10,028 research outputs found
B physics at CDF - the Beauty of hadron collisions
The CDF experiment at the Tevatron p-pbar collider established that extensive
and detailed exploration of the b-quark dynamics is possible in hadron
collisions, with results competitive and supplementary to those from e+e-
colliders. This provides an unique, rich, and highly rewarding program that is
currently reaching full maturity. I report a few recent world-leading results
on rare decays, CP-violation in Bs mixing, and b-> s penguin decays.Comment: 6 pages, 5 figures. Write-up of the proceedings of the "Third
Workshop on Theory, Phenomenology and Experiments in Heavy Flavour Physics"
(Capri2010
Recent QCD results from the Tevatron
Recent QCD related results from the CDF and the D0 experiments are presented
based on proton anti-proton collision data at sqrt(s)=1.96 TeV, taken in Run II
of the Fermilab Tevatron Collider. Measured observables include inclusive
photon and diphoton production, vector boson plus jets production, event shape
variables, and inclusive multijet production. The measurement results are
compared to QCD theory calculations in different approximations. A
determination of the strong coupling constant from jet data is presented.Comment: 12 pages with 14 figures, to appear in the proceedings of the
"Ringberg Workshop: New Trends in HERA Physics 2011", Ringberg Castle,
Germany, 25-28 September, 201
Standard model explanation of a CDF dijet excess in Wjj
We demonstrate the recent observation of a peak in the dijet invariant mass
of the Wjj signal observed by the CDF Collaboration can be explained as the
same upward fluctuation observed by CDF in single-top-quark production. In
general, both t-channel and s-channel single-top-quark production produce
kinematically induced peaks in the dijet spectrum. Since CDF used a Monte Carlo
simulation to subtract the single-top backgrounds instead of data, a peak in
the dijet spectrum is expected. The D0 Collaboration has a small upward
fluctuation in their published t-channel data; and hence we predict they would
see at most a small peak in the dijet invariant mass spectrum of Wjj if they
follow the same procedure as CDF.Comment: 3 pg., 2 figs, revtex, minor clarifications, to appear in Phys. Rev.
A Novel in situ Trigger Combination Method
Searches for rare physics processes using particle detectors in
high-luminosity colliding hadronic beam environments require the use of
multi-level trigger systems to reject colossal background rates in real time.
In analyses like the search for the Higgs boson, there is a need to maximize
the signal acceptance by combining multiple different trigger chains when
forming the offline data sample. In such statistically limited searches,
datasets are often amassed over periods of several years, during which the
trigger characteristics evolve and system performance can vary significantly.
Reliable production cross-section measurements and upper limits must take into
account a detailed understanding of the effective trigger inefficiency for
every selected candidate event. We present as an example the complex situation
of three trigger chains, based on missing energy and jet energy, that were
combined in the context of the search for the Higgs (H) boson produced in
association with a boson at the Collider Detector at Fermilab (CDF). We
briefly review the existing techniques for combining triggers, namely the
inclusion, division, and exclusion methods. We introduce and describe a novel
fourth in situ method whereby, for each candidate event, only the trigger chain
with the highest a priori probability of selecting the event is considered. We
compare the inclusion and novel in situ methods for signal event yields in the
CDF search. This new combination method, by virtue of its scalability to
large numbers of differing trigger chains and insensitivity to correlations
between triggers, will benefit future long-running collider experiments,
including those currently operating on the Large Hadron Collider.Comment: 17 pages, 2 figures, 6 tables, accepted by Nuclear Instruments and
Methods in Physics Research
Stringy origin of Tevatron Wjj anomaly
The invariant mass distribution of dijets produced in association with W
bosons, recently observed by the CDF Collaboration at Tevatron, reveals an
excess in the dijet mass range 120-160 GeV/c^2, 3\sigma beyond Standard Model
expectations. We show that such an excess is a generic feature of low mass
string theory, due to the production and decay of a leptophobic Z', a singlet
partner of SU(3) gluons coupled primarily to the U(1) baryon number. In this
framework, U(1) and SU(3) appear as subgroups of U(3) associated with open
strings ending on a stack of 3 D-branes. In addition, a minimal model contains
two other stacks to accommodate the electro-weak SU(2) \in U(2) and the
hypercharge U(1). Of the three U(1) gauge bosons, the two heavy Z' and Z"
receive masses through the Green-Schwarz mechanism. For a given Z' mass, the
model is quite constrained. Fine tuning three of its free parameters is just
sufficient to simultaneously ensure: a small Z-Z' mixing in accord with the
stringent LEP data on the mass; very small (less than 1%) branching ratio
into leptons; and a large hierarchy between Z" and Z' masses. The heavier
neutral gauge boson Z" is within the reach of LHC.Comment: v1 8 pages revtex; v2 better fit to the data (Z" within LHC reach),
references added; v3 to appear in PL
Present Limits on the Precision of SM Predictions for Jet Energies
We investigate the impact of theoretical uncertainties on the accuracy of
measurements involving hadronic jets. The analysis is performed using events
with a Z boson and a single jet observed in collisions at
= 1.96 TeV in 4.6 of data from the Collider Detector at
Fermilab (CDF). The transverse momenta (\pt) of the jet and the boson should
balance each other due to momentum conservation in the plane transverse to the
direction of the and beams. We evaluate the dependence of the
measured \pt-balance on theoretical uncertainties associated with initial and
final state radiation, choice of renormalization and factorization scales,
parton distribution functions, jet-parton matching, calculations of matrix
elements, and parton showering. We find that the uncertainty caused by parton
showering at large angles is the largest amongst the listed uncertainties. The
proposed method can be re-applied at the LHC experiments to investigate and
evaluate the uncertainties on the predicted jet energies. The distributions
produced at the CDF environment are intended for comparison to those from
modern event generators and new tunes of parton showering.Comment: Submitted to Nucl. Instr. and Meth.
Measurements of the Production, Decay and Properties of the Top Quark: A Review
With the full Tevatron Run II and early LHC data samples, the opportunity for
furthering our understanding of the properties of the top quark has never been
more promising. Although the current knowledge of the top quark comes largely
from Tevatron measurements, the experiments at the LHC are poised to probe
top-quark production and decay in unprecedented regimes. Although no current
top quark measurements conclusively contradict predictions from the standard
model, the precision of most measurements remains statistically limited.
Additionally, some measurements, most notably the forward-backward asymmetry in
top quark pair production, show tantalizing hints of beyond-the-Standard-Model
dynamics. The top quark sample is growing rapidly at the LHC, with initial
results now public. This review examines the current status of top quark
measurements in the particular light of searching for evidence of new physics,
either through direct searches for beyond the standard model phenomena or
indirectly via precise measurements of standard model top quark properties
Background dependence of dimuon asymmetry in interactions at TeV
The D0 Collaboration has reported an anomalous charge asymmetry in the
production of same-sign muon pairs at the Fermilab Tevatron. The magnitude of
this effect depends on the subtraction of several backgrounds, the most notable
of which is due to kaons being misidentified as muons either through decays in
flight or punch-through. The present authors suggested a check on such
backgrounds consisting of a tight restriction on the muon impact parameter ,
to confirm that this excess was indeed due to meson decays. The D0
Collaboration has performed a related check applying transverse impact
parameter (IP) restrictions, whose implications are discussed. We study
background asymmetry predictions for events involving two muons with IP bounds
which are complementary to each other. These predictions may be used in future
measurements of the net charge asymmetry from decays.Comment: To be published in Physics Letters
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