Diffractive heavy quark production in AA collisions at the LHC at NLO*

1
Diffractive heavy quark production in AA
collisions at the LHC at NLO

• Mairon Melo Machado
• GFPAE IF UFRGS
• melo.machado_at_ufrgs.br
• www.if.ufrgs.br/gfpae

Work with M. V. T. Machado and M. B. Gay Ducati
DIFFRACTION 2010 OTRANTO, ITALY, 10 15
SEPTEMBER
2
Outlook

• Motivation
• Diffractive Physics
• Hadroproduction of heavy quarks at LO
• Hadroproduction of heavy quarks at NLO
• Coherent heavy quark production
• Pomeron Structure Function
• Multiple Pomeron Scattering
• Results
• Conclusions

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Motivation

• Heavy quarks will be produced in large
  quantities at LHC
• Very important for physics study and for
  understanding background processes
• Heavy flavoured hadrons may produce high
  momentum leptons
• Potential background to new physics
• Estimate the inclusive, single and Double
  Pomeron Exchange (DPE) in heavy ion collisions
• Coherent and incoherent (single diffraction)
  production of heavy quarks in AA collisions
• Coherent DPE production of heavy quarks in AA
  collisions

signal
background
3
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Introduction
1 M. B. Gay Ducati, M. M. M, M. V. T. Machado,
PRD 75, 114013 (2007) 2 M. B. Gay Ducati, M. M.
M, M. V. T. Machado, PRD 81, 054034 (2010)

• Diffractive processes caractherized by a
  rapidity gap Pomeron
• Pomeron and its reaction mechanisms is not
  completely known
• Regge Theory Pomerons with
  substructure DPDFs
• It does not describe hadron collider data
• Application of multiple Pomeron scattering
  suppress the diffractive cross section
• Gap Survival Probability (GSP) to AA collisions
  ?

1, 2
Studies
Diffractive structure function
Gap Survival Probability (GSP)
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Diffractive events
4 M. Heyssler, Z. Phys. C 73. (1997) 297. 5 B.
Z. Kopeliovich et al, Phys. Rev. Lett. 85, 507
(2000)

• Absence of hadronic energy in angular regions F
  of the final state
• Hard diffractive factorization 4

Rapidity gaps
Single diffraction
DPE exchange

• Introduction of the appropriate absorptive
  effects which cause the suppresion of any LRG
  process 5 and nuclear effects as well

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Heavy quark hadroproduction
6 M. L. Mangano et al, Nucl. Phys. B 373, 295
(1992)

• Focus on the following single diffractive
  processes

• Diffractive ratios as a function of energy
  center-mass ECM

• Diagrams contributing to the lowest order cross
  section 6

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Total cross section LO
6 M. L. Mangano, P. Nason, G. Ridolfi Nucl. Phys.
B373 (1992) 295
6
x1,2 are the momentum fraction
are the parton distributions inner the hadron i1
and j2
Partonical cross section
factorization (renormalization) scale
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NLO Production
6 M. L. Mangano, P. Nason, G. Ridolfi Nucl. Phys.
B373 (1992) 295
6
Running of the coupling constant
n1f 3 (4) charm (bottom)
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NLO functions
8 P. Nason, S. Dawson, R. K. Ellis Nucl. Phys.
B303 (1988) 607
8
a0 0.108068
a1 -0.114997
a2 0.0428630
a3 0.131429
a4 0.0438768
a5 -0.0760996
a6 -0.165878
a7 -0.158246
Auxiliary functions
9
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Diffractive cross section
9 H1 Coll. A. Aktas et al, Eur. J. Phys. J. C48
(2006) 715
10 V. A. Khoze, A. D. Martin, M. G. Ryskin, Eur.
Phys. J. C18, 167 (2000)
Pomeron flux factor
Pomeron Structure Function (H1) 9
KKMR model ltS2gt 0.06 at LHC
single diffractive events 10
Parametrization of the pomeron flux factor and
structure function
H1 Collaboration
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Nuclear single diffractive
11 N. M. Agababyan et al Phys. Atom. Nucl. 62,
1572 (1999) 12 K. Tuchin, arXiv0812.1519v2
hep-ph (2009)
Inclusive case
APb 208 (5.5 TeV)
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Diffractive case

• Coherent process Pomeron
  emmited by the nucleus

• Incoherent process Pomeron
  emmited by a nucleon inner the nucleus

12
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Heavy quarks production at the LHC
Heavy quarks cross sections in NLO to pp
collisions GSP value decreases the diffractive
ratio (ltS2gt 0.06)
Inclusive nuclear cross section at NLO
APbPb
208 (5.5 TeV) 40 (6.3) TeV
difrativo
12
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Diffractive cross sections _at_ LHC
13 M. Gay Ducati, M. M. M, M. V. T. Machado, PRD.
81, 054034 (2010)
14 B. Kopeliovich et al, 0702106 arXivhep-ph
(2007)
Inclusive cross section
Diffractive cross sections
Proton-Nucleus collision
Similar results that 14
Nucleus-Nucleus collision

• Predictions to cross sections possible to be
  verified at the LHC 13

Very small diffractive ratio
13
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Diffractive cross sections _at_ LHC
13 M. Gay Ducati, M. M. M, M. V. T. Machado, PRD.
81, 054034 (2010)

• 13

• No values to ltS2gt for single diffractive
  events in AA collisions
• Estimations to central Higgs production
  ltS2gt 8 x 10-7
• Values of diffractive cross sections possible to
  be verified experimentally

14
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Bialas-Landshoff approach
15 A. Bialas and W. Szeremeta, Phys. Lett. B 296,
191 (1992)
Double Pomeron Exchange
nucleon form-factor

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Differential phase-space factor
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mass of produced quarks
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Bialas-Landshoff approach
Sudakov parametrization for momenta
two-dimensional four-vectors describing the
transverse component of the momenta
momenta for the incoming (outgoing) protons
momentum for the produced quark (antiquark)
momentum for one of exchanged gluons
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Bialas-Landshoff approach
14 A. Bialas and W. Szeremeta, Phys. Lett. B 296,
191 (1992)
Square of the invariant matrix element averaged
over initial spins and summed over final spins 14
effect of the momentum transfer dependence of the
non-perturbative gluon propagator
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DPE results
10 V. A. Khoze, A. D. Martin, M. G. Ryskin, Eur.
Phys. J. C18, 167 (2000)
pp collisions at the LHC (14 TeV)
Ingelman-Schlein
Bialas-Landshoff
10
18
Ingelman-Schlein gt Bialas-Landshoff
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Conclusions

• Theoretical predictions for single and DPE heavy
  quarks production at LHC energies in pp, pA and
  AA collisions
• Diffractive ratio is computed using hard
  diffractive factorization and absorptive
  corrections (NLO)
• There are no predictions to ltS2gt in pA and AA
  collisions
• Diffractive cross sections for AA collisions
  possible to be verified
• Diffractive channel dominates over exclusive
  photoproduction channel in proton-proton case
• Calculation of GSP values to AA collisions is
  highly important

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pA cross sections _at_ LHC

• Suppression factor

spA 0.8 mb
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