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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. Publications. With G. Kramer PLB 508 (2001) 259: g p  2 jets+n

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NLO QCD analysis of single-diffractive dijet production at the Tevatron

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  1. 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

  2. Publications • With G. Kramer • PLB 508 (2001) 259: g p  2 jets+n • EPJC 38 (2004) 39: g p  2 jets+p • PRL 93 (2004) 232002: g*p  2 jets+p • JPG 31 (2005) 1391: New fact. scheme • EPJC 49 (2007) 957: g(*)p 2 jets+n • MPLA 23 (2008) 1885: Review (HERA data) • PRD 80 (2009) 074006: p p  2 jets+p _ _ Michael Klasen, LPSC Grenoble

  3. Motivation • Diffractive Higgs production: • Clean central events, similar to vector-boson fusion • Easier identification of h  gg than in incl. Higgs production • Relies on understanding of pomeron flux / parton densities • Factorization breaking in single-diffractive dijets: • For photoproduction established only at NLO • Direct vs. resolved, x-dependence of S still under discussion • For hadroproduction established already at LO • Thorough NLO analysis was missing since Y2K !! Michael Klasen, LPSC Grenoble

  4. Definition of the SD / ND cross sections • Hadronic cross section: • Non-diffractive PDFs: • CTEQ6L1 / CTEQ6.6M • Diffractive PDFs: • H1 2006 fit A, B • H1 2007 fit jets (no f.b.!) • MY < 1.6 GeV • 1.15largerthanZEUSLPS Michael Klasen, LPSC Grenoble

  5. Experimental cuts by CDF PRL84(2000)5043: • s = 1800 GeV • Run IC (95-96), RPS • |t| < 1 GeV2 • 0.035 < x < 0.095 • R = 0.7, Rsep = 1.3R • ET 1,2 > 7 (6.5) GeV • |h| < 4.2 MK and G. Kramer, PLB 366 (1996) 385 Michael Klasen, LPSC Grenoble

  6. Experimental cuts by CDF PRL84(2000)5043: • s = 1800 GeV • Run IC (95-96), RPS • |t| < 1 GeV2 • 0.035 < x < 0.095 • R = 0.7, Rsep = 1.3R • ET 1,2 > 7 (6.5) GeV • |h| < 4.2 PRL88(2002)151802: • s = 630 and 1800 GeV • Run IC (95-96)  UA8 • |t| < 0.2 GeV2 • 0.035 < x < 0.095 • R = 0.7, Rsep = 1.3R • ET > 10 GeV • |h| < 4.2 _ MK and G. Kramer, PLB 366 (1996) 385 Michael Klasen, LPSC Grenoble

  7. Observables derived from sJJ(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 h1,2 with xp fixed • Integrate also over t and x 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 x Use <x> = 0.063 _ _ _ Michael Klasen, LPSC Grenoble

  8. Average transverse-energy distribution Non-diffractive (ND): Single-diffractive (SD): _ <ET> ≈ 8.7 GeV Michael Klasen, LPSC Grenoble

  9. Average rapidity distribution Non-diffractive (ND): Single-diffractive (SD): large xp _ small xp _ Michael Klasen, LPSC Grenoble

  10. Parton momentum fraction in anti-proton Ratio SD/ND: Suppression factor: NLO≈LO, x-dependent Michael Klasen, LPSC Grenoble

  11. Parton momentum fraction in pomeron Diffr. structure function: Suppression factor: <x> = 0.063 GRV98LO <Q2>=75 GeV2 weaker b-dependence Michael Klasen, LPSC Grenoble

  12. Average transverse-energy distribution Non-diffractive (ND): Single-diffractive (SD): Michael Klasen, LPSC Grenoble

  13. Average rapidity distribution Non-diffractive (ND): Single-diffractive (SD): Perfect! Michael Klasen, LPSC Grenoble

  14. Energy dependence of ratio SD/ND Michael Klasen, LPSC Grenoble

  15. Energy dependence of suppression factor Michael Klasen, LPSC Grenoble

  16. Energy dependence of diffr. structure fct. <x> = 0.063 GRV98LO <Q2>=75 GeV2 <x> = 0.063 GRV98LO <Q2>=75 GeV2 Michael Klasen, LPSC Grenoble

  17. Energy dependence of suppression factor Michael Klasen, LPSC Grenoble

  18. Pomeronmomentumfractioninantiproton • Published in PRL 88 • AgreeswithPRL84data:   taken at b=0.1 • Weak x-dependence <x>=0.063 not bad • Also observed in (N)LO H1pomeronfluxfact. Michael Klasen, LPSC Grenoble

  19. Double Pomeron exchange: Survival probability: Opacity / optical density: Ki = 1  g Kaidalov et al., EPJC 21 (2001) 521 Fit stot, dsel./dt to ISR, SppS, Tevatron data Total cross section: Determines (gIPpp)2 =25mb Starting scale s0 = 1 GeV2 Large distance physics: D = 0.1 Elastic amplitude: Pomeron trajectory: a(t) = 1 + a’ t + D Small distance physics: a’ = 0.15 GeV-2 Pomeron vertex in b-space: B = B0/2 + a’ ln (s/s0) Elastic slope: B0 = 8 GeV-2 pN* transition probability: g = 0.4 Survival probability: S ≈ 0.1 Small abs./size: Val., large xp, small b Large abs./size: Sea, small xp, small b Two-Channel Eikonal Model Michael Klasen, LPSC Grenoble

  20. Conclusion • LO analysis by CDF was very crude: • Cone algorithm, equal ET cuts [in PRL 84 (2000) 5043] • Proton PDFs, Q2 dependence and systematic errors cancel • Integrations over x and t don´t matter • Structure 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 sections • Suppression factor is x-dependent, in particular at small x • Predicted by LO two-channel eikonal model  valence/sea • Less dependence on b, at NLO, 630 GeV, with H1 2007 jets Michael Klasen, LPSC Grenoble

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