9 research outputs found
On the detectability of the CMSSM light Higgs boson at the Tevatron
We examine the prospects of detecting the light Higgs h^0 of the Constrained
MSSM at the Tevatron. To this end we explore the CMSSM parameter space with
\mu>0, using a Markov Chain Monte Carlo technique, and apply all relevant
collider and cosmological constraints including their uncertainties, as well as
those of the Standard Model parameters. Taking 50 GeV < m_{1/2}, m_0 < 4 TeV,
|A_0| < 7 TeV and 2 < tan(beta) < 62 as flat priors and using the formalism of
Bayesian statistics we find that the 68% posterior probability region for the
h^0 mass lies between 115.4 GeV and 120.4 GeV. Otherwise, h^0 is very similar
to the Standard Model Higgs boson. Nevertheless, we point out some enhancements
in its couplings to bottom and tau pairs, ranging from a few per cent in most
of the CMSSM parameter space, up to several per cent in the favored region of
tan(beta)\sim 50 and the pseudoscalar Higgs mass of m_A\lsim 1 TeV. We also
find that the other Higgs bosons are typically heavier, although not
necessarily much heavier. For values of the h^0 mass within the 95% probability
range as determined by our analysis, a 95% CL exclusion limit can be set with
about 2/fb of integrated luminosity per experiment, or else with 4/fb (12/fb) a
3 sigma evidence (5 sigma discovery) will be guaranteed. We also emphasize that
the alternative statistical measure of the mean quality-of-fit favors a
somewhat lower Higgs mass range; this implies even more optimistic prospects
for the CMSSM light Higgs search than the more conservative Bayesian approach.
In conclusion, for the above CMSSM parameter ranges, especially m_0, either
some evidence will be found at the Tevatron for the light Higgs boson or, at a
high confidence level, the CMSSM will be ruled out.Comment: JHEP versio
Prospects for top-prime quark discovery at the Tevatron
We show that a top-prime quark as heavy as 600 GeV can be discovered at the
Tevatron, provided it is resonantly pair-produced via a vector color octet. If
the top-prime originates from a vectorlike quark, then the production of a
single top-prime in association with a top may also be observable, even through
its decay into a Higgs boson and a top. A color octet with mass of about 1 TeV,
which decays into a top-prime pair, may account for the CDF excess of
semileptonic (Wj)(Wj) events.Comment: 22 pages, 6 ps figures. v2: Note added about the new D0 search for
(Wb)(Wb) resonances; section 4.1 expanded; single-top constraint updated in
section 2; references adde
The heavy quark search at the LHC
We explore further the discovery potential for heavy quarks at the LHC, with
emphasis on the and of a sequential fourth family associated with
electroweak symmetry breaking. We consider QCD multijets, ,
and single backgrounds using event generation based on
improved matrix elements and low sensitivity to the modeling of initial state
radiation. We exploit a jet mass technique for the identification of
hadronically decaying 's and 's, to be used in the reconstruction of the
or mass. This along with other aspects of event selection can reduce
backgrounds to very manageable levels. It even allows a search for both
and in the absence of -tagging, of interest for the early running of
the LHC. A heavy quark mass of order 600 GeV is motivated by the connection to
electroweak symmetry breaking, but our analysis is relevant for any new heavy
quarks with weak decay modes.Comment: 12 pages, 7 figure
Is leptogenesis falsifiable at LHC?
It is well known that the leptogenesis mechanism offers an attractive
possibility to explain the baryon asymmetry of the universe. Its particular
robustness however comes with one major difficulty: it will be very hard if not
impossible to test experimentally in a foreseeable future, as most of the
mechanics typically takes place at high energy or results from suppressed
interactions, without unavoidable low-energy implications. An alternate
approach is taken by asking: can it be at least falsified? We show that
possible discoveries at current and future colliders, most notably that of
right-handed gauge interactions, would indeed forbid at least the "canonical"
leptogenesis mechanisms, namely those based on right-handed neutrino decay.
General lower bounds for successful leptogenesis on the mass of the
right-handed gauge boson W_R are given. Other possibilities to falsify
leptogenesis, including from the observation of a Z', are also considered.Comment: 22 pages ; v3: discussion about resonant leptogenesis case added ;
matches JHEP published versio
Present status and future prospects for a Higgs boson discovery at the Tevatron and LHC
Discovering the Higgs boson is one of the primary goals of both the Tevatron
and the Large Hadron Collider (LHC). The present status of the Higgs search is
reviewed and future prospects for discovery at the Tevatron and LHC are
considered. This talk focuses primarily on the Higgs boson of the Standard
Model and its minimal supersymmetric extension. Theoretical expectations for
the Higgs boson and its phenomenological consequences are reviewed.Comment: 13 pages, 9 figures, 2 tables, jpconf documentclass file, invited
talk at PASCOS 2010, the 16th International Symposium on Particles, Strings
and Cosmology, Valencia, Spain, 19--23 July 201
Accurate QCD predictions for heavy-quark jets at the Tevatron and LHC
Heavy-quark jets are important in many of today's collider studies and
searches, yet predictions for them are subject to much larger uncertainties
than for light jets. This is because of strong enhancements in higher orders
from large logarithms, ln(p_t/m_Q). We propose a new definition of heavy-quark
jets, which is free of final-state logarithms to all orders and such that all
initial-state collinear logarithms can be resummed into the heavy-quark parton
distributions. Heavy-jet spectra can then be calculated in the massless
approximation, which is simpler than a massive calculation and reduces the
theoretical uncertainties by a factor of three. This provides the first ever
accurate predictions for inclusive b- and c-jets, and the latter have
significant discriminatory power for the intrinsic charm content of the proton.
The techniques introduced here could be used to obtain heavy-flavour jet
results from existing massless next-to-leading order calculations for a wide
range of processes. We also discuss the experimental applicability of our
flavoured jet definition.Comment: 22 pages, 7 figure
Precise reconstruction of sparticle masses without ambiguities
We critically reexamine the standard applications of the method of
kinematical endpoints for sparticle mass determination. We consider the typical
decay chain in supersymmetry (SUSY) squark -> neutralino -> slepton -> LSP,
which yields a jet j and two leptons ln and lf. The conventional approaches use
the upper kinematical endpoints of the individual distributions m_{jll},
m_{jl(lo)} and m_{jl(hi)}, all three of which suffer from parameter space
region ambiguities and may lead to multiple solutions for the SUSY mass
spectrum. In contrast, we do not use m_{jll}, m_{jl(lo)} and m_{jl(hi)}, and
instead propose a new set of (infinitely many) variables whose upper kinematic
endpoints exhibit reduced sensitivity to the parameter space region. We then
outline an alternative, much simplified procedure for obtaining the SUSY mass
spectrum. In particular, we show that the four endpoints observed in the three
distributions m^2_{ll}, m^2_{jln} U m^2_{jlf} and m^2_{jln}+m^2_{jlf} are
sufficient to completely pin down the squark mass and the two neutralino
masses, leaving only a discrete 2-fold ambiguity for the slepton mass. This
remaining ambiguity can be easily resolved in a number of different ways: for
example, by a single additional measurement of the kinematic endpoint of any
one out of the many remaining 1-dimensional distributions at our disposal, or
by exploring the correlations in the 2-dimensional distribution of m^2_{jln} U
m^2_{jlf} versus m^2_{ll}. We illustrate our method with two examples: the LM1
and LM6 CMS study points. An additional advantage of our method is the expected
improvement in the accuracy of the SUSY mass determination, due to the
multitude and variety of available measurements.Comment: 37 pages, added a new figure in the Appendix, published versio
Using kinematic boundary lines for particle mass measurements and disambiguation in SUSY-like events with missing energy
We revisit the method of kinematical endpoints for particle mass
determination, applied to the popular SUSY decay chain squark -> neutralino ->
slepton -> LSP. We analyze the uniqueness of the solutions for the mass
spectrum in terms of the measured endpoints in the observable invariant mass
distributions. We provide simple analytical inversion formulas for the masses
in terms of the measured endpoints. We show that in a sizable portion of the
SUSY mass parameter space the solutions always suffer from a two-fold
ambiguity, due to the fact that the original relations between the masses and
the endpoints are piecewise-defined functions. The ambiguity persists even in
the ideal case of a perfect detector and infinite statistics. We delineate the
corresponding dangerous regions of parameter space and identify the sets of
"twin" mass spectra. In order to resolve the ambiguity, we propose a
generalization of the endpoint method, from single-variable distributions to
two-variable distributions. In particular, we study analytically the boundaries
of the (m_{jl(lo)}, m_{jl(hi)}) and (m_{ll}, m_{jll}) distributions and prove
that their shapes are in principle sufficient to resolve the ambiguity in the
mass determination. We identify several additional independent measurements
which can be obtained from the boundary lines of these bivariate distributions.
The purely kinematical nature of our method makes it generally applicable to
any model that exhibits a SUSY-like cascade decay.Comment: 47 pages, 19 figure