The HERMES dual-radiator ring imaging Cherenkov detector Akopov, N; Aschenauer, E.C; Bailey, K ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
03/2002, Volume:
479, Issue:
2
Journal Article
Peer reviewed
Open access
The construction and use of a dual radiator Ring Imaging Cherenkov (RICH) detector is described. This instrument was developed for the HERMES experiment at DESY which emphasises measurements of ...semi-inclusive deep-inelastic scattering. It provides particle identification for pions, kaons, and protons in the momentum range from 2 to
15
GeV
, which is essential to these studies. The instrument uses two radiators, C
4F
10, a heavy fluorocarbon gas, and a wall of silica aerogel tiles. The use of aerogel in a RICH detector has only recently become possible with the development of clear, large, homogeneous and hydrophobic aerogel. A lightweight mirror was constructed using a newly perfected technique to make resin-coated carbon-fiber surfaces of optical quality. The photon detector consists of 1934 photomultiplier tubes (PMT) for each detector half, held in a soft steel matrix to provide shielding against the residual field of the main spectrometer magnet.
The optical properties of silica aerogel tiles with a refractive index of 1.03 and dimensions
11×11×1
cm
3
, produced by the Matsushita Electric Works (Japan), have been measured in the wavelength ...range from 200 to 900 nm. The tiles are used as one of the two radiators of the ring imaging Cherenkov counter of the HERMES experiment at DESY-HERA. The transmittance of light has been measured on 200 tiles by means of a double beam spectrophotometer. The light transflectance and reflectance have been measured on one tile by means of a single-beam spectrophotometer and an integrating reflecting sphere. Typical values of the measured transmittances at a wavelength
λ=400 nm are around 0.67. The measured transflectance increases almost linearly from 0.4 to 0.96 in the interval 200–300 nm, and remains nearly constant at the value 0.95 in the complementary
λ-range. The measured reflectance, mostly confined below 400 nm, is completely interpretable as backscattering from inside the aerogel, revealing an absence of light reflection at the aerogel surfaces. The transmittance data have been fitted with the Hunt formula, whose parameters have been used to evaluate the number of unscattered and scattered Cherenkov photons produced by aerogel. For stacks of 5 tiles and quantum efficiencies of phototubes with bialkali photocathodes, rings with up to 19 photoelectrons/event can be expected for
β=1 particles.
The work on aerogel Cherenkov counters was started in Novosibirsk in 1986. Production of aerogels with refractive indices of 1.006–1.13 and thicknesses of blocks up to 50
mm was developed. The light ...absorption length at 400
nm is 5–7
m, the scattering length is 4–5
cm. By these parameters, the Novosibirsk aerogel is one of the best in the world. The ASHIPH Cherenkov counters with light collection on wavelength shifters have been developed. The ASHIPH system of the KEDR detector contains 1000
l of aerogel. The
π
/
K
separation is
4.5
σ
. A project of ASHIPH counters for the SND detector has been developed. Aerogel RICH for LHCb gives a possibility to identify hadrons in the momentum range of 2–10
GeV/
c. The Novosibirsk group is developing an aerogel RICH for the endcap for the SuperBaBar project. Calculations performed by a group of physicists from Novosibirsk and DESY-Zeuthen have shown that aerogel radiators enable to achieve time resolution up to 20
fs.
A measurement of direct photon production in {sup 208}Pb+ {sup 208}Pb collisions at 158A GeV has been carried out in the CERN WA98 experiment. The invariant yield of direct photons in central ...collisions is extracted as a function of transverse momentum in the interval 0.5<p{sub T}<4 GeV/c . A significant direct photon signal, compared to statistical and systematical errors, is seen at p{sub T}>1.5 GeV/c . The result constitutes the first observation of direct photons in ultrarelativistic heavy-ion collisions. It could be significant for diagnosis of quark-gluon-plasma formation.
Silica aerogel radiators for bunch length measurements Bähr, J.; Djordjadze, V.; Lipka, D. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2005, Volume:
538, Issue:
1
Journal Article
Peer reviewed
Open access
Cherenkov radiators based on silica aerogel are used to measure the electron bunch length at the photo injector test facility at DESY Zeuthen (PITZ). The energy range of those electrons is 4–5
MeV. ...In this paper, the time resolution defined by the usage of aerogel is calculated analytically and Monte Carlo simulations are performed. It is shown that silica aerogel gives the possibility to reach a time resolution of about 0.1
ps for high photon intensities and a time resolution of about 0.02
ps can be obtained for thin silica aerogel radiators.
The influence of the nuclear medium on the production of charged hadrons in semi-inclusive deep-inelastic scattering has been studied by the HERMES experiment at DESY using a 27.5 GeV positron beam. ...The differential multiplicity of charged hadrons and identified charged pions from nitrogen relative to that from deuterium has been measured as a function of the virtual photon energy \(\nu\) and the fraction z of this energy transferred to the hadron. There are observed substantial reductions of the multiplicity ratio \(R_M^{h}\) at low \(\nu\) and at high z, both of which are well described by a gluon-bremsstrahlung model of hadronization. A significant difference of the \(\nu\)-dependence of \(R_M^{h}\) is found between positive and negative hadrons. This is interpreted in terms of a difference between the formation times of protons and pions, using a phenomenological model to describe the \(\nu\)- and z-dependence of \(R_M^{h}\).
Development of aerogel Cherenkov detectors at Novosibirsk Barnyakov, A.Yu; Barnyakov, M.Yu; Bähr, J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2005, Volume:
553, Issue:
1
Journal Article
Peer reviewed
Open access
The development of aerogel Cherenkov counters with the light collection using a wavelength shifter is described. 80 counters of this type are working in the KEDR detector. A project of similar ...counters for the SND detector based on “heavy” aerogel with
n
=
1.13
has been developed. Aerogel with a refractive index of 1.006–1.13 and dimensions of blocks up to
200
×
200
×
50
mm
3
is produced by the Novosibirsk group for use in Cherenkov counters of different types. The Novosibirsk group is participating in the development of LHCb RICH as well as a beam diagnostics for a photo-injector test facility at DESY–Zeuthen. Recently we started development of RICH based on focusing aerogel (FARICH) for the endcap of the SuperBaBar. For the first time in the world the focusing aerogel with layers of different refractive indices has been produced.
The restoration of chiral symmetry and its subsequent breaking through a phase transition has been predicted to create regions of Disoriented Chiral Condensates (DCC). This phenomenon has been ...predicted to cause anomalous fluctuations in the relative production of charged and neutral pions in high-energy hadronic and nuclear collisions. The WA98 experiment has been used to measure charged and photon multiplicities in the central region of 158 AGeV Pb+Pb collisions at the CERN SPS. In a sample of 212646 events, no clear DCC signal can be distinguished. Using a simple DCC model, we have set a 90% C.L. upper limit on the maximum DCC production allowed by the data.
The Photo Injector Test facility at DESY Zeuthen (PITZ) was built to develop electron sources for the TESLA Test Facility Free Electron Laser and future linear colliders. The main goal is to study ...the production of minimum transverse emittance beams with short bunch length at medium charge (∼1nC). The facility includes a 1.5 cell L-band cavity with coaxial RF coupler, a solenoid for space charge compensation, a laser capable to generate long pulse trains, an UHV photo cathode exchange system, and different diagnostics tools. Besides an overview of the facility, its main components and their commissioning, this contribution will concentrate on the first measurements at PITZ with photoelectrons. This will include measurements of the transverse and longitudinal laser profile, charge and quantum efficiency, momentum and momentum spread, transverse electron beam profiles at different locations and first results on transverse emittance.
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