# Presentation: 865229

## Open Charm Cross Section and Cronin Effect of Electrons and Identified Hadrons 

-  **Motivation**
-  **Analysis techniques**
- 	 event-mixing technique for D0 analysis
- 	 MRPC-TOFr detector for hadron and electron identification
- 	 single electron spectrum: background subtraction
-  **Physics Result****s**
- 	 open charm total cross section:              direct (D0) and indirect (single electron)
- 	 Cronin effect of identified hadrons and electrons
-  **Conclusions**

- Lijuan Ruan  (*USTC/BNL*)* *
- for the **STAR** Collaboration

- Lijuan Ruan USTC/BNL

## Motivations

- 1) A unique probe to partonic matter
- 2) Sensitive to initial **gluon density** and possible **medium effects**

- Important reference to understand
**possible quark****onium suppression**

- Parton energy loss
- --- heavy quark “**dead cone**” effect

**(I) Study heavy quark (charm) production**

- Measure **R****dAu **of ***p, e* at 200 GeV.

**(II) Nuclear Modification Effects at RHIC**

- Lijuan Ruan USTC/BNL

## STAR Detector: TPC & MRPC-TOFr

**TPC dE/dx PID:**
- pion/kaon ~ 0.6 GeV/c, proton  ~ 1GeV/c

**MinBias Trigger:**
-               ZDC-Au in d+Au, BBCs in p+p

**A new technology** ----
- Multigap Resistive Plate Chamber
-             (MRPC)
- adopted from CERN-Alice.
**Advantages:**
**   ****l****ow cost, **
**   ****high timing resolution (<100ps)**

- A prototype detector of time-of-flight (**TOFr**)
-     was installed in year3
- Just one tray: ~0.3% of TPC coverage (eta
-    coverage (-1.0, 0.0), phi coverage 1/60 of 2,
-    in the forward Au beam outgoing direction)
- Intrinsic timing resolution: 85 ps**  **in year3

- Lijuan Ruan USTC/BNL

## Open charm reconstruction in STAR

- hadronic channel: D0  K– +
- (B.R.  3.80% ± 0.09%)

**First direct open charm measurement at RHIC!**

- STAR Preliminary

- Lijuan Ruan USTC/BNL

**Notes:**
Identify charged Kaon and Pion tracks through energy loss in TPC, Produce oppositely charged K- pair 
invariant mass spectrum in same event, Obtain background spectrum through 
mixed event, Subtract background and get D0 spectrum.

## STAR MRPC-TOFr PID

- Hadron identification:
-      STAR Collaboration, nucl-ex/0309012

**STAR MRPC****-TOFr**** PID**

**Electron identification:**
** ****TOFr  |1/ß-1| < 0.03**
** ****TPC dE/dx             electrons!!!**

***electrons***

- Lijuan Ruan USTC/BNL

## Measurements of electron background

**     ****Electron Pair Topology:**
-       TOFr tagged e+/e-
-       Large TPC acceptance
-       High efficiency of reconstructing
-        electron pair

- γ conversion
- π0 , η Dalitz decays
- Kaon decays
- ρ ω Φ vector meson decays
- heavy quark semi-leptonic decay
- others

- Single
- Electrons
- Spectra

- γ conversion and π0 Dalitz decays are the dominant sources at low pt region.

- background

**signal**

- Lijuan Ruan USTC/BNL

**Notes:**
Let me introduce something about the single electrons spectra first. The electrons may come from the following sources: photons go into the detectors and  convert into electrons, pi zero and eta scalar meson dalitz decays, decay from kaons , vector meson including rho, omega, phi decay and dalitz decay, these four sources are called “photonic sources”; and the electrons can also be from heavy quark semi-leptonic decay and others (direct photon) , these are called “non-photonic” sources. Previous studies show the gamma conversion and pi zero dalitz decays are the dominant sources at low pt region. To get interested non-photonic source contribution, usually we do as these steps: first use MC simulation for the detectors to subtract the gamma conversion contribution, then for the model known sources contribution, get them as precisely as possible and compare with data to get rid of their contribution, these include pi zero, scalar and vector mesons contribution. Then we can extract the non-photonic source contribution and also can estimate the heavy quark production.

## Background subtraction

**Background subtraction**

**Data****: ****background spectra**kinematical selection of  the  conversion and 0 Dalitz decay pairs in TPC
**MC**: ****** conversion and ********0 ****Dalitz decay ****reconstruction ****efficiency**   **~60%**
**c)   ****MC****: ****relative contributions of **
**       ****different sources: **
**       **determined from PYTHIA/HIJING + detector simulations

-  conversion and 0 Dalitz decay reconstruction efficiency :
- ~60% at pT>1.0 GeV/c

- Invariant Mass Square

- Rejected

- Signal

- STAR Preliminary

- Lijuan Ruan USTC/BNL

## Contributions of different sources

- An increasing excess found in higher pt region, pT > 1.0 GeV/c,
- as expected to be contribution of  semi-leptonic decay from heavy flavor hadrons

- pT (1.0-3.0) GeV/c

| Bg Sources | Contribution (%) |
| --- | --- |
| 0 Dalitz decay | 13 ± 1 |
|  conversion | 82 ± 7 |
| Total measured bkgd | ~ 95  |
|   | 3.2 |
|  | 1.0 |
|  | 0.22  |
|  | 0.19 |
| K | 0.21 |
| Total simulated bkgd | ~ 5 |

- Lijuan Ruan USTC/BNL

**Notes:**
Then we can also estimate the contribution from other scalar and vector meson decays. Using decay generators to get the single electrons spectra according to the assumed (pt,y) distributions for eta, rho, omega, phi et. al. Add all these photonic contribution together, we can get the total contribution and also find an increasing excess at high pt region. This is expected to be contribution of semi-leptonic decay from charmed hadrons.

## D0 meson and electron spectra from d+Au and p+p

**D****0**** meson and electron spectra ****from d+Au and p+p**

- Combine D0 and single electron,
- pT coverage for open charm mesons:
**D****0 ****: 0<P****T****<3 GeV/c**
**Single electron for D****0 ****: ~2<P****T****< ~5 GeV/c**

- dN/dy = 0.033 ± 0.005 ± 0.009
- Assuming Nbin scaling
-              0.033/54%/7.542mb4.0
**= 1.36 ± 0.20 ± 0.39 mb**

- Reconstructed D0
- (d+Au at 200 GeV)
- From combined-fit D decay
- (d+Au at 200 GeV)
- From combined-fit D decay
- (p+p at 200 GeV)

- STAR Preliminary

- Lijuan Ruan USTC/BNL

## D meson and electron spectra from STAR

**D meson and electron spectra from STAR**

- An Tai’s talk

**D and electron spectra are consistent!**

**Directly reconstructed **
**D-mesons!**

**Data Points: **Measured electron spectra
**Lines:** D-meson decayed electron spectra!** **

- 1.12 ± 0.20(stat) ± 0.37(syst) mb

- STAR Preliminary

- STAR Preliminary

- Lijuan Ruan USTC/BNL

## Total charm production X-section

**Total**** charm production X-section**

- ---  Curves from H. Wörhi, CIPANP03

**STAR Preliminary**

-   Total charm production cross
-     section has been measured
-     at 200 GeV
-   Default Pythia calculations
-     failed to reproduce data
-   Higher order processes like
-     ***flavor excitation*****, *****gluon***
***   ******splitting*****, *****parton showers*** et al.
-    are needed for charm production
-    at RHIC.

- Lijuan Ruan USTC/BNL

## RdAu of , K, p, e −−− Cronin Effect 

**R****dAu**** of ********, K, p, e** −−− **Cronin Effect**

- 1. RdAu(,K,p): increase with           3. RdAu (e) : ~ 1  **R****dAu****(e)**** ****=**** 1.23 ******** ****0.****26****(stat)**
-     transverse momentum                                                             ****** 0.31(sys)**
-                                                          4. RdAu(p) rises faster than RdAu(, K) and
- 2. RdAu (p) > RdAu (, K)                      becomes larger than Nbin scaling within
-                                                             1.5<pT<3.0 GeV/c.
-  *Needs more data to address Open Charm Cronin effect!*

-      STAR Collaboration, nucl-ex/0309012

- STAR Preliminary

- Lijuan Ruan USTC/BNL

## Conclusions

- ► First results on **direct measurement** of D production (0.1<PT<11.0 GeV/c)
-      at RHIC.
- ► STAR MRPC TOF / TPC provide clean electron spectrum measurement
-      up to pT ~ 3 GeV/c in both 200 GeV p+p and d+Au collisions.
- ► Open charm from d+Au collisions: the directly measured open charm
-       and single electron (from D decay) spectra are consistent!
- ► Open charm total cross section measurements:
-                           D0+e:                   1.36 ± 0.20(stat) ± 0.39(syst) mb
**                         **All D:**                   **1.12 ± 0.20(stat) ± 0.37(syst) mb
**              **
- ► RdAu of e from charm production is consistent with ***N******bin*** scaling within
-      the errors.
-      *This is an important physics and more data are needed to confirm this!*

- Lijuan Ruan USTC/BNL

## Outlook

**PHENIX data:    Phys. Rev. Lett. 88, 192303 (2002)**

- Look forward to the electron spectra from Run 4 Au+Au collisions.

- Lijuan Ruan USTC/BNL

## Backup Slides

- Lijuan Ruan USTC/BNL

## Background Subtraction

- Using TOFr cut select an primary electron/position
-             --- Tag

- Main background subtraction

- Lijuan Ruan USTC/BNL

**Notes:**
With the combination of TOFr PID cut and dEdx information, we can select an primary e/p as a tagged particle, as shown in left plot, then select another opposite sign track in all TPC tracks to construct the kinematical variables: invariant mass and the opening angle.  From the simulation data, we can find these distributions for the backgrounds from gamma conversion and pi0 Dalitz decay. The distribution of signal is expected to be higher. But unfortunately we have no signal in the simulation data. With cuts both on real and simulation data, we can get the cut out background distributions. Then we calculate the expected main background from gamma conversion and pi zero dalitz decay of data.

## Data/background ratio

- Lijuan Ruan USTC/BNL

## Subtract background: step by step

- a)  Use MC Simulation to get the efficiency (~**60%** at PT>1GeV/c) of our background
-      subtraction under the kinematical cuts ( for 0 Dalitz decay and  conversion).

- b) Apply the same cuts on data, get the cutout background, scaled by the  efficiency from
-      simulation, and  get the total background (0  Dalitz decay and  conversion) from data.

- c)  Some other background (η,ρ,ω,Φ) as well as the signals which fall into the cuts and are randomly rejected are also corrected.

- d)  Use decay generators to get the single electrons spectra according to the assumed
-      (pt, y) distributions for η,ρ,ω,Φ, 0 
-      get the background from η,ρ,ω,Φ by comparing through  the background
-      from 0 Dalitz decay in data.

- e)  Background from Kaon decays is also studied from simulation and found to be
-      negligible

- f)  Extract the signal and estimate the heavy quark production

- Lijuan Ruan USTC/BNL

## D0 meson and electron spectra from d+Au and p+p

**D****0**** meson and electron spectra ****from d+Au and p+p**

- Combine D0 and single electron,
- pT coverage for open charm mesons:
**D****0 ****: 0<P****T****<3 GeV/c**
**Single electron for D****0 ****: ~2<P****T****< ~5 GeV/c**

- dN/dy = 0.033 ± 0.005 ± 0.009
- Assuming Nbin scaling:
**1.36± 0.20 ± 0.39 mb**

- Reconstructed D0
- (d+Au at 200 GeV)
- Inclusive electrons
- (d+Au at 200 GeV)
- Inclusive electrons
- (p+p at 200 GeV)

- From combined-fit D decay
- (d+Au at 200 GeV)
- From combined-fit D decay
- (p+p at 200 GeV)

- Lijuan Ruan USTC/BNL

## Charm total cross section

- R. Vogt: hep-ph/0203151

- Lijuan Ruan USTC/BNL

## Saturation model prediction

**Saturation model prediction**

**Phenix: Phys. Rev. Lett. 88, 192303(2002)**
** ****D. Kharzeev,hep-ph/0310358**

- Lijuan Ruan USTC/BNL

## Nuclear Shadowing Effect

- R. Vogt: hep-ph/0111271

- Lijuan Ruan USTC/BNL

## Charm: the ratio of  pA to pp

- R. Vogt: hep-ph/0111271

- Lijuan Ruan USTC/BNL

## RdAu comparison

- ● ccbar RdAu curve from R. Vogt: hep-ph/0111271

- ● decay into electrons in d+Au and p+p collisions assuming
-    D spectrum as STAR measured

- Lijuan Ruan USTC/BNL

## Systematic errors

| Source | d+Au | p+p |
| --- | --- | --- |
| Ratios between diff. D mesons | 10% | 11% |
| D spectrum shape† | 13% | 13% |
| Decay modes ( CERNLIB general and PYTHIA ) | 12% | 12% |
| NFitHits 15->25 | 18% | 14% |
| Rapidity distribution | ~15% | ~15% |
| Nbin in dAu | 5% | - |
| Total sys. errors | 31% | 29% |

- † not needed in the combining fit

- Lijuan Ruan USTC/BNL