Threshold Scan Research Articles

Testing an Energy-Dispersive Counting-Mode Detector With Hard X-Rays From a Synchrotron Source

A counting-mode line detector has been evaluated at a synchrotron radiation source in order to assess its performance for imaging applications. The x-ray detector is based on 3 mm thick CdZnTe arrays with 1 mm pixel pitch and multi-threshold counting electronics. Data readout has been performed in threshold scan mode to provide maximum energy dispersion. The acquired energy spectra are interpreted regarding the characteristics of a periodic source and pulse pile-up in the detector. In particular, energy response and rate behavior of single-photon and double-photon events are investigated. Count rate dynamics are studied up to incident rates of . A further subject of the investigation is the variance of the observed counting rate. Linearity in the energy domain is tested between 40 keV and 140 keV.

CP asymmetries in Higgs decays to ZZ at the LHC

We examine the effect of a general HZZ coupling through a study of the Higgs decay to leptons via Z bosons at the LHC. We discuss various methods for placing limits on additional couplings, including measurement of the partial width, threshold scans, and asymmetries constructed from angular observables. We find that only the asymmetries provide a definitive test of additional couplings. We further estimate the significances they provide.

Material resolving X-ray imaging using spectrum reconstruction with Medipix2

In conventional X-ray imaging of a composed object only the cumulative attenuation is accessible, but the contribution of different materials can not be resolved. We consider the object consisting of known basis materials. Our method of material reconstruction provides the areal densities of these basis materials in each pixel of the image. This method uses the different energy dependences of X-ray attenuation of the basis materials to distinguish between them. It obviously requires a spectroscopic detector. Pixelated hybrid semiconductor X-ray detectors such as the Medipix2 suffer from charge sharing between pixels. This leads to a deteriorated energy response of the detector. To overcome this problem, we present two different methods to reconstruct incident X-ray spectra from threshold scans in each pixel. Both methods, namely spectrum stripping and a linear least squares fit, employ MC-simulated energy response functions to monoenergetic irradiation. Both methods work very well. The reconstructed incident spectra allow the application of material reconstruction with Medipix2. We present the material resolved images of a phantom containing aluminum, acrylic glass (PMMA) and iodine. This method allows new applications in non-destructive testing and medical imaging. This work was carried out within the Medipix-collaboration.

Threshold scans in diffractive W pair production via QED processes at the LHC

We propose a new set of measurements which can be performed at the LHC using roman pot detectors. This new method is based on exploiting excitation curves to measure kinematical properties of produced particles. We illustrate it in the case of central diffractive QED W pair production.

Investigation of charge carrier transport and charge sharing in X-ray semiconductor pixel detectors such as Medipix2

The output of X-ray semiconductor pixel detectors such as Medipix2 depends on various effects, such as the primary energy distribution inside the sensor layer, the diffusion of the generated charge carriers during the drift, the discrimination of the input signal by a threshold, and detection of scattered quanta originating from the detector parts behind the sensor layer. In this study we introduce an advanced Monte Carlo simulation including all these effects. The simulation was verified for energy distribution functions by performing threshold scans of monoenergetic radiation with the Medipix2.

Diffractive supersymmetric particle production at the CERN LHC

We give detailed predictions for the diffractive associated production of SUSY Higgs bosons and top squarks at the LHC via exclusive double pomeron exchange mechanism. We study how the SUSY Higgs production cross section and the signal-over-background ratio are enhanced as a function of $\mathrm{tan}\ensuremath{\beta}$ in different regimes. The prospects are particularly promising in the antidecoupling regime, which we study in detail. We also give prospects for a precise measurement of the top squark mass using the threshold scan of central diffractive associated top squark events at the LHC.

Determining sneutrino masses and physical implications

In some areas of supersymmetry parameter space, sneutrinos are lighter than the charginos and the next-to-lightest neutralino, and they decay into the invisible neutrino plus lightest-neutralino channel with probability one. In such a scenario they can be searched for in decays of charginos that are pair produced in ${e}^{+}{e}^{\ensuremath{-}}$ collisions, and in associated sneutrino-chargino production in photon-electron collisions. The sneutrino properties can be determined with high accuracy from the edges of the decay energy spectra in the first case and from threshold scans in the second. In the final part of the report we investigate the mass difference of sneutrinos and charged sleptons between the third and the first two generations in seesaw-type models of the neutrino/sneutrino sector. For a wide range these mass differences are sensitive to the seesaw scale.

Towards precision determination of the top-quark massfrom $\mathbf M_{b\ell}$ distribution in semi-leptonic decays

We explore a possibility of optimization of the method of determination of the top quark mass from $M_{b\ell}$ distribution in semi-leptonic decays $t \to b \ell\nu$ at LHC and a future linear collider (LC). We discover that the systematic and statistical errors of $M_t$ determination can be diminished if considering the high moments over the distribution. In the case of LHC this allows one to reduce more than in twice the errors, and in the case of LC to approach to the precision expected at studying the threshold scan of the total cross-section $e^+e^- \to t\bar t$.

Reconstructing dark matter density with [formula omitted] linear collider in focus-point supersymmetry

It has been known that, in the focus point scenario of supersymmetry, the thermal relic of the lightest superparticle (LSP) is known to be a good candidate of the cold dark matter. Assuming that the LSP in the focus-point scenario be the cold dark matter, we address a question how and how well the relic density of the LSP can be determined once the superparticles are found at future e + e − linear collider. We will see that the determinations of the mass of the LSP as well as those of the Higgsino-like chargino and neutralinos, which will be possible by a study of the decay kinematics of the chargino or by threshold scan, will give us important information to theoretically reconstruct the relic density. Even if the Higgsino-like superparticles and the LSP are the only superparticles which are kinematically accessible, relic density of the LSP may be calculated with the accuracy of factor ∼2; by adopting a mild theoretical assumption or by determining the masses of the wino-like superparticles, uncertainty can be reduced to ∼10% or smaller.

A study on the potentiostatic current transient and linear sweep voltammogram simulated from fractal intercalation electrode: diffusion coupled with interfacial charge transfer

Potentiostatic current transient and linear sweep voltammogram, theoretically calculated from the well-defined fractal profiles were analysed, with particular emphasis on hydrogen transport under the condition where hydrogen diffusion in the electrode is kinetically coupled with the charge-transfer reaction at the electrode/electrolyte interface. Under such a constraint of mixed control, the simulated current transient from the fractal electrode hardly exhibited the generalised Cottrell behaviour, and, especially, it displayed an inflexion point at the time that corresponds to the temporal outer cut-off of fractality (crossover time required for the fractal to flat transition). In the case of the linear sweep voltammogram computed from the fractal electrode, moreover, the power dependence of the peak current on the scan rate deviated negatively from the generalised Randles–Sevčik behaviour, above the slow threshold scan rate (crossover scan rate needed for the fractal to flat transition). From the analyses of the current transients and the linear sweep voltammograms calculated with various values of the simulation parameters, it was further recognised that during the potential jump as well as the potential scan, the temporal cut-off ranges of fractality under the constraint of mixed control are crucially determined by the interfacial charge-transfer kinetics, even though the spatial cut-off range and the hydrogen diffusivity in the electrode are maintained constant.

Threshold characterisation of the Medipix1 chip

The Medipix1 chip is a hybrid pixel detector working in photon counting mode and has the ability to put a discriminating threshold on each photon signal. To increase the image quality the threshold voltage can be electronically fine tuned with a 3 bit threshold adjust for each pixel. This electronic adjustment can only equalise the inhomogeneities of the electronics, not those of the physical frontend (conversion material and bump bonds). The remaining noise of the threshold has an obvious impact on the image quality. To optimise the uniformity over the whole chip we did threshold scans with a cadmium X-ray source analysing every pixel. With those scans we were able to create a bit mask including the physical frontend. Comparing the results of the different methods we can judge the quality of the electronically generated mask and draw conclusions about the properties of the physical frontend. Furthermore, simulations have been carried out for comparison with the measured data.

Multi-parameter fits to the $t\bar{t}$ threshold observables at a future ee linear collider

A realistic study of the physics reach of a t-tbar threshold scan at a future e+e- linear collider is presented. The results obtained take into account experimental and, to a large extent, theoretical systematic errors, as well as beam effects. Because of the large correlations between the physical parameters that can be extracted from the threshold scan, a multi-parameter fit is seen as mandatory. It is shown that the top mass, the top width and alpha_s(M_Z) can be extracted simultaneously with uncertainties around 20 MeV, 30 MeV and 0.0012, respectively, while the top Yukawa coupling can be measured, with the previous three parameters, to an uncertainty of about 35%, after assuming an external prior on alpha_s of +/-0.001.

Sneutrino mass measurements ate+e−linear colliders

It is generally accepted that experiments at an ${e}^{+}{e}^{\ensuremath{-}}$ linear collider will be able to extract the masses of the selectron as well as the associated sneutrino with a precision of $\ensuremath{\sim}1%$ by determining the kinematic end points of the energy spectrum of daughter electrons produced in their two body decays to a lighter neutralino or chargino. Recently, it has been suggested that by studying the energy dependence of the cross section near the production threshold, this precision can be improved by an order of magnitude, assuming an integrated luminosity of $100 {\mathrm{fb}}^{\ensuremath{-}1}.$ It is further suggested that these threshold scans also allow the masses of even the heavier second and third generation sleptons and sneutrinos to be determined to better than 0.5%. We reexamine the prospects for determining sneutrino masses. We find that the cross sections for the second and third generation sneutrinos are too small for a threshold scan to be useful. An additional complication arises because the cross section for sneutrino pairs to decay into any visible final state(s) necessarily depends on an unknown branching fraction, so that the overall normalization is unknown. This reduces the precision with which the sneutrino mass can be extracted. We propose a different strategy to optimize the extraction of $m({\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\nu}}}_{\ensuremath{\mu}})$ and $m({\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\nu}}}_{\ensuremath{\tau}})$ via the energy dependence of the cross section. We find that even with an integrated luminosity of $500 {\mathrm{fb}}^{\ensuremath{-}1},$ these can be determined with a precision no better than several percent at the 90% C.L. We also examine the measurement of $m({\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\nu}}}_{e})$ and show that it can be extracted with a precision of about 0.5% (0.2%) with an integrated luminosity of $120 {\mathrm{fb}}^{\ensuremath{-}1} (500 {\mathrm{fb}}^{\ensuremath{-}1}).$

Top quark mass definition andtt¯production near threshold at the Next Linear Collider

We suggest an infrared-insensitive quark mass, defined by subtracting the soft part of the quark self-energy from the pole mass. We demonstrate the deep relation of this definition with the static quark-antiquark potential. At leading order in $1/m$ this mass coincides with the PS mass which is defined in a completely different manner. Going beyond the static limit, the small normalization point introduces recoil corrections which are calculated here as well. Using this mass concept and other concepts for the quark mass we calculate the cross section of ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}t\overline{t}$ near threshold at NNLO accuracy adopting three alternative approaches; namely, (1) fixing the pole mass, (2) fixing the PS mass, and (3) fixing the new mass which we call the $\overline{\mathrm{PS}}$ mass. We demonstrate that perturbative predictions for the cross section become much more stable if we use the PS or the $\overline{\mathrm{PS}}$ mass for the calculations. A careful analysis suggests that the top quark mass can be extracted from a threshold scan at NLC with an accuracy of about 100--200 MeV.

SUPERSYMMETRY AT LINEAR COLLIDERS: THE IMPORTANCE OF BEING e-e-

Advantages of the e-e- option at linear colliders for the study of supersymmetry are highlighted. The fermion number violating process [Formula: see text] provides unique opportunities for studies of slepton masses and flavor mixings. In particular, slepton mass measurements at the 100 MeV level through threshold scans of scalar pair production may be possible. Such measurements are over an order of magnitude better than those possible in e+e- mode, require far less integrated luminosity, and may lead to precise, model-independent measurements of tan β. Implications for studying gauginos and the importance of accurate beam polarimetry are also discussed.

Antihyperon-hyperon production in p¯p annihilations near the reaction thresholds

The PS 185 experiment at LEAR/CERN studies strangeness production in antiproton-proton collisions in flight. Exclusive final states containing pairs of antihyperons and hyperons have been analysed. The data have been used to investigate strange quark production dynamics. New data at the highest energies available at LEAR extend the existing data set for the Λ¯Λ channel. Preliminary data from a new threshold scan are available. For the Σ¯ 0 Λ+cc channel first spin correlation data have been extracted. First preliminary differential cross section data from the Σ¯ − Σ − channel are also presented.

Beam tests of a double-sided silicon strip detector with fast binary readout electronics before and after proton-irradiation

A double-sided silicon strip detector with a radiation-tolerant design was fabricated and characterized in a sequence of beam tests at KEK using 4 GeV/ c pions. The detectors were combined with newly designed, fast, lower power, bipolar amplifier-shaper-discriminator chips and CMOS digital pipeline chips to record hit-no hit signals in the strips. Efficiencies, noise occupancies, and spatial resolutions were measured before and after the proton irradiation at an equivalent fluence of 1 × 10 14 p/cm 2, depending on angle of track incidence and strip-pitches. The median pulse height distribution, derived from the threshold scans of the efficiency, allowed to extract the response of the detector. A 1 T magnetic field enabled us to determine the Hall mobilities of electrons and holes.

Implementation of a threshold scanning method for detection of atrial fibrillation in a microprocessor-based pacemaker

Implementation of a threshold scanning method for detection of atrial fibrillation in a microprocessor-based pacemaker

Physics at tt-bar threshold in e+e- collisions.

We present the results from quantitative studies of physics at tt\ifmmode\bar\else\textasciimacron\fi{} threshold, taking into account realistic experimental conditions expected at future linear ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ colliders. A possible experimental strategy is illustrated for a sample case of ${\mathit{m}}_{\mathit{t}}$=150 GeV, where the importance of the measurements of both total and differential cross sections is emphasized for precision determinations of various parameters. The studies are based on a recently developed theoretical formalism which includes full O(${\mathrm{\ensuremath{\alpha}}}_{\mathit{s}}$) corrections. An energy scan of 11 points with 1 ${\mathrm{fb}}^{\mathrm{\ensuremath{-}}1}$ each allows us to measure the top mass and the strong coupling constant with statistical errors of \ensuremath{\Delta}${\mathit{m}}_{\mathit{t}}$=0.2 GeV and \ensuremath{\Delta}${\mathrm{\ensuremath{\alpha}}}_{\mathit{s}}$=0.005, respectively. As for the top width, \ensuremath{\Delta}${\mathrm{\ensuremath{\Gamma}}}_{\mathit{t}}$/${\mathrm{\ensuremath{\Gamma}}}_{\mathit{t}}$=0.2(stat) is expected, if both ${\mathit{m}}_{\mathit{t}}$ and ${\mathrm{\ensuremath{\alpha}}}_{\mathit{s}}$ are known. The measurement of the top momentum at some optimized energy point with 100 ${\mathrm{fb}}^{\mathrm{\ensuremath{-}}1}$ reduces the error on ${\mathrm{\ensuremath{\alpha}}}_{\mathit{s}}$ to \ensuremath{\Delta}${\mathrm{\ensuremath{\alpha}}}_{\mathit{s}}$=0.0015, provided that the 1S peak position is known from the threshold scan. The momentum measurement also improves the precision on the top width to \ensuremath{\Delta}${\mathrm{\ensuremath{\Gamma}}}_{\mathit{t}}$/${\mathrm{\ensuremath{\Gamma}}}_{\mathit{t}}$=0.04, if ${\mathrm{\ensuremath{\alpha}}}_{\mathit{s}}$ is known from other sources. The forward-backward asymmetry in the threshold region provides another interesting method to measure ${\mathrm{\ensuremath{\alpha}}}_{\mathit{s}}$ and ${\mathrm{\ensuremath{\Gamma}}}_{\mathit{t}}$.

Background subtraction: a new approach to the assessment of disease activity in Crohn's disease using 99mTc-HMPAO-labelled leucocytes.

A computer-based technique for the quantification of abnormal bowel uptake in Crohn's disease has been developed and compared with pre-existing clinical, laboratory and scintigraphic methods of assessment. The standard technique for labelling leucocytes with 99mTc-HMPAO is applied. Images were obtained at 40, 120 and 240 min after the injection of radiolabelled leucocytes. The count in the bowel area after subtracting background activity corrected to the injected dose and image acquisition times is the 'scan score', an objective measure of disease activity. The scan score is significantly higher in patients with clinically active disease (mean 82.1 +/- SEM 13.6) than in those with quiescent disease (24.7 +/- 7.0) (p < or = 0.005). Optimum separation between active and quiescent disease is achieved with a threshold scan score of 20. The scan score was comparable in small bowel disease (73.3 +/- 16.2), large bowel (94.4 +/- 33) and disease at both locations (94.1 +/- 19.2). The scan score correlated favourably with Crohn's Disease Activity Index (rs = 52, p < or = 0.0001), Harvey & Bradshow Simple Index (rs = 0.4, p < or = 0.001), serum C-reactive protein (rs = 0.72, p < or = 0.001), serum alpha acid glycoprotein (rs 0.67, p < or = 0.001), haemoglobin (rs = 0.66, p < or = 0.001), platelet count (rs = 0.47, p < or = 0.006), albumin (rs = 0.61, p < or = 0.0001) and faecal 111Indium excretion (rs = 0.78, p < or = 0.001), but not with the ESR (rs = 0.22, p < or = 0.4).(ABSTRACT TRUNCATED AT 250 WORDS)