Köln 2004 – scientific programme
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HK: Physik der Hadronen und Kerne
HK 7: Heavy Ions I
HK 7.8: Talk
Monday, March 8, 2004, 18:00–18:15, F
Dijet production as a centrality trigger for pp collisions at LHC — •C. Weiss3, L. Frankfurt1, and M. Strikman2 — 1Tel Aviv U., Israel — 2Pennsylvania State U., USA — 3Regensburg U.
We show that a trigger on hard dijet production at small rapidities allows to establish a quantitative distinction between central and peripheral collisions in p p and pp collisions at Tevatron and LHC energies. Such a trigger strongly reduces the effective impact parameters as compared to minimum bias events. This happens because the transverse spatial distribution of hard partons (x≥ 10−2) in the proton is considerably narrower than that of soft partons, whose collisions dominate the total cross section. In the central collisions selected by the trigger, most of the partons with x≥ 10−2 interact with a gluon field whose strength rapidly increases with energy. At LHC energies the strength of this interaction approaches the unitarity (“black–body”) limit. This leads to specific modifications of the final state, such as a higher probability of multijet events at small rapidities, a strong increase of the transverse momenta and depletion of the longitudinal momenta at large rapidities, and the appearance of long–range correlations in rapidity between the forward/backward fragmentation regions. Studies of these phenomena would be feasible with the CMS–TOTEM detector setup, and would have considerable impact on the exploration of the physics of strong gluon fields in QCD, as well as the search for new particles (Higgs, SUSY) at LHC [1].
[1] L. Frankfurt, M. Strikman, and C. Weiss, hep-ph/0311231