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
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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
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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
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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
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)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
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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
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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
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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
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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
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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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