production in p+p collisions in

Manuel Calderón de la Barca SánchezUC DavisSTAR Collaboration

23d Winter Workshop on Nuclear DynamicsBig Sky, Montana 2-15-07

STARSTAR

Goal: Quarkonia states in A+ACharmonia: 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 (next talk!)

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))

:Pros for theory interpretation, ’, ’’ sequential suppression (1S) no melting at RHIC (nor LHC?) 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

Both of these affect charmonia, but not bottomonia.

: Experimental Pros and ConsCons Mass resolution pushed to the limit

Ratio extraction (2S/1S) and (3S/1S) possible, but difficult extremely low rate

BR x d/dy(1s+2s+3s)=91 pb from NLO calculations.

Luminosity limited (RHIC II will substantially help) pp Run 6 ~ 9 pb-1 (split into 2 triggered datasets)

Pros Efficient trigger

~80% works in p+p up to central A+A!

Large acceptance at midrapidity Run VI = Run IV x 4

Small background at M~10 GeV/c2.

STAR’s strength are the STAR’s strength are the states states

STAR Detectors Used for Analysis

• EMC

• Acceptance: || < 1 , 0 < < 2• PID : EMC Tower (energy) p/E

• High-energy tower trigger enhance high-pT sample

• Essential for quarkonia triggers

• Luminosity limited for • TPC

• Tracking and dE/dx PID for electrons & positrons

Mass Resolution and expected

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 does not resolve individual states of the Finite p resolution (B=0.5 T) e-bremsstrahlung

Yield is extracted from combined ++ states

FWHM ≈ 0.7 GeV/c2

W.-M. Yao et al. (PDG), J. Phys. G 33, 1 (2006);R. Vogt et al., RHIC-II Heavy Flavor White Paper

STAR Trigger

Fast L0 Trigger (Hardware) Select events with at least one

high energy tower (E~4 GeV) L2 trigger (Software)

Clustering, calculate mee, cos . Very clean to trigger up to central Au+Au Offline: Match TPC tracks to triggered

towers

Sample -triggered Event• e+e- candidate• mee = 9.5 GeV/c2

• cosθ = -0.67• E1 = 5.6 GeV• E2 = 3.4 GeV

Offline: charged tracks +EMC tower

Acceptance in STAR

Simulations Run 6 Conditions Including detector

variations: Calorimeter crates

removed/recovered Hot towers masked

Two Trigger setups: Acc = 0.272±0.01 for |y|

<0.5 (set 1) Acc = 0.263±0.019 for |y|

<0.5 (set 2)– Set 2 used in results shown

today.

Trigger Efficiency

Simulation of Trigger response Level-0: Fast, Hardware

Trigger, Cut on Single Tower Et L0 triggered/accepted =

0.928±0.049

Level-2: Software Trigger, Cut on invariant mass of tower clusters L2 triggered/L0 triggered=

0.855±0.048 Acceptance x Trig Efficiency

~19-21%

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 consistent with trigger

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electrons

K p d

preliminary

preliminary

eπ

Electron PID Efficiency and Purity

Electron Pair PID+Tracking efficiency= 0.47±0.07

dE/dx cut dE/dx cut

dE/dx cut dE/dx cut

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 (0.96 of total)

Peak width consistent with expected mass resolution

STAR Invariant Mass

preliminary

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Cross Section and Uncertainties

0

ee

y

NdBR

dy dy dt

L

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 : geometrical acceptanceL0 : efficiency of L0 L2 : efficiency of L2 (e) : efficiency of e recomass: efficiency of mass cut

preliminary

STAR Cross Section at Midrapidity

N 48±15(stat.)

0.094±0.018

Ldt (5.6±0.8) pb-1

dy 1.0

' ''

0y

d

dy

eeBR 91 28 (stat.) 22 (syst.) pb

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STAR vs. theory and world data

' ''

0y

d

dy

eeBR 91 28(stat.) 22(syst.) pb

STAR 2006 √s=200 GeV p+p ++→e+e- cross section consistent with pQCD and world data trend

Only RHIC peeks at √s=200 GeV range

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Outlook for Run VII Au+Au

Yield estimate: 17 Week run ~ 100 days Run 4 Performance

4-20 M events/day For Run VII:

Assume: 400 – 2000 M events 60 b-1 - 0.3 nb-1

cross section in Au+Au Using with =0.9, (AB) ~ 13,500 dAuAu/dy|y=0=91 pb x 13500 = 1.2 b-1 produced at y=0 in dy=1 ~ 73 – 368 after acc. & eff. ~ 7 – 37

Yes, its tough!!!

Ldt

( )AB pp AB

Run IV Au+AuEvents sampled per day

106

107

Summary 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 BRee×(dσ/dy)y=0=91±28(stat.)±22(syst.)

pb STAR measurement is consistent with

pQCD and world data trend Next run:

Towards a STAR cross section in

Au+Au collisions at √s=200 GeV

18

Extra Slides

STAR J/ Trigger L0 (hardware)

J/ topology trigger: two towers above ET≈1.2 GeV

Separated by 60° in φ L2 (software)

Match EMC high tower to CTB slat photon rejection

Tower clustering Cut on mee=√2E1E2(1-

cosθ) Cut on cosθ

High background contamination ~1.5 GeV/c

Rejection~100 not sampling full luminosity

Challenging analysis!!! Efficiency × acceptance ≈ 12%

Real Data, p+p Run V

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STAR J/ Signal• Signal in 200 GeV p+p from 2006

• Tested and working trigger in p+p

• No trigger for Au+Au until full ToF in 2009

• Integrated luminosity in 2006: 377 nb-1

• Analysis in progress

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