Abstract |
: |
[eng] Deep inelastic scattering and its diffractive component, ep -> e'gamma*p
->e'XN, have been studied at HERA with the ZEUS detector using an integrated
luminosity of 4.2 pb-1. The measurement covers a wide range in the gamma*p c.m.
energy W (37 - 245 GeV), photon virtuality Q2 (2.2 - 80 GeV2) and mass Mx. The
diffractive cross section for Mx > 2 GeV rises strongly with W; the rise is
steeper with increasing Q2. The latter observation excludes the description of
diffractive deep inelastic scattering in terms of the exchange of a single
Pomeron. The ratio of diffractive to total cross section is constant as a
function of W, in contradiction to the expectation of Regge phenomenology
combined with a naive extension of the optical theorem to gamma*p scattering.
Above Mx of 8 GeV, the ratio is flat with Q2, indicating a leading-twist
behaviour of the diffractive cross section. The data are also presented in
terms of the diffractive structure function, F2D(3)(beta,xpom,Q2), of the
proton. For fixed beta, the Q2 dependence of xpom F2D(3) changes with xpom in
violation of Regge factorisation. For fixed xpom, xpom F2D(3) rises as beta ->
0, the rise accelerating with increasing Q2. These positive scaling violations
suggest substantial contributions of perturbative effects in the diffractive
DIS cross section.
Comment: 87 pages, 25 figures |