11/1/06william horowitz 1 jet quenching at rhic and the lhc william horowitz columbia university...

1

11/1/06 William Horowitz

Jet Quenching at RHIC and the LHC

William HorowitzColumbia UniversityNovember 1, 2006

With many thanks to Simon Wicks, Azfar Adil, Magdalena Djordjevic, and Miklos

Gyulassy.

2

11/1/06 William Horowitz

Outline

• What a difference the LHC makes!– HUGE disagreement over LHC

predictions– Why there’s a difference– Why we’re right (hopefully robustly)

• P0, P0, P0…

3

11/1/06 William Horowitz

LHC Predictions

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

4

11/1/06 William Horowitz

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)

BDMPS-Based Predictions

5

11/1/06 William Horowitz

Suppression of BDMPS– LHC predictions require an extrapolation from

RHIC• Their pQCD-based controlling parameter qhat must

be nonperturbatively large to fit RHIC data-pQCD gives qhat = c 3/4, where c ~ 2; they require c ~ 8-20 for RHIC

-Needed because radiative only energy loss (and Pg0 > 1?); R = (1/2) qhat L3

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

6

11/1/06 William Horowitz

BDMPS Extrapolation to the LHC

• Importance of medium density– qhat ~ scatterers

– EKRT used => LHC ~ 7 RHIC

– qhat goes from 14 at RHIC to 100 at the LHC!

– Almost all the energy loss is in (-1) part of P()

7

11/1/06 William HorowitzWH, S. Wicks, M. Gyulassy, M. Djordjevic, in preparation

Asymptopia at the LHCAsymptotic pocket formulae:Erad/E 3 Log(E/2L)/EEel/E 2 Log((E T)1/2/mg)/E

8

11/1/06 William Horowitz

LHC Production Spectra

• Much flatter power law and asymptotic jet energies allows for easy interpretation of LHC predictions

9

11/1/06 William Horowitz

LHC Conclusions• LHC appears to reach jet

asymptopia where pocket formulae hold

• Lack of fragility means pions will make a good, independent probe of the density

• With current predictions, the momentum dependence of RAA at LHC should distinguish between BDMPS and GLV type loss models

10

11/1/06 William Horowitz

A Quick Update on Fragility

11

11/1/06 William Horowitz

Jets as a Tomographic Probe

• Requires:– Theoretical understanding of

underlying physics (esp. quenching mechanisms)

– Mapping from the controlling parameter of the theory to the medium density

– Sensitivity in the model + data for the measurement used (FRAGILITY???)

12

11/1/06 William Horowitz

Recall the BDMPS-based Plots

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)

The lack of sensitivity needs to be more closely examined because (a) unrealistic geometry (hard cylinders) and no expansion and (b) no expansion shown against older data (whose error bars have subsequently shrunk

(a) (b)

13

11/1/06 William Horowitz

Our Jets Probe the Volume and are Sensitive to the Medium

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

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

14

11/1/06 William Horowitz

BDMPS with Realistic Geometryis Not Fragile!

T. Renk and K. J. Eskola, hep-ph/0610059

15

11/1/06 William Horowitz

Heavy Quark Puzzle

16

11/1/06 William Horowitz

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

17

11/1/06 William Horowitz

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)

18

11/1/06 William Horowitz

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)

19

11/1/06 William Horowitz

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

Problem: Qualitatively, RAA~ e- RAA

20

11/1/06 William Horowitz

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

21

11/1/06 William Horowitz

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

22

11/1/06 William Horowitz

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

23

11/1/06 William Horowitz

Is this Plausible?Renk says No

T. Renk and K. J. Eskola, hep-ph/0610059

24

11/1/06 William Horowitz

Our Results

• Inclusion of elastic decreases the discrepancy

• Direct c and b measurements required to truly rule out approaches

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

25

11/1/06 William Horowitz

LHC Predictions for Heavies

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

26

11/1/06 William Horowitz

Conclusions III

– Elastic loss cannot be neglected when considering pQCD jet quenching• 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

– 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

27

11/1/06 William Horowitz

Backup Slides

28

11/1/06 William Horowitz

Our Extended Theory

• Convolve Elastic with Inelastic energy loss fluctuations

• Include path length fluctuations in diffuse nuclear geometry with 1+1D Bjorken expansion

29

11/1/06 William Horowitz

Significance of Nuclear Profile

• Simpler densities create a surface biasHard Cylinder Hard Sphere Woods-Saxon

Illustrative Only! Toy model for purely geometric radiative loss from Drees, Feng, Jia, Phys. Rev. C.71:034909

30

11/1/06 William Horowitz

– Null Control: RAA()~1

– Consistency: RAA()~RAA()

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

31

11/1/06 William Horowitz

Elastic Can’t be Neglected!

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

32

11/1/06 William Horowitz

Length Definitions– Define a mapping from the line integral

through the realistic medium to the theoretical block

– where

– Then

33

11/1/06 William Horowitz

Geometry Can’t be Neglected!

• P(L) is a wide distribution– Flavor

independent

• Flavor dependent fixed length approximations LQ’s not a priori obvious

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

11/1/06 William Horowitz

Comparison to Vitev

35

11/1/06 William Horowitz

Increasing dNg/dy

36

11/1/06 William Horowitz

Our Extended Theory

• Convolve Elastic with Inelastic energy loss fluctuations

• Include path length fluctuations in diffuse nuclear geometry with 1+1D Bjorken expansion

• Separate calculations with BT and TG collisional formulae provide a measure of the elastic theoretical uncertainty

37

11/1/06 William Horowitz

• Qhat = c eps^3/4 \propto rho (density of scattering centers)

• pQCD=> c~=2• To fit RHIC, c ~ 8-20• Extend to LHC, everything crushed

to nothing

38

11/1/06 William Horowitz

BDMPS RHIC ’s

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)

Huge qhat needed!

(a) (b)

Note: fragility due to lack of Bjorken expansion