150,882 research outputs found
Boosting the Standard Model Higgs Signal with the Template Overlap Method
We show that the Template Overlap Method can improve the signal to background
ratio of boosted events produced in association with a
leptonically decaying . We introduce several improvements on the previous
formulations of the template method. Varying three-particle template subcones
increases the rejection power against the backgrounds, while sequential
template generation ensures an efficient coverage in template phase space. We
integrate b-tagging information into the template overlap framework and
introduce a new template based observable, the template stretch. Our analysis
takes into account the contamination from the charm daughters of top decays in
events, and includes nearly-realistic effects of pileup and
underlying events. We show that the Template Overlap Method displays very low
sensitivity to pileup, hence providing a self-contained alternative to other
methods of pile up subtraction. The developments described in this work are
quite general, and may apply to other searches for massive boosted objects.Comment: 28 pages, 35 figures; references added, minor revisions, to appear in
JHE
A Cone Jet-Finding Algorithm for Heavy-Ion Collisions at LHC Energies
Standard jet finding techniques used in elementary particle collisions have
not been successful in the high track density of heavy-ion collisions. This
paper describes a modified cone-type jet finding algorithm developed for the
complex environment of heavy-ion collisions. The primary modification to the
algorithm is the evaluation and subtraction of the large background energy,
arising from uncorrelated soft hadrons, in each collision. A detailed analysis
of the background energy and its event-by-event fluctuations has been performed
on simulated data, and a method developed to estimate the background energy
inside the jet cone from the measured energy outside the cone on an
event-by-event basis. The algorithm has been tested using Monte-Carlo
simulations of Pb+Pb collisions at TeV for the ALICE detector at
the LHC. The algorithm can reconstruct jets with a transverse energy of 50 GeV
and above with an energy resolution of .Comment: 13 pages, 7 figure
Using galaxy pairs as cosmological tracers
The Alcock-Paczynski (AP) effect uses the fact that, when analyzed with the
correct geometry, we should observe structure that is statistically isotropic
in the Universe. For structure undergoing cosmological expansion with the
background, this constrains the product of the Hubble parameter and the angular
diameter distance. However, the expansion of the Universe is inhomogeneous and
local curvature depends on density. We argue that this distorts the AP effect
on small scales. After analyzing the dynamics of galaxy pairs in the Millennium
simulation, we find an interplay between peculiar velocities, galaxy properties
and local density that affects how pairs trace cosmological expansion. We find
that only low mass, isolated galaxy pairs trace the average expansion with a
minimum "correction" for peculiar velocities. Other pairs require larger, more
cosmology and redshift dependent peculiar velocity corrections and, in the
small-separation limit of being bound in a collapsed system, do not carry
cosmological information.Comment: 15 pages, 14 figures, 1 tabl
A measurement of lifetime differences in the neutral D-meson system
Using a high statistics sample of photoproduced charm particles from the
FOCUS experiment at Fermilab, we compare the lifetimes of neutral D mesons
decaying via D0 to K- pi+ and K- K+ to measure the lifetime differences between
CP even and CP odd final states. These measurements bear on the phenomenology
of D0 - D0bar mixing. If the D0 to K-pi+ is an equal mixture of CP even and CP
odd eigenstates, we measure yCP = 0.0342 \pm 0.0139 \pm 0.0074.Comment: 15 pages, 5 figure
First Observation of the decay KL -> pi0 e e gamma
We report on the first observation of the decay KL -> pi0 ee gamma by the
KTeV E799 experiment at Fermilab. Based upon a sample of 48 events with an
estimated background of 3.6 +/- 1.1 events, we measure the KL -> pi0 ee gamma
branching ratio to be (2.34 +/- 0.35 +/- 0.13)x10^{-8}. Our data agree with
recent O(p^6) calculations in chiral perturbation theory that include
contributions from vector meson exchange through the parameter a_V. A fit was
made to the KL -> pi0 ee gamma data for a_V with the result -0.67 +/- 0.21 +/-
0.12, which is consistent with previous results from KTeV.Comment: Submitted to Physical Review Letters, 5 pages, 5 figure
Observation of the Crab Nebula with the HAWC Gamma-Ray Observatory
The Crab Nebula is the brightest TeV gamma-ray source in the sky and has been
used for the past 25 years as a reference source in TeV astronomy, for
calibration and verification of new TeV instruments. The High Altitude Water
Cherenkov Observatory (HAWC), completed in early 2015, has been used to observe
the Crab Nebula at high significance across nearly the full spectrum of
energies to which HAWC is sensitive. HAWC is unique for its wide field-of-view,
nearly 2 sr at any instant, and its high-energy reach, up to 100 TeV. HAWC's
sensitivity improves with the gamma-ray energy. Above 1 TeV the
sensitivity is driven by the best background rejection and angular resolution
ever achieved for a wide-field ground array.
We present a time-integrated analysis of the Crab using 507 live days of HAWC
data from 2014 November to 2016 June. The spectrum of the Crab is fit to a
function of the form . The data is well-fit with values of
, , and
log when
is fixed at 7 TeV and the fit applies between 1 and 37 TeV. Study of the
systematic errors in this HAWC measurement is discussed and estimated to be
50\% in the photon flux between 1 and 37 TeV.
Confirmation of the Crab flux serves to establish the HAWC instrument's
sensitivity for surveys of the sky. The HAWC survey will exceed sensitivity of
current-generation observatories and open a new view of 2/3 of the sky above 10
TeV.Comment: Submitted 2017/01/06 to the Astrophysical Journa
On-line recognition of supernova neutrino bursts in the LVD detector
In this paper we show the capabilities of the Large Volume Detector (INFN
Gran Sasso National Laboratory) to identify a neutrino burst associated to a
supernova explosion, in the absence of an "external trigger", e.g., an optical
observation. We describe how the detector trigger and event selection have been
optimized for this purpose, and we detail the algorithm used for the on-line
burst recognition. The on-line sensitivity of the detector is defined and
discussed in terms of supernova distance and electron anti-neutrino intensity
at the source.Comment: Accepted for pubblication on Astroparticle Physics. 13 pages, 10
figure
In-Medium Effects on K0 Mesons in Relativistic Heavy-Ion Collisions
We present the transverse momentum spectra and rapidity distributions of
and K in Ar+KCl reactions at a beam kinetic energy of 1.756 A
GeV measured with the spectrometer HADES. The reconstructed K sample is
characterized by good event statistics for a wide range in momentum and
rapidity. We compare the experimental and K distributions to
predictions by the IQMD model. The model calculations show that K at low
tranverse momenta constitute a particularly well suited tool to investigate the
kaon in-medium potential. Our K data suggest a strong repulsive in-medium
K potential of about 40 MeV strength.Comment: 10 pages, 10 figures, accepted by Phys. Rev.
Top Physics at ATLAS
The Large Hadron Collider LHC is a top quark factory: due to its high design
luminosity, LHC will produce about 200 millions of top quarks per year of
operation. The large amount of data will allow to study with great precision
the properties of the top quark, most notably cross-section, mass and spin. The
Top Physics Working Group has been set up at the ATLAS experiment, to evaluate
the precision reach of physics measurements in the top sector, and to study the
systematic effects of the ATLAS detector on such measurements. This reports
give an overview of the main activities of the ATLAS Top Physics Working Group
in 2004.Comment: presented at IFAE - Incontri di Fisica delle Alte Energie - Catania
200
- …