Threshold Scan Research Articles

Study of the Fake Hit Effect Observed During the Charge Threshold Scan Procedure of the ALICE Pixel Detector

Study of the Fake Hit Effect Observed During the Charge Threshold Scan Procedure of the ALICE Pixel Detector

Prospects for ditauonium discovery at colliders

The feasibility of observing ditauonium, the bound state of two tau leptons, at e+e− colliders (BES III at s=3.78 GeV, Belle II at s=10.6 GeV, a future super tau-charm factory (STCF) at s≈2mτ, and the FCC-ee at s=91.2 GeV) as well as in hadronic and photon-photon collisions at the LHC, is studied. Cross sections and expected yields for spin-0 para- (T0) and spin-1 ortho- (T1) ditauonium are presented for nine different production and decay processes. Para-ditauonium can be observed at the FCC-ee via photon fusion in its diphoton decay (γγ→T0→γγ). Ortho-ditauonium can be observed at STCF via e+e−→T1→μ+μ−, where a threshold scan with monochromatized beams can also provide a very precise extraction of the tau lepton mass with O(25 keV) uncertainty. Observing pp →T1(μ+μ−)+X at the LHC is possible by identifying its displaced vertex with a good control of the combinatorial dimuon background. In addition, we compute the rare decay branching fractions of ditauonium into quarkonium plus a photon.

LHCb VELO fast calibration

During the long shutdown 2 of the LHC, the LHCb Experiment was upgraded to a trigger-less system reading out the full detector at 40 MHz bunch crossing rate with all selection algorithms executed in a CPU farm. The upgraded Vertex Locator (VELO) of the LHCb is a hybrid pixel detector read out by the “VeloPix” front-end ASIC with on-chip zero-suppression. This paper describes a novel way of calibrating the VELO detector based on dedicated threshold scan firmware. The firmware is implemented in the control and data acquisition back-end boards of the detector. This threshold scan method has multiple advantages compared with the default one: it is faster as the algorithm was moved from software to firmware, it is more deterministic by minimizing software interruptions and data transfer and it is more precise by reducing noise due to ASIC operation.

Readout chip with RISC-V microprocessor for hybrid pixel detectors

Hybrid single-photon counting pixel detectors have recently been widely used for X-ray and ionizing particle detection in medicine, high-energy physics, and material science. Many different chips have been developed for the readout of the semiconductor pixel sensor. Typically, developed ASICs have very limited digital logic and do not provide substantial data processing. In this paper, we present the readout chip that integrates the readout channels matrix with a RISC-V-based microprocessor SoC. The designed device has been prototyped in an FPGA and sent to production in a CMOS 40 nm process. Integration of a pixel matrix with the RISC-V-based central processing unit significantly improved the detector functionality. It enabled the device to work independently without external assistive device usage and execute many algorithms, e.g., calibration, threshold scanning, and data filtering, on-chip. Communication between the CPU and the pixel matrix was carried out through the dedicated Pixel Matrix Controller with the CPU standard I/O operations usage. This specialized peripheral consists of a coprocessor responsible for precise matrix control, a data converter for data conversion acceleration, and control and status registers connected to the core data bus. Many algorithms have been developed and tested, one of which is the intelligent real-time filtering of regions of interest.

The collider landscape: which collider for establishing the SM instability?

Capabilities of future colliders are usually discussed assuming specific hypothetical new physics. We consider the opposite possibility: that no new physics is accessible, and we want to learn if the unnatural Standard Model is part of a vast landscape. We argue that a main step in this direction would be establishing the possible instability scale of the Higgs potential. This primarily needs reducing the uncertainty on the strong coupling and on the top quark mass. We show that the top quark mass can be measured well enough via a toverline{t} threshold scan with low 1033 cm−2sec−1 luminosity, that seems achievable at a ‘small’ e+e− collider in the LEP tunnel, or at a muon collider demonstrator.

Top-quark mass determination in the optimised threshold scan

One of the important goals at the future e^++e^-− colliders is to measure the top-quark mass and width in a scan of the pair production threshold. Presented in this work is the most general approach to the top-quark mass determination from the threshold scan at CLIC, with all relevant model parameters and selected systematic uncertainties included in the fit procedure. In the baseline scan scenario the top-quark mass can be extracted with precision of the order of 30 to 40,MeV, already for 100 fb^{-1}−1 of data collected at the threshold. We present the optimisation procedure based on the genetic algorithm with which the statistical uncertainty of the mass measurement can be reduced by about 20%.

Evaluation of the DECAL Fully Depleted monolithic sensor for outer tracking and digital calorimetry

The DECAL sensor is a depleted monolithic active pixel sensor (DMAPS) being developed to explore technological solutions for digital electromagnetic calorimeters. For this application, the number of pixels above threshold is used to estimate the shower energy and therefore the pixel size is required to be sufficiently small to avoid hit saturation. The DECAL and DECAL Fully Depleted (FD) sensors have been designed and fabricated in the TowerJazz 180 nm CMOS standard and modified imaging processes, respectively. The latter uses modifications to the implant configuration that improve charge collection and radiation hardness, including to the levels required for barrel ECAL regions of FCC-hh (few 1015 neq/cm2). Both DECAL variants feature a matrix of 64 × 64 pixels with a pitch of 55μm, read out every 25 ns. For DECAL FD, the logic has been modified to extend the in-pixel comparator threshold trim range from five to six bits, with the sixth bit used to de-activate the comparator. Characterisation results for the DECAL FD, including the pixel equalisation matrix, threshold scans testing under monochromatic X-rays and 90Sr source, are presented.

EEG-fMRI: Ballistocardiogram Artifact Reduction by Surrogate Method for Improved Source Localization.

For the analysis of simultaneous EEG-fMRI recordings, it is vital to use effective artifact removal tools. This applies in particular to the ballistocardiogram (BCG) artifact which is difficult to remove without distorting signals of interest related to brain activity. Here, we documented the use of surrogate source models to separate the artifact-related signals from brain signals with minimal distortion of the brain activity of interest. The artifact topographies used for surrogate separation were created automatically using principal components analysis (PCA-S) or by manual selection of artifact components utilizing independent components analysis (ICA-S). Using real resting-state data from 55 subjects superimposed with simulated auditory evoked potentials (AEP), both approaches were compared with three established BCG artifact removal methods: Blind Source Separation (BSS), Optimal Basis Set (OBS), and a mixture of both (OBS-ICA). Each method was evaluated for its applicability for ERP and source analysis using the following criteria: the number of events surviving artifact threshold scans, signal-to-noise ratio (SNR), error of source localization, and signal variance explained by the dipolar model. Using these criteria, PCA-S and ICA-S fared best overall, with highly significant differences to the established methods, especially in source localization. The PCA-S approach was also applied to a single subject Berger experiment performed in the MRI scanner. Overall, the removal of BCG artifacts by the surrogate methods provides a substantial improvement for the analysis of simultaneous EEG-fMRI data compared to the established methods.

A special Higgs challenge: measuring the mass and production cross section with ultimate precision at FCC-ee

The FCC-ee offers powerful opportunities to determine the Higgs boson parameters, exploiting over 10^6{ hbox {e}^+hbox {e}^- rightarrow hbox {ZH}} events and almost 10^5{ hbox {WW} rightarrow hbox {H}} events at centre-of-mass energies around 240 and 365 GeV. This essay spotlights the important measurements of the ZH production cross section and of the Higgs boson mass. The measurement of the total ZH cross section is an essential input to the absolute determination of the HZZ coupling—a “standard candle” that can be used by all other measurements, including those made at hadron colliders—at the per-mil level. A combination of the measured cross sections at the two different centre-of-mass energies further provides the first evidence for the trilinear Higgs self-coupling, and possibly its first observation if the cross section measurement can be made accurate enough. The determination of the Higgs boson mass with a precision significantly better than the Higgs boson width (4.1 MeV in the standard model) is a prerequisite to either constrain or measure the electron Yukawa coupling via direct { hbox {e}^+hbox {e}^- rightarrow hbox {H}} production at sqrt{s} = 125 GeV. Approaching the statistical limit of 0.1% and {mathcal {O}}(1) MeV on the ZH cross section and the Higgs boson mass, respectively, sets highly demanding requirements on accelerator operation (ZH threshold scan, centre-of-mass energy measurement), detector design (lepton momentum resolution, hadronic final state reconstruction performance), theoretical calculations, and analysis techniques (efficiency and purity optimization with modern tools, constrained kinematic fits, control of systematic uncertainties). These challenges are examined in turn in this essay

Measurements of charge sharing in a hybrid pixel photon counting CdTe detector

Hybrid pixel radiation detectors working in a single-photon counting mode have gained increasing attention due to their noiseless imaging and high dynamic range. Due to the fact that sensors of different materials can be attached to the readout circuit, they allow operation with a wide range of photon energies. The performance of the single photon counting detectors is limited by pile-up. To allow a detector to work under high flux conditions, the pixel size is reduced, which minimizes detector dead time. However, with smaller pixel sizes the charge sharing effect, a phenomenon that deteriorates both detection efficiency and spatial resolution is more profound.The influence of charge sharing on the detector performance can be quantified using parameterization of the s-curve obtained in the spectral response measurements. The article presents the measurements of the response function of a hybrid pixelated photon counting detector for certain primary energy, which corresponds to the probability of detecting a photon as a function of its energy deposition. The measurements were carried out using an X-ray tube by performing a threshold scan during illumination with X-ray photons of a 1.5 mm and 0.75 mm thick CdTe detector with 100 µm pixel pitch. The charge size cloud depends on the sensor material, the bias voltage, and the sensor thickness. Therefore, the experimental data from a sensor biased with different bias voltages are compared to the theoretical results based on a cascaded model of a single-photon counting segmented silicon detector. The study of the charge sharing influence on the spatial resolution of the CdTe detector will serve for a further study of the possible implementations of the algorithms achieving subpixel resolution, in which the charge sharing becomes the desired effect since the charge division in the pixels is used to interpolate the photon interaction position.

The Study of Calibration for the Hybrid Pixel Detector With Single Photon Counting in HEPS-BPIX

The calibration process for a hybrid pixel detector designed for the High Energy Photon Source in China, called HEPS-BPIX, is presented in this article. The relationship between the energy and threshold is quantified for the threshold calibration based on a threshold scanning. For threshold trimming, a precise algorithm based on local digital to analog converter (LDAC) characteristics and a fast algorithm based on LDAC scanning are proposed in this article to study the performance of threshold digital to analog converters (DACs) that will be applied to pixels. The threshold dispersion was reduced from 46.28 mV without the algorithm to 6.78 mV with the precise algorithm, whereas it was 7.61 mV with the fast algorithm. For temperatures from 5 °C to 60 °C, the threshold dispersion of the precise algorithm varies in the range of 5.69 mV. In contrast, it is 33.21 mV with the fast algorithm, which can be recorrected to 1.49 mV. The measurement results show that the fast algorithm could obtain the applicable threshold dispersion for a silicon pixel module and took less time. In comparison, the precise algorithm could obtain better threshold dispersion but was time-consuming. The temperature dependence of the silicon pixel module noise was also studied to assess the detector working status. The minimum detectable energy threshold could be reduced to 0.83-4.36 keV at a temperature of 5 °C.

Optimising top-quark threshold scan at CLIC using genetic algorithm

One of the important goals at the future e+e− colliders is to measure the top-quark mass and width in a scan of the pair production threshold. However, the shape of the pair-production cross section at the threshold depends also on other model parameters, as the top Yukawa coupling, and the measurement is a subject to many systematic uncertainties. Presented in this work is the study of the top-quark mass determination from the threshold scan at CLIC. The most general approach is used with all relevant model parameters and selected systematic uncertainties included in the fit procedure. Expected constraints from other measurements are also taken into account. It is demonstrated that the top-quark mass can be extracted with precision of the order of 30 to 40 MeV, including considered systematic uncertainties, already for 100 fb−1 of data collected at the threshold. Additional improvement is possible, if the running scenario is optimised. With the optimisation procedure based on the genetic algorithm the statistical uncertainty of the mass measurement can be reduced by about 20%. Influence of the collider luminosity spectra on the expected precision of the measurement is also studied.

A reconfigurable CMOS sensor for tracking, pre-shower and digital electromagnetic calorimetry

Recent advances in CMOS imaging sensor technology have led to designs able to withstand much higher radiation levels, up to those required at hadron colliders for all but the innermost layers. Also, with stitching, wafer scale devices have been fabricated on the same process as used for the prototypes described in this submission, for applications such as, for example, direct electron detection in transmission electron microscopy. A small sensor prototype has been designed and fabricated in the TowerJazz 180 nm CMOS imaging process. The prototype has a pixel matrix of 64x64 pixels with a pitch of 55 x 55μm and reads out using fast logic at 40 MHz. Each pixel contains four collection electrodes, trimming logic, pre-amplifier, shaper and discriminator with digital output. It can be reconfigured to function as either a binary short strip sensor, for particle tracking including as a pre-shower, or as a pad sensor, counting the number of pixels above threshold for digital calorimetry. As well as providing a seamless transition from outer tracking to EM calorimetry, for optimal use of particle flow algorithms, digital calorimetry also can give excellent energy resolution. This concept is proposed as a possible option for future digital calorimeters able to read-out at LHC collision rates with good radiation hardness and realisable in low cost commercial technologies for equipping large areas. Results on physics performance simulation in a FCC-hh context and the characterisation of the prototype sensor are presented. The summing logic is demonstrated and the analogue pixel performance is validated by illuminating a test pixel within the matrix with a laser of wavelength of 1064 nm. The absolute laser intensity is calibrated such that the injected charge is similar to that expected for a minimum ionising particle. The measured pre-amplifier and shaper signals are compared to Cadence simulations. Laser illuminations in the digital pixel area and the response measured using a threshold scan confirm successful digital functionality in strip and pad operation modes.

Data-taking strategy for the precise measurement of the W boson mass with a threshold scan at circular electron positron colliders

Circular electron positron colliders, such as the CEPC and FCC-ee, have been proposed to measure Higgs boson properties precisely, test the Standard Model, search for physics beyond the Standard Model, and so on. One of the important goals of these colliders is to measure the W boson mass with great precision by taking data around the W-pair production threshold. In this paper, the data-taking scheme is investigated to maximize the achievable precisions of the W boson mass and width with a threshold scan, when various systematic uncertainties are taken into account. The study shows that an optimal and realistic data-taking scheme is to collect data at three center-of-mass energies and that precisions of 1.0 MeV and 3.4 MeV can be achieved for the mass and width of the W boson, respectively, with a total integrated luminosity of mathscr {L}=3.2 ab^{-1} and several assumptions of the systematic uncertainty sources.

Beam parameters optimisation at CLIC for the threshold scan of the process [formula omitted] at multi-TeV energies

CLIC offers the ability to measure various proprieties of potential new heavy states with high precision. Beam-beam effects that inevitably occur at the interaction point affect the precision of physics measurements. The beam parameters can be optimised for a given energy and physics benchmark to minimise their impact. In this paper, the smuon mass extraction and spin determination through a threshold scan are investigated. Two main options realise a centre-of-mass energy scan at CLIC, which are either to keep the number of particles and the pulse length unchanged or to reduce the number of particles but to increase the pulse length. We compare the physics potential of both scenarios including the impact of beam polarisation.

Top-quark physics at the CLIC electron-positron linear collider

The Compact Linear Collider (CLIC) is a proposed future high-luminosity linear electron-positron collider operating at three energy stages, with nominal centre-of-mass energies sqrt{s} = 380 GeV, 1.5 TeV, and 3 TeV. Its aim is to explore the energy frontier, providing sensitivity to physics beyond the Standard Model (BSM) and precision measurements of Standard Model processes with an emphasis on Higgs boson and top-quark physics. The opportunities for top-quark physics at CLIC are discussed in this paper. The initial stage of operation focuses on top-quark pair production measurements, as well as the search for rare flavour-changing neutral current (FCNC) top-quark decays. It also includes a top-quark pair production threshold scan around 350 GeV which provides a precise measurement of the top-quark mass in a well-defined theoretical framework. At the higher-energy stages, studies are made of top-quark pairs produced in association with other particles. A study of t̄tH production including the extraction of the top Yukawa coupling is presented as well as a study of vector boson fusion (VBF) production, which gives direct access to high-energy electroweak interactions. Operation above 1 TeV leads to more highly collimated jet environments where dedicated methods are used to analyse the jet constituents. These techniques enable studies of the top-quark pair production, and hence the sensitivity to BSM physics, to be extended to higher energies. This paper also includes phenomenological interpretations that may be performed using the results from the extensive top-quark physics programme at CLIC.

First tests of a reconfigurable depleted MAPS sensor for digital electromagnetic calorimetry

Digital Electromagnetic CALorimetry relies on a highly granular detector where the cell size is sufficiently small so that only a single particle in a shower enters each cell within a single readout cycle. The DECAL sensor, a depleted monolithic active pixel sensor (DMAPS), has been proposed as a possible technology for future digital calorimeters. A DECAL sensor prototype has been designed and fabricated in the TowerJazz 180 nm CMOS imaging process, using a high resistivity 18 μm epitaxial Si layer. The prototype has a pixel matrix of 64 × 64 pixels with a pitch of 55 × 55 μm, and is read out using fast logic at 40 MHz. It can be configured to function as either a strip sensor, for particle tracking, or a pad sensor, counting the number of pixels above threshold for digital calorimetry. Preliminary results of chip characterisation, including digital summing logic, analogue pixel performance and threshold scans under laser illumination are presented.

Improvement of TimePix energy resolution correcting threshold variations

The Timepix detector is an important tool in spectroscopic imaging since it allows the determination of the energy of absorbed photons using its time over threshold capability. In this paper, however, we look at the energy resolution using the single photon counting mode combined with threshold scans. The pixel circuit of the TimePix detector involves a discriminator logic, which compares the collected amount of charge in each pixel with a threshold level (THL). The counter is incremented only if the induced signal surpasses this threshold. The THL is typically calibrated w.r.t. energy in the proximity of the noise edge, however, due to gain mismatch of the individual pixels, the threshold levels of pixels deviate if a DAC value far from the calibration point is set. This energy threshold mismatch far from the calibration point was corrected in this paper based on spectrum matching between individual pixels. The derived method is compared to straightforward calibration using multiple monochromatic peaks. To this end a threshold scan was performed using a TimePix Si-1mm detector (utilizing counting priciples) in presence of a Am-241 gamma source. The peak at energy 59.5 keV was fitted for each pixel to determine the actual THL values for all pixels at this energy. Then the full spectrums for all pixels were matched, using one fixed point. The matching process gave us two matrices of correction factors, the first matrix corrects the THL gain and the second its offset. In a second evaluation we measured and fitted the x-ray fluorescence of zirconium and copper during threshold scan in addition to the Am-241 peak. The gain and offset of each pixel were then determined by linear fit of the peak positions. The two calibration methods were evaluated by measuring the full width of half maximum FWHM of two other fluorescence peaks (23.17 keVand 26.2 keV peaks of cadmium). The evaluation shows that linear fit of multiple peaks results in a comparable FWHM (reduction of 21%) over spectrum matching the (reduction of 20%), while, opposite to spectrum matching, necessitating multiple measurement setps and THL scans.

Evaluation of the safety of MRI scans in patients undergoing dual-chamber pacemaker implantation.

The safety of magnetic resonance imaging (MRI) scans in patients undergoing dual-chamber pacemaker (Medtronic's EnRhythm MRI SureScan IPG (implantable pulse generator) and CapSureFix MRI pacing electrodes) implantation were evaluated. A total of 86 patients undergoing this pacemaker implantation who were admitted to Huanggang Hospital from June 2006 to March 2017 were continuously selected. On average 6.8±2.3 months after the implantation, the first MRI scan was conducted. The mean scan time was 2.2±0.9 and mean duration was 45.6±12.3 min; mean follow-up visit period was 40.5±15.6 months, and after follow-up, all the abnormal symptoms of patients and pacemaker abnormalities after scans were recorded. Causes of receiving MRI scans included neurological diseases (27%), spinal diseases (14%), cancers (26%), joint injuries (25%) and visceral systems (8%). A total of 12 cases (14.0%) showed significant discomfort symptoms, 10 cases (11.6%) showed pacemaker abnormalities, and the incidence rate was 25.6%. Multivariate logistic regression analysis showed that the basic types of cardiovascular diseases, dependence on pacemakers, duration of education, pacing threshold, impedance and MRI scan time were related to the occurrence of adverse scan results (p<0.05). In conclusion, MRI scans show that MRI-compatible dual-chamber pacemaker was relatively safe.

Non-resonant and electroweak NNLO correction to the e+e\u2212 top anti-top threshold

We determine the NNLO electroweak correction to the {e}^{+}{e}^{-}to boverline{b}{W}^{+}{W}^{-}X production cross section near the top-pair production threshold. The calculation includes non-resonant production of the final state as well as electroweak effects in resonant top anti-top pair production with non-relativistic resummation, and elevates the theoretical prediction to NNNLO QCD plus NNLO electroweak accuracy. We then study the impact of the new contributions on the top-pair threshold scan at a future lepton collider.