Proximity Focusing RICH Research Articles

An aerogel RICH detector for the next generation heavy-ion experiment at LHC

The ALICE collaboration is proposing a new apparatus, ALICE 3, to investigate the Quark Gluon Plasma (QGP) properties. In this context, conceptual studies for the development of a RICH detector for ALICE 3 are ongoing. The proposed baseline layout is a proximity-focusing RICH, using aerogel (refractive index n= 1.03 at λph= 400 nm) as Cherenkov radiator and a layer of Silicon Photomultipliers (SiPM) for the photon detection. A multi-layer (focusing) aerogel layout, with increasing refractive index, is also considered. If good time resolution of ≈ 20 ps can be achieved in the SiPM photons detectors, they can be able to identify charged hadrons via TOF measurements. The detector specifications and performance, obtained by means of dedicated Monte Carlo simulation, are presented. The R&D challenges related to the proposed design are also discussed.

Long-term stability and perspectives of the ALICE-HMPID detector at LHC during run 3

The ALICE High Momentum Particle IDentification (HMPID) is a Ring Imaging Cherenkov detector that identifies π, k and p in the transverse momentum interval 1 < pT < 5 GeV/c. The HMPID consists of seven proximity focusing RICH modules, 1.3 × 1.3 m2 each. They are based on liquid C6F14 as Cherenkov radiator, and on MWPCs equipped with CsI pad segmented photocathodes as photon detector. During the LHC Long Shutdown 2 (LS2, 2019–2021) the HMPID underwent upgrading activities that increased the event read out rate up to ∼20 kHz, 10 times faster than in Run 2. The performance of the read-out electronics and the MWPCs status after a stop of 4 years, using the first Run 3 data (2022), are presented. The HMPID will also constraint the measurement of the inelastic (anti-)deuteron inelastic cross section in the momentum interval 0.2–2 GeV/c. For such aim during LS2 two aluminium absorbers 1.3 × 1.3 m2, one with a thickness of 8 cm, half interaction length, and the other with a thickness of 4 cm, were installed in front of two RICH modules. Preliminary Monte Carlo results on the expected uncertainties on the cross section measurement are given. Finally, the projection of the CsI photocathodes stability at the end of Run 3 after the absorption of a charge dose ten times higher than in Run 2, is discussed.

Simulation studies related to the particle identification by the forward and backward RICH detectors at Electron Ion Collider

The Electron-Ion collider (EIC) will be the ultimate facility to study the dynamics played by colored quarks and gluons in the phenomenology of nucleons and nuclei, described by Quantum Chromodynamics. The physics programs will greatly rely on efficient particle identification (PID) in both the forward and the backward regions. The forward and the backward RICHes of the EIC have to be able to cover wide acceptance and momentum ranges; in the forward region a dual radiator RICH (dRICH) is foreseen and in the backward region a proximity-focusing RICH can be foreseen to be employed. The geometry and the performance studies of the dRICH have been performed as prescribed in the EIC Yellow Report using the ATHENA software framework. This part of our work reports the effort following the call for EIC detector proposal and the studies related to the forward and the backward RICH performance. In the forward region, the dRICH performance showed a pion- kaon separation from around 1 GeV/c to 50 GeV/c at a three sigma level; the proximity focusing RICH (pfRICH) foreseen for the backward region can reach three sigma separation up to 3 GeV/c for e/π and up to 10 GeV/c for π/K mass hypotheses.

Recent developments in data reconstruction for aerogel RICH at Belle II

In the forward end-cap of the Belle II spectrometer, particle identification is provided by a proximity focusing RICH detector with an aerogel radiator (ARICH). The ARICH’s primary function is to effectively distinguish between pions and kaons in the momentum range of 0.5GeV/c to about 4GeV/c, as well as to contribute to identification of low-momentum leptons. Since its operation began, Belle II has collected over 420fb−1 of data. Based on this large data sample, studies of several effects that impact the performance of the ARICH detector were carried out. In this paper, we present a comparison of the observed Cherenkov ring image and detector particle identification performance in the measured data and detector simulation. Furthermore, we highlight recent efforts aimed at enhancing the ARICH’s performance by taking into account the effects of particle decay in flight and scattering in materials before the detector, as well as by refining the probability density function used for particle identification likelihood evaluation.

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.

Recent developments in software for the Belle II aerogel RICH

For the Belle II spectrometer a proximity focusing RICH counter with an aerogel radiator (ARICH) will be employed as a PID system in the forward end-cap region of the spectrometer. The detector will provide about 4σ separation of pions and kaons up to momenta of 3.5GeV/c, at the kinematic limits of the experiment. We present the up-to-date status of the ARICH simulation and reconstruction software, focusing on the recent improvements of the reconstruction algorithms and detector description in the Geant4 simulation. In addition, as a demonstration of detector readout software functionality we show the first cosmic ray Cherenkov rings observed in the ARICH.

Studies of a hybrid avalanche photo-detector in magnetic field

For the Belle II spectrometer a proximity focusing RICH counter with an aerogel radiator (ARICH) will be employed as a PID system in the forward endcap region of the spectrometer. The main challenge was the development of a reliable multichannel sensor for single photons that operates in the high magnetic field of the spectrometer (1.5T) and withstands the radiation levels expected at the experiment. A 144-channel Hybrid Avalanche Photo-Detector (HAPD) was developed with Hamamatsu Photonics K.K. and the mass production of ∼480 HAPDs was completed recently. While our first tests of HAPD performance in the magnetic field (before mass production) showed no issues, we lately observed a presence of very large signal pulses (∼5000×single photon signal), generated internally within about 20% of HAPDs, while operating in the magnetic field. The rate of these pulses varies from sample to sample. These pulses impact the HAPD performance in two ways: they introduce periods of dead time and, in some cases, damage to the front-end electronics was observed. Here we present conditions under which such large pulses are generated, their properties and impact on HAPD performance, and discuss possible mechanism of their origin.

Monte Carlo study of a Belle II proximity focusing RICH with aerogel as a radiator

A proximity focusing RICH will be installed in the forward direction of the Belle II spectrometer, inside a super conducting solenoid coil with the magnetic field of 1.5T. Photons emitted in the sequence of two different aerogel radiator layers will be registered by the Hybrid Avalanche Photo Diodes. By detecting more than 11 photons per incident 4GeV/c pion, with 15mrad single photon Cherenkov angle resolution, the designed detector should enable an efficient separation of kaons from pions in the wide range of particle momenta from 0.5GeV/c up to 4GeV/c.The particle separation will be based on a two-dimensional extended maximum-likelihood analysis. The position dependence of the efficiencies for identification of pions and kaons shows a very homogeneous response over the detector area. The performance on the edge of the detector is improved by employing planar mirrors to reflect the Cherenkov photons on the detector plane. The results show that by using a designed detector configuration the kaon pion separation efficiency of more than 95% can be achieved at a very low pion misidentification probability of 1%. In the low momentum region (0.5GeV/c–0.8GeV/c) the variation of detected number of photons due to matching of aerogel refractive index and the gaps between the sensitive areas on the detector plane results in a slightly decreased separation efficiency.

Aerogel RICH for forward PID at Belle II

For the Belle II spectrometer we are preparing a proximity focusing RICH with aerogel as the radiator. It will be positioned in the forward direction of the spectrometer in the small space between the drift chamber and the electromagnetic calorimeter inside a strong magnetic field of 1.5T. The Hybrid Avalanche Photo Diode used as a photo sensor, is able to detect single photons with a high efficiency, can operate in the magnetic field and is resistant to the expected neutron and gamma fluxes in the detector. By detecting more than 11 photons per incident 4GeV/c pion, with 15mrad single photon Cherenkov angle resolution, the designed aerogel RICH should enable an efficient separation of kaons from pions in the wide range of particle momenta from 0.5GeV/c up to 4GeV/c.

Module of silicon photomultipliers as a detector of individual Cherenkov photons

We have studied the possibility of using silicon photomultipliers as single photon detectors in a proximity focusing RICH with aerogel radiator. Such a counter is considered for the upgrade of the Belle detector. The main advantage of silicon over conventional photomultiplier tubes is their operation in high magnetic fields. Their disadvantage is the relatively high dark noise count rate ( ≈ MHz / mm 2 ) which can be overcome by using a narrow time window in the data acquisition. A module, consisting of 64 (8×8) Hamamatsu MPPC S10362-11-100P silicon photomultipliers, has been designed, constructed and tested with Cherenkov photons emitted in an aerogel radiator by 120 GeV/ c pions from the CERN T4-H6 beam. To increase the signal-to-noise ratio, i.e. to increase the effective surface on which light is detected, light concentrators have been employed.

The AMS-02 RICH detector: Performance during ground-based data taking at CERN

The Alpha Magnetic Spectrometer (AMS), whose final version AMS-02 is to be installed on the International Space Station (ISS) in 2011, is a detector designed to measure charged cosmic ray spectra with energies up to the TeV region and with high energy photon detection capability up to a few hundred GeV, using state-of-the art particle identification techniques. Among several detector subsystems, AMS includes a proximity focusing RICH detector enabling precise measurements of particle electric charge (charge identification up to the iron region) and velocity ( Δ β / β ∼ 10 − 3 for Z=1, Δ β / β ∼ 10 − 4 for Z=10–20). The optimization of the RICH reconstruction efficiency imposed a dual radiator configuration with 16 NaF tiles ( n=1.33) in the centre and 92 aerogel tiles ( n=1.050) in the outer region, a pixelized detection matrix with 680 Hamamatsu R7600-M16 photomultipliers (each with 4×4 pixels) and a highly reflective conical mirror to increase photon collection. After its assembly at CIEMAT in Madrid, the RICH was taken to CERN in January 2008 and integrated into the full AMS-02 detector. AMS-02 underwent a pre-assembly in 2008 without magnet followed by a second detector assembly with a superconducting magnet in 2009 and the final assembly with a permanent magnet in mid-2010. Cosmic events were acquired in the context of the 2008 pre-assembly and in 2009, and two beam tests from CERN SPS took place in 2010. Results obtained with data from ground-based tests on the RICH performance are presented. A comparison with the aerogel light yield obtained on previous beam tests with a prototype detector is also discussed.

Tests of a silicon photomultiplier module for detection of Cherenkov photons

Silicon photomultipliers, whose main advantage over conventional photomultiplier tubes is the operation in high magnetic fields, have been considered as position sensitive, single photon detectors in a proximity focusing RICH with aerogel radiator. A module, consisting of 64 (8×8) Hamamatsu MPPC S10362-11-100P silicon photomultipliers, has been constructed and tested with Cherenkov photons emitted in an aerogel radiator by 120 GeV/ c pions from the CERN T4-H6 beam. In order to increase the efficiency, i.e. the effective surface on which light is detected, the potential of using light guides has been investigated.

Cherenkov detectors in the ALICE experiment at LHC

The ALICE experiment is devoted to measure the properties of the strongly interacting matter created in heavy-ion collisions at LHC at S N N = 5.5 TeV . The ALICE-HMPID is a ring imaging Cherenkov detector with liquid C6F14 as radiator, dedicated to the identification of charged pions and kaons in the range 1 ≤ p ≤ 3 GeV/c and protons in the range 2 ≤ p ≤ 5 GeV/c . It consists of seven identical proximity focusing RICH counters, exploiting large area MWPC equipped with CsI photocathodes, for Cherenkov light imaging. Furthermore, results from experiments at RHIC and theoretical studies have shown that to understand the hadronization mechanisms in heavy-ion collisions is very important to identify track-by-track charged hadrons at larger momenta ( 10 − 30 GeV/c ). Therefore an upgrade of ALICE PID capability is advisable. A possible upgrade is under study and it consists of a ring imaging Cherenkov detector, called VHMPID. HMPID characteristics and results from cosmic and first beam data taking are described. Description of VHMPID and performance results from simulation are also reported.

Proximity focusing RICH detector based on multilayer silica aerogel radiator

The performance of a proximity focusing Ring Imaging Cherenkov detector equipped with a radiator of silica aerogel is presented. The aerogel tile used is a monolith with variable index of refraction. Cherenkov photons are detected with high granularity by eight Hamamatsu H9500 flat panel multi anode phototubes.

Studies of a proximity focusing RICH with aerogel radiator for future Belle upgrade

We have been developing a proximity focusing ring imaging Cherenkov counter (RICH) with aerogel radiator, to extend the hadron identification capabilities in the forward endcap region of the Belle detector at the KEK B factory. This paper presents our recent studies on possible improvement of the RICH performance by using precise timing information. Cherenkov photons emitted in the aerogel radiator as well as in the entrance window of the PMT were used for the time-of-flight (TOF) measurement. A beam test using the Burle 85011 MCP PMT showed an excellent resolution of about 35 ps for Cherenkov photons from the PMT window. Such TOF measurement would supplement the RICH performance, and allow to positively identify particles below the Cherenkov threshold in aerogel, such as kaons and protons in the region around 1 GeV/ c.

Upgrade of the proximity focusing RICH at JLab

The Hall A RICH at Jefferson Lab is undergoing an upgrade to adapt to the higher momentum kinematics of the neutron spin structure Transversity experiments planned to run in 2008. The JLab RICH is a proximity focusing detector using liquid C 6 F 14 as Cherenkov radiator, a thin layer of CsI as photon converter, evaporated on segmented pad panels of a proportional chamber. The original RICH had a superior hadron identification up to 2 GeV/ c with pion/kaon rejection at the level of 1:1000 at ∼ 90 % intrinsic efficiency. The upgrade will extend this performance above 2.4 GeV/ c by means of a larger photon detector (a multiwire-multipad proportional chamber) and a longer proximity gap which will improve the photon detection geometrical efficiency and the angular resolution, respectively.

Silicon photomultiplier as a detector of Cherenkov photons

A novel photon detector—i.e. the silicon photomultiplier—whose main advantage over conventional photomultiplier tubes is the operation in high magnetic fields, has been tested as a photon detector in a proximity focusing RICH with aerogel radiator. This type of RICH counter is proposed for the upgrade of the Belle detector at the KEK B-factory. Recently produced silicon photomultipliers show less noise and have larger size, which are important issues for a large area photon detector. We measured the single photon pulse height distribution, the timing resolution and the position sensitivity for different silicon photomultipliers (Hamamatsu MPPC HC025, HC050, and HC100). The silicon photomultipliers were then used to detect Cherenkov photons emitted by cosmic ray particles in a proximity focusing aerogel RICH. Various light guides were investigated in order to increase the detection efficiency.

Design optimization of the proximity focusing RICH with dual aerogel radiator using a maximum-likelihood analysis of Cherenkov rings

The use of a sequence of aerogel radiators with different refractive indices in a proximity focusing Cherenkov ring imaging detector has been shown to improve the resolution of the Cherenkov angle. In order to obtain further information on the capabilities of such a detector, a maximum-likelihood analysis has been performed on simulated data, with the simulation being appropriate for the upgraded Belle detector. The results show that by using a sequence of two aerogel layers with different refractive indices, the K / π separation efficiency is improved in the kinematic region above 3 GeV/ c. In the low momentum region, the focusing configuration (with n 1 and n 2 chosen such that the Cherenkov rings from different aerogel layers at 4 GeV/ c overlap) shows a better performance than the defocusing one (where the two Cherenkov rings are well separated).

Proximity focusing RICH with TOF capabilities

A proximity focusing RICH with aerogel radiator has been studied to extend the hadron identification capabilities in the forward region of the Belle spectrometer. Such a proximity focusing RICH counter is also a very fast detector if a micro-channel plate (MCP) PMT is used as the photon detector. With its excellent timing properties, the same device could also serve as a time-of-flight counter and thus supplement other identification methods. A prototype of this novel device using BURLE 85011 64-anode, microchannel plate PMT, was tested on the bench and in the test beam at KEK. A good separation of pions and protons was observed in the test beam data with a time-of-flight resolution of about 35 ps (rms) for Cherenkov photons produced in the PMT window.

Proximity focusing RICH with TOF capabilities

A proximity focusing RICH with aerogel radiator has been studied to extend the pion-kaon separation power in the forward region of the Belle spectrometer. Such a proximity focusing RICH counter is also a very fast detector, in particular if a micro-channel plate (MCP) PMT is used as the photon detector. With its excellent timing properties, the same device could also serve as a time-of-flight counter and thus supplement other identification methods, in particular for low momentum tracks. Cherenkov photons emitted in the radiator medium (aerogel) as well as in the entrance window of the PMT could be used for the time-of-flight measurement. A prototype of this novel device using BURLE 85011 64-anode, microchannel plate PMT, was tested on the bench and in the test beam at KEK. Excellent performance of this counter could be demonstrated. In particular, a good separation of pions and protons was observed in the test beam data with a time-of-flight resolution of about 35 ps (rms) for Cherenkov photons produced in the PMT window.