gluon radiation of the heavy quark in nuclei
DESCRIPTION
Gluon Radiation of the Heavy Quark in Nuclei. Ben-Wei Zhang Institute of Particle Physics Central China Normal Univeristy Weihai, Shandong --- Augest 4, 2004. Outline. Motivation Twist expansion approach Modified heavy quark fragmentation function Heavy quark energy loss - PowerPoint PPT PresentationTRANSCRIPT
Gluon Radiation of the Heavy Gluon Radiation of the Heavy QuarkQuark
in Nucleiin Nuclei
Ben-Wei ZhangBen-Wei ZhangInstitute of Particle PhysicsInstitute of Particle Physics
Central China Normal UniveristyCentral China Normal Univeristy
Weihai, Shandong --- Augest 4, 2004Weihai, Shandong --- Augest 4, 2004
Ben-Wei Zhang @ Weihai Ben-Wei Zhang @ Weihai 22
OutlineOutline
MotivationMotivationTwist expansion approachTwist expansion approachModified heavy quark fragmentation functionModified heavy quark fragmentation functionHeavy quark energy lossHeavy quark energy loss
------ ------ Heavy Heavy VSVS.. LightLightConclusionsConclusions
Ben-Wei Zhang @ Weihai Ben-Wei Zhang @ Weihai 33
Jet QuenchingJet Quenching
Jet quenching has been observed as a Jet quenching has been observed as a new nuclear phenomenon at RHIC.new nuclear phenomenon at RHIC.
hadrons
ph
parton
E
Ben-Wei Zhang @ Weihai Ben-Wei Zhang @ Weihai 44
From Light to HeavyFrom Light to Heavy
Theory:Theory: A lot of theoretical studies have been devoted to the A lot of theoretical studies have been devoted to the
calculations of the energy loss of a light quark.calculations of the energy loss of a light quark. For massive quarks, the formalism of medium-induced For massive quarks, the formalism of medium-induced
gluon radiation is not developed to the same extent.gluon radiation is not developed to the same extent.
Experiment:Experiment: Open charm suppression, which can now be measured at
RHIC by comparing pt distributions of D-mesons in D-Au and Au-Au collisions, is a novel probe of QGP dynamics.
Ben-Wei Zhang @ Weihai Ben-Wei Zhang @ Weihai 55
Heavy Quark Energy Loss Heavy Quark Energy Loss
There are several theoretical calculations to There are several theoretical calculations to obtain the heavy quark energy loss:obtain the heavy quark energy loss:
Dokshitzer and KharzeevDokshitzer and Kharzeev
Djordjevic and GyulassyDjordjevic and Gyulassy
Armesto, Salgado and WiedemannArmesto, Salgado and Wiedemann
…… ……Twist Expansion approach in pQCDTwist Expansion approach in pQCD
B.W. Zhang,B.W. Zhang, E. Wang and X.N. Wang, Phys. Rev. Lett. 93(2004) in press E. Wang and X.N. Wang, Phys. Rev. Lett. 93(2004) in press
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Jet quenching with pQCDJet quenching with pQCD
How to measure the parton energy loss?How to measure the parton energy loss?Direct measurement is impossibleDirect measurement is impossibleParticle distributions within a jetParticle distributions within a jetModification to Fragmentation FunctionModification to Fragmentation FunctionObtain the energy loss indirectly from Obtain the energy loss indirectly from
measuring the modification of FFmeasuring the modification of FF
Ben-Wei Zhang @ Weihai Ben-Wei Zhang @ Weihai 77
Heavy QuarkHeavy Quark In parton model, for the heavy quark production we In parton model, for the heavy quark production we
obtain :obtain :
Ben-Wei Zhang @ Weihai Ben-Wei Zhang @ Weihai 88
Fragmentation FunctionFragmentation Function
Charm quark fragmentation function in Peterson form:Charm quark fragmentation function in Peterson form:
Ben-Wei Zhang @ Weihai Ben-Wei Zhang @ Weihai 99
Mutiple Scattering in NucleiMutiple Scattering in Nuclei
In order to calculate the heavy quark energy loss In order to calculate the heavy quark energy loss induced by gluon radiation in pQCD, we should induced by gluon radiation in pQCD, we should separate the ‘hard’ part from the ‘soft’ part:separate the ‘hard’ part from the ‘soft’ part:
factorizingfactorizing..
Ben-Wei Zhang @ Weihai Ben-Wei Zhang @ Weihai 1010
Factorization of Twist-4Factorization of Twist-4
Luo, Qiu, Sterman, PLB 279(1992)377;Luo, Qiu, Sterman, PRD 49(1994)4493; PRD 50(1994)1951
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Generalized FactorizationGeneralized Factorization
Ben-Wei Zhang @ Weihai Ben-Wei Zhang @ Weihai 1212
Quark-Gluon Double ScatteringQuark-Gluon Double Scattering
Ben-Wei Zhang @ Weihai Ben-Wei Zhang @ Weihai 1313
Collinear ApproximationCollinear Approximation
Make a collinear approximation:Make a collinear approximation:
The tensor structure can be factorized:The tensor structure can be factorized:
Ben-Wei Zhang @ Weihai Ben-Wei Zhang @ Weihai 1414
LPM EffectLPM Effect
LMP interference effect.
The formation time of gluon radiation.
Ben-Wei Zhang @ Weihai Ben-Wei Zhang @ Weihai 1515
Other ProcessesOther Processes
Ben-Wei Zhang @ Weihai Ben-Wei Zhang @ Weihai 1616
Hard Partonic PartHard Partonic Part
Dead-Cone effect of heavy quark propagatingDead-Cone effect of heavy quark propagating
Ben-Wei Zhang @ Weihai Ben-Wei Zhang @ Weihai 1717
Modified FF of Heavy Quark Modified FF of Heavy Quark With the generalized factorization theorem we With the generalized factorization theorem we
obtain the semi- inclusive hadronic tensor:obtain the semi- inclusive hadronic tensor:
The modified effective fragmentation function is
Ben-Wei Zhang @ Weihai Ben-Wei Zhang @ Weihai 1818
Twist-4 Parton CorrelationTwist-4 Parton Correlation
Ben-Wei Zhang @ Weihai Ben-Wei Zhang @ Weihai 1919
Two-parton Correlation FunctionTwo-parton Correlation Function
Twist-4 parton correlation Twist-4 parton correlation
function is in principle function is in principle
not calculable.not calculable.
With some approximations we can estimate
J. Osborne and Xin-Nian Wang, NPA 710(2002)281
Ben-Wei Zhang @ Weihai Ben-Wei Zhang @ Weihai 2020
Heavy Quark Energy LossHeavy Quark Energy Loss
Twist-4 correlation functions approximated as:Twist-4 correlation functions approximated as:
Heavy quark energy loss can be derived as:
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Two LimitsTwo Limits
(1) When (1) When
2QQ^2
(2) For large values of Q(2) For large values of Q2 2 or small xor small xBB, we have, we have
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Nuclear Size DependenceNuclear Size Dependence
Ben-Wei Zhang @ Weihai Ben-Wei Zhang @ Weihai 2323
Heavy Quark Heavy Quark VS.VS. Light Quark Light Quark
Energy loss of heavy quark is significantly suppressed due to mass effect, in particular, the dead-cone effect.
Ben-Wei Zhang @ Weihai Ben-Wei Zhang @ Weihai 2424
ConclusionsConclusions
Heavy quark energy loss induced by gluon radiation Heavy quark energy loss induced by gluon radiation is derived in terms of Modified FF with pQCD.is derived in terms of Modified FF with pQCD.
Medium size dependence of heavy quark enegy loss Medium size dependence of heavy quark enegy loss is found to change from a linear to a quadratic form is found to change from a linear to a quadratic form when the initial energy and momentum scale are when the initial energy and momentum scale are increasing.increasing.
Heavy quark energy loss is significantly suppressed Heavy quark energy loss is significantly suppressed relative to a light quark due to mass effect. relative to a light quark due to mass effect.
Thanks to my collaborators: Xin-Nian Wang and Enke WangThanks to my collaborators: Xin-Nian Wang and Enke Wang
Ben-Wei Zhang @ Weihai Ben-Wei Zhang @ Weihai 2525
Thank you very much!
谢谢 !
Thank you very much!
谢谢 !