1

Heavy Quark Energy Heavy Quark Energy LossLoss

Tatia EngelmoreTatia Engelmore

Journal Club 7/21Journal Club 7/21

2

Types of Energy LossTypes of Energy Loss

RadiativeRadiative Fast partons interact in a color field, Fast partons interact in a color field,

radiate gluonsradiate gluons CollisionalCollisional

Elastic Scattering of partons off other Elastic Scattering of partons off other partons in the mediumpartons in the medium

Initially radiative energy loss was Initially radiative energy loss was thought to dominate, but collisional thought to dominate, but collisional energy loss is actually of similar energy loss is actually of similar magnitudemagnitude

3

Energy Loss ModelsEnergy Loss Models DGLVDGLV

Radiative e-loss, expanded in opacityRadiative e-loss, expanded in opacity Debye-screened color potentialDebye-screened color potential NN≤≤3 scatterings3 scatterings

BDMPSBDMPS Also radiative, well-separated scattering centersAlso radiative, well-separated scattering centers Applies to infinite matter (NApplies to infinite matter (N»»1)1)

WHDGWHDG DGLV + collisional e-loss and path length DGLV + collisional e-loss and path length

fluctuationsfluctuations AdS/CFT calculationsAdS/CFT calculations Many othersMany others

4

Commonly Used Parameters in Commonly Used Parameters in Energy Loss CalculationsEnergy Loss Calculations

• = mean free path in medium = 1/= mean free path in medium = 1/• = opacity = L/= opacity = L/ (L = size of medium) (L = size of medium)• q = transport coefficient = q = transport coefficient = ^2/^2/

where where = characteristic momentum = characteristic momentum transfertransfer

• = energy of radiated gluon= energy of radiated gluon

5

Energy Loss of Heavy Quarks Energy Loss of Heavy Quarks (Dokshitzer and Kharzeev)(Dokshitzer and Kharzeev)

• Radiated gluons have formation time tRadiated gluons have formation time tformform = = /k/kTT^2, typical momentum ^2, typical momentum kkTT^2=^2=^2*t^2*tformform//..

• Number of scattering centers = tNumber of scattering centers = tformform// =√(=√(//**^2)^2)

• Energy spectrum for emitted gluons Energy spectrum for emitted gluons (scattering centers far apart, use Bethe-(scattering centers far apart, use Bethe-Heitler limit):Heitler limit):

• q = q = ^2/^2/

6

Heavy Quark E-loss cont’d.Heavy Quark E-loss cont’d.

Energy distribution of radiated gluons:Energy distribution of radiated gluons:

Radiation vanishes for Radiation vanishes for >>11 because then because then formation time exceeds length of medium:formation time exceeds length of medium:

Typical transverse momentum of radiated Typical transverse momentum of radiated gluon kgluon kTT^2 = √(^2 = √(*q), characteristic angle*q), characteristic angle

7

Heavy Quark E-loss cont’d.Heavy Quark E-loss cont’d.

Power spectrum of gluon radiation:Power spectrum of gluon radiation:

Modified from light quark spectrum by Modified from light quark spectrum by factor:factor:

If If <<00, radiation is suppressed - heavy , radiation is suppressed - heavy quarks lose less energy than light quarks.quarks lose less energy than light quarks.

8

How do Heavy Quarks Actually How do Heavy Quarks Actually Behave?Behave?

PHENIX single PHENIX single electron data from electron data from Run 4 Au+Au (D and Run 4 Au+Au (D and B meson decays)B meson decays)

Fit to FONLL curve Fit to FONLL curve from p+p data from p+p data (assume binary (assume binary scaling). scaling).

Data match at low pt Data match at low pt but seem to be but seem to be suppressed at high suppressed at high pt.pt.

9

Large Heavy Flavor Large Heavy Flavor SuppressionSuppression

• Left, compare inclusive Left, compare inclusive single e, high pt e single e, high pt e (heavy flavor), (heavy flavor), 0 data0 data

• Inclusive e is weighted Inclusive e is weighted more toward lower pt more toward lower pt (only half (only half charm/bottom)charm/bottom)

• Heavy flavor Heavy flavor suppressed almost as suppressed almost as much as light quarks.much as light quarks.PHENIX final 2007

10

PHENIX + STAR single ePHENIX + STAR single e

PHENIX and STAR results consistent, radiative energy loss model fails to explain the data.

Dong 2005

11

Collisional e-lossCollisional e-loss

If using radiative e-loss alone, need either If using radiative e-loss alone, need either a very large transport coefficient (q=14) a very large transport coefficient (q=14) or almost no contribution of b-quarks to or almost no contribution of b-quarks to single e spectrum.single e spectrum.

Collisional e-loss should not be neglected: Collisional e-loss should not be neglected: significant for heavy quarks.significant for heavy quarks. This is because heavy quarks not ultra-This is because heavy quarks not ultra-

relativistic. relativistic. Even for light quarks, collisional e-loss may be Even for light quarks, collisional e-loss may be

half as strong as radiative e-loss.half as strong as radiative e-loss.

12

WHDGWHDG

Radiative + elastic collisional e-lossRadiative + elastic collisional e-loss Initial + final state e-lossInitial + final state e-loss

Includes path length fluctuation Includes path length fluctuation effects, rather than assuming entire effects, rather than assuming entire length of medium traversed. length of medium traversed. Given initial starting point, parton Given initial starting point, parton

completes random walk: variety of completes random walk: variety of lengths traversed in medium. lengths traversed in medium.

13

Collisional E-loss Collisional E-loss ComparisonComparison

Above left, comparison between radiative e-loss vs. e-loss from radiative + collisional + path length fluctuations. Above left, comparison of scales of radiative vs. collisional e-loss for light and heavy quarks. (Wicks, Horowitz, Djordjevic and Gyulassy 2008).

WHDG 2008

14

Future of Heavy Quark E-Future of Heavy Quark E-loss loss

More realistic modeling of the medium is More realistic modeling of the medium is leading to better consistency with dataleading to better consistency with data

Other methods being testedOther methods being tested Energy loss through resonance formationEnergy loss through resonance formation

(van Hees)(van Hees) AdS/CFT dragAdS/CFT drag

LHC should shed light on e-loss in a new LHC should shed light on e-loss in a new energy regime, potentially verifying or energy regime, potentially verifying or falsifying current theories.falsifying current theories.