1,872 research outputs found
Radiation tolerance studies of silicon microstrip sensors for the CBM Silicon Tracking System
Double-sided silicon microstrip sensors will be used in the Silicon Tracking System of the CBM experiment. During experimental run they will be exposed to a radiation field of up to 1x1014 1 MeV neq cm-2. Radiation tolerance studies were made on prototypes from two different vendors. Results from these prototype detectors before and after irradiation to twice that neutron fluence are discussed
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 charmonium production in b -hadron decays and first evidence for the decay Bs0
Using decays to Ï-meson pairs, the inclusive production of charmonium states in b-hadron decays is studied with pp collision data corresponding to an integrated luminosity of 3.0 fbâ1, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. Denoting byBC ⥠B(b â C X) Ă B(C â ÏÏ) the inclusive branching fraction of a b hadron to a charmonium state C that decays into a pair of Ï mesons, ratios RC1C2 ⥠BC1 /BC2 are determined as RÏc0ηc(1S) = 0.147 ± 0.023 ± 0.011, RÏc1ηc(1S) =0.073 ± 0.016 ± 0.006, RÏc2ηc(1S) = 0.081 ± 0.013 ± 0.005,RÏc1 Ïc0 = 0.50 ± 0.11 ± 0.01, RÏc2 Ïc0 = 0.56 ± 0.10 ± 0.01and Rηc(2S)ηc(1S) = 0.040 ± 0.011 ± 0.004. Here and below the first uncertainties are statistical and the second systematic.Upper limits at 90% confidence level for the inclusive production of X(3872), X(3915) and Ïc2(2P) states are obtained as RX(3872)Ïc1 < 0.34, RX(3915)Ïc0 < 0.12 andRÏc2(2P)Ïc2 < 0.16. Differential cross-sections as a function of transverse momentum are measured for the ηc(1S) andÏc states. The branching fraction of the decay B0s â ÏÏÏ is measured for the first time, B(B0s â ÏÏÏ) = (2.15±0.54±0.28±0.21B)Ă10â6. Here the third uncertainty is due to the branching fraction of the decay B0s â ÏÏ, which is used for normalization. No evidence for intermediate resonances is seen. A preferentially transverse Ï polarization is observed.The measurements allow the determination of the ratio of the branching fractions for the ηc(1S) decays to ÏÏ and p p asB(ηc(1S)â ÏÏ)/B(ηc(1S)â p p) = 1.79 ± 0.14 ± 0.32
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
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
Observation of associated production of a boson with a meson in the~forward region
A search for associated production of a boson with an open charm meson is
presented using a data sample, corresponding to an integrated luminosity of
of proton--proton collisions at a centre-of-mass energy
of 7\,TeV, collected by the LHCb experiment. %% Seven candidate events for
associated production of a boson with a meson and four candidate
events for a boson with a meson are observed with a combined
significance of 5.1standard deviations. The production cross-sections in the
forward region are measured to be where the first uncertainty is statistical and the
second systematic.Comment: 18 pages, 2 figure
Search for hidden-sector bosons in decays
A search is presented for hidden-sector bosons, , produced in the decay
, with and
. The search is performed using -collision data
corresponding to 3.0 fb collected with the LHCb detector. No significant
signal is observed in the accessible mass range
MeV, and upper limits are placed on the branching fraction product
as
a function of the mass and lifetime of the boson. These limits are of
the order of for lifetimes less than 100 ps over most of the
range, and place the most stringent constraints to date on many
theories that predict the existence of additional low-mass bosons.Comment: All figures and tables, along with supplementary material, are
available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2015-036.htm
Study of and decays and determination of the CKM angle
We report a study of the suppressed and favored
decays, where the neutral meson is detected
through its decays to the and CP-even and
final states. The measurement is carried out using a proton-proton
collision data sample collected by the LHCb experiment, corresponding to an
integrated luminosity of 3.0~fb. We observe the first significant
signals in the CP-even final states of the meson for both the suppressed
and favored modes, as well as
in the doubly Cabibbo-suppressed final state of the decay. Evidence for the ADS suppressed decay , with , is also presented. From the observed
yields in the , and their
charge conjugate decay modes, we measure the value of the weak phase to be
. This is one of the most precise
single-measurement determinations of to date.Comment: 22 pages, 9 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-2015-020.htm
Study of boson production in association with beauty and charm
The associated production of a boson with a jet originating from either a
light parton or heavy-flavor quark is studied in the forward region using
proton-proton collisions. The analysis uses data corresponding to integrated
luminosities of 1.0 and collected with the LHCb detector
at center-of-mass energies of 7 and 8 TeV, respectively. The bosons are
reconstructed using the decay and muons with a transverse
momentum, , larger than 20 GeV in the pseudorapidity range
GeV
and . The sum of the muon and jet momenta must satisfy
GeV. The fraction of jet events that originate from beauty
and charm quarks is measured, along with the charge asymmetries of the
and production cross-sections. The ratio of the jet to
jet production cross-sections is also measured using the
decay. All results are in agreement with Standard Model predictions
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