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Heavy flavour jet physics and LHCb Implications of LHCb measurements and future prospect, CERN, 14-16 Oct 2013. Germán Rodrigo. IFIC INSTITUT DE FISICA CORPUSCULAR. Collinear factorization in pQCD. pQCD for hard-scattering processes based on universality : - PowerPoint PPT Presentation
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Germán Rodrigo Heavy flavour jet physics LHCb prospects, CERN, Oct 2013 1
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Heavy flavour jet physics and LHCbImplications of LHCb measurements and future prospect, CERN, 14-16 Oct 2013
Germán Rodrigo
I F I CI N S TI TU T D E F I S I C A C O R P U S C U L A R
Germán Rodrigo Heavy flavour jet physics LHCb prospects, CERN, Oct 2013 2
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Collinear factorization in pQCD
pQCD for hard-scattering processes based on universality:
the sole uncancelled IR divergences are due to partonic states whose momenta are collinear to the collider partons
removed by redefinition of bare parton densities (PDFs)
assumes that colliding partons do not have any intrinsic transverse momentum
Germán Rodrigo Heavy flavour jet physics LHCb prospects, CERN, Oct 2013 3
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Forward jet production
At least one of the colliding partons at small-x longitudinal momenta
PDFs poorly known at small-x. Transverse momentum non-negligible collinear
factorization for fixed order pQCD (LO or NLO) does not work well.
Large logarithms must be resummed BFKL or factorization
Dominated by multi-gluon emission off the t-channel.
𝑝1=𝑥1√ 𝑠/2𝑝2=𝑥2√𝑠 /2
Germán Rodrigo Heavy flavour jet physics LHCb prospects, CERN, Oct 2013 4
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factorizationHigh-energy scattering of two partons ()Differential cross-section as a function of transverse momenta (Mellin space)
Gluon Green´s function : Regge-gluon exchanges
Impact factors : process dependent, free of high-energy gluon exchanges, but collinear singularities due to the initial massless partons which need to be factored out
Scheme dependent scale [Ciafaloni,GR]
From colour coherence: rapidity of extra gluon radiation cannot exceed that of the final quark
Germán Rodrigo Heavy flavour jet physics LHCb prospects, CERN, Oct 2013 5
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Forward heavy quark jet productionNew particles in discovery processes
Reduce background in Higgs searches in vector boson fusion channels, e.g.
Decays of highly boosted heavy states
QCD at an extreme energy regime
Valuable information on the gluon density at small-x, which is poorly constrained from DIS
Promt neutrino flux in cosmic ray cascades from the decay of charm and bottom dominant at large energies (GeV) over the conventional neutrino flux from the decay of pions, kaons, … [Enberg, Reno, Sarcevic]
Germán Rodrigo Heavy flavour jet physics LHCb prospects, CERN, Oct 2013 6
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Heavy quark impact factor at NLx
𝒌
At leading order (Lx)
At next-to-leading log (NLx)
[Ciafaloni,GR]
where
with the gluon Regge trajectory
Free from double logs: and Collinear as predicted by DGLAP
Germán Rodrigo Heavy flavour jet physics LHCb prospects, CERN, Oct 2013 7
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Heavy quark impact factor at NLx revisited[Deak, Chachamis,GR]
Germán Rodrigo Heavy flavour jet physics LHCb prospects, CERN, Oct 2013 8
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Single heavy quark forward production[Deak, Chachamis,Salas, Sabio-Vera, GR]
Single bottom (charm) quark forward production, with soft gluon radiation between the heavy quark and the other parent proton at NLx
The unintegrated gluon density
whose evolution is determined by BFKL
Germán Rodrigo Heavy flavour jet physics LHCb prospects, CERN, Oct 2013 9
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Single bottom quark forward production
Germán Rodrigo Heavy flavour jet physics LHCb prospects, CERN, Oct 2013 10
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Forward production of heavy quarks offers interesting prospects for discovery processes.
and also access to QCD in a new energy regime: probe small-x where PDFs are poorly known.
First steeps towards single bottom/charm quark forward production at NLx
Conclusions