Estimating the diffractive heavy
quark production in heavy ion
collisions at the LHC*
Mairon Melo Machado
GFPAE – IF – UFRGS
www.if.ufrgs.br/gfpae
[email protected]
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Workshop on Diffractive Physics at the LHC – Rio de Janeiro – Sep. 2009
Outlook
 Motivation
 Diffractive Physics
 Hadroproduction of heavy quarks at LO
 Hadroproduction of heavy quarks at NLO
 Coherent and incoherent heavy quark production
 Pomeron Structure Function
 Multiple Pomeron Scattering
 Results
 Conclusions
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Workshop on Diffractive Physics at the LHC – Rio de Janeiro – Sep. 2009
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M. B. Gay Ducati, M. M. Machado, M. V. T. Machado, PRD 75, 114013 (2007)
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M. B. Gay Ducati, M. M. Machado, M. V. T. Machado, arXiv:0908.0507 [hep-ph] (2009)
Motivation
 Cross section for heavy quark production allows to probe the gluon
densities
 Pomeron with substructure
1, 2
Ingelman-Schlein
 Ingelman-Schlein
predictions
 Absorptive corrections
multiple Pomeron Scattering
 Gap survival probability to AA single diffractive collisions
 Coherent and incoherent diffraction is a powerful tool for studying the
low-x processes (gluon saturation)
 HQ are important signals of possible new physics
signal
H BB
background
ggBB
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Workshop on Diffractive Physics at the LHC – Rio de Janeiro – Sep. 2009
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P. D. Collins, An Introduction to Regge Theory and High Energy Physics (1977)
Introduction
 Diffractive processes
rapidity gap
 Exchange of a Pomeron with vacuum quantum numbers
 Pomeron 3 not completely known
 Parton content in the Pomeron
DPDFs
 Diffractive distributions of singlet quarks and gluons in the Pomeron
 Coherent (small-x dynamics) and incoherent cases (color field fluctuations)
Diffractive structure function
Gap Survival Probability (GSP)
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G. Ingelman and P. Schlein, Phys. Lett. 152B (1985) 256.
Diffractive events
 Single diffraction in hadronic collisions
 One of the colliding hadrons emits Pomeron
 Partons in the the Pomeron interact with partons from the another hadron
Ingelman-Schlein Model
 Absence of hadronic energy in angular regions Φ of the final state phase
space
Rapidity gaps
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Workshop on Diffractive Physics at the LHC – Rio de Janeiro – Sep. 2009
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M. L. Mangano et al, Nucl. Phys. B 373, 295 (1992)
Heavy quark hadroproduction
o Focus on the following single diffractive processes
 
pp

p
+
C
C
+
X
 
pp

p
+
B
B+
X
o Diffractive ratios as a function of energy center-mass ECM
g+g
Q+Q
o Diagrams contributing to the lowest order cross section
Workshop on Diffractive Physics at the LHC – Rio de Janeiro – Sep. 2009
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6
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M. L. Mangano, P. Nason, G. Ridolfi Nucl. Phys. B373 (1992) 295
LO hadroproduction
Total cross section
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are the parton distributions inner the hadron i=1 and j=2
Partonical cross section
μF  μR 
factorisation (renormalization) scale
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Workshop on Diffractive Physics at the LHC – Rio de Janeiro – Sep. 2009
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M. L. Mangano arXiv:hep-ph/9711337v1 (1997)
Partonic cross section
αS
is the coupling constant
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m is the heavy quark mass
p1,2 are the parton momenta
V=N 2− 1
Dimension of the SU(N) gauge group
(number of gluons)
N = 3 (4) to charm (bottom)
Workshop on Diffractive Physics at the LHC – Rio de Janeiro – Sep. 2009
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5
M. L. Mangano, P. Nason, G. Ridolfi Nucl. Phys. B373 (1992) 295
NLO Production
g+
g
Q
+
Q
+
g
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Running of the coupling constant
n1f = 3 (4) charm (bottom)
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Workshop on Diffractive Physics at the LHC – Rio de Janeiro – Sep. 2009
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P. Nason, S. Dawson, R. K. Ellis Nucl. Phys. B303 (1988) 607
NLO functions
 Using a physical motivation
fit to the numerically integrated
result 7
 Error of 1%
a0
0.108068
a1
-0.114997
a2
0.0428630
a3
0.131429
a4
0.0438768
a5
-0.0760996
a6
-0.165878
a7
-0.158246
Workshop on Diffractive Physics at the LHC – Rio de Janeiro – Sep. 2009
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P. Nason, S. Dawson, R. K. Ellis Nucl. Phys. B303 (1988) 607
NLO Production
Auxiliary functions
7
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H1 Coll. A. Aktas et al, Eur. J. Phys. J. C48 (2006) 715
V. A. Khoze, A. D. Martin, M. G. Ryskin, Eur. Phys. J. C18, 167 (2000)
Diffractive cross section
Pomeron flux factor
β=
x
x IP
Pomeron Structure Function (H1) 6
KKMR model
<|S|2> = 0.06 at LHC single diffractive events 7
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Workshop on Diffractive Physics at the LHC – Rio de Janeiro – Sep. 2009
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H1 Coll. A. Aktas et al, Eur. J. Phys. J. C48 (2006) 715
H1 Gluon distribution
• In this work we use FIT A. Similar results with FIT B
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Workshop on Diffractive Physics at the LHC – Rio de Janeiro – Sep. 2009
8 N.
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M. Agababyan et al Phys. Atom. Nucl. 62, 1572 (1999)
K. Tuchin, arXiv:0812.1519v2 [hep-ph] (2009)
Diffractive Nuclear heavy quark production
single diffraction 8
 Incoherent diffractive is a process where
A+ A  X + A+ [LRG] + A
*
 A* denotes the excited nucleus that subsequently decays into a system of
colorless hadrons 9
 Diffractive incoherent ratio
 Coherent diffractive is a process where
A
+
A

X
+
A
+
[LRG]
+
A
 Stronger dependence on energy and atomic number
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Workshop on Diffractive Physics at the LHC – Rio de Janeiro – Sep. 2009
qq vs. gg
• Inclusive cross section and
diffractive cross section
Inclusive quarks/gluons
Inclusive gluons
Diffractive
• Charm-anticharm hadroproduction
• Contribution of qq anihillation at
high energies not important
• Diffractive cross section without
GSP
• Mc = 1.5 GeV
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Workshop on Diffractive Physics at the LHC – Rio de Janeiro – Sep. 2009
Diffractive comparison
Inclusive
Diffractive wt/GSP
Diffractive wh/GSP
• Diffractive cross sections to
bottom-antibottom
hadroproduction
• Relevant contribution of GSP
value in the total diffractive
cross section
• <|S|2> = 0.06
• Mb = 4.7 GeV
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Workshop on Diffractive Physics at the LHC – Rio de Janeiro – Sep. 2009
Comparison LO and NLO
• Predictions for inclusive cross sections in pp collisions (LHC)
• NLO cross section is 1.5 higher than LO cross section at high energies
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Workshop on Diffractive Physics at the LHC – Rio de Janeiro – Sep. 2009
Results for heavy quark production
Cross sections in NLO for heavy quarks hadroproduction
GSP value decreases the diffractive rate
<|S|2> = 0.06
Cross sections in NLO to inclusive nuclear cross section
ACa = 40
APb = 208
Workshop on Diffractive Physics at the LHC – Rio de Janeiro – Sep. 2009
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E. Levin; J. Miller arXiv:0801.3593v1 [hep-ph] (2008)
Incoherent results
 There are not values of <|S|2> to single diffraction in AA collisions
 Estimatives to Higgs central production11
<|S|2> ~ 1 x 10-4
 Values of diffractive cross section in a region possible to be verified
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Workshop on Diffractive Physics at the LHC – Rio de Janeiro – Sep. 2009
Coherent results
 Predictions to diffractive cross section in a region possible to be
verified
 Diffractive cross section without GSP is consistent with the literature
 Very small single diffractive ratio
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Workshop on Diffractive Physics at the LHC – Rio de Janeiro – Sep. 2009
Conclusions
•
Theoretical predictions for inclusive and single diffractive heavy quarks
production at LHC energies in pp and AA collisions
•
Estimates for cross sections as a function of energy center mass ECM
•
Diffractive ratio is computed using hard diffractive factorization and
absorptive corrections (NLO)
•
There are not predictions to <|S|2> in AA collisions
•
Important contribution of the absolute value of absorptive corrections
•
Diffractive cross section for AA collisions in a region that is possible to be
verified
•
Evaluation of the gap survival probability for single diffraction in AA
collisions
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Workshop on Diffractive Physics at the LHC – Rio de Janeiro – Sep. 2009