4,219 research outputs found
Determining the Mass of Dark Matter Particles with Direct Detection Experiments
In this article I review two data analysis methods for determining the mass
(and eventually the spin-independent cross section on nucleons) of Weakly
Interacting Massive Particles with positive signals from direct Dark Matter
detection experiments: a maximum likelihood analysis with only one experiment
and a model-independent method requiring at least two experiments.
Uncertainties and caveats of these methods will also be discussed.Comment: 24 pages, 10 figures, 1 reference added, typos fixed, published
version, to appear in the NJP Focus Issue on "Dark Matter and Particle
Physics
Loop induced Higgs and Z boson couplings to Neutralinos and implications for collider and Dark Matter searches
We calculate the one-loop induced couplings of two gaugino-like neutralinos
to the and Higgs bosons in the Minimal Supersymmetric Standard Model. These
couplings, which vanish at the tree level, can be generated through loops
involving fermions and sfermions. We show that, while the neutralino
contribution to the invisible boson decay width remains small, the loop
induced couplings to the lightest Higgs boson might be sufficiently large to
yield a rate of invisible decays of this Higgs boson that should be detectable
at future colliders. We also study the implications of these couplings
for direct searches of Dark Matter and show that they can modify appreciably
the neutralino-nucleon elastic cross section for some parameter range.Comment: LaTeX with 6 (e)ps and 2 axodraw figures, 25 pages in total;
axodraw.sty is included v.2: Added one figure and some discussions; version
to appear in PR
Exploring compressed supersymmetry with same-sign top quarks at the Large Hadron Collider
In compressed supersymmetry, a light top squark naturally mediates efficient
neutralino pair annihilation to govern the thermal relic abundance of dark
matter. I study the LHC signal of same-sign leptonic top-quark decays from
gluino and squark production, which follows from gluino decays to top plus stop
followed by the stop decaying to a charm quark and the LSP in these models.
Measurements of the numbers of jets with heavy-flavor tags in the same-sign
lepton events can be used to confirm the origin of the signal. Summed
transverse momentum observables provide an estimate of an effective
superpartner mass, which is correlated with the gluino mass. Measurements of
invariant mass endpoints from the visible products of gluino decays do not
allow direct determination of superpartner masses, but can place constraints on
them, including lower bounds on the gluino mass as a function of the top-squark
mass.Comment: 22 pages. v2: Discussion of competition between 2-body and 4-body
stop decays corrected. References adde
Loss maps of RHIC
State-of-the-art tracking tools were recently developed at CERN to study the cleaning efficiency of the Large Hadron Collider (LHC) collimation system . These tools are fully transportable, meaning that any accelerator lattice that includes a collimation systemcan be simulated. Each of the two Relativistic Heavy Ion Collider (RHIC) beam lines features a multi-stage collimation system, therefore dedicated datasets from RHIC operations with proton beams can be used to benchmark the tracking codes and assess the accuracy of the predicted hot spots along the LHC
Virtual Photon Strucutre Functions and the Parton Content of the Electron
We point out that in processes involving the parton content of the photon the
usual effective photon approximation should be modified. The reason is that the
parton content of virtual photons is logarithmically suppressed compared to
real photons. We describe this suppression using several simple, physically
motivated ans\"atze. Although the parton content of the electron in general no
longer factorizes into an electron flux function and a photon structure
function, it can still be expressed as a single integral. Numerical examples
are given for the \eplem\ collider TRISTAN as well as the collider HERA.Comment: 16 pages and 3 figures (available from DREES@WSICPHEN as topdraw or
PS files); LaTeX with equation.sty; MAD/PH/819, BU 94-0
Determining Ratios of WIMP-Nucleon Cross Sections from Direct Dark Matter Detection Data
Weakly Interacting Massive Particles (WIMPs) are one of the leading
candidates for Dark Matter. So far the usual procedure for constraining the
WIMP-nucleon cross sections in direct Dark Matter detection experiments have
been to fit the predicted event rate based on some model(s) of the Galactic
halo and of WIMPs to experimental data. One has to assume whether the
spin-independent (SI) or the spin-dependent (SD) WIMP-nucleus interaction
dominates, and results of such data analyses are also expressed as functions of
the as yet unknown WIMP mass. In this article, I introduce methods for
extracting information on the WIMP-nucleon cross sections by considering a
general combination of the SI and SD interactions. Neither prior knowledge
about the local density and the velocity distribution of halo WIMPs nor about
their mass is needed. Assuming that an exponential-like shape of the recoil
spectrum is confirmed from experimental data, the required information are only
the measured recoil energies (in low energy ranges) and the number of events in
the first energy bin from two or more experiments.Comment: 33 pages, 20 eps figures; v2: typos fixed, references added and
updated, revised version for publicatio
Atmospheric Neutrino Anomaly and Supersymmetric Inflation
A detailed investigation of hybrid inflation and the subsequent reheating
process is performed within a mu problem solving supersymmetric model based on
a left-right symmetric gauge group. The process of baryogenesis via
leptogenesis is especially studied. For mu and tau neutrino masses consistent
with the small angle MSW resolution of the solar neutrino problem and the
recent results of the SuperKamiokande experiment, we show that maximal mu-tau
neutrino mixing can be achieved. The required value of the relevant coupling
constant is, however, quite small (of the order 10^{-6}).Comment: 10 pages, 3 figure
SUSY QCD Corrections to Higgs Pair Production from Bottom Quark Fusion
We present a complete next-to-leading order (NLO) calculation for the total
cross section for inclusive Higgs pair production via bottom-quark fusion at
the CERN Large Hadron Collider (LHC) in the minimal supersymmetric standard
model (MSSM) and the minimal supergravity model (mSUGRA). We emphasize the
contributions of squark and gluino loops (SQCD) and the decoupling properties
of our results for heavy squark and gluino masses. The enhanced couplings of
the b quark to the Higgs bosons in supersymmetric models with large tanb yield
large NLO SQCD corrections in some regions of parameter space.Comment: 24 pages, 10 figure
Zeroing in on Supersymmetric Radiation Amplitude Zeros
Radiation amplitude zeros have long been used to test the Standard Model.
Here, we consider the supersymmetric radiation amplitude zero in
chargino-neutralino associated production, which can be observed at the
luminosity upgraded LHC. Such an amplitude zero only occurs if the neutralino
has a large wino fraction and hence this observable can be used to determine
the neutralino eigenstate content. We find that this observable can be measured
by comparing the p_T spectrum of the softest lepton in the trilepton
decay channel to that of a control process such as
or . We test this technique on a
previously generated model sample of the 19 dimensional parameter space of the
phenomenological MSSM, and find that it is effective in determining the wino
content of the neutralino.Comment: 19 pages, 7 figure
Inclusive One- and Two-Jet Cross sections in Reactions at Colliders
We have calculated inclusive one-- and two--jet production in photon--photon
collisions superimposing direct, single resolved and double resolved cross
sections for center of mass energies of the LEP1, LEP2 and NLC range. The
direct and single resolved cross sections are calculated up to
next--to--leading order. The double resolved two--jet cross section is
calculated only in LO with a factor estimated from the NLO one--jet cross
section. Various differential cross sections as functions of transverse momenta
and rapidities of the jets are evaluated.Comment: 25 pages, latex, 15 figures appended as uuencoded fil
- …