2,191 research outputs found
Impact of Muon Anomalous Magnetic Moment on Supersymmetric Models
The recent measurement of a_\mu =\frac{g_\mu -2}{2} by the E821 Collaboration
at Brookhaven deviates from the quoted Standard Model (SM) central value
prediction by 2.6\sigma. The difference between SM theory and experiment may be
easily accounted for in a variety of particle physics models employing weak
scale supersymmetry (SUSY). Other supersymmetric models are distinctly
disfavored. We evaluate a_\mu for various supersymmetric models, including
minimal supergravity (mSUGRA), Yukawa unified SO(10) SUSY GUTs, models with
inverted mass hierarchies (IMH), models with non-universal gaugino masses,
gauge mediated SUSY breaking models (GMSB), anomaly-mediated SUSY breaking
models (AMSB) and models with gaugino mediated SUSY breaking (inoMSB). Models
with Yukawa coupling unification or multi-TeV first and second generation
scalars are disfavored by the a_\mu measurement.Comment: 25 page REVTEX file with 10 PS figures. Minor rewording, typos
corrected, references adde
SUPERSYMMETRY REACH OF AN UPGRADED TEVATRON COLLIDER
We examine the capability of a TeV Tevatron collider
to discover supersymmetry, given a luminosity upgrade to amass of
data. We compare with the corresponding reach of the Tevatron Main Injector
( of data). Working within the framework of minimal supergravity
with gauge coupling unification and radiative electroweak symmetry breaking, we
first calculate the regions of parameter space accessible via the clean
trilepton signal from \tw_1\tz_2\to 3\ell +\eslt production, with detailed
event generation of both signal and major physics backgrounds. The trilepton
signal can allow equivalent gluino masses of up to GeV to
be probed if is small. If is large, then GeV can
be probed for and large values of , the
rate for \tz_2\to\tz_1\ell\bar{\ell} is suppressed by interference effects,
and there is {\it no} reach in this channel. We also examine regions where the
signal from \tw_1\overline{\tw_1}\to \ell\bar{\ell}+\eslt is detectable.
Although this signal is background limited, it is observable in some regions
where the clean trilepton signal is too small. Finally, the signal
\tw_1\tz_2\to jets+\ell\bar{\ell} +\eslt can confirm the clean trilepton
signal in a substantial subset of the parameter space where the trilepton
signal can be seen. We note that although the clean trilepton signal may allow
Tevatron experiments to identify signals in regions of parameter space beyond
the reach of LEP II, the dilepton channels generally probe much the same region
as LEP II.Comment: 19 page REVTEX file; a uuencoded PS file with PS figures is available
via anonymous ftp at ftp://hep.fsu.edu/preprints/baer/FSUHEP950301.u
A Comparison of the Use of Binary Decision Trees and Neural Networks in Top Quark Detection
The use of neural networks for signal vs.~background discrimination in
high-energy physics experiment has been investigated and has compared favorably
with the efficiency of traditional kinematic cuts. Recent work in top quark
identification produced a neural network that, for a given top quark mass,
yielded a higher signal to background ratio in Monte Carlo simulation than a
corresponding set of conventional cuts. In this article we discuss another
pattern-recognition algorithm, the binary decision tree. We have applied a
binary decision tree to top quark identification at the Tevatron and found it
to be comparable in performance to the neural network. Furthermore,
reservations about the "black box" nature of neural network discriminators do
not apply to binary decision trees; a binary decision tree may be reduced to a
set of kinematic cuts subject to conventional error analysis.Comment: 14pp. Plain TeX + mtexsis.tex (latter available through 'get
mtexsis.tex'.) Two postscript files avail. by emai
Hadronic Production with QCD Corrections and Leptonic Decays
The process , where
denotes a lepton, is calculated to order . Total and differential
cross sections, with acceptance cuts imposed on the leptons and photon, are
given for the Tevatron and LHC center of mass energies. In general, invariant
mass and angular distributions are simply scaled up in magnitude by the QCD
radiative corrections, whereas in transverse momentum distributions, the QCD
radiative corrections increase with the transverse momentum.Comment: 16 pages + 9 figures, UCD-94-29. A postscript version and 9
postscript figures are available via anonymous ftp to UCDHEP.UCDAVIS.EDU in
the directory [.ohnemus.ucd-94-29
Sparticle mass spectra from SU(5) SUSY GUT models with Yukawa coupling unification
Supersymmetric grand unified models based on the gauge group SU(5) often
require in addition to gauge coupling unification, the unification of b-quark
and -lepton Yukawa couplings. We examine SU(5) SUSY GUT parameter space
under the condition of Yukawa coupling unification using 2-loop MSSM
RGEs including full 1-loop threshold effects. The Yukawa-unified solutions
break down into two classes. Solutions with low tan\beta ~3-11 are
characterized by gluino mass ~1-4 TeV and squark mass ~1-5 TeV. Many of these
solutions would be beyond LHC reach, although they contain a light Higgs scalar
with mass <123 GeV and so may be excluded should the LHC Higgs hint persist.
The second class of solutions occurs at large tan\beta ~35-60, and are a subset
of unified solutions. Constraining only unification to ~5%
favors a rather light gluino with mass ~0.5-2 TeV, which should ultimately be
accessible to LHC searches. While our unified solutions can be
consistent with a picture of neutralino-only cold dark matter, invoking
additional moduli or Peccei-Quinn superfields can allow for all of our
Yukawa-unified solutions to be consistent with the measured dark matter
abundance.Comment: 19 pages, 5 figures, 1 table, PDFLate
Neutralino dark matter in mSUGRA/CMSSM with a 125 GeV light Higgs scalar
The minimal supergravity (mSUGRA or CMSSM) model is an oft-used framework for
exhibiting the properties of neutralino (WIMP) cold dark matter (CDM). However,
the recent evidence from Atlas and CMS on a light Higgs scalar with mass
m_h\simeq 125 GeV highly constrains the superparticle mass spectrum, which in
turn constrains the neutralino annihilation mechanisms in the early universe.
We find that stau and stop co-annihilation mechanisms -- already highly
stressed by the latest Atlas/CMS results on SUSY searches -- are nearly
eliminated if indeed the light Higgs scalar has mass m_h\simeq 125 GeV.
Furthermore, neutralino annihilation via the A-resonance is essentially ruled
out in mSUGRA so that it is exceedingly difficult to generate
thermally-produced neutralino-only dark matter at the measured abundance. The
remaining possibility lies in the focus-point region which now moves out to
m_0\sim 10-20 TeV range due to the required large trilinear soft SUSY breaking
term A_0. The remaining HB/FP region is more fine-tuned than before owing to
the typically large top squark masses. We present updated direct and indirect
detection rates for neutralino dark matter, and show that ton scale noble
liquid detectors will either discover mixed higgsino CDM or essentially rule
out thermally-produced neutralino-only CDM in the mSUGRA model.Comment: 17 pages including 9 .eps figure
SIGNALS FOR MINIMAL SUPERGRAVITY AT THE CERN LARGE HADRON COLLIDER: MULTI-JET PLUS MISSING ENERGY CHANNEL,
We use ISAJET to perform a detailed study of the missing transverse energy
\eslt plus multi-jet signal expected from superparticle production at the
CERN LHC. Our analysis is performed within the framework of the minimal
supergravity model with gauge coupling unification and radiative electroweak
symmetry breaking. We delineate the region of parameter space where the \eslt
supersymmetry signal should be observable at the LHC and compare it to the
regions explorable via searches for sleptons and for chargino/neutralino
production. We confirm that, given a data sample of 10~\fb^{-1}, GeV can be explored if m_{\tq}\gg m_{\tg}, while GeV
can be probed if m_{\tq}\simeq m_{\tg}. We further examine what information
can be gleaned from scrutinizing this event sample. For instance, the multi-jet
multiplicity yields information on whether squark production makes a
significant contribution to the observed \eslt sample. Furthermore,
reconstructing hemispheric masses may yield a measure of to . Finally, for favourable ranges of parameters, by reconstructing
masses of tagged jet pairs, it may be possible to detect Higgs
bosons produced via sparticle cascade decay chains.Comment: 22 pages (REVTEX); a PS text file (etmiss.ps) and 12 figures
(etlhc.uu or etlhc.ps) can be obtained via anonymous ftp at
ftp://hep.fsu.edu/anonymous.bae
Hepatic Surgery Facilitated by a New Jet Dissector
Increasing experience with major hepatic resections has stimulated the development of improved
resectional techniques and tools. A new high velocity water jet dissector is reported which offers
significant advances over previously developed ultrasonic and low pressure water jet machines. It has
been successfully used in 8 major hepatic resections with minimal blood loss, excellent visibility and
without complications. The dissector is also of value in the exposure of intrahepatic bile ducts for biliaryenteric
anastomosis
Testing Yukawa-unified SUSY during year 1 of LHC: the role of multiple b-jets, dileptons and missing E_T
We examine the prospects for testing SO(10) Yukawa-unified supersymmetric
models during the first year of LHC running at \sqrt{s}= 7 TeV, assuming
integrated luminosity values of 0.1 to 1 fb^-1. We consider two cases: the
Higgs splitting (HS) and the D-term splitting (DR3) models. Each generically
predicts light gluinos and heavy squarks, with an inverted scalar mass
hierarchy. We hence expect large rates for gluino pair production followed by
decays to final states with large b-jet multiplicity. For 0.2 fb^-1 of
integrated luminosity, we find a 5 sigma discovery reach of m(gluino) ~ 400 GeV
even if missing transverse energy, E_T^miss, is not a viable cut variable, by
examining the multi-b-jet final state. A corroborating signal should stand out
in the opposite-sign (OS) dimuon channel in the case of the HS model; the DR3
model will require higher integrated luminosity to yield a signal in the OS
dimuon channel. This region may also be probed by the Tevatron with 5-10 fb^-1
of data, if a corresponding search in the multi-b+ E_T^miss channel is
performed. With higher integrated luminosities of ~1 fb^-1, using E_T^miss plus
a large multiplicity of b-jets, LHC should be able to discover Yukawa-unified
SUSY with m(gluino) up to about 630 GeV. Thus, the year 1 LHC reach for
Yukawa-unified SUSY should be enough to either claim a discovery of the gluino,
or to very nearly rule out this class of models, since higher values of
m(gluino) lead to rather poor Yukawa unification.Comment: 32 pages including 31 EPS figure
Anomaly mediated SUSY breaking scenarios in the light of cosmology and in the dark (matter)
Anomaly mediation is a popular and well motivated supersymmetry breaking
scenario. Different possible detailed realisations of this set-up are studied
and actively searched for at colliders. Apart from limits coming from flavour,
low energy physics and direct collider searches, these models are usually
constrained by the requirement of reproducing the observations on dark matter
density in the universe. We reanalyse these bounds and in particular we focus
on the dark matter bounds both considering the standard cosmological model and
alternative cosmological scenarios. These scenarios do not change the
observable cosmology but relic dark matter density bounds strongly depend on
them. We consider few benchmark points excluded by standard cosmology dark
matter bounds and suggest that loosening the dark matter constraints is
necessary in order to avoid a too strong (cosmological) model dependence in the
limits that are obtained for these models. We also discuss briefly the
implications for phenomenology and in particular at the Large Hadron Collider.Comment: 37 pages, 20 figures, 1 tabl
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