# Presentation: 102163

## Hard probes at RHIC and LHC 

**Magdalena Djordjevic**
**Ohio State University**

## Is the QGP already discovered at RHIC? 

** ****Jet Quenching**** of light partons ****strongly ****suggest that ****QGP is discovered****. **
** ****Further tests of jet tomography using ****heavy quarks**** could be ****decisive**** as a complementary test of the theory.**

**However, single electron measurements are available.**

**Is the QGP *****already***** discovered at RHIC?**** **

**Heavy ion physics has a goal to form and observe a QGP.**

**Heavy mesons not yet measured at RHIC.**

## Single electron suppression measurements at RHIC

**Significant reduction at high pT suggest sizable energy loss!**

**Single electron suppression measurements at RHIC**

**V. Greene, S. Butsyk, QM2005 talks**

**J. Dunlop, J. Bielcik; QM05 talks**

**Can this be explained by the energy loss in QGP? **

## Slide 4

## Single electron suppression

**2) Heavy quark energy loss**
**3) c and b fragmentation functions into D, B mesons **
**4) Decay of heavy mesons to single e****-****.**

**D, B**

**1)**
**production**

**2)**
**medium energy loss**

**3)**
**fragmentation**

**Single electron suppression**

**e****-**

**4)**
**decay**

**To make theoretical predictions for heavy meson and single electron suppression we generalized the GLV method (****PLB538:282,2002****). **

## Initial heavy quark pt distributions

**Parameters values from R.Vogt, Int.J.Mod.Phys.E 12,211(2003).**

**Initial heavy quark pt distributions**

## Radiative heavy quark energy loss 

**Thre****e important medium effects**** control the radiative energy loss:**** **
**Ter-Mikayelian effect ****(M. D. and M. Gyulassy, Phys. Rev. C 68, 034914 (2003))**** **
**Transition radiation ****(M. D., to be published).**** **
**Energy loss due to the interaction with the medium                  ****(M. D. and M. Gyulassy, Phys. Lett. B 560, 37 (2003); Nucl. Phys. A 733, 265 (2004))**

**                    ****1)                                         2)                                         3)**

## Energy loss due to the interaction with the medium

**Energy loss due to the interaction with the medium**

**To compute medium induced radiative energy loss for heavy quarks we generalize GLV method, by introducing both quark *****M***** and gluon mass *****m******g******.***

**Caused by the multiple interactions of partons in the medium.**

## This leads to the computation of the fallowing types of diagrams:

**To compute energy loss to all orders in opacity we ****use algebraic recursive**** method described in ****(****GLV,Nucl.Phys.B594(01)****).**** **

## Final Result to Arbitrary Order in Opacity (L/)n

**Final Result to Arbitrary Order in Opacity (L/********)****n**
** ****M****Q ****and m****g****  > 0**

**Hard, Gunion-Bertsch, and Cascade ampl. in GLV generalized to finite M**

**Generalizes GLV  M****Q**** = m****g **** =0  ****(Nucl. Phys. B 594, 2001)**** **

## The numerical results for induced radiative energy loss are shown for first order in opacity, for L= 5 fm, =1 fm. 

**The numerical results for induced radiative energy loss are shown for first order in opacity, for L= 5 fm, ********=1**** ****fm. **

**For 10 GeV ****heavy quark**** (c, b) jet, thickness dependence is closer to ****linear**** Bethe-Heitler like form L****1****. This is different than the asymptotic energy ****quadratic form**** characteristic for ****light quarks****.****  **

## Quantitative “dead cone effect” for the heavy quark energy loss

**light**

**Quantitative ****“dead cone effect”**** for the heavy quark energy loss**

## RHIC

**RHIC**

**LHC**

**As the jet energy increases, the dead cone effect becomes less important.**

## The numerical results can be understood from:

**The numerical results can be understood from:**

**1****st**** order energy loss can ****not ****be characterized only by a “Dead-cone” effect!**

**LPM**** effects are ****smaller**** for ****heavy**** than for light quarks!**

**Results confirmed by two independent groups:                                                               ****B. W. Zhang, E. Wang and X. N. Wang, ****Phys.Rev.Lett.93:072301,2004;****                           N. Armesto, C. A. Salgado, U. A. Wiedemann, ****Phys.Rev.D69:114003,2004. **

## Pt distributions of charm and bottom before and after quenching at RHIC

**M. D., M. Gyulassy and S. Wicks, Phys. Rev. Lett. 94, 112301 (2005); Euro Phys. J C, in press (2005).**

**Pt distributions of charm and bottom before and after quenching at RHIC**

## Heavy quark suppression as a function of pt 

**(M. D., M. Gyulassy and S. Wicks, Phys. Rev. Lett. 94, 112301 (2005);Euro Phys. J C, press)**

**Moderate D meson**** ****suppression ~ 0.5********0.1**** ****at RHIC.**** **

## Single electrons pt distributions before and after quenching at RHIC

**Panels show ****single e****-**** from ****FONLL**** ****(done by R. Vogt).****                                                                ****(M. D., M. Gyulassy, R. Vogt and S. Wicks, nucl-th/0507019, to appear Phys. Lett. B (2005)) **

**Single electrons pt distributions before and after quenching at RHIC**

**Before quenching**

**After quenching**

**Bottom dominate**** the single**** e****-**** ****spectrum after**** 4.5 GeV****!**

## Domination of bottom in single electron spectra 

**The ratio of charm to bottom decays to electrons obtained by varying the quark mass and scale factors. **

**Domination of bottom in single electron spectra **

**Plot done by Simon Wicks.**

## Single electron suppression as a function of pt 

**Single electron suppression as a function of pt**

**red curves****: b********e;****  ****blue curves****: c********e;**** black curves****: b+c********e;**** **

## Comparison with single electron data

**Comparison with single electron data**

**Disagreement**** with PHENIX preliminary data!**

## How can we solve the problem?

**How can we solve the problem?**

**Reasonable agreement, but the dN****g****/dy=3500 is ****not physical****! **

## Are there other energy loss mechanisms?

**Elastic v.s. radiative energy loss:**

**Are there other energy loss mechanisms?**

**Elastic and radiative energy losses are comparable!**

**(see M. G. Mustafa, Phys.Rev.C72:014905,2005)**

## Heavy quark suppression with the elastic energy loss 

**Heavy quark suppression with the elastic energy loss**

**The elastic energy loss significantly changes the charm and bottom suppression!**

**CHARM**

**BOTTOM**

**Plots done by Simon Wicks.**

## Single electron suppression with the elastic energy loss 

**Reasonable agreement with single electron data, even for dN****g****/dy=1000.**

**(S. Wicks, W. Horowitz, M.D. and M. Gyulassy, in preparation.)**

**However, overprediction of pion suppression results happens.**** ****Solution:**** Include the ****geometrical fluctuations**** (see M. Gyulassy’s talk).**

**Include elastic energy loss**

**Plot done by Simon Wicks.**

## Elastic v.s. radiative energy loss: 

**Radiative energy loss dominates at high pt!**

**Is the elastic energy loss important at LHC?**

## Conclusions

** ****We applied the theory of heavy quark energy loss to compute heavy meson and single electron suppression.**
**We show that bottom quark contribution can not be neglected in the computation of single electron spectra.**
** **
**The recent single electron data show significant discrepancies with theoretical predictions based only on radiative energy loss.**** **
**However, inclusion of the elastic energy loss may lead to    the agreement with experimental results. **

## Acknowledgements:

**Miklos Gyulassy**
**(Columbia University)**
**Ramona Vogt**
**(LBNL, Berkeley and University of California, Davis)**
**Simon Wicks**
**(Columbia University)**