3,480 research outputs found
Anomalous modes drive vortex dynamics in confined Bose-Einstein condensates
The dynamics of vortices in trapped Bose-Einstein condensates are
investigated both analytically and numerically. In axially symmetric traps, the
critical rotation frequency for the metastability of an isolated vortex
coincides with the largest vortex precession frequency (or anomalous mode) in
the Bogoliubov excitation spectrum. As the condensate becomes more elongated,
the number of anomalous modes increases. The largest frequency of these modes
exceeds both the thermodynamic critical frequency and the nucleation frequency
at which vortices are created dynamically. Thus, anomalous modes describe not
only the critical rotation frequency for creation of the first vortex in an
elongated condensate but also the vortex precession in a single-component
spherical condensate.Comment: 4 pages revtex, 3 embedded figure
Search for Top Squark Pair Production in the Dielectron Channel
This report describes the first search for top squark pair production in the
channel stop_1 stopbar_1 -> b bbar chargino_1 chargino_1 -> ee+jets+MEt using
74.9 +- 8.9 pb^-1 of data collected using the D0 detector. A 95% confidence
level upper limit on sigma*B is presented. The limit is above the theoretical
expectation for sigma*B for this process, but does show the sensitivity of the
current D0 data set to a particular topology for new physics.Comment: Five pages, including three figures, submitted to PRD Brief Report
Differential branching fraction and angular analysis of the decay B0âKâ0ÎŒ+ÎŒâ
The angular distribution and differential branching fraction of the decay B 0â K â0 ÎŒ + ÎŒ â are studied using a data sample, collected by the LHCb experiment in pp collisions at sâ=7 TeV, corresponding to an integrated luminosity of 1.0 fbâ1. Several angular observables are measured in bins of the dimuon invariant mass squared, q 2. A first measurement of the zero-crossing point of the forward-backward asymmetry of the dimuon system is also presented. The zero-crossing point is measured to be q20=4.9±0.9GeV2/c4 , where the uncertainty is the sum of statistical and systematic uncertainties. The results are consistent with the Standard Model predictions
Second Generation Leptoquark Search in p\bar{p} Collisions at = 1.8 TeV
We report on a search for second generation leptoquarks with the D\O\
detector at the Fermilab Tevatron collider at = 1.8 TeV.
This search is based on 12.7 pb of data. Second generation leptoquarks
are assumed to be produced in pairs and to decay into a muon and quark with
branching ratio or to neutrino and quark with branching ratio
. We obtain cross section times branching ratio limits as a function
of leptoquark mass and set a lower limit on the leptoquark mass of 111
GeV/c for and 89 GeV/c for at the 95%\
confidence level.Comment: 18 pages, FERMILAB-PUB-95/185-
Measurement of the Top Quark Pair Production Cross Section in the All-jets Decay Channel
We present a measurement of tbar-t production using multijet final states in
pbar-p collisions at a center-of-mass energy of 1.8 TeV, with an integrated
luminosity of 110.3 pb(-1). The analysis has been optimized using neural
networks to achieve the smallest expected fractional uncertainty on the tbar-t
production cross section, and yields a cross section of 7.1 +/- 2.8(stat.) +/-
1.5(syst.) pb, assuming a top quark mass of 172.1 GeV/c^(2). Combining this
result with previous D0 measurements, where one or both of the W bosons decay
leptonically, gives a tbar-t production cross section of 5.9 +/- 1.2(stat) +/-
1.1(syst) pb.Comment: 6 pages, 3 figures; no substative change in revisio
Observation of excited Lambda_b0 baryons
Using pp collision data corresponding to 1.0 fb-1 integrated luminosity
collected by the LHCb detector, two narrow states are observed in the
Lambda_b0pi+pi- spectrum with masses 5911.97 +- 0.12(stat) +- 0.02(syst) +-
0.66(Lambda_b0 mass) MeV/c^2 and 5919.77 +- 0.08(stat) +- 0.02(syst) +-
0.66(Lambda_b0 mass) MeV/c^2. The significances of the observations are 5.2 and
10.2 standard deviations, respectively. These states are interpreted as the
orbitally-excited Lambda_b0 baryons, Lambda_b*0(5912) and Lambda_b*0(5920).Comment: Replaced by version published in Phys. Rev. Lett, modified fit with
better mass resolution treatmen
Observation of two new baryon resonances
Two structures are observed close to the kinematic threshold in the mass spectrum in a sample of proton-proton collision data, corresponding
to an integrated luminosity of 3.0 fb recorded by the LHCb experiment.
In the quark model, two baryonic resonances with quark content are
expected in this mass region: the spin-parity and
states, denoted and .
Interpreting the structures as these resonances, we measure the mass
differences and the width of the heavier state to be
MeV,
MeV,
MeV, where the first and second
uncertainties are statistical and systematic, respectively. The width of the
lighter state is consistent with zero, and we place an upper limit of
MeV at 95% confidence level. Relative
production rates of these states are also reported.Comment: 17 pages, 2 figure
Study of DJ meson decays to D+Ïâ, D0Ï+ and Dâ+Ïâ final states in pp collisions
A study of D+Ïâ, D0Ï+ and Dâ+Ïâ final states is performed using pp collision data, corresponding to an integrated luminosity of 1.0 fbâ1, collected at a centre-of-mass energy of 7 TeV with the LHCb detector. The D1(2420)0 resonance is observed in the Dâ+Ïâ final state and the Dâ2(2460) resonance is observed in the D+Ïâ, D0Ï+ and Dâ+Ïâ final states. For both resonances, their properties and spin-parity assignments are obtained. In addition, two natural parity and two unnatural parity resonances are observed in the mass region between 2500 and 2800 MeV. Further structures in the region around 3000 MeV are observed in all the Dâ+Ïâ, D+Ïâ and D0Ï+ final states
Opposite-side flavour tagging of B mesons at the LHCb experiment
The calibration and performance of the oppositeside
flavour tagging algorithms used for the measurements
of time-dependent asymmetries at the LHCb experiment
are described. The algorithms have been developed using
simulated events and optimized and calibrated with
B
+ âJ/ÏK
+, B0 âJ/ÏK
â0 and B0 âD
ââ
Ό
+
ΜΌ decay
modes with 0.37 fbâ1 of data collected in pp collisions
at
â
s = 7 TeV during the 2011 physics run. The oppositeside
tagging power is determined in the B
+ â J/ÏK
+
channel to be (2.10 ± 0.08 ± 0.24) %, where the first uncertainty
is statistical and the second is systematic
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