# Presentation: 174936

## Slide 1

## Outline

- Why is heavy flavor interesting?
- Single Electron analysis in STAR
- Detectors
- Backgrounds
- Consistency checks
- Results
- Prospects for di-electrons in STAR.

## Heavy Flavor Production in Hadronic Collisions

- Heavy quark production
- Charm produced in early stage, mostly from initial gluon fusion
- Sensitive to early conditions:
- initial gluon density
- nuclear effects
- medium effects
- Are heavy-quarks mesons suppressed as well as light quarks ones?
- Probe of energy loss mechanism
- Thermalization probe?
- Eliptic flow.

## Heavy Quark Energy Loss

- Without medium heavy quark jets differ from light quark/gluon
- jets due to suppression of gluon radiation at small angles,
- the **Dead Cone Effect** (Y. Dokshitzer et al, J.Phys.G17,1481)

**What will happen in the medium?**
**Reduced medium energy loss?**
- Y. Dokshitzer and D. Kharzeev, Phys.Lett.B519, 199 M. Djordjevic and M. Gyulassy, Phys.Lett.B560, 37 N. Armesto, C. Salgado, U. Wiedemann PRD69, 114003

****** ****< *****m*****Q****/*****E*****Q**

- suppressed for

## Heavy quark suppression?

- Propagation of heavy quarks in QCD matter
- Energy loss through gluon radiation
- dead cone effect
- Gluon radiation suppressed for  < M/E (Dokshitzer & Kharzeev, PLB 519 (2001) 199)
- Medium induced radiation reduces effect but still sizeable (Arnesto, Salgado, Wiedemann, hep-ph/0312106)
- large enhancement of D/ ratio at moderate high pT (5-10 GeV/c)

## Heavy Flavor Production in A+A Collisons

- So far
- Production little studied (CERN/SPS low )
- Charmonium suppression (melting of J/ due to color screening) used as signature of QGP
- But:
- Low x: heavy quark pair produced over long distances
- can exceed the size of the nuclei (even though matrix element of hard processes dominated by short distances)
-      sensitive to medium  good probe for high density matter
- RHIC and LHC:
- gluon density in nucleii ?
- energy loss due to interaction with medium ?
- shadowing
- cannot study J/ suppression without understanding open charm

## Hidden and Open Charm – Both Needed

- RHIC
- s = 200 GeV

- SPS
- s = 17 GeV

- At RHIC open charm production provides reference and may be the only mean to understand charmonium suppression (same gluon conditions in the initial stage)

## Heavy Flavor in STAR

**Direct reconstruction of open charm hadrons **
**using invariant mass technique:**

- D0 -> K , D+ -> K , D*+ -> D0 , D0 ->K 

- See Xin Dong’s talk later today

**(Semi-) leptonic decays into electrons:**
- D+ -> e+ anything (17.2%)	B+ -> e+ anything (10.2%)
- D0 -> e+ anything (6.87%)	B0 -> e+ anything (10.5%)
- J/ -> e+ e- (5.9%)	  -> e+ e- (2.38%)

- Sensitive to both charm and bottom

## The STAR Detector

**Electron ID**
- energy loss in the tracking detectors (TPC dE/dx)
- time of flight measurement (TOF)
- calorimetric measurements (EMC)

## Electron ID (1)

**Energy loss (dE/dx) in the **
**tracking detectors (TPC)**
- e/h ~ 500 (depending onmomentum)
- Limited to certain momentum windows

**Time of Flight + dE/dx**
- allows clear electron ID in largemomentum range (0.2 < p < 3)
- Only prototype installed: Smallcoverage (1 unit in eta, 6 in phi)

## Barrel EMC identification

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

## Electron ID (2)

**Calorimetric Measurements **
**(EMC + tracking + dE/dx)**
-  large coverage 	0 <  < 1, in FY03,	-1 <  < 1 after completion	-1 <  < 2 including Endcap
-  Provides measurements of
-  energy deposit in towers
-  shower shape
-  electron ID starting at 1.5 GeV/c

## EMC Trigger

- The EMC as trigger detector
- provides fast information
- on energy deposition in towers
- up to 3 ADC (~energy) thresholds

**Gives STAR access to **
**hight pT electrons**

## Inclusive Electrons

**Large “photonic background”**
-  conversions in the detector material
- light meson (0,) Dalitz decays

**Combining detectors: electron pt spectrum**
**for d+Au collisions**
- pT coverage 0.2 to 7 GeV/c
- nice agreement between differenttechniques in overlap regions
- Time-of-Flight, Calorimetry

## Misidentified hadron background

- Obtained by shifting the TPC dE/dx selection over the hadrons region

## Photonic Background

**Measuring the background:**
- electron pair invariant mass
- reconstruction and pair
- opening angle
-  conversions
- 0 dalitz decays
- other decays (... )scaled to 0

## Other Background sources

- Obtain via simulation
- Pythia/HIJING + GEANT
- ratio with respect to π0 Dalitz decay

- Signal/Background is pT dependent
- ~1/1 at 2 GeV/c
- ~2/1 at 7 GeV/c

## “Non-photonic” Electrons

- After correction for electrons from photonic sources and background
- measure up to pT = 8 GeV/c
- EMC, ToF  and dE/dX electrons agree within errors
- Systematic uncertainties
- Trigger bias ~ 0.5σsys
- Efficiency ~ 0.2σsys
- Other sources ~ 0.3σsys

*STAR Preliminary*

## PYTHIA Electron Sources

## Consistency with D Measurement

- Direct reconstruction
- of open charm mesons
- using invariant mass
- technique in d+Au
- (Xin Dong’s talk!)

**Is data consistent with the electron measurement?**

## Electrons from D Decays

**Consistency check**
- Use D mesons pT spectrum
- Use PYTHIA to decay Ds into electrons
- Non-photonic Electron spectra seems to be accounted for by decay of open charm.

## Towards heavy quark energy loss...

- Nuclear modification of
- Charged hadrons in dAu
- And AuAu is well established.
- First steps:
- Primary electron RdAu

- Within errors consistent
- with binary scaling, some
- indication of Cronin effect

## Quarkonium Analysis in STAR

- J/Psi and Upsilon mesons are of great interest in HI collisions
- STAR has some capabilities to detect them through their decay in the e+e- channel
- Particle ID:
- dE/dx (TPC, maybe SVT) at low p
- EM Calorimeter at higher p
- Obstacle: They are rare
- Develop triggers to enhance the events
- If triggering not possible, need a large data set.

- Quarkonium LEVEL 0 Trigger in STAR

- Divide  into 6 sections
- Find a tower above a threshold
- Look in the 3 opposite sections in 
- If another tower above threshold, trigger.
- Level-2: Individual tower information.

##  Trigger: L2 Efficiency and Rejection

- Using High-Tower at level 0 and L2 fast invariant mass:

- Minimum Bias

- Central

- Efficiency can be kept above 85%
- Rejection is high, so rates are low.
- ~100 Hz out of Level-0 (at high luminosity)
- ~2 Hz out of Level-2
- Rejections of 103

## 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
-     360 J/
- Central ~50 M
-  ~1500 J/

## Prospects for Run IV

- J/ Analysis will rely on large minbias and central data sets for Au+Au.
- 50 x 106 minbas + 50 x 106 central
- 3  signal + 5  signal in central (conservative)
- Upsilon Trigger looks promising in Au+Au
- Conservative estimate: ~few 10’s Upsilons in 2004
-  has never been measured in heavy ions before, proof of principle measurement.

## L0+L2 Trigger Performance

## Summary

- Electrons allow us to access heavy flavor physics
- Analysis of electrons in STAR is on shell!
- Single electron results in pp, dAu soon to be finalized
- RdAu : e scale with binary collisions (small Cronin effect)
- Comparisons
- PYTHIA: Beauty starts to dominate ~4-5 GeV/c (model dep.)
- D meson: can account for full non-photonic spectrum
- Future: dielectrons 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

## Extra Slides

## Did the trigger work?

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

- With the trigger, we can reach m~10 GeV/c2

## L2 Trigger: Get invariant mass quickly

- Use individual calorimeter towers
- Energy & position information
- p1 = (EEMC-12-m2)1⁄2   EEMC
- p2 = (EEMC-22-m2)1⁄2   EEMC
- cos x1x2/(|x1| |x2|)
- m2  2 p1 p2 (1 – cos )

- Pro:
-  simple, fast
-  avoids ambiguity