QCD predictions for the transverse energy flow in deep-inelastic scattering in the DESY HERA smallxregime

Abstract

The distribution of transverse energy, E T , which accompanies deep-inelastic electron-proton scattering at small x, is predicted in the central region away from the current jet and proton remnants. We use BFKL dynamics, which arises from the summation of multiple gluon emissions at small x, to derive an analytic expression for the E T flow. One interesting feature is an x −ǫ increase of the E T distribution with decreasing x, where ǫ = (3α s /π)2 log 2. We perform a numerical study to examine the possibility of using characteristics of the E T distribution as a means of identifying BFKL dynamics at HERA.

Structure Functions of the Nucleon and Their Interpretation

“…The x; Q 2 dependence of the hE T i also agrees with the analytical BFKL calculation 356 , but this calculation was only made at the parton level, thus we see that it leaves room for only 10 20% more of hE T i to come from hadronization cc .…”

“…If we suppose that there is no strong k T ordering then we expect to nd more transverse energy, E T , emitted in the central region between the current jet and the proton remnant (in the lab frame this is the experimentally problematic forward region) than would result from conventional evolution. Parton level calculations incorporating BFKL dynamics yield a fairly at central plateau with E T ' 2 GeV per unit of rapidity in the HERA regime 356 . Early observations 367 of such a level of E T were taken as indicating a need for BFKL dynamics, particularly since comparison of the data with LEPTO and ARIADNE favoured the latter.…”

“…The transverse momentum follows a kind of random walk in k T space: the k T i v alue is close to the k T i 1 v alue, but it can be both larger or smaller 355 . As a consequence, BFKL evolution is expected to produce more gluons with substantial transverse energy E T in the region between the struck quark and the proton remnant, for low x events, compared to DGLAP evolution 356 .…”

Transverse energy and forward jet production in the low x regime at HERA

“…Intriguingly, a numerical BFKL calculation of the transverse energy flow [14] came out close to the measurements published by H1 [15], while the DGLAP prediction is too low. In addition, the DGLAP calculation predicts an increase in transverse energy with rising x, while the BFKL calculation predicts the opposite [13]. With increased statistics, the x dependence of this effect can be studied in more detail in this paper.…”

“…The transverse momentum follows a kind of random walk in k T space: the value of k T i is close to that of k T i−1 , but it can be both larger or smaller [12]. As a consequence, BFKL evolution is expected to produce more transverse energy E T than DGLAP evolution [13,14] in the region between the struck quark and the remnant for low x events. Intriguingly, a numerical BFKL calculation of the transverse energy flow [14] came out close to the measurements published by H1 [15], while the DGLAP prediction is too low.…”