3,567 research outputs found
A Tunable Lyot Filter at Prime Focus: a Method for Tracing Supercluster Scales at z ~ 1
Tunable narrow-band, emission-line surveys have begun to show the ease with
which star forming galaxies can be identified in restricted redshift intervals
to z ~ 5 with a 4m class telescope. These surveys have been carried out with
imaging systems at the Cassegrain or Nasmyth focus and are therefore restricted
to fields smaller than 10 arcmin. We now show that tunable narrowband imaging
is possible over a 30 arcmin field with a high-performance Lyot filter placed
directly in front of a CCD mosaic at the prime focus. Our design is intended
for the f/3.3 prime focus of the AAT 3.9m, although similar devices can be
envisaged for the Subaru 8m (f/2), Palomar 5m (f/3.4), VISTA 4m (f/6), Mayall
4m (f/2.6) or CFHT 3.6m (f/4). A modified Wynne doublet ensures sub-arcsecond
performance over the field. In combination with the new Wide-Field Imaging 8K x
8K mosaic (WFI) at the AAT, the overall throughput (35%) of the system to
unpolarised light is expected to be comparable to the TAURUS Tunable Filter
(TTF). Unlike the TTF, the field is fully monochromatic and the instrumental
profile has much better wing suppression. For targetted surveys of
emission-line sources at z ~ 1, a low-resolution (R ~ 150 at 550nm) Lyot filter
on a 4m telescope is expected to be comparable or superior to current
instruments on 8-10m class telescopes. We demonstrate that the 30 arcmin field
is well matched to superclusters at these redshifts such that large-scale
structure should be directly observable.Comment: Astrophysical Journal, accepted. 53 pages, 16 figures, aaste
Evidence for the exclusive decay Bc+- to J/psi pi+- and measurement of the mass of the Bc meson
We report first evidence for a fully reconstructed decay mode of the
B_c^{\pm} meson in the channel B_c^{\pm} \to J/psi \pi^{\pm}, with J/psi \to
mu^+mu^-. The analysis is based on an integrated luminosity of 360 pb$^{-1} in
p\bar{p} collisions at 1.96 TeV center of mass energy collected by the Collider
Detector at Fermilab. We observe 14.6 \pm 4.6 signal events with a background
of 7.1 \pm 0.9 events, and a fit to the J/psi pi^{\pm} mass spectrum yields a
B_c^{\pm} mass of 6285.7 \pm 5.3(stat) \pm 1.2(syst) MeV/c^2. The probability
of a peak of this magnitude occurring by random fluctuation in the search
region is estimated as 0.012%.Comment: 7 pages, 3 figures. Version 3, accepted by PR
The Patient Deficit Model Overturned: a qualitative study of patients' perceptions of invitation to participate in a randomized controlled trial comparing selective bladder preservation against surgery in muscle invasive bladder cancer (SPARE, CRUK/07/011)
BACKGROUND: Evidence suggests that poor recruitment into clinical trials rests on a patient âdeficitâ model â an inability to comprehend trial processes. Poor communication has also been cited as a possible barrier to recruitment. A qualitative patient interview study was included within the feasibility stage of a phase III non-inferiority Randomized Controlled Trial (RCT) (SPARE, CRUK/07/011) in muscle invasive bladder cancer. The aim was to illuminate problems in the context of randomization. METHODS: The qualitative study used a âFramework Analysisâ that included âconstant comparisonâ in which semi-structured interviews are transcribed, analyzed, compared and contrasted both between and within transcripts. Three researchers coded and interpreted data. RESULTS: Twenty-four patients agreed to enter the interview study; 10 decliners of randomization and 14 accepters, of whom 2 subsequently declined their allocated treatment. The main theme applying to the majority of the sample was confusion and ambiguity. There was little indication that confusion directly impacted on decisions to enter the SPARE trial. However, confusion did appear to impact on ethical considerations surrounding âinformed consentâ, as well as cause a sense of alienation between patients and health personnel. Sub-optimal communication in many guises accounted for the confusion, together with the logistical elements of a trial that involved treatment options delivered in a number of geographical locations. CONCLUSIONS: These data highlight the difficulty of providing balanced and clear trial information within the UK health system, despite best intentions. Involvement of multiple professionals can impact on communication processes with patients who are considering participation in RCTs. Our results led us to question the âdeficitâ model of patient behavior. It is suggested that health professionals might consider facilitating a context in which patients feel fully included in the trial enterprise and potentially consider alternatives to randomization where complex interventions are being tested. TRIAL REGISTRATION: ISRCTN6112646
Top quark mass measurement using the template method at CDF
We present a measurement of the top quark mass in the lepton+jets and
dilepton channels of decays using the template method. The data
sample corresponds to an integrated luminosity of 5.6 fb of
collisions at Tevatron with TeV, collected with the CDF II
detector. The measurement is performed by constructing templates of three
kinematic variables in the lepton+jets and two kinematic variables in the
dilepton channel. The variables are two reconstructed top quark masses from
different jets-to-quarks combinations and the invariant mass of two jets from
the decay in the lepton+jets channel, and a reconstructed top quark mass
and , a variable related to the transverse mass in events with two
missing particles, in the dilepton channel. The simultaneous fit of the
templates from signal and background events in the lepton+jets and dilepton
channels to the data yields a measured top quark mass of Comment: submitted to Phys. Rev.
Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt(s) = 1.96 TeV
We present a measurement of the top quark pair production cross section in
ppbar collisions at sqrt(s)=1.96 TeV using 318 pb^{-1} of data collected with
the Collider Detector at Fermilab. We select ttbar decays into the final states
e nu + jets and mu nu + jets, in which at least one b quark from the t-quark
decays is identified using a secondary vertex-finding algorithm. Assuming a top
quark mass of 178 GeV/c^2, we measure a cross section of 8.7 +-0.9 (stat)
+1.1-0.9 (syst) pb. We also report the first observation of ttbar with
significance greater than 5 sigma in the subsample in which both b quarks are
identified, corresponding to a cross section of 10.1 +1.6-1.4(stat)+2.0-1.3
(syst) pb.Comment: Accepted for publication in Physics Review Letters, 7 page
Measurement of the cross-section and charge asymmetry of bosons produced in proton-proton collisions at TeV with the ATLAS detector
This paper presents measurements of the and cross-sections and the associated charge asymmetry as a
function of the absolute pseudorapidity of the decay muon. The data were
collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with
the ATLAS experiment at the LHC and correspond to a total integrated luminosity
of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements
varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the
1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured
with an uncertainty between 0.002 and 0.003. The results are compared with
predictions based on next-to-next-to-leading-order calculations with various
parton distribution functions and have the sensitivity to discriminate between
them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables,
submitted to EPJC. All figures including auxiliary figures are available at
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13
Polarizations of J/psi and psi(2S) Mesons Produced in ppbar Collisions at 1.96 TeV
We have measured the polarizations of \jpsi and \psiprime mesons as
functions of their transverse momentum \pt when they are produced promptly in
the rapidity range with \pt \geq 5 \pgev. The analysis is performed
using a data sample with an integrated luminosity of about 800 \ipb collected
by the CDF II detector. For both vector mesons, we find that the polarizations
become increasingly longitudinal as \pt increases from 5 to 30 \pgev. These
results are compared to the predictions of nonrelativistic quantum
chromodynamics and other contemporary models. The effective polarizations of
\jpsi and \psiprime mesons from -hadron decays are also reported.Comment: 8 pages, 7 figures, published in Physical Review Letter
Observation and Mass Measurement of the Baryon
We report the observation and measurement of the mass of the bottom, strange
baryon through the decay chain , where
, , and .
Evidence for observation is based on a signal whose probability of arising from
the estimated background is 6.6 x 10^{-15}, or 7.7 Gaussian standard
deviations. The mass is measured to be (stat.) (syst.) MeV/.Comment: Minor text changes for the second version. Accepted by Phys. Rev.
Let
Search for New Particles Leading to Z+jets Final States in Collisions at TeV
We present the results of a search for new particles that lead to a \Z boson
plus jets in collisions at TeV using the Collider
Detector at Fermilab (CDF II). A data sample with a luminosity of 1.06 \ifb\
collected using \Z boson decays to and is used. We describe a
completely data-based method to predict the dominant background from
standard-model \Z+jet events. This method can be similarly applied to other
analyses requiring background predictions in multi-jet environments, as shown
when validating the method by predicting the background from +jets in \ttbar
production. No significant excess above the background prediction is observed,
and a limit is set using a fourth generation quark model to quantify the
acceptance. Assuming and using a leading-order
calculation of the cross section, quark masses below 268 \gev/c^2
are excluded at 95% confidence level.Comment: To be submitted to PR
Search for chargino-neutralino production with mass splittings near the electroweak scale in three-lepton final states in âs=13âTeV pp collisions with the ATLAS detector
A search for supersymmetry through the pair production of electroweakinos with mass splittings near the electroweak scale and decaying via on-shell W and Z bosons is presented for a three-lepton final state. The analyzed proton-proton collision data taken at a center-of-mass energy of âs=13ââTeV were collected between 2015 and 2018 by the ATLAS experiment at the Large Hadron Collider, corresponding to an integrated luminosity of 139ââfbâ1. A search, emulating the recursive jigsaw reconstruction technique with easily reproducible laboratory-frame variables, is performed. The two excesses observed in the 2015â2016 data recursive jigsaw analysis in the low-mass three-lepton phase space are reproduced. Results with the full data set are in agreement with the Standard Model expectations. They are interpreted to set exclusion limits at the 95% confidence level on simplified models of chargino-neutralino pair production for masses up to 345 GeV
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