LHCb

Abstract:

TORCH (Time Of internally Reflected CHerenkov light) is a novel time-of-flight detector, designed to provide π /K/p particle identification up to 0∼ 1 GeV/c momentum and beyond. To achieve this, a time resolution of ∼ 15 ps combining information from 0∼ 3 detected photons is required over a 10 m flight path. Large areas can be covered with TORCH, nominally up to 30 m 2 . One such application is for the LHCb experiment, to complement the particle identification capabilities of its RICH detectors. TORCH has a DIRC-like construction with 10 mm-thick synthetic amorphous fused-silica plates as a radiator. Cherenkov photons propagate by total internal reflection to the plate edges and there are focussed onto an array of position-sensitive photodetectors. Custom-built micro-channel plate photo-multipliers (MCP-PMTs) are being developed in collaboration with industry to provide the lifetime, granularity and time resolution to meet the TORCH specifications. In the present paper, laboratory tests of the MCP-PMTs developed for TORCH and its readout electronics are presented. Test beam measurements of a prototype TORCH detector in a low-momentum mixed beam of pions and protons are highlighted. Time resolutions for individual photons approaching 100 ps is achieved, after correction for dispersion effects in the quartz medium. In addition to the particle identification capabilities, the high-precision timing information that TORCH provides could be used at the high-luminosity LHC to associate high-energy photons with the correct primary interaction vertex amongst the many expected.

Abstract:

© CERN 2017 for the benefit of the LHCb collaboration. 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.

Abstract:

The first full amplitude analysis of $B^+\to J/\psi \phi K^+$ with $J/\psi\to\mu^+\mu^-$, $\phi\to K^+K^-$ decays is performed with a data sample of 3 fb$^{-1}$ of $pp$ collision data collected at $\sqrt{s}=7$ and $8$ TeV with the LHCb detector. The data cannot be described by a model that contains only excited kaon states decaying into $\phi K^+$, and four $J/\psi\phi$ 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 is best described as a $D_s^{\pm}D_s^{*\mp}$ cusp, but a resonant interpretation is also possible with 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 $K^{*}(1680)^+\to\phi K^+$ transition.

Abstract:

The first full amplitude analysis of $B^+\to J/\psi \phi K^+$ with $J/\psi\to\mu^+\mu^-$, $\phi\to K^+K^-$ decays is performed with a data sample of 3 fb$^{-1}$ of $pp$ collision data collected at $\sqrt{s}=7$ and $8$ TeV with the LHCb detector. The data cannot be described by a model that contains only excited kaon states decaying into $\phi K^+$, and four $J/\psi\phi$ 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 is best described as a $D_s^{\pm}D_s^{*\mp}$ cusp, but a resonant interpretation is also possible with mass consistent with, but width much larger than, previous measurements of the claimed $X(4140)$ state.