Evidence for multiple scattering of high energy partons in nuclei

Abstract

New experimental information is presented about the effect of a nucleus on patrons which have undergone a hard scatter. We have observed clear dijet events from 400 GeV/c p-nucleus interactions and compared them to dijets from pp interactions. Our results show that the angular width of the individual jets is only slightly affected by the presence of the nucleus, but the acoplanarity of the jet pairs is sharply increased.

Initial/final state interaction in di-jet production off nuclei

“…Since this experiment has lower bottom bound on p T of jets, than that used in [1], one may expect that α is slightly smaller as well. In such a case the result of [2] provide k 2 0 ≥ 1 GeV 2 ,…”

“…Thus the accuracy of (12) is about ±0.15 GeV 2 for heavy nuclei, whereas the whole nuclear contribution, δ k 2 T , is a few GeV 2 [1,2].…”

“…Much bigger effect was observed by the E609 Collaboration [1] in production of di-jets with p T > 4 GeV by 400 GeV protons. The broadening of out-of-plane transverse momentum squared, δ k 2 T ≈ 2 − 3 GeV 2 on heavy nuclei, is more than an order of magnitude larger than that in the Drell-Yan reaction.…”

“…Indeed, α is usually A-independent or decreases with A. On the other hand, k 2 T rises with A [1,2]. However, the derivation of (4), (5) silently assumed n ≪ A, what is true only for heavy nuclei.…”

“…Using available experimental information for δ k 2 T ≈ 2 − 3 GeV 2 [1] and α = 1.18 ± 0.5 [9], we estimate the mean momentum transfer squared, in a single rescattering of a parton in nuclear matter, k 2 0 ≥ 2 GeV 2 . This value exceeds even the out-of-plane transverse momentum squared, k 2 T ≈ 1 GeV 2 , detected on a proton target [1], what looks puzzling.…”