# Presentation: 080320

## Electrons (and Electron Pairs) in STAR

- Charm (onium) and Bottom (onium!) in STAR

- 22/July/2004

## Heavy Flavor Program  In STAR

- Learn about charm/beauty physics (Peter and Matt)
- Suppression? Potential for direct probe of deconfinement?
- Very long term: quarkonium spectroscopy
- Measurements:
- Open Charm via D’s: H. Zhang (yesterday)
- Single electrons: Access charm (and bottom at higher pt!)
- e+e- pairs:Quarkonium J/, 
- Electron ID capabilites
- Single electron data
- TPC+EMC
- Electron pairs: towards quarkonium
- Run IV data

- 22/July/2004

## Electron Identification, dE/dx

- Use TPC for dE/dx
- Look at p>1.5 GeV/c
- Can see a region where the electron band sits.
- Not ideal, but...
- LARGE acceptance:
- ||1, 0<<2
- TOF in limited 

- 22/July/2004

## Electron Identification dE/dx 

- Can select two regions
-  around electron band
-  signal
- Outside electron band
- Background
- e/h ~ 500 (p dependent)

- 22/July/2004

## Electron Identification, Barrel EMC

- Run IV acc:
- 0<<1, 0<<2
- Distance from track to center of a tower
- Tower Energy
- High-granularity Shower Maximum information

- 22/July/2004

## Barrel EMC Electron ID

**p/E for electron and hadron candidates**
- p is the track momentum, E is the tower energy
- Peak position depends on the distance to the center of the tower
- EMC e/h ~ 250
- (pT-dependent)
- Combined EMC+TPC e/h~105

- 22/July/2004

## High-pT electron trigger

- EMC provides a Level 0 high-pT  electron trigger
- Runs for every RHIC crossing (10 MHz)
- Two ET thresholds
**2.5 and 5 GeV**
- Enhancement as high as 1000 for pT > 5 GeV/c

- 22/July/2004

## Deconstructing the spectrum

- Total electron spectra
- Background
- Instrumental sources
- γ convertion
- Hadron background
- Dalitz decays (π0, η)
- Kaon decays
- vector meson decays (ρ ω Φ)
- Signal
- heavy quark semi-leptonic decay
- Drell-Yan, Thermal, etc

- 22/July/2004

## Background finding efficiency

- Need knowledge of background finding efficiency vs. p
- Shape of 0 spectrum
- Measure most of the background (avoids cocktail)

- 22/July/2004

## Inclusive spectrum

- Awaiting final reproduction of d+Au data

- Preliminary

- 22/July/2004

## “Non-Photonic” spectrum

- EMC & TOF analysis agree
- Can calculate e from Open Charm
- Charm could be dominant source below ~4-5 GeV/c

- Preliminary

- 22/July/2004

## RdAu

- Also see Cronin for e in dAu (Cronin for charm)

- 22/July/2004

## Bottom?

**PYTHIA 6.22**
- width of primordial kT distribution: 1.5 GeV/c
- mc = 1.25 GeV/c2, mb = 4.8/5.0 GeV/c2
- K-factor  obtain from fit
- Definition in 22 hard parton scattering Q2=ŝ
- HF production:         MSEL = 4
- parton virtuality:       PARP(67) =1
- PDF:		               CTEQ5L, GRV 94D
- Vary parameters
- for each parameter set fit measured spectrum with either common or separate K factor for c and b components
- Match measured cc
- Extractbb cross-section
- bb rather stable against variation
- bb  5 b

- In Progress

- 22/July/2004

## Electron Pairs: Quarkonium Trigger

- Divide  in 6 sections
- Find a tower above a threshold
- Look in the 3 opposite sections in 
- If another tower above threshold, trigger!

- 22/July/2004

## AuAu Production Rates

|  | Minbias | Top 5% | Top 10% | Top 20% |
| --- | --- | --- | --- | --- |
| J/ | 1.35 x 10-4 | 6.21 x 10-4 | 5.54 x 10-4 | 4.46 x 10-4 |
| ’ | 4.96 x 10-6 | 2.28 x 10-5 | 2.03 x 10-5 | 1.64 x 10-5 |
|  | 1.18 x 10-7 | 5.43 x 10-7 | 4.84 x 10-7 | 3.89 x 10-7 |
| ’+ ’’ | 4.31 x 10-8 | 1.98 x 10-7 | 1.77 x 10-7 | 1.42 x 10-7 |

- (BR x  in pp @ s=200 GeV
- Rates per event, into e+e-, per unit y at y=0

- 22/July/2004

## So, How many in Run IV?

- J/ Yield:
- ~12 J/  e+e-, p>1.2 GeV per 1M min-bias events
- ~50 J/  e+e-, p>1.2 GeV
- per 1M 10% central events

-  Yield:
- 0.02   e+e-, p>3 GeV per 1M min-bias events
- 0.1   e+e-, p>3 GeV
- per 1M 10% central events
- (Triggered event ~ central)

- Include:
- - fAB (hard fraction)
- - 1 unit  4
- - Acceptance (1/2 Barrel)
- Assuming 0.5x(3/4 Barrel)
- - momentum cut

- Run IV
- Min bias
- ~30M 12x30 = 360
-  Central
- 50x30 =1500

- 22/July/2004

## Did the trigger work?

- minimum bias 7854 events
- Central 26581
- Upsilon triggers 1159

- 22/July/2004

## Summary

- BEMC analysis electrons in STAR is on shell!
- Single electron results in pp, dAu soon to be finalized
- E seem to show Cronin
- Beauty starts to dominate ~4-5 GeV/c (model dep.)
- bb ~ 5b
- Electron pairs can be accessed in STAR
- Trigger on J/ in pp; offline search in AuAu Run IV
- Trigger on  in all systems; caveat small 
- Getting ready for the production of Run IV data
- For theorists in the house: predictions!

- 22/July/2004

- 22/July/2004

## Trigger Bias

- Sufficient overlap between minimum bias and EMC triggered data
- Can combine all 3 datasets

- 22/July/2004