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NLO jet production at central rapidities in $k_T$ factorization

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 Added by Florian Schwennsen
 Publication date 2006
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and research's language is English




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In this contribution we discuss the inclusive production of jets in central regions of rapidity in the context of $k_T$-factorization at next-to-leading order (NLO). We work in the Regge limit of QCD and use the NLO BFKL results. A jet cone definition is proposed together with a phase-space separation into multi-Regge and quasi-multi-Regge kinematics. We discuss scattering of highly virtual photons, with a symmetric energy scale to separate the impact factors from the gluon Greens function, and hadron-hadron collisions, with a non-symmetric scale choice.

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132 - J. Bartels 2007
We discuss the inclusive production of jets in the central region of rapidity in the context of k_T-factorization at next-to-leading order (NLO). Calculations are performed in the Regge limit making use of the NLO BFKL results. We introduce a jet cone definition and carry out a proper phase--space separation into multi-Regge and quasi-multi-Regge kinematic regions. We discuss two situations: scattering of highly virtual photons, which requires a symmetric energy scale to separate impact factors from the gluon Greens function, and hadron-hadron collisions, where a non-symmetric scale choice is needed.
The inclusive production of jets in the central region of rapidity is studied in $k_T$-factorization at next-to-leading order (NLO) in QCD perturbation theory. Calculations are performed in the Regge limit making use of the NLO BFKL results. A jet cone definition is introduced and a proper phase--space separation into multi-Regge and quasi-multi-Regge kinematic regions is carried out. Two situations are discussed: scattering of highly virtual photons, which requires a symmetric energy scale to separate the impact factors from the gluon Greens function, and hadron-hadron collisions, where a non--symmetric scale choice is needed.
We describe the current status of the diffractive vector meson production calculations within the k_t-factorization approach. Since the amplitude of the vector meson production off a proton is expressed via the differential gluon structure function (DGSF), we take a closer look at the latter and present results of our new improved determination of the DGSF from the structure function F_2p. Having determined the differential glue, we proceed to the k_t-factorization results for the production of various vector mesons. We argue that the properties of the vector meson production can reveal the internal spin-angular and radial structure of the vector meson.
Photon-jet azimuthal correlations in proton-nucleus collisions are a promising tool for gaining information on the gluon distribution of the nucleus in the regime of non-linear color fields. We compute such correlations from the process $g+Ato q bar{q} gamma$ in the rapidity regime where both the projectile and target light-cone momentum fractions are small. By integrating over the phase space of the quark which emits the photon, subject to the restriction that the photon picks up most of the transverse momentum (to pass an isolation cut), we effectively obtain a $g+Ato q gamma$ process. For nearly back-to-back photon-jet configurations we find that it dominates over the leading order process $q+Ato q gamma$ by two less powers of $Q_perp / Q_S$, where $boldsymbol{Q}_perp$ and $Q_S$ denote the net photon-jet pair momentum and the saturation scale of the nucleus, respectively. We determine the transverse momentum dependent gluon distributions involved in $g+Ato q gamma$ and the scale where they are evaluated. Finally, we provide analytic expressions for $langlecos nphirangle$ moments, where $phi$ is the angle between $boldsymbol{Q}_perp$ and the average photon-jet transverse momentum $tilde{boldsymbol{P}}_perp$, and first qualitative estimates of their transverse momentum dependence.
Final states with a vector boson and a hadronic jet allow one to infer the Born-level kinematics of the underlying hard scattering process, thereby probing the partonic structure of the colliding protons. At forward rapidities, the parton collisions are highly asymmetric and resolve the parton distributions at very large or very small momentum fractions, where they are less well constrained by other processes. Using theory predictions accurate to next-to-next-to-leading order (NNLO) in QCD for both $mathrm{W}^{pm}$ and $mathrm{Z}$ production in association with a jet at large rapidities at the LHC, we perform a detailed phenomenological analysis of recent LHC measurements. The increased theory precision allows us to clearly identify specific kinematical regions where the description of the data is insufficient. By constructing ratios and asymmetries of these cross sections, we aim to identify possible origins of the deviations, and highlight the potential impact of the data on improved determinations of parton distributions.
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