EXPERIMENTS
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 LE21 EXPERIMENT, RESPONSIBLE: Matteo Beccaria

KEYWORDS:

200 Phenomenology
220 QED, Standard Model and Beyond
224 Super-Symmetric Extensions of the Standard Model

TITLE: PRECISION PHYSICS AT FUTURE ACCELERATORS

One major aim of the research project LE21 for the 2006 year was that of a COMPLETE systematic analysis of the electroweak virtual effects at one loop in the Minimal Supersymmetric Standard Model for the process of single top production at LHC. For the three processes of single top production we worked in collaboration with F.M.Renard, G.Montagna, O.Nicrosini and F.Piccinini. There is no previous electroweak calculation for these single top production processes at the one loop level.We expected to have concluded the full analysis within the 2006 year.

At the moment, we have in fact concluded the complete one loop calculation for the two dominant processes of single top production, the so called t-channel (td) production and the so called associated (tW) production. The results have appeared in two papers, one of which (the tW) already published on Phys. Rev.D, the other one (td) accepted for publication on Phys. Rev. D. The electroweak one loop effect has been found to be large ,larger than the QCD effect in the t channel,and potentially measurable. We have completed two C++ programs for the two processes, that are working and are available. We are completing the calculation ot the third s-channel process (tbbar production) and are ready to derive the complete program for the "crossed" processes of t production and for the corresponding processes of single antitop production.

During the year 2007, we expect to combine all the calculations of single top production with the analogous ones of single stop production at LHC, having in mind possible supersymmetric scenarios involving a very light stop (motivated by baryogenesis models).The ATLAS top group with M.Cobal and S.Bentvelsen is continuing his collaboration with us and is completing the experimental study for the overall processes of single top production, which should be ready at the beginning of 2007.Combining the different results, the possibility of performing a precision test of Supersymmetric models in the process of single top and stop production at LHC will be considered with realistic attitude.The final step of combining our electroweak calculation with the QCD one for single top production is actively being considered and preliminary discussions e.g. with Fabio Maltoni and his Louvain group are now beginning. Also, an interaction with the Lubiana Montecarlo group of Borut Kersevan , aiming to insert in 2007 our complete one loop electroweak effects in a Montecarlo program, has already started.

In parallel with this search, a second component of the group will continue a more speculative activity in the framework of electroweak radiative corrections at high LHC energies, considering observables that are fully inclusive with respect to soft gauge boson emission and where a certain number of non abelian isospin charges in the initial and/or final states are detected . A general formalism has beeen produced to evaluate leading, all order resummed electroweak corrections.At the moment,
the most relevant case appears to be that of the third family quark production.In the case of bottom-antibottom pairs, it has been found that the production cross section can become one order of magnitude bigger than the tree level value due to the interplay between strong and weak interactions.
In the year 2007, the component wants to proceed in the analysis of real and virtual W boson emission in heavy quark production and Drell Yan processes at high momentum transfer at LHC.

 GOALS OF LE21 EXPERIMENT
 KEYWORDS: 200 Phenomenology 220 QED, Standard Model and Beyond 224 Super-Symmetric Extensions of the Standard Model TITLE: PRECISION PHYSICS AT FUTURE ACCELERATORS The activity of LE21 in 2011 hinged on three topics: topic 1: electroweak and QCD corrections at LHC Many extensions of the Standard Model involve two Higgs doublet fields to break the electroweak symmetry, leading to the existence of three neutral and two charged Higgs particles. In particular, this is the case of the Minimal Supersymmetric extension of the Standard Model, the MSSM. A very important parameter is $\tan\beta$ defined as the ratio of the vacuum expectation value of the two Higgs doublets. We focused on the left-right asymmetry in the production of polarised top quarks in association with charged Higgs bosons at the LHC. This quantity allows for a theoretically clean determination of $\tan\beta$. In the MSSM, the asymmetry remains sensitive to the strong and electroweak radiative corrections and, thus, to the superparticle spectrum. Some possible implications of these results are discussed. topic 2: electroweak corrections and Dark Matter The computation of the energy spectra of Standard Model particles originated from the annihilation/decay of dark matter particles is of primary importance in indirect searches of dark matter. We computed how the inclusion of electroweak corrections significantly alter such spectra when the mass M of dark matter particles is larger than the electroweak scale: soft electroweak gauge bosons are copiously radiated opening new channels in the final states which otherwise would be forbidden if such corrections are neglected. All stable particles are therefore present in the final spectrum, independently of the primary channel of dark matter annihilation/decay. Such corrections are model independent. topic 3: electroweak corrections at low energy The activity focussed on the determination of the two-nucleon electromagnetic charge operator up to the 1-loop order, and of the subleading component of the short-range 3-nucleon interaction, within the framework of the low-energy effective field theory of QCD.

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