Rapidity Gaps Between Jets at HERA and the Tevatron Brian Cox

Review of results from

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”

BFKL will enhance the rate, but … “a subject beyond the scope of this paper and the competence of its author”

• How big are the strong interaction backgrounds?

• What is the gap survival probability?

“The frequency of rapidity gaps between jets must be understood before these new physics signatures can be used”

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.

• Overall agreement in gap fraction ~ 1% at Tevatron, ~ 10 % at HERA

• D0 – “BFKL ruled out”

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.

The new H1 and ZEUS measurementsDemanding ‘no energy’ in a rapidity region is not infra-red safe, and generates numerically important 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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ijetT

gapT EE

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• 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

• Run inclusive KT algorithm

• All objects are included in jets

cutT

gapT EE

http://jetweb.hep.ucl.ac.uk

Energy Flow and Rapidity Gaps Between Jets in Photoporduction at HERA

Eur. Phys. J C24 (2002) 4, 517-527

Gap Fractions as a function of

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

Gap Fractions as a function of xp

Fractional longitudinal momentum of proton participating in the production of the two highest ET jets

Summary of the BFKL pomeron model

• CFL fit Tevatron data with s=0.17, gap survival = 0.2

• H1 fit data with s=0.18, gap survival not included in signal

• ZEUS fit data with s=0.17, 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

Should the LHC listen more closely to Bjorken?

invisible

+ missing ET

e.g. ATL-PHYS-2003-006