Anatoly Ronzhin

Timing Performances of Large Area Silicon Photomultipliers Fabricated at STMicroelectronics

In this paper the results of charge and timing resolution characterization realized at Fermi National Accelerator Laboratory (Fermilab) on 3.5 × 3.5 mm2 Silicon PhotoMultipliers fabricated at STMicroelectronics Catania R&D clean room facilities are presented. The device consists of 4900 microcells and has a geometrical fill factor of 36%. Timing measurements were realized at different wavelengths by varying the overvoltage and the temperature applied to the photodetector. The results shown in this manuscript demonstrate that the device, in spite of its large area, exhibits relevant features in terms of low dark current density, fast timing and very good single photoelectron resolution. All these characteristics can be considered very appealing in view of the utilization of this technology in applications requiring detectors with high timing and energy resolution performances.

Electro-Optical Performances of p-on-n and n-on-p Silicon Photomultipliers

Silicon photomultipliers (SiPMs) are fabricated in two different configurations: p-on-n and n-on-p junctions. p-on-n SiPMs turn out to be more suitable for application in positron emission tomography (PET), due to their higher sensitivity in blue wavelength range where common PET scintillators have their emission spectrum. In this paper, we report on the electro-optical performances of the first p-on-n SiPMs manufactured at STMicroelectronics, Catania. The results obtained on these devices are compared with those measured on the standard n-on-p technology.

Calorimeters for Precision Timing Measurements in High Energy Physics

Current and future high energy physics particle colliders are capable to provide instantaneous luminosities of 1034 cm-2s-1 and above. The high center of mass energy, the large number of simultaneous collision of beam particles in the experiments and the very high repetition rates of the collision events pose huge challenges. They result in extremely high particle fluxes, causing very high occupancies in the particle physics detectors operating at these machines. To reconstruct the physics events, the detectors have to make as much information as possible available on the final state particles. We discuss how timing information with a precision of around 10 ps and below can aid the reconstruction of the physics events under such challenging conditions. High energy photons play a crucial role in this context. About one third of the particle flux originating from high energy hadron collisions is detected as photons, stemming from the decays of neutral mesons. In addition, many key physics signatures under study are identified by high energy photons in the final state. They pose a particular challenge in that they can only be detected once they convert in the detector material. The particular challenge in measuring the time of arrival of a high energy photon lies in the stochastic component of the distance to the initial conversion and the size of the electromagnetic shower. They extend spatially over distances which propagation times of the initial photon and the subsequent electromagnetic shower which are large compared to the desired precision. We present studies and measurements from test beams and a cosmic muon test stand for calorimeter based timing measurements to explore the ultimate timing precision achievable for high energy photons of 10 GeV and above. We put particular focus on techniques to measure the timing with a precision of about 10 ps in association with the energy of the photon. For calorimeters utilizing scintillating materials and light guiding components, the propagation speed of the scintillation light in the calorimeter is important. We present studies and measurements of the propagation speed on a range of detector geometries. Finally, possible applications of precision timing in future high energy physics experiments are discussed.

Testing a silicon photomultiplier time-of-flight (TOF) system in Fermilab Test Beam Facility

The first results from a time-of-flight beam test of silicon photomultipliers (SiPm) with quartz Cherenkov radiators obtained in the Fermilab Test Beam Facility are discussed. The timing measurement was performed with commercial electronics that were commissioned in the Fermilab SiPm timing facility. The plan for a new time-of-flight system for the test beam facility, with the goal of obtaining a few tens picosecond time resolution is presented.

SCINTILLATORS IN MAGNETIC FIELDS UP TO 20 T

Abstract Plastic scintillators and wavelength shifting fibers have been placed in magnetic fields of up to 20 T and the change in light yield measured. The light yield in scintillators increases at very low magnetic fields and continues to increase with increasing field until saturation at about 2 T. The maximum increase is between 6% and 8%, depending on the plastic composition. This increase is due to the polymer and not due to the dyes (fluors) used in the scintillators. No change of light yield due to magnetic fields has been observed in wavelength shifting fibers.

Enhanced blue-light sensitivity P on N Silicon Photomultipliers

Silicon Photomultipliers (SiPMs) have known a fast development in recent years, due to their excellent single photon detection capability and very fast timing response. In this paper we present the results of the electro-optical characterization performed on the first STMicroelectronics P on N SiPMs prototypes properly designed for their possible application in Positron Emission Tomography (PET). We will show that the performances of the new devices are extremely promising in terms of high photon detection efficiency and fast timing response in blue wavelength range.

Precision Timing Calorimeter for High Energy Physics

We present studies on the performance and characterization of the time resolution of LYSO-based calorimeters. Results for an LYSO sampling calorimeter and an LYSO-tungsten Shashlik calorimeter are presented. We demonstrate that a time resolution of 30 ps is achievable for the LYSO sampling calorimeter. We discuss timing calorimetry as a tool for mitigating the effects due to the large number of simultaneous interactions in the high luminosity environment foreseen for the Large Hadron Collider.

A silicon photomultiplier signal readout using transmission-line and waveform sampling for Positron Emission Tomography

We are investigating a new way of SiPM signal readout for Time-of-flight Positron Emission Tomography detector. Our new method adopts a transmission-line connected to multiple SiPMs in a row and high speed waveform sampling technology. The event information are retrieved from the digitized waveform measured at the two ends of the transmission-line; the interaction position along the strip direction is inferred from the arrival time difference at the two ends. With this approach, the number of readout channels can be efficiently reduced for larger detection area coverage by exploiting the fast time characteristic of SiPM while preserving the advantages of its compact size. We have built prototype transmission-line boards which holds up to eight SiPMs (3.5x3.5 mm2 and 5.0 mm pitch) on the strip. The waveforms of signals from the strip were recorded using DRS4 evaluation board at 5 GHz sampling rate. From the tests using pulsed laser and light emitting diode, the position along the strip could be determined in ~1 mm FWHM from the measured time difference on the strip. The responses to 511 keV photon were measured also in a coincidence setup; two LYSO scintillators (3×3×10 mm3) were coupled to the SiPMs on each transmission-line board, and a 22Na source was placed in the middle of the two LYSO scintillators with the distance of 12 cm. Preliminary results show that the position resolution of ~3 mm along the strip-line is achieved with LYSO+SiPM signal in addition to ~15% energy resolution at 511 keV and ~560 ps FWHM of coincidence time resolution. The results indicate that the investigated approach is a promising way for SiPM signal readout for TOF PET.

High fill factor P-on-N Silicon Photomultipliers for blue light detection

Silicon Photomultipliers (SiPMs) are fabricated in two different configurations: P-on-N and N-on-P junctions. More particularly P-on-N SiPMs are more suitable for application in Positron Emission Tomography (PET), due to their higher sensitivity in blue wavelength range where common PET scintillators have their emission spectrum. In this paper we will report on the electro-optical performances of the first P-on-N SiPMs manufactured at STMicroelectronics-Catania. The results obtained on these devices are compared with those measured on the standard N-on-P technology. We will show that the performances of the new devices are extremely promising in terms of higher photon detection efficiency in blue wavelength range and lower cross talk effects.

Study of timing properties of silicon photomultipiers

A new setup has been made at Fermilab for detector timing measurements at picosecond level. The core timing resolution of the amplifiers, discriminators and TAC/ADC combination is approximately 2 picosecond. We have made a study of a single photoelectron time resolution (SPTR) measured for signals coming from silicon photomultipliers (SiPm) made by different manufacturers. The obtained SPTR is of the order of 180 picosecond with SiPms illuminated by red (635 nm) PiLas laser light. IRST SiPms show better SPTR when illuminated by the blue laser light (405 nm). Most of the data were taken with 1 Volt of the overvoltage. The SiPms time resolution is inversely proportional to the square root of the number of photoelectrons. A time-of-flight (TOF) system with few tens of picosecond time resolution, based SiPms with quartz Cherenkov radiators looks practically achievable. A simple model is proposed to explain the difference in SPTR of the IRST SiPms when illuminating by the blue and red light. The explanation of the origin of the tail in the MPPC SiPm’s single photoelectron time spectra is presented. Finally, requirements for the SiPms temperature and bias voltage stability to maintain few picosecond time resolution are discussed.