M. Šumbera NPI ASCR 1

Selected Results from STAR Beam Energy Scan Program

Michal ŠumberaNuclear Physics Institute AS CR, Řež/Prague

(for the STAR Collaboration)

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1) Turn-off of sQGP signatures

2) Search for the signals of phase boundary 3) Search for the QCD critical point

The RHIC Beam Energy Scan Motivation

M. Šumbera

http://arxiv.org/abs/1007.2613

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TPC:Detects Particles in the |h|<1 rangep, K, p through dE/dx and TOFK0

s, , , , L X W f through invariant mass

Coverage: 0 < f < 2 p |h| < 1.0Uniform acceptance: All energies and particles

M. Šumbera NPI ASCR 4

Triggering required effort, but was a solvable problem.Geometric acceptance remains the same, track density gets lower.Detector performance generally improves at lower energies.

Year √sNN [GeV] events(106)

2010 39 130

2011 27 70

2011 19.6 36

2010 11.5 12

2010 7.7 5

2012* 5 Test Run

BES-I Data:

Central Au+Au at 7.7 GeV in STAR TPC

Uncorrected Nch

dNev

t / (N

evt d

Nch

)BES Au+Au Data Taking

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STAR TPC - Uniform Acceptance over all RHIC EnergiesAu+Au at 7.7 GeV Au+Au at 39 GeV Au+Au at 200 GeV

Crucial for all analyses

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Selected Results

M. Šumbera

STAR publications on BES resultsObservation of an energy-dependent difference in elliptic flow between particles and antiparticles in relativistic heavy ion collisions, Phys. Rev. Lett. 110 (2013) 142301

Elliptic flow of identified hadrons in Au+Au collisions at √sNN= 7.7--62.4 GeV ,Phys. Rev. C 88 (2013) 14902

Inclusive charged hadron elliptic flow in Au + Au collisions at √sNN= 7.7--62.4 GeV , Phys. Rev. C 86 (2012) 54908

Energy Dependence of Moments of Net-proton Multiplicity Distributions at RHIC STAR , e-Print: arXiv:1309.5681 [nucl-ex]

+ many conference proceedings…

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(0-5

%/6

0-8

0%

)

Suppression of Charged Hadrons …

PRL 91, 172302 (2003)

M. Šumbera

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(0-5

%/6

0-8

0%

)

STAR Preliminary

… and its Disappearance

RCP ≥ 1 at lower energies - Cronin effect?

PRL 91, 172302 (2003)

M. Šumbera

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Enhancement vs. QGP suppression

Motivation: Agreement between the simulation and the data at low beam energies and its break down at higher energies could help to find the energy at which QGP becomes dominant.In HIJING (jet quenching off) RCP at lower energies is enhanced, but there is no quantitative agreement with charged hadron RCP from data. No suppression at higher energies observed, as expected (quenching was turned off).

M. Šumbera

S. Horvat (STAR): arXiv: 1303.7260

HIJING 1.35: Gyulassy M. and Wang X. Com. Phys. Com. 83 307(1994)

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Positive particlesSTAR Preliminary

RCP : Identified Particles

Proton RCP > pion RCP, similar to d+Au at √sNN=200 GeV⇒Pions may serve as a better gauge for jet quenching within the pT range available through particle identification.

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Antiproton RCP < pion RCP for pT <1GeV/c

Pion RCP suppressed for √sNN ≥39GeV

Negative particlesSTAR Preliminary

RCP : Identified Particles

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φ meson pT spectra

Fit by Levy(straight line) works well

STAR Preliminary

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Ks0 RCP: (0-5%)/(40-60%)

f RCP: (0-10%)/(40-60%) and (0-5%)/(40-60%) for 200GeV

RCP : φ and Ks0

STAR Preliminary

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φ RCP: energy dependence

f RCP ≥ 1 at intermediate pT for √sNN ≤ 39GeV

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Strange Quark Dynamics

At intermediate pT Ω/φ ratios show different behavior for √sNN ≥ 19.6 and √sNN = 11.5 GeV.

Derived strange quark pT distributions show a similar trend.

STAR Preliminary

Change of particle production mechanism ?Hwa & Yang, Phys. Rev. C 75, 054904 (2007), Phys. Rev. C 78, 034907 (2008).

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NCQ Scaling Test: particles

M. Šumbera

STAR: Phys.Rev. C88, 014902 (2013)

Universal trend for most of particles – ncq scaling not broken at low energies ϕ meson v2 deviates from other particles in Au+Au@(11.5 & 7.7) GeV: ~ 2σ at the highest pT data point. Needs more data to make clear conclusion.

Reduction of v2 for ϕ meson and absence of ncq scaling during the evolution the system remains in the hadronic phase [B. Mohanty and N. Xu: J. Phys. G 36, 064022(2009)]

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NCQ Scaling Test: antiparticles

M. Šumbera

STAR: Phys.Rev. C88, 014902 (2013)

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Δv2: v2(Particles) - v2 (Antiparticles)

The difference between particles and anti-particles is observed.A linear increase Δv2 = a × μB for all particle species for 7.7 GeV ≤ √sNN ≤ 62.4 GeV. The baryon chemical potential is directly connected to the difference in v2 between particles and antiparticles.

M. Šumbera

STAR: PRL 110 (2013) 142301 STAR: Phys.Rev. C88, 014902 (2013)

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Beam Energy Scan Phase- II

M. Šumbera

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STAR BES Program Summary

206 5851120 420

2.557.719.639

775

√sNN (GeV)

mB (MeV)

QG

P pr

oper

ties

BES

phas

e-I

Test

Run

Fixe

d Ta

rget

BES

phas

e-II

Large range of mB in the phase diagram !!!

Explore QCD Diagram

M. Šumbera

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Explore QCD Diagram

STAR BES Program Summary

206 5851120 420

2.557.719.639

775

√sNN (GeV)

mB (MeV)

QG

P pr

oper

ties

BES

phas

e-I

Test

Run

Fixe

d Ta

rget

BES

phas

e-II

Large range of mB in the phase diagram !!!

M. Šumbera

Is there another way?

Can another facility do this faster? Or better?

The Alternatives

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•Time Line: 2009-2015•Energy Range: √sNN=4.9 - 17.3 GeV •mB = 0.560 - 0.230 GeV

BES I

Runn

+ Running now, that’s good+ Energy range is good- But fixed-target- And light ions Not Ideal

Super Proton Synchrotron (SPS)

23M. Šumbera NPI ASCR

Nuclotron based Ion Collider fAcility (NICA)•Time Line: Not yet funded. Plan is to submit documents by end of 2012.

Operations could not begin before 2017 (probably much later)•Energy Range: √sNN = 3.9 - 11 GeV for Au+Au; mB = 0.630 - 0.325 GeV.

Multi-Purpose Detector (MPD)

+ Collider, that’s good+ High Luminosity expected• MPD similar to STAR• Maybe as early as 2017- (But probably later)- Energy is too low!- Will miss the critical point

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Facility for Antiproton and Ion Research (FAIR)Time Line:SIS-100 is funded and will be complete by 2018SIS-300 will need additional funding (no time estimate)

Energy Range:SIS-100: Au+Au @ √sNN =2.9 GeVSIS-300: Au+Au √sNN = 2.7 - 8.2 GeV mB =0.730 - 0.410 GeV

Compressed Baryonic Matter (CBM)

STS

MVD

TOF

TRDRICH

ECAL

++ Very High Interaction Rate- Fixed target geometry- No time estimate for SIS-300

Probably after 2022- Even with SIS-300, the energy is too low!- Will miss the critical point

M. Šumbera NPI ASCR 25

SPS

NA61

2009

4.9-17.3

100 Hz

CP&OD

Facilty

Exp.:

Start:

Au+Au Energy:

Event Rate:

Physics:

RHIC BESII

STAR

2017

7.7– 19.6+

100 Hz

CP&OD

NICA

MPD

>2017?

2.7 - 11

<10 kHz

OD&DHM

SIS-300

CBM

>2022?

2.7-8.2

<10 MHZ

OD&DHM

√sNN (GeV)

At 8 GeV

PHENIX

CP = Critical PointOD = Onset of DeconfinementDHM = Dense Hadronic Matter

Comparison of Facilities

Fixed TargetLighter ion collisions

Fixed Target

Conclusion:RHIC is the best option

M. Šumbera NPI ASCR

M. Šumbera NPI ASCR 27

Fixed Target Proposal

- Annular 1% gold target inside the STAR beam pipe - 2m away from the center of STAR- Data taking concurrently with collider mode at beginning of each fill

M. Šumbera NPI ASCR 28

Fixed Target Proposal Simulation

UrQMD simulated Au+Al (beampipe) event ©Chris Flores, UC Davis

B. Haag DNP F13

Fixed-Target (Beampipe)Events

Event Selection & Kinematics

√sNN = 3.0 GeV

B. H a a g DNP F13

•Each set of points is a different rapidity slice; bottom to top: 0.0< y < 0.1 to1.5< y <1.6

•Curves are offset by powers of ten

•The nucleon- nucleon center-of- mass rapidity slice is indicated in red

√sNN = 3.5 GeV

B. H a a g DNP F13

•Each set of points is a different rapidity slice; bottom to top: 0.0< y < 0.1 to1.5< y <1.6

•Curves are offset by powers of ten

•The nucleon- nucleon center-of- mass rapidity slice is indicated in red

√sNN = 4.5 GeV

B. H a a g DNP F13

•Each set of points is a different rapidity slice; bottom to top: 0.0< y < 0.1 to1.5< y <1.6

•Curves are offset by powers of ten

•The nucleon- nucleon center-of- mass rapidity slice is indicated in red

Rapidity Density Distributions

10 .26 .03 B. Haag DNP F13 3 4

•The rapidity density distributions have been measured from target rapidity to the nucleon- nucleon center-of- mass rapidity.

•The distributions are fit with Gaussians.

Error are statistical only•dN/dy distributions forAuLike+Al may not peak at zero.

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SummarySTAR results from BES program covering large mB

range provide important constraint on QCD phase diagram: – RCP of unidentified charged hadrons turns-off near 39 GeV.

– Identified RCP is qualitatively similar and suggests that pions are less affected by (still unquantified) sources of enhancement.

– Particles-antiparticles v2 difference increases with decreasing √sNN and is directly connected to baryon chemical potential.

– Baryon–meson splitting is observed when collisions energy ≥ 19.6 GeV for both particles and the corresponding anti-particles.

– ...and many other results not covered in this talk.

Search for the critical point continues:- Proposed BES-II program - Fixed target proposal to extend mB coverage up to 800 MeV

M. Šumbera

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STAR CollaborationArgonne National Laboratory, Argonne, Illinois 60439Brookhaven National Laboratory, Upton, New York 11973University of California, Berkeley, California 94720University of California, Davis, California 95616University of California, Los Angeles, California 90095Universidade Estadual de Campinas, Sao Paulo, BrazilUniversity of Illinois at Chicago, Chicago, Illinois 60607Creighton University, Omaha, Nebraska 68178Czech Technical University in Prague, FNSPE, Prague, 115 19, Czech RepublicNuclear Physics Institute AS CR, 250 68 Řež/Prague, Czech RepublicUniversity of Frankfurt, Frankfurt, GermanyInstitute of Physics, Bhubaneswar 751005, IndiaIndian Institute of Technology, Mumbai, IndiaIndiana University, Bloomington, Indiana 47408Alikhanov Institute for Theoretical and Experimental Physics, Moscow, RussiaUniversity of Jammu, Jammu 180001, IndiaJoint Institute for Nuclear Research, Dubna, 141 980, RussiaKent State University, Kent, Ohio 44242University of Kentucky, Lexington, Kentucky, 40506-0055Institute of Modern Physics, Lanzhou, ChinaLawrence Berkeley National Laboratory, Berkeley, California 94720Massachusetts Institute of Technology, Cambridge, MA Max-Planck-Institut f"ur Physik, Munich, GermanyMichigan State University, East Lansing, Michigan 48824Moscow Engineering Physics Institute, Moscow Russia

NIKHEF and Utrecht University, Amsterdam, The NetherlandsOhio State University, Columbus, Ohio 43210Old Dominion University, Norfolk, VA, 23529Panjab University, Chandigarh 160014, IndiaPennsylvania State University, University Park, Pennsylvania 16802Institute of High Energy Physics, Protvino, RussiaPurdue University, West Lafayette, Indiana 47907Pusan National University, Pusan, Republic of KoreaUniversity of Rajasthan, Jaipur 302004, IndiaRice University, Houston, Texas 77251Universidade de Sao Paulo, Sao Paulo, BrazilUniversity of Science \& Technology of China, Hefei 230026, ChinaShandong University, Jinan, Shandong 250100, ChinaShanghai Institute of Applied Physics, Shanghai 201800, ChinaSUBATECH, Nantes, FranceTexas A&M University, College Station, Texas 77843University of Texas, Austin, Texas 78712University of Houston, Houston, TX, 77204Tsinghua University, Beijing 100084, ChinaUnited States Naval Academy, Annapolis, MD 21402Valparaiso University, Valparaiso, Indiana 46383Variable Energy Cyclotron Centre, Kolkata 700064, IndiaWarsaw University of Technology, Warsaw, PolandUniversity of Washington, Seattle, Washington 98195Wayne State University, Detroit, Michigan 48201Institute of Particle Physics, CCNU (HZNU), Wuhan 430079, ChinaYale University, New Haven, Connecticut 06520University of Zagreb, Zagreb, HR-10002, Croatia

Than

k Yo

u

M. Šumbera

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Backup slides

M. Šumbera

M. Šumbera NPI ASCR 38

The RHIC Beam Energy Scan Project

A landmark of the QCD phase diagram

• Since the original design of RHIC (1985), running at lower energies has been envisioned

• RHIC has studied the possibilities of running lower energies with a series of test runs: 19.6 GeV Au+Au in 2001, 22.4 GeV Cu+Cu in 2005, and 9.2 GeV Au+Au in 2008

• In 2009 the RHIC PAC approved a proposal to run a series of six energies to search for the critical point and the onset of deconfinement.

• These energies were run during the 2010 and 2011 running periods.

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HIJING captures beam energy dependence of spectra.

Jet quenching as modeled in HIJING has a greater effect on higher beam energies.

For AMPT, lower beam energies are better matched by SM off, while SM on better captures the beam energy dependence.

⇒Physics of hadronization shifts from coalescence to fragmentation?

Model summary

M. Šumbera

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NCQ Scaling Quality: particles

M. Šumbera

STAR: Phys.Rev. C88, 014902 (2013)

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NCQ Scaling Quality: antiparticles

M. Šumbera

STAR: Phys.Rev. C88, 014902 (2013)

Azimuthal Anisotropy

Directed flow v1 is due to the sideward motion of the particles within the reaction plane. It is sensitive to baryon transport, space-momentum correlations and QGP formation.

Elliptic flow v2 results from the interaction among produced particles and is directly related to transport coefficients of produced matter.

M. Šumbera 42

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STAR Preliminary

v 1

Directed Flow of p and πp π-

STAR Preliminary

10 – 40%

STAR Preliminary√sNN

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Directed Flow of p and π: mid-central

STAR Preliminary

Proton v1 slope: changes sign frompositive at 7.7 GeV to negative at 11.5 GeV and remains small negative up to √sNN =200GeV.Pion and antiproton v1 slope: always negative. For √sNN ≥11.5 GeV contradicts baryon stopping picture predicting opposite slope for protons and pions.Net-proton v1 slope: shows double sign change. Can not be explained by URQMD model but is qualitatively consistent with a prediction of hydrodynamic model with a first order phase transition*.*)H. Stocker, Nucl. Phys. A 750, 121 (2005).

E895: PRL 84, 5488 (2000)NA49: PR C68, 034903 (2003)STAR: NP A904, 357 (2013)STAR: PRL 108, 202301(2012)

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v2(pT): Transport model comparisons

Purely hadronic system (UrQMD) does not explain relatively large elliptic flow at these energies.

AMPT-SM provides the best description of the data (except of protons and anti-protons @ 7.7 GeV).

In all other cases both AMPT and UrQMD under-predict v2(pT).

M. Šumbera

0-80% central Au+Au

UrQMD 2.23: M. Bleicher et al, J. Phys. G 25, 1859 (1999).AMPT 1.11: Z.-W. Lin et al., Phys. Rev. C 72, 064901 (2005).AMPT-SM: string melting versionSTAR: Phys.Rev. C88, 014902 (2013)

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Corresponding anti-particlesParticles

v2 vs. mT-m0

Baryon–meson splitting is observed when collisions energy ≥ 19.6 GeV for both particles and the corresponding anti-particles For anti-particles the splitting is almost gone within errors at 11.5 GeV

STAR: Phys.Rev. C88, 014902 (2013)

M. Šumbera NPI ASCR

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NCQ Scaling Test: particles

M. Šumbera

STAR: Phys.Rev. C88, 014902 (2013)

Universal trend for most of particles – ncq scaling not broken at low energies ϕ meson v2 deviates from other particles in Au+Au@(11.5 & 7.7) GeV: ~ 2σ at the highest pT data point. Needs more data to make clear conclusion.

Reduction of v2 for ϕ meson and absence of ncq scaling during the evolution the system remains in the hadronic phase [B. Mohanty and N. Xu: J. Phys. G 36, 064022(2009)]

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NCQ Scaling Test: antiparticles

M. Šumbera

STAR: Phys.Rev. C88, 014902 (2013)

H.J.Specht, Erice 2012 49

Beam conditions: CERN vs. GSI/FAIR

Luminosity at the SPS comparable to that of SIS100/300 No losses of beam quality at lower energies except for emittance growth RP limits at CERN in EHN1, not in (former) NA60 cave

< 11 – 35 (45) SPS SIS100/300

beam target interaction intensity thickness rate

2.5×106 5×105

[λi ] [Hz] [Hz]

20% NA60 (2003)

new injection scheme

108 10% 107 108 1% 106

interaction rate [Hz]

105 - 107

Energy range: 10 – 158 [AGeV]

LHC AA 5×104

Pb beams scheduled for the SPS in 2016-2017, 2019-2021 M. Šumbera NPI ASCR

How to optimize the physics outcome for the next 10-15 y

Proposal: split HADES and CBM at SIS-100

HADES at SIS-100

CBM at SPS

Upgrade HADES, optimized for e+e-, to also cope with Au-Au (now Ni-Ni)

Modify CBM to be optimal (magnet) for either e+e- or μ+μ-; role of hadrons?

Merge with part of personell of CBM

Merge with ‘CERN’ effort towards a NA60 successor experiment

Profit from suitable R&D of CBM

Profit from suitable R&D of CBM, in particular for Si

If SIS-300 would be approved in >2020, one could continue CBM there in >2027H.J.Specht, Erice 2012M. Šumbera NPI ASCR 50

v2(φ) vs. v2(p)

• Mass: proton ~ φ• At low pT, v2(φ)/v2(p) decreases with decreasing beam energies

→ Indicating less partonic collectivity with decreasing beam energy.

STAR Collaborati on: arXiv: Phys. Rev. C 88, 014902 (2013) and Phys. Rev. Lett. 110, 142301 (2013). Phys. Rev C 87, 014903 (2013)