K0production in AuAu collisions atpsNN 7.7 11.5 14.5 19.6 27 and 39 GeV from RHIC beam energy scan M. S. Abdallah1B. E. Aboona2J. Adam3L. Adamczyk4J. R. Adams5J. K. Adkins6

2025-05-06 1 0 2.93MB 17 页 10玖币

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K∗0production in Au+Au collisions at √sNN = 7.7, 11.5, 14.5, 19.6, 27 and

39 GeV from RHIC beam energy scan

M. S. Abdallah,1B. E. Aboona,2J. Adam,3L. Adamczyk,4J. R. Adams,5J. K. Adkins,6

I. Aggarwal,7M. M. Aggarwal,7Z. Ahammed,8D. M. Anderson,2E. C. Aschenauer,9J. Atchison,10

V. Bairathi,11 W. Baker,12 J. G. Ball Cap,13 K. Barish,12 R. Bellwied,13 P. Bhagat,14 A. Bhasin,14

S. Bhatta,15 J. Bielcik,3J. Bielcikova,16 J. D. Brandenburg,9X. Z. Cai,17 H. Caines,18

M. Calder´on de la Barca S´anchez,19 D. Cebra,19 I. Chakaberia,20 P. Chaloupka,3B. K. Chan,21

Z. Chang,22 A. Chatterjee,23 D. Chen,12 J. Chen,24 J. H. Chen,25 X. Chen,26 Z. Chen,24 J. Cheng,27

Y. Cheng,21 S. Choudhury,25 W. Christie,9X. Chu,9H. J. Crawford,28 M. Csan´ad,29 G. Dale-Gau,30

M. Daugherity,10 I. M. Deppner,31 A. Dhamija,7L. Di Carlo,32 L. Didenko,9P. Dixit,33 X. Dong,20

J. L. Drachenberg,10 E. Duckworth,34 J. C. Dunlop,9J. Engelage,28 G. Eppley,35 S. Esumi,36

O. Evdokimov,30 A. Ewigleben,37 O. Eyser,9R. Fatemi,6F. M. Fawzi,1S. Fazio,38 C. J. Feng,39 Y. Feng,40

E. Finch,41 Y. Fisyak,9C. Fu,42 C. A. Gagliardi,2T. Galatyuk,43 F. Geurts,35 N. Ghimire,44 A. Gibson,45

K. Gopal,46 X. Gou,24 D. Grosnick,45 A. Gupta,14 W. Guryn,9A. Hamed,1Y. Han,35 S. Harabasz,43

M. D. Harasty,19 J. W. Harris,18 H. Harrison,6S. He,42 W. He,25 X. H. He,47 Y. He,24 S. Heppelmann,19

N. Herrmann,31 E. Hoﬀman,13 L. Holub,3C. Hu,47 Q. Hu,47 Y. Hu,20 H. Huang,39 H. Z. Huang,21

S. L. Huang,15 T. Huang,30 X. Huang,27 Y. Huang,27 T. J. Humanic,5D. Isenhower,10 M. Isshiki,36

W. W. Jacobs,22 C. Jena,46 A. Jentsch,9Y. Ji,20 J. Jia,9, 15 K. Jiang,26 C. Jin,35 X. Ju,26 E. G. Judd,28

S. Kabana,11 M. L. Kabir,12 S. Kagamaster,37 D. Kalinkin,22, 9 K. Kang,27 D. Kapukchyan,12 K. Kauder,9

H. W. Ke,9D. Keane,34 M. Kelsey,32 Y. V. Khyzhniak,5D. P. Kiko la,23 B. Kimelman,19 D. Kincses,29

I. Kisel,48 A. Kiselev,9A. G. Knospe,37 H. S. Ko,20 L. K. Kosarzewski,3L. Kramarik,3L. Kumar,7

S. Kumar,47 R. Kunnawalkam Elayavalli,18 J. H. Kwasizur,22 R. Lacey,15 S. Lan,42 J. M. Landgraf,9

J. Lauret,9A. Lebedev,9J. H. Lee,9Y. H. Leung,31 N. Lewis,9C. Li,24 C. Li,26 W. Li,17 W. Li,35 X. Li,26

Y. Li,26 Y. Li,27 Z. Li,26 X. Liang,12 Y. Liang,34 R. Licenik,16, 3 T. Lin,24 Y. Lin,42 M. A. Lisa,5F. Liu,42

H. Liu,22 H. Liu,42 T. Liu,18 X. Liu,5Y. Liu,2T. Ljubicic,9W. J. Llope,32 R. S. Longacre,9E. Loyd,12

T. Lu,47 N. S. Lukow,44 X. F. Luo,42 L. Ma,25 R. Ma,9Y. G. Ma,25 N. Magdy,15 D. Mallick,49

S. Margetis,34 C. Markert,50 H. S. Matis,20 J. A. Mazer,51 G. McNamara,32 S. Mioduszewski,2

B. Mohanty,49 M. M. Mondal,49 I. Mooney,18 A. Mukherjee,29 M. I. Nagy,29 A. S. Nain,7J. D. Nam,44

Md. Nasim,33 K. Nayak,46 D. Neﬀ,21 J. M. Nelson,28 D. B. Nemes,18 M. Nie,24 T. Niida,36 R. Nishitani,36

T. Nonaka,36 A. S. Nunes,9G. Odyniec,20 A. Ogawa,9S. Oh,20 K. Okubo,36 B. S. Page,9R. Pak,9J. Pan,2

A. Pandav,49 A. K. Pandey,36 T. Pani,51 A. Paul,12 B. Pawlik,52 D. Pawlowska,23 C. Perkins,28 J. Pluta,23

B. R. Pokhrel,44 J. Porter,20 M. Posik,44 T. Protzman,37 V. Prozorova,3N. K. Pruthi,7M. Przybycien,4

J. Putschke,32 Z. Qin,27 H. Qiu,47 A. Quintero,44 C. Racz,12 S. K. Radhakrishnan,34 N. Raha,32

R. L. Ray,50 R. Reed,37 H. G. Ritter,20 M. Robotkova,16, 3 J. L. Romero,19 D. Roy,51 P. Roy Chowdhury,23

L. Ruan,9A. K. Sahoo,33 N. R. Sahoo,24 H. Sako,36 S. Salur,51 S. Sato,36 W. B. Schmidke,9N. Schmitz,53

F-J. Seck,43 J. Seger,54 R. Seto,12 P. Seyboth,53 N. Shah,55 P. V. Shanmuganathan,9M. Shao,26

T. Shao,25 R. Sharma,46 A. I. Sheikh,34 D. Y. Shen,25 K. Shen,26 S. S. Shi,42 Y. Shi,24 Q. Y. Shou,25

E. P. Sichtermann,20 R. Sikora,4J. Singh,7S. Singha,47 P. Sinha,46 M. J. Skoby,56, 40 N. Smirnov,18

Y. S¨ohngen,31 W. Solyst,22 Y. Song,18 B. Srivastava,40 T. D. S. Stanislaus,45 M. Stefaniak,23

D. J. Stewart,32 B. Stringfellow,40 A. A. P. Suaide,57 M. Sumbera,16 C. Sun,15 X. M. Sun,42 X. Sun,47

Y. Sun,26 Y. Sun,58 B. Surrow,44 Z. W. Sweger,19 P. Szymanski,23 A. H. Tang,9Z. Tang,26

T. Tarnowsky,59 J. H. Thomas,20 A. R. Timmins,13 D. Tlusty,54 T. Todoroki,36 C. A. Tomkiel,37

S. Trentalange,21 R. E. Tribble,2P. Tribedy,9S. K. Tripathy,29 T. Truhlar,3B. A. Trzeciak,3

O. D. Tsai,21, 9 C. Y. Tsang,34, 9 Z. Tu,9T. Ullrich,9D. G. Underwood,60, 45 I. Upsal,35 G. Van Buren,9

J. Vanek,9I. Vassiliev,48 V. Verkest,32 F. Videbæk,9S. A. Voloshin,32 F. Wang,40 G. Wang,21

J. S. Wang,58 P. Wang,26 X. Wang,24 Y. Wang,42 Y. Wang,27 Z. Wang,24 J. C. Webb,9P. C. Weidenkaﬀ,31

G. D. Westfall,59 D. Wielanek,23 H. Wieman,20 G. Wilks,30 S. W. Wissink,22 R. Witt,61 J. Wu,42

J. Wu,47 X. Wu,21 Y. Wu,12 B. Xi,17 Z. G. Xiao,27 G. Xie,20 W. Xie,40 H. Xu,58 N. Xu,20 Q. H. Xu,24

Y. Xu,24 Z. Xu,9Z. Xu,21 G. Yan,24 Z. Yan,15 C. Yang,24 Q. Yang,24 S. Yang,62 Y. Yang,39 Z. Ye,35

Z. Ye,30 L. Yi,24 K. Yip,9Y. Yu,24 H. Zbroszczyk,23 W. Zha,26 C. Zhang,15 D. Zhang,42 J. Zhang,24

S. Zhang,26 S. Zhang,25 Y. Zhang,47 Y. Zhang,26 Y. Zhang,42 Z. J. Zhang,39 Z. Zhang,9Z. Zhang,30

F. Zhao,47 J. Zhao,25 M. Zhao,9C. Zhou,25 J. Zhou,26 Y. Zhou,42 X. Zhu,27 M. Zurek,60 and M. Zyzak48

arXiv:2210.02909v2 [nucl-ex] 5 Apr 2023

(STAR Collaboration)

1American University of Cairo, New Cairo 11835, New Cairo, Egypt

2Texas A&M University, College Station, Texas 77843

3Czech Technical University in Prague, FNSPE, Prague 115 19, Czech Republic

4AGH University of Science and Technology, FPACS, Cracow 30-059, Poland

5Ohio State University, Columbus, Ohio 43210

6University of Kentucky, Lexington, Kentucky 40506-0055

7Panjab University, Chandigarh 160014, India

8Variable Energy Cyclotron Centre, Kolkata 700064, India

9Brookhaven National Laboratory, Upton, New York 11973

10Abilene Christian University, Abilene, Texas 79699

11Instituto de Alta Investigaci´on, Universidad de Tarapac´a, Arica 1000000, Chile

12University of California, Riverside, California 92521

13University of Houston, Houston, Texas 77204

14University of Jammu, Jammu 180001, India

15State University of New York, Stony Brook, New York 11794

16Nuclear Physics Institute of the CAS, Rez 250 68, Czech Republic

17Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800

18Yale University, New Haven, Connecticut 06520

19University of California, Davis, California 95616

20Lawrence Berkeley National Laboratory, Berkeley, California 94720

21University of California, Los Angeles, California 90095

22Indiana University, Bloomington, Indiana 47408

23Warsaw University of Technology, Warsaw 00-661, Poland

24Shandong University, Qingdao, Shandong 266237

25Fudan University, Shanghai, 200433

26University of Science and Technology of China, Hefei, Anhui 230026

27Tsinghua University, Beijing 100084

28University of California, Berkeley, California 94720

29ELTE E¨otv¨os Lor´and University, Budapest, Hungary H-1117

30University of Illinois at Chicago, Chicago, Illinois 60607

31University of Heidelberg, Heidelberg 69120, Germany

32Wayne State University, Detroit, Michigan 48201

33Indian Institute of Science Education and Research (IISER), Berhampur 760010 , India

34Kent State University, Kent, Ohio 44242

35Rice University, Houston, Texas 77251

36University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan

37Lehigh University, Bethlehem, Pennsylvania 18015

38University of Calabria & INFN-Cosenza, Italy

39National Cheng Kung University, Tainan 70101

40Purdue University, West Lafayette, Indiana 47907

41Southern Connecticut State University, New Haven, Connecticut 06515

42Central China Normal University, Wuhan, Hubei 430079

43Technische Universit¨at Darmstadt, Darmstadt 64289, Germany

44Temple University, Philadelphia, Pennsylvania 19122

45Valparaiso University, Valparaiso, Indiana 46383

46Indian Institute of Science Education and Research (IISER) Tirupati, Tirupati 517507, India

47Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou, Gansu 730000

48Frankfurt Institute for Advanced Studies FIAS, Frankfurt 60438, Germany

49National Institute of Science Education and Research, HBNI, Jatni 752050, India

50University of Texas, Austin, Texas 78712

51Rutgers University, Piscataway, New Jersey 08854

52Institute of Nuclear Physics PAN, Cracow 31-342, Poland

53Max-Planck-Institut f¨ur Physik, Munich 80805, Germany

54Creighton University, Omaha, Nebraska 68178

55Indian Institute Technology, Patna, Bihar 801106, India

56Ball State University, Muncie, Indiana, 47306

57Universidade de S˜ao Paulo, S˜ao Paulo, Brazil 05314-970

58Huzhou University, Huzhou, Zhejiang 313000

59Michigan State University, East Lansing, Michigan 48824

60Argonne National Laboratory, Argonne, Illinois 60439

61United States Naval Academy, Annapolis, Maryland 21402

62South China Normal University, Guangzhou, Guangdong 510631

(Dated: April 6, 2023)

We report the measurement of K∗0meson at midrapidity (|y|<1.0) in Au+Au collisions at

√sNN = 7.7, 11.5, 14.5, 19.6, 27 and 39 GeV collected by the STAR experiment during the RHIC

beam energy scan (BES) program. The transverse momentum spectra, yield, and average transverse

momentum of K∗0are presented as functions of collision centrality and beam energy. The K∗0/K

yield ratios are presented for diﬀerent collision centrality intervals and beam energies. The K∗0/K

ratio in heavy-ion collisions are observed to be smaller than that in small system collisions (e+e and

p+p). The K∗0/K ratio follows a similar centrality dependence to that observed in previous RHIC

and LHC measurements. The data favor the scenario of the dominance of hadronic rescattering over

regeneration for K∗0production in the hadronic phase of the medium.

PACS numbers: 25.75.Ld

I. INTRODUCTION

Resonances are very short-lived particles and

provide an excellent probe of properties of QCD

medium in heavy-ion collisions (HIC) [1]. They

decay through strong interactions within roughly

10−23 seconds or a few fm/c which is of a simi-

lar order to the lifetime of the medium created in

heavy-ion collisions. Due to their short lifetime,

some resonances decay within the medium. Hence,

they are subjected to in-medium interactions. Dur-

ing the evolution of HIC, the chemical (CFO) and

kinetic (KFO) freeze-out temperatures play impor-

tant roles. At CFO, the inelastic interactions among

the constituents are expected to cease [2–7]. Af-

terward, the constituents can interact among them-

selves via elastic (or pseudo-elastic) interactions un-

til the KFO, when their mean free path increases

and all interactions cease. Between CFO and KFO,

there can be two competing eﬀects, rescattering and

regeneration. The momentum of resonance daugh-

ters (e.g pions and kaons from K∗0) can be altered

due to the scattering with other hadrons present in

the medium. Thus the parent resonance (e.g. K∗0)

is not reconstructible using the re-scattered daugh-

ters. This may result in a reduced resonance yield.

On the other hand, resonances may be regenerated

via pseudo-elastic interactions (e.g. πK ↔K∗0) un-

til KFO is reached. Such regeneration may result in

an increase of resonance yield. The K∗0regeneration

depends on the kaon-pion interaction cross section

(σKπ), the time scale allowed for this re-generation,

and the medium density. The rescattering depends

on resonance lifetime, daughter particle’s interaction

cross-section with the medium (e.g. σKπ, ππ, KK ),

the medium density, and the time scale between

CFO and KFO. The ﬁnal resonance (e.g. K∗0) yield

is aﬀected by the relative strength of these two com-

peting processes. Since the σππ is about a factor of

ﬁve larger than σKπ [8–10], one naively expects a loss

of K∗0signal due to rescattering over regeneration.

Furthermore, the mass peak position and width of

resonances may be modiﬁed due to in-medium ef-

fects and late stage rescattering.

Due to the short lifetime of about 4.16 fm/c, the

K∗0meson is one of the ideal candidates to probe

the hadronic phase of the medium between CFO and

KFO. If rescattering plays a dominant role, then one

naively expects a smaller resonance to non-resonance

particle yield ratio (e.g. K∗0/K) in central collisions

compared to that in peripheral and small system

(p+p) collisions. On the contrary, if regeneration is

dominant, the above ratio is expected to be larger in

central compared to peripheral (and small system)

collisions. In previous RHIC [11–15], SPS [16, 17],

and LHC [18–24] measurements, it is observed that

the K∗0/K ratio is indeed smaller in central heavy-

ion collisions than in peripheral, and elementary

(e.g. p+p) collisions. The observation indicates the

dominance of hadronic rescattering over regenera-

tion. Such an observation is also supported by sev-

eral transport model calculations [25–27]. The mea-

surement of K∗0in the Beam Energy Scan range

can provide information on the interactions in the

hadronic phase of the medium at these energies.

In this article, we report on the measurement of

K∗0mesons at midrapidity (|y|<1.0) using data

from Au+Au collisions at √sNN = 7.7, 11.5, 14.5,

19.6, 27 and 39 GeV collected by the STAR experi-

ment during 2010-2014 in the 1st phase of the Beam

Energy Scan (called BES-I) program. The paper is

organized as follows: Section II brieﬂy describes the

sub-detectors of STAR used in this analysis along

with the event and track selection criteria and the

data-analysis methods. The results for K∗0mesons,

which include transverse momentum (pT) spectra,

yield (dN/dy), average transverse momentum (hpTi)

and ratios to non-resonances are discussed in section

III. The results are summarized in Section IV.

II. EXPERIMENTAL DETAILS AND DATA

ANALYSIS

A. STAR detector

The details of the STAR detector system are dis-

cussed in [28]. The detector conﬁguration during

2010 and 2011 are similar, while during 2014 the

Heavy Flavor Tracker [29] was installed inside the

TPC. Minimum-bias events are selected using the

scintillator-based Beam Beam Counter (BBC) detec-

tors. The BBCs are located on the two sides of the

beam pipe in the pseudo-rapidity range 3.3<|η|<

5.0. The Time Projection Chamber (TPC) [30] is the

main tracking detector in STAR and is used for track

reconstruction for the decay daughters of K∗0. The

TPC has an acceptance of ±1.0 in pseudo-rapidity

and 2πin azimuth. With the TPC, one can identify

particles in the low momentum range by utilizing en-

ergy loss (dE/dx) and momentum information. The

Time of Flight (TOF) [31, 32] detector can be used

to identify particles in the momentum region where

the TPC dE/dx bands for pions and kaons over-

lap. The TOF works on the principle of Multigap

Resistive Plate Chamber (MRPC) technology and

provides pseudorapidity coverage |η|<0.9 with full

2πazimuth.

B. Event selection

Minimum-bias events are selected using the co-

incidence between the BBC detectors [33]. The pri-

mary vertex of each event is reconstructed by ﬁnding

the best common point from which most of the pri-

mary tracks originate. The vertex position along

the beam direction (Vz) is required to be within

±50 cm for √sNN ≥11.5 GeV and ±70 cm for

7.7 GeV in a coordinate system whose origin is at

the center of TPC. The vertex in radial direction

(Vr=qV2

x+V2

y) is required to be smaller than 2.0

cm for all energies except 14.5 GeV where the vertex

is not centered at (0, 0) in the xy plane and slightly

oﬀset at (0.0, -0.89). Hence the Vris selected to be

Vr=pV2

x+ (Vy+ 0.89)2<1 cm for 14.5 GeV [34].

The Vrselection excludes events where the incoming

Au nuclei collide with the beam pipe. The above ver-

tex selection criteria also ensure uniform acceptance

within the ηrange (|η|<1.0) studied. A typical ver-

tex resolution 350 µm can be achieved using about

1000 tracks with a maximum 45 hit points in TPC

[35]. The number of good events selected after these

criteria are listed in Table I.

TABLE I: Au+Au collision datasets, vertex position Vz

and Vrselection, number of events analyzed.

Year Energy |VZ|(cm) Vr(cm) Events (M)

2010 7.7 GeV <70 <2 4.7

2010 11.5 GeV <50 <2 12.1

2014 14.5 GeV <50 <1 15.3

2011 19.6 GeV <50 <2 27.7

2011 27 GeV <50 <2 53.7

2010 39 GeV <50 <2 128.5

C. Centrality selection

The collision centrality is determined via a ﬁt to

the charged particle distribution within |η|<0.5

in the TPC using a Glauber Monte Carlo simula-

tion [36]. The minimum bias triggered events are

divided into nine diﬀerent intervals as 0 – 5%, 5 –

10%, 10 – 20%, 20 – 30%, 30 – 40%, 40 – 50%, 50 –

60%, 60 – 70% and 70 – 80%. The average number

of participant nucleons hNpartifor BES-I energies

are evaluated using a Glauber simulation and are

reported in [34, 37].

D. Track selection

Good quality tracks are selected by requiring at

least 15 hit points in the TPC. In order to re-

duce track splitting, the tracks are required to in-

clude more than 55% of the maximum number of

hits possible for their geometry. Particles are re-

quired to have transverse momentum greater than

0.15 GeV/c. To reduce contamination from sec-

ondary particles (e.g. weak decay contributions), the

distance of closest approach (DCA) to the primary

vertex is required to be smaller than 2 cm. Lastly,

to ensure uniform acceptance, tracks are required to

fall within ±1 in pseudo-rapidity.

E. Particle identiﬁcation

Particle identiﬁcation (PID) is carried out utiliz-

ing both the TPC and TOF detectors. The pion and

kaon candidates are identiﬁed using the energy loss

dE/dx of the particles inside the TPC. In the STAR

TPC, pions and kaons can be distinguished up to

about 0.7 GeV/cin momenta, while (anti-) protons

can be distinguished up to about 1.1 GeV/cin mo-

menta. Particle tracks in the TPC are characterized

by the Nσ variable, which is deﬁned as:

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K0productioninAu+AucollisionsatpsNN=7.7,11.5,14.5,19.6,27and39GeVfromRHICbeamenergyscanM.S.Abdallah,1B.E.Aboona,2J.Adam,3L.Adamczyk,4J.R.Adams,5J.K.Adkins,6I.Aggarwal,7M.M.Aggarwal,7Z.Ahammed,8D.M.Anderson,2E.C.Aschenauer,9J.Atchison,10V.Bairathi,11W.Baker,12J.G.BallCap,13K.Barish,12R.Bellwied,13P....

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K0production in AuAu collisions atpsNN 7.7 11.5 14.5 19.6 27 and 39 GeV from RHIC beam energy scan M. S. Abdallah1B. E. Aboona2J. Adam3L. Adamczyk4J. R. Adams5J. K. Adkins6

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