2,256 research outputs found
Beam tests of a large-scale TORCH time-of-flight demonstrator
The TORCH time-of-flight detector is designed to provide particle
identification in the momentum range 2-10 GeV/c over large areas. The detector
exploits prompt Cherenkov light produced by charged particles traversing a 10
mm thick quartz plate. The photons propagate via total internal reflection and
are focused onto a detector plane comprising position-sensitive Micro-Channel
Plate Photo-Multiplier Tubes (MCP-PMT) detectors. The goal is to achieve a
single-photon timing resolution of 70 ps, giving a timing precision of 15 ps
per charged particle by combining the information from around 30 detected
photons. The MCP-PMT detectors have been developed with a commercial partner
(Photek Ltd, UK), leading to the delivery of a square tube of active area 53
53mm with a granularity of 8 128 pixels equivalent. A
large-scale demonstrator of TORCH, having a quartz plate of dimensions 660
1250 10 mm and read out by a pair of MCP-PMTs with custom
readout electronics, has been verified in a test beam campaign at the CERN PS.
Preliminary results indicate that the required performance is close to being
achieved. The anticipated performance of a full-scale TORCH detector at the
LHCb experiment is presented.Comment: 12 pages, 7 figures, Paper submitted to Nuclear Instruments & Methods
in Physics Research, Section A - Special Issue VCI 201
Evidence for an ηc(1S)π−resonance in B0→ηc(1S)K+π−decays
A Dalitz plot analysis of B0→ηc(1S)K+π− decays is performed using data samples of pp collisions collected with the LHCb detector at centre-of-mass energies of s√=7, 8 and 13TeV, corresponding to a total integrated luminosity of 4.7 fb −1. A satisfactory description of the data is obtained when including a contribution representing an exotic ηc(1S)π− resonant state. The significance of this exotic resonance is more than three standard deviations, while its mass and width are 4096±20 +18−22MeV and 152±58 +60−35MeV, respectively. The spin-parity assignments JP=0+ and JP=1− are both consistent with the data. In addition, the first measurement of the B0→ηc(1S)K+π− branching fraction is performed and gives B(B0→ηc(1S)K+π−)=(5.73±0.24±0.13±0.66)×10−4, where the first uncertainty is statistical, the second systematic, and the third is due to limited knowledge of external branching fractions
Status of the TORCH time-of-flight project
TORCH is a time-of-flight detector, designed to provide charged pi/K particle
identification up to a momentum of 10 GeV/c for a 10 m flight path. To achieve
this level of performance, a time resolution of 15 ps per incident particle is
required. TORCH uses a plane of quartz of 1 cm thickness as a source of
Cherenkov photons, which are then focussed onto square Micro-Channel Plate
Photomultipliers (MCP-PMTs) of active area 53 x 53 mm^2, segmented into 8 x 128
pixels equivalent. A small-scale TORCH demonstrator with a customised MCP-PMT
and associated readout electronics has been successfully operated in a 5 GeV/c
mixed pion/proton beam at the CERN PS facility. Preliminary results indicate
that a single-photon resolution better than 100 ps can be achieved. The
expected performance of a full-scale TORCH detector for the Upgrade II of the
LHCb experiment is also discussed.Comment: 9 pages, 6 figures, Paper submitted to Nuclear and Methods A :
Proceedings of the 10th International Workshop on Ring Imaging Cherenkov
Detectors (RICH 2018), Moscow, Russia, July 29 to August 4 201
Study of prompt D 0 meson production in pPb collisions at √sNN=5 TeV
Production of prompt D 0 mesons is studied in proton-lead and lead-proton collisions recorded at the LHCb detector at the LHC. The data sample corresponds to an integrated luminosity of 1.58±0.02 nb −1 recorded at a nucleon-nucleon centre-of-mass energy of sNN=5 TeV. Measurements of the differential cross-section, the forward-backward production ratio and the nuclear modification factor are reported using D 0 candidates with transverse momenta less than 10 GeV/c and rapidities in the ranges 1.5 < y ∗ < 4.0 and −5.0 < y ∗ < −2.5 in the nucleon-nucleon centre-of-mass system
Measurement of the J/ψ pair production cross-section in pp collisions at √s = 13 TeV
The production cross-section of J/ψ pairs is measured using a data sample of pp collisions collected by the LHCb experiment at a centre-of-mass energy of s=13 TeV, corresponding to an integrated luminosity of 279 ±11 pb −1 . The measurement is performed for J/ψ mesons with a transverse momentum of less than 10 GeV/c in the rapidity range 2.0 < y < 4.5. The production cross-section is measured to be 15.2 ± 1.0 ± 0.9 nb. The first uncertainty is statistical, and the second is systematic. The differential cross-sections as functions of several kinematic variables of the J/ψ pair are measured and compared to theoretical predictions
Observation of the B+→D∗-K+π+ decay
The B+→D∗-K+π+ decay potentially provides an excellent way to investigate charm meson spectroscopy. The decay is searched for in a sample of proton-proton collision data collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb-1. A clear signal is observed, and the ratio of its branching fraction to that of the B+→D∗-π+π+ normalization channel is measured to be B(B+→D∗-K+π+)/B(B+→D∗-π+π+)=(6.39±0.27±0.48)×10-2, where the first uncertainty is statistical and the second is systematic. This is the first observation of the B+→D∗-K+π+ decay
Measurement of the mass and lifetime of the baryon
A proton-proton collision data sample, corresponding to an integrated
luminosity of 3 fb collected by LHCb at and 8 TeV, is used
to reconstruct , decays. Using the , decay mode for calibration, the lifetime ratio and absolute
lifetime of the baryon are measured to be \begin{align*}
\frac{\tau_{\Omega_b^-}}{\tau_{\Xi_b^-}} &= 1.11\pm0.16\pm0.03, \\
\tau_{\Omega_b^-} &= 1.78\pm0.26\pm0.05\pm0.06~{\rm ps}, \end{align*} where the
uncertainties are statistical, systematic and from the calibration mode (for
only). A measurement is also made of the mass difference,
, and the corresponding mass, which
yields \begin{align*} m_{\Omega_b^-}-m_{\Xi_b^-} &= 247.4\pm3.2\pm0.5~{\rm
MeV}/c^2, \\ m_{\Omega_b^-} &= 6045.1\pm3.2\pm 0.5\pm0.6~{\rm MeV}/c^2.
\end{align*} These results are consistent with previous measurements.Comment: 11 pages, 5 figures, All figures and tables, along with any
supplementary material and additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2016-008.htm
Study of decays to the final state and evidence for the decay
A study of decays is performed for the first time
using data corresponding to an integrated luminosity of 3.0
collected by the LHCb experiment in collisions at centre-of-mass energies
of and TeV. Evidence for the decay
is reported with a significance of 4.0 standard deviations, resulting in the
measurement of
to
be .
Here denotes a branching fraction while and
are the production cross-sections for and mesons.
An indication of weak annihilation is found for the region
, with a significance of
2.4 standard deviations.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2016-022.html,
link to supplemental material inserted in the reference
Observation of resonances consistent with pentaquark states in decays
Observations of exotic structures in the channel, that we refer to
as pentaquark-charmonium states, in decays are
presented. The data sample corresponds to an integrated luminosity of 3/fb
acquired with the LHCb detector from 7 and 8 TeV pp collisions. An amplitude
analysis is performed on the three-body final-state that reproduces the
two-body mass and angular distributions. To obtain a satisfactory fit of the
structures seen in the mass spectrum, it is necessary to include two
Breit-Wigner amplitudes that each describe a resonant state. The significance
of each of these resonances is more than 9 standard deviations. One has a mass
of MeV and a width of MeV, while the second
is narrower, with a mass of MeV and a width of MeV. The preferred assignments are of opposite parity, with one
state having spin 3/2 and the other 5/2.Comment: 48 pages, 18 figures including the supplementary material, v2 after
referee's comments, now 19 figure
Study of the production of and hadrons in collisions and first measurement of the branching fraction
The product of the () differential production
cross-section and the branching fraction of the decay () is
measured as a function of the beauty hadron transverse momentum, ,
and rapidity, . The kinematic region of the measurements is and . The measurements use a data sample
corresponding to an integrated luminosity of collected by the
LHCb detector in collisions at centre-of-mass energies in 2011 and in 2012. Based on previous LHCb
results of the fragmentation fraction ratio, , the
branching fraction of the decay is
measured to be \begin{equation*} \mathcal{B}(\Lambda_b^0\rightarrow J/\psi
pK^-)= (3.17\pm0.04\pm0.07\pm0.34^{+0.45}_{-0.28})\times10^{-4},
\end{equation*} where the first uncertainty is statistical, the second is
systematic, the third is due to the uncertainty on the branching fraction of
the decay , and the
fourth is due to the knowledge of . The sum of the
asymmetries in the production and decay between and
is also measured as a function of and .
The previously published branching fraction of , relative to that of , is updated.
The branching fractions of are determined.Comment: 29 pages, 19figures. All figures and tables, along with any
supplementary material and additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2015-032.htm
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