Cherenkov Signal Research Articles

Radiation emission at Langmuir frequency from laser wake in longitudinally stratified plasma column

Theoretical analysis shows that a small-amplitude laser wake (an electrostatic Langmuir wave), driven in a periodically stratified, cylindrical plasma column, generates a superluminal, azimuthally polarized rotational current at a Langmuir frequency. The current radiates a radially polarized (i.e. transverse magnetic) Cherenkov signal into the plasma-free space. The opening angle of the Cherenkov emission cone is defined by the spatial period of stratification. Lifetime of the laser wake, limited by wave breaking in the inhomogeneous plasma, defines the terahertz (THz) signal length. This length ranges from a few picoseconds to hundreds of picoseconds, depending on the wake amplitude, amplitude of background density modulation, and stratification period. Monochromaticity and coherence distinguishes this THz signal from the ultrashort, uncollimated, broadband signals generated by photoionization currents in plasma filaments. The efficiency of electromagnetic energy conversion, from optical to THz, reaches its peak when the drive pulse waist size is close to the column radius. The efficiency increases with an increase in the drive pulse wavelength, and reaches the maximum when the drive pulse becomes near-critical for relativistic self-focusing. Numerical examples with sub-Joule, near-infrared terawatt drive pulses demonstrate the highest conversion efficiency of the order 10−5, with the total emitted energy of several µJ, a few-hundred MV m−1 electric field at the column surface, and an MV m−1 field 10 cm away from the source.

Space-based extensive air shower optical Cherenkov and fluorescence measurements using SiPM detectors in context of POEMMA

Developed as NASA Astrophysics Probe-class mission, the Probe Of Extreme Multi-Messenger Astrophysics (POEMMA) is designed to identify the sources of ultra-high energy cosmic rays (UHECRs) and to observe cosmic neutrinos. POEMMA consists of two spacecraft flying in a loose formation at 525 km altitude, 28.5°inclination orbits. Each spacecraft hosts a Schmidt telescope with a large collecting area and wide Field-of-View (FoV). A novel focal plane is employed that is optimized to observe both the UV fluorescence signal from extensive air showers (EASs) and the optical Cherenkov signals from EASs. In UHECR stereo fluorescence mode, POEMMA will measure the spectrum, composition, and full-sky distribution of the UHECRs above 20 EeV with high statistics along with remarkable sensitivity to UHE neutrinos. The POEMMA spacecraft are designed to quickly re-orient to a Target-of-Opportunity (ToO) neutrino mode to observe transient astrophysical sources with unique sensitivity. In this mode, POEMMA will be able to detect cosmic tau neutrino events above 20 PeV by measuring the upward-moving EASs for τ-lepton decays induced from tau neutrino interactions in the Earth. In this paper, POEMMA’s science goals and instrument design are summarized with a focus on the SiPM implementation in POEMMA, along with a detailed discussion of the properties of the Cherenkov EAS signal in the context of wide wavelength sensitivity offered by SiPMs. A comparison of the fluorescence response between SiPMs and the MAPMTs currently planned for use in POEMMA will also be discussed, assessing the potential for SiPMs to perform EAS fluorescence measurements.

Measuring the depth of shower maximum of extensive air showers using Cherenkov light

A method is proposed to reconstruct the depth at which showers reach the maximum number of charged particles (Xmaxcharged) using atmospheric Cherenkov telescopes. The dependence of the Cherenkov signal with telescope distance from shower core is explored and a region in which the measurement is possible is determined (150 to 200 m). A parametrization is presented to reconstruct Xmaxcharged. The resolution of the method is studied as a function of energy, for different primary particle types and for telescope fields of view ranging from 3.5∘ to 10∘. Good resolution ( ∼ 25 g/cm2) is achieved for most of the cases of primary particle type (gamma ray, proton and iron nuclei) and energy (10 TeV < E < 300 TeV). Very good resolution ( < 15 g/cm2) is achieved in the best cases and not so good resolution ( > 40 g/cm2) is seen for energies below 30 TeV. The results presented here contribute to the understanding of the development of gamma-ray showers and suggest another possibility of using atmospheric Cherenkov telescopes to study cosmic rays in the TeV-PeV energy range.

Discriminating the muon noise at the PMT windows in calorimeters

In particle physics experiments, stray muons are known to be a source of anomalous signals when they produce Cherenkov photons in the PMT window. Most recent of such events were reported by CMS Hadronic Forward calorimeters, where PMTs read out the Cherenkov signal generated within the quartz fibers. This study focuses on finding an efficient way to discriminate the Cherenkov signal coming from the quartz fibers from the ones generated at the face of the PMT due to stray muons. We report that these two different signals can be discriminated based on their pulse widths. The study also shows the performance of a proof-of-concept circuit prototype that effectively tags the two types of pulses.

Imaging radiation dose in breast radiotherapy by X-ray CT calibration of Cherenkov light

Imaging Cherenkov emission during radiation therapy cancer treatments can provide a real-time, non-contact sampling of the entire dose field. The emitted Cherenkov signal generated is proportional to deposited dose, however, it is affected by attenuation from the intrinsic tissue optical properties of the patient, which in breast, ranges from primarily adipose to fibroglandular tissue. Patients being treated with whole-breast X-ray radiotherapy (n = 13) were imaged for 108 total fractions, to establish correction factors from the linear relationships between Cherenkov light and CT number (HU). This study elucidates this relationship in vivo, and a correction factor approach is used to scale each image to improve the linear correlation between Cherenkov emission intensity and dose (R_{6X}^2 = 0.85,,R_{10X}^2 = 0.95). This study provides a major step towards direct quantitative radiation dose imaging in humans by utilizing non-contact camera sensing of Cherenkov emission during the radiation therapy treatment.

Theia: an advanced optical neutrino detector

New developments in liquid scintillators, high-efficiency, fast photon detectors, and chromatic photon sorting have opened up the possibility for building a large-scale detector that can discriminate between Cherenkov and scintillation signals. Such a detector could reconstruct particle direction and species using Cherenkov light while also having the excellent energy resolution and low threshold of a scintillator detector. Situated deep underground, and utilizing new techniques in computing and reconstruction, this detector could achieve unprecedented levels of background rejection, enabling a rich physics program spanning topics in nuclear, high-energy, and astrophysics, and across a dynamic range from hundreds of keV to many GeV. The scientific program would include observations of low- and high-energy solar neutrinos, determination of neutrino mass ordering and measurement of the neutrino CP-violating phase delta , observations of diffuse supernova neutrinos and neutrinos from a supernova burst, sensitive searches for nucleon decay and, ultimately, a search for neutrinoless double beta decay, with sensitivity reaching the normal ordering regime of neutrino mass phase space. This paper describes Theia, a detector design that incorporates these new technologies in a practical and affordable way to accomplish the science goals described above.

ZICOS - A new project for neutrinoless double beta decay using Zirconium complex in organic liquid scintillator

A liquid scintillator containing 96Zr has been developed for ZICOS experiment. We will use 180 tons of liquid scintillator with 64 % photo coverage of 20 inch photomultiplier. In order to reach the sensitivity [math] ≥ 1027 years, we have to achieve 50 % enrichment of 96 Zr and reduce 95 % of 208Tl decay backgrounds. Using Monte Carlo simulation, we could reduce 93 % of 208Tl background with 78 % efficiency for 0νββ signal using difference of Cherenkov hit pattern. For the separation of Cherenkov and scintillation signals, we measured the timing pulse shape of Zr loaded liquid scintillator using FADC digitizer, and we found an inconsistent pulse shape at the rising time with the template of scintillation. Also the event rate with an inconsistent pulse shape seems to have a directionality.

Cosmic tau neutrino detection via Cherenkov signals from air showers from Earth-emerging taus.

We perform a new, detailed calculation of the flux and energy spectrum of Earth-emerging τ-leptons generated from the interactions of tau neutrinos and antineutrinos in the Earth. A layered model of the Earth is used to describe the variable density profile of the Earth. Different assumptions regarding the neutrino charged- and neutral-current cross sections as well as the τ-lepton energy loss models are used to quantify their contributions to the systematic uncertainty. A baseline simulation is then used to generate the optical Cherenkov signal from upward-moving extensive air showers generated by the τ-lepton decay in the atmosphere, applicable to a range of space-based instruments. We use this simulation to determine the neutrino sensitivity for E ν ≳ 10 PeV for a space-based experiment with performance similar to that for the Probe of Extreme Multi-Messenger Astrophysics (POEMMA) mission currently under study.

Assembly and validation of SiPM optical modules for the SCT Medium Size Telescope proposed for the CTA observatory

Silicon Photomultipliers are particularly suitable as optical units of Imaging Air Cherenkov Telescopes to detect the fast and low-intensity Cherenkov signal emitted by high energy atmospheric showers. The third generation of high density NUV SiPMs (NUV-HD3) produced by Fondazione Bruno Kessler (FBK) in collaboration with INFN have been used to equip optical modules intended to be integrated on a possible upgrade of the focal plane camera of the Schwarzschild-Couder Telescope prototype (pSCT) in the framework of the Cherenkov Telescope Array (CTA) project. NUV-HD3 SiPMs are 6 × 6 mm2 devices based on 40 × 40 μm2 microcells with excellent photo detection efficiency for the NUV wavelengths. Optical modules, each composed of a matrix of 4 × 4 SiPMs, have been assembled and tested in the laboratories of INFN to be integrated on the pSCT camera. In this contribution we report on the development and on the assembly of the optical modules, on their validation and on their integration on the pSCT camera.

Assessment of imaging Cherenkov and scintillation signals in head and neck radiotherapy

The goal of this study was to test the utility of time-gated optical imaging of head and neck (HN) radiotherapy treatments to measure surface dosimetry in real-time and inform possible interfraction replanning decisions. The benefit of both Cherenkov and scintillator imaging in HN treatments is direct daily feedback on dose, with no change to the clinical workflow. Emission from treatment materials was characterized by measuring radioluminescence spectra during irradiation and comparing emission intensities relative to Cherenkov emission produced in phantoms and scintillation from small plastic targets. HN treatment plans were delivered to a phantom with bolus and mask present to measure impact on signal quality. Interfraction superficial tumor reduction was simulated on a HN phantom, and cumulative Cherenkov images were analyzed in the region of interest (ROI). HN human patient treatment was imaged through the mask and compared with the dose distribution calculated by the treatment planning system. The relative intensity of radioluminescence from the mask was found to be within 30% of the Cherenkov emission intensity from tissue-colored clay. A strong linear relationship between normalized cumulative Cherenkov intensity and tumor size was established (). The presence of a mask above a scintillator ROI was found to decrease mean pixel intensity by >40% and increase distribution spread. Cherenkov imaging through mask material is shown to have potential for surface field verification and tracking of superficial anatomy changes between treatment fractions. Imaging of scintillating targets provides a direct imaging of surface dose on the patient and through transparent bolus material. The first imaging of a patient receiving HN radiotherapy was achieved with a signal map which qualitatively matches the surface dose plan.

Geometrical constraints of observing very high energy Earth-skimming neutrinos from space

The detection of very-high-energy (VHE) neutrinos (Eν ≳ 10 PeV) is a challenge that future generations of experiments are being designed and constructed to address. One promising method relies on using the Earth as a neutrino target for indirect detection of skimming tau neutrinos interacting within the Earth and producing tau leptons that are able to escape and decay in the atmosphere. The tau decay produces upward-moving Extensive Air Showers (EASs). A space-based or suborbital instrument observing the ground near the Earth limb can search for the beamed Cherenkov signal produced by the up-going EAS resulting from the tau-lepton decay. In this paper, we derive the geometrical constraints for such an observation in general and for the specific case of the Probe Of Extreme Multi-Messenger Astrophysics (POEMMA) mission currently under study, focusing on the Cherenkov signal detection. We show that, using reasonable orbital parameters, POEMMA can achieve full-sky coverage to search for potential neutrino sources over the length of its mission. We also show that follow-up of a transient Target-of-Opportunity (ToO), such as a flaring source, can be achieved within an orbit time scale depending on the source location on the celestial sphere and its relative position with respect to the Sun and the Moon.

High-frequency SiPM readout advances measured coincidence time resolution limits in TOF-PET

Scintillator based radiation detectors readout by SiPMs successively break records in their reached time resolution. Nevertheless, new challenges in time of flight positron emission tomography (TOF-PET) and high energy physics are setting unmatched goals in the 10 ps range. Recently it was shown that high frequency (HF) readout of SiPMs significantly improves the measured single photon time resolution (SPTR), allowing to evaluate the intrinsic performance of large area devices; e.g. FBK NUV-HD SiPMs of mm2 area and 40 m single photon avalanche diode (SPAD) size achieve 90 ps FWHM. In TOF-PET such readout allows to lower the leading edge detection threshold, so that the fastest photons produced in the crystal can be utilized. This is of utmost importance if a high SPTR and prompt Cherenkov light generated by the hot-recoil electron upon 511 keV photo-absorption should improve timing. This paper shows that high-frequency bipolar transistor readout of state-of-the-art SiPMs coupled to high-performance scintillators can substantially improve the best achievable coincidence time resolution (CTR) in TOF-PET. In this context a CTR of 158 3 ps FWHM with mm3 BGO crystals coupled to FBK SiPMs is achieved. This faint Cherenkov signal is as well present in standard LSO scintillators, which together with low SPTR values (<90 ps FWHM) improves the CTR of mm3 LSO:Ce:Ca coupled to FBK NUV-HD mm2 with 25 m SPAD size to 61 2 ps FWHM using HF-electronics, as compared to 73 2 ps when readout by the NINO front-end ASIC. When coupling the LSO:Ce:Ca crystals to FBK NUV-HD SiPMs of mm2 and 40 m SPAD size, using HF-electronics, a CTR of even 58 3 ps for mm3 and 98 3 ps for mm3 is achieved. This new experimental data will allow to further discuss the timing limits in scintillator-based detectors.

Analysis of runaway electron expulsion during tokamak instabilities detected by a single-channel Cherenkov probe in FTU

The expulsion of runaway electrons (REs) during different types of tokamak instabilities is analysed by means of a Cherenkov probe inserted into the scrape-off layer of the FTU tokamak. One such type of instability, the well-known tearing mode, is involved in disruptive plasma termination events, during which the risk of RE avalanche multiplication is highest. The second type, known as anomalous Doppler instability, influences RE dynamics by enhancing pitch angle scattering. Three scenarios are analysed here, characterised by different RE generation rates and mechanisms. The main conclusions are drawn from correlations between the Cherenkov probe and other diagnostics. In particular, the Cherenkov probe permits the detection of fast electron expulsion with a high level of detail, presenting peaks with 100% signal contrast during tearing mode growth and rotation, and sub-peak structures reflecting the interplay between the magnetic island formed by the tearing mode, RE diffusion during island rotation and the geometry of obstacles in the vessel. Correlations between the Cherenkov signal, hard x-ray emission and electron cyclotron emission reveal the impulsive development of the anomalous Doppler instability with instability rise time in the microsecond scale resolved by the high time-resolution of the Cherenkov probe.

An algorithmic approach to single-probe Cherenkov removal in pulsed x-ray beams.

The removal of Cherenkov light in an optical dosimetry system is an important process to ensure accurate dosimetry without compromising spatial resolution. Many solutions have been presented in the literature, each with advantages and disadvantages. We present a methodology to remove Cherenkov light from a scintillator fiber optic dosimeter in a pulsed megavoltage x-ray beam using the temporal waveform across the pulse. A sample waveform of Cherenkov light can be measured by exposing only the fiber to the beam. By assuming that the Cherenkov waveform closely matches the intensity of incident radiation, this waveform can be convoluted with the instantaneous scintillation response function to generate an expected scintillation signal. By finding the least-squares fit between these two functions and the experimental data, the estimated Cherenkov contribution can be subtracted off the net signal. This can be applied for arbitrarily complex Cherenkov waveforms (within the 2ns timing resolution of the data acquisition), and in fact, the results suggest more fluctuations in the waveforms provide a better fit to data. Four beam profiles for different field sizes and energies were found with this method. They closely matched references data measured with ionization chamber with average differences across the beam no more than 4%. Noisy waveforms are assumed to be the primary cause of differences between the analyzed scintillator and IC results. We propose methods for improving the results and optimizing the data acquisition and analysis processes. These results demonstrate that it is possible and effective with a single probe to use function fitting of expected data to experimental to remove a complicated Cherenkov signal from the net light signal in pulsed-beam optical dosimetry.

Detecting Cherenkov light from 1–2 MeV electrons in linear alkylbenzene

The FlatDot detector has been used to demonstrate the separation of Cherenkov and scintillation light for 1 to 2 MeV electrons in linear alkylbenzene (LAB). With an average PMT transit time spread (TTS) of 200 ps, the early light in each event is clearly dominated by the Cherenkov signal, which on average comprises 86+2−3% of the light collected in the first 4.1 ns of each event. The spatial distributions of the Cherenkov and scintillation light are found to match those predicted in Monte Carlo simulations. This is a key step towards demonstrating direction reconstruction of β decays, a technique that could reduce 8B solar neutrino backgrounds for neutrinoless double-beta decay experiments in liquid scintillator.

The relevance of fluorescence radiation in Cherenkov telescopes

Cherenkov telescopes are also sensitive to the atmospheric fluorescence produced by the extensive air showers. However this contribution is neglected by the reconstruction algorithms of imaging air Cherenkov telescopes IACTs and wide-angle Cherenkov detectors WACDs. In this paper we evaluate the fluorescence contamination in the Cherenkov signals from MC simulations in both kinds of Cherenkov telescopes and for some typical observational situations. Results for an observation level of 2200 m a.s.l. are shown. In addition, the feasibility and capabilities of IACTs working as fluorescence telescopes are discussed with the assistance of some geometrical calculations.

POEMMA: Probe Of Extreme Multi-Messenger Astrophysics

Developed as a NASA Astrophysics Probe mission concept study, the Probe Of Extreme Multi-Messenger Astrophysics (POEMMA) science goals are to identify the sources of ultra-high energy cosmic rays (UHECRs) and to observe cosmic neutrinos above 20 PeV. POEMMA consists of two satellites flying in loose formation at 525 km altitudes. A novel focal plane design is optimized to observe the UV air fluorescence signal from extensive air showers (EASs) in a stereoscopic UHECR observation mode and the Cherenkov signals from EASs from UHECRs and neutrino-induced τ-leptons in an Earth-limb viewing mode. POEMMA is designed to achieve full-sky coverage and significantly higher sensitivity to the highest energy cosmic messengers compared to what have been achieved so far by ground-based experiments. POEMMA will measure the spectrum, composition, and full sky distribution of the UHECRs above 30 EeV to identify the most energetic cosmic accelerators in the universe and study the acceleration mechanism(s). POEMMA will also have sensitivity to cosmic neutrinos by observing the upward-moving air showers induced from tau neutrino interactions in the Earth. POEMMA will also be able to re-orient to a Target-of-Opportunity (ToO) neutrino mode to view transient astrophysical sources with unique sensitivity. This paper discusses the science goals, instrument design, mission profile, and the simulated UHECR and neutrino measurement capabilities for POEMMA.

Dual-readout fibre-sampling calorimetry with SiPM light sensors

In this paper we present the most significant testbeam results of a dual-readout fibre calorimeter module equipped with silicon photomultipliers (SiPMs) to sense the scintillation and Cherenkov light signals. The main challenges of this detector are the minimization of the optical crosstalk between the two signals and the potential saturation of the digital SiPM-based readout. Both topics have been investigated with encouraging results. As a by-product of this extremely granular readout, the lateral profile of electromagnetic showers was sampled with an unprecedented precision close to the shower axis and significant differences were observed between the scintillating and Cherenkov signals.

An analog-to-digital converter and intelligent controller for use in a DAQ system processing PMT signals from very high energy astrophysics experiments

Abstract Modern instrumentation for very high energy gamma-ray astronomy and astrophysics requires efficient and precise digitization of PMT signals from Cherenkov light generated by incoming cosmic ray particles over the energy range from hundreds of GeV up to several hundred TeV. This dynamic range of more than 1000 is coupled with a requirement for very low noise operation. We have developed modern multi-channel analog-to-digital converters (model BPA-8) together with a data acquisition system, managed with an intelligent crate-controller (model K-167) which controls the measurement modules. The electronics described in this paper is accepted to be used to record PMT signals with high precision and efficiency, allowing reliable extraction and precise analysis of Cherenkov signals from high energy gamma-rays emitted by astrophysical objects.

Correcting Cherenkov light attenuation in tissue using spatial frequency domain imaging for quantitative surface dosimetry during whole breast radiation therapy.

.Imaging Cherenkov emission during radiotherapy permits real-time visualization of external beam delivery on superficial tissue. This signal is linear with absorbed dose in homogeneous media, indicating potential for quantitative dosimetry. In humans, the inherent heterogeneity of tissue optical properties (primarily from blood and skin pigment) distorts the linearity between detected Cherenkov signal and absorbed dose. We examine the potential to correct for superficial vasculature using spatial frequency domain imaging (SFDI) to map tissue optical properties for large fields of view. In phantoms, applying intensity corrections to simulate blood vessels improves Cherenkov image (CI) negative contrast by 24% for a vessel 1.9-mm-in diameter. In human trials, SFDI and CI are acquired for women undergoing whole breast radiotherapy. Applied corrections reduce heterogeneity due to vasculature within the sampling limits of the SFDI from a 22% difference as compared to the treatment plan, down to 6% in one region and from 14% down to 4% in another region. The optimal use for this combined imaging system approach is to correct for small heterogeneities such as superficial blood vessels or for interpatient variations in blood/melanin content such that the corrected CI more closely represents the surface dose delivered.