| RM21 EXPERIMENT, RESPONSIBLE: Luca Silvestrini
The activity in testing the Standard Model and looking for New Physics (NP) in the flavour sector has continued. In particular, evidence of NP in Bs oscillations has been pointed out combining all available information.
A detailed analysis of flavour changing neutral currents and CP violation in grand-unified SUSY models has been performed.
We have refined comparison with experimental data and extracted the CKM parameter Vub.
The |Vub| value has been obtained from the available measured semileptonic branching fractions in limited regions of the phase–space.
The |Vub| value obtained is in complete agreement with the value coming from exclusive B decays and from an over–all fit to the Standard Model parameters, while the agreement is less good (1.7 s) with respect to previous inclusive measurements. We have shown that the
latter difference is not related to different choices for the b (and c) masses but to
a different modelling of the threshold (Sudakov) region.
Deviations from the Standard Model expectations of the
Lepton Flavor Universality (LFU) breaking represent a powerful tool
to test the Standard Model and to constrain or obtain indirect hints
of New Physics beyond it. Lepton flavor violating contributions
can be present in SUSY extensions of the Standard Model.
We performed a general analisys on the lepton flavor violations in SUSY
which includes the purely leptonic decays of all charged mesons (pion, kaon and B).
We are studying radiative generation of masses and mixings for
charged fermions in models beyond the Standard Model, such as
supersimmetric extensions or models with extended Higgs sector (several Higgs doublets).
Analyses and discussions on neutrino properties and oscillations, on high energy (astrophysical) neutrinos and on cosmic rays are under way. A reanalysis of the proposal
to determine the electron neutrino mass using the EC decay of 163Ho is in progress, in view of the improved experimental possibilities.
The study of production and detection of new physics signals at the LHC within and beyond the standard model is continuing. In particular :
a) Study of LHC potential in detecting a Higgs Boson anomalously coupled to the muon lepton, as foreseen by a few SM extensions.
b) In the framework of the two-Higgs-doublets MSSM models,
heavier neutral Higgs bosons production accompanied by a high-pt photon at the LHC has been considered.
This process can provide a clean probe of the b-quark parton densities in the proton.
We have suggested a new approach for the fully numerical evaluation of one-loop scattering amplitudes in perturbative quantum field theory. We use dispersion relations techniques to perform the calculation of 1-loop amplitudes represented as convolutions of tree-level amplitudes. This allows to take advantage of the iterative numerical algorithms, like ALPHA used in ALPGEN, for the evaluation of leading order matrix elements.
We have explored the possibility that radially excited aggregations of spin zero or spin one diquarks might exist and discuss the possibility of the Y(2175) state observed by BaBar and confirmed by BES could be such state. Reanalizing BaBar data we find that the Y(2175) mostly decays into baryon-antibaryon thus favoring a tetraquark picture.
In the framework of large N scalar QCD in two dimensions, the 't Hooft model, we compute the discrete hadron mass spectrum making the Ansatz that that the "fundamental" colored scalar fields of this model represent spin zero diquarks. We estimate the minimum allowed mass for the first radial excitation of the lowest diquark-antidiquark scalar meson concluding that in the 't Hooft model, scalar mesons above 1 GeV are likely qqbar bound states.
|PARTICLE THEORY AND PHENOMENOLOGY WITHIN AND BEYOND THE
Research activities, goals achieved and future projects
1) Fit of the Unitarity Triangle in the Standard Model and beyond.
The web site of the UTfit collaboration is maintained and continuously updated with the new experimental and theoretical results. Updated results are presented at major conferences. Papers are written for major updates or novelties, and for specific New Physics scenarios. Computational tools are extended to take into account theoretical and experimental developments.
2) Nonleptonic B decays, rare decays, CP and Flavor violation in the
Standard Model and SUSY.
The study of nonleptonic B decays continues with new analyses of modes with vector mesons in the final states. NLO QCD corrections to gluino contributions have been computed (in the MSSM ) for DeltaF=2 processes and for the electric dipole moment of the neutron. A phenomenological analysis is under way. Combined analyses of flavour and CP violation in the hadronic and leptonic sectors in SUSY-GUT models have been performed, new analyses are in progress.
3) Physics at the present and future colliders:
Some physical issues of LHC , in particular the Higgs production, have been analyzed. The complete O(alpha) calculation and higher order QED corrections to Higgs decay into four leptons and the full simulation of Higgs plus two forward jets final production have been performed.
Moreover an activity has been initiated to study the interplay of flavour and high-pt data in the study of new physics at the LHC.
The physical potential of Linear e+e- Collider has been analyzed, in order to motivate a future decision for the project with c.m. energy equal or larger than 500 GeV.
4) Mechanisms of electroweak symmetry breaking.
The implications of a particular scenarios in which the Higgs boson is a composite state of a strongly interacting sector have been analyzed. It has been shown how ,in composite Higgs models, the Zbbar coupling can be protected by the same custodial symmetry that protects the rho parameter.
A specific model which implements this new idea is now under investigation.
The quantum level problems for models where the Higgs field is generated from the extra-dimensional components of the gauge fields are been analyzed, in these models the parameters of the Supersymmetry breaking or of flavour symmetry breaking are related to the geometrical properties of the fundamental theory.
5) Meson Spectroscopy.
Interesting evidence for the existence of exotic mesons made by diquark-antidiquark has been obtained in connection with the new resonance Y discovered by BaBar.
A model independent way to analyse phi ->S gamma decays has been presented , in connection with data obtained by KLOE at Frascati.
6) Resummation of logarithms in hadronic processes.
The threshold logarithmic resummation for semi-inclusive and radiative
B decays has been performed. The resummation of large logarithms of the jet mass for jets intiated by massive quarks is in progress. Also phenomenological analyses of B semileptonic-decay spectra and of
B fragmentation data are in progress.
7) Spectral shape and flavor composition of Very High Energy Astrophysical Neutrinos.
An analysis of the implications of the high energy (E > 1 TeV) neutrinos eventually emitted by galactic and extragalactic astrophysical sources is in progress.
8) Mixing in leptonic sector.
The effects of lepton flavor violating contributions (eventually present in Supersymmetric (SUSY) extensions of the Standard Model) have been studied in leptonic decays K_l2 of K meson. It has been shown that mu-e
non-universality in K_l2 is quite effective in constraining relevant regions of SUSY models with lepton flavor violating sources.
The study of essentially all the previous research items will be pursued in the next year. Some specific projects are:
- A study of rare decays within the MSSM with minimal flavour violation and beyond, which is now under way.
- The development of a common analysis framework for flavour and high-pt future LHC data.
- The building of specific models for EW breaking with composite Higgs.
Istituto Nazionale di Fisica Nucleare - Piazza dei Caprettari, 70 - 00186 Roma
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