# Presentation: 547336

## Jaroslav Bielcik
Yale

**Jaroslav Bielcik**
**Yale**

- Heavy Flavor and Quarkonia Production Workshop
-               RHIC&AGS User’s meeting 2007

- Open heavy flavor with the STAR detector

- for STAR collaboration

##  Heavy quarks as a probe

-  Heavy quarks as a probe

-  Studying  energy loss of heavy quarks                                                     independent way to extract properties of the medium
-  Due to their large mass heavy quarks are primarily produced by gluon fusion  production rates calculable by pQCD sensitive to initial gluon distribution M. Gyulassy and Z. Lin, PRC 51, 2177 (1995)
-  Heavy quarks lose less energy due to suppression of small angle gluon radiation (dead-cone effect) Dokshitzer and Kharzeev, PLB 519, 199 (2001)
-  Amount of collisional and radiative energy losses seems to be similarM.G. Mustafa, PRC72, 014905

- 2007 RHIC&AGS Annual Users' Meeting

## Open heavy flavor  

- Direct:  reconstruction of all decay products

- Indirect: charm and beauty electrons

- c  e+ + anything   (B.R.: 9.6%)
- b  e+ + anything   (B.R.: 10.9%)

-  charm (and beauty) muons

- c  + + anything (B.R.: 9.5%)

- Azimuthal** **Correlations**: ****e-h, e-D**

- 2007 RHIC&AGS Annual Users' Meeting

## Charm  via hadronic decays

**TPC only**

-   D0 in d+Au and Au+Au at 200GeV   (pT  0.1- 3.0 GeV/c)

- d+Au

- Au+Au

- 2007 RHIC&AGS Annual Users' Meeting

## D0 + D0 in Cu+Cu at 200GeV 

**Significance**

**TPC only**

- 2007 RHIC&AGS Annual Users' Meeting

## D/Ds Peak in d+Au

- STAR Preliminary

**D****+**

**D****s****+**

**D****s****+**** Significance  **
**D****+**** Significance **

-   No negatively charged D or Ds found yet

**TPC only**

- 2007 RHIC&AGS Annual Users' Meeting

## Muon measurement

- Low-pT (pT < 0.25 GeV/c) muons can be measured with TPC + ToF
-    - this helps to constrain  charm    cross-section
- Separate different muon contributions using MC simulations:
- K and  decay
- charm decay
- DCA (distance of closest approach) distribution is very different

**TPC+TOF**

- (STAR), Hard Probes 2006

**m****2****=(p/********/********)****2**

- 2007 RHIC&AGS Annual Users' Meeting

## Non-photonic electrons (part I)

**TPC+TOF**

** **only TOF patch =/30
-    instrumented
** ****non-photonic electrons: **
**   ****p****T**** 0.9-5.0 GeV/c**

-  Photonic background must
-    be reconstructed and subtracted

-   D0+electrons+muons
-    90% of total kinematic range covered

- 2007 RHIC&AGS Annual Users' Meeting

## Charm total cross sections

-  1.4  0.2(stat.)  0.4(sys.) mb
-     in 200GeV minbias d+Au
-  1.29  0.12  0.36 mb
-     in 200GeV minbias Au+Au
-  1.40  0.11  0.39 mb
-     in 200GeV central 12% Au+Au

-  FONLL underestimates measured
-              cross-section by factor ~5

- 2007 RHIC&AGS Annual Users' Meeting

## Non-photonic electrons (part II)

-     => high pT   electrons
-  Photonic electrons reconstructed
-    and subtracted
-  FONLL  scaled by ~5,,
-    describes shape of p+p spectra well
-         suggesting bottom contribution

-  **Phys. Rev. Lett. 98 (2007) 192301**

**TPC+EMC**

- 2007 RHIC&AGS Annual Users' Meeting

## 	Non-photonic electrons vs. FONLL

-  FONLL underestimates measured
-              electrons by factor 4-5
-  PHENIX high-pT data differs from
-              STAR by factor 2

**Non-photonic electrons p+p 200 GeV**

-  not understood yet
-  STAR low material run planned

-  **STAR**** ****Phys. Rev. Lett. 98 (2007) 192301**** **

- PHENIX Phys. Rev. Lett. 97 (2006) 252002

- 2007 RHIC&AGS Annual Users' Meeting

## RAA from d+Au to central Au+Au

- RAA from d+Au to central Au+Au

- Nuclear modification factor

- 2007 RHIC&AGS Annual Users' Meeting

## Electron RAA Radiative energy loss (c+b)

- Electron RAA Radiative energy loss (c+b)

** ****Radiative energy**** **loss alone
-    in medium with reasonable
-    parameters** ****does not describe**** **
**   **the data** **

**    ****Djordjevic, Phys. Lett. B632 81 (2006)**

**Armesto, Phys. Lett. B637 362 (2006)**

** ****What are the other sources**
**   ****of energy loss ?**** **

-  parameters of medium in
-    models extracted from hadron data

- 2007 RHIC&AGS Annual Users' Meeting

## Role of collisional energy loss

**Wicks, nucl-th/0512076**
**van Hess, Phys. Rev. C73 034913 (2006)              **

-  **Collisional**/elastic **energy loss** may
-    be **important** for heavy quarks
-  Still not good agreement at high-pT

- 2007 RHIC&AGS Annual Users' Meeting

## Charm alone?

-  Since the suppression of
-    b quark electrons is  smaller

-  **charm alone agrees better**

-  **What is b contribution?**

- 2007 RHIC&AGS Annual Users' Meeting

## In medium fragmentation

**Adil and Vitev, **Phys.Lett.B649 (2007) 139

-  **Other effects** may contribute to the
-    observed suppression
-  both **b+c** taken into account

-  heavy quarks can **fragment **
**inside the medium** and can
- be suppressed by **dissociation**

- 2007 RHIC&AGS Annual Users' Meeting

## Can we tell how much beauty?

-  Use e-h Correlation
- Large B mass compared to D
- Semileptonic decay:
-       e gets larger kick from B
- Broadened e-h correlation on near-side.
-  **Extract B contribution**
- Use PYTHIA shapes
- Con: Model dependent
- Pro: Depends on decay kinematics well described
- Fit ratio **B/(B+D)**

**STAR QM2006**

**nucl-ex/0701050**

**TPC+EMC**

- p+p 200 GeV

- 2007 RHIC&AGS Annual Users' Meeting

## Relative bottom  contribution to nonphotonic electrons vs. pT

**p+p 200 GeV**

- Relative bottom  contribution to nonphotonic electrons vs. pT

- Fit **e-h**** **correlation with **PYTHIA**      D and B
**Data  **shows non-zero** **
**     ****B contribution**
- Contribution **consistent** with FONLL
**Model dependent (PYTHIA)**
**Depends mainly on kinematics of D/B decay (not on Fragmentation)**
- Dominant systematic uncertainty:
- photonic background rejection efficiency
- Additional uncertainties under study

**STAR QM2006**

- Bottom !

- 2007 RHIC&AGS Annual Users' Meeting

## Heavy flavor tagged correlations

-  **Underlying production mechanism** can be identified using second charm/bottom particle
-  **Experimental approach**
- - **n****on-photonic electrons** from semi-leptonic c/b decays are used to **trigger** on **c-cbar** or **b-bbar** pairs
-  **associate D****0** mesons are reconstructed via their **hadronic decay** channel (probe)

*heavy quark production*

*trigger side*

*probe side*

**TPC+EMC**

- 2007 RHIC&AGS Annual Users' Meeting

## electron-D0 azimuthal correlations

-  Clear **D****0**** signal**
- - S/B ratio factor ~100 better than signal w/o electron trigger
-  Near- and away-side correlation peak with similar yields observed
-  Evidence for heavy flavor correlations
-  Next: Separate charm and bottom contribution as well as sub-processes (e.g. gluon splitting) using
- - dedicated simulations
- - charge-sign requirement on (e, D0) pairs

- electron-D0 azimuthal correlations

- D0+D0

*PDG mass*

*statistical  errors only*

- pTele>1.5 GeV/c

**p+p**** ********s****NN ****= 200 GeV, ********Ldt = 9 pb****-1**

**STAR nucl-exp 0705.2089**

- 2007 RHIC&AGS Annual Users' Meeting

## Mid-Term Upgrades at RHIC

**Detector Upgrades** relevant for heavy flavor physics

| Particle identification | improved electron PID
improved PID range for charm decay daughters   | STAR
Full barrel ToF
Barrel  Detector  |
| --- | --- | --- |
| Displaced vertex detection | direct open charm and bottom measurements | STAR high precision vertex tracking    HFT (Silicon pixel & strip layers) |
| Increased rate and acceptance | larger open heavy flavor yields | STAR:
New TPC Readout Electronics
DAQ upgrade |

**Machine Upgrade** (RHIC-II):Increased luminosity (x 40) via electron cooling

- See Z.Xu talk on STAR upgrades

- 2007 RHIC&AGS Annual Users' Meeting

## HFT Direct Charm Measurements

| pT (GeV/c) | pT (GeV/c) | #  of Events 
(p + p) | # of Events 
0-10% Au + Au
(Nbin = 950) | # of Events
0-80% Au + Au
(Nbin = 290) |
| --- | --- | --- | --- | --- |
| 1.0 | 0.5 | 44  106 | 0.45 × 106 | 1.75 × 106 |
| 2.0 | 0.5 | 70 × 106 | 0.45 × 106 | 1.75 × 106 |
| 3.5 | 1.0 | 70 × 106 | 0.45 × 106 | 1.75 × 106 |
| 5.5 | 1.0 | 350 × 106 | 0.75 × 106 |   3 × 106 |
| 7.5 | 1.0 | 1200 × 106 | 3.5 × 106 | 11 × 106 |
| 10.5 | 1.5 | 7500 × 106 | 9 × 106 | 30 × 106 |

| pT (GeV/c) | pT (GeV/c) | # of Events
qc does flow | # of Events
qc does not flow |
| --- | --- | --- | --- |
| 0.6 | 0.2 | 260 × 106 | 525 × 106 |
| 1.0 | 0.5 |   70 × 106 | 140 × 106 |
| 2.0 | 0.5 |   53 × 106 | 125 × 106 |
| 3.0 | 1.0 | 105 × 106 | 175 × 106 |
| 5.0 | 1.0 | 210 × 106 | 440 × 106 |

- Spectra vs pT at 10% error

- Elliptic flow v2 vs pT at 10% error

- Current data rate: 100x106 per run
- DAQ1000: x10 rate

- 2007 RHIC&AGS Annual Users' Meeting

## Open bottom 

-  possible with displaced vertex measurement and RHIC II luminosity
-  enough for measurement of cross section and RAA ~ pT,y
-  not enough for v2 measurement

- B-> J/psi+X

- 12 weeks run; HFT in; D assumes 100Hz min.bias rate

- 2007 RHIC&AGS Annual Users' Meeting

## Conclusions and considerations

**Heavy flavor** is an **important** tool to understand HI physics **at RHIC**
- First RHIC results are **interesting** and challenging
- Large **differences** in cross section between **Phenix** and **STAR**
**Binary scaling** in charm production
- Why so much **suppression** at high-pT?
- Charm and bottom **relative production**. Where bottom starts dominating?
- First attempts from STAR indicates a non-zero **contribution of bottom** to the non-photonic electron spectra
- First observation of **heavy flavor correlations**
- Very first step on the understanding of **heavy quark energy loss**
**RHIC II** higher-luminosities and detector upgrades
-  more **precise** measurements of **charm**
-  direct **access** to **bottom** physics

- 2007 RHIC&AGS Annual Users' Meeting

## Conversion from dN/dy to Cross-Section

**p+p inelastic cross section**

**conversion to full rapidity**

**ratio from e****+****e****-**** collider data**

**number of binary collisions**

***Systematic error measurement for  dN/dy in progress.**

- 2007 RHIC&AGS Annual Users' Meeting

## Muon measurement

**TPC+TOF**

-   There are no photonic muons !!!
-    **p****T**** 0.16-0.26 GeV/c**
-    it is good that it is so low pT

- 2007 RHIC&AGS Annual Users' Meeting

## RAA from d+Au to central Au+Au

- RAA from d+Au to central Au+Au

- Nuclear modification factor

-  Phys. Rev. Lett. **98 **(2007) 192301

- 2007 RHIC&AGS Annual Users' Meeting

## Electron RAA Radiative energy loss (c+b)

** ****Radiative energy**** **loss alone
-    in medium with reasonable
-    parameters** ****does not describe**** **
**   **the data** **

**    ****Djordjevic, Phys. Lett. B632 81 (2006)**

**Armesto, Phys. Lett. B637 362 (2006)**

** ****What are the other sources**
**   ****of energy loss ?**** **

-  parameters of medium in
-    models extracted from hadron data

- 2007 RHIC&AGS Annual Users' Meeting

## Role of collisional energy loss

**Wicks, nucl-th/0512076**
**van Hess, Phys. Rev. C73 034913 (2006)              **

-  **Collisional**/elastic **energy loss** may
-    be **important** for heavy quarks
-  Still not good agreement at high-pT

- 2007 RHIC&AGS Annual Users' Meeting

## Charm alone?

-  Since the suppression of
-    b quark electrons is  smaller

-  **charm alone agrees better**

-  **What is b contribution?**

- 2007 RHIC&AGS Annual Users' Meeting

## In medium fragmentation

**Adil and Vitev, **Phys.Lett.B649 (2007) 139

-  **Other effects** may contribute to the
-    observed suppression
-  both **b+c** taken into account

-  heavy quarks can **fragment **
**inside the medium** and can
- be suppressed by **dissociation**

- 2007 RHIC&AGS Annual Users' Meeting

## Uncertainty of c/b relative contribution

** ****FONLL:**
**   ****Large uncertainty**** on c/b crossing**
**    ****3 to 9 GeV/c**

**  ****Beauty ****predicted**** to be significant**** above ****4-5 GeV/c**

- 2007 RHIC&AGS Annual Users' Meeting

## Electron ID in STAR – EMC

**TPC:**** dE/dx for p > 1.5 GeV/c**
**Only primary tracks **
**           ****(reduces effective radiation length)**
**Electrons can be discriminated well from hadrons up to 8 GeV/c**
**Allows to determine the remaining hadron contamination after EMC**
**EMC****:**
**Tower E  ⇒ p/E~1 for e****-**
**Shower Max Detector**** **
**Hadrons/Electron shower develop different shape**
-   **85-90% purity of electrons **
**                     ****(p****T**** dependent)**
** **

- all

- p>1.5 GeV/c2

- p/E

- SMD

- 2007 RHIC&AGS Annual Users' Meeting

## Photonic electrons background

-  **Background**: **Mainly from ******** conv and **************** Dalitz **
** ****Rejection strategy:**
**     **For _every electron candidate  _
-   Combinations with all TPC
-     electron candidates
-    Me+e-<0.14 GeV/c2    flagged *photonic*
-   Correct for primary electrons
-     misidentified as background
-   Correct for background rejection efficiency
-      ~50-60% for central Au+Au

- 2007 RHIC&AGS Annual Users' Meeting