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This paper presents the measurements on first very thin Ultra-Fast Silicon Detectors (UFSDs) produced by Fondazione Bruno Kessler; the data have been collected in a beam test setup at the CERN PS, using beam with a momentum of 12 GeV/c. UFSDs with a nominal thickness of 25 and 35 μ m and an area of 1 × 1 mm 2 have been considered, together with an additional HPK 50- μ m thick sensor, taken as reference. Their timing performances have been studied as a function of the applied voltage and gain. A time resolution of about 25 ps and of 22 ps at a voltage of 120 and 240 V has been obtained for the 25 and 35 μ m thick UFSDs, respectively.

This paper describes the new concept of the double LGAD (low-gain avalanche diodes). The goal was to increase the charge at the input of the electronics, keeping a time resolution equal to or better than a standard (single) LGAD; this has been realized by adding the charges of two coupled LGADs while still using a single front-end electronics. The study here reported has been done starting from single LGAD with a thickness of 25 µm, 35 µm and 50 µm.

In this paper, different Silicon PhotoMultiplier (SiPM) sensors have been tested with charged particles to characterize the Cherenkov light produced in the sensor protection layer. A careful position scan of the SiPM response has been performed with different prototypes, confirming the large number of firing cells and proving almost full efficiency, with the SiPM filling factor essentially negligible. This study also allowed us to study the time resolution of such devices as a function of the number of firing cells, reaching values below 20 ps. These measurements provide significant insight into the capabilities of SiPM sensors in direct detection of charged particles and their potential for several applications.

In this paper, evidence that the increased response of SiPM sensors to the passage of charged particles is related mainly to Cherenkov light produced in the protection layer is reported. The response and timing properties of sensors with different protection layers have been studied.

The evolution of serological tests for syphilis (STSs) after therapy in HIV+ patients is a major point of controversy, with possible seroreactivation and illicit seroreversion in these patients. The aim of our study was to evaluate the long-term outcome of STSs in a cohort of HIV+ male homosexuals with a history of treated syphilis as compared with HIV– controls. Patients and Methods: Sixty-nine HIV+ male homosexuals with a documented history of treated syphilis and positive baseline treponemal tests were prospectively studied between 1986 and 1993. A medical examination, HIV staging, CD4+ cell count, VDRL, FTA-Abs tests and TPHA were performed every 6 months. Controls consisted of 49 HIV– patients with similar inclusion criteria over the same period. Comparisons between subgroups were based on χ 2 and Kruskal-Wallis tests. Analysis of negativation of the STS used the failure data methods (Kaplan-Meier, log-rank and Cox’s model). Results: Patients had a mean age of 38 years, a baseline CD4+ cell count of 578/mm 3 , elapsed time since last syphilis of 7.5 years and a median follow-up of 4.3 years. Controls had a mean age of 42 years, elapsed time since last syphilis of 5.3 years and a median follow-up of 4.7 years. Time to seroreversion was shorter in HIV+ patients for TPHA (p = 0.009, log-rank test) and FTA-Abs test (p = 0.001, log-rank test), even after adjustment for stage of syphilis, age and time since the last episode of syphilis. The decrease in VDRL titres was not different between the 2 groups (p = 0.053, log-rank test). Seroreversion of the TPHA, FTA-Abs test and VDRL test was not significantly related to stage of syphilis, time elapsed since the last episode of syphilis, age or history of STDs in both groups. Seroreversion of the TPHA and VDRL test was not related to baseline CD4+ cell count. However, seroreversion of the FTA-Abs test was related to a low baseline CD4+ cell count (p = 0.003). In HIV+ patients, a significant decrease in titres was noticed for TPHA, FTA-Abs test and VDRL test over time, but this time effect remained only for TPHA titres after adjustment for the CD4+ cell count. Conclusion: TPHA may serorevert in HIV+ patients. Thus, a non-reactive TPHA does not exclude a past syphilis infection in such patients. Evolution of the VDRL test after therapy is regular in HIV+ patients. The VDRL test remains adequate for controlling the efficacy of treatment in these patients.

The direct response of Silicon PhotoMultipliers being traversed by a MIP charged particle have been studied in a systematic way for the first time. Using beam test data, time resolution and the crosstalk probability have been measured. A characterization of the SiPM by means of a laser beam is also reported. The results obtained for different sensors indicate a measured time resolution around 40-70 ps. Although particles are expected to traverse only one SPAD per event, crosstalk measurements on different sensors indicate an unexpected higher value with respect to the one related to the sensor noise.

This paper presents a method to identify electrons using the Cherenkov light emitted when a charged particle travels in air and photons are detected with a Silicon PhotoMultiplier (SiPM). The analysis is based on a photon-counting approach using SPAD cells and uses data collected during a test beam at CERN PS. The results are well described by a simple Monte Carlo simulation, which further demonstrates that a very good electron identification and a strong pion/hadron rejection could be obtained over a wide momentum range.

This paper presents a method to identify electrons using the Cherenkov light emitted when a charged particle travels in air and photons are detected with a Silicon PhotoMultiplier (SiPM). The analysis is based on a photon-counting approach using SPAD cells and uses data collected during a test beam at CERN PS. The results are well described by a simple Monte Carlo simulation, which further demonstrates that a very good electron identification and a strong pion/hadron rejection could be obtained over a wide momentum range.

In this paper the efficiency of direct charged particle detection with different Silicon PhotoMultiplier (SiPM) sensors has been measured to be close to 100%. Time resolution of about 20 ps has also been confirmed for sensors with an active area of around 3x3 mm\\(^\\text{2}\\) and a single-cell area of 40 \\(\\mu\\)m\\(^\\text{2}\\). In addition, the SiPM performance after irradiation, in terms of timing response and dark count rate, has been evaluated for sensors with a 1x1 mm\\(^\\text{2}\\) area, demonstrating that SiPMs can maintain excellent timing capabilities and a low dark count rate when an appropriate threshold is applied to the signal.