The LHCb RICH detectors: Operations and performance Gambetta, S.
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2020, Letnik:
952
Journal Article
Recenzirano
The LHCb experiment has collected an unprecedented data sample to investigate beauty and charm hadrons decays. One of its key detector components is the RICH system providing excellent particle ...identification (PID) over a wide momentum range (2–100 GeV/c). Last year for the first time the RICH detectors have been operated in the automatic LHCb online alignment framework that, together with the well established calibration system, provided an excellent performance. The operations and performance of the RICH system during Run II are presented together with the activities performed during the winter shutdown to prepare for the last running period of the current RICH detectors before the LHCb upgrade.
•The LHCb RICH detectors are described including the main structural and functional elements.•The alignment and calibration system of the RICH detectors is describe in details.•The RICH excellent stability and PID performance are described.•A dedicated analysis focused on the radiator purity is shown.
In 2019 the LHCb RICH detector will be upgraded to increase the read out rate from 1MHz to 40MHz. As a consequence, the current Hybrid Photon Detectors will have to be replaced. Multi-anode ...Photomultiplier Tubes (MaPMTs) from Hamamatsu with 64-channels will be used: the 1-in. R13742 and the 2-in. R13743 MaPMTs (custom modifications of the MaPMTs R11625 and R12699). Quality assurance testing of these MaPMTs using custom-developed readout electronics has started. We present the design and realisation of the test facilities to ensure consistency in testing and validation. A total of 3100 units of the R13742 and 450 units of the R13743 will be tested requiring high efficiency and reliability from the test stations. We report on the test programme and protocols, characterising the units and assuring compliance with specifications. First results of testing and detector characterisation will be presented, based on the pre-series production, comprising 54 units of R13742 and 20 units of R13743.
A key feature of the LHCb upgrade, scheduled for 2019, is to remove the first level trigger and its data reduction from 40MHz to 1MHz, which is implemented in the on-detector readout electronics. The ...consequence for the LHCb Ring Imaging Cherenkov (RICH) detectors is that the Hybrid Photon Detectors need to be replaced as the readout chip is inside the detector vacuum. The baseline for replacement are Multi-anode Photomultiplier tubes (MaPMT) and new readout electronics. The MaPMTs will be located in the fringe field of the LHCb dipole magnet with residual fields up to 25G. Therefore, their behavior in magnetic fields is critical. Here we report about studies of the Hamamatsu model R11265 in a magnetic field in an effort to qualify it for use in the LHCb RICH upgrade. Comparisons to the known model R7600 are also made. Measurements of the collection efficiency and gain were performed for all three space directions as a function of the magnetic field strength. In addition to measurements with bare tubes, measurements with different mu-metal shielding configurations were performed to optimize the configuration. This is important input for the layout of the upgraded LHCb RICH detector.
•The performance of multi-anode photomultipliers in magnetic field has been characterized showing the need for local shielding.•Different magnetic shields have been designed, produced and characterized.•A full recovery of the performance of MaPMTs in magnetic field is possible with the shields designed.
Abstract
Signal-induced noise is observed in Hamamatsu R11265
Multianode Photomultiplier Tubes, manifesting up to several
microseconds after the single photoelectron response signal and
localised in ...specific anodes. The mean number of noise pulses varies
between devices, and shows significant dependence on the applied
high-voltage. The characterisation of this noise and the mitigation
strategies to perform optimal single-photon counting at 40 MHz, as
required by the LHCb Ring-Imaging Cherenkov detectors, are
reported.
The LHCb detector will be upgraded to make more efficient use of the available luminosity at the LHC in Run III and extend its potential for discovery. The Ring Imaging Cherenkov detectors are key ...components of the LHCb detector for particle identification. In this paper we describe the setup and the results of tests in a charged particle beam, carried out to assess prototypes of the upgraded opto-electronic chain from the Multi-Anode PMT photosensor to the readout and data acquisition system.
A search for a long-lived scalar particle χ is performed, looking for the decay B+→K+χ with χ→μ+μ− in pp collision data corresponding to an integrated luminosity of 3 fb−1, collected by the LHCb ...experiment at center-of-mass energies of s=7 and 8 TeV. This new scalar particle, predicted by hidden sector models, is assumed to have a narrow width. The signal would manifest itself as an excess in the dimuon invariant mass distribution over the Standard Model background. No significant excess is observed in the accessible ranges of mass 250<m(χ)<4700 MeV/c2 and lifetime 0.1<τ(χ)<1000 ps. Upper limits on the branching fraction B(B+→K+χ(μ+μ−)) at 95% confidence level are set as a function of m(χ) and τ(χ), varying between 2×10−10 and 10−7. These are the most stringent limits to date. The limits are interpreted in the context of a model with a light inflaton particle.
The Ξ_{c}^{+}K^{-} mass spectrum is studied with a sample of pp collision data corresponding to an integrated luminosity of 3.3 fb^{-1}, collected by the LHCb experiment. The Ξ_{c}^{+} is ...reconstructed in the decay mode pK^{-}π^{+}. Five new, narrow excited Ω_{c}^{0} states are observed: the Ω_{c}(3000)^{0}, Ω_{c}(3050)^{0}, Ω_{c}(3066)^{0}, Ω_{c}(3090)^{0}, and Ω_{c}(3119)^{0}. Measurements of their masses and widths are reported.
The doubly charmed baryon decay Ξ_{cc}^{++}→Ξ_{c}^{+}π^{+} is observed for the first time, with a statistical significance of 5.9σ, confirming a recent observation of the baryon in the ...Λ_{c}^{+}K^{-}π^{+}π^{+} final state. The data sample used corresponds to an integrated luminosity of 1.7 fb^{-1}, collected by the LHCb experiment in pp collisions at a center-of-mass energy of 13 TeV. The Ξ_{cc}^{++} mass is measured to be 3620.6±1.5(stat)±0.4(syst)±0.3(Ξ_{c}^{+}) MeV/c^{2} and is consistent with the previous result. The ratio of branching fractions between the decay modes is measured to be B(Ξ_{cc}^{++}→Ξ_{c}^{+}π^{+})×B(Ξ_{c}^{+}→pK^{-}π^{+})/B(Ξ_{cc}^{++}→Λ_{c}^{+}K^{-}π^{+}π^{+})×B(Λ_{c}^{+}→pK^{-}π^{+})=0.035±0.009(stat)±0.003(syst).
Two-particle angular correlations are studied in proton-lead collisions at a nucleon–nucleon centre-of-mass energy of sNN=5 TeV, collected with the LHCb detector at the LHC. The analysis is based on ...data recorded in two beam configurations, in which either the direction of the proton or that of the lead ion is analysed. The correlations are measured in the laboratory system as a function of relative pseudorapidity, Δη, and relative azimuthal angle, Δϕ, for events in different classes of event activity and for different bins of particle transverse momentum. In high-activity events a long-range correlation on the near side, Δϕ≈0, is observed in the pseudorapidity range 2.0<η<4.9. This measurement of long-range correlations on the near side in proton-lead collisions extends previous observations into the forward region up to η=4.9. The correlation increases with growing event activity and is found to be more pronounced in the direction of the lead beam. However, the correlation in the direction of the lead and proton beams are found to be compatible when comparing events with similar absolute activity in the direction analysed.
A
bstract
Measurements are reported of the central exclusive production of
J/ψ
and
ψ
(2
S
) mesons in
pp
collisions at a centre-of-mass energy of 13 TeV. Backgrounds are significantly reduced ...compared to previous measurements made at lower energies through the use of new forward shower counters. The products of the cross-sections and the branching fractions for the decays to dimuons, where both muons are within the pseudorapidity range 2
.
0
< η <
4
.
5, are measured to be
σ
J
/
ψ
→
μ
+
μ
−
=
435
±
18
±
11
±
17
p
b
σ
ψ
2
S
→
μ
+
μ
−
=
11.1
±
1.1
±
0.3
±
0.4
p
b
.
The first uncertainties are statistical, the second are systematic, and the third are due to the luminosity determination. The cross-sections are also measured differentially for meson rapidities between 2.0 and 4.5. Good agreement is observed with theoretical predictions. Photoproduction cross-sections are derived and compared to previous experiments, and a deviation from a pure power-law extrapolation of lower energy data is observed.
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