18 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
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
Measurement of the inelastic pp cross-section at a centre-of-mass energy of âs = 7 TeV
The cross-section for inelastic proton-proton collisions, with at least one
prompt long-lived charged particle of transverse momentum pT > 0.2GeV/c in the pseudorapidity
range 2.0 > η > 4.5, is measured by the LHCb experiment at a centre-ofmass
energy of â
s = 7 TeV. The cross-section in this kinematic range is determined to
be Ï
acc
inel = 55.0 ± 2.4 mb with an experimental uncertainty that is dominated by systematic
contributions. Extrapolation to the full phase space, using Pythia 6, yields
Ïinel = 66.9 ± 2.9 ± 4.4 mb, where the first uncertainty is experimental and the second is
due to the extrapolation
Study of η â ηâČ mixing from measurement of B (s) 0 â J/Ïη(âČ) decay rates
A study of B and B0
s meson decays into J/Ïη and J/Ïη0 final states is performed
using a data set of proton-proton collisions at centre-of-mass energies of 7 and 8 TeV,
collected by the LCHb experiment and corresponding to 3.0 fbâ1
of integrated luminosity.
The decay B0 â J/Ïη0
is observed for the first time. The following ratios of branching
fractions are measured:
B(B0 â J/Ïη0
)
B(B0
s â J/Ïη0)
= (2.28 ± 0.65 (stat) ± 0.10 (syst) ± 0.13 (fs/fd)) Ă 10â2
,
B(B0 â J/Ïη)
B(B0
s â J/Ïη)
= (1.85 ± 0.61 (stat) ± 0.09 (syst) ± 0.11 (fs/fd)) Ă 10â2
,
where the third uncertainty is related to the present knowledge of fs/fd, the ratio between
the probabilities for a b quark to form a B0
s or a B0 meson. The branching fraction ratios
are used to determine the parameters of ηâη
0 meson mixing. In addition, the first evidence
for the decay B0
s â Ï(2S)η
0
is reported, and the relative branching fraction is measured,
B(B0
s â Ï(2S)η
0
)
B(B0
s â J/Ïη0)
= (38.7 ± 9.0 (stat) ± 1.3 (syst) ± 0.9(B)) Ă 10â2
,
where the third uncertainty is due to the limited knowledge of the branching fractions of
J/Ï and Ï(2S) mesons
Measurement of the Z+b-jet cross-section in pp collisions at âs = 7 TeV in the forward region
The associated production of a Z boson or an off-shell photon Îł
â with a bottom
quark in the forward region is studied using proton-proton collisions at a centre-of-mass energy
of 7 TeV. The Z bosons are reconstructed in the Z/Îłâ â ”
+”
â final state from muons
with a transverse momentum larger than 20 GeV, while two transverse momentum thresholds
are considered for jets (10 GeV and 20 GeV). Both muons and jets are reconstructed
in the pseudorapidity range 2.0 < η < 4.5. The results are based on data corresponding
to 1.0 fbâ1
recorded in 2011 with the LHCb detector. The measurement of the Z+b-jet
cross-section is normalized to the Z+jet cross-section. The measured cross-sections are
Ï(Z/Îłâ
(”
+”
â) + b-jet) = 295 ± 60 (stat) ± 51 (syst) ± 10 (lumi) fb (0.1)
for pT(jet) > 10 GeV, and
Ï(Z/Îłâ
(”
+”
â) + b-jet) = 128 ± 36 (stat) ± 22 (syst) ± 5 (lumi) fb (0.2)
for pT(jet) > 20 GeV
Search for long-lived particles decaying to jet pairs
A search is presented for long-lived particles with a mass between 25 and 50 GeV/c2 and a lifetime between 1 and 200ps in a sample of protonâproton collisions at a centre-of-mass energy of sâ=7 TeV, corresponding to an integrated luminosity of 0.62  fb â1, collected by the LHCb detector. The particles are assumed to be pair-produced by the decay of a standard model-like Higgs boson. The experimental signature of the long-lived particle is a displaced vertex with two associated jets. No excess above the background is observed and limits are set on the production cross-section as a function of the long-lived particle mass and lifetime
Angular analysis of the B-0 -> K*(0) e(+) e(-) decay in the low-q(2) region
An angular analysis of the B-0 -> K(*0)e(+) e(-) decay is performed using a data sample, corresponding to an integrated luminosity of 3.0 fb(-1), collected by the LHCb experiment in pp collisions at centre-of-mass energies of 7 and 8TeV during 2011 and 2012. For the first time several observables are measured in the dielectron mass squared (q(2)) interval between 0.002 and 1.120 GeV2/c(4). The angular observables F-L and A(T)(Re) which are related to the K-*0 polarisation and to the lepton forward-backward asymmetry, are measured to be F-L = 0.16 +/- 0.06 +/- 0.03 and A(T)(Re) = 0.10 +/- 0.18 +/- 0.05, where the first uncertainty is statistical and the second systematic. The angular observables A(T)((2)) and A(T)(Im) which are sensitive to the photon polarisation in this q(2) range, are found to be A(T)((2)) = - 0.23 +/- 0.23 +/- 0.05 and A(T)(Im) = 0.14 +/- 0.22 +/- 0.05. The results are consistent with Standard Model predictions
Measurement of indirect CP asymmetries in D 0 â K â K + and D 0 â Ï â Ï + decays using semileptonic B decays
No abstract available
Search for long-lived particles decaying to jet pairs
A search is presented for long-lived particles with a mass between 25 and 50
GeV and a lifetime between 1 and 200 ps in a sample of proton-proton
collisions at a centre-of-mass energy of TeV, corresponding to an
integrated luminosity of 0.62 fb, collected by the LHCb detector. The
particles are assumed to be pair-produced by the decay of a Standard Model-like
Higgs boson. The experimental signature of the long-lived particle is a
displaced vertex with two associated jets. No excess above the background is
observed and limits are set on the production cross-section as a function of
the long-lived particle mass and lifetime