# Presentation: 735561

## Heavy Quark Energy Loss

- William Horowitz
- Columbia University
- June 6, 2006

- With many thanks to Simon Wicks, Azfar Adil, Miklos Gyulassy, Magdalena Djordjevic, and Brian Cole

- Simon Wicks

- Azfar Adil

## RAA()=RAA(1+2v2Cos(2)+...)

- Glue and Lights

- Charm and Bottom

- Correlations of back-to-back jets, etc.

## Jets as a Tomographic Probe

- Tomography requires precision measurements AND precision, pQCD theory

- Probe the unknown QGP with energy loss

- Quark or Glue Jet probes:
-     (, pT,  - reac, MQ) init

- Hadron jet fragments:
-      (, pT,  – reac ) final

## Jets as a Tomographic Probe (cont’d)

- to understand the medium

***If*** pQCD makes the correct predictions, we can use

- Otherwise, jet suppression is just another non-perturbative anomaly of ***A+A*** collisions (like J/ suppression)

## Before the e- RAA, the picture looked pretty good:

- Null Control: RAA()~1

- Consistency: RAA()~RAA()

- GLV Prediction: Theory~Data for reasonable fixed L~5 fm and dNg/dy~dN/dy

- Y. Akiba *for the PHENIX collaboration*, hep-ex/0510008

## But with Hints of Trouble:

- Theory v2 too small

- Fragile Probe?

- A. Drees, H. Feng, and J. Jia, Phys. Rev. **C71**:034909 (2005)
- (first by E. Shuryak, Phys. Rev. **C66**:027902 (2002))

- K. J. Eskola, H. Honkanen, C. A. Salgado, and U. A. Wiedemann, Nucl. Phys. **A747**:511:529 (2005)

## What Can Heavies Teach Us?

- Provide a unique test of our understanding of energy loss
- Mass => Dead Cone => Reduction in E loss

- Bottom Quark

- =

- (Gratuitous Pop Culture Reference)

##    Entropy-constrained radiative-dominated loss FALSIFIED by e- RAA

- Problem: Qualitatively,  RAA~ ***e******-*** RAA

## Inherent Uncertainties in Production Spectra 

- M. Djordjevic, M. Gyulassy, R. Vogt, S. Wicks, Phys. Lett. **B632**:81-86 (2006)

- How large is bottom’s role?

- Vertex detectors could de-convolute the ***e***- contributions

- N. Armesto, M. Cacciari, A. Dainese, C. A. Salgado, U. A. Wiedemann, hep-ph-0511257

## The BDMPS-Z-WS Approach

- Increase    to 14 to push curve down

- Fragility in the model allows for consistency with pions

- N. Armesto, M. Cacciari, A. Dainese, C. A. Salgado, U. A. Wiedemann, hep-ph-0511257

## What Does             Mean?

- We believe it’s nonperturbative:
-   = .5 => dNg/dy ~ 13,000

- R. Baier, Nucl. Phys. **A715**:209-218 (2003)

- “Proportionality constant ~ 4-5 times larger than perturbative estimate”

- K. J. Eskola, H. Honkanen, C. A. Salgado, and U. A. Wiedemann, Nucl. Phys. **A747**:511:529 (2005)

- “Large numerical value of 	not yet understood”

- U. A. Wiedemann, SQM 2006

## Is this Plausible?  Maybe

- Flow nonperturbative at low-pT
- v2 possibly nonperturbative at mid-pT
- Asymptotic Freedom MUST occur
- But at what momentum?

- WH, nucl-th/0511052

- D. Winter, QM2005

## But what if we Neglected an Important Effect?

- M. Mustafa, Phys. Rev. **C72**:014905 (2005)                          S. Wicks, WH, M. Gyulassy, and M. Djordjevic, nucl-th/0512076

## Elastic History

- J. D. Bjorken, FERMILAB-PUB-82-059-THY (Quantal)
- M. H. Thoma and M. Gyulassy, Nucl. Phys. **B351**:491-506 (1991) (Classical)
- E. Braaten and M. H. Thoma, Phys. Rev. **D24**:2625-2630 (1991) (Quantal)
- P. Romatschke and M. Strickland, Phys. Rev. **D71**:125008 (2005) (Quantal)

-    People have thought about Elastic Loss for a long time, and in different ways—all assume parton starts in asymptotic past

- Bottom				       Charm

-    Most correct (infinite time) elastic loss calculation approximately bounded by BT and TG curves

## Include Path Length Fluctuations with Realistic Geometry

- For fixed ***L***~5 fm, Collisional+Radiative leads to pion overquenching
- Use Woods-Saxon density
- hard production ~ ***T******AA***
- medium ~ *******participant*
- This allows a self-
- 	consistent pion prediction
-    without “fixed ***L***”approx

- S. Wicks, WH, M. Gyulassy, and M. Djordjevic, nucl-th/0512076

## Our Extended Theory

- Convolve Elastic with Inelastic energy loss fluctuations
- Include path length fluctuations in diffuse nuclear geometry
- Separate calculations with BT and TG collisional formulae provide a measure of the elastic theoretical uncertainty

## Conservative Results

- S. Wicks, WH, M. Gyulassy, and M. Djordjevic, nucl-th/0512076

- Elastic loss improves quench
- keeping
-    dNg/dy	= 1000
-              s	= .3
-  and No change in c or b production cross sections
- Extended Theory is consistent with data for pT > 7 GeV

## Consistency Test with Pions

- 	Not flat, which requires a balance of many competing effects (Cronin, EMC, etc.) but not at odds with data

- S. Wicks, WH, M. Gyulassy, and M. Djordjevic, nucl-th/0512076

## El+Rad+Geom NOT a Fragile Probe

- Why? First, experimental error bars have shrunk considerably since 2004.  Second, ***el*** < *rad*

- WH, S. Wicks, M. Gyulassy, M. Djordjevic, *in preparation*

## Why Widths are Vital

- The whole distribution is important:
- 				         , but ***el*** < *rad*

- S. Wicks, WH, M. Gyulassy, and M. Djordjevic, nucl-th/0512076

## Elastic Objections

- All derivations start parton at asymptotic past: are there formation time effects?
- Peigne ***et al***. (Classical):
- This is unintuitive: one expects effects to disappear by ***L ***~*** 1/******D*** ~ .5 fm, the screening scale; but perhaps there is a hidden  factor
- What about interference effects?

- S. Peigne, P.-B. Gossiaux, and T. Gousset, JHEP0604:011 (2006)

- They claim NO elastic loss until ***L*** > 10 fm!

## Adil et al. Classical Refutation of Peigne et al.

- Two issues:
- Peigne *et al.* do not disentangle known radiative effects
- small

-  Peigne *et al.* neglect a term in

- their classical current, thereby

- violating current conservation

- and resulting in a spurious

- A. Adil, M. Gyulassy, WH, and S. Wicks, nucl-th/0606010

- subtraction of the (negative) binding energy of the quark-antiquark pair
- HUGE

## Classical Finite Time Results

- A. Adil, M. Gyulassy, WH, and S. Wicks, nucl-th/0606010

- By ***L*** ~ 1/D, stable field reaches ~ 90% of the asymptotic

- 10 GeV Charm

- 10 GeV Charm

## Quantal Finite Time Results

- Again, formation effects negligible beyond 1/D

- X. N. Wang, nucl-th/0604040

- M. Djordjevic, nucl-th/0603066

- No one as yet fully combines El+Rad with interference

## Heavy Quark Tomography of the LHC 

- Additional systematic tests of the energy loss theory
- 2-3 times RHIC medium densities
- Enormous pT range
- At very high momenta, GLV and BDMPS-Z-WS results converge, but elastic effects persist!

- WH, S. Wicks, M. Gyulassy, M. Djordjevic, *in preparation*

## LHC Predictions

- WH, S. Wicks, M. Gyulassy, M. Djordjevic, *in preparation*

## Conclusions

- Fantastic new RHIC data challenging, surprising
- Better understanding of heavy quark loss mechanisms, production critical for interpreting experimental results
- Large uncertainties in ratio of charm to bottom contribution to non-photonic electrons
- Direct measurement of ***D*** spectra would help separate the different charm and bottom jet dynamics
- FON_N_LL would provide better information on theoretical production error

## Conclusions (cont’d)

- BDMPS-Z-WS:
- IF extreme     is assumed
- IF elastic loss is assumed to vanish
- IF they assume fragility
- Then not inconsistent with data
- No hope for tomography

## Conclusions (cont’d)

- DGLV:
- Include elastic, inelastic, and path length fluctuations
- Consistent results for high-pT ***e***- RAA
- Pion RAA predictions agree well with data over large momentum range, are sensitive to changes in medium density, consistent with multiplicity constraints

## Conclusions (cont’d)

- Far from finished:
- Coherence and correlation effects between elastic and inelastic processes that occur in a finite time over multiple collisions must be sorted out
- Fixed  must be allowed to run; the size of the irreducible error due to integration over low, nonperturbative momenta, where  > .5, needs to be determined
- Where will ***e***- RAA data and theoretical calculations settle down as research progresses and error bars are reduced over time?

## Conclusions (cont’d)

- AMY: a third approach?
- Produced a pion RAA; no calculation of ***e***- RAA, a crucial consistency check
- The LHC will provide an excellent new testing ground for systematic study (falsification?) of energy loss theory
- Jet tomography is an elusive, but achievable goal

- P. Arnold, G.D. Moore, and L. Yaffe, JHEP **011**:057 (2001)
- S. Turbide, C. Gale, S. Jeon, G. D. Moore, Phys. Rev. **C72**:014906 (2005)

- Backup Slides

## WH, S. Wicks, M. Gyulassy, M. Djordjevic, in preparation

- WH, S. Wicks, M. Gyulassy, M. Djordjevic, *in preparation*

## S. Wicks, WH, M. Gyulassy, and M. Djordjevic, nucl-th/0512076

## WH, S. Wicks, M. Gyulassy, M. Djordjevic, in preparation

- WH, S. Wicks, M. Gyulassy, M. Djordjevic, *in preparation*

## WH, S. Wicks, M. Gyulassy, M. Djordjevic, in preparation

## WH, S. Wicks, M. Gyulassy, M. Djordjevic, in preparation

- WH, S. Wicks, M. Gyulassy, M. Djordjevic, *in preparation*

## K. J. Eskola, H. Honkanen, C. A. Salgado, and U. A. Wiedemann, Nucl. Phys. A747:511:529 (2005)

- A. Dainese, C. Loizides, G. Paic, Eur. Phys. J. **C38**:461-474 (2005)

## N. Armesto, M. Cacciari, A. Dainese, C. A. Salgado, U. A. Wiedemann, hep-ph-0511257

- A. Dainese, C. Loizides, G. Paic, Eur. Phys. J. **C38**:461-474 (2005)

## A. Dainese, C. Loizides, G. Paic, Eur. Phys. J. C38:461-474 (2005)

- A. Dainese, C. Loizides, G. Paic, Eur. Phys. J. **C38**:461-474 (2005)

## S. Wicks, WH, M. Gyulassy, and M. Djordjevic, nucl-th/0512076