421 research outputs found
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Design objectives for a GeV C. W. electron accelerator
Design objectives are proposed for a continuous beam 2 GeV electron accelerator. Various accelerator concepts are examined in light of these requirements. A double-sided microtron shows promise for yielding major savings in capital cost and excellent beam characteristics
Z decays into light gluinos: a calculation based on unitarity
The Z boson can decay to a pair of light gluinos through loop-mediated
processes. Based on unitarity of the S-matrix, the imaginary part of the decay
amplitude is computed in the presence of a light bottom squark. This imaginary
part can provide useful information on the full amplitude. Implications are
discussed for a recently proposed light gluino and light bottom squark
scenario.Comment: 19 pages, LaTeX, 3 figures, submitted to Phys. Rev.
Squark Mixing in Electron-Positron Reactions
Squark mixing plays a large role in the phenomenology of the minimal
supersymmetric standard model, determining the mass of the lightest Higgs boson
and the electroweak interactions of the squarks themselves. We examine how
mixing may be investigated in high energy reactions, both at LEP-II
and the proposed linear collider. In particular, off-diagonal production of one
lighter and one heavier squark allows one to measure the squark mixing angle,
and would allow one to test the mass relations for the light Higgs boson. In
some cases off-diagonal production may provide the best prospects to discover
supersymmetry. In the context of the light bottom squark scenario, we show that
existing data from LEP-II should show definitive evidence for the heavier
bottom squark provided that its mass GeV.Comment: 22 pages, latex, 6 figure
Implications of the Higgs Discovery in the MSSM Golden Region
If the lightest CP-even Higgs boson in the MSSM is discovered at the LHC, two
measurements could be made simultaneously: the Higgs mass m_h and the event
rate Bs(gg -> h -> gamma gamma). We study to what extent the combination of
these two measurements would allow us to extract parameters in the stop mass
matrix, including the off-diagonal mixing term, with a focus on the MSSM golden
region where the stops are light and the mixing is large. Even though both the
production cross-section and the decay amplitude are not sensitive to
supersymmetric parameters outside of the stop sector, the branching ratio
depends on the total decay width, which is dominated by the Higgs decay to b
quarks and sensitive to both the pseudo-scalar mass m_A and the supersymmetric
Higgs mass \mu. In the end we find m_A is an important input in extracting the
stop mass parameters, while a fair estimate of the off-diagonal mixing term
could be obtained without prior knowledge of \mu.Comment: 17 pages and 6 figures; v2: minor revision and added references to
match JHEP versio
Implications of the Muon Anomalous Magnetic Moment for Supersymmetry
We re-examine the bounds on supersymmetric particle masses in light of the
E821 data on the muon anomalous magnetic moment. We confirm, extend and
supersede previous bounds. In particular we find (at one sigma) no lower limit
on tan(beta) or upper limit on the chargino mass implied by the data at
present, but at least 4 sparticles must be lighter than 700 to 820 GeV and at
least one sparticle must be lighter than 345 to 440 GeV. However, the E821
central value bounds tan(beta) > 4.7 and the lighter chargino mass by 690 GeV.
For tan(beta) < 10, the data indicates a high probability for direct discovery
of SUSY at Run II or III of the Tevatron.Comment: 20 pages LaTeX, 14 figures; references adde
Lepton polarization correlations in
In this work we will study the polarizations of both leptons () in the
decay channel . In the case of the dileptonic inclusive
decay , where apart from the polarization asymmetries
of single lepton , one can also observe the polarization asymmetries of
both leptons simultaneously. If this sort of measurement is possible then we
can have, apart from decay rate, FB asymmetry and the six single lepton
polarization asymmetries (three each for and ), nine more
double polarization asymmetries. This will give us a very useful tool in more
strict testing of SM and the physics beyond. We discuss the double polarization
asymmetries of leptons in the decay mode within
the SM and the Minimal Supersymmetric extensions of it.Comment: 21 pages, 21 figures; version to match paper to appear in PR
Higgs boson mass limits in perturbative unification theories
Motivated in part by recent demonstrations that electroweak unification into
a simple group may occur at a low scale, we detail the requirements on the
Higgs mass if the unification is to be perturbative. We do this for the
Standard Model effective theory, minimal supersymmetry, and next-to-minimal
supersymmetry with an additional singlet field. Within the Standard Model
framework, we find that perturbative unification with sin2(thetaW)=1/4 occurs
at Lambda=3.8 TeV and requires mh<460 GeV, whereas perturbative unification
with sin2(thetaW)=3/8 requires mh<200 GeV. In supersymmetry, the presentation
of the Higgs mass predictions can be significantly simplified, yet remain
meaningful, by using a single supersymmetry breaking parameter Delta_S. We
present Higgs mass limits in terms of Delta_S for the minimal supersymmetric
model and the next-to-minimal supersymmetric model. We show that in
next-to-minimal supersymmetry, the Higgs mass upper limit can be as large as
500 GeV even for moderate supersymmetry masses if the perturbative unification
scale is low (e.g., Lambda=10 TeV).Comment: 20 pages, latex, 6 figures, references adde
Dynamic nuclear polarization and spin-diffusion in non-conducting solids
There has been much renewed interest in dynamic nuclear polarization (DNP),
particularly in the context of solid state biomolecular NMR and more recently
dissolution DNP techniques for liquids. This paper reviews the role of spin
diffusion in polarizing nuclear spins and discusses the role of the spin
diffusion barrier, before going on to discuss some recent results.Comment: submitted to Applied Magnetic Resonance. The article should appear in
a special issue that is being published in connection with the DNP Symposium
help in Nottingham in August 200
Super AutoDipole
The publicly available package for an automated dipole subtraction,
AutoDipole, is extended to include the SUSY dipoles in the MSSM. All fields in
the SM and the MSSM are available. The code is checked against the analytical
expressions for a simple process. The extended package makes it possible to
compute the QCD NLO corrections to SUSY multi-parton processes like the stop
pair production plus jets at the LHC.Comment: 16 pages, 1 figure, v2: a few typos to match the published version in
Eur. Phys. J.
Muon anomalous magnetic moment in the standard model with two Higgs doublets
The muon anomalous magnetic moment is investigated in the standard model with
two Higgs doublets (S2HDM) motivated from spontaneous CP violation. Thus all
the effective Yukawa couplings become complex. As a consequence of the non-zero
phase in the couplings, the one loop contribution from the neutral scalar
bosons could be positive and negative relying on the CP phases. The
interference between one and two loop diagrams can be constructive in a large
parameter space of CP-phases. This will result in a significant contribution to
muon anomalous magnetic moment even in the flavor conserving process with a
heavy neutral scalar boson ( 200 GeV) once the effective muon Yukawa
coupling is large (). In general, the one loop contributions
from lepton flavor changing scalar interactions become more important. In
particular, when all contributions are positive in a reasonable parameter space
of CP phases, the recently reported 2.6 sigma experiment vs. theory deviation
can be easily explained even for a heavy scalar boson with a relative small
Yukawa coupling in the S2HDM.Comment: 8 pages, RevTex file, 5 figures, published version Phys. Rev. D 54
(2001) 11501
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