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Scientific Report 2007-2009
Particle physics
P4. Supersymmetric Higgs search at hadron colliders and
perspectives towards the futures electron-positron linear colliders.
The Minimal Supersymmetric Standard Model
(MSSM) is the most investigated extension of the
Standard Model (SM). The theory requires two Higgs
doublets giving origin to five Higgs bosons: two neutral
scalars, h and H (h is the lighter of the two), one neutral
pseudoscalar, A, and one pair of charged Higgs bosons,
H ± . Their discovery is an irrefutable proof for physics
beyond the SM. This is a key point in the physics
program of future accelerators and in particular of the
LHC. After the conclusion of the LEP program in the
year 2000, the experimental limit on the mass of the
Standard Model Higgs boson was established at 114.4
GeV with 95% CL. Limits were also set on the mass of
neutral and charged MSSM Higgs bosons for most of
the representative sets of model parameters.
The motivation [1] of the searches carried on in Rome
in the last years is to explore the potential of the AT-
LAS detector at LHC for the discovery of neutral MSSM
Higgs bosons in the parameter region not excluded by the
LEP and Tevatron data. Two decays channel of MSSM
Higgs have been explored one in µ pairs, the second in
supersymmetric particles.
The first was focused on the search for h, the lightest
of the neutral Higgs bosons decaying in µ pair. Its mass,
taking account of radiative corrections, is predicted to
be smaller than 140 GeV. The conclusion achieved can
be summarized as that the discovery of a neutral h/A
MSSM boson decaying into two muons, h→ µ + µ − and
A→ µ + µ − , accompanied by two b-jets is possible in a
mass range of 100 to 120 GeV at tanβ > 15, with an integrated
luminosity ∫ L dt = 10 fb −1 , which corresponds
to one year of data taking [2].
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80 90 100 110 120 130 140 150 ×
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inv 3
M µ
µ
[10
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Figure 1: Distributions of the reconstructed µ + µ − invariant
mass, M inv , for signal and backgrounds events,(tanβ = 45,
m A = 110 GeV, m h = 110 GeV) at ∫ L dt= 300 fb −1 . The
h/A signal (light blue) emerge over the background (dark
brown).
Moreover, to achieve an uncontroversial proof of the
existence of models beyond SM, the discovery of the
heavier bosons H and A is demanded, since the light
h boson is indistinguishable from the SM Higgs boson.
Many signatures of MSSM neutral Higgs bosons
have been studied involving decays into known SM particles,
in a scenario where it is assumed that sparticles
are too heavy to participate in the process. If the MSSM
Higgs decay into sparticles is kinematically allowed, decay
channels involving neutralinos (˜χ 0 ), charginos (˜χ ∓ )
and sleptons (˜l) can be considered, enlarging the possibilities
of discovery.
In this second search, we have studied the potential
for the discovery of neutral supersymmetric Higgs
bosons, considering the decays of A/H into neutralino
and chargino pairs, with subsequent decay into lighter
neutralinos and leptons and an experimental final state
signature of four leptons and missing energy (due to the
presence of ˜χ 0 1-s), extending the search to charged Higgs
boson. The analysis is performed in four different superymmetric
model scenarios, two for MSSM and two
for mSUGRA. With high luminosity, ∫ L dt = 300 fb −1 ,
a signal may be detected in three of the four supersymmetric
scenario; in two of them discovery may be reached
also with a lower luminosity, 100 fb −1 .
The Higgs discovery is expected to be achieved at
hadron colliders, but its properties have to be studied
at electron positron colliders (ILC,CLIC). The next generation
of high energy colliders is intended to operate
at a centre of mass energy ranging up to the TeV scale.
The physics scope includes precise measurements of the
triple- and quartic-gauge bosons interactions, as well as
the characterisation of the Higgs-boson and top-quark
sectors.
The final states are typically multiple hadronic jets,
accompanied frequently by low-momentum leptons
and/or missing energy. The signature of the final
states of interest often relies on the identification of
Z or/and W bosons by their decay modes into two
jets. In order to distinguish them efficiently, a good jet
energy resolution and a precise reconstruction of the jet
direction is also required. These are among the main
requirements driving the detector design in general and
the calorimetry design in particular. The crucial point
of this design is the choice of photodetectors. A novel
photodector technology has been recently proposed,
SiPM, SiliconPhotoMultipliers. In a laboratory in
Rome, we have studied and characterized the response
at different wavelenghts (380nm-650nm) of these innovative
detectors [3,4].
References
1. M. Fidecaro et al., Giornale di Fisica ,1XLIX, 10071
(2008).
2. S. Gentile et al., Eur. Phys. J.C,52, 229 (2007).
3. C. Bosio et al., Nuovo Cimento C, 30, 529 (2007).
4. C. Bosio et al., Nucl.Instrum.Meth., A596, 134 (2008).
Authors
S. Gentile, F. Meddi
Sapienza Università di Roma 111 Dipartimento di Fisica