Forward production of Drell-Yan dileptons at high energies and low dilepton invariant masses in a $k_t$-factorization approach: Do we see onset of saturation?

Apr 14, 2016, 9:40 AM
15m
SR4b (DESY Hamburg)

SR4b

DESY Hamburg

Small-x, Diffraction and Vector Mesons WG5 Small-x and Diffraction

Speakers

Prof. Antoni Szczurek (Institute of Nuclear Physics PAN, Krakow and Rzeszow University, Rzeszow) Wolfgang Schafer (Institute of Nuclear Physics PAN, Krakow)

Description

We discuss Drell-Yan production of dileptons at high energies in forward rapidity region in a hybrid high-energy approach which uses unintegrated gluon distributions in one proton and collinear quark/antiquark distributions in the second proton. Corresponding momentum-space formula for the differential cross sections in high-energy approximation has been derived and will be presented. The relation to the commonly used dipole approach is discussed. We conclude and illustrate that some results of the dipole approaches are too approximate, as far as kinemtics is considered, and in fact cannot be used when comparing with real experimental data. We find that the dipole formula is valid only in very forward/backward rapidity regions ($|y| >$ 5) that cannot be studied experimentally in the moment. We performed calculations of some differential cross sections for low-mass dilepton production by the LHCb and ATLAS collaborations. In distinction to most dipole approaches, we include all the four Drell-Yan structure functions, although the impact of interference structure functions is rather small for the relevant experimental cuts. We find that both side contributions ($g q/\bar q$ and $q/\bar q g$) have to be included even for the LHCb rapidity coverage which is in contradiction with what is usually done in the dipole approach. We present results for different unintegrated gluon distributions from the literature (some of them include saturation effects). We see no clear hints of saturation even at small $M_{ll}$ when comparing with the LHCb data. The presentation will be based on our upcoming paper [1]. [1] W. Sch\"afer and A. Szczurek, a paper in preparation, to appear 02/16.

Primary author

Prof. Antoni Szczurek (Institute of Nuclear Physics PAN, Krakow and Rzeszow University, Rzeszow)

Co-author

Wolfgang Schafer (Institute of Nuclear Physics PAN, Krakow)

Presentation materials