1,097 research outputs found
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
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
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
Measurement of charged particle multiplicities in collisions at TeV in the forward region
The charged particle production in proton-proton collisions is studied with
the LHCb detector at a centre-of-mass energy of TeV in different
intervals of pseudorapidity . The charged particles are reconstructed
close to the interaction region in the vertex detector, which provides high
reconstruction efficiency in the ranges and
. The data were taken with a minimum bias trigger, only requiring
one or more reconstructed tracks in the vertex detector. By selecting an event
sample with at least one track with a transverse momentum greater than 1 GeV/c
a hard QCD subsample is investigated. Several event generators are compared
with the data; none are able to describe fully the multiplicity distributions
or the charged particle density distribution as a function of . In
general, the models underestimate the charged particle production
Measurement of the CP-violating phase phi_s in the decay Bs->J/psi phi
We present a measurement of the time-dependent CP-violating asymmetry in B_s
-> J/psi phi decays, using data collected with the LHCb detector at the LHC.
The decay time distribution of B_s -> J/psi phi is characterized by the decay
widths Gamma_H and Gamma_L of the heavy and light mass eigenstates of the
B_s-B_s-bar system and by a CP-violating phase phi_s. In a sample of about 8500
B_s -> J/psi phi events isolated from 0.37 fb^-1 of pp collisions at sqrt(s)=7
TeV we measure phi_s = 0.15 +/- 0.18 (stat) +/- 0.06 (syst) rad. We also find
an average B_s decay width Gamma_s == (Gamma_L + Gamma_H)/2 = 0.657 +/- 0.009
(stat) +/- 0.008 (syst) ps^-1 and a decay width difference Delta Gamma_s ==
Gamma_L - Gamma_H} = 0.123 +/- 0.029 (stat) +/- 0.011 (syst) ps^-1. Our
measurement is insensitive to the transformation (phi_s,DeltaGamma_s --> pi -
phi_s, - Delta Gamma_s.Comment: 9 pages, 3 figure
Measurement of the ratio of branching fractions BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma)
The ratio of branching fractions of the radiative B decays B0 -> K*0 gamma
and Bs0 -> phi gamma has been measured using 0.37 fb-1 of pp collisions at a
centre of mass energy of sqrt(s) = 7 TeV, collected by the LHCb experiment. The
value obtained is BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma) = 1.12 +/- 0.08
^{+0.06}_{-0.04} ^{+0.09}_{-0.08}, where the first uncertainty is statistical,
the second systematic and the third is associated to the ratio of fragmentation
fractions fs/fd. Using the world average for BR(B0 -> K*0 gamma) = (4.33 +/-
0.15) x 10^{-5}, the branching fraction BR(Bs0 -> phi gamma) is measured to be
(3.9 +/- 0.5) x 10^{-5}, which is the most precise measurement to date.Comment: 15 pages, 1 figure, 2 table
Measurements of the branching fractions of B+âppK+ decays
The branching fractions of the decay B+ â ppÌK+ for different intermediate states are measured using data, corresponding to an integrated luminosity of 1.0 fb-1, collected by the LHCb experiment. The total branching fraction, its charmless component MppÌ < 2.85 GeV/c2 and the branching fractions via the resonant ccÌ states η c(1S) and Ï(2S) relative to the decay via a J/Ï intermediate state are [Equation not available: see fulltext.] Upper limits on the B + branching fractions into the η c(2S) meson and into the charmonium-like states X(3872) and X(3915) are also obtained
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
Precision measurement of violation in decays
The time-dependent asymmetry in decays is
measured using collision data, corresponding to an integrated luminosity
of fb, collected with the LHCb detector at centre-of-mass energies
of and TeV. In a sample of 96 000 decays, the
-violating phase is measured, as well as the decay widths
and of the light and heavy mass eigenstates of the
system. The values obtained are rad, ps, andps, where the first uncertainty is
statistical and the second systematic. These are the most precise single
measurements of those quantities to date. A combined analysis with decays gives rad. All
measurements are in agreement with the Standard Model predictions. For the
first time the phase is measured independently for each polarisation
state of the system and shows no evidence for polarisation
dependence.Comment: 6 figure
Measurements of the , , meson and baryon lifetimes
Measurements of -hadron lifetimes are reported using collision data,
corresponding to an integrated luminosity of 1.0fb, collected by the
LHCb detector at a centre-of-mass energy of Tev. Using the exclusive decays
, , ,
and the average decay
times in these modes are measured to be = 0.004 0.003 ps, =
0.006 0.004 ps, = 0.013
0.005 ps, = 0.027
0.006 ps and = 0.011
0.005 ps, where the first uncertainty is statistical and the second is
systematic. These represent the most precise lifetime measurements in these
decay modes. In addition, ratios of these lifetimes, and the ratio of the
decay-width difference, , to the average width, , in
the system, , are
reported. All quantities are found to be consistent with Standard Model
expectations.Comment: 28 pages, 4 figures. Updated reference
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