2,264 research outputs found
Possible Excess in Charged Current Events with High-Q^2 at HERA from Stop and Sbottom Production
We investigate a production process e^+p \to \st X \to \sb W^+ X at HERA,
where we consider a decay mode \sb \to \bar{\nu}_e d of the sbottom in the
framework of an R-parity breaking supersymmetric standard model. Both processes
of the stop production e^+ d \to \st and the sbottom decay \sb \to
\bar{\nu}_e d are originated from an R-parity breaking superpotential
. One of signatures of the
process should be a large missing transverse momentum plus multijet events
corresponding to hadronic decays of the . It is shown that the signal could
appear as an event excess in the charged current (CC) processes with the high at HERA. We compare expected event distributions with
the CC data recently reported by the H1 and ZEUS groups at HERA. Methods for
extracting the signal from the standard CC processes are also discussed.Comment: 13 pages, LaTeX, 3 figure
Single scalar top production with polarized beams in ep collisions at HERA
From the point of view of the R-parity breaking supersymmetric model, we
propose a scalar top (stop) search with longitudinally polarized electron (e-)
and positron(e+) beams which will soon be available at the upgraded HERA. Fully
polarized e- or e+ beams could produce the stop two times as much as
unpolarized beams, while they increase background events due to the process of
the standard model by about 30% in comparison with unpolarized ones. We show
that right-handed e+ beams at HERA is efficient to produce the stop in the
model. With 1 fb**(-1) of integrated luminosity we estimate reach in the
coupling constant lambda'(131) for masses of the stop in the range 160-400 GeV.
We can set a 95% confidence-level exclusion limit for lambda'(131) > 0.01-0.05
in the stop mass range of 240-280 GeV if no singal of the stop is observed. We
also point out that y(=Q**2/sx) distributions of e+ coming from the stop shows
the different behavior from those of the standard model.Comment: 12 pages, 6 eps figure
GRACE/SUSY Automatic Generation of Tree Amplitudes in the Minimal Supersymmetric Standard Model
GRACE/SUSY is a program package for generating the tree-level amplitude and
evaluating the corresponding cross section of processes of the minimal
supersymmetric extension of the standard model (MSSM). The Higgs potential
adopted in the system, however, is assumed to have a more general form
indicated by the two-Higgs-doublet model. This system is an extension of GRACE
for the standard model(SM) of the electroweak and strong interactions. For a
given MSSM process the Feynman graphs and amplitudes at tree-level are
automatically created. The Monte-Carlo phase space integration by means of
BASES gives the total and differential cross sections. When combined with
SPRING, an event generator, the program package provides us with the simulation
of the SUSY particle productions.Comment: 39 page, 1 figur
Automatic Computation of Cross Sections in HEP
For the study of reactions in High Energy Physics (HEP) automatic computation
systems have been developed and are widely used nowadays. GRACE is one of such
systems and it has achieved much success in analyzing experimental data. Since
we deal with the cross section whose value can be given by calculating hundreds
of Feynman diagrams, we manage the large scale calculation, so that effective
symbolic manipulation, the treat of singularity in the numerical integration
are required. The talk will describe the software design of GRACE system and
computational techniques in the GRACE.Comment: 6 pages, Latex, ICCP
Implications of the HERA Events for the R-Parity Breaking SUSY Signals at Tevatron
The favoured R-parity violating SUSY scenarios for the anomalous HERA events
correspond to top and charm squark production via the and
couplings. In both cases the corresponding electronic
branching fractions of the squarks are expected to be . Consequently the
canonical leptoquark signature is incapable of probing these scenarios at the
Tevatron collider over most of the MSSM parameter space. We suggest alternative
signatures for probing them at Tevatron, which seem to be viable over the
entire range of MSSM parameters.Comment: 20 pages Latex file with 4 ps files containing 4 figure
One-Parameter Squeezed Gaussian States of Time-Dependent Harmonic Oscillator and Selection Rule for Vacuum States
By using the invariant method we find one-parameter squeezed Gaussian states
for both time-independent and time-dependent oscillators. The squeezing
parameter is expressed in terms of energy expectation value for
time-independent case and represents the degree of mixing positive and negative
frequency solutions for time-dependent case. A {\it minimum uncertainty
proposal} is advanced to select uniquely vacuum states at each moment of time.
We show that the Gaussian states with minimum uncertainty coincide with the
true vacuum state for time-independent oscillator and the Bunch-Davies vacuum
for a massive scalar field in a de Sitter spacetime.Comment: 13 Pages, ReVTeX, no figure
Minimal versus specialist equipment for the delivery of pulmonary rehabilitation in COPD
Background: Evidence for pulmonary rehabilitation(PR)largely comes from trials where the intervention used specialist aerobic and/or resistance equipment.Limited data exist to demonstrate the efficacy of PR in community settings with minimal equipment.
Aims: To compare completion rates and outcomes in COPD patients undergoing PR in a community setting with minimal equipment(PR-min)with a matched sample undergoing PR in a gym setting with specialist aerobic and resistance equipment(PR-gym).
Methods: Using propensity score matching,318 patients with COPD referred for 8 weeks of PR-min were matched 1:1 with a control group of 318 patients who undertook 8 weeks of PR-gym. Completion rate(attendanceâ„8 supervised sessions)and changes in incremental shuttle walk(ISW),Chronic Respiratory Disease Questionnaire(CRQ)and quadriceps maximal voluntary contraction(QMVC)were compared.
Results: Groups were matched for age(70.8v70.7years),FEV1%predicted(46.8v45.8),ISW(192v195m),%current smoking status(19v20)and depression scores(6.5v6.6).No between group differences were seen in ISW,CRQ or QMVC change. Completion rates were better in the PR-gym(73%)as opposed to the PR-min(64%);p=0.01.
Conclusion: This case-control study shows that PR-min had similar benefits to PR-gym.A randomised non-inferiority trial is needed to confirm the findings of this study
Much Ado About Leptoquarks: A Comprehensive Analysis
We examine the phenomenological implications of a 200 GeV leptoquark in light
of the recent excess of events at HERA. Given the relative predictions of
events rates in e^+p versus e^-p, we demonstrate that classes of leptoquarks
may be excluded, including those contained in E_6 GUT models. It is shown that
future studies with polarized beams at HERA could reveal the chirality of the
leptoquark fermionic coupling and that given sufficient luminosity in each
e^\pm_{L,R} channel the leptoquark quantum numbers could be determined. The
implications of 200-220 GeV leptoquarks at the Tevatron are examined. While
present Tevatron data most likely excludes vector leptoquarks and leptogluons
in this mass region, it does allow for scalar leptoquarks. We find that while
leptoquarks have little influence on Drell-Yan production, further studies at
the Main Injector are possible in the single production channel. We investigate
precision electroweak measurements as well as the process e^+e^-\to q\bar q at
LEP II and find they provide no further restrictions on these leptoquark
models. We then ascertain that cross section and polarization asymmetry
measurements at the NLC provide the only direct mechanism to determine the
leptoquark's electroweak quantum numbers. The single production of leptoquarks
in \gamma e collisions by both the backscattered laser and Weisacker-Williams
techniques at the NLC is also discussed. Finally, we demonstrate that we can
obtain successful coupling constant unification in models with leptoquarks,
both with or without supersymmetry. The supersymmetric case requires the GUT
group to be larger than SU(5) such as flipped SU(5)\times U(1)_X.Comment: Corrected single production cross section at Tevatron, updated atomic
parity violation constraints, 55 page
Don't Stop Thinking About Leptoquarks: Constructing New Models
We discuss the general framework for the construction of new models
containing a single, fermion number zero scalar leptoquark of mass GeV which can both satisfy the D0/CDF search constraints as well as
low energy data, and can lead to both neutral and charged current-like final
states at HERA. The class of models of this kind necessarily contain new
vector-like fermions with masses at the TeV scale which mix with those of the
Standard Model after symmetry breaking. In this paper we classify all models of
this type and examine their phenomenological implications as well as their
potential embedding into SUSY and non-SUSY GUT scenarios. The general coupling
parameter space allowed by low energy as well as collider data for these models
is described and requires no fine-tuning of the parameters.Comment: Modified text, added table, and updated reference
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