124 research outputs found
The Challenge of Determining SUSY Parameters in Focus-Point-Inspired Cases
We discuss the potential of combined LHC and ILC experiments for SUSY
searches in a difficult region of the parameter space, in which all sfermion
masses are above the TeV scale. Precision analyses of cross sections of light
chargino production and forward--backward asymmetries of decay leptons and
hadrons at the ILC, together with mass information on \tilde{\chi}^0_2 and
squarks from the LHC, allow us to fit rather precisely the underlying
fundamental gaugino/higgsino MSSM parameters and to constrain the masses of the
heavy virtual sparticles. For such analyses the complete spin correlations
between the production and decay processes have to be taken into account. We
also took into account expected experimental uncertainties.Comment: 4 pages, talk given at XLI Rencontres de Moriond on Electroweak
Interactions and Unified Theories, La Thuile, Italy, 11-18 Mar 200
The NMSSM lives: with the 750 GeV diphoton excess
We propose an NMSSM scenario that can explain the excess in the diphoton
spectrum at 750 GeV recently observed by ATLAS and CMS. We show that in a
certain limit with a very light pseudoscalar one can reproduce the experimental
results without invoking exotic matter. The 750 GeV excess is produced by two
resonant heavy Higgs bosons with masses ~750 GeV, that subsequently decay to
two light pseudoscalars. Each of these decays to collimated photon pairs that
appear as a single photon in the electromagnetic calorimeter. A mass gap
between heavy Higgses mimics a large width of the 750 GeV peak. The production
mechanism, containing a strong component via initial b quarks, ameliorates a
possible tension with 8 TeV data compared to other production modes. We also
discuss other constraints, in particular from low energy experiments. Finally,
we discuss possible methods that could distinguish our proposal from other
physics models describing the diphoton excess in the Run-II of the LHC.Comment: 24 pages, 4 figures; minor text improvements; to appear in EPJ
A resonance without resonance: scrutinizing the diphoton excess at 750 GeV
Motivated by the recent diphoton excesses reported by both ATLAS and CMS
collaborations, we suggest that a new heavy spinless particle is produced in
gluon fusion at the LHC and decays to a couple of lighter pseudoscalars which
then decay to photons. The new resonances could arise from a new strongly
interacting sector and couple to Standard Model gauge bosons only via the
corresponding Wess-Zumino-Witten anomaly. We present a detailed recast of the
newest 13 TeV data from ATLAS and CMS together with the 8 TeV data to scan the
consistency of the parameter space for those resonances.Comment: 8 pages, 4 figures, extended discussion of underlying models, new
plots with varying mass of the heavy scalar, to appear in PL
Reducing the fine-tuning of gauge-mediated SUSY breaking
Despite their appealing features, models with gauge-mediated supersymmetry breaking (GMSB) typically present a high degree of fine-tuning, due to the initial absence of the top trilinear scalar couplings, At = 0. In this paper, we carefully evaluate such a tuning, showing that is worse than per mil in the minimal model. Then, we examine some existing proposals to generate At ≠ 0 term in this context. We find that, although the stops can be made lighter, usually the tuning does not improve (it may be even worse), with some exceptions, which involve the generation of At at one loop or tree level. We examine both possibilities and propose a conceptually simplified version of the latter; which is arguably the optimum GMSB setup (with minimal matter content), concerning the fine-tuning issue. The resulting fine-tuning is better than one per mil, still severe but similar to other minimal supersymmetric standard model constructions. We also explore the so-called “little A2t /m2 problem”, i.e. the fact that a large At -term is normally accompanied by a similar or larger sfermion mass, which typically implies an increase in the fine-tuning. Finally, we find the version of GMSB for which this ratio is optimized, which, nevertheless, does not minimize the fine-tuningThis work has been partially supported by the MICINN, Spain, under contract FPA2013-44773-P, Consolider-Ingenio CPAN CSD2007-00042, as well as MULTIDARK CSD2009-00064. We also thank the Spanish MINECO Centro de excelencia Severo Ochoa Program under Grant SEV-2012-0249. S.R. is supported by the Campus of Excellence UAM+CSIC and K.R. by the Spanish Research Council (CSIC) within the JAE-Doc progra
(N)LO Simulation of Chargino Production and Decay
We consider NLO chargino production and decays at the ILC. For this, we
present an NLO extension of the Monte Carlo Event Generator Whizard including
the NLO production. For photonic corrections, we use both a fixed order and a
resummation approach. The latter method evades the problem of negative event
weights and automatically includes leading higher order corrections. We present
results for cross sections and event generation for both methods. As a first
step towards a full NLO Monte Carlo, we consider a LO implementation of the
chargino production and subsequent leptonic decay and investigate the precision
of the sneutrino mass determination by means of lepton energy distributions in
chargino decays. The SM and SUSY backgrounds are included in our study using
full matrix elements as well as smearing effects from ISR and beamstrahlung.
Without using energy distribution fits, the sneutrino mass can be determined
with an error in the percent regime.Comment: 10 pages, 6 figures; Talk presented at the Cracow Epiphany Conference
on LHC Physics 2008; Submitted to Acta Physica Polonica
CP violation at one loop in the polarization-independent chargino production in e+e- collisions
Recently Osland and Vereshagin noticed, based on sample calculations of some
box diagrams, that in unpolarised e+e- collisions CP-odd effects in the
non-diagonal chargino-pair production process are generated at one-loop. Here
we perform a full one-loop analysis of these effects and point out that in some
cases the neglected vertex and self-energy contributions may play a dominant
role. We also show that CP asymmetries in chargino production are sensitive not
only to the phase of mu parameter in the chargino sector but also to the phase
of stop trilinear coupling A_t.Comment: 14 pages, 5 figure
LHC/ILC Interplay in SUSY Searches
Combined analyses at the Large Hadron Collider and at the International
Linear Collider are important to reveal precisely the new physics model as, for
instance, supersymmetry. Examples are presented where ILC results as input for
LHC analyses could be crucial for the identification of signals as well as of
the underlying model. The synergy of both colliders leads also to rather
accurate SUSY parameter determination and powerful mass constraints even if the
scalar particles have masses in the multi-TeV range.Comment: 5 pages, contribution to the proceedings of EPS0
Normal tau polarisation as a sensitive probe of CP violation in chargino decay
CP violation in the spin-spin correlations in chargino production and
subsequent two-body decay into a tau and a tau-sneutrino is studied at the ILC.
From the normal polarisation of the tau, an asymmetry is defined to test the
CP-violating phase of the higgsino mass parameter \mu. Asymmetries of more than
\pm70% are obtained, also in scenarios with heavy first and second generation
sfermions. Bounds on the statistical significances of the CP asymmetries are
estimated. As a result, the normal tau polarisation in the chargino decay is
one of the most sensitive probes to constrain or measure the phase \phi_\mu at
the ILC, motivating further detailed experimental studies.Comment: 20 pages, 10 figures, gzipped tar fil
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