# Presentation: 401791

## Dilepton Simulations

- Lepton program
- In-medium vector meson properties
- Heavy flavor
- HFT+TOF
- Select primary electrons
- Reject gamma conversion
- Reduce charm combinatorics

- Zhangbu Xu
- BNL

## Critical needs from future experiments 

**v2 scaling ****for coalescence**** **
**jet quenching as ** **parton energy loss**
**energy dependence ****testing model prediction**
**Heavy flavor yields and flow:** **color screening and partonic ollectivity.**
**forward** **jet correlation:****CGC**

**Thermometers**: **dilepton, photon**
**heavy quarkonium species**.
**jet fragments tagged** by a hard direct photon, a heavy flavor
**elliptic flow in U+U collisions**.
- LHC and GSI energies
**fundamental QCD symmetries**

- Near Term

- Long Term

**PID spectra**
- freeze-outs
- hadronization
**PID correlations**
- In-medium jet
- Fluctuations and correlations
**Lepton program**
- In-medium Vector Meson
- Heavy Flavor
**Baseline detector for future upgrades **

- TOF+HFT

**Near/Long Term: STAR white paper Nucl. Phys. A 757 (2005) 102 **

## QCD Phase Diagram

**A thermodynamic state** is specified by a set of values of all
- the thermodynamic parameters necessary for the description of the system. --- statistical mechanics by K. Huang
- Temperature (**T**), chemical potential (****, pressure(**P**) ...

- Chemical/thermal Equilibrium at certain stage of the evolution
- At the predicted QCD phase boundary
- persistent from SPS to RHIC
- Below the phase boundary atAGS and SIS

## The Origin of Mass

- Others used this as a fact
- the mass reflects in the measurable Vector Meson in-medium properties
- This is fundamental

## QGP Signature

- Vector Meson Properties
- Thermal Dileptons/photons
- Heavy Flavor

## Dilepton measurements

- Excess at low mass di-electon
- Large rho mass shift ruled out?

- NA60

## Dimuon at IMR

- Dimuon excess at IMR
- Source from prompt muons?

- Need good vertexing and lepton PID

## Electron Identification

- TPC dE/dx: large hadron background
- EMC: pT>1.5 GeV/c

- Not able to do without TOF!10-5 hadron rejection

- A prototype TOF tray (TOFr)

- Nucl-ex/0505026, M. Shao et al.
- X. Dong PHD Thesis (USTC 2005)

## Dilepton

- Total bkgd:
-    ~10-4/25MeV (ω)
-    ~2∙10-5/25MeV (Φ)

- Dalitz decay bkgd:
-    ~5∙10-6/25MeV (ω)
-    ~5∙10-7/25MeV (Φ)

- γ conversion
- π0 , η Dalitz decays
- ρ ω Φ vector meson decays

| Au+Au | #events forω
with 3σsignal | #events for Φ with 3σsignal |
| --- | --- | --- |
| TOF+TPC | 7M | 2M |

## Open Charm

- Full TOF improves (x5) charm hadronic reconstruction
- Charm semi-leptonic decay (c100m)
- Cross section and spectra (prototype TOF) in p+p, d+Au Published Phys. Rev. Lett. **94** (2005) 062301

## Prototype TOF related Charm Results

**Total Cross Section ****scales**** approximately with ****Nbin**
**Charm produced at ****initial**** impact, ****sensitive to the early  evolution/thermalization**
**Suppression**** at p****T****(e)>1.5 GeV/c****Strong energy loss even for charm **

## J/at low pT

- Thermalization & Color DOF
- Test Color Screen
- Coalescence of charm quarks

- PHENIX PRC 69(2004)014901

- PHENIX J/

- STAR J/

- PHENIX Acceptance:                    ||<0.35,=2*/2
- STAR TOF-Upgrade Acceptance: ||<0.9,=2*
**J****/******** Acceptance:  STAR=100*PHENIX**

## TOF+HFT

- TOF provides 2 and ||<0.9 coverage
- Future upgrades will benefit from or enhance the capability of this detector
- .e.g. Heavy Flavor Tracker  (HFT) and TOF can be a powerful device for dilepton and heavy flavor programs

## Reject gamma conversion

| Detectors |  |  |
| --- | --- | --- |
| TPC+TOF | 8 M | 2 M |
| TPC+TOF+HFT | 200K | 100K |

- Background:   e+e-
-  HFT discriminates background !
-  Need low mass detector

## Charm Correlation

- Correlated charm pair
- Decay electron pair is correlated
- Need charm pair measurements or charm electron rejection
- Shengli Huang (LBL)

## HFT Charm rejection

- DCA distributions of electrons from D and primary (HFT)
- Integrated percentage
-  c(D+-)=315m,c(D0)=123m
- A factor of 2 rejection for charm electron pair
- Chen Zhong (SINAP/BNL)

## Dalitz Decay

- TPC e+e- invariant mass
- γ conversion
- π0 Dalitz decay

- 8

- Inner Tracking only: SSD+HFT+Vertexin progress

## Money plot

- TOF: vector meson
- TOF+HFT: thermal radiation

## Muon PID at midrapidity?

- 1.5 GeV/c,  unused CTB (replaced by TOF) as muon telescope
- HFT rejects K decays, no gamma conversions, Dalitz decays

## Conclusions

- TPC+TOF+EMC =electron clean PID pT>0.2 GeV/c
- HFT: Select primary electrons, reject gamma conversions, reduce charm background
- Large Coverage, generic detector system
- Dilepton program very promising with TOF+HFT

## Dalitz/charm Decays

**Dalitz decays:**
- TPC rejects 2/3 of Dalitz decays
- Inter Tracker Tracking

**Charm Semileptonic decays ****DDbar ******** e****+****e****- :**
**  **reject electrons event-by-event
-   HFT resolution <10m

- R. Seto

- Color codes:
- Thermal radiation
- Drell-Yang
- Cocktails
- In-medium hadrons
- charm