Jaroslav Bielčíkfor STAR collaboration

Czech Technical University

in Prague

Rencontres de Moriond QCD and High Energy Interactions La Thuile, March 9-16, 2013

Heavy flavor and dilepton production in STAR experiment

• Motivation.

• Open heavy flavor.

• J/y and Upsilon measurements.

• Dilepton production.

• Summary.

Outline

2

jaroslav.bielcik@fjfi.cvut.cz3

Heavy quarks as a probe of QGP

• p+p data: baseline of heavy ion measurements. test of pQCD calculations.

• Due to their large mass heavy quarks are primarily produced by gluon fusion in early stage of collision. production rates calculable by pQCD.M. Gyulassy and Z. Lin, PRC 51, 2177 (1995)

• heavy ion data:

• Studying energy loss of heavy quarks. independent way to extract properties of the medium.

• Dead cone effect.

light

M.Djordjevic PRL 94 (2004)

Radiative energy loss

Wicks et al, Nucl. Phys. A784 (2007) 426

The STAR Detector

Vertex Position Detector

4

• VPD: minimum bias trigger.

• TPC: PID, tracking.

• TOF: PID.

• BEMC: PID, trigger.

5

D0 and D* pT spectra in p+p collisions

D0 yield scaled by ND0/Ncc= 0.565

D* yield scaled by ND*/Ncc= 0.224

bdy

ds

y

cc 3859

GeV200

0

45170

• FONLL upper band is

consistent with charm

spectra

FONLL: 200 GeV M. Cacciari, PRL 95 (2005) 122001 500 GeV Ramona Vogt µF = µR = mc, |y| < 1 .

STAR Preliminary

200GeV: Phys. Rev. D 86 (2012) 72013

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D0 spectra in Au+Au 200 GeV

• Suppression at high pT in central and mid-central collisions.

• Suppression at high pT in central collisions similar to light hadrons.

• Enhancement at intermediate pT ~ models suggest radial flow of light quarks coalescence with charm. P. Gossiaux: arXiv: 1207.5445

• Strong suppression at high pT in central collisions

• D0, NPE results seems to be consistent kinematics smearing & charm/bottom mixing

• Uncertainty dominated by p+p result.

• High quality p+p data from Run09 and Run12 are on disk.

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Non-photonic Electron RAA in Au+Au 200 GeV

Non-photonic Electrons arefrom semileptonic c and b decays

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Quarkonia states in A+ACharmonia: J/y, Y’, cc Bottomonia: (1S), (2S), (3S)

Key Idea: Quarkonia melt in the QG plasma due to color screening of potential between heavy quarks

• Suppression of states is determined by TC and their binding energy

• Lattice QCD: Evaluation of spectral functions Tmelting

Sequential disappearance of states: Color screening Deconfinement

QCD thermometer Properties of QGP

H. Satz, HP2006

When do states really melt?Tdiss(y’) Tdiss(cc)< Tdiss((3S)) < Tdiss(J/y) Tdiss((2S)) < Tdiss((1S))

J/y in Au+Au collisions

jaroslav.bielcik@fjfi.cvut.cz9

Liu et al., PLB 678:72 (2009) and private comminication Zhao et al., PRC 82,064905(2010) and private communication

STAR high-pT : arxiv:1208.2736

• J/ψ suppression increases with collision centrality and decreases with pT

• Low-pT data agrees with two models including color screening and regeneration ef.• At high pT Liu et al. model describes data reasonable well,

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Mod

els

from

M. S

tric

klan

d an

d D

. Baz

ow, a

rXiv

:111

2.27

61v4

• Indications of suppression of (1S+2S+3S) getting stronger with centrality.

Nuclear modification factor of Upsilon

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ϒ RAA Comparison to models • Incorporating lattice-based

potentials, including real and imaginary parts– A: Free energy

• Disfavored.

– B: Internal energy • Consistent with data vs.

Npart

• Includes sequential melting and feed-down contributions– ~50% feed-down from cb.

M. Strickland, PRL 107, 132301 (2011).

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Dilepton Physics

Chronological division:• High Mass Range (HMR)

Mee > 3 GeV/c2

– primordial emission, Drell-Yan– J/Ψ and ϒ suppression

• Intermediate Mass Range (IMR)1.1 < Mee< 3 GeV/c2

– QGP thermal radiation– heavy-flavor modification

• Low Mass Range (LMR) Mee< 1.1 GeV/c2

– in-medium modification of vector mesons– possible link to chiral symmetry restoration

Dileptons are excellent penetrating probes– very low cross-section with QCD medium– created throughout evolution of system

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Production in p+p at 200 GeV• Understand the p+p reference

Cocktail simulation consistent with dataL. Ruan (STAR), Nucl. Phys. A855 (2011) 269

Charm contribution dominates IMR– consistent with STAR charm cross-

section

Adams et al (STAR), Phys. Rev. Lett. 94 (2005) 062301

Uncertainties:• vertical bars: statistical• boxes: systematic• grey band: cocktail simulation systematic• not shown: 11% normalization

Phys. Rev. C 86, 024906 (2012)

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Production in Au+Au 200 GeVLow Mass:

• enhancementwhen compared to cocktail (w/o ρ meson)

little centrality

dependence

Intermediate Mass: cocktail “overshoots” data in central collisionsbut, consistent within errors

modification of charm?

difficult to disentangle (modified) charm from thermal QGP contributions future detector upgrades required HFT+MTD

STAR Preliminary

STAR Preliminary

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Beam Energy Scan Dielectrons 2010 – 2011:

Au+Au at 62.4, 39, and 19.6 GeV

STAR data samples: 55M, 99M, and 34M min-bias events

Dielectron Production at lower √sNN

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Compare to Theory: in-medium ρ

• Robust theoretical description top RHIC down to SPS energies– calculations by Ralf Rapp (priv. comm.)– black curve: cocktail + in-medium ρ

• Measurements consistent with in-medium ρ broadening– expected to depend on total baryon density– tool to look for chiral symmetry restoration

STARPreliminary

Summary and Outlook

jaroslav.bielcik@fjfi.cvut.cz17

• Large suppression of heavy quark production at high-pT in D0 and non-photonic electrons measurements in 200 GeV central Au+Au collisions. Similar to light quarks.

• J/ψ suppression increases with collision centrality and decreases with pT.

• Increasing of ϒ suppression vs. centrality. RAA consistent with suppression of feed down from excited states only (~50%).

• Dielectron measurement in p+p 200 GeV. Cocktail describes the data well. • Dielectron measurement in Au+Au 19.6 – 200 GeV. Low mass enhancement down to low (SPS) energies observed. Consistent with in- medium ρ broadening.

• Heavy flavor tracker and Muon telescope detector upgrades. Significant improvement of heavy flavor, quarkonium and dilepton measurements.

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Heavy Flavor Tracker

TPC Volume

Solenoid

Outer Field Cage

Inner Field Cage

SSDISTPXL

EASTWEST

FGT

HFT

Detector Radius(cm)

Hit Resolution R/ - Z (m - m)

Radiation length

SSD 22 20 / 740 1% X0

IST 14 170 / 1800 <1.5% X0

PIXEL8 12 / 12 ~0.4% X0

2.5 12 / 12 ~0.4% X0

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Physics projections – punchline for Y13,14

RCP=a*N10%/N(60-80)%

Assuming D0 v2 distribution from quark coalescence.

500M Au+Au m.b. events at 200 GeV.

- Charm v2 Medium thermalization degreeDrag coefficients!

Assuming D0 Rcp distribution as charged hadron.

500M Au+Au m.b. events at 200 GeV.

- Charm RAA Energy loss mechanism!Color charge effect!Interaction with QCD matter!

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Future: ϒ via STAR MTD

• A detector with long-MRPCs – Covers the whole iron bars and leave the gaps in between uncovered. – Acceptance: 45% at ||<0.5– 118 modules, 1416 readout strips, 2832 readout channels

• Long-MRPC detector technology, electronics same as used in STAR-TOF• Run 2012 -- 10%; 2013 – 60%+; 2014 – 100%: ϒ via m+m-

MTD (MRPC)

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STAR Dileptons: Present & Future

• 2009 – 2011– TPC + TOF + EMC

• dielectron continuum• dielectron spectra, and v2 (pT)

– vector meson in-medium modifications

– LMR enhancement– modification in IMR?

• 2012-2013– TPC + TOF + EMC + MTD (partial)

• e-μ measurements

– IMR: Improve our understanding of thermal QGP radiation

– LMR: vector meson in-medium modifications

• 2014 and beyond– TPC + TOF + EMC +

MTD + HFT• dimuon continuum• e-μ spectra and v2

– LMR: vector meson in-medium modifications

– IMR: measure thermal QGP radiation

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D0 and D* pT spectra in p+p 200 GeV

Fixed-Order Next-to-Leading Logarithm: M. Cacciari, PRL 95 (2005) 122001.

• The charm cross section

at mid-rapidity:

Phys. Rev. D 86 (2012) 072013.

• Upper limit of FONLL

describes the data well

D0 and D* pT spectra in p+p collisions

[1] C. Amsler et al. (Particle Data Group), PLB 667 (2008) 1.

[2] FONLL calculation: Ramona Vogt µF = µR = mc, |y| < 1

STAR preliminary

D0 yield scaled by ND0/Ncc= 0.565[1]

D* yield scaled by ND*/Ncc= 0.224[1]

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FONLL upper band consistent with 500GeV (200GeV) charm spectra.

Manuel Calderón de la Barca Sánchez

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in Au+Au 200 GeV, Centrality

14/Nov/12

Peripheral Central

STAR Preliminary

STAR Preliminary

STAR Preliminary

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• Advantage: has negligible recombination; smaller co-mover absorption

• Raw yield of e+e- with |y|<0.5 = 197 ± 36 ∫L dt ≈ 1400 µb-1

in Au+Au 200 GeV

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Dileptons Au+Au theory comparison• STAR central 200 GeV Au+Au• hadronic cocktail (STAR)

Ralf Rapp (priv. comm.)R. Rapp, Phys.Rev. C 63 (2001) 054907

R. Rapp & J. Wambach, EPJ A 6 (1999) 415

Complete evolution (QGP+HG)

cocktail + HG + QGP: Agreement w/in uncertainties

Rap

p, W

amba

ch,

van

Hee

sar

Xiv

:090

1.3

289 hadronic phase: ρ “melts” when

extrapolated close to phase transition boundary• total baryon density plays the essential role

top-down extrapolated QGP rate closely coincides with bottom-up extrapolated hadronic rates