207 research outputs found
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
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
High-Resolution Timing Observations of Spin-Powered Pulsars with the AGILE Gamma-Ray Telescope
AGILE is a small gamma-ray astronomy satellite mission of the Italian Space
Agency dedicated to high-energy astrophysics launched in 2007 April. Its 1
microsecond absolute time tagging capability coupled with a good sensitivity in
the 30 MeV-30 GeV range, with simultaneous X-ray monitoring in the 18-60 keV
band, makes it perfectly suited for the study of gamma-ray pulsars following up
on the CGRO/EGRET heritage. In this paper we present the first AGILE timing
results on the known gamma-ray pulsars Vela, Crab, Geminga and B 1706-44. The
data were collected from 2007 July to 2008 April, exploiting the mission
Science Verification Phase, the Instrument Timing Calibration and the early
Observing Pointing Program. Thanks to its large field of view, AGILE collected
a large number of gamma-ray photons from these pulsars (about 10,000 pulsed
counts for Vela) in only few months of observations. The coupling of AGILE
timing capabilities, simultaneous radio/X-ray monitoring and new tools aimed at
precise photon phasing, exploiting also timing noise correction, unveiled new
interesting features at sub-millisecond level in the pulsars' high-energy
light-curves.Comment: Accepted for publication in The Astrophysical Journal. 14 pages in
emulate-apj style, 2 tables, 9 figures (1 color). Replacement corrected
Figure
Computing at SuperB
Domenico Del Prete*, Fabrizio Bianchi, Vania Boccia, Vincenzo Ciaschini, Marco Corvo, Guglielmo De Nardo, Andrea Di Simone, Giacinto Donvito, Armando Fella, Paolo Franchini, Francesco Giacomini, Alberto Gianoli, Giuliano Laccetti, Stefano Longo, Steffen Luitz, Eleonora Luppi, Matteo Manzali, Leonardo Merola, Silvio Pardi, Alejandro Perez, Matteo Rama, Guido Russo, Bruno Santeramo, Roberto Stroili, Luca Tommasett
Measurement of charged particle multiplicities and densities in pp collisions root s=7 TeV in the forward region
Charged particle multiplicities are studied in proton-proton collisions in the forward region at a centre-of-mass energy of TeV with data collected by the LHCb detector. The forward spectrometer allows access to a kinematic range of in pseudorapidity, momenta greater than and transverse momenta greater than . The measurements are performed using events with at least one charged particle in the kinematic acceptance. The results are presented as functions of pseudorapidity and transverse momentum and are compared to predictions from several Monte Carlo event generators
Differential branching fractions and isospin asymmetries of B -> K ((*)) Ό(+) Ό(-) decays
The isospin asymmetries of B -> K Ό(+) Ό(-) and B -> K (*) Ό(+) Ό(-) decays and the partial branching fractions of the B (0) -> K (0) Ό(+) Ό(-), B (+) -> K (+) Ό(+) Ό(-) and B (+) -> K (*+) Ό(+) Ό(-) decays are measured as functions of the dimuon mass squared, q (2). The data used correspond to an integrated luminosity of 3 fb(-1) from proton-proton collisions collected with the LHCb detector at centre-of-mass energies of 7 TeV and 8 TeV in 2011 and 2012, respectively. The isospin asymmetries are both consistent with the Standard Model expectations. The three measured branching fractions favour lower values than their respective theoretical predictions, however they are all individually consistent with the Standard Model
Study of Beauty Hadron Decays into Pairs of Charm Hadrons
First observations of the decays A(b)(0) -> A(c)(+)D((s))(-) are reported using data corresponding to an integrated luminosity of 3 fb(-1) collected at 7 and 8 TeV center-of- ass energies in proton-proton collisions with the LHCb detector. In addition, the most precise measurement of the branching fraction B(B-s(0) -> D+Ds-) is made and a search is performed for the decays B-0((s)) -> A(c)(+)A(c)(-). The results obtained are B(A(b)(0) -> A(c)(+)D(-))/B(A(b)(0) -> A(c)(+)D(s)(-)) = 0.042 +/- 0.003 (stat) +/- 0.003 (syst), [B(A(b)(0) -> A(c)(+)D(s)(-))/B((B) over bar (0) -> D+Ds-)]/[B(A(b)(0) -> A(c)(+)pi(-))/B((B) over bar (0) -> D+pi(-))] = 0.96 +/- 0.02 (stat) +/- 0.06 (syst), B(B-s(0) -> D+Ds-)/B((B) over bar (0) -> D+Ds-) = 0.038 +/- 0.004 (stat) +/- (syst), B((B) over bar (0) -> A(c)(+)A(c)(-))/B((B) over bar (0) -> D+Ds-) A(c)(+)A(c)(-)) /B(B-s(0) -> D+Ds-) < 0.30[95% C.L.]. Measurement of the mass of the A(b)(0) baryon relative to the (B) over bar (0) meson gives M(A(b)(0)) Âż M((B) over bar (0)) = 339.72 +/- 0.24 (stat) +/- 0.18 (syst) MeV/c(2). This result provides the most precise measurement of the mass of the A(b)(0) baryon to date
Observation of the Resonant Character of the Z(4430)(-) State
Resonant structures in B-0 -> psi'pi K--(+) decays are analyzed by performing a four-dimensional fit of the decay amplitude, using pp collision data corresponding to 3 fb(-1) collected with the LHCb detector. The data cannot be described with K+pi(-) resonances alone, which is confirmed with a model-independent approach. A highly significant Z(4430)(-) -> psi'pi(-) component is required, thus confirming the existence of this state. The observed evolution of the Z(4430)(-) amplitude with the psi'pi(-) mass establishes the resonant nature of this particle. The mass and width measurements are substantially improved. The spin parity is determined unambiguously to be 1(+)
A study of CP violation in B-+/- -> DK +/- and B-+/- -> D pi(+/-) decays with D -> (KSK +/-)-K-0 pi(-/+) final states
A first study of CP violation in the decay modes B-+/- -> [(KSK +/-)-K-0 pi(-/+)](D)h(+/-) and B-+/- -> [(KSK +/-)-K-0 pi(-/+)](D)h(+/-), where h labels a K or pi meson and D labels a D-0 or (D) over bar (0) meson, is performed. The analysis uses the LHCb data set collected in pp collisions, corresponding to an integrated luminosity of 3 fb(-1). The analysis is sensitive to the CP-violating CKM phase gamma through seven observables: one charge asymmetry in each of the four modes and three ratios of the charge-integrated yields. The results are consistent with measurements of gamma using other decay modes
Measurement of polarization amplitudes and CP asymmetries in B-0 -> phi K*(892)(0)
An angular analysis of the decay B (0) -> phi K (*)(892)(0) is reported based on a pp collision data sample, corresponding to an integrated luminosity of 1.0 fb(-1), collected at a centre-of-mass energy of root S = 7 TeV with the LHCb detector. The P-wave amplitudes and phases are measured with a greater precision than by previous experiments, and confirm about equal amounts of longitudinal and transverse polarization. The S-wave K+ pi(-) and K+ K- contributions are taken into account and found to be significant. A comparison of the B (0) -> phi K (*)(892)(0) and results shows no evidence for direct CP violation in the rate asymmetry, in the triple-product asymmetries or in the polarization amplitudes and phases
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