Cryogenic Si detectors for ultra radiation hardness in SLHC environment Li, Zheng; Abreu, M.; Anbinderis, P. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2007, Letnik:
579, Številka:
2
Journal Article
Recenzirano
Radiation hardness up to 10
16
n
eq/cm
2 is required in the future HEP experiments for most inner detectors. However, 10
16
n
eq/cm
2 fluence is well beyond the radiation tolerance of even the most ...advanced semiconductor detectors fabricated by commonly adopted technologies: the carrier trapping will limit the charge collection depth to an effective range of 20–30
μm regardless of depletion depth. Significant improvement of the radiation hardness of silicon sensors has been taken place within RD39. Fortunately the cryogenic tool we have been using provides us a convenient way to solve the detector charge collection efficiency (CCE) problem at SLHC radiation level (10
16
n
eq/cm
2). There are two key approaches in our efforts: (1) use of the charge/current injection to manipulate the detector internal electric field in such a way that it can be depleted at a modest bias voltage at cryogenic temperature range (⩽230
K); and (2) freezing out of the trapping centers that affects the CCE at cryogenic temperatures lower than that of the LN
2 temperature.
In our first approach, we have developed the advanced radiation hard detectors using charge or current injection, the current injected diodes (CID). In a CID, the electric field is controlled by injected current, which is limited by the space charge, yielding a nearly uniform electric field in the detector, independent of the radiation fluence. In our second approach, we have developed models of radiation-induced trapping levels and the physics of their freezing out at cryogenic temperatures. In this approach, we intend to study the trapping effect at temperatures below LN
2 temperature. A freeze-out of trapping can certainly help in the development of ultra-radiation hard Si detectors for SLHC. A detector CCE measurement system using ultra-fast picosecond laser with a He cryostat has been built at CERN. This system can be used to find out the practical cryogenic temperature range that can be used to freeze out the radiation-induced trapping levels, and it is ready for measurements on extremely heavily irradiated silicon detectors. Initial data from this system will be presented.
Bose-Einstein correlations (BEC) between final state particles in the reaction \(\rm e^ + e^- \to W^ + W^- \to q_1\overline{q_2}q_3\overline{q_4}\) have been studied. Data corresponding to a total ...integrated luminosity of 550 pb-1, recorded by the DELPHI detector at centre-of-mass energies ranging from 189 to 209 GeV, were analysed. An indication for inter-W BEC between like-sign particles has been found at the level of 2.4 standard deviations of the combined statistical and systematic uncertainties.
There are two key approaches in our CERN RD 39 Collaboration efforts to obtain ultra-radiation-hard Si detectors: (1) use of the charge/current injection to manipulate the detector internal electric ...field in such a way that it can be depleted at a modest bias voltage at cryogenic temperature range (⩽150
K), and (2) freezing out of the trapping centers that affects the CCE at cryogenic temperatures lower than that of the liquid nitrogen (LN
2) temperature.
In our first approach, we have developed the advanced radiation hard detectors using charge or current injection, the current injected diodes (CID). In a CID, the electric field is controlled by injected current, which is limited by the space charge, yielding a nearly uniform electric field in the detector, independent of the radiation fluence. In our second approach, we have developed models of radiation-induced trapping levels and the physics of their freezing out at cryogenic temperatures.
The charged particle multiplicity in hadronic three-jet events from Z decays is investigated. The topology dependence of the event multiplicity is found to be well described by a modified leading ...logarithmic prediction. A parameter fit of the prediction to the data yields a measurement of the colour factor ratio CA/CF with the result in agreement with the SU(3) expectation of QCD. The quark-related contribution to the event multiplicity is subtracted from the three-jet event multiplicity resulting in a measurement of the multiplicity of two-gluon colour-singlet states over a wide energy range. The ratios \(r = N_{gg}(s)/N_{q\bar q}(s)\) of the gluon and quark multiplicities and \(r^{(1)} = N_{gg}'(s)/N_{q\bar q}'(s)\) of their derivatives are compared with perturbative calculations. While a good agreement between calculations and data is observed for r(1), larger deviations are found for r indicating that non-perturbative effects are more important for r than for r(1).
The DELPHI experiment at the LEP e + e- collider collected almost 700 pb-1 at centre-of-mass energies above the Z0 mass pole and up to 208 GeV. Those data were used to search for SUSY in the Anomaly ...Mediated SUSY Breaking (AMSB) scenario with a flavour independent common sfermion mass parameter. The searches covered several possible signatures experimentally accessible at LEP, with either the neutralino, the sneutrino or the stau being the Lightest Supersymmetric Particle (LSP). They included: the search for nearly mass-degenerate chargino and neutralino, which is a typical feature of AMSB; the search for Standard-Model-like or invisibly decaying Higgs boson; the search for stable staus; the search for cascade decays of SUSY particles resulting in the LSP and a low multiplicity final state containing neutrinos. No evidence of a signal was found, and thus constraints were set in the space of the parameters of the model.
Neutral Higgs bosons of the Standard Model (SM) and the Minimal Supersymmetric Standard Model (MSSM) were searched for in the data collected in 1999 by the DELPHI experiment at centre-of-mass ...energies between 191.6 and 201.7 GeV with a total integrated luminosity of 228 pb(-1). These analyses, in combination with our results at lower energies, set 95% confidence level lower mass bounds on the Standard Model Higgs boson (107.3 GeV/c(2)) and on the lightest neutral scalar (85.9 GeV/c(2)) and neutral pseudoscalar (86.5 GeV/c(2)) Higgs bosons in representative scans of the MSSM parameter space. An extended scan of the MSSM parameter space was also performed to test the robustness of these limits.
A precise measurement of the tau lifetime Abdallah, J.; Abreu, P.; Adam, W. ...
European physical journal. C, Particles and fields,
08/2004, Letnik:
36, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The tau lepton lifetime has been measured with the \({\rm e}^ + {\rm e}^- \rightarrow {\rm\tau}^ + {\rm\tau}^-\) events collected by the DELPHI detector at LEP in the years 1991-1995. Three different ...methods have been exploited, using both one-prong and three-prong \(\tau\) decay channels. Two measurements have been made using events in which both taus decay to a single charged particle. Combining these measurements gave \(\tau_\tau \mbox{(1 prong)} = 291.8\pm 2.3_{\mathrm{stat}} \pm 1.5_{\mathrm{sys}} \mathrm{fs}\). A third measurement using taus which decayed to three charged particles yielded \(\tau_\tau \mbox{(3 prong)} = 288.6\pm 2.4_{\mathrm{stat}} \pm 1.3_{\mathrm{sys}} \mathrm{fs}. \) These were combined with previous DELPHI results to measure the tau lifetime, using the full LEP1 data sample, to be \(\tau_\tau = 290.9\pm 1.4_{\mathrm{stat}} \pm 1.0_{\mathrm{sys}} \mathrm{fs}\).
The recovery of the charge collection efficiency (CCE) at low temperatures, the so-called ”Lazarus effect”, was studied in Si detectors irradiated by fast reactor neutrons, by protons of medium and ...high energy, by pions and by gamma-rays. The experimental results show that the Lazarus effect is observed: (a) after all types of irradiation; (b) before and after space charge sign inversion; (c) only in detectors that are biased at voltages resulting in partial depletion at room temperature. The experimental temperature dependence of the CCE for proton-irradiated detectors shows non-monotonic behaviour with a maximum at a temperature defined as the CCE recovery temperature. The model of the effect for proton-irradiated detectors agrees well with that developed earlier for detectors irradiated by neutrons. The same midgap acceptor-type and donor-type levels are responsible for the Lazarus effect in detectors irradiated by neutrons and by protons. A new, abnormal “zigzag”-shaped temperature dependence of the CCE was observed for detectors irradiated by all particles (neutrons, protons and pions) and by an ultra-high dose of γ-rays, when operating at low bias voltages. This effect is explained in the framework of the double-peak electric field distribution model for heavily irradiated detectors. The redistribution of the space charge region depth between the depleted regions adjacent to p+ and n+ contacts is responsible for the “zigzag”- shaped curves. It is shown that the CCE recovery temperature increases with reverse bias in all detectors, regardless of the type of radiation.
A measurement of the FV mass and width has been performed by the DELPHI Collaboration using the data collected during 1998. The data sample has an integrated luminosity of 155 pb(-1) and an average ...centre-of-mass energy of 188.6 GeV. Results are obtained
Lymphadenitis due to atypical mycobacteria Hauler, Barbara F; Monnier, Philippe; Cherpillod, Jacques ...
Revue médicale suisse,
2008-Oct-01, Letnik:
4, Številka:
173
Journal Article
Recenzirano
Cervical lymphadenitis is common in childhood and is a frequent source of consultation at the pediatrician's or ENT's office. It is usually caused by a viral upper respiratory tract infection and is ...self limited. In children with subacute or chronic cervical lymphadenitis which fails to respond to conventional antibiotics, infection due to atypical mycobacteria should always be considered. Infections occur predominantly in an otherwise healthy child of 1 to 5 years of age. The early diagnosis is essential as the treatment of choice is early surgical excision before skin necrosis and fistula occur. This article reviews the specific clinical manifestations, diagnostic tools and treatment of lymphadenitis due to atypical mycobacteria.
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