3,735 research outputs found
Boosted Top Quark Pair Production in Soft Collinear Effective Theory
We review a Soft Collinear Effective Theory approach to the study of
factorization and resummation of QCD effects in top-quark pair production. In
particular, we consider differential cross sections such as the top-quark pair
invariant mass distribution and the top-quark transverse momentum and rapidity
distributions. Furthermore, we focus our attention on the large invariant mass
and large transverse momentum kinematic regions, characteristic of boosted top
quarks. We discuss the factorization of the differential cross section in the
double soft gluon emission and small top-quark mass limit, both in Pair
Invariant Mass (PIM) and One Particle Inclusive (1PI) kinematics. The
factorization formulas can be employed in order to implement the simultaneous
resummation of soft emission and small mass effects up to
next-to-next-to-leading logarithmic accuracy. The results are also used to
construct improved next-to-next-to-leading order approximations for the
differential cross sections.Comment: 6 pages. Proceedings of the Second Annual Conference on Large Hadron
Collider Physics (LHCP 2014), Columbia University, New York, June 2-7, 201
The complete radiative corrections to the gaugino and Higgsino masses in the Minimal Supersymmetric Model
We determine the radiative corrections to the masses of the gauginos and
Higgsinos in the MSSM, including all sectors of the theory in a one-loop
calculation in the on-mass-shell renormalization scheme. We find that a gluino
which is massless at tree level receives a mass of between 0 and 3 GeV,
primarily due to the top/stop contribution. This radiatively generated mass
depends directly on the off-diagonal element of the squark mass matrix. In the
case of a massive gluino, its mass receives typically large corrections, as
large as 40\% for a 125 GeV gluino. We find that the contributions to the
neutralino and chargino mass corrections from the gauge/Higgs/gaugino/Higgsino
sector are typically +-1%. The lightest neutralino, which can receive
corrections larger than 25%, receives 5% corrections over most of the parameter
space. We combine our results with the results of LEP and CDF searches to
obtain the lower bounds on the neutralino and chargino masses at one-loop. We
also demonstrate how the radiative corrections affect the presently excluded
region of parameter space.Comment: 16 pages, JHU-TIPAC-940001, PURD-TH-94-04. 6 uuencoded postscript
figures included. Uncomment the line "%\input epsf" to embed the figures in
the tex
Radiative Decay of Vector Quarkonium: Constraints on Glueballs and Light Gluinos
Given a resonance of known mass, width, and J^{PC}, we can determine its
gluonic branching fraction, b(R->gg), from data on its production in radiative
vector quarkonium decay, V -> gamma+R. For most resonances b(R->gg) is found to
be O(10%), consistent with being q-qbar states, but we find that both
pseudoscalars observed in the 1440 MeV region have b(R->gg) ~ 1/2 - 1, and
b(f_0^{++}->gg) ~ 1/2. As data improves, b(R->gg) should be a useful
discriminator between q-qbar and gluonic states and may permit quantitative
determination of the extent to which a particular resonance is a mixture of
glueball and q-qbar. We also examine the regime of validity of pQCD for
predicting the rate of V -> gamma+eta_gluino, the ``extra'' pseudoscalar bound
state which would exist if there were light gluinos. From the CUSB limit on
peaks in Upsilon -> gamma X, the mass range 3 GeV < m(eta_gluino) < 7 GeV can
be excluded. An experiment must be significantly more sensitive to exclude an
eta_gluino lighter than this.Comment: 36pp (inc figs),RU-94-04. (Replaces original which didn't latex
correctly and didn't have figures.
Can We Identify a Light Neutralino in B-Factories
If a light gaugino sector exists, then the lightest supersymmetric particle
(LSP) has a chance of being pair-produced in rare B-decays. As a consequence of
neutral flavour violation in most supersymmetric models, such decays can occur
at the tree-level and reinforce the channels . We discuss how a study of such decay spectra in B-factories can
help us either identify or exclude a light LSP.Comment: 14 pages, 5 figures (hard copies available from authors on request
Experiments to Find or Exclude a Long-Lived, Light Gluino
Gluinos in the mass range ~1 1/2 - 3 1/2 GeV are absolutely excluded. Lighter
gluinos are allowed, except for certain ranges of lifetime. Only small parts of
the mass-lifetime parameter space are excluded for larger masses unless the
lifetime is shorter than ~ 2 10^{-11} (m_{gluino}/ GeV) sec. Refined mass and
lifetime estimates for R-hadrons are given, present direct and indirect
experimental constraints are reviewed, and experiments to find or definitively
exclude these possibilities are suggested.Comment: 27 pp, latex with 1 uufiled figure, RU-94-35. New version amplifies
discussion of some points and corresponds to version for Phys. Rev.
Higher Twist Contributions To R-Hadron Phenomenology In The Light Gluino Scenario
The open light gluino window allows non-trivial higher twist gluino
contributions to the proton wave function. Using a two-component model
originally developed for charm hadroproduction, higher twist intrinsic gluino
contributions to final state R-hadron formation are shown to enhance leading
twist production in the forward region. We calculate R-hadron
production at GeV in pp, pBe, and pCu interactions with
light gluino masses of 1.2, 1.5, 3.5, and 5.0 GeV.Comment: 22 pages, 10 figures, revte
Light Neutralinos in B-Decays
We consider the decays of a -meson into a pair of lightest
supersymmetric particles (LSP) in the minimal supersymmetric standard model. It
is found that the parameter space for light LSP's in the range of 1 GeV can be
appreciably constrained by looking for such decays.Comment: 9 pages, LaTex, 2 figures (hard copies of the figures available from
the Authors on request
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Closing the Light Gluino Window in Supersymmetric Grand Unified Models
We study the light gluino scenario giving special attention to constraints
from the masses of the light CP-even neutral Higgs , the lightest chargino
, and the second lightest neutralino , and from
the decay. We find that minimal supergravity, with
a radiatively broken electroweak symmetry group and universality of scalar and
gaugino masses at the unification scale, is incompatible with the existence of
a light gluino.Comment: 12 pages (plain tex), 1 figure not included, VAND-TH-94-7-R. An error
is corrected. Modifications to the text and the figure are mad
Light Gluino And Tevatroin Dijet Angular Distributions
We consider the effects of a light gluino on the dijet angular distributions
in p - pbar collisions at sqrt(s)=1800 GeV. We show that the slower running of
alpha_s and the production q qbar, g g -> Gino Gino do not significantly alter
the expected angular distributions. On the other hand, single U, D squark
production q g -> Q Gino with subsequent Q -> q g results in dijets whose
angular distributions are dramatically different from that in SM. The CDF data
on dijet angular distributions with integrated luminosity of 106 pb^(-1)
exclude U, D squarks in the mass ranges 170 < m < 650 and 190 < m < 600 GeV, We
consider lower energies as well and show that in a future experimental analysis
for dijet mass below 240 GeV squarks could be observed or ruled out.Comment: 10 pages, LaTeX with 2 epsf figure
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