1,734 research outputs found
Constraints on B and Higgs Physics in Minimal Low Energy Supersymmetric Models
We study the implications of minimal flavor violating low energy
supersymmetry scenarios for the search of new physics in the B and Higgs
sectors at the Tevatron collider and the LHC. We show that the already
stringent Tevatron bound on the decay rate B_s -> mu+ mu- sets strong
constraints on the possibility of generating large corrections to the mass
difference Delta M_s of the B_s eigenstates. We also show that the B_s -> mu+
mu- bound together with the constraint on the branching ratio of the rare decay
b -> s gamma has strong implications for the search of light, non-standard
Higgs bosons at hadron colliders. In doing this, we demonstrate that the former
expressions derived for the analysis of the double penguin contributions in the
Kaon sector need to be corrected by additional terms for a realistic analysis
of these effects. We also study a specific non-minimal flavor violating
scenario, where there are flavor changing gluino-squark-quark interactions,
governed by the CKM matrix elements, and show that the B and Higgs physics
constraints are similar to the ones in the minimal flavor violating case.
Finally we show that, in scenarios like electroweak baryogenesis which have
light stops and charginos, there may be enhanced effects on the B and K mixing
parameters, without any significant effect on the rate of B_s -> mu+ mu-.Comment: 40 pages, 14 figures; added references and note about recent
measurement
Anomaly-Free Sets of Fermions
We present new techniques for finding anomaly-free sets of fermions. Although
the anomaly cancellation conditions typically include cubic equations with
integer variables that cannot be solved in general, we prove by construction
that any chiral set of fermions can be embedded in a larger set of fermions
which is chiral and anomaly-free. Applying these techniques to extensions of
the Standard Model, we find anomaly-free models that have arbitrary quark and
lepton charges under an additional U(1) gauge group.Comment: 21 (+1) page
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LC HCAL Absorber And Active Media Comparisons Using a Particle-Flow Algorithm
We compared Stainless Steel (SS) to Tungsten (W) as absorber for the HCAL in simulation using single particles (pions) and a Particle-Flow Algorithm applied to e{sup +}e{sup -} -> Z -> qqbar events. We then used the PFA to evaluate the performance characteristics of a LC HCAL using W absorber and comparing scintillator and RPC as active media. The W/Scintillator HCAL performs better than the SS/Scintillator version due to finer {lambda}{sub I} sampling and narrower showers in the dense absorber. The W/Scintillator HCAL performs better than the W/RPC HCAL except in the number of unused hits in the PFA. Since this represents the confusion term in the PFA response, additional tuning and optimization of a W/RPC HCAL might significantly improve this HCAL configuration
Supersymmetry Without Prejudice at the 7 TeV LHC
We investigate the model independent nature of the Supersymmetry search
strategies at the 7 TeV LHC. To this end, we study the
missing-transverse-energy-based searches developed by the ATLAS Collaboration
that were essentially designed for mSUGRA. We simulate the signals for ~71k
models in the 19-dimensional parameter space of the pMSSM. These models have
been found to satisfy existing experimental and theoretical constraints and
provide insight into general features of the MSSM without reference to a
particular SUSY breaking scenario or any other assumptions at the GUT scale.
Using backgrounds generated by ATLAS, we find that imprecise knowledge of these
estimated backgrounds is a limiting factor in the potential discovery of these
models and that some channels become systematics-limited at larger
luminosities. As this systematic error is varied between 20-100%, roughly half
to 90% of this model sample is observable with significance S>5 for 1 fb^{-1}
of integrated luminosity. We then examine the model characteristics for the
cases which cannot be discovered and find several contributing factors. We find
that a blanket statement that squarks and gluinos are excluded with masses
below a specific value cannot be made. We next explore possible modifications
to the kinematic cuts in these analyses that may improve the pMSSM model
coverage. Lastly, we examine the implications of a null search at the 7 TeV LHC
in terms of the degree of fine-tuning that would be present in this model set
and for sparticle production at the 500 GeV and 1 TeV Linear Collider.Comment: 51 pages, 26 figure
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Interpretation of the atmospheric muon charge ratio in MINOS
MINOS is the first large magnetic detector deep underground and is the first to measure the muon charge ratio with high statistics in the region near 1 TeV.[1] An approximate formula for the muon charge ratio can be expressed in terms of {eta}{sub {pi}} = 115 GeV, {eta}{sub K} = 850 GeV and E{sub {mu}}{sup surface}The implications for K production in the atmosphere will be discussed
A Method for the Precision Mass Measurement of the Stop Quark at the International Linear Collider
Many supersymmetric models predict new particles within the reach of the next
generation of colliders. For an understanding of the model structure and the
mechanism(s) of symmetry breaking, it is important to know the masses of the
new particles precisely. In this article the measurement of the mass of the
scalar partner of the top quark (stop) at an e+e- collider is studied. A
relatively light stop is motivated by attempts to explain electroweak
baryogenesis and can play an important role in dark matter relic density. A
method is presented which makes use of cross-section measurements near the
pair-production threshold as well as at higher center-of-mass energies. It is
shown that this method not only increases the statistical precision, but also
greatly reduces the systematic uncertainties, which can be important. Numerical
results are presented, based on a realistic event simulation, for two signal
selection strategies: using conventional selection cuts, and using an Iterative
Discriminant Analysis (IDA). Our studies indicate that a precision of
\Delta\mstop = 0.42 GeV can be achieved, representing a major improvement
over previous studies. While the analysis of stops is particularly challenging
due to the possibility of stop hadronization, the general procedure could be
applied to the mass measurement of other particles as well. We also comment on
the potential of the IDA to discover a stop quark in this scenario, and we
revisit the accuracy of the theoretical predictions for the neutralino relic
densityComment: 41 pages, 14 figures, in JHEP forma
Initial OTR Measurements of 150 GeV Protons in the Tevatron at FNAL
Fermilab has developed standard optical transition radiation (OTR) detectors as part of its Run II upgrade program for measuring intense proton and antiproton beams. These detectors utilize radiation-hardened CID cameras to image the OTR and produce high-resolution two-dimensional beam profiles. One of these detectors has been installed in the Tevatron next to the new ionization profile monitor (IPM). Initial OTR measurements are presented for 150 GeV injected coalesced and uncoalesced proton bunches. OTR images are taken for one-turn and two-turn injections over an intensity range of 1.5e11 to 3.5e11 protons. Preliminary profile measurements give uncoalesced beam size sigmas of 1.0 mm horizontally by 0.7 mm vertically and coalesced beam size sigmas of 1.8 mm horizontally by 0.70 mm vertically. OTR images are also presented for changes in the Tevatron skew quadrupole magnet currents, which produce a rotation to the OTR image, and for changes to the Tevatron RF, which can be used to measure single-turn dispersion. Operational aspects of this detector for beam studies and Tevatron tuneup are also discussed
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