arXiv subjects
Publications and source records attributed to C. M. Carloni Calame.
This report summarizes the activity on comparisons of existings tools for the standard model and on issues in jet physics by the SMHC working group during and subsequent to the Workshop "Physics at TeV Colliders", Les Houches, France, 11-29 June, 2007.
We present a high-precision QED calculation, with 0.1% theoretical accuracy, of two photon production in $e^+ e^-$ annihilation, as required by more and more accurate luminosity monitoring at flavour factories. The accuracy of the approach, which is based on the matching of exact next-to-leading order corrections with a QED Parton Shower algorithm, is demonstrated through a detailed analysis of the impact of the various sources of radiative corrections to the experimentally relevant observables. The calculation is implemented in the latest version of the event generator BabaYaga, available for precision simulations of photon pair production at $e^+ e^-$ colliders of moderately high energies.
We compute, in the MSSM framework, the sum of the one-loop electroweak and of the total QED radiation effects for the process $pp \to t W+X$, initiated by the parton process $bg\to tW$. Combining these terms with the existing NLO calculations of SM and SUSY QCD corrections, we analyze the overall one-loop supersymmetric effects on the partial rates of the process, obtained by integrating the differential cross section up to a final variable invariant mass. We conclude that, for some choices of the SUSY parameters and for relatively small final invariant masses, they could reach the relative ten percent level, possibly relevant for a dedicated experimental effort at LHC.
We present a detailed study of the production of a high transverse-momentum lepton pair at hadron colliders, which includes the exact O(alpha) electroweak corrections properly matched with leading logarithmic effects due to multiple photon emission, as required by the experiments at the Fermilab Tevatron and the CERN LHC. Numerical results for the relevant observables of single Z-boson production at hadron colliders are presented. The impact of the radiative corrections is discussed in detail. The presence in the proton of a photon density is considered and the effects of the photon-induced partonic subprocesses are analyzed. The calculation has been implemented in the new version of the event generator HORACE, which is available for precision simulations of the neutral and charged current Drell-Yan processes.
The top quark and electroweak bosons (W and Z) represent the most massive fundamental particles yet discovered, and as such refer directly to the Standard Model's greatest remaining mystery: the mechanism by which all particles gained mass. This report summarizes the work done within the top-ew group of the Tevatron-for-LHC workshop. It represents a collection of both Tevatron results, and LHC predictions. The hope is that by considering and comparing both machines, the LHC program can be improved and aided by knowledge from the Tevatron, and that particle physics as a whole can be enriched. The report includes measurements of the top quark mass, searches for single top quark production, and physics of the electroweak bosons at hadron colliders.
We report on a high-precision calculation of the Bhabha process in Quantum Electrodynamics, of interest for precise luminosity determination of electron-positron colliders involved in R measurements in the region of hadronic resonances. The calculation is based on the matching of exact next-to-leading order corrections with a Parton Shower algorithm. The accuracy of the approach is demonstrated in comparison with existing independent calculations and through a detailed analysis of the main components of theoretical uncertainty, including two-loop corrections, hadronic vacuum polarization and light pair contributions. The calculation is implemented in an improved version of the event generator BABAYAGA with a theoretical accuracy of the order of 0.1%. The generator is now available for high-precision simulations of the Bhabha process at flavour factories.
A concise review about the status of the calculation of radiative corrections to the Drell-Yan processes is presented. The effect of matching together exact electroweak O(alpha) corrections with higher-order QED effects due to multiple photon emission is displayed in some physical distributions in the charged current channel, which have obtained with the new version of the event generator HORACE.
A new version of the event generator BABAYAGA is presented, which is based on an original matching of the Parton Shower approach with the complete exact O(alpha) matrix element for the inclusion of the QED radiative corrections to the Bhabha process at flavour factories. The theoretical accuracy of the improved generator is conservatively estimated to be 0.2%, by comparison with independent calculations. The generator is a useful tool for precise luminosity determination at flavour factories, for center of mass energies below 10 GeV.
We report on a high-precision calculation of the Bhabha process in QED, of interest for precise luminosity determination of low-energy electron-positron colliders. The calculation is based on the matching of exact next-to-leading order corrections with a Parton Shower algorithm. The structure of the algorithm (implemented in an improved version of the event generator BABAYAGA) is illustrated, with a discussion on the resulting theoretical uncertainty, of the order of 0.1 %.
We present a detailed study of the charged current Drell-Yan process, which includes the exact O(alpha) electroweak corrections properly matched with leading-log effects due to multiple-photon emission, as required by the experiments at the Tevatron and the LHC. Numerical results for the relevant observables of single W boson production at hadron colliders are presented. The impact of the radiative corrections and of some sources of theoretical uncertainty is discussed in detail. The calculation has been implemented in the new version of the event generator HORACE, which is available for precision simulations of the charged current Drell-Yan process.
At the LHC a precise measurement of the Higgs boson mass (if discovered), at the level of 0.1-1%, will be possible through the channel g g --> H --> 4l for a wide range of Higgs mass values. To match such an accuracy, the systematic effects induced by QED corrections need to be investigated. In the present study the calculation of O(alpha) and higher order QED corrections is illustrated as well as their impact on the Higgs mass determination, once realistic event selection criteria for charged leptons and photons are considered.
We present the comparisons of two independent Monte Carlo event generators, HORACE and WINHAC, for single-W-boson production in hadronic collisions with multiphoton effects in leptonic W decays. These comparisons were performed first at the parton level with fixed quark-beams energy, and then at the hadron level for proton-proton collisions at the LHC. In general, a good agreement between the two programs has been found. Possible sources of differences in some of the presented results are discussed. We also present and discuss the effects of including non-zero quark masses for the main single-W-boson observables at the LHC.
At present and future hadron colliders, the precision physics program started in the past will be continued. In particular, a precise determination of the W boson mass will be carried out. This requires the calculation of the radiative corrections and their implementation in Monte Carlo event generators for data analysis. In this talk, the status of the calculation of the order alpha electroweak radiative corrections is reviewed and a study of the impact of higher order QED corrections on the W boson mass is presented.
The program BABAYAGA is an event generator for QED processes at flavour factories, mainly intended for luminosity measurement of e+ e- colliders in the center of mass range 1-10 GeV. Recently, the pi+ pi- channel has been added as well. The relevant (photonic) radiative corrections are simulated by means of a Parton Shower in QED. The theoretical precision of the approach is estimated and some phenomenological results are discussed.
The impact of higher-order final-state photonic corrections on the precise determination of the W-boson mass at the Tevatron and LHC colliders is evaluated. The W-mass shift from a fit to the transverse mass distribution is found to be about 10 MeV in the W --> mu nu channel and a few MeV in the W --> e nu channel. The calculation, which is implemented in the Monte Carlo event generator HORACE for data analysis, can contribute to reduce the uncertainty associated to the W mass measurement at present and future hadron collider experiments.
The impact of higher-order final-state photonic corrections on the precise determination of the W-boson mass at the Tevatron and LHC colliders is evaluated. In the presence of realistic selection criteria, the shift in the W mass from a fit to the transverse mass distribution is found to be about 10 MeV in the $W \to μν$ channel and almost negligible in the $W \to e ν$ channel. The calculation, which is implemented in a Monte Carlo event generator for data analysis, can contribute to reduce the uncertainty associated to the W mass measurement at future hadron collider experiments.
The luminosity determination of electron-positron colliders operating in the region of low-lying hadronic resonances (E_cm ~ 1-10 GeV), such as BEPC/BES, DAPHNE, KEKB, PEP-II and VEPP-2M, requires the precision calculation of the Bhabha process at large scattering angles. In order to achieve a theoretical accuracy at a few 0.1% level, the inclusion of radiative corrections is mandatory. The phenomenologically relevant effect of QED corrections is taken into account in the framework of the Parton Shower (PS) method, which is employed both for cross section calculation and event generation. To test the reliability of the approach, a benchmark calculation, including exact O(alpha) corrections and higher-order leading logarithmic contributions, is developed as well and compared in detail with the PS predictions. The effect of O(alpha) next-to-leading and higher-order leading corrections is investigated in the presence of realistic event selections for the Bhabha process at the Phi-factories. A new Monte Carlo generator for data analysis (BABAYAGA) is presented, with an estimated accuracy of 0.5%. Possible developments aiming at improving its precision and range of applicability are discussed.
The accurate knowledge of luminosity at e^+ e^- flavour factories requires the precision calculation of the Bhabha cross section at large scattering angles. In order to achieve a theoretical accuracy at the 0.1% level, the relevant effect of QED radiative corrections is taken into account in the framework of the Parton Shower method, which allows exclusive event generation. On this scheme, a Monte Carlo event generator (BABAYAGA) is developed for data analysis. To test the reliability of the approach, a benchmark calculation, including exact O(alpha) corrections and higher-order leading logarithmic contributions, is developed as well, implemented in a Monte Carlo integrator (LABSPV) and compared in detail with the BABAYAGA predictions. The effect of initial-state and final-state radiation, O(alpha) next-to-leading and higher-order leading corrections is investigated and discussed in the presence of realistic event selections. The theoretical precision of BABAYAGA is estimated to be at the 0.5% level.