182 research outputs found
Search for the Proton Decay Mode proton to neutrino K+ in Soudan 2
We have searched for the proton decay mode proton to neutrino K+ using the
one-kiloton Soudan 2 high resolution calorimeter. Contained events obtained
from a 3.56 kiloton-year fiducial exposure through June 1997 are examined for
occurrence of a visible K+ track which decays at rest into mu+ nu or pi+ pi0.
We found one candidate event consistent with background, yielding a limit,
tau/B > 4.3 10^{31} years at 90% CL with no background subtraction.Comment: 13 pages, Latex, 3 tables and 3 figures, Accepted by Physics Letters
Application of coded apertures in tomographic head scanning
A circular ring tomograph, designated SPRINT, is under development for single photon emission tomography of the human head. Most data to date have been gathered using a single rotating slit inside the detector ring to define ray directions. As an alternative method, we have also investigated the use of multiplexed slit patterns consisting of a pseudorandom binary code. From theoretical considerations, one would expect that the substitution of the code for the single slit would have potential advantages in reducing statistical noise in tomographic images of small objects. It has been our experience that this improvement is marginal at best for the types of source distributions encountered in clinical brain imaging. However, the code shows substantial advantage in suppressing uncorrelated backgrounds and the effects of highly penetrating gamma ray components in the source.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24867/1/0000294.pd
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
Measurement of isolated photon production in pp and PbPb collisions at sqrt(sNN) = 2.76 TeV
Isolated photon production is measured in proton-proton and lead-lead
collisions at nucleon-nucleon centre-of-mass energies of 2.76 TeV in the
pseudorapidity range |eta|<1.44 and transverse energies ET between 20 and 80
GeV with the CMS detector at the LHC. The measured ET spectra are found to be
in good agreement with next-to-leading-order perturbative QCD predictions. The
ratio of PbPb to pp isolated photon ET-differential yields, scaled by the
number of incoherent nucleon-nucleon collisions, is consistent with unity for
all PbPb reaction centralities.Comment: Submitted to Physics Letters
Microwave determination of the quasiparticle scattering time in YBa2Cu3O6.95
We report microwave surface resistance (Rs) measurements on two very-high-quality YBa2Cu3O6.95 crystals which exhibit extremely low residual loss at 1.2 K (2-6 ΟΊ at 2 GHz), a broad, reproducible peak at around 38 K, and a rapid increase in loss, by 4 orders of magnitude, between 80 and 93 K. These data provide one ingredient in the determination of the temperature dependence of the real part of the microwave conductivity, Ď1(T), and of the quasiparticle scattering time. The other necessary ingredient is an accurate knowledge of the magnitude and temperature dependence of the London penetration depth, Îť(T). This is derived from published data, from microwave data of Anlage, Langley, and co-workers and from, high-quality ÎźSR data. We infer, from a careful analysis of all available data, that Îť2(0)/Îť2(T) is well approximated by the simple function 1-t2, where t=T/Tc, and that the low-temperature data are incompatible with the existence of an s-wave, BCS-like gap. Combining the Rs and Îť(T) data, we find that Ď1(T), has a broad peak around 32 K with a value about 20 times that at Tc. Using a generalized two-fluid model, we extract the temperature dependence of the quasiparticle scattering rate which follows an exponential law, exp(T/T0), where T0â12 K, for T between 15 and 84 K. Such a temperature dependence has previously been observed in measurements of the nuclear spin-lattice relaxation rate. Both the uncertainties in our analysis and the implications for the mechanism of high-temperature superconductivity are discussed
Meta-analysis of type 2 Diabetes in African Americans Consortium
Type 2 diabetes (T2D) is more prevalent in African Americans than in Europeans. However, little is known about the genetic risk in African Americans despite the recent identification of more than 70 T2D loci primarily by genome-wide association studies (GWAS) in individuals of European ancestry. In order to investigate the genetic architecture of T2D in African Americans, the MEta-analysis of type 2 DIabetes in African Americans (MEDIA) Consortium examined 17 GWAS on T2D comprising 8,284 cases and 15,543 controls in African Americans in stage 1 analysis. Single nucleotide polymorphisms (SNPs) association analysis was conducted in each study under the additive model after adjustment for age, sex, study site, and principal components. Meta-analysis of approximately 2.6 million genotyped and imputed SNPs in all studies was conducted using an inverse variance-weighted fixed effect model. Replications were performed to follow up 21 loci in up to 6,061 cases and 5,483 controls in African Americans, and 8,130 cases and 38,987 controls of European ancestry. We identified three known loci (TCF7L2, HMGA2 and KCNQ1) and two novel loci (HLA-B and INS-IGF2) at genome-wide significance (4.15 Ă 10(-94)<P<5 Ă 10(-8), odds ratio (OR)â = 1.09 to 1.36). Fine-mapping revealed that 88 of 158 previously identified T2D or glucose homeostasis loci demonstrated nominal to highly significant association (2.2 Ă 10(-23) < locus-wide P<0.05). These novel and previously identified loci yielded a sibling relative risk of 1.19, explaining 17.5% of the phenotypic variance of T2D on the liability scale in African Americans. Overall, this study identified two novel susceptibility loci for T2D in African Americans. A substantial number of previously reported loci are transferable to African Americans after accounting for linkage disequilibrium, enabling fine mapping of causal variants in trans-ethnic meta-analysis studies.Peer reviewe
Studies of jet quenching using isolated-photon + jet correlations in PbPb and pp collisions at sqrt(s[NN]) = 2.76 TeV
Results from the first study of isolated-photon + jet correlations in
relativistic heavy ion collisions are reported. The analysis uses data from
PbPb collisions at a centre-of-mass energy of 2.76 TeV per nucleon pair
corresponding to an integrated luminosity of 150 inverse microbarns recorded by
the CMS experiment at the LHC. For events containing an isolated photon with
transverse momentum pt(gamma) > 60 GeV and an associated jet with pt(Jet) > 30
GeV, the photon + jet pt imbalance is studied as a function of collision
centrality and compared to pp data and PYTHIA calculations at the same
collision energy. Using the pt(gamma) of the isolated photon as an estimate of
the momentum of the associated parton at production, this measurement allows an
unbiased characterisation of the in-medium parton energy loss. For more central
PbPb collisions, a significant decrease in the ratio pt(Jet)/pt(gamma) relative
to that in the PYTHIA reference is observed. Furthermore, significantly more
pt(gamma) > 60 GeV photons in PbPb are observed not to have an associated
pt(Jet) > 30 GeV jet, compared to the reference. However, no significant
broadening of the photon + jet azimuthal correlation is observed.Comment: Submitted to Physics Letters
Measurement of the inclusive production cross sections for forward jets and for dijet events with one forward and one central jet in pp collisions at sqrt(s) = 7 TeV
The inclusive production cross sections for forward jets, as well for jets in
dijet events with at least one jet emitted at central and the other at forward
pseudorapidities, are measured in the range of transverse momenta pt = 35-150
GeV/c in proton-proton collisions at sqrt(s) = 7 TeV by the CMS experiment at
the LHC. Forward jets are measured within pseudorapidities 3.2<|eta|<4.7, and
central jets within the |eta|<2.8 range. The double differential cross sections
with respect to pt and eta are compared to predictions from three approaches in
perturbative quantum chromodynamics: (i) next-to-leading-order calculations
obtained with and without matching to parton-shower Monte Carlo simulations,
(ii) PYTHIA and HERWIG parton-shower event generators with different tunes of
parameters, and (iii) CASCADE and HEJ models, including different non-collinear
corrections to standard single-parton radiation. The single-jet inclusive
forward jet spectrum is well described by all models, but not all predictions
are consistent with the spectra observed for the forward-central dijet events.Comment: Submitted to the Journal of High Energy Physic
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