Small-cone Approximation Research Articles

The NLO jet vertex in the small-cone approximation for kt and cone algorithms

We determine the jet vertex for Mueller-Navelet jets and forward jets in the small-cone approximation for two particular choices of jet algoritms: the kt algorithm and the cone algorithm. These choices are motivated by the extensive use of such algorithms in the phenomenology of jets. The differences with the original calculations of the small-cone jet vertex by Ivanov and Papa, which is found to be equivalent to a formerly algorithm proposed by Furman, are shown at both analytic and numerical level, and turn out to be sizeable. A detailed numerical study of the error introduced by the small-cone approximation is also presented, for various observables of phenomenological interest. For values of the jet "radius" R=0.5, the use of the small-cone approximation amounts to an error of about 5% at the level of cross section, while it reduces to less than 2% for ratios of distributions such as those involved in the measure of the azimuthal decorrelation of dijets.

The next-to-leading order forward jet vertex in the small-cone approximation

We consider within QCD collinear factorization the process p+p to jet + jet +X, where two forward high-$p_T$ jets are produced with a large separation in rapidity $\Delta y$ (Mueller-Navelet jets). In this case the (calculable) hard part of the reaction receives large higher-order corrections $\sim \alpha^n_s (\Delta y)^n$, which can be accounted for in the BFKL approach. In particular, we calculate in the next-to-leading order the impact factor (vertex) for the production of a forward high-$p_T$ jet, in the approximation of small aperture of the jet cone in the pseudorapidity-azimuthal angle plane. The final expression for the vertex turns out to be simple and easy to implement in numerical calculations.

Single-inclusive jet production in polarized pp collisions at RHIC to next-to-leading logarithmic accuracy

We perform the resummation of large logarithmic corrections to the partonic cross sections for single-inclusive jet production in polarized pp collisions. We reach the next-to-leading logarithmic accuracy for this observable with the corresponding matching to the next-to-leading order calculation performed in the small-cone approximation. We present numerical results for the BNL-RHIC collider at \sqrt{S}=200 GeV and 500 GeV. We find an enhancement of the spin-dependent cross section, specially at high transverse momentum for the jet, resulting in a rather small increase of the double-spin asymmetry A_LL for this process.

Photoproduction of single inclusive jets at futureepcolliders in next-to-leading order QCD

A next-to-leading order QCD calculation for single-inclusive jet photoproduction in unpolarized and longitudinally polarized lepton-hadron collisions is presented which consistently includes ``direct'' and ``resolved'' photon contributions. The computation is performed within the ``small-cone approximation'' in a largely analytical form. Phenomenological aspects of jet production at future $ep$ colliders such as the CERN Large Hadron electron Collider and the polarized Brookhaven National Laboratory eRHIC are discussed, placing particular emphasis on the perturbative stability of the predictions and the possibility to constrain the parton content of the photon.

Order(αs2)QCD corrections to inclusive jet production in deep inelastic scattering

We analyze the order ${\ensuremath{\alpha}}_{s}^{2}$ corrections to the single inclusive jet cross section in lepton-nucleon deep inelastic scattering. The full calculation is done analytically, in the small cone approximation, obtaining finite NLO partonic level cross sections for these processes. A detailed study of the different underlying partonic reactions is presented focusing in the size of the corrections they get at NLO accuracy, their relative weight, and the residual scale uncertainty they leave in the full cross section depending on the kinematical region explored. In agreement with what has already been found in forward production of ${\ensuremath{\pi}}^{0}$, we show that the dominant partonic process in very forward jet production is found to start at order ${\ensuremath{\alpha}}_{s}^{2}$, being effectively a lowest order estimate, with the consequent large factorization scale uncertainty, and the likelihood of non-negligible corrections at the subsequent order in perturbation theory.

High-pT photon production at pp-bar colliders.

It is demonstrated by consistent next-to-leading order (NLO) calculations for isolated prompt photon production, performed within the small-cone approximation, that previous discrepancies between NLO expectations for the direct [gamma] production rates at small [ital p][sub [ital T]][sup [gamma]]([approx gt]11 GeV) and isolated prompt photon data are removed. This is not only due to the use of experimentally confirmed steep small [ital x] parton distributions, but also due to a consistent inclusion of isolated photonic fragmentation contributions in NLO. The latter contributions are even more important for fully inclusive predictions.