upsilon production in star pibero djawotho indiana university cyclotron facility october 12, 2007...
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Upsilon production in STAR
Pibero DjawothoIndiana University Cyclotron Facility
October 12, 2007
DNP 2007
2
Why Quarkonia? Charmonia: J/, ’, c Bottomonia: (1S), (2S), (3S)
Key Idea: Melting in the plasma• Color screening of static potential between heavy quarks:
– J/suppression: Matsui and Satz, Phys. Lett. B 178 (1986) 416
• 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(’) Tdiss(c)< Tdiss((3S)) < Tdiss(J/) Tdiss((2S)) < Tdiss((1S))
3
and J/ States in STARJ/, ’• J/ likely to melt at RHIC• ’ melts at RHICPros• moderate rate• J/ and ’ can be separatedCons• co-mover absorption affects
yield• recombination affects yield• trigger only in pp (still low eff.)• moderate electron PID in J/
momentum range
, ’, ’’ (1S) no melting at RHIC
standard candle (reference) (2S) likely to melt at RHIC
(analog J/) (3S) melts at RHIC (analog ’)Pros• co-mover absorption negligible• recombination negligible at RHIC• STAR efficient trigger and large
acceptanceCons• extremely low rate• need good resolution to separate 3
S states
STAR’s strength are the states
4
STAR Detectors Used for Quarkonia
• EMC
• Acceptance: || < 1 , 0 < < 2• PID with EMC detectors
• Tower (energy) p/E
• High-energy tower trigger enhance high-pT sample
• Essential for quarkonia triggers
• Luminosity limited for
5
STAR Trigger
• Similar L0+L2 triggers– Higher mass state higher energy
threshold
– Pros: Easier and cleaner to trigger
– Cons: Small yield; need large luminosity and acceptance
• Full EMC acceptance |η|<1 in Run 6
• Integrated luminosity ≈ 9 pb-1 in Run 6
Sample -triggered Event• e+e-
• mee = 9.5 GeV/c2
• cosθ = -0.67• E1 = 5.6 GeV• E2 = 3.4 GeV
charged tracks
6
STAR Mass Resolution
State Mass [GeV/c2] Bee [%] (dσ/dy)y=0 Bee×(dσ/dy)y=0
9.46030 2.38 2.6 nb 62 pb
10.02326 1.91 0.87 nb 17 pb
10.3552 2.18 0.53 nb 12 pb
++ 91 pb
• STAR detector is able to resolve individual states of the albeit:– Finite p resolution– e-bremsstrahlung
• Yield is extracted from combined ++ states
• FWHM ≈ 1 GeV/c2
W.-M. Yao et al. (PDG), J. Phys. G 33, 1 (2006);R. Vogt et al., RHIC-II Heavy Flavor White Paper
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Analysis: Electron ID with TPC and EMC
trigger enhances electrons• Use TPC for charged tracks selection• Use EMC for hadron rejection• Electrons identified by dE/dx ionization
energy loss in TPC• Select tracks with TPC, match to EMC
towers above 3 GeV
pre
lim
ina
ry
electrons
K p d
preliminary
preliminary
e
π
8
• Signal + Background unlike-sign electron pairs• Background like-sign electron pairs
(1S+2S+3S) total yield: integrated from 7 to 11 GeV from background-subtracted mee distribution
• Peak width consistent with expected mass resolution• Significance of signal is 3σ
preliminary
pre
limin
ary
in Run 6 p+p at √s=200 GeV:Invariant Mass
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in Run 6 p+p at √s=200 GeV:Cross Section
dtdy
N
dy
dB
y
eeL
0
geo 0.263±0.019
L0 0.928±0.049
L2 0.855±0.048
2(e) 0.47±0.07
mass 0.96±0.04
0.094±0.018
=geo×L0×L2×2(e)×mass
geo is geometrical acceptanceL0 is efficiency of L0 triggerL2 is efficiency of L2 trigger(e) is efficiency of e recomass is efficiency of mass cut
preliminary
10
STAR Run 6 Cross Section in p+p at Midrapidity at √s=200 GeV
N 48±15(stat.)
0.094±0.018
Ldt (5.6±0.8) pb-1
dy 1.0
pb(syst.)22(stat.)2891dy
dσB
Υ"Υ'Υ
0y
ee
pre
limin
ary
11
pb22(syst.)28(stat.)91dy
dσB
'Υ'Υ'Υ
0y
ee
STAR 2006 √s=200 GeV p+p ++→e+e- cross section consistent with pQCD and world data
pre
limin
ary
STAR vs. Theory and World Data
12
Past: in Run 4 Au+Au at √sNN=200 GeV• Cannot resolve different S states
(1S+2S+3S) e+e-
• STAR– Large acceptance (|| < 1, full
EMC) – PID for electrons (EMC, TPC)– Trigger
• Very efficient > 80%– Luminosity limited
triggerthreshold No N+++N--
subtracted
Scaling from Au+Au to elementary: =1
• First look in 2004: ½ EMC, little statistics
• 90% C.L.: signal < 4.91• B·d/dy C.L. < 7.6 b
STAR Preliminary
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Rare Trig Int Lumi Goal=600ub-1
0.00
100.00
200.00
300.00
400.00
500.00
600.00
700.00
3/29/2007
4/8/2007
4/18/2007
4/28/2007
5/8/2007
5/18/2007
5/28/2007
6/7/2007
6/17/2007
6/27/2007
7/7/2007
Future:Run 7 Au+Au at √sNN=200 GeV Trigger
• 605.69 μb-1 integrated luminosity for L2-upsilon during Run 7
• ~37 expected at y=0 for |y|<0.5 or ~70 for |y|<1. Assume:– S/B=48/83 significance
3.3σ from 2006 p+p at √s=200 GeV
– Binary scaling and nuclear effects σAB=σpp(AB)α
preliminary
14
Summary and Outlook
• Full EMC + trigger quarkonium program in STAR• Run 6: first midrapidity measurement of
++→e+e- cross section at RHIC in p+p collisions at √s=200 GeV – Bee×(dσ/dy)y=0=91±28(stat.)±22(syst.) pb
– STAR in p+p measurement is consistent with pQCD and world data
• Run 7: expect cross section at midrapidity in Au+Au collisions at √s=200 GeV (37-70 raw yield) and nuclear modification factor RAA
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