Measurements of DS± - meson

production in Au+Au collisions at √sNN = 200 GeV in STAR

Md. Nasim University of California, Los Angeles

(for the STAR Collaboration)

Outline • Motivation •  STAR detector and analysis details

•  pT spectra, particle ratio and RAA

•  Elliptic flow (v2) of DS

•  Summary

2  

Why Study Ds± ?

3  

DS  meson  

Charm                  quark  

 Strange      quark  

o  DS meson : one charm and one strange quark

o  Strangeness enhancement due to QGP is expected to affect the yield of DS

Why Study Ds± ?

4  

o  DS meson : one charm and one strange quark

o  Strangeness enhancement due to QGP is expected to affect the yield of DS

o  RCP or RAA of DS > D0 predicted

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

Why Study Ds± ?

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

Good  Probe  to  study  the      hadroniza2on  and  strangeness  enhancement  

o  DS meson : one charm and one strange quark

o  Strangeness enhancement due to QGP is expected to affect the yield of DS

o  RCP or RAA of DS > D0 predicted

o  Elliptic flow of DS < D0 is expected due to earlier freeze out of DS

STAR Detector in Year 2014

6  

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

SSD  

STAR Detector in Year 2014

7  

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

For  Details  about  HFT  :    See  talk  by  G.  ConLn  (Tuesday,  3.00  PM,  Futute  Exp.  Fac.  Upgr.    

SSD  

Analysis Details

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

•  Branching Ratio: 2.32 ± 0.14 %

•  Decay Length : 150 ± 2 µm

•  Mass : 1968.47 ± 0.33 MeV/c2

8  

Secondary Vertex : Using HFT

π+  

K+  

K-­‐  

Prim. Vertex

Sec. Vertex θ  

DS                    K*  +    K  decay  channel  :  See  Poster  by  L.  Zhou  (ID  :336)    

•  Au+Au at √sNN = 200 GeV in 2014

•  750 M minimum bias events analyzed (70% of collected data)

•  |Vz| <= 6 cm

•  Centrality using raw charged particle measured in TPC and Glauber Model

Particle Identification

9  

π   K   p  

TPC PID: Using dE/dx TOF PID: Using Time of Flight (β)*

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

d  

TPC  

Particle Identification

10  

π   K   p  

TPC PID: Using dE/dx TOF PID: Using Time of Flight (β)*

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

d  

TOF  

pT integrated DS± Signal

11  

)2 (GeV/c!

-K+KInvariant mass, m

1.9 1.95 2 2.05 2.1

)2C

ount

s (p

er 5

MeV

/c

20

40

60

80

100

120STAR Preliminary

= 200 GeVNNsAu+Au RHIC Run 2014

750 MinBias Events = 8S+BS/

)2 (GeV/c!

-K+KInvariant mass, m1.9 1.95 2 2.05 2.1

)2C

ount

s (p

er 5

MeV

/c

0

10

20

30

40

50 STAR Preliminary = 200 GeVNNsAu+Au

RHIC Run 2014

10-40% Centrality =6S+BS/

2.5  <pT  <  5.0  GeV/c  

•  First measurement of DS meson at RHIC. •  We will present DS spectra for 10-40% centrality and for 2.5 <pT<5.0 GeV/c. •  Lower pT and more peripheral collisions studies are underway.

Mass and width

12  

Mass is consistent with PDG value Width is consistent with the results from detector simulations.

(GeV/c)T

p2 2.5 3 3.5 4 4.5 5

)2M

ass

(GeV

/c

1.96

1.965

1.97

1.975

1.9810-40% Data

PDG MassSTAR  Preliminary  

(GeV/c)T

p2 2.5 3 3.5 4 4.5 5

)2W

idth

(GeV

/c

0

0.01

0.02

0.03

10-40%Data

Monte-CarloSTAR  Preliminary  

RAA of DS

13  

The RAA of DS is higher than unity but statistically not significant.

€

RAA =1NBin

×dNAA

dpTdN pp

dpT

DS  spectra  for  p+p  collision  has  been  calculated  from  measured  charm  cross-­‐secLon  in  STAR.  FragmentaLon  factor  from  charm  to  DS  is  0.09±0.01  *      

*Ref:  H1  CollaboraLon,    Eur.Phys.J.C38(2005)447  and    ZEUS  CollaboraLon,  Eur.Phys.J.C44(2005)351  

STAR  charm  cross-­‐secLon:  Phys.  Rev.  D  86  (2012)  72013  

STAR  D0  RAA:  Phys.  Rev.  Lee.  113  (2014)  142301  

(GeV/c)T

p0 1 2 3 4 5 6

-2) (

GeV

/c)

Tdy

dpTp

evt

N!N

/(22 d 7"10

5"10

3"10

1"10

1 (Au+Au, 10-40%)SD

p+p reference)# Bin

(NSD

LevySTAR  Preliminary  

STAR  Preliminary  

Invariant Yield and DS/D0

14  

The ratio DS/D0 is less than unity and seems to be higher than prediction for p+p collision from PYTHIA

STAR  Au+Au  D0:  Phys.  Rev.  Lee.  113  (2014)  142301  

STAR  Preliminary  

(ver.  6.4)  

(GeV/c)T

p0 1 2 3 4 5 6

-2) (

GeV

/c)

Tdy

dpTp

evt

N!N

/(22 d 5"10

3"10

1"10

1

with HFT (Run 14)SD w/o HFT (Run 10+11)0D

LevyLevy Fit 68% C.I.

= 200 GeV, 10-40%NNsAu+Au

STAR  Preliminary  

Invariant Yield and DS/D0

15  

STAR and ALICE data are consistent with large uncertainties

STAR  Au+Au  D0:  Phys.  Rev.  Lee.  113  (2014)  142301  

STAR  Preliminary  

(ver.  6.4)  

 Pb+Pb  (ALICE:  arXiv:1509.07287)  

STAR  Preliminary  

(GeV/c)T

p0 1 2 3 4 5 6

-2) (

GeV

/c)

Tdy

dpTp

evt

N!N

/(22 d 5"10

3"10

1"10

1

with HFT (Run 14)SD w/o HFT (Run 10+11)0D

LevyLevy Fit 68% C.I.

= 200 GeV, 10-40%NNsAu+Au

STAR  Preliminary  

EllipLc  Flow  Analysis  

16  

STAR  Preliminary  

STAR  Preliminary  

Method:  Full  Event  Plane  Event  Plane:  Using  TPC  tracks    ResoluLon:  Using  Eta  sub-­‐event  

DS  v2  :        By  fi>ng  Yield  vs      with    funcDon  p0(1+2 v2

raw cos(2 ))    

€

v2 =< cos(2(φ −ψ2)) > ×R−1

Centrality (%)0 10 20 30 40 50 60 70 80

Res

olut

ion

0

0.2

0.4

0.6

0.8

1STAR  Preliminary  

raw  

EllipLc  Flow  of  DS      

17  

First measurement of DS v2 in heavy-ion experiment. Need more statistics.

For  D0  v2  :      See  talk  by  M.  Lomnitz    (Tuesday,  9  AM,      CollecLve  Dynamics)    

φ -meson v2 e-­‐Print  :1507.05247  

STAR  Preliminary  

Summary

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•  We have observed a clear signal of DS at RHIC for the first time

•  DS in Au+Au 200 GeV for 10-40% central collisions: - DS/D0 seems to be higher than p+p prediction (from PYTHIA 6.4) at pT = 2.8 and 3.9 GeV/c

- RAA = 2.1±0.5±0.7 and 1.7±0.4±0.5 at pT = 2.8 and 3.9

GeV/c, respectively •  First measurement of elliptic flow of DS is presented •  Stay tuned for Run 16 Data with increased statistics

and improved detector performance

Thank You

0.7 0.7

Back-­‐up  

19  

RAA    

20  

 DS  Pb+Pb  (ALICE:  arXiv:1509.07287)  

D0Au+Au  (STAR:  PRL  113  (2014)  142301)  STAR  Preliminary  

φ-­‐meson  signal    

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