko,18 J. Chiba,24
C.Y. Chi,9M. Chiu,9, 19 I.J. Choi,58 T. Chujo,55 P. Chung,49 A. Churyn,18 V. Cianciolo,39 C.R. Cleven,16
Y. Cobigo,11 B.A. Cole,9M.P. Comets,40 P. Constantin,21,31 M. Csan´ad,13 T. Cs¨org˝o,25 T. Dahms,50 K. Das,15
G. David,3M.B. Deaton,1K. Dehmelt,14 H. Delagrange,51 A. Denisov,18 D. d’Enterria,9A. Deshpande,44,50
E.J. Desmond,3O. Dietzsch,47 A. Dion,50 M. Donadelli,47 J.L. Drachenberg,1O. Drapier,29 A. Drees,50
A.K. Dubey,57 A. Durum,18 V. Dzhordzhadze,4, 52 Y.V. Efremenko,39 J. Egdemir,50 F. Ellinghaus,8W.S. Emam,4
A. Enokizono,17, 30 H. En’yo,43, 44 B. Espagnon,40 S. Esumi,54 K.O. Eyser,4D.E. Fields,37, 44 M. Finger,5, 22
F. Fleuret,29 S.L. Fokin,27 B. Forestier,32 Z. Fraenkel,57 J.E. Frantz,9, 50 A. Franz,3A.D. Frawley,15 K. Fujiwara,43
Y. Fukao,28, 43 S.-Y. Fung,4T. Fusayasu,36 S. Gadrat,32 I. Garishvili,52 F. Gastineau,51 M. Germain,51 A. Glenn,8, 52
H. Gong,50 M. Gonin,29 J. Gosset,11 Y. Goto,43, 44 R. Granier de Cassagnac,29 N. Grau,21 S.V. Greene,55
M. Grosse Perdekamp,19, 44 T. Gunji,7H.-˚
A. Gustafsson,33 T. Hachiya,17, 43 A. Hadj Henni,51 C. Haegemann,37
J.S. Haggerty,3M.N. Hagiwara,1H. Hamagaki,7R. Han,41 H. Harada,17 E.P. Hartouni,30 K. Haruna,17 M. Harvey,3
E. Haslum,33 K. Hasuko,43 R. Hayano,7M. Heffner,30 T.K. Hemmick,50 T. Hester,4J.M. Heuser,43 X. He,16
H. Hiejima,19 J.C. Hill,21 R. Hobbs,37 M. Hohlmann,14 M. Holmes,55 W. Holzmann,49 K. Homma,17 B. Hong,26
T. Horaguchi,43, 53 D. Hornback,52 M.G. Hur,23 T. Ichihara,43,44 K. Imai,28, 43 M. Inaba,54 Y. Inoue,45, 43
D. Isenhower,1L. Isenhower,1M. Ishihara,43 T. Isobe,7M. Issah,49 A. Isupov,22 B.V. Jacak,50, J. Jia,9J. Jin,9
O. Jinnouchi,44 B.M. Johnson,3K.S. Joo,35 D. Jouan,40 F. Kajihara,7, 43 S. Kametani,7, 56 N. Kamihara,43, 53
J. Kamin,50 M. Kaneta,44 J.H. Kang,58 H. Kanou,43, 53 T. Kawagishi,54 D. Kawall,44 A.V. Kazantsev,27
S. Kelly,8A. Khanzadeev,42 J. Kikuchi,56 D.H. Kim,35 D.J. Kim,58 E. Kim,48 Y.-S. Kim,23 E. Kinney,8
A. Kiss,13 E. Kistenev,3A. Kiyomichi,43 J. Klay,30 C. Klein-Boesing,34 L. Kochenda,42 V. Kochetkov,18
B. Komkov,42 M. Konno,54 D. Kotchetkov,4A. Kozlov,57 A. Kr´al,10 A. Kravitz,9P.J. Kroon,3J. Kubart,5, 20
G.J. Kunde,31 N. Kurihara,7K. Kurita,45, 43 M.J. Kweon,26 Y. Kwon,52, 58 G.S. Kyle,38 R. Lacey,49 Y.-S. Lai,9
J.G. Lajoie,21 A. Lebedev,21 Y. Le Bornec,40 S. Leckey,50 D.M. Lee,31 M.K. Lee,58 T. Lee,48 M.J. Leitch,31
M.A.L. Leite,47 B. Lenzi,47 H. Lim,48 T. Liˇska,10 A. Litvinenko,22 M.X. Liu,31 X. Li,6X.H. Li,4B. Love,55
D. Lynch,3C.F. Maguire,55 Y.I. Makdisi,3A. Malakhov,22 M.D. Malik,37 V.I. Manko,27 Y. Mao,41, 43 L. Maˇsek,5, 20
H. Masui,54 F. Matathias,9, 50 M.C. McCain,19 M. McCumber,50 P.L. McGaughey,31 Y. Miake,54 P. Miks,5, 20
K. Miki,54 T.E. Miller,55 A. Milov,50 S. Mioduszewski,3G.C. Mishra,16 M. Mishra,2J.T. Mitchell,3M. Mitrovski,49
A. Morreale,4D.P. Morrison,3J.M. Moss,31 T.V. Moukhanova,27 D. Mukhopadhyay,55 J. Murata,45, 43
S. Nagamiya,24 Y. Nagata,54 J.L. Nagle,8M. Naglis,57 I. Nakagawa,43,44 Y. Nakamiya,17 T. Nakamura,17
K. Nakano,43, 53 J. Newby,30 M. Nguyen,50 B.E. Norman,31 A.S. Nyanin,27 J. Nystrand,33 E. O’Brien,3S.X. Oda,7
C.A. Ogilvie,21 H. Ohnishi,43 I.D. Ojha,55 H. Okada,28,43 K. Okada,44 M. Oka,54 O.O. Omiwade,1A. Oskarsson,33
I. Otterlund,33 M. Ouchida,17 K. Ozawa,7R. Pak,3D. Pal,55 A.P.T. Palounek,31 V. Pantuev,50 V. Papavassiliou,38
J. Park,48 W.J. Park,26 S.F. Pate,38 H. Pei,21 J.-C. Peng,19 H. Pereira,11 V. Peresedov,22 D.Yu. Peressounko,27
C. Pinkenburg,3R.P. Pisani,3M.L. Purschke,3A.K. Purwar,31,50 H. Qu,16 J. Rak,21, 37 A. Rakotozafindrabe,29
I. Ravinovich,57 K.F. Read,39,52 S. Rembeczki,14 M. Reuter,50 K. Reygers,34 V. Riabov,42 Y. Riabov,42
G. Roche,32 A. Romana,29, M. Rosati,21 S.S.E. Rosendahl,33 P. Rosnet,32 P. Rukoyatkin,22 V.L. Rykov,43
S.S. Ryu,58 B. Sahlmueller,34 N. Saito,28, 43, 44 T. Sakaguchi,3, 7, 56 S. Sakai,54 H. Sakata,17 V. Samsonov,42
H.D. Sato,28, 43 S. Sato,3, 24, 54 S. Sawada,24 J. Seele,8R. Seidl,19 V. Semenov,18 R. Seto,4D. Sharma,57 T.K. Shea,3
I. Shein,18 A. Shevel,42, 49 T.-A. Shibata,43, 53 K. Shigaki,17 M. Shimomura,54 T. Shohjoh,54 K. Shoji,28, 43
A. Sickles,50 C.L. Silva,47 D. Silvermyr,39 C. Silvestre,11 K.S. Sim,26 C.P. Singh,2V. Singh,2S. Skutnik,21
M. Sluneˇcka,5, 22 W.C. Smith,1A. Soldatov,18 R.A. Soltz,30 W.E. Sondheim,31 S.P. Sorensen,52 I.V. Sourikova,3
F. Staley,11 P.W. Stankus,39 E. Stenlund,33 M. Stepanov,38 A. Ster,25 S.P. Stoll,3T. Sugitate,17 C. Suire,40
2
J.P. Sullivan,31 J. Sziklai,25 T. Tabaru,44 S. Takagi,54 E.M. Takagui,47 A. Taketani,43, 44 K.H. Tanaka,24
Y. Tanaka,36 K. Tanida,43, 44 M.J. Tannenbaum,3A. Taranenko,49 P. Tarj´an,12 T.L. Thomas,37 M. Togawa,28, 43
A. Toia,50 J. Tojo,43 L. Tom´sek,20 H. Torii,43 R.S. Towell,1V-N. Tram,29 I. Tserruya,57 Y. Tsuchimoto,17,43
S.K. Tuli,2H. Tydesj¨o,33 N. Tyurin,18 C. Vale,21 H. Valle,55 H.W. van Hecke,31 J. Velkovska,55 R. Vertesi,12
A.A. Vinogradov,27 M. Virius,10 V. Vrba,20 E. Vznuzdaev,42 M. Wagner,28, 43 D. Walker,50 X.R. Wang,38
Y. Watanabe,43, 44 J. Wessels,34 S.N. White,3N. Willis,40 D. Winter,9C.L. Woody,3M. Wysocki,8W. Xie,4, 44
Y. Yamaguchi,56 A. Yanovich,18 Z. Yasin,4J. Ying,16 S. Yokkaichi,43, 44 G.R. Young,39 I. Younus,37
I.E. Yushmanov,27 W.A. Zajc,9O. Zaudtke,34 C. Zhang,9, 39 S. Zhou,6J. Zim´anyi,25, and L. Zolin22
(PHENIX Collaboration)
1Abilene Christian University, Abilene, TX 79699, U.S.
2Department of Physics, Banaras Hindu University, Varanasi 221005, India
3Brookhaven National Laboratory, Upton, NY 11973-5000, U.S.
4University of California - Riverside, Riverside, CA 92521, U.S.
5Charles University, Ovocn´y trh 5, Praha 1, 116 36, Prague, Czech Republic
6China Institute of Atomic Energy (CIAE), Beijing, People’s Republic of China
7Center for Nuclear Study, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan
8University of Colorado, Boulder, CO 80309, U.S.
9Columbia University, New York, NY 10027 and Nevis Laboratories, Irvington, NY 10533, U.S.
10Czech Technical University, Zikova 4, 166 36 Prague 6, Czech Republic
11Dapnia, CEA Saclay, F-91191, Gif-sur-Yvette, France
12Debrecen University, H-4010 Debrecen, Egyetem er 1, Hungary
13ELTE, otv¨os Lor´and University, H - 1117 Budapest, azm´any P. s. 1/A, Hungary
14Florida Institute of Technology, Melbourne, FL 32901, U.S.
15Florida State University, Tallahassee, FL 32306, U.S.
16Georgia State University, Atlanta, GA 30303, U.S.
17Hiroshima University, Kagamiyama, Higashi-Hiroshima 739-8526, Japan
18IHEP Protvino, State Research Center of Russian Federation, Institute for High Energy Physics, Protvino, 142281, Russia
19University of Illinois at Urbana-Champaign, Urbana, IL 61801, U.S.
20Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8, Czech Republic
21Iowa State University, Ames, IA 50011, U.S.
22Joint Institute for Nuclear Research, 141980 Dubna, Moscow Region, Russia
23KAERI, Cyclotron Application Laboratory, Seoul, South Korea
24KEK, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801, Japan
25KFKI Research Institute for Particle and Nuclear Physics of the Hungarian Academy
of Sciences (MTA KFKI RMKI), H-1525 Budapest 114, POBox 49, Budapest, Hungary
26Korea University, Seoul, 136-701, Korea
27Russian Research Center “Kurchatov Institute”, Moscow, Russia
28Kyoto University, Kyoto 606-8502, Japan
29Laboratoire Leprince-Ringuet, Ecole Polytechnique, CNRS-IN2P3, Route de Saclay, F-91128, Palaiseau, France
30Lawrence Livermore National Laboratory, Livermore, CA 94550, U.S.
31Los Alamos National Laboratory, Los Alamos, NM 87545, U.S.
32LPC, Universit´e Blaise Pascal, CNRS-IN2P3, Clermont-Fd, 63177 Aubiere Cedex, France
33Department of Physics, Lund University, Box 118, SE-221 00 Lund, Sweden
34Institut f¨ur Kernphysik, University of Muenster, D-48149 Muenster, Germany
35Myongji University, Yongin, Kyonggido 449-728, Korea
36Nagasaki Institute of Applied Science, Nagasaki-shi, Nagasaki 851-0193, Japan
37University of New Mexico, Albuquerque, NM 87131, U.S.
38New Mexico State University, Las Cruces, NM 88003, U.S.
39Oak Ridge National Laboratory, Oak Ridge, TN 37831, U.S.
40IPN-Orsay, Universite Paris Sud, CNRS-IN2P3, BP1, F-91406, Orsay, France
41Peking University, Beijing, People’s Republic of China
42PNPI, Petersburg Nuclear Physics Institute, Gatchina, Leningrad region, 188300, Russia
43RIKEN, The Institute of Physical and Chemical Research, Wako, Saitama 351-0198, Japan
44RIKEN BNL Research Center, Brookhaven National Laboratory, Upton, NY 11973-5000, U.S.
45Physics Department, Rikkyo University, 3-34-1 Nishi-Ikebukuro, Toshima, Tokyo 171-8501, Japan
46Saint Petersburg State Polytechnic University, St. Petersburg, Russia
47Universidade de ao Paulo, Instituto de F´ısica, Caixa Postal 66318, ao Paulo CEP05315-970, Brazil
48System Electronics Laboratory, Seoul National University, Seoul, South Korea
49Chemistry Department, Stony Brook University, Stony Brook, SUNY, NY 11794-3400, U.S.
50Department of Physics and Astronomy, Stony Brook University, SUNY, Stony Brook, NY 11794, U.S.
51SUBATECH (Ecole des Mines de Nantes, CNRS-IN2P3, Universit´e de Nantes) BP 20722 - 44307, Nantes, France
3
52University of Tennessee, Knoxville, TN 37996, U.S.
53Department of Physics, Tokyo Institute of Technology, Oh-okayama, Meguro, Tokyo 152-8551, Japan
54Institute of Physics, University of Tsukuba, Tsukuba, Ibaraki 305, Japan
55Vanderbilt University, Nashville, TN 37235, U.S.
56Waseda University, Advanced Research Institute for Science and
Engineering, 17 Kikui-cho, Shinjuku-ku, Tokyo 162-0044, Japan
57Weizmann Institute, Rehovot 76100, Israel
58Yonsei University, IPAP, Seoul 120-749, Korea
(Dated: February 1, 2008)
Azimuthal angle (∆φ) correlations are presented for charged hadrons from dijets for 0.4< pT<
10 GeV/cin Au+Au collisions at sNN = 200 GeV. With increasing pT, the away-side distribution
evolves from a broad to a concave shape, then to a convex shape. Comparisons to p+pdata suggest
that the away-side can be divided into a partially suppressed “head” region centered at φπ, and
an enhanced “shoulder” region centered at φπ±1.1. The pTspectrum for the “head” region
softens toward central collisions, consistent with the onset of jet quenching. The spectral slope for
the “shoulder” region is independent of centrality and trigger pT, which offers constraints on energy
transport mechanisms and suggests that the “shoulder” region contains the medium response to
energetic jets.
PACS numbers: 25.75.Dw
High transverse momentum (pT) partons are valuable
probes of the high energy density matter created at the
Relativistic Heavy-Ion Collider (RHIC). These partons
lose a large fraction of their energy in the matter prior to
forming hadrons, a phenomenon known as jet-quenching.
Such energy loss is predicted to lead to strong suppres-
sion of both single- and correlated away-side dihadron
yields at high pT[1], consistent with experimental find-
ings [2, 3]. The exact mechanism for energy loss is not
yet understood. Recent results of dihadron azimuthal
angle (∆φ) correlations have indicated strong modifica-
tion of the away-side jet [3, 4, 5, 6]. For high pThadron
pairs, such modification is manifested by a partially sup-
pressed away-side peak at φπ[3]. This has been
interpreted as evidence for the fragmentation of jets that
survive their passage through the medium.
For intermediate pTcharged hadron pairs, the away-
side jet was observed to peak at φπ±1.1 [4, 5],
suggesting that the energy lost by high pTpartons is
transported to lower pThadrons at angles away from
φπ. The proposed mechanisms for such energy
transport include medium deflection of hard [7] or shower
partons [8],large-angle gluon radiation [9, 10], Cherenkov
gluon radiation [11], and “Mach Shock” medium excita-
tions [12].
In this letter we present a detailed “mapping” of the
pTand centrality dependence of away-side jet shapes and
yields. These measurements (1) allow a detailed inves-
tigation of the jet distributions centered around φ
π±1.1 and φπ, (2) provide new insight on the in-
terplay between jet quenching and the response of the
medium to the lost energy, and (3) provide new con-
straints for distinguishing the competing mechanisms for
energy transport.
The results presented here are based on minimum-
bias (MB) Au+Au and p+p datasets as well as a “pho-
ton” level-1 triggered (PT) p+p dataset [13] collected
with the PHENIX detector [14] at sNN=200 GeV, dur-
ing the 2004-2005 RHIC running periods. The collision
vertex zwas required to be within |z|<30cm of the
nominal crossing point. The event centrality was deter-
mined via the method in Ref. [14]. A total of 840 million
Au+Au events were analyzed. Charged particles were
reconstructed in the two central arms of PHENIX, each
covering -0.35 to 0.35 in pseudo-rapidity and 90in az-
imuth. The tracking system consists of the drift cham-
bers and two layers of multi-wire proportional chambers
with pad readout (PC1 and PC3), achieving a momen-
tum resolution of 0.7% L1.1% p(GeV/c) [2].
Dihadron azimuthal angle correlations are obtained by
correlating “trigger” (type A) hadrons with “partner”
(type B) hadrons. The MB and PT p+p datasets are
used for trigger pT<5 GeV/cand pT>5 GeV/c,
respectively. To reduce background from decays and
conversions, tracks are required to have a matching hit
within a ±2.3σwindow in PC3. For pT>4 GeV/c, ad-
ditional matching hit at the electromagnetic calorimeter
(EMC) was required to suppress background tracks that
randomly associate with the PC3 [2]. For triggers with
pT>5 GeV/c, a pTdependent energy cut in the EMC
and a tight ±1.5σmatching cut at the PC3 were applied
to reduce the background to <10% [15]. This energy
cut greatly reduces PT trigger bias effects. The PT p+p
results are consistent with the MB p+p data for trigger
pT>5 GeV/c.
The jet associated partner yield per trigger, Yjet (∆φ),
is obtained from the φcorrelations as [4, 15]:
Yjet =»Ns(∆φ)
Nm(∆φ)b01 + 2vA
2vB
2cos 2∆φRdφNm(∆φ)
2πNAεB
(1)
where NAis the number of triggers, εBis the single
particle efficiency for partners in the full azimuth and
|η|<0.35; Ns(∆φ) and Nm(∆φ) are pair distributions
4
from the same- and mixed-events, respectively. Mixed-
event pairs are obtained by selecting partners from dif-
ferent events with similar centrality and vertex. The
εBvalues include detector acceptance and reconstruc-
tion efficiency, with an uncertainty of 10% [2, 16]. The
harmonic term, 2vA
2vB
2cos 2∆φ, reflects the elliptic flow
modulation of the combinatoric pairs in Au+Au colli-
sions [4]. Values for vA
2and vB
2for each centrality class
are measured via the reaction plane (RP) method [17]
using the Beam-Beam Counters at 3 <|η|<4. The sys-
tematic errors on v2are dominated by the RP resolution,
and are estimated to be 6% for central and mid-central
collisions, and 10% for the peripheral collisions [4].
To fix the value of b0, we followed the subtraction pro-
cedure of Refs. [4, 18] and assumed that Yjet has zero
yield at its minimum φmin (ZYAM). To estimate the
possible over-subtraction at φmin, we calculate b0val-
ues independently by fitting Yjet(∆φ) to a function con-
sisting of one near-side and two symmetric away-side
Gaussians. The fitting procedure is similar to that used
in [5], except that a region around π(|φπ|<1) is
excluded to avoid “punch-through” jets around π(see
Fig.1). This fit accounts for the overlap of the near- and
away-side Gaussians at φmin, and thus gives system-
atically lower b0values than that for ZYAM. We assign
the differences as one-sided systematic errors on b0. This
over-subtraction error is only significant in central colli-
sions and at pTA,B <3 GeV/c.
The per-trigger yield distributions for p+pand 0-
20% central Au+Au collisions are compared in Fig. 1
for various combinations of trigger and partner pTranges
(pTApTB) as indicated. The p+pdata show essentially
Gaussian away-side peaks centered at φπfor all pTA
and pTB. In contrast, the Au+Au data show substantial
shape modifications dependent on pTAand pTB. For a
fixed value of pTA, Figs. 1(a)-(d) reveal a striking evolu-
tion from a broad, roughly flat peak to a local minimum
at φπwith side-peaks at φπ±1.1. Interestingly,
the location of the side-peaks in φis roughly constant
with increasing pTB(see also [5]). Such pTindependence
is compatible with the away-side jet modification ex-
pected from a medium-induced “Mach Shock” [12] but
disfavors models which incorporate large angle gluon ra-
diation [9, 10], Cherenkov gluon radiation [11] or de-
flected jets [7, 8].
For relatively high values of pTApTB, Figs. 1(e)-(h)
show that the away-side jet shape for Au+Au gradually
becomes peaked as for p+p, albeit suppressed. This “re-
appearance” of the away-side peak seems due to a reduc-
tion of the yield centered at φπ±1.1 relative to that
at φπ, rather than a merging of the peaks centered
at φπ±1.1. This is consistent with the dominance
of dijet fragmentation at large pTApTB, possibly due
to jets that “punch-through” the medium [19] or those
emitted tangentially to the medium’s surface [20].
The evolution of the away-side jet shape with pT(cf.
0
0.2
0.4 0.4-1 GeV/c3-4 1-2 GeV/c3-4 1.5×
0
0.02
0.04
SR HR SR
2-3 GeV/c3-4 3-4 GeV/c3-4
3.5×
0
0.05
0.1
0.15 2-3 GeV/c5-10 4-5 GeV/c4-5
10×
0 2 4
0
0.02
0.04
0.06 3-5 GeV/c5-10
0 2 4
5-10 GeV/c5-10
2.5×
(rad)φ
=
jet
Yφ/d
AB
dN
A
1/N
(a) (b)
(c) (d)
(e) (f)
(g) (h)
Au + Au 0-20%
p + p
FIG. 1: Per-trigger yield versus φfor various trigger and
partner pT(pT
ApT
B), arranged by increasing pair mo-
mentum (sum of pT
Aand pB
T), in p+pand 0-20% Au+Au
collisions. The Data in some panels are scaled as indicated.
Solid lines (shaded bands) indicate elliptic flow (ZYAM) un-
certainties. Arrows in (c) indicate “head” (HR) and “shoul-
der” (SR) regions.
Fig. 1) suggests separate contributions from a medium-
induced component centered at φπ±1.1 and a frag-
mentation component centered at φπ. A model
independent study of these contributions can be made
by dividing the away-side jet function into equal-sized
“head” (|φπ|< π/6, HR) and “shoulder” (π/6<
|φπ|< π/2, SR) regions, as indicated in Fig. 1(c).
We characterize the relative amplitude of these two re-
gions with the ratio, RHS ,
RHS =RφHR dφYjet(∆φ)
φHR RφSR dφYjet(∆φ)
φSR
(2)
Since NAin Eq.1 cancels in the ratio, RHS is a
pure pair variable and is symmetric w.r.t pA
Tand pB
T:
RHS(pA
T, pB
T) = RHS(pB
T, pA
T). For concave and convex
shapes, one expects RHS <1 and RHS >1, respectively.
Figure 2 summarizes the pB
Tdependence of RHS for
both p+pand central Au+Au collisions in four pA
Tbins.
The ratios for p+pare always above one and increase
with pB
T. This reflects the narrowing of a peaked jet
shape with increasing pTB[15]. In contrast, the ra-
tios for Au+Au show a non-monotonic dependence on
pTA,B. They evolve from RHS 1 for pA,B
T.1 GeV/c
through RHS <1 for 1 .pA,B
T.4 GeV/cfollowed by
RHS >1 for pA,B
T&5 GeV/c. These trends reflect the
competition between medium-induced modification and
jet fragmentation, and suggest that the latter dominates
at pA,B
T&5 GeV/c. The results shown in Fig. 1 indicate
that, relative to p+p, the Au+Au yield is suppressed in
5
1
10
<3.0 GeV/c
A
T
2.0<p <4.0 GeV/c
A
T
3.0<p
0 2 4 6
HS
R
1
10
<5.0 GeV/c
A
T
4.0<p
2 4 6
<10.0 GeV/c
A
T
5.0<p
(GeV/c)
B
T
p
p + p
Au + Au 0-20%
FIG. 2: RHS versus pT
Bfor p+p(open) and Au+Au
(filled) collisions for four trigger selections. Since RHS is
purely hadron pair variable, the result is unchanged by swap-
ping pT
Aand pT
B. Shaded bars (brackets) represent pT-
correlated uncertainties due to elliptic flow (ZYAM proce-
dure).
the HR but is enhanced in the SR. We quantify this sup-
pression/enhancement via IAA, the ratio of jet yield Yjet
between Au+Au and p+pcollisions over a φregion,
W, IW
AA =RφWdφY Au+Au
jet .RφWdφY p+p
jet .
Figure 3 shows IAA as a function of pTBfor the HR
and the HR+SR, respectively, in four pTAbins. For trig-
gers of 2 < pTA<3 GeV/c,IAA for HR+SR exceeds one
at low pTB, but falls and crosses one at 3.5 GeV/c. A
similar trend is observed for the higher pTtriggers, but
the enhancement (at low pTB) is smaller and the sup-
pression (at high pTB) is stronger. The IAA values in HR
are lower relative to HR+SR for all pTA,B. For the low
pTtriggers, the suppression sets in around 1 .pTB.3
GeV/c, followed by a fall-off for pTB&4 GeV/c. For
higher pTtriggers, a constant level of 0.20.3 is ob-
served above 2 GeV/csimilar to the suppression level
of inclusive hadrons [2]. These results provide clear ev-
idence for significant yield enhancement in the SR and
suppression in the HR. The data suggest that the SR
reflects the dissipative processes that redistribute the en-
ergy lost in the medium; The suppression for the HR is
consistent with jet quenching. However, we note that the
IAA values for the HR are upper limit estimates for the
jet fragmentation component. This is because the HR
yield includes possible contributions from the tails of the
SR, as well as from bremsstrahlung gluon radiations [9].
To further explore the interplay between the HR and
the SR, we focus on the intermediate pTregion, 1 <
pTB<5 GeV/c, where the medium-induced component
dominates the away-side yield. We characterize the in-
verse local slope of the partner yield in this pTrange via
a truncated mean pT,hpTi hpTBi|1<pTB<5GeV/c- 1
GeV/c.hpTiis calculated from the jet yields used to
0
1
2
3
4<3.0 GeV/c
A
T
2.0<p
0-20%
<4.0 GeV/c
A
T
3.0<p
0 1 2 3 4 5
0
1
2
3
4<5.0 GeV/c
A
T
4.0<p
1 2 3 4 5
<10.0 GeV/c
A
T
5.0<p
AA
I
(GeV/c)
B
T
p
Head + Shoulder
Head region only
FIG. 3: IAA versus pT
Bfor four trigger pTbins in HR+SR
(|φπ|< π/2) and HR (|φπ|< π/6). The total
systematic errors for the two regions, represented by shaded
bars and brackets respectively, are strongly correlated. Grey
bands around IAA = 1 represent 14% combined uncertainty
on the single particle efficiency in Au+Au and p+p.
make IAA in Fig. 3. Fig. 4 shows the hpTivalues for
the HR, SR and a near-side region (|φ|< π/3, NR),
as a function of the number of participating nucleons,
Npart. The hpTivalues for NR have a weak central-
ity dependence. Their overall levels for Npart >100 are
0.533 ±0.024, 0.605 ±0.032 and 0.698 ±0.040 GeV/cfor
the pTAranges 2-3, 3-4 and 4-5 GeV/c, respectively [21].
This finding is consistent with the dominance of jet frag-
mentation on the near-side, i.e. a harder spectrum for
partner hadrons is expected for higher pTtrigger hadrons.
A very weak centrality dependence is observed for
the SR for Npart &100. In this case, the values for
hpTiare lower (0.45 GeV/c) and do not depend on
pTA. They are, however, larger than the values mea-
sured for inclusive charged hadrons (0.38 GeV/cshown
by solid lines) [2]. The relatively sharp increase in hpTi
for Npart .100 may reflect a significant jet fragmenta-
tion contribution in peripheral collisions. In contrast,
the hpTivalues for the HR show a gradual decrease
with Npart, starting close to that for the near-side jet,
and approaches the value for the inclusive spectrum for
Npart &150.
The different patterns observed for the yields in the HR
and SR suggest a different origin for these yields. The
suppression of the HR yield and the softening of its spec-
trum are consistent with a depletion of yield due to jet
quenching. The observed HR yield could be comprised
of contributions from “punch-through” jets, radiated glu-
ons and feed-in from the SR. By contrast, the enhance-
ment of the SR yield for pTA,B <4 GeV/csuggests a
remnant of the lost energy from quenched jets. How-
ever, the very weak dependence on pTand centrality (for
Npart &100) for its peak location and mean pTmay re-
6
0.4
0.6
0.8
0.4
0.6
0.8
0 100 200 300
0.4
0.6
0.8
0 100 200 300
2.0<p <3.0 GeV/c
A
T
3.0<p <4.0 GeV/c
A
T
4.0<p <5.0 GeV/c
A
T
Nearside
Awayside Shoulder Awayside Head
Inclusive
part
N
< 5.0 GeV/c]
B
T
[1.0 < p
> (GeV/c)
T
<p
FIG. 4: Truncated mean hpTiin 1 < pT
B<5 GeV/cver-
sus Npart for the near-side (diamonds), away-side shoulder
(circles) and head (squares) regions for Au+Au (filled) and
p+p (open) for three trigger pTbins. Solid lines represent
measured values for inclusive charged hadrons [2]. Error bars
represent the statistical errors. Shaded bars represent the sum
of Npart-correlated elliptic flow and ZYAM error.
flect an intrinsic property of the response of the medium
to the energetic jets. These observations are inconsistent
with simple deflected jet [7, 8] and Cherenkov gluon ra-
diation [11] models, since both the deflection/radiation
angle and jet spectra slope would depend on the pTAor
pTB. However, these results are consistent with expecta-
tions for “Mach Shock” in a near-ideal hydrodynamical
medium [12, 22], and thus they can be used to constrain
medium transport properties such as speed of sound and
viscosity to entropy ratio.
In conclusion, we have observed strong medium mod-
ification of away-side shapes and yields for jet-induced
pairs in Au+Au collisions at sNN=200 GeV. The de-
tailed dependence of these results on pTand centrality
gives strong evidence for two distinct contributions from
the regions of φπand φπ±1.1. The former is
consistent with jet quenching. The latter exhibits pTand
centrality independent shape and mean pT, possibly re-
flecting an intrinsic property of the medium response to
energetic jets. These results provide strong constraints
on competing mechanisms for the energy transport.
We thank the staff of the Collider-Accelerator and
Physics Departments at BNL for their vital contribu-
tions. We acknowledge support from the Department of
Energy and NSF (U.S.A.), MEXT and JSPS (Japan),
CNPq and FAPESP (Brazil), NSFC (China), MSMT
(Czech Republic), IN2P3/CNRS and CEA (France),
BMBF, DAAD, and AvH (Germany), OTKA (Hun-
gary), DAE (India), ISF (Israel), KRF and KOSEF
(Korea), MES, RAS, and FAAE (Russia), VR and
KAW (Sweden), U.S. CRDF for the FSU, US-Hungarian
NSFOTKA- MTA, and US-Israel BSF.
PHENIX Spokesperson: jacak@skipper.physics.sunysb.edu
Deceased
[1] M. Gyulassy, I. Vitev, X. N. Wang and B. W. Zhang,
nucl-th/0302077; A. Kovner and U. A. Wiedemann,
hep-ph/0304151.
[2] S. S. Adler et al. Phys. Rev. C 69, 034910 (2004)
[3] J. Adams et al. Phys. Rev. Lett. 97, 162301 (2006)
[4] S. S. Adler et al. Phys. Rev. Lett. 97, 052301 (2006)
[5] A. Adare et al. nucl-ex/0611019.
[6] J. Adams et al. Phys. Rev. Lett. 95, 152301 (2005)
[7] C. Chiu and R. Hwa, Phys. Rev. C 74, 064909 (2006)
[8] N. Armesto, C. A. Salgado and U. A. Wiedemann, Phys.
Rev. Lett. 93, 242301 (2004)
[9] I. Vitev, Phys. Lett. B 630, 78 (2005)
[10] A. D. Polosa and C. A. Salgado, Phys. Rev. C 75, 041901
(2007)
[11] I. M. Dremin, JETP Lett. 30 (1979) 140; V. Koch,
A. Majumder and X. N. Wang, Phys. Rev. Lett. 96,
172302 (2006)
[12] J. Casalderrey-Solana, E. V. Shuryak and D. Teaney, J.
Phys. Conf. Ser. 27, 22 (2005); hep-ph/0602183.
[13] A. Adare et al. Phys. Rev. Lett. 97, 252002 (2006)
[14] K. Adcox et al. Nucl. Instrum. Meth. A 499, 469 (2003).
[15] S. S. Adler et al. Phys. Rev. C 73, 054903 (2006)
[16] S. S. Adler et al. Phys. Rev. Lett. 95, 202001 (2005)
[17] S. S. Adler et al. [PHENIX Collaboration], Phys. Rev.
Lett. 91, 182301 (2003)
[18] N. N. Ajitanand et al., Phys. Rev. C 72, 011902 (2005)
[19] T. Renk and K. J. Eskola, hep-ph/0610059.
[20] C. Loizides, Eur. Phys. J. C 49, 339 (2007)
[21] Values at Npart >100 are slightly lower than in p+p,
possibly due to a contribution from a near-side “ridge” [6]
in PHENIX ηacceptance.
[22] T. Renk and J. Ruppert, Phys. Rev. C 73, 011901 (2006)
... For instance, TMB is responsible for the jet energy loss by deflecting soft medium-induced gluons at larger angles than the jet cone size R [15] leading to the suppression of the jet cross section in nucleus-nucleus collisions [16][17][18][19]. Another important and historical signature of jet quenching is the dijet azimuthal asymmetry [20][21][22][23]. This observable is believed to be sensitive to TMB of jets propagating in the quark-gluon plasma through the suppression of the back-to-back peak that signals the azimuthal decorrelation of the di-jet system [24,25]. ...
... We therefore need to study the evolution equation (49) with the pole structure of the NLL BFKL kernel given by Eq. (20). As shown in [51], the DLA running coupling involves a modified geometric scaling limit which takes the formq ðρ; YÞ ¼ e ρ s ðYÞ−Y e βx fðx; YÞ; x¼ ...
Article
Full-text available
We study, to all orders in perturbative QCD, the universal behavior of the saturation momentum Qs(L) controlling the transverse momentum distribution of a fast parton propagating through a dense QCD medium with large size L. Due to the double logarithmic nature of the quantum evolution of the saturation momentum, its large L asymptotics is obtained by slightly departing from the double logarithmic limit of either next-to-leading log (NLL) BFKL or leading order DGLAP evolution equations. At fixed coupling, or in conformal N=4 SYM theory, we derive the large L expansion of Qs(L) up to order αs3/2. In QCD with massless quarks, where conformal symmetry is broken by the running of the strong coupling constant, the 1-loop QCD β-function fully accounts for the universal terms in the Qs(L) expansion. Therefore, the universal coefficients of this series are known exactly to all orders in αs.
... The experimental attempts started at the BNL Relativistic Heavy Ion Collider (RHIC) with the observation of suppression in the yield of single inclusive hadrons [20][21][22][23][24] and associated hadrons (dihadrons) [25][26][27] produced with high transverse momentum relative to the yield in proton-proton collisions. Since 2010, starting at the Large Hadron Collider (LHC) and later at RHIC, the ability of experiments evolved from single hadrons and dihadrons to jets [28][29][30]. ...
Article
Full-text available
We present predictions and postdictions for a wide variety of hard jet-substructure observables using a multistage model within the framework. The details of the multistage model and the various parameter choices are described in []. A novel feature of this model is the presence of two stages of jet modification: a high-virtuality phase [modeled using the modular all twist transverse-scattering elastic-drag and radiation model ()], where modified coherence effects diminish medium-induced radiation, and a lower virtuality phase [modeled using the linear Boltzmann transport model ()], where parton splits are fully resolved by the medium as they endure multiple scattering induced energy loss. Energy-loss calculations are carried out on event-by-event viscous fluid dynamic backgrounds constrained by experimental data. The uniform and consistent descriptions of multiple experimental observables demonstrate the essential role of modified coherence effects and the multistage modeling of jet evolution. Using the best choice of parameters from [], and with no further tuning, we present calculations for the medium modified jet fragmentation function, the groomed jet momentum fraction z g and angular separation r g distributions, as well as the nuclear modification factor of groomed jets. These calculations provide accurate descriptions of published data from experiments at the Large Hadron Collider. Furthermore, we provide predictions from the multistage model for future measurements at the BNL Relativistic Heavy Ion Collider. Published by the American Physical Society 2024
Article
Full-text available
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 sN  N=5.02 \sqrt{s_{\mathrm{N}\;\mathrm{N}}}=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 Δr=(Δη)2+(Δϕ)2 \varDelta \mathrm{r}=\sqrt{{\left(\varDelta \eta \right)}^2+{\left(\varDelta \phi \right)}^2} . This analysis uses data collected with the CMS detector at the LHC, corresponding to integrated luminosities of 404 μb−1 and 27.4 pb−1 for PbPb and pp collisions, respectively. Charged particle number densities, jet fragmentation functions, and jet shapes are presented as a function of PbPb collision centrality and charged-particle track transverse momentum, providing a differential description of jet modifications due to interactions with the quark-gluon plasma.
Article
Full-text available
Multiplicity fluctuations play a crucial role in relativistic heavy-ion collisions. In this work, we explore how the multiplicity fluctuations can be effectively suppressed in the measurement of particle correlations. In particular, through proper normalization, particle correlations can be evaluated in a manner irrelevant to multiplicity. When the multiplicity fluctuations are adequately extracted, Monte Carlo simulations show that the remaining correlations possess distinct features buried in the otherwise overwhelming fluctuations. Moreover, we argue that such a normalization scheme naturally agrees with the multi-particle correlator, which can be evaluated using the Q-vectors. The implications of the present study in the data analysis are also addressed.
Article
We present the first measurement of event-by-event fluctuations in the kaon sector in Pb – Pb collisions at sNN=2.76 TeV with the ALICE detector at the LHC. The robust fluctuation correlator νdyn is used to evaluate the magnitude of fluctuations of the relative yields of neutral and charged kaons, as well as the relative yields of charged kaons, as a function of collision centrality and selected kinematic ranges. While the correlator νdyn[K+,K−] exhibits a scaling approximately in inverse proportion of the charged particle multiplicity, νdyn[KS0,K±] features a significant deviation from such scaling. Within uncertainties, the value of νdyn[KS0,K±] is independent of the selected transverse momentum interval, while it exhibits a pseudorapidity dependence. The results are compared with HIJING, AMPT and EPOS–LHC predictions, and are further discussed in the context of the possible production of disoriented chiral condensates in central Pb – Pb collisions.
Article
We report studies of charge-independent and charge-dependent two-particle differential number correlation functions, R2(Δη,Δφ), and transverse momentum correlation functions, P2(Δη,Δφ), of charged particles produced in Pb–Pb collisions at the LHC center-of-mass energy sNN= 2.76 TeV with the UrQMD, AMPT, and EPOS models. Model calculations for R2 and P2 correlation functions are presented for inclusive charged hadrons (h±) in selected transverse momentum ranges and with full azimuthal coverage in the pseudorapidity range |η|<1.0. We compare these calculations for the strength, shape, and particularly the width of the correlation functions with recent measurements of these observables by the ALICE collaboration. Our analysis indicates that comparative studies of R2 and P2 correlation functions provide valuable insight towards the understanding of particle production in Pb–Pb collisions. We find, in particular, that these models produce quantitatively different magnitudes and shapes for these correlation functions and none reproduce the results reported by the ALICE collaboration. Accounting for quantum number conservation in models, particularly charge conservation, is mandatory to reproduce the detailed measurements of number and transverse momentum correlation functions.
Preprint
Full-text available
Phd thesis with BRAHMS collaboration at RHIC. Investigation of jet quenching in sqrt(S_NN) 62.4GeV Cu+Cu and Au+Au collision.
Article
By means of the nuclear parton distributions determined only with lepton-nuclear deep inelastic scattering experimental data and the analytic parameterization of quenching weight based on BDMPS formalism, a phenomenological analysis of the nuclear Drell–Yan differential cross section ratio as a function of Feynman variable is performed from Fermilab E906 and E866 experimental data. With the nuclear geometry effect on nuclear Drell–Yan process and the quark transport coefficient as a constant, our predictions are in good agreement with the experimental measurements. It is found that nuclear geometry effect has a significant impact on the quark transport coefficient in cold nuclear matter. It is necessary to consider the detailed nuclear geometry in studying the nuclear Drell–Yan process. Our calculated results reveal that the difference in the values of quark transport coefficient exists from E906 and E866 experiments. However, confirming the conclusion, that the quark transport coefficient depends on the target-quark momentum fraction, still needs more accurate experimental data on the Drell–Yan differential cross section ratio in the future. Three models are proposed and discussed for the quark transport coefficient as a function of the measurable kinematic variables. The quark transport coefficient is determined as a function of the Bjorken variable x2x_2 and scale Q2Q^2.
Article
Using the CUJET3=DGLV+VISHNU jet-medium interaction framework, we show that dijet azimuthal acoplanarity in high energy A + A collisions is sensitive to possible non-perturbative enhancement of the jet transport coefficient, qˆ(T,E), in the QCD crossover temperature T ∼ 150–300 MeV range. With jet-medium couplings constrained by global RHIC& LHC χ² fits to nuclear modification data on RAA(pT > 20) GeV, we compare predictions of the medium induced dijet transverse momentum squared, Qs2∼〈qˆL〉∼Δϕ2E2, in two models of the temperature, T, and jet energy E dependence of the jet medium transport coefficient, qˆ(T,E)). In one model, wQGP, the chromo degrees of freedom (dof) are approximated by a perturbative dielectric gas of quark and gluons dof. In the second model, sQGMP, we consider a nonperturbative partially confined semi-Quark-Gluon-Monopole-Plasma with emergent color magnetic dof constrained by lattice QCD data. Unlike the slow variation of the scaled jet transport coefficient, qˆwQGP/T3, the sQGMP model qˆsQGMP/T3 features a sharp maximum in the QCD confinement crossover T range. We show that the dijet path averaged medium induced azimuthal acoplanarity, Δϕ², in sQGMP is robustly ∼ 2 times larger than in perturbative wQGP. even though the radiative energy loss in both models is very similar as needed to fit the same RAA data. Future A+A dijet acoplanarity measurements constrained together with single jet RAA and νn measurements therefore appears to be a promising strategy to search for possible signatures of critical opalescence like phenomena in the QCD confinement temperature range.
Article
Full-text available
The first study of charm quark diffusion with respect to the jet axis in heavy ion collisions is presented. The measurement is performed using jets with p_{T}^{jet}>60 GeV/c and D^{0} mesons with p_{T}^{D}>4 GeV/c in lead-lead (Pb-Pb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of sqrt[s_{NN}]=5.02 TeV, recorded by the CMS detector at the LHC. The radial distribution of D^{0} mesons with respect to the jet axis is sensitive to the production mechanisms of the meson, as well as to the energy loss and diffusion processes undergone by its parent parton inside the strongly interacting medium produced in Pb-Pb collisions. When compared to Monte Carlo event generators, the radial distribution in pp collisions is found to be well described by pythia, while the slope of the distribution predicted by sherpa is steeper than that of the data. In Pb-Pb collisions, compared to the pp results, the D^{0} meson distribution for 4<p_{T}^{D}<20 GeV/c hints at a larger distance on average with respect to the jet axis, reflecting a diffusion of charm quarks in the medium created in heavy ion collisions. At higher p_{T}^{D}, the Pb-Pb and pp radial distributions are found to be similar.
Article
Full-text available
Azimuthal correlations of jet-induced high-pT charged hadron pairs are studied at midrapidity in Au+Au collisions at sNN=200GeV. The distribution of jet-associated partner hadrons (1.0
Article
Full-text available
Methodology is presented for analysis of two-particle azimuthal angle correlation functions obtained in collisions at ultrarelativistic energies. We show that harmonic and di-jet contributions to these correlation functions can be reliably decomposed by two techniques to give an accurate measurement of the jet-pair distribution. Results from detailed Monte Carlo simulations are used to demonstrate the efficacy of these techniques in the study of possible modifications to jet topologies in heavy ion reactions.
Article
Full-text available
Charged hadrons in [EQUATION: SEE TEXT] associated with particles of [EQUATION: SEE TEXT] are reconstructed in pp and Au+Au collisions at sqrt[sNN]=200 GeV. The associated multiplicity and p magnitude sum are found to increase from pp to central Au+Au collisions. The associated p distributions, while similar in shape on the nearside, are significantly softened on the awayside in central Au+Au relative to pp and not much harder than that of inclusive hadrons. The results, consistent with jet quenching, suggest that the awayside fragments approach equilibration with the medium traversed.
Article
The PHENIX experiment at the Relativistic Heavy Ion Collider has measured charged hadron yields at midrapidity over a wide range of transverse momenta (0.5<pT<10GeV∕c) in Au+Au collisions at sNN=200GeV. The data are compared to π0 measurements from the same experiment. For both charged hadrons and neutral pions, the yields per nucleon-nucleon collision are significantly suppressed in central compared to peripheral and nucleon-nucleon collisions. The suppression sets in gradually and increases with increasing centrality of the collisions. Above 4–5GeV∕c in pT, a constant and almost identical suppression of charged hadrons and π0’s is observed. The pT spectra are compared to published spectra from Au+Au at sNN=130 in terms of xT scaling. Central and peripheral π0 as well as peripheral charged spectra exhibit the same xT scaling as observed in p+p data.
Article
Final state medium-induced gluon radiation in ultradense nuclear matter is examined and shown to favor large angle emission when compared to vacuum bremsstrahlung due to the suppression of collinear gluons. Perturbative expression for the contribution of its hadronic fragments to the back-to-back particle correlations is derived. It is found that in the limit of large jet energy loss gluon radiation determines the yield and angular distribution of |Δφ|⩾π2 dihadrons to high transverse momenta pT2 of the associated particles. Clear transition from enhancement to suppression of the away-side hadron correlations is established at moderate pT2 and its experimentally accessible features are predicted versus the trigger particle momentum pT1.
Article
The anisotropy parameter (v2), the second harmonic of the azimuthal particle distribution, has been measured with the PHENIX detector in Au+Au collisions at sNN=200 GeV for identified and inclusive charged particle production at central rapidities (|η|<0.35) with respect to the reaction plane defined at high rapidities (|η|=3–4 ). We observe that the v2 of mesons falls below that of (anti)baryons for pT>2 GeV/c, in marked contrast to the predictions of a hydrodynamical model. A quark-coalescence model is also investigated.
Article
Dihadron correlations at high transverse momentum pT in d+Au collisions at √sNN=200 GeV at midrapidity are measured by the PHENIX experiment at the Relativistic Heavy Ion Collider. From these correlations, we extract several structural characteristics of jets: the root-mean-squared transverse momentum of fragmenting hadrons with respect to the jet √〈jT2〉, the mean sine-squared of the azimuthal angle between the jet axes 〈sin2ϕjj〉, and the number of particles produced within the dijet that are associated with a high-pT particle (dN/dxE distributions). We observe that the fragmentation characteristics of jets in d+Au collisions are very similar to those in p+p collisions and that there is little dependence on the centrality of the d+Au collision. This is consistent with the nuclear medium having little influence on the fragmentation process. Furthermore, there is no statistically significant increase in the value of 〈sin2ϕjj〉 from p+p to d+Au collisions. This constrains the effect of multiple scattering that partons undergo in the cold nuclear medium before and after a hard collision.
Article
The PHENIX detector is designed to perform a broad study of A–A, p–A, and p–p collisions to investigate nuclear matter under extreme conditions. A wide variety of probes, sensitive to all timescales, are used to study systematic variations with species and energy as well as to measure the spin structure of the nucleon. Designing for the needs of the heavy-ion and polarized-proton programs has produced a detector with unparalleled capabilities. PHENIX measures electron and muon pairs, photons, and hadrons with excellent energy and momentum resolution. The detector consists of a large number of subsystems that are discussed in other papers in this volume. The overall design parameters of the detector are presented.
Article
We discussed methods used by the PHENIX to constrain the flow background in the two particle jet correlation. Both the background level and elliptic flow can be reliably decomposed from the jet contribution. We found the jet bias is negligible in PHENIX, when the reaction plane is measured at BBC acceptance (3<|η|<4).
Article
In nucleus-nucleus collisions, high-p(T) partons interact with a dense medium, which possesses strong collective flow components. Here, we demonstrate that the resulting medium-induced gluon radiation does not depend solely on the energy density of the medium, but also on the collective flow. Both components can be disentangled by the measurement of particle production associated with high-p(T) trigger particles, jetlike correlations, and jets. In particular, we show that flow effects lead to a characteristic breaking of the rotational symmetry of the average jet energy and jet multiplicity distribution in the eta x phi plane. We argue that data on the medium-induced broadening of jetlike particle correlations in Au + Au collisions at the Relativistic Heavy-Ion Collider may provide evidence for a significant distortion of parton fragmentation due to the longitudinal collective flow.