Pile-up Suppression Research Articles

A Flexible and Efficient Approach to Missing Transverse Momentum Reconstruction

Missing transverse momentum is a crucial observable for physics at hadron colliders, being the only constraint on the kinematics of “invisible” objects such as neutrinos and hypothetical dark matter particles. Computing missing transverse momentum at the highest possible precision, particularly in experiments at the energy frontier, can be a challenging procedure due to ambiguities in the distribution of energy and momentum between many reconstructed particle candidates. This paper describes a novel solution for efficiently encoding information required for the computation of missing transverse momentum given arbitrary selection criteria for the constituent reconstructed objects. Pileup suppression using information from both the calorimeter and the inner detector is an integral component of the reconstruction procedure. Energy calibration and systematic variations are naturally supported. Following this strategy, the ATLAS Collaboration has been able to optimise the use of missing transverse momentum in diverse analyses throughout Runs 2 and 3 of the Large Hadron Collider and for future analyses.

La- and La-/Ce-Doped BaF2 Crystals for Future HEP Experiments at the Energy and Intensity Frontiers Part I

In addition to La-doped barium fluoride (BaF2) crystals, La/Ce co-doped BaF2 crystals were also investigated at the California Institute of Technology, Pasadena, CA, USA. Strong cerium-induced emissions peaked at 305 and 320 nm with a decay time of 25 ns were observed, in addition to the fast and slow scintillation at 220 and 300 nm, respectively. The La/Ce co-doping was also found effective in suppressing the slow component in BaF2. Compared to La-doped crystals, the La/Ce co-doped crystals have a better light output in both 50- and 2500-ns gate. The fast/slow ratio of La/Ce co-doped crystal was found to be about 1/1, similar to La-doping, which is also considered not sufficient for pile-up suppression. A 20-cm-long La/Ce co-doped BaF2 crystal shows also excellent optical quality and light response uniformity.

La- and La-/Ce-Doped BaF2 Crystals for Future HEP Experiments at the Energy and Intensity Frontiers Part II

In addition to La-doped barium fluoride (BaF2) crystals, La/Ce co-doped BaF2 crystals were also investigated at the California Institute of Technology, Pasadena, CA, USA. Strong cerium-induced emissions peaked at 305 and 320 nm with a decay time of 25 ns were observed, in addition to the fast and slow scintillation at 220 and 300 nm, respectively. The La/Ce co-doping was also found effective in suppressing the slow component in BaF2. Compared to La-doped crystals, the La/Ce co-doped crystals have a better light output in both 50- and 2500-ns gate. The fast/slow ratio of La/Ce co-doped crystal was found to be about 1/1, similar to La-doping, which is also considered not sufficient for pile-up suppression. A 20-cm-long La/Ce co-doped BaF2 crystal shows also excellent optical quality and light response uniformity.

Upgrade of the ATLAS detectors and trigger for the High Luminosity LHC: Tracking and timing for pile-up suppression

The High Luminosity-Large Hadron Collider is expected to start data-taking in 2026 and to provide an integrated luminosity of 3000 fb −1 , giving a factor 10 more data than that will be collected by 2023. This high statistics will make it possible to perform precise measurements in the Higgs sector and improve searches of new physics at the TeV scale. The peak luminosity is expected to be 7.5 × 10 34 cm −2 s −1 , corresponding to about 200 proton–proton interactions per event (pile-up), which will increase the rates at each level of the trigger and degrade the reconstruction performance. To cope with such a harsh environment many sub-detectors of the ATLAS experiment will be upgraded and some completely substituted. The Trigger-DAQ system will be upgraded. In this talk an overview of two new sub-detectors enabling powerful pile-up suppression, a new Inner Tracker and a High Granularity Timing Detector, will be given, describing the two technologies, their performance, and their interplay. Emphasis will also be given to the possibility of using tracking and timing information at the earliest, hardware based, ATLAS trigger stage. • Pileup suppression techniques for jets reconstruction at HL-LHC. • Tracking and Timing detectors of ATLAS detector at HL-LHC. • Tracking for Trigger at HL-LHC.

Performance of pile-up mitigation techniques for jets in pp collisions with the ATLAS detector

The large rate of multiple simultaneous proton–proton interactions, or pile-up, generated by the Large Hadron Collider in Run 1 required the development of many new techniques to mitigate the adverse effects of these conditions. The methods employed to correct for the impact of pile-up on jet energy, shapes and multiplicity with the ATLAS detector are presented here. They include energy correction techniques based on estimates of the average pile-up energy density and jet-to-vertex association techniques. Extensions of these methods to reduce the impact of pile-up on jet shapes use both subtraction and grooming procedures. Prospects for pile-up suppression at the HL-LHC are also shown.

A low-noise and fast pre-amplifier and readout system for SiPMs

To operate silicon photomultipliers (SiPMs) in a demanding environment with large temperature gradients, different amplifier concepts were characterized by analyzing SiPM pulse-shapes and charge distributions. A fully differential 4-wire SiPM pre-amplifier with separated tracks for the bias voltage and with good common-mode noise suppression was developed and successfully tested. To achieve highest single-pixel resolutions an online after-pulse and pile-up suppression was realized with fast readout electronics based on digital filters.

Development and implementation of optimal filtering in a Virtex FPGA for the upgrade of the ATLAS LAr calorimeter readout

In the context of upgraded read-out systems for the Liquid-Argon Calorimeters of the ATLAS detector, modified front-end, back-end and trigger electronics are foreseen for operation in the high-luminosity phase of the LHC. Accuracy and efficiency of the energy measurement and reliability of pile-up suppression are substantial when processing the detector raw-data in real-time. Several digital filter algorithms are investigated for their performance to extract energies from incoming detector signals and for the needs of the future trigger system. The implementation of fast, resource economizing, parameter driven filter algorithms in a modern Virtex FPGA is presented.

Optimization of 18O measurement using NRA for studies of isotopic content in fossil meteorites

In this work, we discuss the possibility of a new approach to measuring oxygen isotope ratios in fossil meteorite samples, specifically one based on nuclear reaction analysis (NRA). Variations of oxygen ratios within meteoritic chromite grains can help to determine the type of meteorite to which the grains originally belonged. In this work, we have evaluated the possibility to use the reaction 18O(p, α)15N just above the 846keV resonance to estimate the relative oxygen-18 content in a number of test samples. Another technique has to be employed for oxygen-16 measurements. A large area segmented silicon detector is used to detect the produced α particles. Results of the experimental 18O measurements for a number of samples including four extraterrestrial chromite grains are presented and compared with SIMNRA simulations. The advantage of a segmented silicon detector in the form of inherent pile-up suppression can be clearly seen in the current work.

Design of Floating-Boundary Multi-Zone Scintillation Camera With Pileup Prevention and Misplaced Pileup Suppression (MPS)

Image quality in nuclear medicine is a trade-off between image contrast and resolution, since there are conflicting requirements of crystal thickness and collimator-hole dimensions. The sensitivity, or efficiency, which determines the contrast-to-noise ratio, however, is constrained primarily by pulse-mode operation, in which gamma ray interactions are recorded once every deadtime period. Nuclear images also suffer from image blurring due to gamma rays penetrating the collimator septa and due to misplaced pileup events arising from the coincidence detection of Compton-scattered gamma rays. Multi-zone detector architecture (MZDA) and the use of pileup prevention circuitry (PPC) lead to reduction of the detector's effective deadtime, and hence to significant extension of the count-rate range of the camera. This in turn allows the source activity to be increased to make up for sensitivity that will be lost on changing the detector and collimator-hole dimensions to improve spatial resolution. Misplaced pileup suppression (MPS) circuitry, also described in this paper, enables image blurring from Compton-scattered radiation to be reduced to 1/P of its level in a single zone detector, P being the PMT array size. The paper first develops the theoretical relationships relating to the trade-offs between efficiency and resolution, the distribution of scintillation light from interaction points in the crystal, the share of the light exposure of individual PMTs and of clusters of PMTs, and the cross-talk between clusters of PMTs. The paper then presents an outline of the implementation of an S-zone camera with PPC of order 1, based on hexagonal and rectangular arrays of PMTs. A hexagonal array of 331 1.27-cm PMTs, which will have S ap 35 detector-zones on average, can, for instance, use a 1.7-mm thick and 29-cm diameter NaI(Tl) crystal to design a camera with twice the sensitivity of a single-zone camera of the same array size, which will also provide a spatial resolution of 2.1 mm at the collimator face and 3.4 mm at 10 cm from the collimator face.

Pile-up suppression in backscattering spectrometry using particle identification technique

The extra information provided due to the detection of a single event by two detectors is used to eliminate the pile-up background in the conventional backscattering spectra. The simultaneous measurement of the registered particle specific energy loses along with its total energy enables to distinguish the pile-up signals which do not meet the requirements derived from Bethe-Bloch formula. The particle identification technique with on-line operating mathematic processor was used to select undistorted signals. The demonstrative experiment has been performed to show the practically complete elimination of the pile-up background in the wide energy region of the backscattering spectrum.

Elimination of distortions of nuclear energy spectra caused by pulse pile-up

Distortions of nuclear energy spectra at high counting rates have been efficiently reduced by two different signal processing methods: pile-up suppression by pulse shortening and pile-up rejection by detection and rejection of the piled-up pulses. By combining these methods new circuits have been developed increasing the limit for the quality gamma ray spectrometry from available, up to now, 100000 s-1 to the range of up to 500000 s-1.

Noise and pileup suppression by digital signal processing

The accumulation and analysis of spectra from high resolution detectors is difficult in the presence of very high counting rates in the detector and the presence of electronic noise in the system. The usual solutions to these problems are to introduce electronic filters to reduce the noise and to discard the events that are badly distorted due to pileup. This approach is not very efficient, and valuable information is lost in the process. This study is a step in the development of a system that would incorporate digital techniques for correction of pulse distortion due to electronic noise and pulse pileup. The main components of the system are the pulse amplifier, the time trigger, the transient wave form recorder, and a computer. When the detector detects a signal it is amplified and passed to the transient wave form recorder to be put into the digital form for high-speed processing on the computer. Tests of the system show a marked improvement in the resolution of the system.

Trace element analysis by means of particle induced X-ray emission with triggered beam pulsing

Abstract A triggered beam deflection system is described which is of advantage in PIXE analysis. It offers high counting rate capability due to efficient pile-up suppression, strongly reduced target damage, and it does not require dead-time corrections in quantitative analysis.

Influence of the Temperature Dependence of the NaI(Tl) Decay Time Constant on NaI(Tl) Detector Applications

Pulse shape discrimination is used in important NaI(Tl) detector applications, such as, Phoswich applications, particle separation, and pile-up suppression. These applications utilizing only pulse height spectra gated by a PSD window can be compromised by temperature excursions in the detector. We present measurements of the NaI(Tl) decay time constant over the range 0°C - 24°C. A temperature variation of ~5 nsec/°C was measured. The implications of the temperature variation on detector performance are discussed.

One-crystal NaI spectrometer

A total absorption gamma-ray spectrometer has been developed using one large NaI(Tl) crystal (24 cm × 24 cm) surrounded by a plastic scintillator operated in anticoincidence. An energy resolution of 3.6% with a detection efficiency of 24% is achieved for 22 MeV gamma rays. The use of fast electronics for both scintillators makes efficient pileup suppression possible with negligible deadtime even in the presence of high background. The effects produced by changing the collimation of the gamma rays and the detection level of the anticoincidence pulses are investigated.

A pulse shape discriminator for particle separation and pile-up suppression

The double delay-line clipped pulses from a DD2 amplifier show a zero crossover point, which is constant within ≈2×10 −8 sec for a wide range of pulse amplitudes. Changes in the risetime of the input pulses due to different decay times of signals produced by particles with different ionization densities in a scintillation crystal result in a change of the zero crossover time. The same effect will take place due to pile-up of two pulses. The bipolar output pulses of the amplifier are analyzed in two channels: one for the positive going part of the pulses, another for the negative one. In both channels discriminators prevent triggering by suprious pulses. A variable delay of high resolution in the first channel brings the two output pulses to coincidence for a certain risetime of the detector pulses. A Garwin circuit detects the fast coincidence. The resolution of the coincidence is controlled by an output trigger stage, which delivers signals for the gate of a multi-channel analyzer. With (n,p) and (n,α) reactions produced by neutron bombardement of KI(Tl) and NaI(Tl) scintillation crystals, appreciable pulse shape discrimination was obtained. Pulse height spectra showing pulse shape discrimination and pile up suppression as well as the circuit schematics and its detailed description are given.