Ring Imaging Cherenkov Research Articles

Performance of the MCP-PMT for the Belle II TOP counter in a magnetic field

The time of propagation (TOP) counter is a novel particle identification device for the Belle II experiment, utilizing the ring imaging Cherenkov technique. It is composed of a 2.7m long quartz bar and 32 micro channel plate photomultiplier tubes (MCP-PMTs) attached on the end of the bar. The MCP-PMT has a typical quantum efficiency of 28%, a photoelectron collection efficiency of about 55%, and a transit time spread (TTS) less than 50ps for single photon detection. Since the TOP counters are installed in the 1.5T magnetic field of the Belle II detector, the MCP-PMTs are required to keep those characteristics with gain of more than 5×105 in the magnetic field. Therefore, we investigated gain, TTS, and single photon detection efficiency of the MCP-PMTs in the magnetic field and found that they satisfy the requirements. We are starting complete inspections for more than 500 MCP-PMTs, and have inspected up to 87 MCP-PMTs.

Event reconstruction in the RICH detector of the CBM experiment at FAIR

The Compressed Baryonic Matter (CBM) experiment at the future FAIR facility will investigate the QCD phase diagram at high net-baryon densities and moderate temperatures. One of the key signatures will be di-leptons emitted from the hot and dense phase in heavy-ion collisions. Measuring di-electrons, a high purity of identified electrons is required in order to suppress the background. Electron identification in CBM will be performed by a Ring Imaging Cherenkov (RICH) detector and Transition Radiation Detectors (TRD). In order to access the foreseen rare probes, the detector and the data acquisition have to handle interaction rates up to 10MHz. Therefore, the development of fast and efficient event reconstruction algorithms is an important and challenging task in CBM. In this contribution event reconstruction and electron identification algorithms in the RICH detector are presented. So far they have been developed on simulated data but could already be tested on real data from a RICH prototype testbeam experiment at the CERN-PS. Efficient and fast ring recognition algorithms in the CBM-RICH are based on the Hough Transform method. Due to optical distortions of the rings, an ellipse fitting algorithm was elaborated to improve the ring radius resolution. An efficient algorithm based on the Artificial Neural Network was implemented for electron identification in RICH. All algorithms were significantly optimized to achieve maximum speed and minimum memory consumption.

Production of π/K/p in pp and Pb-Pb collisions measured with ALICE

The ALICE experiment is a dedicated heavy-ion physics detector at the LHC, with unique capabilities for the study of identified particle production. In this paper, an overview of ALICE results on the measurement of pion, kaon and proton transverse momentum (pT) spectra at mid-rapidity in proton-proton and Pb-Pb collisions at different energies is presented. The particle identification is performed using the following detectors: the Time Projection Chamber (TPC), the Inner Tracking System (ITS), the Time of Flight system (TOF) and a Ring-imaging Cherenkov system (HMPID).

Ring imaging Cherenkov counter of HERMES for pion, kaon, proton and anti-proton identification

RICH of HERMES was built for identification of pion, kaon, proton and anti-proton in the momentum range of 2–15GeV/c. It was a dual-radiator RICH. The radiators were aerogel and C4F10 gas. Produced hadrons in electron–nucleon deep inelastic scattering were identified by the RICH and spin structure of the nucleon was studied by correlation between the directions of the target spin, scattered electron and produced hadrons.

The assembly of the Belle II TOP counter

A new type of ring-imaging Cherenkov counter, called TOP counter, has been developed for particle identification at the Belle II experiment to run at the SuperKEKB accelerator in KEK, Japan. The detector consists of 16 identical modules arranged azimuthally around the beam line. The assembly procedure for a TOP module is described. This procedure includes acceptance testing of the quartz mirror, prism, and quartz bar radiators. The acceptance tests include a chip search and measurements of bulk transmittance and total internal reflectance. The process for aligning and gluing the optical components together is described.

Performance in space of the AMS-02 RICH detector

AMS-02 was successfully installed on the International Space Station (ISS) in May 2011, to perform precise measurements of galactic cosmic rays in the 100MV to few TV magnetic rigidity range. Among several specialized sub-detectors, AMS-02 includes a Ring Imaging Cherenkov detector (RICH), which provides a precise measurement of the particle charge and velocity. The Cherenkov light is produced in a radiator made of silica aerogel and sodium fluoride and collected by means of an array of photomultiplier tubes. Since its launch to space, the detector has been taking data without failures; its functionality and data integrity are monitored and show stable response. In order to achieve the optimal detector performance, calibrations have been performed to account for the dependence of the photodetectors response on temperature and for effective non-uniformities in the detector. The knowledge gathered of the photon yield at the percent level resulted in a charge resolution of 0.3 charge units for He and 0.5 charge units for Si ions. The required precision in the measurements of the particle velocity at the per mil level demanded a more accurate determination of the aerogel refractive index. A map of the aerogel radiator refractive index has been directly inferred from in-flight high statistics data with a precision of Δn/n<2×10−5 on average and its stability with time has also been checked. Finally, a velocity resolution of ~0.8×10−3 for He and ~0.5×10−3 for Z>5 ions has been obtained.

Silica aerogel radiator for use in the A-RICH system utilized in the Belle II experiment

This paper presents recent progress in the development and mass production of large-area hydrophobic silica aerogels for use as radiators in the aerogel-based ring-imaging Cherenkov (A-RICH) counter, which will be installed in the forward end cap of the Belle II detector. The proximity-focusing A-RICH system is especially designed to identify charged kaons and pions. The refractive index of the installed aerogel Cherenkov radiators is approximately 1.05, and we aim for a separation capability exceeding 4σ at momenta up to 4GeV/c. Large-area aerogel tiles (over 18×18×2cm3) were first fabricated in test productions by pin drying in addition to conventional methods. We proposed to fill the large end-cap region (area 3.5m2) with 124 water-jet-trimmed fan-shaped dual-layer-focusing aerogel combinations of different refractive indices (1.045 and 1.055). Guided by the test production results, we decided to manufacture aerogels by the conventional method and are currently proceeding with mass production. In an electron beam test undertaken at the DESY, we confirmed that the K/π separation capability of a prototype A-RICH counter exceeded 4σ at 4GeV/c.

Investigation of surface homogeneity of mirrors for the CBM-RICH detector and low-mass di-electron feasibility studies

The Compressed Baryonic Matter (CBM) experiment at the future FAIR facility will investigate high net-baryon density matter at moderate temperatures in A+A collisions from 4-45 AGeV. One of the key observables of the CBM physics program is electromagnetic radiation as a probe of strongly interacting matter in heavy-ion collisions, carrying undistorted information on its conditions to the detector. This includes detailed investigations of low-mass vector mesons in their di-electron channel. A clean and efficient identification of electrons is required for such measurements. In CBM the electron identification will be performed by a Ring Imaging Cherenkov detector and several layers of Transition Radiation Detectors. The RICH detector will be operated with CO2 radiator gas, MAPMTs as photodetector and spherical glass mirrors as focusing elements. A high quality of the mirrors in terms of reflectivity and surface homogeneity is required. In the first part of the contribution results on measurements of the mirror surface homogeneity are presented. Results on the feasibility studies of low-mass di-electron measurements with realistic detector response are discussed in the second part of the contribution.

Progress of the NA62 RICH detector

NA62 is the last generation Kaon experiment at CERN.Its main goal is to collect about 100 K+→π+νν̄ events with 10% background.This implies to collect more than 1013 K+ decays with a backgound rejection factor better than 1012.The challenging aspect of the experiment is the suppression of Kaon decays with branching ratioes up to 10 orders ofmagnitude higher than the signal and similar experimental signature, such as K+→μ+ν.To this purpose good PID (Particle IDentification) and kinematic rejection are required.Precise timing is also needed to correctly associate the π+ with the parent K+ in an high rate environment.A RICH (Ring Imaging Cherenkov) detector is proposed as PID element, to identify μ contaminating the π samplein the 15-35 GeV/c momentum range with inefficiency lower than 1% and to measure the arrival time with precisionsmaller than 100 ps.It will also be a key element for the NA62 trigger.A vacuum-proof cylindrical vessel with 4 m diameter, 17 m long, will be filled with Neon gas atatmospheric pressure.The Cherenkov light will be reflected by a mosaic of 20 hexagonal mirrors with 17 m focal length andcollected by 2000 photomultipliers.The progress in the construction of the detector is described: the installation will start in January 2014,with completion foreseen in time for the first physics run of the NA62 experiment in the fall of 2014.

Time and charge characterization of Hamamatsu Photonics silicon photomultipliers

Two Hamamatsu Photonics silicon photomultipliers (SiPM) with same cell size 50×50 µm 2 and different sensitive area (1×1 mm 2 vs. 3×3 mm 2 ) have been characterized in charge and time by means of a 409 nm pico-laser. The time resolution was studied for the detection of few photoelectrons. The results obtained are relevant for the employment of SiPM in ring imaging Cherenkov detectors (RICH).

The RICH detector for CLAS12 at Jefferson Lab

The CLAS12 spectrometer at JLab will offer unique possibilities to study the 3D nucleon structure in terms of TMDs and GPDs in the poorly explored valence region, and to perform high precision hadron spectroscopy. A large area ring-imaging Cherenkov detector has been designed to achieve the required hadron identification capability in the momentum range 3-8 GeV/c. The detector, based on a novel hybrid imaging design, foresees an aerogel radiator and an array of multi-anode photomultipliers. The detector concept and preliminary results of test-beams on a prototype are presented.

Studies of single-photoelectron response and of performance in magnetic field of a H8500C-03 photomultiplier tube

We studied the single-photoelectron detection capabilities of a multianode photomultiplier tube H8500C-03 and its performance in high magnetic field. Our resultsshow that the device can readily resolve signals at the singlephotoelectron level making it suitable for photon detection in boththreshold and ring imaging Cherenkov detectors. We also found that alarge longitudinal magnetic field, up to 300 Gauss, induces a changein the relative output of at most 55% for an edge pixel, and of atmost 15% for a central pixel. The H8500C-03 signal loss intransverse magnetic fields it is significantly more pronounced thanfor the longitudinal case. Our studies of single photoelectronreduction in magnetic fields point to the field induced misfocusing ofthe photoelectron extracted from the photocathode as primary cause ofsignal loss. With appropriate shielding this PMT could function inhigh magnetic field environments.

R&D studies of a RICH detector using pressurized C4F8O radiator gas and a CsI-based gaseous photon detector

We report on studies of layout and performance of a new Ring Imaging Cherenkov detector using for the first time pressurized C4F8O radiator gas and a photon detector consisting of a MWPC equipped with a CsI photocathode. In particular, we present here the results of beam tests of a MWPC having an adjustable anode–cathode gap, aiming at the optimization of single photoelectron detection and Cherenkov angle resolution. This system was proposed as a Very High Momentum Particle Identification (VHMPID) upgrade for the ALICE experiment at LHC to provide charged hadron track-by-track identification in the momentum range 5–25GeV/c.

A ring imaging Cherenkov detector for CLAS12

The energy increase of Jefferson Lab's Continuous Electron Beam Accelerator Facility (CEBAF) to 12GeV promises to greatly extend the physics reach of its experiments. This will include an upgrade of the CEBAF Large Acceptance Spectrometer (CLAS) to CLAS12, offering unique possibilities to study internal nucleon dynamics. For this excellent hadron identification over the full kinematical range of 3–8GeV/c is essential. This will be achieved by the installation of a Ring Imaging CHerenkov (RICH) detector. A novel hybrid imaging design incorporating mirrors, aerogel radiators and Hamamatsu H8500 multianode photomultiplier tubes is proposed. Depending on the incident particle track angle, Cherenkov light will either be imaged directly or after two reflections and passes through the aerogel. The detector design is described, along with preliminary results on individual detector components tests and from recent testbeam studies.

The ring imaging Cherenkov detector of the NA62 experiment at CERN

A Ring Imaging Cherenkov (RICH) detector is the key element for particle identification in the NA62 experiment at CERN. Its purposes are to distinguish pions from muons in the momentum range from 15GeV/c to 35GeV/c with a muon suppression factor at the 0.5% level, to measure the particle arrival time with better than 100ps resolution and to provide the reference time and a fast signal for the trigger system. This paper describes the updated detector design, the present status of the construction, the final results of a prototype beam test and a possible application of Graphics Processing Units in the NA62 trigger system based on RICH information.

Light-flavour identified charged-hadron production in pp and Pb–Pb collisions at the LHC

Thanks to the unique detector design adopted to fulfill tracking and particle-identification (PID) requirements (e.g. low momentum cut-off and low material budget), the ALICE experiment provides significant information about hadron production both in pp and Pb–Pb collisions. In particular, the pT-differential and integrated production yields of identified particles play a key role in the study of the collective and thermal properties of the matter formed in high-energy heavy-ion collisions. Furthermore, the production of high-pT particles provides insights into the property of the hot medium created in such collisions and the in-medium energy-loss mechanisms.Transverse momentum spectra of π±, K±, p and p̄ are measured at mid-rapidity (|y| < 0.5) over a wide momentum range, from ~ 100 MeV/c up to ~ 20 GeV/c. The measurements are performed exploiting the dE/dx in silicon and gas, the time-of-flight and the ring-imaging Cherenkov particle-identification techniques, which will be briefly reviewed in this report. The current results on light-flavour charged-hadron production will be presented for pp collisions at and 7 TeV and for Pb–Pb collisions at TeV. Integrated production yields, transverse momentum spectra and particle ratios in pp are discussed as a function of the collision energy and compared to previous experiments and commonly-used Monte Carlo models. Pb–Pb collisions at the LHC feature the highest radial flow ever observed and an unexpectedly low p/π production ratio. The results are presented as a function of collision centrality and compared to RHIC data in Au-Au collisions at GeV and predictions from thermal and hydrodynamic models. The nuclear modification factor (RAA) of identified hadrons will also be discussed and compared to unidentified charged particles and theoretical predictions. This is observed to be identical for all particle species at high-pT.

Performance of the LHCb RICH detector at the LHC.

The LHCb experiment has been taking data at the Large Hadron Collider (LHC) at CERN since the end of 2009. One of its key detector components is the Ring-Imaging Cherenkov (RICH) system. This provides charged particle identification over a wide momentum range, from 2–100 GeV/c. The operation and control, software, and online monitoring of the RICH system are described. The particle identification performance is presented, as measured using data from the LHC. Excellent separation of hadronic particle types (π, K, p) is achieved.

The Ring Imaging Cherenkov detector for the CBM-Experiment

The mission of the future Compressed Baryonic Matter experiment, to be operated at the FAIR facility at GSI, Darmstadt, is the exploration of the properties of super-dense nuclear matter. In particular, the search for in-medium modifications of hadrons, the study of the transition from dense hadronic matter to quark-gluon matter, and the location of a critical endpoint in the phase diagram of strongly interacting matter are the principal physics goals of CBM. Detailed measurements of di-leptons and open charm probes are hoped to shed light to the existence of such effects.The Ring Imaging Cherenkov detector of CBM aims at a clean and efficient electron identification. It is foreseen to have CO2 as radiator gas and to be equipped with Hamamatsu multi-anode photomultiplier tubes. Herewith we present selected results of R&D studies and beam test measurements of the RICH prototype performed in October 2011 at the CERN/PS with negatively charged particles.

Characterization of a Hamamatsu R7600 multi-anode photomultiplier tube with single photon signals

The characterization of the single photon response of the Hamamatsu R7600 multi-anode photomultiplier tube (MaPMT) is presented, in view of a possible application in Ring Imaging Cherenkov (RICH) detectors and high rate single photon counting applications in general. For most of the measurements the main source of single photons was a commercial blue LED biased with a small current of a few nA. The spectra obtained with this source match those obtained with Cherenkov light from a PbF2 crystal illuminated with a 22Na gamma source, confirming that the test signals are single photons. Dark current and cross-talk were measured at the single photoelectron level. The single photon response of the PMT was also studied as a function of the bias ratio between dynodes. The sensitivity to magnetic field up to 30 G and the effectiveness of three magnetic shields with different geometries were evaluated. Gain loss due to aging was also studied up to 2000 hours of operation at high counting rate.

New optics for resolution improving of Ring Imaging Cherenkov detectors

The Ring Imaging Cherenkov detector (RICH) of the COMPASS experiment at CERN is key tool for particle identification. Two reflecting spherical mirror surfaces, covering a total area of about 21 m2 hosted in the radiator vessel, provide Cherenkov radiation focusing to photon detectors. These ones are based on the use of multi-anode photo-multiplier tubes. They are coupled to individual lens telescopes, made from special fused silica aspherical lenses. Design, construction, and Hartmann test of lenses qualities and alignment were described. The RICH detector uses C4F10 as radiator gas. The refractive index of the radiator gas is substantial parameter. It varies with temperature, atmospheric pressure and gas purity. Its accurate knowledge is essential for the particle identification performance. A modified Jamin’s interferometer was proposed, constructed and tested to allow on-line refractive index measurement with accuracy better than 10-6 The new types of fused silica Cherenkov radiators was designed to the tests of electron multiplier detector too.