15 research outputs found
Measurement of the Gluino Mass via Cascade Decays for SPS 1a
If R-parity conserving supersymmetry is realised with masses below the TeV
scale, sparticles will be produced and decay in cascades at the LHC. In the
case of a neutral LSP, which will not be detected, decay chains cannot be fully
reconstructed, complicating the mass determination of the new particles. In
this paper we extend the method of obtaining masses from kinematical endpoints
to include a gluino at the head of a five-sparticle decay chain. This
represents a non-trivial extension of the corresponding method for the squark
decay chain. We calculate the endpoints of the new distributions and assess
their applicability by examining the theoretical distributions for a variety of
mass scenarios. The precision with which the gluino mass can be determined by
this method is investigated for the mSUGRA point SPS 1a. Finally we estimate
the improvement obtained from adding a Linear Collider measurement of the LSP
mass.Comment: 40 pages; extended discussion of error
Difficult Scenarios for NMSSM Higgs Discovery at the LHC
We identify scenarios not ruled out by LEP data in which NMSSM Higgs
detection at the LHC will be particularly challenging. We first review the
`no-lose' theorem for Higgs discovery at the LHC that applies if Higgs bosons
do not decay to other Higgs bosons - namely, with L=300 fb^-1, there is always
one or more `standard' Higgs detection channel with at least a 5 sigma signal.
However, we provide examples of no-Higgs-to-Higgs cases for which all the
standard signals are no larger than 7 sigma implying that if the available L is
smaller or the simulations performed by ATLAS and CMS turn out to be overly
optimistic, all standard Higgs signals could fall below 5 sigma even in the
no-Higgs-to-Higgs part of NMSSM parameter space. In the vast bulk of NMSSM
parameter space, there will be Higgs-to-Higgs decays. We show that when such
decays are present it is possible for all the standard detection channels to
have very small significance. In most such cases, the only strongly produced
Higgs boson is one with fairly SM-like couplings that decays to two lighter
Higgs bosons (either a pair of the lightest CP-even Higgs bosons, or, in the
largest part of parameter space, a pair of the lightest CP-odd Higgs bosons). A
number of representative bench-mark scenarios of this type are delineated in
detail and implications for Higgs discovery at various colliders are discussed.Comment: 31 pages, 5 figure
Production and FCNC decay of supersymmetric Higgs bosons into heavy quarks in the LHC
We analyze the production and subsequent decay of the neutral MSSM Higgs
bosons (h = h^0, H^0, A^0) mediated by flavor changing neutral currents (FCNC)
in the LHC collider. We have computed the h-production cross-section times the
FCNC branching ratio, \sigma(pp -> h -> qq') = \sigma(pp -> h) B(h -> qq'), in
the LHC focusing on the strongly-interacting FCNC sector. Here qq' is an
electrically neutral pair of quarks of different flavors, the dominant modes
being those containing a heavy quark: tc or bs. We determine the maximum
production rates for each of these modes and identify the relevant regions of
the MSSM parameter space, after taking into account the severe restrictions
imposed by low energy FCNC processes. The analysis of \sigma(pp -> h -> qq')
singles out regions of the MSSM parameter space different from those obtained
by maximizing only the branching ratio, due to non-trivial correlations between
the parameters that maximize/minimize each isolated factor. The production
rates for the bs channel can be huge for a FCNC process (0.1-1 pb), but its
detection can be problematic. The production rates for the tc channel are more
modest (10^{-3}-10^{-2} pb), but its detection should be easier due to the
clear-cut top quark signature. A few thousand tc events could be collected in
the highest luminosity phase of the LHC, with no counterpart in the SM.Comment: 25 pages, 9 figures, 2 tables, LaTeX 2e. Typos corrected. Version to
appear in JHE
l W nu production at CLIC: a window to TeV scale non-decoupled neutrinos
We discuss single heavy neutrino production e+ e- -> N nu -> l W nu, l = e,
mu, tau, at a future high energy collider like CLIC, with a centre of mass
energy of 3 TeV. This process could allow to detect heavy neutrinos with masses
of 1-2 TeV if their coupling to the electron V_eN is in the range 0.004-0.01.
We study the dependence of the limits on the heavy neutrino mass and emphasise
the crucial role of lepton flavour in the discovery of a positive signal at
CLIC energy. We present strategies to determine heavy neutrino properties once
they are discovered, namely their Dirac or Majorana character and the size and
chirality of their charged current couplings. Conversely, if no signal is
found, the bound V_eN < 0.002-0.006 would be set for masses of 1-2 TeV,
improving the present limit up to a factor of 30. We also extend previous work
examining in detail the flavour and mass dependence of the corresponding limits
at ILC, as well as the determination of heavy neutrino properties if they are
discovered at this collider.Comment: LaTeX 32 pages. Added comments and references. Matches version to
appear in JHE
Constraining Dark Matter in the MSSM at the LHC
In the event that R-Parity conserving supersymmetry (SUSY) is discovered at
the LHC, a key issue which will need to be addressed will be the consistency of
that signal with astrophysical and non-accelerator constraints on SUSY Dark
Matter. This issue is studied for the SPA benchmark model based on measurements
of end-points and thresholds in the invariant mass spectra of various
combinations of leptons and jets. These measurements are used to constrain the
soft SUSY breaking parameters at the electroweak scale in a general MSSM model.
Based on these constraints, we assess the accuracy with which the Dark Matter
relic density can be measured.Comment: 21 pages, 12 figure
Determination of the Higgs-boson couplings and H-A mixing in the generalized SM-like Two Higgs Doublet Model
The feasibility of measuring the Higgs-boson properties at the Photon
Collider at TESLA has been studied in detail for masses between 200 and 350
GeV, using realistic luminosity spectra and detector simulation. We consider
the Two Higgs Doublet Model (II) with SM-like Yukawa couplings for h,
parametrized by only one parameter (tan(beta)). The combined measurement of the
invariant-mass distributions in the ZZ and W+W- decay-channels is sensitive to
both the two-photon width Gamma_{gamma gamma} and phase Phi_{gamma gamma}. From
the analysis including systematic uncertainties we found out that after one
year of Photon Collider running with nominal luminosity the expected precision
in the measurement of tan(beta) is of the order of 10%, for both light (h) and
heavy (H) scalar Higgs bosons. The H-A mixing angle Phi_{HA}, characterizing a
weak CP violation in the model with two Higgs doublets, can be determined to
about 100 mrad, for low tan(beta).Comment: 17 pages, 9 figures; published versio
Measurement of SUSY masses via cascade decays for SPS 1a
If R-parity conserving supersymmetry exists below the TeV-scale, new particles will be produced and decay in cascades at the LHC. The lightest supersymmetric particle will escape the detectors, thereby complicating the full reconstruction of the decay chains. In this paper we expand on existing methods for determining the masses of the particles in the cascade from endpoints of kinematical distributions. We perform scans in the mSUGRA parameter space to delimit the region where this method is applicable. From the examination of theoretical distributions for a wide selection of mass scenarios it is found that caution must be exerted when equating the theoretical endpoints with the experimentally obtainable ones. We provide analytic formulae for the masses in terms of the endpoints most readily available. Complications due to the composite nature of the endpoint expressions are discussed in relation to the detailed analysis of two points on the SPS 1a line. Finally we demonstrate how a Linear Collider measurement can improve dramatically on the precision of the masses obtained
Supersymmetry and the LHC Inverse Problem
Given experimental evidence at the LHC for physics beyond the standard model,
how can we determine the nature of the underlying theory? We initiate an
approach to studying the "inverse map" from the space of LHC signatures to the
parameter space of theoretical models within the context of low-energy
supersymmetry, using 1808 LHC observables including essentially all those
suggested in the literature and a 15 dimensional parametrization of the
supersymmetric standard model. We show that the inverse map of a point in
signature space consists of a number of isolated islands in parameter space,
indicating the existence of "degeneracies"--qualitatively different models with
the same LHC signatures. The degeneracies have simple physical
characterizations, largely reflecting discrete ambiguities in electroweak-ino
spectrum, accompanied by small adjustments for the remaining soft parameters.
The number of degeneracies falls in the range 1<d<100, depending on whether or
not sleptons are copiously produced in cascade decays. This number is large
enough to represent a clear challenge but small enough to encourage looking for
new observables that can further break the degeneracies and determine at the
LHC most of the SUSY physics we care about. Degeneracies occur because
signatures are not independent, and our approach allows testing of any new
signature for its independence. Our methods can also be applied to any other
theory of physics beyond the standard model, allowing one to study how model
footprints differ in signature space and to test ways of distinguishing
qualitatively different possibilities for new physics at the LHC.Comment: 55 pages, 30 figure
Determining Supersymmetric Parameters With Dark Matter Experiments
In this article, we explore the ability of direct and indirect dark matter
experiments to not only detect neutralino dark matter, but to constrain and
measure the parameters of supersymmetry. In particular, we explore the
relationship between the phenomenological quantities relevant to dark matter
experiments, such as the neutralino annihilation and elastic scattering cross
sections, and the underlying characteristics of the supersymmetric model, such
as the values of mu (and the composition of the lightest neutralino), m_A and
tan beta. We explore a broad range of supersymmetric models and then focus on a
smaller set of benchmark models. We find that by combining astrophysical
observations with collider measurements, mu can often be constrained far more
tightly than it can be from LHC data alone. In models in the A-funnel region of
parameter space, we find that dark matter experiments can potentially determine
m_A to roughly +/-100 GeV, even when heavy neutral MSSM Higgs bosons (A, H_1)
cannot be observed at the LHC. The information provided by astrophysical
experiments is often highly complementary to the information most easily
ascertained at colliders.Comment: 46 pages, 76 figure