1,618 research outputs found
Search for the rare decay Îc+ âpÎŒ+ÎŒ-
The flavor-changing neutral-current (FCNC) decay ÎĂŸ c â pÎŒĂŸÎŒâ (inclusion of the charge-conjugate processes is implied throughout) is expected to be heavily suppressed in the Standard Model (SM) by the Glashow-IliopoulosMaiani mechanism [1]. The branching fractions for shortdistance c â ulĂŸlâ contributions to the transition are expected to be of OĂ°10â9Ă in the SM but can be enhanced by effects beyond the SM. However, long-distance contributions proceeding via a tree-level amplitude, with an intermediate meson resonance decaying into a dimuon pair [2,3], can increase the branching fraction up to OĂ°10â6Ă [4]. The short-distance and hadronic contributions can be separated by splitting the data set into relevant regions of dimuon mass. The ÎĂŸ c â pÎŒĂŸÎŒâ decay has been previously searched for by the BABAR Collaboration [5], yielding 11.1 5.0 2.5 events and an upper limit on the branching fraction of 4.4 Ă 10â5 at 90% C.L. Similar FCNC transitions for the b-quark system (b â slĂŸlâ) exhibit a pattern of consistent deviations from the current SM predictions both in branching fractions [6] and angular observables [7], with the combined significance reaching 4 to 5 standard deviations [8,9]. Processes involving c â ulĂŸlâ transitions are far less explored at both the experimental and theoretical levels, which makes such measurements desirable. Similar analyses of the D system have reported evidence for the longdistance contribution [10]; however, the short-distance contributions have not been established [11]
A measurement of the CP asymmetry difference between Îc + â pK â K + and pÏâÏ+ decays
The difference between the CP asymmetries in the decays Î + c â pKâK+ and Î + c â pÏâÏ + is presented. Proton-proton collision data taken at centre-of-mass energies of 7 and 8 TeV collected by the LHCb detector in 2011 and 2012 are used, corresponding to an integrated luminosity of 3 fbâ1 . The Î + c candidates are reconstructed as part of the Î 0 b â Î + c ” âX decay chain. In order to maximize the cancellation of production and detection asymmetries in the difference, the final-state kinematic distributions of the two samples are aligned by applying phase-space-dependent weights to the Î + c â pÏâÏ + sample. This alters the definition of the integrated CP asymmetry to A wgt CP (pÏâÏ +). Both samples are corrected for reconstruction and selection efficiencies across the five-dimensional Î + c decay phase space. The difference in CP asymmetries is found to be âA wgt CP = ACP (pKâK+) â A wgt CP (pÏâÏ +) = (0.30 ± 0.91 ± 0.61) %, where the first uncertainty is statistical and the second is systemati
Quantum numbers of the X (3872 ) state and orbital angular momentum in its Ï0J /Ï decay
Angular correlations in B+ â X(3872)K+ decays, with X(3872) â Ï 0J/Ï, Ï 0 â Ï +Ï â and J/Ï â ” +” â, are used to measure orbital angular momentum contributions and to determine the J P C value of the X(3872) meson. The data correspond to an integrated luminosity of 3.0 fbâ1 of proton-proton collisions collected with the LHCb detector. This determination, for the first time performed without assuming a value for the orbital angular momentum, confirms the quantum numbers to be J P C = 1++. The X(3872) is found to decay predominantly through S wave and an upper limit of 4% at 95% C.L. is set on the D-wave contribution
Search for beautiful tetraquarks in the Ï(1S)ÎŒ + ÎŒ â invariant-mass spectrum
Abstract: The ΄(1S)” +” â invariant-mass distribution is investigated for a possible exotic meson state composed of two b quarks and two b quarks, Xbbbb . The analysis is based on a data sample of pp collisions recorded with the LHCb detector at centre-of-mass energies â s = 7, 8 and 13 TeV, corresponding to an integrated luminosity of 6.3 fbâ1 . No significant excess is found, and upper limits are set on the product of the production cross-section and the branching fraction as functions of the mass of the Xbbbb state. The limits are set in the fiducial volume where all muons have pseudorapidity in the range [2.0, 5.0], and the Xbbbb state has rapidity in the range [2.0, 4.5] and transverse momentum less than 15 GeV/c. Keywords: B physics, Exotics, Hadron-Hadron scattering (experiments), Heavy quark productio
Search for lepton-flavour-violating decays of Higgs-like bosons
A search is presented for a Higgs-like boson with mass in the range 45 to 195 GeV/c2 decaying into a muon and a tau lepton. The dataset consists of proton-proton interactions at a centre-of-mass energy of 8 TeV, collected by the LHCb experiment, corresponding to an integrated luminosity of 2 fbâ1 . The tau leptons are reconstructed in both leptonic and hadronic decay channels. An upper limit on the production cross-section multiplied by the branching fraction at 95% confidence level is set and ranges from 22 pb for a boson mass of 45 GeV/c2 to 4 pb for a mass of 195 GeV/c2
DIRAC - Distributed Infrastructure with Remote Agent Control
This paper describes DIRAC, the LHCb Monte Carlo production system. DIRAC has
a client/server architecture based on: Compute elements distributed among the
collaborating institutes; Databases for production management, bookkeeping (the
metadata catalogue) and software configuration; Monitoring and cataloguing
services for updating and accessing the databases. Locally installed software
agents implemented in Python monitor the local batch queue, interrogate the
production database for any outstanding production requests using the XML-RPC
protocol and initiate the job submission. The agent checks and, if necessary,
installs any required software automatically. After the job has processed the
events, the agent transfers the output data and updates the metadata catalogue.
DIRAC has been successfully installed at 18 collaborating institutes, including
the DataGRID, and has been used in recent Physics Data Challenges. In the near
to medium term future we must use a mixed environment with different types of
grid middleware or no middleware. We describe how this flexibility has been
achieved and how ubiquitously available grid middleware would improve DIRAC.Comment: Talk from the 2003 Computing in High Energy and Nuclear Physics
(CHEP03), La Jolla, Ca, USA, March 2003, 8 pages, Word, 5 figures. PSN
TUAT00
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
Search for CP violation in decays
A model-independent search for direct CP violation in the Cabibbo suppressed
decay in a sample of approximately 370,000 decays is
carried out. The data were collected by the LHCb experiment in 2010 and
correspond to an integrated luminosity of 35 pb. The normalized Dalitz
plot distributions for and are compared using four different
binning schemes that are sensitive to different manifestations of CP violation.
No evidence for CP asymmetry is found.Comment: 13 pages, 8 figures, submitted to Phys. Rev.
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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