nlo qcd analysis of single-diffractive dijet production at the tevatron

NLO QCD analysis of single-diffractive dijet production at the

Tevatron

Michael Klasen (LPSC Grenoble)in collaboration with G. Kramer (U Hamburg)

April 20, 2010

Phys. Rev. D 80 (2009) 074006

April 20, 2010 Michael Klasen, LPSC Grenoble 2

Publications

With G. Kramer

PLB 508 (2001) 259: p 2 jets+n

EPJC 38 (2004) 39: p 2 jets+p

PRL 93 (2004) 232002: p 2 jets+p

JPG 31 (2005) 1391: New fact. scheme

EPJC 49 (2007) 957:p 2 jets+n

MPLA 23 (2008) 1885: Review (HERA data)

PRD 80 (2009) 074006: p p 2 jets+p

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Motivation

Diffractive Higgs production:Clean central events, similar to vector-boson fusion

Easier identification of h than in incl. Higgs productionRelies on understanding of pomeron flux / parton densities

Factorization breaking in single-diffractive dijets:For photoproduction established only at NLODirect vs. resolved, x-dependence of S still under discussionFor hadroproduction established already at LOThorough NLO analysis was missing since Y2K !!

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Definition of the SD / ND cross sections

Hadronic cross section:

Non-diffractive PDFs:CTEQ6L1 / CTEQ6.6M

Diffractive PDFs:H1 2006 fit A, BH1 2007 fit jets (no f.b.!)MY < 1.6 GeV

1.15 larger than ZEUS LPS

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Experimental cuts by CDF

PRL 84 (2000) 5043:

s = 1800 GeVRun IC (95-96), RPS

|t| < 1 GeV2

0.035 < < 0.095

R = 0.7, Rsep = 1.3R

ET 1,2 > 7 (6.5) GeV

|| < 4.2

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MK and G. Kramer, PLB 366 (1996) 385

Experimental cuts by CDF

PRL 84 (2000) 5043:

s = 1800 GeVRun IC (95-96), RPS

|t| < 1 GeV2

0.035 < < 0.095

R = 0.7, Rsep = 1.3R

ET 1,2 > 7 (6.5) GeV

|| < 4.2

PRL 88 (2002)

151802:

s = 630 and 1800 GeVRun IC (95-96) UA8

|t| < 0.2 GeV2

0.035 < < 0.095

R = 0.7, Rsep = 1.3R

ET > 10 GeV

|| < 4.2

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MK and G. Kramer, PLB 366 (1996) 385

Observables derived from JJ(th)/NJJ(exp)

Parton momentum fraction in antiproton, pomeron: directly from jets, but in convolution

Ratio of SD to ND cross sections:

Integrated over ET 1,2 and 1,2 with xp fixed

Integrate also over t and ranges, assume similar Q2 ≈ ET2

Naive estimate of non-diffractive structure function: (t-channel gluon exchange)

GRV 98 LO, <Q2> = 75 GeV2 (<ET> ≈ 8.7 GeV)

Diffractive structure function:

Weak dependence on Use <> = 0.063

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Average transverse-energy distribution

Non-diffractive (ND): Single-diffractive (SD):

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<ET> ≈ 8.7 GeV_

Average rapidity distribution

Non-diffractive (ND): Single-diffractive (SD):

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small xp_large xp

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Parton momentum fraction in anti-proton

Ratio SD/ND: Suppression factor:

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NLO≈LO,x-dependent

Parton momentum fraction in pomeron

Diffr. structure function:

Suppression factor:

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<> = 0.063GRV98LO

<Q2>=75 GeV2

weaker -dependence

Average transverse-energy distribution

Non-diffractive (ND): Single-diffractive (SD):

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Average rapidity distribution

Non-diffractive (ND): Single-diffractive (SD):

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Perfe

ct!

Energy dependence of ratio SD/ND

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Energy dependence of suppression factor

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Energy dependence of diffr. structure fct.

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<> = 0.063GRV98LO

<Q2>=75 GeV2

<> = 0.063GRV98LO

<Q2>=75 GeV2

Energy dependence of suppression factor

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Pomeron momentum fraction in

antiproton

Published in PRL 88Agrees with PRL 84

data:

taken at =0.1

Weak -dependence <>=0.063 not badAlso observed in (N)LO H1 pomeron flux fact.

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June 7, 2006 Michael Klasen, LPSC Grenoble 19

Two-Channel Eikonal ModelDouble Pomeron exchange:

Survival probability:

Opacity / optical density: Ki = 1

Kaidalov et al., EPJC 21 (2001) 521

Fit tot, del./dt to ISR, SppS, Tevatron data

Total cross section: Determines (gIP

pp)2 = 25 mbStarting scale s0 = 1 GeV2

Large distance physics: = 0.1

Elastic amplitude: Pomeron trajectory: (t) = 1 + ’ t + Small distance physics: ’ = 0.15 GeV-2

Pomeron vertex in b-space:B = B0/2 + ’ ln (s/s0)Elastic slope: B0 = 8 GeV-2

p N* transition probability: = 0.4

Survival probability: S ≈ 0.1Small abs./size: Val., large xp, small Large abs./size: Sea, small xp, small

ConclusionLO analysis by CDF was very crude:

Cone algorithm, equal ET cuts [in PRL 84 (2000) 5043]

Proton PDFs, Q2 dependence and systematic errors cancelIntegrations over and t don´t matterStructure function ≈ t-channel gluon exchange

Still, NLO analysis confirms main conclusions:SD/ND K-factors of 1.6 (630 GeV) and 1.35 (1800 GeV)Partially compensated by exact ratios of NLO cross sectionsSuppression factor is x-dependent, in particular at small xPredicted by LO two-channel eikonal model valence/seaLess dependence on , at NLO, 630 GeV, with H1 2007 jets

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