95,966 research outputs found
Improving estimates of the number of fake leptons and other mis-reconstructed objects in hadron collider events: BoB's your UNCLE. (Previously "The Matrix Method Reloaded")
We consider current and alternative approaches to setting limits on new
physics signals having backgrounds from misidentified objects; for example jets
misidentified as leptons, b-jets or photons. Many ATLAS and CMS analyses have
used a heuristic matrix method for estimating the background contribution from
such sources. We demonstrate that the matrix method suffers from statistical
shortcomings that can adversely affect its ability to set robust limits. A
rigorous alternative method is discussed, and is seen to produce fake rate
estimates and limits with better qualities, but is found to be too costly to
use. Having investigated the nature of the approximations used to derive the
matrix method, we propose a third strategy that is seen to marry the speed of
the matrix method to the performance and physicality of the more rigorous
approach.Comment: v1 :11 pages, 5 figures. v2: title change requested by referee, and
other corrections/clarifications found during review. v3: final tweaks
suggested during review + move from revtex to jhep styl
Resummation of Large Endpoint Corrections to Color-Octet J/psi Photoproduction
An unresolved problem in J/psi phenomenology is a systematic understanding of
the differential photoproduction cross section, dsigma/dz [gamma + p -> J/psi +
X], where z= E_psi/E_gamma in the proton rest frame. In the non-relativistic
QCD (NRQCD) factorization formalism, fixed-order perturbative calculations of
color-octet mechanisms suffer from large perturbative and nonperturbative
corrections that grow rapidly in the endpoint region, z -> 1. In this paper,
NRQCD and soft collinear effective theory are combined to resum these large
corrections to the color-octet photoproduction cross section. We derive a
factorization theorem for the endpoint differential cross section involving the
parton distribution function and the color-octet J/psi shape functions. A one
loop matching calculation explicitly confirms our factorization theorem at
next-to-leading order. Large perturbative corrections are resummed using the
renormalization group. The calculation of the color-octet contribution to
dsigma/dz is in qualitative agreement with data. Quantitative tests of the
universality of color-octet matrix elements require improved knowledge of shape
functions entering these calculations as well as resummation of the
color-singlet contribution which accounts for much of the total cross section
and also peaks near the endpoint.Comment: 30 pages, 6 figure
Numerical calculations of a high brilliance synchrotron source and on issues with characterizing strong radiation damping effects in non-linear Thomson/Compton backscattering experiments
A number of theoretical calculations have studied the effect of radiation
reaction forces on radiation distributions in strong field counter-propagating
electron beam-laser interactions, but could these effects - including quantum
corrections - be observed in interactions with realistic bunches and focusing
fields, as is hoped in a number of soon to be proposed experiments? We present
numerical calculations of the angularly resolved radiation spectrum from an
electron bunch with parameters similar to those produced in laser wakefield
acceleration experiments, interacting with an intense, ultrashort laser pulse.
For our parameters, the effects of radiation damping on the angular
distribution and energy distribution of \emph{photons} is not easily
discernible for a "realistic" moderate emittance electron beam. However,
experiments using such a counter-propagating beam-laser geometry should be able
to measure such effects using current laser systems through measurement of the
\emph{electron beam} properties. In addition, the brilliance of this source is
very high, with peak spectral brilliance exceeding
photonssmmmrad% bandwidth with
approximately 2% efficiency and with a peak energy of 10 MeV.Comment: 11 figures, 11 page
CI emission in Ultra Luminous Infrared Galaxies as a molecular gas mass tracer
We present new sensitive wide-band measurements of the fine structure line
3^P_1 -> 3^P_0 (J=1-0, 492GHz) of neutral atomic carbon (CI) in the two typical
Ultra Luminous Infrared Galaxies NGC6240 and Arp220. We then use them along
with several other CI measurements in similar objects found in the literature
to estimate their global molecular gas content under the assumption of a full
CI-H_2 concomitance. We find excellent agreement between the H_2 gas mass
estimated with this method and the standard methods using 12^CO. This may
provide a new way to measure H_2 gas mass in galaxies, and one which may be
very valuable in ULIRGs since in such systems the bright 12^CO emission is
known to systematically overestimate the gas mass while their 13^CO emission is
usually very weak. At redshifts z>=1 the CI J=1-0 line shifts to much more
favorable atmospheric windows and can become a viable alternative tracer of the
H_2 gas fueling starburst events in the distant Universe.Comment: 11 pages, 2 figures. Accepted for publication in ApJ Letter
Measuring physiological responses to the arts in people with dementia
The dementias are a group of progressive symptoms that have multiple causes, usually caused by disease or injury of the brain, affecting higher brain functions such as language, perception, memory, reasoning and mood; they can also be associated with changes in personality. Arts interventions and interaction with the arts can create meaningful, positive experiences for people with a dementia, as well as improve quality of life. Qualitative research in particular, has been able to describe the emotional responses the arts can produce, but quantifiable changes have not been well documented. Physiological measurements such as stress hormone levels and galvanic skin response show promise in being able to quantify such responses. When taken together, these can give a picture of the kinds of physiological outcomes that are associated with positive affect and improvements in mental wellbeing in the context of arts interventions.
This review provides a critical overview of the studies which measure some form of physiological outcome in response to the arts or an arts intervention in people with dementia, and indicates how future research in this area can help to broaden our understanding of the effects of the arts in dementia research and care
A nonlinear Schr\"odinger equation for water waves on finite depth with constant vorticity
A nonlinear Schr\"odinger equation for the envelope of two dimensional
surface water waves on finite depth with non zero constant vorticity is
derived, and the influence of this constant vorticity on the well known
stability properties of weakly nonlinear wave packets is studied. It is
demonstrated that vorticity modifies significantly the modulational instability
properties of weakly nonlinear plane waves, namely the growth rate and
bandwidth. At third order we have shown the importance of the coupling between
the mean flow induced by the modulation and the vorticity. Furthermore, it is
shown that these plane wave solutions may be linearly stable to modulational
instability for an opposite shear current independently of the dimensionless
parameter kh, where k and h are the carrier wavenumber and depth respectively
Magnetic spin moment reduction in photoexcited ferromagnets through exchange interaction quenching: Beyond the rigid band approximation
The exchange interaction among electrons is one of the most fundamental
quantum mechanical interactions in nature and underlies any magnetic phenomena
from ferromagnetic ordering to magnetic storage. The current technology is
built upon a thermal or magnetic field, but a frontier is emerging to directly
control magnetism using ultrashort laser pulses. However, little is known about
the fate of the exchange interaction. Here we report unambiguously that
photoexcitation is capable of quenching the exchange interaction in all three
ferromagnetic metals. The entire process starts with a small number of
photoexcited electrons which build up a new and self-destructive potential that
collapses the system into a new state with a reduced exchange splitting. The
spin moment reduction follows a Bloch-like law as , where is
the absorbed photon energy and is a scaling exponent. A good agreement
is found between the experimental and our theoretical results. Our findings may
have a broader implication for dynamic electron correlation effects in
laser-excited iron-based superconductors, iron borate, rare-earth
orthoferrites, hematites and rare-earth transition metal alloys.Comment: 16 pages, 3 figures, one supplementary material fil
The principle of equivalence and projective structure in space-times
This paper discusses the extent to which one can determine the space-time
metric from a knowledge of a certain subset of the (unparametrised) geodesics
of its Levi-Civita connection, that is, from the experimental evidence of the
equivalence principle. It is shown that, if the space-time concerned is known
to be vacuum, then the Levi-Civita connection is uniquely determined and its
associated metric is uniquely determined up to a choice of units of
measurement, by the specification of these geodesics. It is further
demonstrated that if two space-times share the same unparametrised geodesics
and only one is assumed vacuum then their Levi-Civita connections are again
equal (and so the other metric is also a vacuum metric) and the first result
above is recovered.Comment: 23 pages, submitted to Classical and Quantum Gravit
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