# Presentation: 747271

## Azimuthal correlations between non-photonic electrons and charged hadrons in p+p   collisions from STAR

**Xiaoyan Lin**
**IOPP/UCLA**
***For the STAR Collaboration***

**Motivation**
**Electron identification**
**Photonic electron background**
**Electron-hadron correlation**
**Comparison to PYTHIA  **
**Summary**

- Hard Probes 2006, Asilomar, June 9-16

## Features in H-Q Measurements at RHIC

**Features in H-Q Measurements at RHIC**

**Heavy Quark R****AA ****      =       Light Quark R****AA**

***Curves: S. Wicks, et al, nucl-th/0512076***

- Hard Probes 2006, Asilomar, June 9-16

## Features in H-Q Measurements at RHIC

**Features in H-Q Measurements at RHIC**

**Heavy Meson Flows !**
**Note the decay kinematics **
**  ****of D and B mesons**
**  ****are different!**
**Electrons from B decays**
**  ****cannot follow the B meson**
**  ****momentum direction as **
**  ****good as electrons from**
**  ****D decays!**

- Non-photonic electron *V**2*

*Curves: Greco, Ko, Rapp, PLB 595 (2004) 202*

- Hard Probes 2006, Asilomar, June 9-16

## Charm versus b quark contribution

**Quantitative understanding of features in **
**    ****heavy quark measurements requires Charm versus b **
**quark contributions to non-photonic electrons !**

**Such information should be best obtained from direct**
**  ****measurement of hadronic decays of charm and bottom mesons.**
** **
**This motivates the STAR and PHENIX vertex detector upgrade!**
**See Dr. Nu Xu’s talk.**

**Non-photonic electron and hadron correlations can help to **
**  ****estimate the C and B contribution !**
**	****	****X. Lin hep-ph/0602067**

- Hard Probes 2006, Asilomar, June 9-16

## PYTHIA Simulation

** ****Significant difference between D decays and B decays in the near-side correlations.**
** ****The difference is largely due to decay kinematics, not the production dynamics.**
** ****The large difference in the near-side Δφ**** ****between D and B mesons can help us to estimate relative B and D contributions to non-photonic electrons. **

**PYTHIA Simulation**

**2.5<P****T****(trig)<3.5 GeV/c**

**3.5<P****T****(trig)<4.5 GeV/c**

**4.5<P****T****(trig)<5.5 GeV/c**

**Associated P****T**** > 0.1 GeV/c**

- Hard Probes 2006, Asilomar, June 9-16

## Major Detectors Used

- Non-photonic
- electron
- Background:
- Hadron
- Photonic electron

**Major Detectors Used**

**Time Projection Chamber (TPC)**
**Electro-Magnetic Calorimeter (EMC)**
**Shower Maximum Detector (SMD)**

- Charm decay
- Bottom decay

- Photon conversion
- π0 Dalitz decay
- η Dalitz decay
- kaon decay
- vector meson decays

- Data Sample:
- About 20M p+p collisions at sNN = 200 GeV** **in year 5 run.

- Hard Probes 2006, Asilomar, June 9-16

## Electron Identification: dE/dx

**Electron Identification: dE/dx**

-  TPC can identify charged particles to some extent
-  Two orders of magnitude more hadrons than electrons
-  Additional information needed to identify electrons

- (-0.4σ, 3.0σ)

- Hard Probes 2006, Asilomar, June 9-16

## Electron Identification: P/E

-  P is measured by TPC. E is the sum of the associated BEMC points’ energy measured by BEMC.
-  Electrons will deposit almost all of their energy in the BEMC towers. 0.3 < P/E <1.5 was used to keep electrons and reject hadrons.

- Hard Probes 2006, Asilomar, June 9-16

## Electron Identification: Shower Size

-  Number of SMD hits per shower indicates shower size.
-  Electrons have larger number of BSMD hits than those for hadrons.
-  Electron candidates have to satisfy Number of BSMD hits > 1.

- Hard Probes 2006, Asilomar, June 9-16

## Electron Identification: Projection Distance

-  -3σ < ZDist < 3σ and -3σ < PhiDist < 3σ were set to remove lots of random associations between TPC tracks and BEMC points.

- Hard Probes 2006, Asilomar, June 9-16

## Purity of Inclusive Electron Sample

**Purity of Inclusive Electron Sample**

| electron pT | purity |
| --- | --- |
| 2.5-3.5 GeV/c | 99.99% |
| 3.5-4.5 GeV/c | 99.34% |
| 4.5-5.5 GeV/c | 99.14% |

- Hard Probes 2006, Asilomar, June 9-16

## Photonic Background

-  The combinatorial background is small.
-  Reconstructed photonic electron is the subtraction.
-  Photonic electron is the reconstructed-photonic/eff
-  eff ~ 60-70% from simulation for pp year 4. Still working on progress for pp year 5.

- M<100 MeV/c2

- Hard Probes 2006, Asilomar, June 9-16

## Method to Extract the Signal of E-H Correlation 

-  Start with Semi-Inclusive electron sample.
* *If tracks pass the electron identification cuts, then they are **inclusive electrons**. In this inclusive electron sample we throw away those electrons which satisfy the photon conversion condition. The sample remaining is called **semi-inclusive electrons****.**
- Semi-Inclusive = non-phtonic + not reconstructed-photonic - combinatorics

-  Combinatorics can be estimated by Same-Sign.

-  Not reco-photonic = photonic – reco-photonic = (1/eff – 1) (reco-photonic). For the e-h correlation analysis, we have to remove the photonic partner of the reco-photonic.

** ****Δφ****non-pho**** = Δφ****semi-inc ****+**** ****Δφ****combinatorics**** - (1/ε -1) (Δφ****opp-sign-NoPartner**** - Δφ****same-sign-NoPartner****) **

- Hard Probes 2006, Asilomar, June 9-16

##  Δφ Distributions

-  **Δφ ****Distributions**

**2.5<P****T****(trig)<3.5 GeV/c**

**3.5<P****T****(trig)<4.5 GeV/c**

**4.5<P****T****(trig)<5.5 GeV/c**

**Associated P****T**** > 0.1 GeV/c**

**Semi-inc**

**Semi-inc**

**Combinatorics**

**Combinatorics**

- Hard Probes 2006, Asilomar, June 9-16

##  Δφ Distributions

**2.5<P****T****(trig)<3.5 GeV/c**

**3.5<P****T****(trig)<4.5 GeV/c**

**4.5<P****T****(trig)<5.5 GeV/c**

**Opposite-Sign**

**Opposite-Sign**

**Same-Sign**

**Same-Sign**

- Hard Probes 2006, Asilomar, June 9-16

##  Comparison to PYTHIA Simulation

**Assume the photonic b.g. reconstruction efficiency is 70%**

-  At low pT 2.5 - 3.5 GeV/c, the preliminary data indicates D contribution is dominate.

- Hard Probes 2006, Asilomar, June 9-16

##  Comparison to PYTHIA Simulation

**Assume the photonic b.g. reconstruction efficiency is 70%**

-  At high pT 4.5-5.5 GeV/c , the preliminary data indicates D contribution is larger than B.

- Hard Probes 2006, Asilomar, June 9-16

## Summary

-  We find that non-photonic electron and hadron correlations are sensitive to D and B contributions.
-  The preliminary data indicates D contribution is larger than B contribution up to PT ~ 5.5 GeV/c.
-  To quantitatively estimate B contribution, we need more study on the background, photonic electron reconstruction efficiency...

- Hard Probes 2006, Asilomar, June 9-16

## Back up slides

- Hard Probes 2006, Asilomar, June 9-16

##  Photonic b.g. reco. efficiency uncertainty 

- Hard Probes 2006, Asilomar, June 9-16

## Photonic b.g. reco. efficiency uncertainty

**Photonic b.g. reco. efficiency uncertainty**

- Hard Probes 2006, Asilomar, June 9-16

## Photonic b.g. reco. efficiency uncertainty

**Photonic b.g. reco. efficiency uncertainty**

- Hard Probes 2006, Asilomar, June 9-16

## Width of near-side peak in PYTHIA simulation

| electron Pt (GeV/c) | 2.5-3.5 | 3.5-4.5 | 4.5-4.5 |
| --- | --- | --- | --- |
| All hadrons
e from D decays | 0.359± 
0.003  | 0.29 ± 0.003 
 | 0.2532 ± 0.0042 
 |
| Hadrons from D decays
e from D decays | 0.3792 ± 0.0096  | 0.2992 ± 0.0098  | 0.2457 ± 0.0106 
 |

- Hard Probes 2006, Asilomar, June 9-16

## Slide 24

- Hard Probes 2006, Asilomar, June 9-16