Rapidity Gaps Between Jets at HERA and the Tevatron

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Rapidity Gaps Between Jets at HERA and the
Tevatron
Brian Cox
Review of results from
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A little bit of History
Bjorken Phys. Rev. D 47, 1(1993) Rapidity gaps
between jets as a new physics signature in very
high energy hadron hadron collisions

• How big are the strong interaction backgrounds?

• What is the gap survival probability?

BFKL will enhance the rate, but a subject
beyond the scope of this paper and the competence
of its author
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The first gaps between jets analysis from
Tevatron and HERA

• ZEUS Collaboration Phys. Lett. B369 (1996) 55.
• D0 Collaboration Phys. Rev. Lett. 76 (1996)
  734.
• CDF Collaboration Phys. Rev. Lett. 80 (1998)
  1156.
• D0 Collaboration Phys. Lett. B440 (1998) 189.

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• Overall agreement in gap fraction 1 at
  Tevatron, 10 at HERA
• D0 BFKL ruled out

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Is BFKL really ruled out ?
B.C. Jeff Forshaw, Leif Lonnblad JHEP 9910 (1999)
023 , R. Enberg, G. Ingelman, L. Motyka Phys.
Rev. Lett. B524 (2002) 273
The Mueller Tang asymptotic approximation in
numerator (and Mueller Navelet jet production in
denominator) as implemented in HERWIG is not
sufficient at Tevatron or HERA energies.
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The new H1 and ZEUS measurements
Demanding no energy in a rapidity region is not
infra-red safe, and generates numerically
important non-global logarithms

• Run inclusive KT algorithm
• All objects are included in jets

• Gap event defined as

• Infra red safe definition of gap
• Increases rapidity gap region
• Reduces sensitivity to hadronisation effects
• Reduces sensitivity to non-global logarithms

G. Oderda and G. Sterman, Phys. Rev. Lett. 81,
3591 (1998) M. Dasgupta and G. P. Salam JHEP 0203
(2002) 017 R. B. Appleyby and M. H. Seymour JHEP
0212 (2002) 063
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Energy Flow and Rapidity Gaps Between Jets in
Photoporduction at HERA
Eur. Phys. J C24 (2002) 4, 517-527
http//jetweb.hep.ucl.ac.uk
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Gap Fractions as a function of ??
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Cross Sections and Gap Fractions as a function of
x?
Fractional longitudinal momentum of photon
participating in the production of the two
highest ET jets
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Gap Fractions as a function of xp
Fractional longitudinal momentum of proton
participating in the production of the two
highest ET jets
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Summary of the BFKL pomeron model

• CFL fit Tevatron data with ?s0.17, gap survival
  0.2

• H1 fit data with ?s0.18, gap survival not
  included in signal

• ZEUS fit data with ?s0.17, gap survival from
  JIMMY

• Potentially large NLO corrections to BFKL not
  included at HERA, partially included at Tevatron
  (EIM)

• H1 and ZEUS find that data not sensitive to
  underlying dynamics

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Should the LHC listen more closely to Bjorken?
e.g. ATL-PHYS-2003-006
invisible