4,852 research outputs found
Chemical fracture and distribution of extreme values
When a corrosive solution reaches the limits of a solid sample, a chemical
fracture occurs. An analytical theory for the probability of this chemical
fracture is proposed and confirmed by extensive numerical experiments on a two
dimensional model. This theory follows from the general probability theory of
extreme events given by Gumbel. The analytic law differs from the Weibull law
commonly used to describe mechanical failures for brittle materials. However a
three parameters fit with the Weibull law gives good results, confirming the
empirical value of this kind of analysis.Comment: 7 pages, 5 figures, to appear in Europhysics Letter
Material-independent crack arrest statistics: Application to indentation experiments
An extensive experimental study of indentation and crack arrest statistics is
presented for four different brittle materials (alumina, silicon carbide,
silicon nitride, glass). Evidence is given that the crack length statistics can
be described by a universal (i.e. material independent) distribution. The
latter directly derives from results obtained when modeling crack propagation
as a depinning phenomenon. Crack arrest (or effective toughness) statistics
appears to be fully characterized by two parameters, namely, an asymptotic
crack length (or macroscopic toughness) value and a power law size dependent
width. The experimental knowledge of the crack arrest statistics at one given
scale thus gives access to its knowledge at all scales
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
Search for Neutral Higgs Bosons in Events with Multiple Bottom Quarks at the Tevatron
The combination of searches performed by the CDF and D0 collaborations at the
Fermilab Tevatron Collider for neutral Higgs bosons produced in association
with b quarks is reported. The data, corresponding to 2.6 fb-1 of integrated
luminosity at CDF and 5.2 fb-1 at D0, have been collected in final states
containing three or more b jets. Upper limits are set on the cross section
multiplied by the branching ratio varying between 44 pb and 0.7 pb in the Higgs
boson mass range 90 to 300 GeV, assuming production of a narrow scalar boson.
Significant enhancements to the production of Higgs bosons can be found in
theories beyond the standard model, for example in supersymmetry. The results
are interpreted as upper limits in the parameter space of the minimal
supersymmetric standard model in a benchmark scenario favoring this decay mode.Comment: 10 pages, 2 figure
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
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
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
Measurements of branching fraction ratios and CP-asymmetries in suppressed B^- -> D(-> K^+ pi^-)K^- and B^- -> D(-> K^+ pi^-)pi^- decays
We report the first reconstruction in hadron collisions of the suppressed
decays B^- -> D(-> K^+ pi^-)K^- and B^- -> D(-> K^+ pi^-)pi^-, sensitive to the
CKM phase gamma, using data from 7 fb^-1 of integrated luminosity collected by
the CDF II detector at the Tevatron collider. We reconstruct a signal for the
B^- -> D(-> K^+ pi^-)K^- suppressed mode with a significance of 3.2 standard
deviations, and measure the ratios of the suppressed to favored branching
fractions R(K) = [22.0 \pm 8.6(stat)\pm 2.6(syst)]\times 10^-3, R^+(K) =
[42.6\pm 13.7(stat)\pm 2.8(syst)]\times 10^-3, R^-(K)= [3.8\pm 10.3(stat)\pm
2.7(syst]\times 10^-3, as well as the direct CP-violating asymmetry A(K) =
-0.82\pm 0.44(stat)\pm 0.09(syst) of this mode. Corresponding quantities for
B^- -> D(-> K^+ pi^-)pi^- decay are also reported.Comment: 8 pages, 1 figure, accepted by Phys.Rev.D Rapid Communications for
Publicatio
- …