We discuss polarized lepton-proton scattering with special emphasis on the difference between target polarization defined relative to the lepton beam or to the virtual photon direction. In particular, this difference influences azimuthal distributions in the final state. We provide a general framework of analysis and apply it to the specific cases of semi-inclusive deep inelastic scattering, of exclusive meson production, and of deeply virtual Compton scattering.1

Predictions for charged hadron, identified light hadron, quarkonium, photon, jet and gauge bosons in p+ Pb collisions at [Formula: see text] are compiled and compared. When test run data are available, they are compared to the model predictions.

This writeup is a compilation of the predictions for the forthcoming Heavy Ion Program at the Large Hadron Collider, as presented at the CERN Theory Institute ‘Heavy Ion Collisions at the LHC—Last Call for Predictions’, held from 14th May to 10th June 2007.

We study saturation effects in the production of dijets in p-p and p-Pb collisions using the framework of high energy factorization. We focus on central-forward jet configurations, which allow for probing gluon density at low longitudinal momentum fraction. We find significant suppression of the central-forward jet decorrelations in p-Pb compared to p-p, which we attribute to saturation of gluon density in nuclei.

Hadronic observables in Z+jet events can be subject to large NLO corrections at TeV scales, with K-factors that even reach values of order 50 in some cases. We develop a method, LoopSim, by which approximate NNLO predictions can be obtained for such observables, supplementing NLO Z+jet and NLO Z+2-jet results with a unitarity-based approximation for missing higher loop terms. We first test the method against known NNLO results for Drell-Yan lepton p t spectra. We then show our approximate NNLO results for the Z+jet observables. Finally we examine whether the LoopSim method can provide useful information even in cases without giant K-factors, with results for observables in dijet events that can be compared to early LHC data.

The measurement of the underlying event (UE) and its separation from hard interactions in hadron-collider events is a conceptually and practically challenging task. We develop a simple, mostly analytical toy model for the UE in order to understand how different UE measurement approaches fare on the practical aspects of this problem, comparing the traditional approach used so far at Tevatron with a recently proposed "jet-area/median" approach. Both are found to perform comparably well in measuring average properties of the UE, such as the mean transverse momentum flow, but the jet-area/median approach has distinct advantages in determining its fluctuations. We then use the jet-area/median method to investigate a range of UE properties in existing Monte Carlo event-generator tunes, validating the main results of the toy-model and highlighting so-far unmeasured characteristics of the UE such as its rapidity dependence, as well as its intra-and interevent fluctuations and correlations.

We study forward dijet production in dilute-dense hadronic collisions. By considering the appropriate limits, we show that both the transverse-momentum-dependent (TMD) and the high-energy factorization formulas can be derived from the Color Glass Condensate framework. Respectively, this happens when the transverse momentum imbalance of the dijet system, k t , is of the order of either the saturation scale, or the hard jet momenta, the former being always much smaller than the latter. We propose a new formula for forward dijets that encompasses both situations and is therefore applicable regardless of the magnitude of k t . That involves generalizing the TMD factorization formula for dijet production to the case where the incoming small-x gluon is off-shell. The derivation is performed in two independent ways, using either Feynman diagram techniques, or color-ordered amplitudes.

A new method of including the complete NLO QCD corrections to hard processes in the LO parton-shower Monte Carlo (PSMC) is presented. This method, called KrkNLO, requires the use of parton distribution functions in a dedicated Monte Carlo (MC) factorization scheme, which is also discussed in this paper. In the future, it may simplify introduction of the NNLO corrections to hard processes and the NLO corrections to PSMC. Details of the method and numerical examples of its practical implementation as well as comparisons with other calculations, such as MCFM, MC@NLO, POWHEG, for single Z/γ * -boson production at the LHC are presented.the sense that it presents a simplified method of correcting the hard process to the NLO level in combination with the LO parton shower (PS). In other words, it offers a simpler alternative to the MC@NLO and POWHEG methods of Refs. [2,3], which may hopefully pave the way to the NNLO hard process combined with NLO PSMC.The new method described here, nicknamed as KrkNLO, was already proposed in Ref. [19], where its first numerical implementation was done on top of the dedicated toy model PSMC and was limited to the gluonstrahlung subset of the NLO corrections. Later on it was tested numerically in a more detail in Refs. [15,20]. In the present work the KrkNLO method is implemented within the standard PSMC Sherpa 2.0.0 [11]. A pilot study of KrkNLO implementation outside PS MC, using MC event encoded in the event records produced by Herwig++ 2.7.0 [9,21,22] and Sherpa 2.0.0 was also done. Let us stress, however, that the overall simplifications of the KrkNLO method comes not completely for free, as it requires to use parton distribution functions (PDFs) in a special Monte Carlo (MC) factorization scheme (obtained, however, easily from reprocessing the MS PDFs), and it is required that the basic LO PSMC provides for the NLO-complete coverage of the hard process phase space (this is also not a problem for all modern PSMCs). Our method is simpler to implement in the case of PSMC with an ordering based on the transverse momentum k T or a q 2 variable of Ref.[23], inspired by the classic Catani-Seymour work [24]. However, it can be also easily implemented on top of PSMC that uses the angular ordering -without the need of the so-called truncated showers required in the POWHEG method, see Refs. [20,25] for more discussion on that.The main advantage of the KrkNLO method is a simplification of the NLO corrections due to the use of PDFs in the MC factorization scheme. The implementation of the entire NLO corrections with the help of a single multiplicative simple weight on top of the LO distribution is a quite unique feature of the KrkNLO method.Numerical studies presented here will be extended in the future publications to a wider range of distributions, energies, implementation variants, including comparisons with experimental data.The paper is organized as follows. In Section 2 we introduce the kinematics and the phase space parametrization for the considered process. In Section 3 we describe in ...