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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
Md.Nasim