RICH Detector Research Articles

Developing a silica aerogel radiator for the HELIX ring-imaging Cherenkov system

This paper reports the successful fabrication of silica aerogel Cherenkov radiators produced in the first batches from a 96-tile mass production performed using pin-drying technique in our laboratory. The aerogels are to be used in a ring-imaging Cherenkov detector in the spectrometer of a planned balloon-borne cosmic-ray observation program, HELIX (High Energy Light Isotope eXperiment). A total of 36 transparent, hydrophobic aerogel tiles with a high refractive index of 1.16 and dimensions of 10 cm $\times $ 10 cm $\times $ 1 cm will be chosen as the flight radiators. Thus far, 40 out of the 48 tiles fabricated were confirmed as having no tile cracking. In the first screening, 8 out of the first 16 tiles were accepted as flight-qualified candidates, based on basic optical measurement results. To fit the aerogel tiles into a radiator support structure, the trimming of previously manufactured prototype tiles using a water-jet cutting device was successful.

Calibration of the Belle II aerogel ring imaging detector

Abstract For efficient separation of hadrons in the forward end-cap of the Belle II spectrometer , an aerogel proximity focusing Ring Imaging Detector is installed in the high magnetic field between the central drift chamber and electromagnetic calorimeter . Cherenkov photons , emitted in the double layer aerogel radiator are expanded through the empty space and detected on the photon detector consisting of Hybrid Avalanche Photo diodes . The readout electronics working in a threshold mode records hit patterns registered during beam collisions. A particle identification algorithm based on the two dimensional extended maximum likelihood technique is used to assign probabilities for different particle hypotheses of tracks traversing the aerogel RICH detector. For efficient discrimination, the Aerogel RICH detector has to be calibrated. We present the key calibration steps used to optimize the detector performance.

The large-area hybrid-optics CLAS12 RICH: Assembling, commissioning and first data-taking

Abstract The first module of a Ring Imaging Cherenkov detector has been recently installed on the CLAS12 spectrometer at the Jefferson Laboratory (JLab) to provide the experiment with kaon identification in the momentum range between 3 and 8 GeV/c. The detector adopts a hybrid optics solution with aerogel radiator, light planar and spherical mirrors and highly-segmented photon detectors. We report here on the assembly and installation of the RICH and we show the first preliminary results obtained during the commissioning of the detector and the first physics data taking.

Efficiency and temporal response of p-terphenyl based wavelength shifting films on H12700 multi anode photomultipliers

Abstract Wavelength-shifting (WLS) films of p-terphenyl have been applied by means of dip-coating on the entrance window of the H12700 multi anode photomultiplier (MAPMT) in order to enhance the UV sensitivity. Using coated and uncoated MAPMTs in a CBM RICH testbox in a proton testbeam at the COSY accelerator, an enhancement of the number of hits per ring of 15%–20% depending on cuts has been observed. Due to new fast readout electronics of the RICH detector for the CBM/ HADES experiments, the time response of p-terphenyl has been measured to show a decay constant of 2.35 ns. This compares well with time-resolved fluorescence measurements of the films.

Photon detectors and front-end electronics for RICH detectors in high particle density environments

Abstract Photon detectors capable of operating in high photon rate environments are required for next generation ring imaging Cherenkov (RICH) detectors at high luminosity accelerators, like HL-LHC. These photodetectors will have to sustain single photon rate in excess of 1 GHz∕cm 2 , while being able to resist to high radiation levels of several Mrad and a 1 MeV-equivalent neutron fluence up to 10 14 n eq ∕ cm 2 . The characteristics of latest models of commercial silicon photomultipliers (SiPMs) and micro-channel plates photomultiplier tubes (MCP-PMT) are investigated in order to verify whether they satisfy the required performance, with particular emphasis on radiation hardness and high rate operation. Their innovative characteristics require tailored front-end electronics, whose architecture can be adapted to deal with higher pixel occupancy, as it will be described.

NA62 RICH performance: measurement and optimization

Abstract The Ring Imaging Cherenkov detector of the NA62 experiment at CERN SPS was commissioned in 2014, but the optimal performance was achieved in 2016 after the precise mirror alignment with reconstructed tracks. The measurement and monitoring of basic performance parameters is discussed: ring radius resolution, ring centre resolution, single hit resolution and mean number of hits per ring. The performance is measured with 2016 data on the positron sample. Different contributions to the resolutions are calculated.

Final design of a monitoring system and software correction cycle for the mirror alignment of the CBM RICH detector

Abstract The Compressed Baryonic Matter (CBM) experiment at the future Facility for Anti-proton and Ion Research (FAIR) complex will explore the phase diagram of strongly interacting matter at high baryon density and moderate temperatures in A+A collisions. The energy spectrum will start at 2 AGeV/c and extend up to 11 AGeV/c for the heaviest nuclei at the SIS 100 accelerator set-up. To explore the physics program of CBM, a RICH detector will be employed for electron identification and pion suppression in a momentum range up to 8 GeV/c. Mirror alignment is a key issue for a proper detector operation. The final conceptual design for a monitoring system of the alignment of the mirrors of the CBM RICH detector will be introduced. It consists of a fast qualitative check of the alignment as well as two different methods to derive quantitative numbers for misalignments. A software correction cycle had been developed which, once applied allows to get back to physics performances as in an ideally aligned case.

The AMS-02 RICH detector: Status and physics results

The Alpha Magnetic Spectrometer (AMS-02) is a high-energy particle physics magnetic spectrometer installed on the International Space Station since May 2011, and operating continuously since then. Because of its large acceptance, long exposure time and particle identification capabilities, AMS-02 measures cosmic ray (CR) fluxes in the kinetic energy range between a fraction of GeV/n to multi-TeV/n with unprecedented precision. The AMS-02 Ring Imaging Cherenkov detector (RICH) provides a precise measurement of the particle velocity and charge. The detector has shown stable and nominal response during the past 7 years of continuous data taking without showing significant degradation. In combination with the Silicon Tracker momentum measurement, the RICH is able to measure the isotopic composition of the light elements (up to charge Z=5) in the kinetic energy range from a few GeV/n to about 10 GeV/n. This paper will focus on the separation of cosmic rays species with |Z|=1. For positive rigidities (Z=+1), the measurement of individual p and d fluxes and their ratio are important for the understanding of CR propagation in our galaxy, since deuterons are almost entirely the secondary products of interactions of cosmic rays with interstellar matter, while protons are mainly produced in astrophysical sources. The negative rigidity sample (Z=-1) is promising for indirect search of Dark Matter, looking at the p̄ and d̄ components. These species are rare secondary products of CR propagation and therefore an excess due to new physics could be more significantly seen on top of their faint expected flux. In particular, d̄ have never been observed so far in CR.

Single photon detection with SiPMs irradiated up to 1014 cm−2 1-MeV-equivalent neutron fluence

Silicon photomultipliers (SiPM) are solid state light detectors with sensitivity to single photons. Their use in high energy physics experiments, and in particular in ring imaging Cherenkov (RICH) detectors, is hindered by their poor tolerance to radiation. At room temperature the large increase in dark count rate makes single photon detection practically impossible already at 1011 cm−2 1-MeV-equivalent neutron fluence. The neutron fluences foreseen by many subdetectors to be operated at the high luminosity LHC range up to 1014 cm−2 1-MeV-equivalent. In this paper we present the effects of such high neutron fluences on Hamamatsu and SensL SiPMs of different cell size. The advantage of annealing at high temperature (up to 175 ∘C) is discussed. We demonstrate that, after annealing, operation at the single photon level with a SiPM irradiated up to 1014 cm−2 1-MeV-equivalent neutron fluence is possible at cryogenic temperature (77 K) with a dark count rate below 1 kHz.

Machine Learning based Global Particle Identification Algorithms at the LHCb Experiment

One of the most important aspects of data processing at flavor physics experiments is the particle identification (PID) algorithm. In LHCb, several different sub-detector systems provide PID information: the Ring Imaging Cherenkov detectors, the hadronic and electromagnetic calorimeters, and the muon chambers. The charged PID based on the sub-detectors response is considered as a machine learning problem solved in different modes: one-vs-rest, one-vs-one and multi-classification, which affect the models training and prediction. To improve charged particle identification for pions, kaons, protons, muons and electrons, neural network and gradient boosting models have been tested. This paper presents these models and their performance evaluated on Run 2 data and simulation samples. A discussion of the performances is also presented.

Event reconstruction of free-streaming data for the RICH detector in the CBM experiment

The Compressed Baryonic Matter (CBM) experiment is a dedicated heavy ion collision experiment at the FAIR facility. It will be one of the first HEP experiments which works in a triggerless mode: data received in the DAQ from the detectors will not be associated with events by a hardware trigger anymore. All raw data within a giventime period will be collected continuously in containers, so-called time-slices. The task of the reconstruction algorithms is to create events out of this raw data stream. In this contribution, the optimization of the reconstruction software in the RICH detector to the free-streaming data flow is presented. The implementation of ring reconstruction algorithms which use time measurements of the hits as an additional parameter is discussed.

The Super C-τ Factory particle identification system options

The Super C-τ (SCT) Factory at Novosibirsk is a project of new colliding beam experiment proposed in Budker Institute of Nuclear Physics. Electron-positron collider based on Crab-Waist technique for operation energy range 2–5 GeV in center of mass is suggested. The luminosity up to 1035cm−1s−1 (in 100 times higher than in operated today experiments in this energy region) is expected. To perform broad experimental program of the project successfully the excellent particle identification (PID) system is needed. A number of options are under consideration. Three of them are described in the paper: Focusing Aerogel RICH (FARICH) detector, threshold Cherenkov counters based on ASHIPH (Aerogel SHifter PHotomultiplier) technique with 6000 litres of aerogel of two refractive indexes and time-of-flight counters with TOP (Time of Propagation) approach with time resolution better than 30 ps. Comparison of PID capabilities with help of parametric simulation is given.

Future upgrades of the LHCb RICH

The two RICH detectors in LHCb have successfully collected data corresponding to 7 fb−1 of integrated luminosity since 2010 and have been essential for most of the physics programme of LHCb. Preparations are underway to upgrade them for the run starting in 2021. The long term physics goals of LHCb call for a further major upgrade of the detector system to collect data corresponding to 50 fb−1 of integrated luminosity by 2029 and 300 fb−1 thereafter. Feasibility studies are underway for measuring the time of arrival of the photons on the RICH detector plane in addition to their spatial coordinates. Simulation studies show how the RICH hit time information can be used to improve the particle identification performance. Silicon photomultipliers help to improve the RICH angular resolution without reducing the photon yield. Options to use novel radiators for extending the momentum coverage are being considered.

The upgrade of the LHCb RICH detectors

Abstract The LHCb Ring-Imaging Cherenkov (RICH) detector system has been operated with very high availability in the LHCb experiment since 2009, performing charged hadron identification in a wide momentum range with high efficiency and providing crucial information for most physics analyses. The LHCb experiment will undergo a major upgrade during the second LHC long shutdown (2019–2020), improving many of its detector systems in order to sustain the current particle identification performance in conditions of a five-fold increase of the instantaneous luminosity (up to 2 × 10 33 cm−2 s−1 ) compared to the current running conditions. In particular, a substantial change in the LHCb trigger and read-out schemes will be implemented to allow 40 MHz continuous data taking. The RICH detectors will be upgraded by installing new single-photon detectors (multi-anode photomultiplier tubes in place of hybrid photo-detectors) read out by 40 MHz capable electronics, and by modifying the upstream RICH optics and mechanics. An overview of the RICH upgrade program is presented, including a summary of the expected performances and the result of the latest tests of the complete photo-electronics chain in the laboratory and test-beams.

Front-end electronics of the Belle II aerogel ring imaging detector

A proximity focusing RICH detector with an aerogel radiator is used for charged particle identification in the forward end-cap of the Belle II spectrometer. The detector, consisting of a 4 cm aerogel radiator, a 16 cm expansion volume and a photon detector with 420 Hybrid Avalanche Photo Detectors, is mounted in a very confined space between Central Drift Chamber and Electromagnetic Calorimeter, allowing only 5 cm of space for the readout electronics. In our solution, low power front-end read-out boards are mounted at the back side of each of the HAPD photosensors. These boards have each been tested individually before their installation onto the photosensors and into the spectrometer. Most important design issues and first experiences with the aforementioned front-end read-out boards are presented in this contribution.

Study of MicroPattern Gaseous detectors with novel nanodiamond based photocathodes for single photon detection in EIC RICH

Identification of high momentum hadrons at the future EIC is crucial, gaseous RICH detectors are therefore viable option. Compact collider setups impose to construct RICHes with small radiator length, hence significantly limiting the number of detected photons. More photons can be detected in the far UV region, using a windowless RICH approach. QE of CsI degrades under strong irradiation and air contamination. Nanodiamond based photocathodes (PCs) are being developed as an alternative to CsI. Recent development of layers of hydrogenated nanodiamond powders as an alternative photosensitive material and their performance, when coupled to the THick Gaseous Electron Multipliers (THGEM)-based detectors, are the objects of an ongoing R\&D. We report about the initial phase of our studies.

The MPGD-based photon detectors for the upgrade of COMPASS RICH-1 and beyond

After pioneering gaseous detectors of single photon for RICH applications using CsI solid state photocathodes in MWPCs within the RD26 collaboration and by the constructions for the RICH detector of the COMPASS experiment at CERN SPS, in 2016 we have upgraded COMPASS RICH by novel gaseous photon detectors based on MPGD technology. Four novel photon detectors, covering a total active area of 1.5m2 have been installed in order to cope with the challenging efficiency and stability requirements of the COMPASS physics programme. They are the first application in an experiment of MPGD-based single photon detectors. All aspects of the upgrade are presented, including engineering, mass production, quality assessment and performance. Perspectives for further developments in the field of gaseous single photon detectors are also presented.

First experience with Belle II Aerogel RICH detector

Abstract The Aerogel Ring-Imaging Cherenkov (ARICH) detector provides particle identification information in the forward endcap part of Belle II. It efficiently separates charged kaons from pions for momenta between 0.5 GeV/c and 4.0 GeV/c. Optical photons are emitted in a double layer aerogel radiator and detected by Hybrid Avalanche Photo Detectors. ARICH was installed in Belle II at the end of 2017, the first phase of a complex detector calibration of electronic signals and preparation for physics signals calibration has been successfully concluded. Cherenkov rings, created by cosmic rays as well as by charged particles from beam collisions, have been observed. The kaon identification efficiency using D ± ∗ decays has been studied and its calibration is expected by the end of the commissioning phase when sufficient data is available.

Machine-Learning-based global particle-identification algorithms at the LHCb experiment

One of the most important aspects of data analysis at the LHC experiments is the particle identification (PID). In LHCb, several different sub-detectors provide PID information: two Ring Imaging Cherenkov (RICH) detectors, the hadronic and electromagnetic calorimeters, and the muon chambers. To improve charged particle identification, we have developed models based on deep learning and gradient boosting. The new approaches, tested on simulated samples, provide higher identification performances than the current solution for all charged particle types. It is also desirable to achieve a flat dependency of efficiencies from spectator variables such as particle momentum, in order to reduce systematic uncertainties in the physics results. For this purpose, models that improve the flatness property for efficiencies have also been developed. This paper presents this new approach and its performance.

Robust circle reconstruction with the Riemann fit

Finding and fitting circles from a set of points is a frequent problem in the data analysis of high-energy physics experiments. In a tracker immersed in a homogeneous magnetic field, tracks are close to perfect circles if projected to the bending plane. In a ring-imaging Cherenkov (RICH) detector, circles of photons around the crossing point of charged particles have to be found and their radii estimated. In both cases, non-negligible background may be present that tends to complicate the pattern recognition and to bias the circle fit. In this contribution we present a robust circle fit based on a modified Riemann fit that removes or significantly reduces the effect of background points. As in the standard Riemann fit, the measured points are projected to the Riemann sphere or paraboloid, and a plane is fitted to the projected points. The fit is made robust by replacing the usual least-squares regression by a least median of squares (LMS) regression. Because of the high breakdown point of the LMS estimator, the fit is insensitive to background points. The LMS plane is used to initialize the weights of an M-estimator that refits the plane in order to suppress eventual remaining outliers and to obtain the final circle parameters. The method is demonstrated on three sets of artificial data: points on a circle plus a comparable number of background points; points on two overlapping circles with additional background; and points obtained by the simulation of tracks in a drift chamber with mirror points and additional background. The results show high circle finding efficiency and small contamination of the final fitted circles.