# Presentation: 729033

## Quarkonia Measurements with the STAR Detector (RHIC & RHIC II)

- Pibero Djawotho
- Indiana University Cyclotron Facility
- June 20, 2007

- RHIC & AGS Users’ Meeting

##  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))

##   and J/ States in STAR

- J/, ’
- J/ likely to melt at RHIC
-  ’ melts at RHIC
- Pros
- moderate rate
- J/ and ’ can be separated
- Cons
- 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 acceptance
- Cons
- extremely low rate
- need good resolution to separate 3 S states

-  STAR’s strength are the  states

## 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 

## 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%

## STAR J/ψ Signal

**J/********e****+****e****-**** Au+Au √s****NN****=200 GeV**

**J/********e****+****e****-**** p+p √s=200 GeV**

- STAR J/ψ Signal

- Signal in 200 GeV p+p from 2005
- Tested and working trigger in p+p
- No trigger for AuAu until full ToF in 2009
- Also signal in Au+Au with TPC only
-  Large hadron contamination
- Need full EMC

**STAR Preliminary**

**STAR Preliminary**

***Johann Gonzalez***

## STAR J/ Signal

- Signal in 200 GeV p+p from 2006
- Integrated luminosity in Run 6 ~ 377 nb-1

## STAR  Trigger

- 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

## 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 does not resolve individual states of the 
- 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

##  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

**e**

- π

##  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

- First look in 2004: 1⁄2 EMC, little statistics
- 90% C.L.: signal < 4.91
- B·d/dy C.L. < 7.6 b

- STAR Preliminary

***Thorsten Kollegger***

## 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

- 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

-  in Run 6 p+p at √s=200 GeV:Invariant Mass

##  in Run 6 p+p at √s=200 GeV:Cross Section

| 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 acceptance
- L0 is efficiency of L0 trigger
- L2 is efficiency of L2 trigger
- (e) is efficiency of e reco
- mass is efficiency of mass cut

## 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 |

## STAR  vs. theory and world data

- STAR  *vs.* theory and world data

## Run 7 Au+Au at √sNN=200 GeV  Trigger Integrated Luminosity

- Goal ~ 300 μb-1 for Run 7
- L2-upsilon integrated luminosity ~ 210 μb-1 per 6/5/2007
- ~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

***James Dunlop***

## Vertex Position Detector in Run 7

- First time  trigger uses VPD
- Mostly to reduce rate
- Helps restrict  to low material region
- Vertex resolution ~ 5 cm in central collisions
- Offline TPC vertex σ ~ 18 cm

***Lijuan Ruan***

## Parameter:
State-of-the-art Multi-Gap Resistive Plate Chamber
-0.9<<0.9, 0<<2
6 gap, 3×6 cm2 pad, 23,000 channels
Most important USA-China collaborative effort to date in HEP detector research
Status:
Run 8 ~ 11 trays
Run 9 ~ 65 trays (half detector)
Run 10 ~ 120 trays (full detector)
Impact on Heavy Flavor:
Excellent Electron ID (J/ψ range 0.2<p<4 GeV/c)
J/ψ trigger in Au+Au
Low-pT μ ID (0.2 GeV/c)

- State-of-the-art Multi-Gap Resistive Plate Chamber
- -0.9<<0.9, 0<<2
- 6 gap, 3×6 cm2 pad, 23,000 channels
- Most important USA-China collaborative effort to date in HEP detector research
- Status:
- Run 8 ~ 11 trays
- Run 9 ~ 65 trays (half detector)
- Run 10 ~ 120 trays (full detector)
- Impact on Heavy Flavor:
- Excellent Electron ID (J/ψ range 0.2<p<4 GeV/c)
- J/ψ trigger in Au+Au
- Low-pT μ ID (0.2 GeV/c)

- Full Barrel Time-of-Flight Detector

## The Muon Telescope Detector

- Muons penetrate iron bars; other particles are stopped
- Timing resolution ~60 ps
- Background rejection >100
- No γ conversion
- Suppressed Dalitz decays
- Online trigger possible in Au+Au central collisions
- Enhancement of high-pT particles

***Guoji Lin***

- MTD prototype

## Separation of  States

***Manuel Calderon***

***Guoji Lin***

- →e+e-
- Resolution degraded by electron bremsstrahlung

- →μ+μ-
- Able to resolve different S states

## Inner Tracking Detectors

- Relies on TPC-SSD-IST-PIXEL tracking for graded point matching and resolution
- Essential for direct D0 topological reconstruction
- Distinction between B→J/ψ and prompt J/ψ

***F. Videbaek***

## RHIC-I & RHIC-II STAR Projections

- 12 weeks of running
- Heavy Flavor Tracking with vertex ±10 cm

| Species | Signal |η|<1 | RHIC-I | RHIC-II |
| --- | --- | --- | --- |
| p+p | J/ψ→e+e-
Ψ’→e+e-
→e+e- | 1,260,000
23,000
6,600 | 1,600,000
29,000
8,300 |
| Au+Au | J/ψ→e+e-
Ψ’→e+e-
→e+e- | 16,000
300
830 | 220,000
4,000
11,200 |

| Species | RHIC-I (current) | RHIC-I (projected) | RHIC-II (projected) |
| --- | --- | --- | --- |
| p+p | 0.9 pb-1 | 26 pb-1 | 33 pb-1 |
| Au+Au | 160 μb-1 | 327 μb-1 | 2,500 μb-1 |

**STAR Quarkonia Yields**

**RHIC weekly luminosity**

- http://rhicii-science.bnl.gov/heavy/

- Medium term upgrades:
- Replacement of CTB with ToF
- New TPC FEE
- DAQ-1000
- Heavy Flavor Tracking

## 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 better J/ψ measurement from minimum bias dataset
- Near term STAR detector upgrades (ToF, MTD, HFT) and RHIC & RHIC II luminosity improvements will significantly benefit the STAR quarkonium program by opening up other decay channels (μ+μ-) and making feed-down discrimination possible

## Extra Slides

## Fermilab physicists discover "triple-scoop" baryon

- http://www.fnal.gov/pub/presspass/press_releases/Dzero_baryon.html

*Three-quark particle contains one quark from each family.*
- Batavia, Ill. - Physicists of the DZero experiment at the Department of Energy's Fermi National Accelerator Laboratory have discovered a new heavy particle, the Ξb (pronounced "zigh sub b") baryon, with a mass of 5.774±0.019 GeV/c2, approximately six times the proton mass. The newly discovered electrically charged Ξb baryon, also known as the "cascade b," is made of a down, a strange and a bottom quark. It is the first observed baryon formed of quarks from all three families of matter. Its discovery and the measurement of its mass provide new understanding of how the strong nuclear force acts upon the quarks, the basic building blocks of matter...

- arXiv:0706.1690v2 [hep-ex]