# Presentation: 302227

## The Quenching of BeautyLast Hope for a Grey Probe of the QGP

- James Dunlop
- Brookhaven National Laboratory

- Heavy Quark Workshop, Berkeley

- 11/1/2007

## The Promise of Jet Tomography

- Simplest way to establish the properties of a system
- Calibrated probe
- Calibrated interaction
- Suppression pattern tells about density profile
- Heavy ion collisions
- Hard processes serve as calibrated probe
- Suppression provides density measure

- +

- =

- Heavy Quark Workshop, Berkeley

- 11/1/2007

## The Limitations of RAA: “Fragility”

- The Limitations of RAA: “Fragility”

- Surface bias leads effectively to saturation of RAA with density
- Challenge: Increase sensitivity to the density of the medium

***K.J. Eskola, H. Honkanken, C.A. Salgado, U.A. Wiedemann, Nucl. Phys. A747 (2005) 511***

***A. Dainese, C. Loizides, G. Paic, Eur. Phys. J. C38(2005) 461 ***

- Heavy Quark Workshop, Berkeley

- 11/1/2007

## Black and White

- Medium extremely black to hadrons, limiting sensitivity to density
- Medium transparent to photons (white): no sensitivity
- Is there something grey?

***S.S. Adler et al, Phys. Rev. Lett. 94, 232301 (2005)***

- Heavy Quark Workshop, Berkeley

- 11/1/2007

## Calibrated Interaction? Grey Probes

- Problem: interaction with the medium so strong that information lost: “Black”
- Significant differences between predicted RAA, depending on the probe
- Experimental possibility: recover sensitivity to the properties of the medium by varying the probe

***Wicks et al, Nucl. Phys. A784 (2007) 426***

- Heavy Quark Workshop, Berkeley

- 11/1/2007

## Gluons vs Quarks: Method

**q jets or g jets**  **gluon jet contribution to protons is significantly larger than to pions at high p****T**** in p+p collisions at RHIC; pbar/******** < 0.1 from quark jet fragmentation at low beam energy .**** **STAR Collaboration, PLB 637, 161 (2006).
**From Kretzer fragmentation function, the g/q jet contribution is similar to AKK.** S. Kretzer, PRD 62, 054001 (2000).

- Heavy Quark Workshop, Berkeley

- 11/1/2007

## Gluons vs. Quarks: No shade of gray

- Gluons should lose more energy than quarks
- Pions have larger quark contribution than protons
- SO, Protons should be more suppressed than pions
- Experimentally NOT observed: equal suppression for pT>6 GeV/c
- Perhaps: If medium already black to quarks, can’t be blacker than black
- Other methods to be tried: kinematics in  (as done in e.g. dijet Sivers)

- gluon  jet

- quark  jet

- quark  jet

- STAR Collaboration, PRL 97 (152301) 2006

- Heavy Quark Workshop, Berkeley

- 11/1/2007

## Charm/Beauty: No shade of gray

- Unexpectedly strong suppression of non-photonic electrons a major issue
- Calls into question the calibration of the interaction of the probe with the medium
- Uncertainties in B contribution: need to measure c and b separately

*STAR,  PRL 98 (2007) 192301**	*

*PHENIX, PRL 98 (2007) 172301*

- Heavy Quark Workshop, Berkeley

- 11/1/2007

## Mechanisms for Energy Loss

- QED: different momenta, different mechanisms
- Just beginning the exploration of this space in QCD

- Bremsstrahlung
- Radiative dE/dx

- “Passage of Particles through Matter”, Particle Data Book

- Heavy Quark Workshop, Berkeley

- 11/1/2007

## Calibrated Probe?  Electrons in p+p

- Large uncertainties in non-photonic electrons, even in p+p
- STAR and PHENIX factor of 2 discrepancy in measurements
-  STAR: runs 8 and 9 low material (same as PHENIX), PHENIX...?
- Theoretical uncertainties, esp. in b vs. c contribution
- Need to measure c and b separately, in all systems, with precision

- Crossing from c to b:
- anywhere from 3-10 GeV

*STAR,  PRL 98 (2007) 192301**	*

- b

- c

- Heavy Quark Workshop, Berkeley

- 11/1/2007

## Correlations

- WMAP: 10-5 level
- One sample
- Only photons
- Well-defined separation of sources

- RHIC: 10-1 to 10-3 level
- Multiple samples
- Multiple probes
- Model dependence in separation of sources
- quite a few “two-component” models, with different components

- Heavy Quark Workshop, Berkeley

- 11/1/2007

## Heavy Flavor Correlations

- Isolate b from c
- Isolate production mechanism
- In medium: what is losing energy, and how much?

- gluon splitting/fragmentation

- 0

- 

- Flavor creation

- Heavy Quark Workshop, Berkeley

- 11/1/2007

## Correlations: 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)
- There is more information from correlations that is not currently being used (momentum, charge, etc.)

*Xiaoyan Lin, QM2006*

- Heavy Quark Workshop, Berkeley

- 11/1/2007

## B contribution to NP electrons vs. pT

**p+p 200 GeV**

- B contribution to NP electrons vs. pT

- Fit e-h correlation with PYTHIA Ds and Bs
**Non-zero B contribution**
- Contribution consistent with FONLL
**Model dependent (PYTHIA)**
**Depends mainly on kinematics of D/B decay (not Fragmentation)**
- Dominant systematic uncertainty:
- photonic background rejection efficiency
- Additional uncertainties under study
- There is more information from correlations that is not currently being used

*Xiaoyan Lin, QM2006*

- Heavy Quark Workshop, Berkeley

- 11/1/2007

## Future at RHIC: “RHIC II” or the fb era

- RHIC: luminosity + upgraded detectors for precision
- Beauty: last hope for a “grey” probe; needs detector upgrades to both STAR and PHENIX to isolate from charm
-  -jet: precision probe of energy loss
- Upsilon: precision tests of Debye screening with a “standard candle”

- Previous Au Run, year 4

- STAR HFT

- PHENIX VTX

- Current Au Run, year 7

- One year at RHIC II ~ 30 nb-1
- 30 nb-1*1972 =~ 1 fb-1 p+p equivalent

- Heavy Quark Workshop, Berkeley

- 11/1/2007

## Grey Correlations: Heavy Flavor in the fb era

- Identified heavy flavor correlations: promising, but statistical power still low
- RHIC II: many orders of magnitude (>~x1000 with luminosity, S/B improvements)

- Light Hadrons

- Heavy flavor

- Inclusive Spectra

- Correlations

- From 5 pb-1

- Heavy Quark Workshop, Berkeley

- 11/1/2007

## Quarkonium: Upsilon

- Sequential dissociation of quarkonia to measure energy density of plasma
- Requires full luminosity of RHIC II for definitive measurements

**RHIC**

- Proof of principle measurement: run 6 p+p

- Upsilon(1S+2S+3S)→e+e-

- Heavy Quark Workshop, Berkeley

- 11/1/2007

## Other initiatives: Muons and dileptons

- Muon Tracking Detector: use magnet steel as absorber
**Physics: dileptons from intermediate mass up to quarkonia states**
**Best method for separating Upsilon states (a la CDF)**
**R+D stage: Brookhaven LDRD 2007-2008**
- Dielectrons using TOF for ID and HFT for background rejection

- Heavy Quark Workshop, Berkeley

- 11/1/2007

## Conclusion

- Watershed in coming years from RHIC II luminosity and detector upgrades
- Precision studies with , b, c, and associated multi-hadron correlations
- IF beauty is less suppressed than other parton species, we will be able to probe the properties of the QGP with exquisite precision

*Idunn’s Apples of Youth, D’Alair’s Book of Norse Mythology*

- Is Beauty Grey?

- We need more apples to tell

- Heavy Quark Workshop, Berkeley

- 11/1/2007