# Presentation: 793433

## Open heavy flavor in STAR

*Alex Suaide*
*University of S**ão Paulo*
*HQ workshop, Berkeley, 2007*

## Measuring heavy quarks in STAR

*Measuring heavy quarks in STAR*

- Hadronic reconstruction
- D0  K-  (c.c)
- B.R. (3.80 _+_ 0.07)%
- Ds+  +  K+ K- +
- B.R. (2.16 _+_ 0.28)%

- Semileptonic decays
- Nonphotonic electrons
- c  e+ + anything B.R.: 9.6%
- b  e+ + anything B.R.: 10.9%
- Muons
- c  + + anything B.R.: 9.5%

## D0 (hadronic)measurements in STAR

- Limited momentum range: pT < 3 GeV/c

## Ds+ and D+ (hadronic) reconstruction in STAR

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

-   No negatively charged D or Ds found yet

## Muons measurements

- Low-pT (pT < 0.25 GeV/c)
- ToF + TPC
- Important constrain of charm cross section measurement
- Background
- Separate different muon contributions using MC simulations:
- K and  decay
- DCA (distance of closest approach) distribution is very different

## Nonphotonic electrons

- Low-pT electrons
- pT < 4 - 5 GeV/c
- Important for cross section measurements
- TPC dE/dx + ToF
- High-pT electrons
- pT > 1.5 - 2.0 GeV/c
- Medium effects and correlations
- TPC + EMC

## Photonic background

- Non-zero amount of material in STAR
- Most of electrons are originated from sources other than heavy flavors
- e+ + e-
- e+ + e-
-  etc.
- STAR has the advantage of being capable of measuring the background despite the amount of material

## Photonic background

- Non-zero amount of material in STAR
- Most of electrons are originated from sources other than heavy flavors
- e+ + e-
- e+ + e-
-  etc.
- STAR has the advantage of being capable of measuring the background despite the amount of material

## Charm cross section

- Combined fit (where available) of D0, muons and electron spectra
- ~ 90% of kinematic range
- ~ 70% in the case of D0 alone

## Charm cross section

**PHENIX:**
**	****S. Adler, et al. Phys. Rev. Lett. 94 082301 (2005)**
**	****S. Adler, et al. Phys. Rev. Lett. 97 252002 (2005)**
- NLO Ref: R. Vogt, arXiv:0709.2531v1 [hep-ph]

**STAR:**
**C. Adler, et al. Phys. Rev. Lett. 91 172302 (2003)**
**Y. Zhang, arXiv:nucl-ex/0607011**

- FONLL underestimates measured
- cross-section by factor ~ 5
- But need to note uncertainties

## p + p reference

- Factor ~ 5 discrepancy with FONLL is present at high-pT
- The same as for the discrepancy with PHENIX
- Large uncertainties
- Relative production between charm and bottom

- STAR PRL 98 (2007) 192301

## Au + Au NPE spectra

## Medium effects:energy loss of heavy quarks

- Data show increasing suppression of NPE with centrality
- Suppression is as high as light hadrons in central Au+Au collisions
- Many open questions
- EL mechanisms
- Radiative, colisional, in medium dissociation, etc.
- Charm/bottom contribution

## Too many openquestions

*Too many open**questions*

## Using e - h correlations to evaluate bottom/charm

- Different decay kinematics between D and B mesons
- Near side e-h correlations will depend on kinematics
- Not much dependent on F.F.

## Procedure to obtain e-h correlations

**Semi-inclusive electron**

-  NPE = (semi-inclusive) + SameSign – (not-reco-photonic)
-  Advantage: Smaller overall uncertainties.
-  Each item has its own corresponding Δφ histogram.

*Procedure to obtain e-h correlations*

## NPE e-h correlations in p+p collisions

- Near side correlation dominated by kinematics

## Consistent values from different fit range

*Consistent values from different fit range*

## Charm and bottom contribution to NPE

- Data shows a non-zero contribution from bottom on NPE
- Very close to FONLL predictions
- Bottom suppression in Au+Au collisions!

## How to address B/D @ higher pT?

- Instead of looking at just one of the quarks, lets look at the full q-qbar pair!
- Use electron as trigger particle
- Reconstruct the D meson
- For c-cbar pairs D meson is in the away side

## Charm and bottomuse decayed Kaon to disentangle

*Charm and bottom**use decayed Kaon to disentangle*

- Bottom has
- near side D’ s

- We can use
- The Kaon charge
- As tool for
- discrimination

## Use e-D correlations to look for production mechanisms

*Use e-D correlations to look for **production mechanisms*

- The charged sign correlations can be used as discrimination between flavor creation and gluon splitting
- Need intensive simulations to understand relative contributions
- Pythia for LO processes
- MC@NLO for NLO
- FONLL not usable

****

*Flavor creation – LO process*

*Gluon splitting – NLO process*

******0**

## e - D0 correlations from Pythia3<pTtrg<7 GeV/c

- Same charge and opposite charge gives constrain on D/B contributions
- This pTtrg probes the about same pT range of D and B mesons

## Reconstructing D0 mesons

- Calculate K invariant mass
- Background using like sign
- No D0 signal without electron trigger
- Clear signal with electron trigger
- S/B ~ 1/7
- 100 times better than inclusive analysis

## e - D0 correlations in 200 GeV p + p collisions

*statistical errors only*

- like-sign (e,K) pairs:
- (e- - D0) + (e+ -D0)

- How to learn about production mechanisms and B/D contribution?

## Comparing data to Pythia

*Comparing data to Pythia*

- Away-side yield for unlike-sign (e,K) pairs is essentially from B decays
- Scale PYTHIA distribution to fit measured away-side yield
- Compare near-side yield from scaled PYTHIA distribution for like-sign (e,K) pairs to data
- Difference is expected to come from gluon splitting
- Compare away-side yield from scaled PYTHIA distribution for like-sign (e,K) pairs to data
- Disentangle charm and beauty contribution

## B/D contribution and FONLL prediction

- Same charge e-K pairs
- Comparison with Pythia yields about 30% of charm and 70% of bottom in this pTtrg range
- Compatible with FONLL
- More statistics needed
- Better error bars
- Higher pT

## Gluon splitting mechanism

-  Remarkable agreement of the away-side peak shape between PYTHIA and MC@NLO
-  Indications for small gluon-splitting contribution (~310-4)
-  More statistics needed for final conclusions

-  Near-side yield for _like-sign (e,K) pairs_
-  yielddata ~ 0.011 0.0046
-  yieldPYTHIA (scaled) = 0.0096
-  Difference is attributed to gluon splitting

*Gluon splitting mechanism*

## Conclusions

*Conclusions*

## Some final considerations

*Some final **considerations*

## Extras

## Conversion from dN/dy to Cross-Section

**p+p inelastic cross section**

**conversion to full rapidity**
**(using PYTHIA simulation, ver. 6.152)**

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

**number of binary collisions**

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