quark pair production in the color glass condensate
DESCRIPTION
Quark Pair Production in the Color Glass Condensate. Raju Venugopalan Brookhaven National Laboratory. AGS users-Quarkonium workshop, June 6th, 2006. Work done in collaboration with J.-P. Blaizot, H. Fujii and F. Gelis. Based on, a) F. Gelis, RV, PRD 69 : 014019, (2004) - PowerPoint PPT PresentationTRANSCRIPT
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Quark Pair Production in the Color Glass Condensate
Raju Venugopalan
Brookhaven National Laboratory
AGS users-Quarkonium workshop, June 6th, 2006
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Work done in collaboration with J.-P. Blaizot, H. Fujii and F. Gelis.
Based on,
a) F. Gelis, RV, PRD 69: 014019, (2004) b) J.-P. Blaizot, F. Gelis, RV, NPA 743:57, (2004) c) H. Fujii, F. Gelis, RV, PRL 95:162002 (2005) d) H. Fujii, F. Gelis, RV, hep-ph/0603099 & in preparation.
Related work by
Kharzeev & Tuchin; Tuchin; Kovchegov & Tuchin; Gelis, Kajantie and Lappi
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Outline of TalkThe kt factorization formalism (and its breaking) for heavy quark production in the CGC
Isolating multiple scattering & quantum evolution effects -results in MV & BK models
Summary and outlook
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Universality: collinear versus k_t factorization
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Heavy quark production at colliders
Collinear factorization:
Collins,Soper,Sterman
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Novel regime of QCD at high energies
“Higher twists”Leading twist shadowing
A
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Are these “un-integrated gluon distributions” universal?
In CGC, “Dipoles”- with evolution a la JIMWLK / BK RG equations
Kt factorization:
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Solve Yang-Mills equations for two light cone sources:
For observables average over
HADRONIC COLLISIONS IN THE CGC FRAMEWORK
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Inclusive pair production in CGC framework
Gelis, RVhep-ph/0310090
Abelian Non-Abelian Lipatov vertex
To lowest order in sources:
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Identical to Collins-Ellis+
Catani-Ciafaloni-Hautmann k_t factorization result
is the un-integrated gluon distribution in the Gaussian MV model
K_t factorization compared to RHIC D-Au data by Kharzeev & Tuchin (hep-ph/0310358)
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Quark production to all orders in pA
Neither quark pair production nor single quark production is kt-factorizable
Blaizot,Gelis, RV
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= …
Pair cross-section:
Amputated time ordered quark propagator in classical background field
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Result can however still be “factorized” into novel multi-parton distributions
These multi-parton distributions can be computed in closed form in the Gaussian (MV) approximation
Quantum evolution of these distributions can be computedBy solving the JIMWLK or BK renorm. group equations
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Interpretation:
Wilson line correlators - the last appears in pair productiononly
Simplify greatly in large N_c limit x-evolution can be computed with Balitsky-Kovchegov eqn.
Blaizot, Gelis, RV; Tuchin
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Results
I) Violation of k_t factorization in the MV model
(multiple scattering only-no x evolution of target)
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Large N_c results - good approximation to exact result
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Cronin effect for quark production:
(MV model- re-scattering but no evolution)
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Simple “Non-local” Gaussian model-simulates effects of (extreme) quantum evolution
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Results in the MV model: multiple-scattering effects
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Collinear logs: Relation to pQCD
LO in pQCD
Logs can be absorbed into structure functions
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Collinear logs:
NLO in pQCD
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K_t factorization => pair scatters off medium like a gluon (is collinear)For small P_t (< Q_s) , and large M, re-scatterings are significant.
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R_pA: suppression
Frankfurt, Strikman; Matsui, Fujii
Chudakov effect
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x_F dependence Kharzeev-Tuchin, Hep-ph/0510358
Need to also consider color octet contributions if matrix elements are large
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II) Rapidity dependence
No rapidity dependence in the MV model-multiple scattering but no x-evolution
Y-dependence via JIMWLK RG equations-simplified large N_c & Large A limit is the BK equation
Compute ``dipole” correlators solving BK with MV initial conditions
Important for forward physics at RHIC and at LHC energies
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PHENIX
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A) BK equation for the unintegrated distribution:
Non-linear equation for dipole amplitude
BFKL kernel
U’s in fund. rep.
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Large Nc limit:
F.T. ofdipoleamplitude
Above equation
Gelis, Stasto, RV
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Rapidity dist. of pairs from BK evolution
Sensitive toLarge x (> 0.01)extrapolation
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R_pA from BK:
Dots denote region “uncontaminated” by large x extrapolation
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R_pA vs Y:
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Quark Production in A-A
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Solve Dirac equation in background field of two nuclei…
Gelis,Kajantie,Lappi PRL 2005
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Ratio of quarks to glue roughly consistent with a chemically equilibrated QGP
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Quark production in AA collisions can be computed at the earliest stages. Same order as NLO gluon production.
Computationally intensive effort in progress.
Outlook
We can compute both small x evolution (shadowing) and multiple scattering effects in quark production on same footing.
More detailed studies (in color octet and color evaporation framework for J/Psi) in progress for D-Au collisions
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Quark mass dependence…
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Q_s dependence…