Threshold Cherenkov Detector Research Articles

Particle identification in the low-GeV/c regime using Octafluoropropane (R-218) as Cherenkov radiator

Particle identification with threshold Cherenkov detectors, using a moderately pressurized radiating gas with an adequate refractive index, is one of the most common techniques employed in high-energy physics. However, available gases with relatively high refractive indices, that simultaneously preserve their gaseous phase at room temperature and moderate pressures, are rare. Until recently, R-12 (Freon-12) was broadly used, but to date, it is generally unavailable due to its high global warming potential. In this work, we present an estimation of the refractive index of an alternative gas, Octafluoropropane (R-218), and we explore its feasibility as a Cherenkov radiator, for tagging charged particles at momenta as low as 2 GeV/c.

Development of a threshold aerogel Cherenkov detector for [formula omitted] separation in the H-dibaryon search at J-PARC

We have developed a new threshold Cherenkov detector for online triggering in the H-dibaryon search experiment at the K1.8 beam line at J-PARC. Silica aerogel radiators with a refractive index of n=1.04 will cover an effective area of 550 × 220 mm2. The Cherenkov detector will be placed in a high magnetic field between two spectrometer magnets. Three prototypes and a real-size mockup module have been tested using pions and protons from photoproduction at SPring-8. For momentum ranging from 1.0 to 1.1 GeV ∕c, a suppression factor of 103 could be achieved for pions, with a factor of 10−2 for proton misidentification.

Candidates to Replace R-12 as a Radiator Gas in Cherenkov Detectors.

Dichlorodifluoromethane (R-12) has been widely used as a radiator gas in pressure threshold Cherenkov detectors for high-energy particle physics. However, that compound is becoming unavailable due to the Montreal Protocol. To find a replacement with suitably high refractive index, we use a combination of theory and experiment to examine the polarizability and refractivity of several non-ozone-depleting compounds. Our measurements show that the fourth-generation refrigerants R-1234yf (2,3,3,3-tetrafluoropropene) and R-1234ze(E) (trans-1,3,3,3-tetrafluoropropene) have sufficient refractivity to replace R-12 in this application. If the slight flammability of these compounds is a problem, two nonflammable alternatives are R-218 (octafluoropropane), which has a high Global Warming Potential, and R-13I1 (trifluoroiodomethane), which has low Ozone Depletion Potential and Global Warming Potential but may not be sufficiently inert.

A RICH detector for hadron identification at JLab

The "standard" Hall A apparatus at Jefferson Lab (TOF and aerogel threshold Cherenkov detectors) does not provide complete identification for proton, kaon and pion. To this aim, a proximity focusing C(6)F(14)/CsI RICH (Ring Image CHerenkov) detector has been designed, built, tested and operated to separate kaons from pions with a pion contamination of a few percent up to 2.4GeV/c. Two quite different experimental investigations have benefitted of the RICH identification: on one side, the high-resolution hypernuclear spectroscopy series of experiments on carbon, beryllium and oxygen, devoted to the study of the lambda-nucleon potential. On the other side, the measurements of the single spin asymmetries of pion and kaon on a transversely polarized (3)He target are of utmost interest in understanding QCD dynamics in the nucleon. We present the technical features of such a RICH detector and comment on the presently achieved performance in hadron identification.

Very high momentum particle identification in ALICE at the LHC

We propose to construct and install a limited acceptance detector to identify hadrons (pions, K, p) up to 30 GeV/ c on a track-by-track basis in space available in ALICE. Details and PID performance simulation results will be presented for two possible options, including a high transverse momentum ( p T ) trigger for this detector. The first option is a RICH design with a C 4 F 10 gas UV-photon radiator, UV-mirror, quartz window and pad-readout. This design requires additional tracking detectors to enable high p T triggering. A second option is a combination of three detectors: a RICH with CF 4 gas both as a UV-photon radiator and as a gas amplification medium (a windowless approach); and a threshold Cherenkov detector ( C 4 F 10 ) with a quartz window and pad readout. The response for minimum ionizing particles (MIP) and UV-photons in these detectors can be well separated. With an additional tracking detector this design will also provide high p T triggering. The simulation includes UV-photon production due to CF 4 scintillation.

A Cherenkov Radiation Detector With High Density Aerogels

We have designed a threshold Cherenkov detector at the Rutherford-Appleton Laboratory to identify muons with momenta between 230 and 350 MeV/c. We investigated the properties of three aerogels for the design. The nominal indices of refraction were <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> = 1.03, 1.07, 1.12, respectively. Two of the samples are of high density aerogel not commonly used for Cherenkov light detection. We present results of an examination of some optical properties of the aerogel samples and present basic test beam results.

Aerogel detector with a Fresnel lens focalization

The use of threshold Cherenkov detectors for the identification of high momentum particles in high energy physics experiments is connected with the efficiency of detection of light in the aerogel. As one goes lower in the refractive index, less photons are emitted, and more attention should be paid to the improvements of the detection efficiency. The light integration box method relies on photomultipliers of large size and requires even two of them. We have studied the possibility to use a thin focalizing element (Fresnel lens) between the aerogel and the photomultiplier to focalize the light onto a smaller diameter photomultiplier. The results show that for good aerogel and low indices of refraction ( < 1.01 ) the scheme with the aerogel and the Fresnel lens may be superior and less costly than the conventional set-up.

A threshold Cherenkov detector for [formula omitted] separation using silica aerogel

A new threshold Cherenkov detector has been built for the detection of charged pions in the focal plane of a magnetic spectrograph. Silica aerogel with refractive index of n = 1.05 is applied as a radiator. The detector exhibits a very high detection efficiency for pions with momenta ⩾ 900 MeV / c . Using two Cherenkov detectors in series a very high pion suppression factor of 10 5 was achieved.

The C 4F 10 Cherenkov detector for DIRAC-II

A new threshold Cherenkov detector using C 4F 10 gas radiator was built and put into operation in the DIRAC-II experiment at CERN. Running on the C 4F 10 at room temperature and atmospheric pressure, the detector discriminates between pions and kaons in the momentum range of 4– 8 GeV / c . A compact radiator–gas recirculation system including a gas–liquid separation unit, hollow-fibre membranes and molecular sieves ensures gas purity for a long term of operation without a significant loss of the gas. The system is robust and stable and the pressure in the two detector vessels is regulated in the range of ± 0.5 mbar . We report on the design and the technical aspects of the detector and its response in the DIRAC 2007 run.

A new aerogel Cherenkov detector for DIRAC-II

A new threshold Cherenkov detector using silica aerogel radiators is in operation in the DIRAC-II experiment at CERN. A duplex design was chosen to discriminate between kaons and protons in the momentum range 4–8 GeV/ c. The counter consists of overlapping modules with two different refractive indices, 1.015 and 1.008, covering the low and high momentum regions, respectively. We developed a new design of alternating layers of aerogel tiles and diffusive reflector foils coated with wavelength shifter to improve light collection in the aerogel. A pyramidal shape of the aerogel radiator was also adopted for best signal uniformity over a large sensitive area. We report on the detector status and its performance in the DIRAC 2007 run.

A novel aerogel Cherenkov detector for DIRAC-II

We present a new threshold Cherenkov detector using silica aerogel radiators with wavelength shifter. A duplex design was chosen to discriminate between kaons and protons in the momentum range 4–8 GeV/ c for the DIRAC-II experiment at CERN. The counter consists of overlapping modules with two different refractive indices, 1.015 and 1.008, covering the low and high momentum regions, respectively. The detector performance was optimized with cosmic rays and Monte-Carlo simulations. Thereby we developed a new design of alternating layers of aerogel tiles and diffusive reflector foils coated with wavelength shifter. The best results were obtained with p-terphenyl giving 50% increase in light yield. A pyramidal shape of the aerogel radiator was also adopted for the best signal uniformity over a large sensitive area.

The aerogel threshold Cherenkov detector for the High Momentum Spectrometer in Hall C at Jefferson Lab

We describe a new aerogel threshold Cherenkov detector installed in the HMS spectrometer in Hall C at Jefferson Lab. The Hall C experimental program in 2003 required an improved particle identification system for better identification of π / K / p , which was achieved by installing an additional threshold Cherenkov counter. Two types of aerogel with n = 1.030 and n = 1.015 allow one to reach ∼ 10 - 3 proton and 10 - 2 kaon rejection in the 1–5 GeV/ c momentum range with pion detection efficiency better than 99% (97%). The detector response shows no significant position dependence due to a diffuse light collection technique. The diffusion box was equipped with 16 Photonis XP4572 photo multiplier tubes (PMTs). The mean number of photo-electrons in saturation was ∼ 16 and ∼ 8 , respectively. This allows even for separation of slower particles slightly above threshold.

A RICH detector for strangeness physics in Hall A at Jefferson Lab

The high-resolution hypernuclear spectroscopy experiment at Jefferson Lab, Hall A (E94-107), needs unambiguous kaon identification. Due to the huge pion and proton background, the standard Hall A hadron particle identification, based on a time of flight and two aerogel threshold Cherenkov detectors, is not sufficient. For this task a proximity focusing C 6F 14/CsI RICH has been built. Recently, after some improvements to the mechanical structure of its wire chamber and to its electronics rate capability, the RICH has been tested with cosmic rays. This paper represents a status report of the RICH detector.

Particle identification in the PHENIX experiment at RHIC (present and future)

The PHENIX (Nucl. Instr. and Meth. A 499 (2003)) detector at the Relativistic Heavy Ion Collider, BNL is designed to perform a broad study of A–A, p–A and p–p collisions to investigate nuclear matter under extreme conditions. The charged particle identification is currently provided for kaons and pions to a momentum of 2.4 GeV/ c and protons to 5 GeV/ c. These limits would be greatly extended by the now under construction Aerogel Threshold Cherenkov detector (refractive index n=1.012).

A proximity focusing RICH detector for kaon physics at Jefferson lab hall A

Important information on the LN interaction can be obtained from High Resolution Hypenuclear Spectroscopy experiments with electromagnetic probes. A challenging experiment on electroproduction of hypernuclei is scheduled for 2003 in Hall A at Jefferson Lab. One of the challenges is the high performance particle identification system needed. The signal is expected to be rare compared to the very high pion and proton backgrounds due to the small electron and kaon detection angles. The ‘‘standard’’ Hall A PID apparatus (TOF and two aerogel threshold Cherenkov detectors) does not provide sufficient suppression of the background. Simulations and calculations have shown that a RICH detector would solve the problem. A proximity focusing fluorocarbon/CsI detector similar to the ALICE RICH detector has been designed, built, tested and commissioned. The results show that the detector performs as expected. r 2003 Published by Elsevier Science B.V. PACS: 29.40.Ka; 85.60.Gz

Light-weight spherical mirrors for Cherenkov detectors

Light-weight spherical mirrors have been appositely designed and built for the gas threshold Cherenkov detectors of the two Hall A spectrometers. The mirrors are made of a 1mm thick aluminized plexiglass sheet, reinforced by a rigid backing consisting of a phenolic honeycomb sandwiched between two carbon fiber mats epoxy glued. The produced mirrors have a thickness equivalent to 0.55% of radiation length, and an optical slope error of about 5.5mrad. These characteristics make these mirrors suitable for the implementation in Cherenkov threshold detectors. Ways to improve the mirror features are also discussed in view of their possible employment in RICH detectors.

The CHARON detector—an emulsion/counter hybrid set-up to measure the mean free path of near-elastic pion scattering in nuclear emulsion (white kink) at 2, 3 and 5 GeV/ c

White and grey kink events define a special class of soft hadron interactions in nuclear emulsion in which only one track (the scattered hadron) is leaving the interaction vertex. Due to their small and sometimes invisible activity at the scattering point, they represent a potential background source for all emulsion experiments hunting for decay topologies of short-lived particles like the lepton and charm mesons. For an extensive study of such hadronic kink signatures a dedicated experimental set-up has been built and exposed at the CERN PS hadron beam facility and it has collected about 300 000 pions with a fixed momentum ranging from 2 to 5 GeV/ c. Each particle was tracked by silicon strip detectors to connect it to the proper track in the nuclear emulsion located in between. Threshold Cherenkov detectors for electron discrimination, a muon counter and an MWPC-based magnetic spectrometer completed the experimental configuration. A total of 222 white and 271 grey kinks could be successfully located in the emulsion target. Their angular and transverse momentum distributions were extensively studied.

The GDH-Detector

For the GDH-Experiment at E LSA, the helicity dependent total photoabsorption cross-section is to be determined. These measurements will be performed with the newly developed GDH-Detector which is presented here. The concept of the GDH-Detector is to detect at least one reaction product from all possible hadronic processes with almost complete acceptance concerning solid angle and efficiency. This is realized by an arrangement of scintillators and lead. The overall acceptance for hadronic processes is better than 99%. The electromagnetic background is suppressed by about five orders of magnitude by means of a threshold Cherenkov detector. In dedicated tests, it has been demonstrated that all individual components of the GDH-Detector fulfill the design goals. Measurements of unpolarized total photoabsorption cross-sections were performed to ensure that the complete GDH-Detector is operational.

A prototype HBD for PHENIX

We constructed and tested a threshold Cherenkov detector (inspired by the conceptual design of Giomataris and Charpak (Nucl. Instr. and Meth. A 310 (1991) 589 ) consisting of a gas radiator followed by a photosensitive wire chamber using a solid CsI photocathode. The detector was operated with C 2F 6 radiator gas and a 95%He+5%CH 4 mixture for the avalanche gas. At 95% electron efficiency, the pion efficiency was 1 333 , 1 150 , and 1 100 for each of the lengths listed above.

DISTO: a large acceptance multiparticle spectrometer for 1–3 GeV proton beams

A magnetic spectrometer system has been constructed for the study of reactions with multiple charged particles in the final state, induced by polarized proton beams of few GeV energy. The system is based on a large-gap dipole magnet, with a liquid hydrogen target and scintillating fiber tracking detectors embedded inside the magnet. Multiwire proportional chambers, plastic scintillator hodoscopes, and threshold Cherenkov detectors placed outside the magnet provide additional tracking, triggering and particle identification capabilities. The system has been applied to study exclusive hyperon as well as pseudoscalar and vector meson production reactions at bombarding energies below 3 GeV. Additionally, it has been used to monitor the proton beam polarization at Laboratoire National Saturne. The components and performance of the system are reported.