Positron Identification Research Articles

Identification of positrons and electrons at TeV energy scale using the AMS tracker, time-of-flight counters, and electromagnetic calorimeter

The Alpha Magnetic Spectrometer, AMS, is successfully collecting data since its installation on the International Space Station on May 19, 2011. One of the main AMS objectives is the measurement of cosmic ray positrons and electrons at the highest energies. We present a new technique for the identification of electrons and positrons, which is used in the AMS data analysis in the energy range up to a few TeV. The focus of this article is on the rejection of the proton background using the AMS silicon tracker, the time-of-flight counters, and the electromagnetic calorimeter.

Commissioning and operation of the readout system for the SoLid neutrino detector

The SoLid experiment aims to measure neutrino oscillation at a baseline of 6.4 m from the BR2 nuclear reactor in Belgium. Anti-neutrinos interact via inverse beta decay (IBD), resulting in a positron and neutron signal that are correlated in time and space. The detector operates in a surface building, with modest shielding, and relies on extremely efficient online rejection of backgrounds in order to identify these interactions. A novel detector design has been developed using 12800 5 cm cubes for high segmentation. Each cube is formed of a sandwich of two scintillators, PVT and 6LiF:ZnS(Ag), allowing the detection and identification of positrons and neutrons respectively. The active volume of the detector is an array of cubes measuring 80× 80× 250 cm (corresponding to a fiducial mass of 1.6 T), which is read out in layers using two dimensional arrays of wavelength shifting fibres and silicon photomultipliers, for a total of 3200 readout channels. Signals are recorded with 14 bit resolution, and at 40 MHz sampling frequency, for a total raw data rate of over 2 Tbit/s. In this paper, we describe a novel readout and trigger system built for the experiment, that satisfies requirements on: compactness, low power, high performance, and very low cost per channel. The system uses a combination of high price-performance FPGAs with a gigabit Ethernet based readout system, and its total power consumption is under 1 kW. The use of zero suppression techniques, combined with pulse shape discrimination trigger algorithms to detect neutrons, results in an online data reduction factor of around 10000. The neutron trigger is combined with a large per-channel history time buffer, allowing for unbiased positron detection. The system was commissioned in late 2017, with successful physics data taking established in early 2018.

Method of positron detection using the Earth magnetic field in orbital experiment

The phenomenon of a positron anomaly in cosmic rays at energies above 10 GeV can not be explained within the framework of secondary positron production mechanisms into interstellar media. One possible explanation can be that positron excess is generated by ∼ TeV dark matter particles annihilation or decay. Very high energies are not available for modern magnetic spectrometers because of their small size, but magnetic analysis with geomagnetic field extending for thousands of kilometres can be used. One approach to the high energy positron detection deals with allowed and forbidden trajectories Earth’s magnetic field. It was shown that at the equatorial position of the detector it is possible to separate positrons and electrons using only a position-sensitive electromagnetic calorimeter up to energies ∼ 250 GeV using detector with angular resolution of about 5 degrees. Second approach consists in the joint registration of an electron, or positron, and the synchrotron photons emitted by them into magnetosphere. It is shown that for space born detector at about ∼ 400 km orbit identification of positrons up to tens TeV is possible using synchrotron radiation detector and imaging calorimeter.

Observation of ortho-positronium formation in Double Chooz

The aim of the Double Chooz experiment is to measure the neutrino mixing angle θ13 by detecting the reactor electron anti-neutrino via inverse beta decay. The positron-neutron delayed coincidence yields a sizeable background suppression; a further contribution might come from the development of techniques for an efficient identification of positrons. Pulse shape discrimination, a well-established technique for background rejection in liquid scintillator detectors, fails in separating positrons from electrons, as they give rise to identical light pulses. However, in some cases the positron decay is delayed by the formation of a positron-electron metastable bound state, called ortho-positronium (o-Ps), which introduces a delay between the light signal from the positron energy deposition in the scintillator and the one from the annihilation gammas. The consequent deformation in the positron-induced light pulse can be exploited to identify positrons with the pulse shape discrimination, as already successfully done statistically in Borexino.In Double Chooz, we performed the first o-Ps formation tagging on an event-by-event basis. We also measured the o-Ps formation probability and its lifetime, finding (44 ± 13)% and (3.68 ± 0.23) ns respectively. These values are in good agreement with independent measurements obtained with a dedicated setup.

Ortho-positronium observation in the Double Chooz experiment

The Double Chooz experiment measures the neutrino mixing angle θ 13 by detecting reactor $$ {\overline{\nu}}_e $$ via inverse beta decay. The positron-neutron space and time coincidence allows for a sizable background rejection, nonetheless liquid scintillator detectors would profit from a positron/electron discrimination, if feasible in large detector, to suppress the remaining background. Standard particle identification, based on particle dependent time profile of photon emission in liquid scintillator, can not be used given the identical mass of the two particles. However, the positron annihilation is sometimes delayed by the ortho-positronium (o-Ps) metastable state formation, which induces a pulse shape distortion that could be used for positron identification. In this paper we report on the first observation of positronium formation in a large liquid scintillator detector based on pulse shape analysis of single events. The o-Ps formation fraction and its lifetime were measured, finding the values of 44 % ±12 % (sys.) ±5 % (stat.) and 3.68 ns ±0.17 ns (sys.) ±0.15 ns (stat.) respectively, in agreement with the results obtained with a dedicated positron annihilation lifetime spectroscopy setup.

ϕ(1020) and ω(782) Mesons from Dielectron Decays at STAR

The measurement of masses, widths, transverse momentum spectrum, and yields of ϕ → e + e − at mid-rapidity ( | y | < 1 ) from STAR experiment in Au + Au collisions at s N N = 200 GeV are presented and compared to the ϕ meson result from the hadronic decay channel. The ω → e + e − spectrum is also presented. Particle identification based on the STAR Time-of-Flight (TOF) detector upgrade in conjunction with ionization energy-loss (dE/dx) measurements from the Time Projection Chamber (TPC) is used for a clean electron and positron identification.

Operation of the AMS-02 TRD in Space

The AMS-02 detector was installed on May 2011 on the International Space Station and has since collected billions of cosmic ray events. AMS will measure with unprecedent precision cosmic ray spectra up to the TeV energy scale, achieving a sensitivity to the presence of anti-nuclei of one part in a billion, as well as providing important information on the origin of dark matter. A Transition Radiation Detector (TRD), filled with a Xe/CO2 mixture, is used to reach the sensitivity to positron identification needed for the detection of a neutralino dark matter candidate. The control of a gaseous detector in Space is a challenging task. The operational procedures, and the performances achieved, will be described.

Leptonic decay of $\phi$(1020) meson measured with the STAR experiment

We present the measurement of the $\phi$(1020)$\rightarrow e^{+}e^{-}$ transverse momentum spectrum and yield for $0.3 < p_{T} < 2.5$ GeV at mid-rapidity ($|y| < 1$) from the STAR experiment in Au+Au collisions at $\sqrt{s_{_{NN}}} = 200$ GeV and compare it to the yield and spectrum from the hadronic decays. We also compare the $\phi$(1020) mass and width obtained by fitting Breit-Wigner function to simulated values. Particle identification based on the newly installed STAR Time-Of-Flight (TOF) detector in conjunction with energy-loss (dE/dx) based particle identification measurements from the Time Projection Chamber (TPC) are used for a clean electron and positron identification.

Design concept and modeling of a new Positron Identification by Coincident Annihilation Photons (PICAP) system

The Positron Identification by Coincident Annihilation Photons (PICAP) system is a new design concept to measure moderate energy (∼few MeV) positrons and negatrons in space. Positron measurements in this energy range would open a window on cosmic ray propagation in the Galaxy, Solar modulation of cosmic rays (particularly charge-sign effects) and Solar energetic particles. Electrons of both charge signs are first identified by the conventional d E/d x versus residual energy technique. Coincident 511 keV annihilation photons are used to identify stopping positrons. This technique is far simpler than magnet spectrometers, which require elaborate tracking systems and associated electronics. We present a baseline design and Monte-Carlo modeling results using EGS4. We estimate the baseline instrument would mass ∼4 kg and use ∼3 W of power making such an instrument highly attractive for resource-constrained space missions.

Cosmic-Ray Positron Identification through Bremsstrahlung Conversion

The main challenge of cosmic-ray positron measurements is the suppression of the vast proton background. An approach to the positron identification which is based on the reconstruction of pair production by bremsstrahlung photons is presented. It has been applied to data taken by the AMS-01 experiment and yields a proton rejection of more than 10 5 , allowing to extend the positron sensitivity limit of the experiment from 3 GeV to 50 GeV.

Study of the combined particle identification capability of a transition radiation detector and a silicon imaging calorimeter during the TS93 balloon flight

Abstract The WiZard Collaboration is involved in a program studying the antimatter components of the cosmic rays. A transition radiation detector and a silicon-tungsten calorimeter with imaging capabilities have been built as part of this program. We present the combined performance of these two detectors for positron identification during a balloon flight on September 8, 1993. The flight was dedicated to the measurement of the positron spectrum in the energy range 4–50 GeV and was launched from Ft. Summer, New Mexico.

Positron identification by TRDs in TS93 and PAMELA experiments

We are involved in a program to study the antimatter components of the cosmic rays in outer space. We present the performances of a transition radiation detector we have built for positron identification during a balloon flight in 1993. The flight (TS93) was dedicated to the measurement of the positron spectrum in the energy range 4–50 Gev . We present also the design and expected performances of a similar detector we intend to build for a future experiment (PAMELA), to be run on a satellite by the end of 1999, in order to complete this program with higher statistics and at higher energies, namely about 200 GeV.

A transition radiation detector for positron identification in a balloon-borne particle astrophysics experiment

We have built and tested a transition radiation detector of about 76 × 80 cm 2 active surface to discriminate positrons from protons in an experiment performed on a balloon flight to search for primordial antimatter. The TRD is made of ten modules each consisting of a carbon fiber radiator followed by a multiwire proportional chamber. In order to achieve a proton-electron rejection factor of the order of 10 −3 with a strict limitation on power consumption to about 40 mW per chamber channel, as required by experimental constraints, we have developed a low power consumption “cluster counting” electronics. Different analysis procedures of calibration data are shown. In addition, comparisons of the performances of this detector are also made with a previous similar prototype equipped with standard fast electronics and similar detectors from other authors.

A neural network for positron identification by transition radiation detector

A neural network algorithm has been applied in order to distinguish positrons from protons by a transition radiation detector (TRD). New variables are introduced, that simultaneously take into account spatial and energy TRD information. This method is found to be better than the one based on classical analysis: the results improve the detector performance in particle identification for efficiency higher than 90%. The high accuracy achieved with this method is used to identify positrons versus protons with 3 × 10 −3 contamination, as required by TRAMP-SI cosmic ray space experiment on the NASA Balloon-Borne Magnet Facility.

An identification method of positron production in laser beam interaction with targets

A simple electromagnetic transport system was constructed to identify very rare positrons produced in a powerful laser beam interaction with a target. Testing experiments were carried out with CO2-laser (1012 W/cm2) beam pulses (τ=50 ns,f=0.01 Hz) focused on the copper target, as well as with a 96 MeV alpha-particle beam irradiated carbon target. The results showed that the developed system could be effectively used for positron identification and evaluation of their energy by means of a time-of-flight method. The computerized system to deal with this problem, together with others related to the power laser beam interaction with targets, has been constructed.