6,835 research outputs found
Flavour changing strong interaction effects on top quark physics at the LHC
We perform a model independent analysis of the flavour changing strong
interaction vertices relevant to the LHC. In particular, the contribution of
dimension six operators to single top production in various production
processes is discussed, together with possible hints for identifying signals
and setting bounds on physics beyond the standard model.Comment: Authors corrections (references added
Are There Hints of Light Stops in Recent Higgs Search Results?
The recent discovery at the LHC by the CMS and ATLAS collaborations of the
Higgs boson presents, at long last, direct probes of the mechanism for
electroweak symmetry breaking. While it is clear from the observations that the
new particle plays some role in this process, it is not yet apparent whether
the couplings and widths of the observed particle match those predicted by the
Standard Model. In this paper, we perform a global fit of the Higgs results
from the LHC and Tevatron. While these results could be subject to
as-yet-unknown systematics, we find that the data are significantly better fit
by a Higgs with a suppressed width to gluon-gluon and an enhanced width to
gamma gamma, relative to the predictions of the Standard Model. After
considering a variety of new physics scenarios which could potenially modify
these widths, we find that the most promising possibility is the addition of a
new colored, charged particle, with a large coupling to the Higgs. Of
particular interest is a light, and highly mixed, stop, which we show can
provide the required alterations to the combination of gg and gamma gamma
widths.Comment: 6 pages, 5 figure
Supersymmetric QCD flavor changing top quark decay
We present a detailed and complete calculation of the gluino and scalar
quarks contribution to the flavour-changing top quark decay into a charm quark
and a photon, gluon, or a Z boson within the minimal supersymmetric standard
model including flavour changing gluino-quarks-scalar quarks couplings in the
right-handed sector. We compare the results with the ones presented in an
earlier paper where we considered flavour changing couplings only in the
left-handed sector. We show that these new couplings have important
consequences leading to a large enhancement when the mixing of the scalar
partners of the left- and right-handed top quark is included. Furthermore CP
violation in the flavour changing top quark decay will occur when a SUSY phase
is taken into account.Comment: 14 pages, latex, 3 figure
Anomalous t-c-g coupling: The connection between single top production and top decay
Continuing earlier work, we examine the constraint on an anomalous t-c-g
coupling from top quark decay. We find that from current CDF measurements of
the branching ratio , the minimum scale at which new physics
can strongly modify the t-c-g coupling is \Ltcg about 950 GeV. At the
upgraded Tevatron, single top production can constrain \Ltcg 4.5 TeV.
The connection between t-c production and the decay is
examined, showing how constraints on one lead to a constraint on the other.Comment: 5 pages. Requires epsf.sty to process .eps formatted figure
Time and Amplitude of Afterpulse Measured with a Large Size Photomultiplier Tube
We have studied the afterpulse of a hemispherical photomultiplier tube for an
upcoming reactor neutrino experiment. The timing, the amplitude, and the rate
of the afterpulse for a 10 inch photomultiplier tube were measured with a 400
MHz FADC up to 16 \ms time window after the initial signal generated by an LED
light pulse. The time and amplitude correlation of the afterpulse shows several
distinctive groups. We describe the dependencies of the afterpulse on the
applied high voltage and the amplitude of the main light pulse. The present
data could shed light upon the general mechanism of the afterpulse.Comment: 11 figure
Bounds on TeV Seesaw Models from LHC Higgs Data
We derive bounds on the Dirac Yukawa couplings of the neutrinos in seesaw
models using the recent Large Hadron Collider (LHC) data on Higgs decays for
the case where the Standard Model singlet heavy leptons needed for the seesaw
mechanism have masses in the 100 GeV range. Such scenarios with large Yukawa
couplings are natural in Inverse Seesaw models since the small neutrino mass
owes its origin to a small Majorana mass of a new set of singlet fermions.
Large Yukawas with sub-TeV mass right-handed neutrinos are also possible for
certain textures in Type-I seesaw models, so that the above bounds also apply
to them. We find that the current Higgs data from the LHC can put bounds on
both electron- and muon-type Yukawa couplings of order 10^{-2}.Comment: 24 pages, 3 figures, 8 tables; version accepted for publication in
PR
Operational experience, improvements, and performance of the CDF Run II silicon vertex detector
The Collider Detector at Fermilab (CDF) pursues a broad physics program at
Fermilab's Tevatron collider. Between Run II commissioning in early 2001 and
the end of operations in September 2011, the Tevatron delivered 12 fb-1 of
integrated luminosity of p-pbar collisions at sqrt(s)=1.96 TeV. Many physics
analyses undertaken by CDF require heavy flavor tagging with large charged
particle tracking acceptance. To realize these goals, in 2001 CDF installed
eight layers of silicon microstrip detectors around its interaction region.
These detectors were designed for 2--5 years of operation, radiation doses up
to 2 Mrad (0.02 Gy), and were expected to be replaced in 2004. The sensors were
not replaced, and the Tevatron run was extended for several years beyond its
design, exposing the sensors and electronics to much higher radiation doses
than anticipated. In this paper we describe the operational challenges
encountered over the past 10 years of running the CDF silicon detectors, the
preventive measures undertaken, and the improvements made along the way to
ensure their optimal performance for collecting high quality physics data. In
addition, we describe the quantities and methods used to monitor radiation
damage in the sensors for optimal performance and summarize the detector
performance quantities important to CDF's physics program, including vertex
resolution, heavy flavor tagging, and silicon vertex trigger performance.Comment: Preprint accepted for publication in Nuclear Instruments and Methods
A (07/31/2013
Single Top Quark Production via FCNC Couplings at Hadron Colliders
We calculate single top-quark production at hadron colliders via the
chromo-magnetic flavor-changing neutral current couplings and . We find that the strength for the anomalous ()
coupling may be probed to () at the Tevatron with of data and
() at the LHC with of data. The two couplings may be
distinguished by a comparision of the single top signal with the direct top and
top decay signals for these couplings.Comment: 18 pages, 6 figures, 3 table
P Pbar to T Tbar H: A Discovery mode for the Higgs boson at the Tevatron
The production of a Standard Model Higgs boson in association with a top
quark pair at the upcoming high luminosity run (15 inverse fb integrated
luminosity) of the Fermilab Tevatron (root s = 2.0 TeV) is revisited. For Higgs
masses below 140 GeV we demonstrate that the production cross section times
branching ratio for H->B Bbar decays yields a significant number of events and
that this mode is competitive with and complementary to the searches using P
Pbar -> WH, ZH associated production. For higher mass Higgs bosons the H -> W+
W- decays are more difficult but have the potential to provide a few
spectacular events.Comment: 10 pages, Latex, RevTex, 3 ps figures: Updated reconstruction
efficiency and figure
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