Measurement of the Diffractive DIS Cross Section at low Q^2

Reference F-p.Schilling, talk at ICHEP 2002, July 2002
Document Conference paper
Figures  (1)  (2a)  (2b)  (2c)  (2d)  (2e)  (2f)  (3a)  (3b)  (3c)  (3d)  (3e)  (4)  (5)  (6)  (7)  (8)  (9)  (10)  (11)  (12)  (13)  (14)  (15)  (16)  (17)  (Stamp_explode)
Contact P Newman, F Schilling
Abstract A new measurement is presented of the diffractive deep-inelastic scattering process ep ightarrow eXY, where Y is a proton or low mass excitation. The results are obtained from a data sample of 3.4 pb-1 taken by the H1 experiment at HERA, with unbiased triggers. The measurement is presented in the form of a 3-dimensional reduced cross section sigma_r^{D(3)}(beta,Q^2,xpom) which is integrated over the region M_Y<1.6 GeV and |t|<1 GeV^2 and covers the kinematic range 1.5 \leq Q^2 \leq 12 GeV^2, 0.01 \leq eta \leq 0.9 and 10^{-4} < xpom<0.03. The results extend and improve the precision at the lowest Q^2 considerably compared to previous measurements. Interpreted through Regge-motivated fits to the xpom dependence, the data suggest a lower value of the effective pomeron intercept than that obtained from higher Q^2 data. The data are also compared with the predictions of a NLO DGLAP QCD fit to higher Q^2 data. In the perturbative region Q^2 >3 GeV^2, the data confirm the dominance of a gluon distribution extending to large fractional momenta in the diffractive parton densities. A colour dipole model based on the exchange of pairs of gluons is also compared wth the data.
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