arXiv subjects
D. de Florian
Publications and source records attributed to D. de Florian.
WGamma and ZGamma production at Hadron Colliders
We present a general purpose Monte Carlo program for the calculation of any infrared safe observable in WGamma and ZGamma production at hadron colliders at next-to-leading order in alpha_s. We treat the leptonic decays of the W and Z-boson in the narrow-width approximation, but retain all spin information via decay angle correlations. The effect of anomalous triple gauge boson couplings is investigated and we give the analytical expressions for the corresponding amplitudes. Furthermore, we propose a way to study the effect of anomalous couplings without introducing the ambiguity of form factors.
Two photons plus jet al LHC: the NNLO contribution from the gg initiated process
The production of the Standard Model Higgs boson of mass ~ 100-140 GeV at the LHC likely gives clear signals in the $γγ$ (1) and in the $γγjet$ (2) channels. The quantitative evaluation of the background to channel (1) is very hard since the next-to-leading order (NLO) and next-to-next-to-leading order (NNLO) QCD corrections are large. In particular, the contributions of the NNLO QCD subprocess $gg -> γγ$ to inclusive $γγ$ production is comparable to the contribution of the leading order subprocess $q\bar{q} -> γγ$. The quantitative description of the background to channel (1), therefore, requires to calculate all corrections up to the NNNLO level. In this letter we present results on the contribution of the NNLO QCD subprocess $gg -> g γγ$ to the production rate of channel (2). We have found that in this case this NNLO contribution is less than 20% of the Born contribution. Since the NNLO contributions will likely be dominated by this subprocess one can argue that in the case of channel (2) - contrary to the case of channel (1)- a quantitative description of the background can be achieved already at next-to-leading order accuracy.
Jet cross sections in polarized photon-hadron collisions
We present a computation of one- and two-jet cross sections in polarized photon-hadron collisions, which is accurate to next-to-leading order in QCD. Our results can be used to compute photoproduction cross sections in electron-proton scattering. To this purpose, we investigate the structure of the polarized Weizsaecker-Williams function, where we include a universal, non-logarithmic term, neglected in the literature. We construct a Monte Carlo code, within the framework of the subtraction method, and we use it to study the phenomenology of jet production in the energy range relevant to HERA. In particular, we investigate the perturbative stability of our results, and we discuss the possibility of constraining polarized parton densities of the proton and the photon using jet data.
Higgs production with large transverse momentum in hadronic collisions at next-to-leading order
Inclusive associated production of a light Higgs boson (m_H < m_t) with one jet in pp collisions is studied in next-to-leading order QCD. Transverse momentum (p_T < 30 GeV) and rapidity distributions of the Higgs boson are calculated for the LHC in the large top-quark mass limit. It is pointed out that, as much as in the case of inclusive Higgs production, the K-factor of this process is large (~1.6) and depends weakly on the kinematics in a wide range of transverse momentum and rapidity intervals. Our result confirms previous suggestions that the production channel p+p -> H+jet -> gamma+gamma+jet gives a measurable signal for Higgs production at the LHC in the mass range 100-140 GeV, crucial also for the ultimate test of the Minimal Supersymmetric Standard Model.
Fracture Functions for Diffractive and Leading Proton DIS
We present a combined QCD analysis of diffractive and leading proton deep inelastic scattering data using the framework of fracture functions. It is shown that this framework allows a precise and unified perturbative QCD description for the data, alternative to those that relay on Regge factorization.
Next-to-leading order jet cross sections in polarized hadronic collisions
We present a next-to-leading order computation in QCD of one-jet and two-jet cross sections in polarized hadronic collisions. Our results are obtained in the framework of a general formalism that deals with soft and collinear singularities using the subtraction method. We construct a Monte Carlo program that generates events at the partonic level. We use this code to give phenomenological predictions for $pp$ collisions at $\sqrt{S}=500$ GeV, relevant for the spin physics program at RHIC. The possibility of using jet data to constrain the poorly known polarized parton densities is examined.
Bounds on Transverse Spin Asymmetries for Lambda Baryon Production in pp Collisions at BNL RHIC
We study inclusive Lambda hyperon production in pp collisions at BNL RHIC, with just one transversely polarized proton. We show that the measurement of the spin transfer between the initial proton and the produced Lambda is sensitive to the proton transversity distributions and to the corresponding Lambda transversity fragmentation functions. In view of our present ignorance of these distributions and fragmentation functions, we resort to positivity bounds for making some predictions for the corresponding spin transfer asymmetry.
QCD Analysis of Diffractive and Leading-Proton DIS Structure Functions in the Framework of Fracture Functions
We present a combined QCD analysis of recent data produced by the H1 and ZEUS collaborations on the diffractive and leading-proton deep inelastic positron--proton scattering structure functions, $F_2^{D(3)}$ and $F_2^{LP(3)}$, respectively. It is shown that the QCD framework for semi-inclusive processes, based on fracture functions, allows a unified treatment of both diffractive and leading-proton processes, and offers a precise perturbative QCD description for them, alternative to those that rely on model-dependent assumptions, such as Regge factorization, or other non-perturbative approaches
Polarized Lambda-Baryon Production in pp Collisions
We study the production of longitudinally polarized Lambda-baryons in single-spin pp collisions at RHIC and HERA-N as a means of determining the spin-dependent Lambda fragmentation functions. It is shown that a measurement of the rapidity distribution of the Lambda's would provide an excellent way of clearly discriminating between various recently suggested sets of polarized Lambda fragmentation functions that are all compatible with present e^+e^- data. We also address the main theoretical uncertainties, which appear to be well under control.
Next-to-leading order QCD corrections to inclusive-hadron photoproduction in polarized lepton-proton collisions
We calculate the next-to-leading order QCD corrections to the `direct' part of the spin-dependent cross section for single-inclusive charged-hadron photoproduction. This process could be studied experimentally in future polarized fixed-target lepton-nucleon experiments, but also at the HERA ep collider after an upgrade to both beams being polarized. We present a brief numerical evaluation of our results by studying the K-factors and the scale dependence of the NLO cross section.
Next-to-Leading Order Analysis of Inclusive and Semi-inclusive Polarized Data
We present a combined next-to-leading order QCD analysis to data on both inclusive and semi-inclusive polarized deep inelastic scattering asymmetries. Performing NLO QCD global fits with different sets of observables, we evaluate the impact of the very recent semi-inclusive results presented by SMC in the extraction of NLO polarized parton distributions.
QCD Analysis of Unpolarized and Polarized Lambda - Baryon Production in Leading and Next-to-Leading Order
We analyze experimental data for the production of Lambda baryons in e^+e^- annihilation in terms of scale dependent, QCD evolved, Lambda fragmentation functions. Apart from the vast majority of the data for which the polarization of an observed Lambda was not determined, we also consider the recent LEP measurements of the longitudinal polarization of Lambda's produced on the Z-resonance. Such data correspond to spin-dependent fragmentation functions for the Lambda. We point out that the present data are insufficient to satisfactorily fix these. We therefore suggest several different sets of fragmentation functions, all compatible with present data, and study the prospects for conceivable future semi-inclusive deep-inelastic scattering experiments to discriminate between them. We provide the complete next-to-leading order QCD framework for all the processes we consider.
Target Fragmentation at Polarized HERA: A Test of Universal Topological Charge Screening in QCD
Topological charge screening has been proposed as the mechanism responsible for the anomalous suppression in the first moment of the polarized proton structure function -- the `proton spin' effect. An immediate consequence is that this suppression should be target-independent, since the screening is a fundamental property of the QCD vacuum. Here, we study the possibility of testing the target-independent suppression in semi-inclusive target fragmentation processes at polarized HERA.
Polarized Lambda Production at HERA
We study the prospects for HERA with polarized electron and/or proton beams to determine the functions describing the fragmentation of a longitudinally polarized parton into a polarized Lambda baryon. We examine both semi-inclusive deep-inelastic scattering (SIDIS) and photoproduction of Lambda.
Target Fragmentation and Fracture Functions
We analyse recent data on the production of forward neutrons in deep inelastic scattering at HERA in the framework of a perturbative QCD description for semi-inclusive processes, which includes fracture functions.
Next to Leading Order QCD Corrections to Polarized $Λ$ Production in DIS
We calculate next to leading order QCD corrections to semi-inclusive polarized deep inelastic scattering and $e^+e^-$ annihilation cross sections for processes where the polarization of the identified final-state hadron can also be determined. Using dimensional regularization and the HVBM prescription for the $γ_5$ matrix, we compute corrections for different spin-dependent observables, both in the $\overline{MS}$ and $\overline{MS_p}$ factorization schemes, and analyse their structure. In addition to the well known corrections to polarized parton distributions, we also present those for final-state polarized fracture functions and polarized fragmentation functions, in a consistent factorization scheme.
Photoproduction of jets and the virtual structure of the photon
We compute the ratio between the direct and the resolved photon components of single jet and dijet production in $ep$ collisions for the kinematical range covered by the most recent ZEUS data. We analyse the phenomenological consequences of different models for the structure of virtual photons in these observables and compare them with the available data. We also comment on the correlation between the so called $x_γ^{obs}$ and the `true' $x_γ$, that can be inferred from the data.