128 research outputs found
Updated measurements of exclusive J/Ï and Ï(2S) production cross-sections in pp collisions at âs = 7 TeV
The differential cross-section as a function of rapidity has been measured for the exclusive production of J/Ï and Ï(2S) mesons in protonâproton collisions at âs = 7 TeV, using data collected by the LHCb experiment, corresponding to an integrated luminosity of 930 pbâ1. The cross-sections times branching fractions to two muons having pseudorapidities between 2.0 and 4.5 are measured to be where the first uncertainty is statistical and the second is systematic. The measurements agree with next-to-leading order QCD predictions as well as with models that include saturation effects
Observation of Two New Excited Îb0 States Decaying to Îb0 K-Ï+
Two narrow resonant states are observed in the Îb0K-Ï+ mass spectrum using a data sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the LHCb experiment and corresponding to an integrated luminosity of 6 fb-1. The minimal quark content of the Îb0K-Ï+ system indicates that these are excited Îb0 baryons. The masses of the Îb(6327)0 and Îb(6333)0 states are m[Îb(6327)0]=6327.28-0.21+0.23±0.12±0.24 and m[Îb(6333)0]=6332.69-0.18+0.17±0.03±0.22 MeV, respectively, with a mass splitting of Îm=5.41-0.27+0.26±0.12 MeV, where the uncertainties are statistical, systematic, and due to the Îb0 mass measurement. The measured natural widths of these states are consistent with zero, with upper limits of Î[Îb(6327)0]<2.20(2.56) and Î[Îb(6333)0]<1.60(1.92) MeV at a 90% (95%) credibility level. The significance of the two-peak hypothesis is larger than nine (five) Gaussian standard deviations compared to the no-peak (one-peak) hypothesis. The masses, widths, and resonant structure of the new states are in good agreement with the expectations for a doublet of 1D Îb0 resonances
Studies of beauty baryon decays to D0phâ and Î+châ final states
Decays of beauty baryons to the D0phâ and Î+châ final states (where h indicates a pion or a kaon) are studied using a data sample of pp collisions, corresponding to an integrated luminosity of 1.0ââfbâ1, collected by the LHCb detector. The Cabibbo-suppressed decays Î0bâD0pKâ and Î0bâÎ+cKâ are observed, and their branching fractions are measured with respect to the decays Î0bâD0pÏâ and Î0bâÎ+cÏâ. In addition, the first observation is reported of the decay of the neutral beauty-strange baryon Î0b to the D0pKâ final state, and a measurement of the Î0b mass is performed. Evidence of the Î0bâÎ+cKâ decay is also reported
Measurement of the CKM angle using with decays
A model-dependent amplitude analysis of the decay is performed using proton-proton collision data
corresponding to an integrated luminosity of 3.0fb, recorded at
and by the LHCb experiment. The CP violation observables
and , sensitive to the CKM angle , are measured to
be \begin{eqnarray*} x_- &=& -0.15 \pm 0.14 \pm 0.03 \pm 0.01, y_- &=& 0.25 \pm
0.15 \pm 0.06 \pm 0.01, x_+ &=& 0.05 \pm 0.24 \pm 0.04 \pm 0.01, y_+ &=&
-0.65^{+0.24}_{-0.23} \pm 0.08 \pm 0.01, \end{eqnarray*} where the first
uncertainties are statistical, the second systematic and the third arise from
the uncertainty on the amplitude model. These
are the most precise measurements of these observables. They correspond to
and , where is
the magnitude of the ratio of the suppressed and favoured decay amplitudes, in a mass region of around the
mass and for an absolute value of the cosine of the decay
angle larger than .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-2016-007.htm
Search for dark photons produced in 13 TeV collisions
Searches are performed for both promptlike and long-lived dark photons,
A
0
, produced in proton-proton
collisions at a center-of-mass energy of 13 TeV, using
A
0
â
Ό
ĂŸ
Ό
â
decays and a data sample corresponding
to an integrated luminosity of
1
.
6
fb
â
1
collected with the LHCb detector. The promptlike
A
0
search covers
the mass range from near the dimuon threshold up to 70 GeV, while the long-lived
A
0
search is restricted to
the low-mass region
214
<m
Ă°
A
0
Ă
<
350
MeV. No evidence for a signal is found, and 90% confidence
level exclusion limits are placed on the
Îł
â
A
0
kinetic-mixing strength. The constraints placed on promptlike
dark photons are the most stringent to date for the mass range
10
.
6
<m
Ă°
A
0
Ă
<
70
GeV, and are
comparable to the best existing limits for
m
Ă°
A
0
Ă
<
0
.
5
GeV. The search for long-lived dark photons is the
first to achieve sensitivity using a displaced-vertex signature
Species diversification â which species should we use?
Large detector systems for particle and astroparticle physics; Particle tracking detectors; Gaseous detectors; Calorimeters; Cherenkov detectors; Particle identification methods; Photon detectors for UV. visible and IR photons; Detector alignment and calibration methods; Detector cooling and thermo-stabilization; Detector design and construction technologies and materials. The LHCb experiment is dedicated to precision measurements of CP violation and rare decays of B hadrons at the Large Hadron Collider (LHC) at CERN (Geneva). The initial configuration and expected performance of the detector and associated systems. as established by test beam measurements and simulation studies. is described. © 2008 IOP Publishing Ltd and SISSA
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