1,176 research outputs found
Probabilistic Particle Flow Algorithm for High Occupancy Environment
Algorithms based on the particle flow approach are becoming increasingly
utilized in collider experiments due to their superior jet energy and missing
energy resolution compared to the traditional calorimeter-based measurements.
Such methods have been shown to work well in environments with low occupancy of
particles per unit of calorimeter granularity. However, at higher instantaneous
luminosity or in detectors with coarse calorimeter segmentation, the overlaps
of calorimeter energy deposits from charged and neutral particles significantly
complicate particle energy reconstruction, reducing the overall energy
resolution of the method. We present a technique designed to resolve
overlapping energy depositions of spatially close particles using a
statistically consistent probabilistic procedure. The technique is nearly free
of ad-hoc corrections, improves energy resolution, and provides new important
handles that can improve the sensitivity of physics analyses: the uncertainty
of the jet energy on an event-by-event basis and the estimate of the
probability of a given particle hypothesis for a given detector response. When
applied to the reconstruction of hadronic jets produced in the decays of tau
leptons using the CDF-II detector at Fermilab, the method has demonstrated
reliable and robust performance.Comment: Accepted by Nuclear Instruments and Methods
Standard Model Higgs boson searches with the ATLAS detector at the Large Hadron Collider
The investigation of the mechanism responsible for electroweak symmetry
breaking is one of the most important tasks of the scientific program of the
Large Hadron Collider. The experimental results on the search of the Standard
Model Higgs boson with 1 to 2 fb^-1 of proton proton collision data at sqrt s=7
TeV recorded by the ATLAS detector are presented and discussed. No significant
excess of events is found with respect to the expectations from Standard Model
processes, and the production of a Higgs boson is excluded at 95% Confidence
Level for the mass regions 144-232, 256-282 and 296-466 GeV.Comment: Proceedings of the Lepton Photon 2011 Conference, to appear in
"Pramana - journal of phsyics". 11 pages, 13 figure
A data-driven method of pile-up correction for the substructure of massive jets
We describe a method to measure and subtract the incoherent component of
energy flow arising from multiple interactions from jet shape/substructure
observables of ultra-massive jets. The amount subtracted is a function of the
jet shape variable of interest and not a universal property. Such a correction
is expected to significantly reduce any bias in the corresponding distributions
generated by the presence of multiple interactions, and to improve measurement
resolution. Since in our method the correction is obtained from the data, it is
not subject to uncertainties coming from the use of theoretical calculations
and/or Monte Carlo event generators. We derive our correction method for the
jet mass, angularity and planar flow. We find these corrections to be in good
agreement with data on massive jets observed by the CDF collaboration. Finally,
we comment on the linkage with the concept of jet area and jet mass area.Comment: 7 pages and 3 figures, minor correction
Observation of Exclusive Gamma Gamma Production in p pbar Collisions at sqrt{s}=1.96 TeV
We have observed exclusive \gamma\gamma production in proton-antiproton
collisions at \sqrt{s}=1.96 TeV, using data from 1.11 \pm 0.07 fb^{-1}
integrated luminosity taken by the Run II Collider Detector at Fermilab. We
selected events with two electromagnetic showers, each with transverse energy
E_T > 2.5 GeV and pseudorapidity |\eta| < 1.0, with no other particles detected
in -7.4 < \eta < +7.4. The two showers have similar E_T and azimuthal angle
separation \Delta\phi \sim \pi; 34 events have two charged particle tracks,
consistent with the QED process p \bar{p} to p + e^+e^- + \bar{p} by two-photon
exchange, while 43 events have no charged tracks. The number of these events
that are exclusive \pi^0\pi^0 is consistent with zero and is < 15 at 95% C.L.
The cross section for p\bar{p} to p+\gamma\gamma+\bar{p} with |\eta(\gamma)| <
1.0 and E_T(\gamma) > 2.5$ GeV is
2.48^{+0.40}_{-0.35}(stat)^{+0.40}_{-0.51}(syst) pb.Comment: 7 pages, 4 figure
A search for resonant production of pairs in $4.8\ \rm{fb}^{-1}p\bar{p}\sqrt{s}=1.96\ \rm{TeV}$
We search for resonant production of tt pairs in 4.8 fb^{-1} integrated
luminosity of ppbar collision data at sqrt{s}=1.96 TeV in the lepton+jets decay
channel, where one top quark decays leptonically and the other hadronically. A
matrix element reconstruction technique is used; for each event a probability
density function (pdf) of the ttbar candidate invariant mass is sampled. These
pdfs are used to construct a likelihood function, whereby the cross section for
resonant ttbar production is estimated, given a hypothetical resonance mass and
width. The data indicate no evidence of resonant production of ttbar pairs. A
benchmark model of leptophobic Z \rightarrow ttbar is excluded with m_{Z'} <
900 GeV at 95% confidence level.Comment: accepted for publication in Physical Review D Sep 21, 201
Combined search for the standard model Higgs boson decaying to a bb pair using the full CDF data set
We combine the results of searches for the standard model Higgs boson based
on the full CDF Run II data set obtained from sqrt(s) = 1.96 TeV p-pbar
collisions at the Fermilab Tevatron corresponding to an integrated luminosity
of 9.45/fb. The searches are conducted for Higgs bosons that are produced in
association with a W or Z boson, have masses in the range 90-150 GeV/c^2, and
decay into bb pairs. An excess of data is present that is inconsistent with the
background prediction at the level of 2.5 standard deviations (the most
significant local excess is 2.7 standard deviations).Comment: To be published in Phys. Rev. Lett (v2 contains minor updates based
on comments from PRL
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