445 research outputs found
Supersymmetric LHC phenomenology without a light Higgs boson
After a brief discussion of the mass of the Higgs in supersymmetry, I
introduce \lambdaSUSY, a model with an extra chiral singlet superfield in
addition to the MSSM field content. The key features of the model are: the
superpotential W=\lambda S H_d H_u with a large coupling \lambda and the
resulting lightest Higgs with mass above 200GeV. The main part of my
contribution will be about how \lambdaSUSY manifests itself at the LHC.
Discoveries of gluino, squarks and in particular of the three lightest neutral
Higgs bosons are discussed.Comment: Submitted for the SUSY07 proceedings, 4 pages, LaTeX, 4 eps figure
Energy peaks: a high energy physics outlook
Energy distributions of decay products carry information on the kinematics of
the decay in ways that are at the same time straightforward and quite hidden. I
will review these properties and discuss their early historical applications as
well as more recent ones in the context of i) methods for the measurement of
masses of new physics particle with semi-invisible decays, ii) the
characterization of Dark Matter particles produced at colliders, iii) precision
mass measurements of Standard Model particles, in particular of the top quark.
Finally I will give an outlook of further developments and applications of
energy peaks method for high energy physics at colliders and beyond.Comment: Review written for MPLA; typos corrected, references adde
RPV stops bump off the background
We study the 8 TeV LHC reach on pair produced heavy flavored di-jet
resonances. Motivated by theories of R-parity violation in supersymmetry we
concentrate on a final state with two b-jets and two light jets. We exploit
b-tagging to reject the background and discuss its importance at the trigger
level to probe light stops. We present kinematical selections that can be used
to isolate the signal as a bump in the mass distribution of the candidate
resonances. We find that stops with R-parity violating couplings giving rise to
fully hadronic final states can be observed in the current run of the LHC.
Remarkably, the LHC can probe stop masses well within the range predicted by
naturalness.Comment: 9 pages, 1 figure, 1 table; references added, matches the published
versio
Using Energy Peaks to Measure New Particle Masses
We discussed in arXiv:1209.0772 that the laboratory frame distribution of the
energy of a massless particle from a two-body decay at a hadron collider has a
peak whose location is identical to the value of this daughter's (fixed) energy
in the rest frame of the corresponding mother particle. For that result to hold
we assumed that the mother is unpolarized and has a generic boost distribution
in the laboratory frame. In this work we discuss how this observation can be
applied for determination of masses of new particles, without requiring a full
reconstruction of their decay chains or information about the rest of the
event. We focus on a two-step cascade decay of a massive particle that has one
invisible particle in the final state: C -> Bb -> Aab, where C, B and A are new
particles of which A is invisible and a, b are visible particles. Combining the
measurements of the peaks of energy distributions of a and b with that of the
edge in their invariant mass distribution, we demonstrate that it is in
principle possible to determine separately all three masses of the new
particles, in particular, without using any measurement of missing transverse
momentum. Furthermore, we show how the use of the peaks in an inclusive energy
distribution is generically less affected by combinatorial issues as compared
to other mass measurement strategies. For some simplified, yet interesting,
scenarios we find that these combinatorial issues are absent altogether. As an
example of this general strategy, we study SUSY models where gluino decays to
an invisible lightest neutralino via an on-shell bottom squark. Taking into
account the dominant backgrounds, we show how the mass of the bottom squark,
the gluino and (for some class of spectra) that of the neutralino can be
determined using this technique.Comment: 42 pages, 11 figure
Resonance at 125 GeV: Higgs or Dilaton/Radion?
We consider the possibility that the new particle that has been observed at
125 GeV is not the Standard Model (SM) Higgs, but instead the dilaton
associated with an approximate conformal symmetry that has been spontaneously
broken. We focus on dilatons that arise from theories of technicolor, or from
theories of the Higgs as a pseudo-Nambu-Goldstone boson (pNGB), that involve
strong conformal dynamics in the ultraviolet. In the pNGB case, we are
considering a framework where the Higgs particle is significantly heavier than
the dilaton and has therefore not yet been observed. In each of the technicolor
and pNGB scenarios, we study both the case when the SM fermions and gauge
bosons are elementary, and the case when they are composites of the strongly
interacting sector. Our analysis incorporates conformal symmetry violating
effects, which are necessarily present since the dilaton is not massless, and
is directly applicable to a broad class of models that stabilize the weak scale
and involve strong conformal dynamics. Since the AdS/CFT correspondence relates
the radion in Randall-Sundrum (RS) models to the dilaton, our results also
apply to RS models with the SM fields localized on the infrared brane, or in
the bulk. We identify the parameters that can be used to distinguish the
dilatons associated with the several different classes of theories being
considered from each other, and from the SM Higgs. We perform a fit to all the
available data from several experiments and highlight the key observations to
extract these parameters. We find that at present, both the technicolor and
pNGB dilaton scenarios provide a good fit to the data, comparable to the SM
Higgs. We indicate the future observations that will help to corroborate or
falsify each scenario.Comment: 41 pages, 4 figures. Analysis updated using current theoretical
limits on dimensions of CFT operators. References added. Version to appear on
JHE
Beyond the Standard Model physics at CLIC
A summary of the recent results from CERN Yellow Report on the CLIC potential
for new physics is presented, with emphasis on the direct search for new
physics scenarios motivated by the open issues of the Standard Model.Comment: 21 pages, 11 figures. Talk presented at the International Workshop on
Future Linear Colliders (LCWS2018), Arlington, Texas, 22-26 October 2018.
C18-10-22. arXiv admin note: text overlap with arXiv:1812.0798
Supersymmetry without a light Higgs boson
In this thesis I shall discuss a class of supersymmetric models characterized by a
Higgs sector with a strongish self-coupling and a relatively heavy spectrum, with the
mass of the lightest CP-even Higgs boson around 200-300 GeV. The effective field theory
for these models is SUSY [1] that is to say the Next-To-Minimal Supersymmetric
Standard Model with large coupling SH1H2 in the superpotential.
I shall discuss in detail a model with scale-invariant superpotential, with particular
focus on the dynamical origin of the term and its relation with the mass of the Higgs
boson.
I shall discuss the fine tuning of the model and various experimental constraints
from LEP direct searches, precision data and direct DM searches. I shall argue that the
model naturally accommodates the current limits and I shall discuss the main features
of the signatures at the LHC.
The material of this thesis comes mostly from two papers [2, 3]. Furthermore,
during my PhD years in Pisa I have worked on other problems in collider phenomenology
[4] and astro-particle physics [5]. As they do not have direct connection with supersymmetry
and the Higgs boson they are not discussed in this thesis
Light stop squarks and b-tagging
A significant part of the parameter space for light stop squarks still
remains unconstrained by collider searches. For both R-Parity Conserving (RPC)
and R-Parity Violating (RPV) scenarios there are regions in which the stop mass
is around or below the top quark mass that are particularly challenging
experimentally. Here we review the status of light stop searches, both in RPC
and RPV scenarios. We also propose strategies, generally based on exploiting
b-tagging, to cover the unconstrained regions.Comment: To appear in the Proceedings of the Corfu Summer Institute 2014
"School and Workshops on Elementary Particle Physics and Gravity", Corfu,
Greec
- …