1,128 research outputs found
Why do Particle Clouds Generate Electric Charges?
Grains in desert sandstorms spontaneously generate strong electrical charges;
likewise volcanic dust plumes produce spectacular lightning displays. Charged
particle clouds also cause devastating explosions in food, drug and coal
processing industries. Despite the wide-ranging importance of granular charging
in both nature and industry, even the simplest aspects of its causes remain
elusive, because it is difficult to understand how inert grains in contact with
little more than other inert grains can generate the large charges observed.
Here, we present a simple yet predictive explanation for the charging of
granular materials in collisional flows. We argue from very basic
considerations that charge transfer can be expected in collisions of identical
dielectric grains in the presence of an electric field, and we confirm the
model's predictions using discrete-element simulations and a tabletop granular
experiment
Effects of Mindfulness-Based Cognitive Therapy on Specificity of Life Goals
This study explored the immediate effects of a course of Mindfulness-Based Cognitive Therapy (MBCT) for chronically depressed participants with a history of suicidality on the specificity of important goals for the future. Participants were randomly allocated to immediate treatment with MBCT or to a waitlist condition and life goals were assessed both before and after the treatment or waiting period. Results showed that participants receiving MBCT reported significantly more specific goals post-treatment whereas those allocated to the waitlist condition showed no significant change. Similarly, participants allocated to MBCT regarded themselves as significantly more likely to achieve their important goals post-treatment, whilst again there was no significant change in the waitlist group. Increases in goal specificity were associated with parallel increases in autobiographical memory specificity whereas increases in goal likelihood were associated with reductions in depressed mood. These results suggest that MBCT may enable participants to clarify their important goals and in doing so increase their confidence in their capacity to move in valued life directions
Evidence for an excess of B -> D(*) Tau Nu decays
Based on the full BaBar data sample, we report improved measurements of the
ratios R(D(*)) = B(B -> D(*) Tau Nu)/B(B -> D(*) l Nu), where l is either e or
mu. These ratios are sensitive to new physics contributions in the form of a
charged Higgs boson. We measure R(D) = 0.440 +- 0.058 +- 0.042 and R(D*) =
0.332 +- 0.024 +- 0.018, which exceed the Standard Model expectations by 2.0
sigma and 2.7 sigma, respectively. Taken together, our results disagree with
these expectations at the 3.4 sigma level. This excess cannot be explained by a
charged Higgs boson in the type II two-Higgs-doublet model. We also report the
observation of the decay B -> D Tau Nu, with a significance of 6.8 sigma.Comment: Expanded section on systematics, text corrections, improved the
format of Figure 2 and included the effect of the change of the Tau
polarization due to the charged Higg
Search for the decay modes D^0 â e^+e^-, D^0 â ÎŒ^+ÎŒ^-, and D^0 â e^±Όâ
We present searches for the rare decay modes D^0âe^+e^-, D^0âÎŒ^+ÎŒ^-, and D^0âe^±Ό^â in continuum e^+e^-âcc events recorded by the BABAR detector in a data sample that corresponds to an integrated luminosity of 468ââfb^(-1). These decays are highly GlashowâIliopoulosâMaiani suppressed but may be enhanced in several extensions of the standard model. Our observed event yields are consistent with the expected backgrounds. An excess is seen in the D^0âÎŒ^+ÎŒ^- channel, although the observed yield is consistent with an upward background fluctuation at the 5% level. Using the FeldmanâCousins method, we set the following 90% confidence level intervals on the branching fractions: B(D^0âe^+e^-)<1.7Ă10^(-7), B(D^0âÎŒ^+ÎŒ^-) within [0.6,8.1]Ă10^(-7), and B(D^0âe^±Ό^â)<3.3Ă10^(-7)
A search for the decay modes B+/- to h+/- tau l
We present a search for the lepton flavor violating decay modes B+/- to h+/-
tau l (h= K,pi; l= e,mu) using the BaBar data sample, which corresponds to 472
million BBbar pairs. The search uses events where one B meson is fully
reconstructed in one of several hadronic final states. Using the momenta of the
reconstructed B, h, and l candidates, we are able to fully determine the tau
four-momentum. The resulting tau candidate mass is our main discriminant
against combinatorial background. We see no evidence for B+/- to h+/- tau l
decays and set a 90% confidence level upper limit on each branching fraction at
the level of a few times 10^-5.Comment: 15 pages, 7 figures, submitted to Phys. Rev.
Observation and study of baryonic B decays: B -> D(*) p pbar, D(*) p pbar pi, and D(*) p pbar pi pi
We present a study of ten B-meson decays to a D(*), a proton-antiproton pair,
and a system of up to two pions using BaBar's data set of 455x10^6 BBbar pairs.
Four of the modes (B0bar -> D0 p anti-p, B0bar -> D*0 p anti-p, B0bar -> D+ p
anti-p pi-, B0bar -> D*+ p anti-p pi-) are studied with improved statistics
compared to previous measurements; six of the modes (B- -> D0 p anti-p pi-, B-
-> D*0 p anti-p pi-, B0bar -> D0 p anti-p pi- pi+, B0bar -> D*0 p anti-p pi-
pi+, B- -> D+ p anti-p pi- pi-, B- -> D*+ p anti-p pi- pi-) are first
observations. The branching fractions for 3- and 5-body decays are suppressed
compared to 4-body decays. Kinematic distributions for 3-body decays show
non-overlapping threshold enhancements in m(p anti-p) and m(D(*)0 p) in the
Dalitz plots. For 4-body decays, m(p pi-) mass projections show a narrow peak
with mass and full width of (1497.4 +- 3.0 +- 0.9) MeV/c2, and (47 +- 12 +- 4)
MeV/c2, respectively, where the first (second) errors are statistical
(systematic). For 5-body decays, mass projections are similar to phase space
expectations. All results are preliminary.Comment: 28 pages, 90 postscript figures, submitted to LP0
Study of the reaction e^{+}e^{-} -->J/psi\pi^{+}\pi^{-} via initial-state radiation at BaBar
We study the process with
initial-state-radiation events produced at the PEP-II asymmetric-energy
collider. The data were recorded with the BaBar detector at center-of-mass
energies 10.58 and 10.54 GeV, and correspond to an integrated luminosity of 454
. We investigate the mass
distribution in the region from 3.5 to 5.5 . Below 3.7
the signal dominates, and above 4
there is a significant peak due to the Y(4260). A fit to
the data in the range 3.74 -- 5.50 yields a mass value
(stat) (syst) and a width value (stat)(syst) for this state. We do not
confirm the report from the Belle collaboration of a broad structure at 4.01
. In addition, we investigate the system
which results from Y(4260) decay
Search for CP violation in D+âÏÏ+ and D+sâK0SÏ+ decays
A search for CP violation in D + â ÏÏ + decays is performed using data collected in 2011 by the LHCb experiment corresponding to an integrated luminosity of 1.0 fbâ1 at a centre of mass energy of 7 TeV. The CP -violating asymmetry is measured to be (â0.04 ± 0.14 ± 0.14)% for candidates with K â K + mass within 20 MeV/c 2 of the Ï meson mass. A search for a CP -violating asymmetry that varies across the Ï mass region of the D + â K â K + Ï + Dalitz plot is also performed, and no evidence for CP violation is found. In addition, the CP asymmetry in the D+sâK0SÏ+ decay is measured to be (0.61 ± 0.83 ± 0.14)%
Measurement of B meson production cross-sections in proton-proton collisions at âs= 7 TeV
The production cross-sections of B mesons are measured in pp collisions at a centre-of-mass energy of 7 TeV using data collected with the LHCb detector corresponding to a integrated luminosity of 0.36fbâ1. The B+, B0 and B0s mesons are reconstructed in the exclusive decays B+âJ/ÏK+, B0âJ/ÏKâ0 and B0sâJ/ÏÏ, with J/ÏâÎŒ+ÎŒâ, Kâ0âK+Ïâ and ÏâK+Kâ. The differential cross-sections are measured as functions of B meson transverse momentum pT and rapidity y, in the range 0 < pT<40GeV/c2 and 2.0<y<4.5. The integrated cross-sections in the same pT and y ranges, including charge-conjugate states, are measured to be
Ï(ppâB++X)=38.9±0.3(stat.)±2.5(syst.)±1.3(norm.)ÎŒb,
Ï(ppâB0+X)=38.1±0.6(stat.)±3.7(syst.)±4.7(norm.)ÎŒb,
Ï(ppâB0s+X)=10.5±0.2(stat.)±0.8(syst.)±1.0(norm.)ÎŒb,
where the third uncertainty arises from the pre-existing branching fraction measurements
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