Production of DS mesons in Au+Au collisions at √sNN = 200 GeV

Md.Nasim(fortheSTARCollabora8on)

UniversityofCaliforniaLosAngeles

Outline

• Motivation

• STAR experiment • Results • Summary

Md.Nasim 2

Ø  pT spectra of DS

Ø Elliptic flow of DS

Ø DS/D0 ratio

Ø RAA of DS

Motivation

3

DSfreezesoutearlyandexpectedtohavesmallerhadronicinterac8oncross-sec8onscomparedtoD0Be#ermeasureofthepartoniccontribu3ontothecharmhadronv2

•  Strangeness enhancement in QGP is expected to affect the yield of DS (if charm quarks participate in coalescence)

•  DS/D0 (Au+Au) > DS/D0 (p+p) predicted

Good Probe to study the charm quark hadronization

Ref: M. He et al., PRL 110, 112301 (2013) Md.Nasim

(GeV/c)T

p0 1 2 3 4 5

0/D SD

0

0.1

0.2

0.3

0.4 = 200 GeV, b = 7.24 fm)NNsTAMU (Au+Au,

ee/pp/ep average

STAR Detector in Year 2014

4

SSD

Md.Nasim

IST

PXL

o  Full 2π coverage o  Pseudorapidity coverage ±1 unit ~

STAR Detector in Year 2014

5

SSD

Md.Nasim

IST

PXL

o  Full 2π coverage o  Pseudorapidity coverage ±1 unit ~

•  Decay channel : DS± φ ( K++K-) + π±

•  Branching ratio: 2.32 ± 0.14 % •  Decay length : 150 ± 2 µm •  Mass : 1.96847 ± 0.00033 GeV/c2

6

Decay Topology :

•  Au+Au at √sNN = 200 GeV in 2014 •  ~ 900 M minimum bias events analyzed •  |Vz| <= 6 cm

Analysis Details

K+

K-

DS+

π+

Md.Nasim

Particle Identification

7

TPC PID: Energy loss dE/dx TOF PID: Flight time (β)*

*TOF PID has been applied only when β information is available.

Md.Nasim

|Momentum| (GeV/c)0 0.5 1 1.5 2 2.5

β1/

0.5

1

1.5

2

2.5

3

3.5

1

10

210

310

π

K

p

= 200 GeVNNsAu+Au

c tL = βTOF PID:

STAR Preliminary - RHIC Year 2014

Cut Optimization

8Tue Jul 18 16:02:47 2017

Dca120.01 0.02 0.03 0.04 0.05

0.00

115

/ (1

/N) d

N

0

100

200

300

400

500SignalBackground

U/O

-flow

(S,B

): (0

.0, 0

.0)%

/ (0

.0, 0

.0)%

Input variable: Dca12

Dca30.02 0.04 0.06 0.08 0.1

0.00

241

/ (1

/N) d

N

020406080

100120140160180200220240

U/O

-flow

(S,B

): (0

.0, 0

.0)%

/ (0

.0, 0

.0)%

Input variable: Dca3

Pt120.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4

0.04

51

/ (1

/N) d

N

0

1

2

3

4

5

6

U/O

-flow

(S,B

): (0

.0, 0

.0)%

/ (0

.0, 0

.0)%

Input variable: Pt12

Pt31 1.5 2 2.5 3 3.5 4

0.09

73

/ (1

/N) d

N

00.5

11.5

22.5

33.5

44.5

U/O

-flow

(S,B

): (0

.0, 0

.0)%

/ (0

.0, 0

.0)%

Input variable: Pt3

dcaDaughters0.005 0.01 0.015 0.02

0.00

051

/ (1

/N) d

N

0

20

40

60

80

100

120

U/O

-flow

(S,B

): (0

.0, 0

.0)%

/ (0

.0, 0

.0)%

Input variable: dcaDaughters

dcaToPv0 0.005 0.01 0.015 0.02 0.025

0.00

0641

/

(1/N

) dN

020406080

100120140160180200220

U/O

-flow

(S,B

): (0

.0, 0

.0)%

/ (0

.0, 0

.0)%

Input variable: dcaToPv

•  Topological cuts optimized using TMVA package.!•  Background extracted from real data using wrong-sign method !•  Signal simulated with data-driven fast simulation !

DCA between ! daughters!Momentum of Pion!

Momentum of Kaon!

DCA of Ds!to Prim. Vtx !

DCA of Pion !to Prim. Vtx.!!

DCA of Kaon !to Prim. Vtx.!

Md.NasimRef: A. Hoecker et. al, PoS ACAT:040,2007

Dca 12 (cm) Dca 3(cm) pt12 (GeV/c)

pt3 (GeV/c) Dca123 (cm) DCAtoPvt(cm)

coun

ts

coun

ts

coun

ts

coun

ts

coun

ts

coun

ts

DS Meson Reconstruction

9

ClearsignalofDS

±andD±

SignificanceofDS

±~25

Md.Nasim

2) GeV/cπ+K-Invariant Mass M(K1.85 1.9 1.95 2 2.05 2.1 2.15

)2En

tries

/ (8

.0 M

eV/c

0

100

200

300

400Au+Au@200 GeV,0-80%

<8.0 GeV/cT

2.5<p

±D

±sD

STAR Preliminary

Right-SignWrong-SignRS-WS

EmbeddingforTPCtrackingefficiency•  FullSTARGEANTsimula8on->singletracksembeddedinrawdata->datareconstruc8onchain

10

⊗DSefficiency=TPCtrackingeff.HFTtrackingeff.topologicalcuts⊗

Data-drivensimula8on•  HFTmatchingefficiencyandresolu8onextractedfrom

data:–  HFTeff.×geometricalacceptance:(HFTmatchedtracks)/(TPC

tracks).–  Spa8alresolu8on:DCAdistribu8onsofHFTmatchedtracks(inXYplaneandZdirec8on).

Efficiency and Acceptance Correction

Md.Nasim

(GeV/c)T

p0 1 2 3 4 5 6 7 8

Acce

ptan

ce×

Effic

ienc

y

4−10×2

4−10×34−10×4

3−10

3−10×2

3−10×33−10×4

0-10%10-40%

= 200 GeVNNsAu+Au,

STAR Preliminary

Transverse Momentum Spectra

11

(GeV/c)T

p2 3 4 5 6 7

-2dy

) (G

eV/c

)T

dp TpπN

/(22 d

7−10

6−10

5−10

4−10

3−10

πφ→+sD, 0-10%+

sD, 10-40%/10+

sD

Au+Au @ 200 GeV

STAR Preliminary

(GeV/c)T

p2 3 4 5 6 7 8

-2dy

) (G

eV/c

)T

dp TpπN

/(22 d

7−10

6−10

5−10

4−10

3−10

2−10, 0-10%+πφ→+D, 10-40%/10+πφ→+D

, 0-10%+π+π-K→+D

Au+Au @ 200 GeV

STAR Preliminary

•  The𝐷+pTspectrafromtwodecaychannelsareconsistent

-  𝐷+→𝜋+𝜋+𝐾−(B.R.=9.46%)-  𝐷+→𝜙𝜋+→𝜋+𝐾−𝐾+(B.R.=0.27%)

•  The𝐷SpTspectrain0-10%and10-40%collisioncentrali>es

DS = DS+ + DS

- !

Md.Nasim

D+ = D+ + D-!

Nuclear Modification Factor (RAA)

12

RAA =1Ncoll

×dN AA

dpTdN pp

dpT

DS spectra for p+p collisions have been calculated from !measured D0/D* cross-section by STAR. !Fragmentation factor !(c to DS) = 0.079±0.004 !

Md.Nasim

Ref: M Lisovyi, et. al. EPJ C 76, 397 (2016) STAR: PRD 86, 72013 (2012)

(GeV/c)T

p0 1 2 3 4 5 6 7

-2) (

GeV

/c)

Tdy

dpTpπ

N/(2

2 d

6−10

5−10

4−10

3−10

2−10

1−100-10% 10-40%0-10% 10-40% (Au+Au)SD

coll N× (p+p) SD

STAR Preliminary

= 200 GeVNNs

RAA of DS

13

RAA (K0S) ≤ RAA (DS)!

Indication of suppression for high pT (> 5 GeV/c) DS w.r.t. the p+p reference !!

Ref: K0S RAA : PRL 108 (2012) 72302 [STAR]

Md.Nasim

(GeV/c)T

p1 2 3 4 5 6

AAR

0.20.30.4

1

234

Error from pp ref. uncertaintycollN

(0-10%)SD(10-40%)SD(0-12%)S

0K

= 200 GeVNNsAu+Au,

STAR Preliminary

DS/D0 Ratio: Probe of Charm Hadronization

14

(GeV/c)T

p2 3 4 5 6 7 8

0/D sD

0

0.2

0.4

0.6

0.8

1Au+Au @ 200 GeVSTAR Preliminary

0-10%10-40%ee/pp/ep average

•  Substantial enhancement in DS/D0 ratio in Au+Au collisions w.r.t. the fragmentation baseline.

− Indicates that the charm quark recombination plays a crucial role in open charm meson production in central Au+Au collisions. !!

Md.Nasim

Ref: ee/ep/pp average (pT integrated) : M Lisovyi, et. al. EPJ C 76, 397 (2016)

DS/D0 Ratio : Comparison with Model Prediction

15

(GeV/c)T

p0 1 2 3 4 5 6 7 8

0/D sD

0

0.2

0.4

0.6

0.8

1Au+Au @ 200 GeVSTAR Preliminary

0-10%10-40%ee/pp/ep averagePYTHIA(ver. 6.4)TAMU(b=7.24fm)

•  Substantial enhancement in DS/D0 ratio in Au+Au collisions w.r.t. the fragmentation baseline.

•  DS/D0 in Au+Au is higher than the PYTHIA model

prediction.

•  TAMU model under-predicts measured DS/D0 ratio.

Ref: TAMU: H. Min et al. PRL 110, 112301 (2013) Md.Nasim

DS/D0 Ratio : Comparison with LHC

16

•  Substantial enhancement in DS/D0 ratio in Au+Au collisions w.r.t. the fragmentation baseline.

•  Comparable to LHC data.

Ref: Pb+Pb : Quark Matter 17 (ALICE Preliminary) Md.Nasim

(GeV/c)T

p2 3 4 5 6 7 8 9 10 11 12

0/D SD

0.10.20.30.40.50.60.70.80.9

1Au+Au (200 GeV, 0-10%)Au+Au (200 GeV, 10-40%)Pb+Pb (5.02 TeV, 30-50%)ee/pp/ep average

STAR Preliminary

DS v2 Measurement: Event Plane Method

17

− Eventplane(ψ2)isreconstructedusingTPCtracks− Non-uniformityinacceptanceiscorrectedbyre-centeringandshiling

Md.Nasim

Pressure gradient transfers initial !spatial anisotropy to final state !momentum space anisotropy !

Ref: A.M. Poskanzer and S.A. Voloshin. PRC 58 (1998) 1671

(radian)2

ψ0 0.5 1 1.5 2 2.5 3

Cou

nts

700

800

900

1000

1100

310×Before Correction

After Correction

DS v2 Measurement: Event Plane Method

18Md.Nasim

DS yield as a function of (ϕ-ψ2) is fitted with the following function, !!!!where p0 and v2

obs are fit parameters. !!

dNd(φ −ψ2 )

= p0[1+ 2vobs2 cos{2(φ −ψ2 )}]

2Ψ-φ

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Wei

ghte

d Yi

eld

35

40

45

50

55

60

= 200 GeVNNs10-40% Au+Au, < 3.5 GeV/c

T2.0 < p

STAR Preliminary

0.0448± = 0.0873 2obsv

Ref: A.M. Poskanzer and S.A. Voloshin. PRC 58 (1998) 1671

Elliptic Flow vs Transverse Momentum

19

− Finite positive DS v2 observed − DS v2 is comparable to non- strange D0 meson within large uncertainties.

Ref: D0 v2 : PRL 118 (2017) 212301 [STAR ]

More precise measurements !of DS v2 are underway including 2016 data.!

Md.Nasim

(GeV/c)T

p0 1 2 3 4 5 6

2v

0

0.1

0.2

0.3SD0D

= 200 GeVNNs10-40% Au+Au,

STAR Preliminary

DS v2: NCQ Scaling and Comparison with LHC

20

Ref: STAR: PRL 118 (2017) 212301 ALICE: arXiv:1707.01005[nucl-ex]

HintsofNCQscalinginDSv2STAR and ALICE data are !consistent within large !uncertainties!

Md.Nasim

q)/n0-mT

(m0 1 2

q/n 2v

0

0.05

0.1

0.15 SD0D

S0K

Λ

Ξ

=200 GeVNNs10-40% Au+Au,

STAR Preliminary

(GeV/c)T

p2 3 4 5 6 7 8 9 10

2v

0

0.1

0.2

0.3

0.4

0.5 = 200 GeV)NNsSTAR (10-40% Au+Au, = 5.02 TeV)NNsALICE (30-50% Pb+Pb,

STAR Preliminary

DS v2 : Model Comparison

21

Ref: TAMU: H. Min et al. PRL 110, 112301 (2013) AMPT: R. Esha et al. JPG 44, 045107 (2017)

TAMU:

AMPT:

Charm-quark coupling to the QGP and subsequent recombination with equilibrated strange quarks.!

Partonic interaction generates v2.!Hadronization via Dynamic Coalescence Model. !!

Model predictions are consistent with data within 1σ confidence level.

Md.Nasim

(GeV/c)T

p0 1 2 3 4 5 6

2v

0

0.1

0.2

0.3 STAR (10-40%)/s =0.18)ηAMPT (10-40%,

TAMU (b=7.24 fm)

= 200 GeVNNsAu+Au,

STAR Preliminary

Summary

22

² Nuclear modification factor of DS is measured in 0-40% Au+Au collisions at 200 GeV: − Production of high pT (> 5 GeV/c) DS seems to be suppressed w.r.t. the p+p reference − RAA (K0

S) ≤ RAA (DS) : light strange mesons seem to be more suppressed than heavy DS ² The production ratio DS/D0 is measured in 0-40% Au+Au collisions at 200 GeV: − Enhancement in DS/D0 ratio w.r.t. the fragmentation baseline is observed − This indicates that coalescence plays an important role for charm quark hadronization in the QGP ² Elliptic flow of DS meson is measured in Au+Au collisions (10-40%) at 200 GeV: − Observed DS v2 is comparable to non-strange D0 v2 within large uncertainties

Md.Nasim

Back-Up

23Md.Nasim

Heavy Flavor Tracker

24

Poin>ngresolu>on:∼20μmathigh𝑝T(exceedstherequirementof55μmfor750MeV/𝑐kaons)

ThePixeldetector:FirstMAPStechnologyinacolliderexperiment

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