293 research outputs found
The HeRSCheL detector: high-rapidity shower counters for LHCb
No full textThe HERSCHEL detector consists of a set of scintillating counters, designed to increase the coverage of the LHCb experiment in the high-rapidity regions on either side of the main spectrometer. The new detector improves the capabilities of LHCb for studies of diffractive interactions, most notably Central Exclusive Production. In this paper the construction, installation, commissioning, and performance of HERSCHEL are presented.The HeRSCheL detector consists of a set of scintillating counters, designed to increase the coverage of the LHCb experiment in the high-rapidity regions on either side of the main spectrometer. The new detector improves the capabilities of LHCb for studies of diffractive interactions, most notably Central Exclusive Production. In this paper the construction, installation, commissioning, and performance of HeRSCheL are presented
The LHCb Upgrade I
No full textThe LHCb upgrade represents a major change of the experiment. The detectors have been almost completely renewed to allow running at an instantaneous luminosity five times larger than that of the previous running periods. Readout of all detectors into an all-software trigger is central to the new design, facilitating the reconstruction of events at the maximum LHC interaction rate, and their selection in real time. The experiment's tracking system has been completely upgraded with a new pixel vertex detector, a silicon tracker upstream of the dipole magnet and three scintillating fibre tracking stations downstream of the magnet. The whole photon detection system of the RICH detectors has been renewed and the readout electronics of the calorimeter and muon systems have been fully overhauled. The first stage of the all-software trigger is implemented on a GPU farm. The output of the trigger provides a combination of totally reconstructed physics objects, such as tracks and vertices, ready for final analysis, and of entire events which need further offline reprocessing. This scheme required a complete revision of the computing model and rewriting of the experiment's software
Amplitude analysis of B⁺→J/ψΦK⁺ decays
No full textThe first full amplitude analysis of B+→J/ψφK+ with J/ψ→μ+μ-, φ→K+K- decays is performed with a data sample of 3 fb-1 of pp collision data collected at s=7 and 8 TeV with the LHCb detector. The data cannot be described by a model that contains only excited kaon states decaying into φK+, and four J/ψφ structures are observed, each with significance over 5 standard deviations. The quantum numbers of these structures are determined with significance of at least 4 standard deviations. The lightest has mass consistent with, but width much larger than, previous measurements of the claimed X(4140) state. The model includes significant contributions from a number of expected kaon excitations, including the first observation of the K∗(1680)+→φK+ transition
Observation of new Xi(0)(c) baryons decaying to lambda K-+(c)-
No full textThe
Λ
+
c
K
−
mass spectrum is studied with a data sample of
p
p
collisions at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of
5.6
fb
−
1
collected by the LHCb experiment. Three
Ξ
0
c
states are observed with a large significance and their masses and natural widths are measured to be
m
[
Ξ
c
(
2923
)
0
]
=
2923.04
±
0.25
±
0.20
±
0.14
MeV
,
Γ
[
Ξ
c
(
2923
)
0
]
=
7.1
±
0.8
±
1.8
MeV
,
m
[
Ξ
c
(
2939
)
0
]
=
2938.55
±
0.21
±
0.17
±
0.14
MeV
,
Γ
[
Ξ
c
(
2939
)
0
]
=
10.2
±
0.8
±
1.1
MeV
,
m
[
Ξ
c
(
2965
)
0
]
=
2964.88
±
0.26
±
0.14
±
0.14
MeV
,
Γ
[
Ξ
c
(
2965
)
0
]
=
14.1
±
0.9
±
1.3
MeV
, where the uncertainties are statistical, systematic, and due to the limited knowledge of the
Λ
+
c
mass. The
Ξ
c
(
2923
)
0
and
Ξ
c
(
2939
)
0
baryons are new states. The
Ξ
c
(
2965
)
0
state is in the vicinity of the known
Ξ
c
(
2970
)
0
baryon; however, their masses and natural widths differ significantly
Analysis of neutral -meson decays into two muons
No full textBranching fraction and effective lifetime measurements of the rare decay and searches for the decays and are reported using proton-proton collision data collected with the LHCb detector at centre-of-mass energies of TeV, TeV and TeV, corresponding to a luminosity of 9 fb. The branching fraction and the effective lifetime are measured, where the first uncertainty is statistical and the second systematic. No significant signal for and decays is found and upper limits . The results are in agreement with the Standard Model expectations.Branching fraction and effective lifetime measurements of the rare decay Bs0→μ+μ- and searches for the decays B0→μ+μ- and Bs0→μ+μ-γ are reported using proton-proton collision data collected with the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV, corresponding to a luminosity of 9 fb-1. The branching fraction B(Bs0→μ+μ-)=(3.09-0.43-0.11+0.46+0.15)×10-9 and the effective lifetime τ(Bs0→μ+μ-)=2.07±0.29±0.03 ps are measured, where the first uncertainty is statistical and the second systematic. No significant signal for B0→μ+μ- and Bs0→μ+μ-γ decays is found and upper limits B(B0→μ+μ-)<2.6×10-10 and B(Bs0→μ+μ-γ)<2.0×10-9 at the 95% C.L. are determined, where the latter is limited to the range mμμ>4.9 GeV/c2. The results are in agreement with the standard model expectations.Branching fraction and effective lifetime measurements of the rare decay and searches for the decays and are reported using proton-proton collision data collected with the LHCb detector at centre-of-mass energies of TeV, TeV and TeV, corresponding to a luminosity of fb. The branching fraction and the effective lifetime are measured, where the first uncertainty is statistical and the second systematic. No significant signal for and decays is found and upper limits GeV. The results are in agreement with the Standard Model expectations
Observation of the semileptonic decay B+ → ppµ¯+νµ
No full textThe Cabibbo-suppressed semileptonic decay B+ → ppµ¯
+νµ is observed for the
first time using a sample of pp collisions corresponding to an integrated luminosity of 1.0,
2.0 and 1.7 fb−1 at centre-of-mass energies of 7, 8 and 13 TeV, respectively. The differential
branching fraction is measured as a function of the pp¯ invariant mass using the decay mode
B+ → J/ψK+ for normalisation. The total branching fraction is measured to be
B(B
+ → ppµ¯
+νµ) = (5.27+0.23
−0.24 ± 0.21 ± 0.15) × 10−6
,
where the first uncertainty is statistical, the second systematic and the third is from the
uncertainty on the branching fraction of the normalisation channel
Measurement of CP-Averaged Observables in the B-0 -> K-star 0 mu(+)mu(-) Decay
No full textAn angular analysis of the
B
0
→
K
*
0
(
→
K
+
π
−
)
μ
+
μ
−
decay is presented using a dataset corresponding to an integrated luminosity of
4.7
fb
−
1
of
p
p
collision data collected with the LHCb experiment. The full set of
C
P
-averaged observables are determined in bins of the invariant mass squared of the dimuon system. Contamination from decays with the
K
+
π
−
system in an
S
-wave configuration is taken into account. The tension seen between the previous LHCb results and the standard model predictions persists with the new data. The precise value of the significance of this tension depends on the choice of theory nuisance parameters
Updated Measurement of Decay-Time-Dependent CP Asymmetries in D0 → K+ K− and D0 → π+ π− Decays
No full textA search for decay-time-dependent charge-parity (CP) asymmetry in D0 → K+ K− and D0 → π+ π− decays is performed at the LHCb experiment using proton-proton collision data recorded at a center-of-mass energy of 13 TeV, and corresponding to an integrated luminosity of 5.4 fb^−1. The D0 mesons are required to originate from semileptonic decays of b hadrons, such that the charge of the muon identifies the flavor of the neutral D meson at production. The asymmetries in the effective decay widths of D0 and anti-D0 mesons are determined to be A_Γ(K+ K−) = (−4.3 ± 3.6 ± 0.5) × 10^−4 and A_Γ(π+ π−) = (2.2 ± 7.0 ± 0.8) × 10^−4 , where the uncertainties are statistical and systematic, respectively. The results are consistent with CP symmetry and, when combined with previous LHCb results, yield A_Γ(K+ K−) = (−4.4 ± 2.3 ± 0.6) × 10^−4 and A_Γ(π+ π−) = (2.5 ± 4.3 ± 0.7) × 10^−4
Measurement of vertical bar V-cb vertical bar with B-s(0) -> D-s(()*()-) mu(+)nu(mu) decays
No full textThe element vertical bar V-cb vertical bar of the Cabibbo-Kobayashi-Maskawa matrix is measured using semileptonic B-s(0) decays produced in proton-proton collision data collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb(-1). Rates of B-s0 -> D-s(-) mu(+)nu(mu) and B-s0 -> D-s*(-) mu(+)nu(mu) decays are analyzed using hadronic form-factor parametrizations derived either by Caprini, Lellouch and Neubert (CLN) or by Boyd, Grinstein and Lebed (BGL). The measured values of vertical bar V-cb vertical bar are (41.4 +/- 0.6 +/- 0.9 +/- 1.2) x 10(-3) and (42.3 +/- 0.8 +/- 0.9 +/- 1.2) x 10(-3) in the CLN and BGL parametrization, respectively. The first uncertainty is statistical, the second systematic, and the third is due to the external inputs used in the measurement. These results are in agreement with those obtained from decays of B+ and B-0 mesons. They are the first determinations of vertical bar V-cb vertical bar at a hadron-collider experiment and the first using B-s(0) meson decays.LPHEPublished by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license
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