6,913 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
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
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
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
Search for charged Higgs decays of the top quark using hadronic tau decays
We present the result of a search for charged Higgs decays of the top quark,
produced in collisions at 1.8 TeV. When the charged
Higgs is heavy and decays to a tau lepton, which subsequently decays
hadronically, the resulting events have a unique signature: large missing
transverse energy and the low-charged-multiplicity tau. Data collected in the
period 1992-1993 at the Collider Detector at Fermilab, corresponding to
18.70.7~pb, exclude new regions of combined top quark and charged
Higgs mass, in extensions to the standard model with two Higgs doublets.Comment: uuencoded, gzipped tar file of LaTeX and 6 Postscript figures; 11 pp;
submitted to Phys. Rev.
Inclusive jet cross section in collisions at TeV
The inclusive jet differential cross section has been measured for jet
transverse energies, , from 15 to 440 GeV, in the pseudorapidity region
0.10.7. The results are based on 19.5 pb of data
collected by the CDF collaboration at the Fermilab Tevatron collider. The data
are compared with QCD predictions for various sets of parton distribution
functions. The cross section for jets with GeV is significantly
higher than current predictions based on O() perturbative QCD
calculations. Various possible explanations for the high- excess are
discussed.Comment: 8 pages with 2 eps uu-encoded figures Submitted to Physical Review
Letter
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Measurement of the Top Quark Mass using Quantities with Minimal Dependence on the Jet Energy Scale
Observation of Hadronic W Decays in t-tbar Events with the Collider Detector at Fermilab
We observe hadronic W decays in t-tbar -> W (-> l nu) + >= 4 jet events using
a 109 pb-1 data sample of p-pbar collisions at sqrt{s} = 1.8 TeV collected with
the Collider Detector at Fermilab (CDF). A peak in the dijet invariant mass
distribution is obtained that is consistent with W decay and inconsistent with
the background prediction by 3.3 standard deviations. From this peak we measure
the W mass to be 77.2 +- 4.6 (stat+syst) GeV/c^2. This result demonstrates the
presence of two W bosons in t-tbar candidates in the W (-> l nu) + >= 4 jet
channel.Comment: 20 pages, 4 figures, submitted to PR
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