M. Swartz

We consider the effect of a doubly charged Higgs boson (${\ensuremath{\Delta}}^{\ensuremath{-}\ensuremath{-}}$) on several processes. We find that the effective Hamiltonian that is normally used to interpret the results of muonium-antimuonium oscillation experiments also describes the $t$-channel exchange of a ${\ensuremath{\Delta}}^{\ensuremath{-}\ensuremath{-}}$. A limit on the existence of the ${\ensuremath{\Delta}}^{\ensuremath{-}\ensuremath{-}}$ is extracted from the most recent muonium oscillation result. The effect of ${\ensuremath{\Delta}}^{\ensuremath{-}\ensuremath{-}}$ exchange on high-energy Bhabha scattering is discussed, and a limit is extracted from the published cross sections of several experiments at the SLAC and DESY storage rings PEP and PETRA. The case of a nondiagonal coupling of the ${\ensuremath{\Delta}}^{\ensuremath{-}\ensuremath{-}}$ to the charged leptons (nondiagonal in lepton flavor) is considered. A limit is extracted from the result of the most recent search for the rare decay $\ensuremath{\mu}\ensuremath{\rightarrow}3e$. Finally, a coupling-independent limit is extracted from a recent measurement of the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}4 \mathrm{leptons}$ at PETRA.

Using a sample of events collected by UA2 and corresponding to an integrated luminosity of 116 nb−1. we have searched for electron-“neutrino” pairs in which the transverse momenta of the electron and of the “neutrino” exceed 15 GeV/c and 25 GeV/c respectively. A total of 35 events are observed in low background conditions. Most events can be interpreted in terms of W± production from QCD processes. Events in which the observation of hard jets makes this interpretation unlikely are described in detail. Possible sources of background contamination are considered.

The production of very large transverse momentum (pT) hadron jets has been measured in the UA2 experiment at the CERN pp Collider for s=630 GeV. The inclusive jet production cross sections exhibit a pT-dependent increase with respect to the s=546 GeV data from previous Collider runs. This increase can be described both by QCD calculations and by approximate xT=2pT/√s scaling. No significant deviation of the data from QCD predictions is observed at very large pT, placing a lower limit on the characteristic scale Λc of a hypothetical superstrong contact interaction responsible for the binding of preons in the quark (Λc>370 GeV at 95% CL).

The total UA2 data sample at the CERN pp̄ Collider corresponds to an integrated luminosity of 910 nb−1. Limits on various hypothetical processes, such as production of excited electrons, additional charged or neutral vector bosons, or supersymmetric particles, are presented from the analysis of this sample.

The CMS experiment at the (LHC) includes a hybrid silicon pixel detector for the reconstruction of charged tracks and of the interaction vertices. The barrel region consists of n-in-n sensors with 100×150μm2 cell size processed on diffusion oxygenated float zone silicon. A biasing grid is implemented and pixel isolation is achieved with the moderated p-spray technique. An extensive test program was carried out on the H2 beam line of the CERN-SPS. In this paper we describe the sensor layout, the beam test setup and the results obtained with both irradiated and non-irradiated prototype devices. Measurements of charge collection, hit detection efficiency, Lorentz angle and spatial resolution are presented.

We have developed a new technique for inclusive reconstruction of the energy of B hadrons. The excellent efficiency and resolution of this technique allow us to make the most precise determination of the b-quark fragmentation function, using e(+)e(-)-->Z0 decays recorded in the SLAC Large Detector experiment. We compared our measurement with the predictions of a number of fragmentation models. We excluded several of these models and measured the average scaled energy of weakly decaying B hadrons to be <x(B)> = 0.714+/-0. 005(stat)+/-0.007(syst)+/-0.002 (model dependence).

We reevaluate the hadronic part of the electromagnetic vacuum expectation value using the standard dispersion integral approach that utilizes the hadronic cross section measured in $\ee$ experiments as input. Previous analyses are based upon point-by-point trapezoidal integration which does not treat experimental errors in an optimal way. We use a technique that weights the experimental inputs by their stated uncertainties, includes correlations, and incorporates some refinements. We find the five-flavor hadronic contribution to the fractional change in the electromagnetic coupling constant at $q^2=M_Z^2$, $Δα(MZ)$, to be $0.02752\pm0.00046$, which leads to a value of the electromagnetic coupling constant, $α^{-1}(M_Z^2) = 128.96\pm0.06$. [This is an updated version of SLAC-PUB-6710 (hep-ph/9411353) which fixes a small bias in the fitting procedure (1/3 of the change) and incorporates a new and precise cross section measurement near charm threshold (2/3 of the change).]

The production of electrons with very high transverse momentum has been studied in the UA2 experiment at the CERN $$\bar pp$$ collider ( $$\sqrt s$$ =540 GeV). From a sample of events containing an electron candidate withp T >15 GeV/c, we extract a clear signal resulting from the production of the charged intermediate vector bosonW ±, which subsequently decays into an electron and a neutrino. We study theW production and decay properties. Further-more, we refine our results on the production and decay of the neutral vector bosonZ 0. Finally, we compare the experimental results to the predictions of the standard model of the unified electro-weak theory.

Fragmentation properties of a sample of two-jet events measured by the UA2 detector at the CERN pp Collider are described. The energy flow is compared with different model predictions. The charged particle multiplicity in jets is found to exceed extrapolations from lower energy e+e− jet data.

High granularity silicon pixel sensors are at the heart of energy frontier particle physics collider experiments. At an collision rate of 40\,MHz, these detectors create massive amounts of data. Signal processing that handles data incoming at those rate and intelligently reduces the data within the pixelated region of the detector \textit{at rate} will enhance physics performance and enable physics analyses that are not currently possible. Using the shape of charge clusters deposited in an array of small pixels, the physical properties of the traversing particle can be extracted with locally customized neural networks. In this first work, we present a neural network that can be embedded into the on-sensor readout and filter out hits from low momentum tracks, reducing the detector's data volume by 54.4-75.4\%. The network is designed and simulated as a custom readout integrated circuit with 28\,nm CMOS technology and is expected to operate at less than 300\,$\mu W$ with an area of less than 0.2\,mm$^2$.

Charge collection measurements performed on heavily irradiated p-spray DOFZ pixel sensors with a grazing angle hadron beam provide a sensitive determination of the electric field within the detectors. The data are compared with a complete charge transport simulation of the sensor which includes free carrier trapping and charge induction effects. A linearly varying electric field based upon the standard picture of a constant type-inverted effective doping density is inconsistent with the data. A two-trap double junction model implemented in the ISE TCAD software can be tuned to produce a double peak electric field which describes the data reasonably well. The modeled field differs somewhat from previous determinations based upon the transient current technique. The model can also account for the level of charge trapping observed in the data.

This Letter reports measurements of the ratios of $\ensuremath{\pi}$, $K$, and $p$ production at large values of transverse momentum in ${\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{-}p$ collisions. The charge ratios, such as $\frac{{\ensuremath{\pi}}^{\ensuremath{-}}}{{\ensuremath{\pi}}^{+}}$, $\frac{{K}^{\ensuremath{-}}}{{K}^{+}}$, and $\frac{\overline{p}}{p}$ are seen to be quite different from those measured in $p\ensuremath{-}p$ collisions. These ratios are sensitive tests of hard-scattering models, and are compared with the-oretical predictions. The particle ratios have also been studied as a function of center-of-mass angle (${\ensuremath{\theta}}^{*}$) at ${\ensuremath{\theta}}^{*}=90\ifmmode^\circ\else\textdegree\fi{}, 77\ifmmode^\circ\else\textdegree\fi{}, \mathrm{and} 60\ifmmode^\circ\else\textdegree\fi{}$.

We compute the bounds from precision observables on alternative theories of electroweak symmetry breaking. We show that a cutoff as large as 3 TeV can be accommodated by the present data, without any new particles or unnatural fine tuning.

Measurements of the production cross sections at large values of transverse momentum (${P}_{T}$) for ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$, ${K}^{\ifmmode\pm\else\textpm\fi{}}$, $p$, and $\overline{p}$ in 200 and 300 GeV ${\ensuremath{\pi}}^{\ensuremath{-}}p$ collisions are presented. The dependences of the cross section on ${P}_{T}$ and the transverse scaling variable ${x}_{T}=\frac{2{P}_{T}}{\sqrt{s}}$ are discussed. The ratios of production of different particle types, such as $\frac{{\ensuremath{\pi}}^{\ensuremath{-}}}{{\ensuremath{\pi}}^{+}}$, $\frac{{K}^{+}}{{\ensuremath{\pi}}^{+}}$, etc., are given, and are shown to be quite different from those in $\mathrm{pp}$ collisions. Data have been taken at three laboratory angles; the angular dependence is given and compared with theoretical models. Data on three nuclear targets allow an evaluation of the atomic-weight ($A$) dependence.

A detailed simulation of the CMS pixel sensor is described. The simulation incorporates: a physical model of charge deposition; a realistic electric field map; a realistic carrier transport including mobilities, Hall effect, and 3-d diffusion; radiation damage and charge trapping effects; and finally, electronic noise, response, and threshold effects. The simulation agrees well with published measurements of the average Lorentz angle in irradiated pixel detectors and suggests that limited electronic dynamic range improves detector performance by suppressing large delta-ray induced fluctuations.

The tracking system of the CMS experiment, currently under construction at the Large Hadron Collider (LHC) at CERN (Geneva, Switzerland), will include a silicon pixel detector providing three spacial measurements in its final configuration for tracks produced in high-energy pp collisions. In this paper, we present the results of test beam measurements performed at CERN on irradiated silicon pixel sensors. Lorentz angle and charge collection efficiency were measured for two sensor designs and at various bias voltages.

We show that doubly peaked electric fields are necessary to describe grazing-angle charge collection measurements of irradiated silicon pixel sensors. A model of irradiated silicon based upon two defect levels with opposite charge states and the trapping of charge carriers can be tuned to produce a good description of the measured charge collection profiles in the fluence range from 0.5×1014 to 5.9×1014neq/cm2. The model correctly predicts the variation in the profiles as the temperature is changed from -10 to -25∘C. The measured charge collection profiles are inconsistent with the linearly varying electric fields predicted by the usual description based upon a uniform effective doping density. This observation calls into question the practice of using effective doping densities to characterize irradiated silicon.

In this paper we discuss the measurement of charge collection in irradiated silicon pixel sensors and the comparison with a detailed simulation. The simulation implements a model of radiation damage by including two defect levels with opposite charge states and trapping of charge carriers. The modeling proves that a doubly peaked electric field generated by the two defect levels is necessary to describe the data and excludes a description based on acceptor defects uniformly distributed across the sensor bulk. In addition, the dependence of trap concentrations upon fluence is established by comparing the measured and simulated profiles at several fluences and bias voltages.

This work describes the investigation of neuromorphic computing-based spiking neural network (SNN) models used to filter data from sensor electronics in high energy physics experiments conducted at the High Luminosity Large Hadron Collider (HL-LHC). We present our approach for developing a compact neuromorphic model that filters out the sensor data based on the particle's transverse momentum with the goal of reducing the amount of data being sent to the downstream electronics. The incoming charge waveforms are converted to streams of binary-valued events, which are then processed by the SNN. We present our insights on the various system design choices---from data encoding to optimal hyperparameters of the training algorithm---for an accurate and compact SNN optimized for hardware deployment. Our results show that an SNN trained with an evolutionary algorithm and an optimized set of hyperparameters obtains a signal efficiency of about 91% with nearly half as many parameters as a deep neural network.

The barrel region of the CMS pixel detector will be equipped with “n-in-n” type silicon sensors. They are processed on diffusion oxygenated float zone (DOFZ) material, use the moderated p-spray technique for inter pixel isolation and feature a bias grid. The latter leads to a small fraction of the pixel area to be less sensitive to particles. In order to quantify this inefficiency prototype pixel sensors irradiated to particle fluences between 4.7×1013 and 2.6×1015neq/cm2 have been bump bonded to un-irradiated readout chips and tested using high energy pions at the H2 beam line of the CERN SPS. The readout chip allows a non-zero suppressed analog readout and is therefore well suited to measure the charge collection properties of the sensors. In this paper we discuss the fluence dependence of the collected signal and the particle detection efficiency. Further the position dependence of the efficiency is investigated.

New techniques for the reconstruction/validation and the simulation of hits in the pixel detectors of the Compact Muon Solenoid (CMS) Experiment are described.The techniques are based upon the use of pre-computed projected cluster shapes or "templates".A detailed simulation called Pixelav that has successfully described the profiles of clusters measured in beam tests of radiationdamaged sensors is used to generate the templates.Although the reconstruction technique was originally developed to optimally estimate the coordinates of hits after the detector became radiation damaged, it also has superior performance before irradiation.The technique requires a priori knowledge of the track angle which makes it suitable for the second in a two-pass reconstruction algorithm.However, the same modest angle sensitivity allows the algorithm to determine if the sizes and shapes of the cluster projections are consistent with the input angles.This information may be useful in suppressing spurious hits caused by secondary particles and in validating seeds used in track finding.The seed validation is currently under study but has the potential to significantly increase the speed of track finding in the CMS reconstruction software.Finally, a new procedure that uses the templates to re-weight clusters generated by the CMS offline simulation is described.The first tests of this technique are encouraging and when fully implemented, the technique will enable the fast simulation of pixel hits that have the characteristics of the much more CPU-intensive Pixelav hits.In particular, it may be the only practical technique available to simulate hits from a radiation damaged detector in the CMS offline software.

The construction of a computer code to calculate the cross sections for the spin-polarized processes ${e}^{\ensuremath{-}}\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}}{e}^{\ensuremath{-}}\ensuremath{\gamma}{,e}^{\ensuremath{-}}\ensuremath{\gamma}\ensuremath{\gamma}{,e}^{\ensuremath{-}}{e}^{+}{e}^{\ensuremath{-}}$ to order ${\ensuremath{\alpha}}^{3}$ is described. The code calculates cross sections for circularly polarized initial-state photons and arbitrarily polarized initial-state electrons. The application of the code to the SLD Compton polarimeter indicates that the order-${\ensuremath{\alpha}}^{3}$ corrections produce a fractional shift in the SLC polarization scale of $\ensuremath{-}0.1%$ which is too small and of the wrong sign to account for the discrepancy in the $Z$-pole asymmetries measured by the SLD Collaboration and the CERN LEP Collaborations.

This paper reports on the sensor R&D activity for the CMS pixel detector. Devices featuring several design and technology options have been irradiated up to a proton fluence of 1/spl times/10/sup 15/ n/sub eq//cm/sup 2/ at the CERN PS. Afterward, they were bump bonded to unirradiated readout chips and tested using high energy pions in the H2 beam line of the CERN SPS. The readout chip allows a nonzero suppressed full analogue readout and therefore a good characterization of the sensors in terms of noise and charge collection properties. The position dependence of signal is presented and the differences between the two sensor options are discussed.

We have measured the fraction of bb\ifmmode\bar\else\textasciimacron\fi{} events in hadronic ${\mathit{Z}}^{0}$ decays, ${\mathit{R}}_{\mathit{b}\mathit{b}\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}}$, using the vertex detector system of the Mark II detector at the SLAC Linear Collider. We tag bb\ifmmode\bar\else\textasciimacron\fi{} events by requiring the coincidence of three or more tracks with significant impact parameters. This tag is 50% efficient and results in a sample of 85% purity. We find ${\mathit{R}}_{\mathit{b}\mathit{b}\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}}$=0.251\ifmmode\pm\else\textpm\fi{}0.049\ifmmode\pm\else\textpm\fi{}0.030, in good agreement with other measurements and the standard model prediction.

We describe a search for the decay of the Z boson into pairs of doubly charged Higgs bosons with the Mark II detector operating at the SLAC Linear Collider. Each Higgs boson is assumed to decay into a same-sign leptonic pair. No event candidates are found in a sample of 528 Z decays. At the 95% confidence level, this result excludes the region of leptonic coupling ${\mathit{g}}_{\mathit{l}\mathit{l}}$&gt;3\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}7}$ and Higgs-boson mass 6.5${\mathit{M}}_{\mathit{H}}$36.5 GeV/${\mathit{c}}^{2}$ for isotriplet (left-handed) Higgs bosons. Isosinglet (right-handed) Higgs bosons are excluded in the same ${\mathit{g}}_{\mathit{l}\mathit{l}}$ interval and in the mass interval 7.3${\mathit{M}}_{\mathit{H}}$34.3 GeV/${\mathit{c}}^{2}$.

We present measurements of the differential cross section for the production of massive muon pairs in 225-GeV/c ${\ensuremath{\pi}}^{\ensuremath{-}}$-nucleus collisions. We have used the data between the $\ensuremath{\psi}$ and $\ensuremath{\Upsilon}$ resonances in the framework of the Drell-Yan quark-antiquark annihilation model to predict the behavior of the cross section in the high-mass (${m}_{\ensuremath{\mu}\ensuremath{\mu}}>11$ GeV/${\mathit{c}}^{2}$) region. The data are consistent with this extrapolation provided that a QCD leading-logarithmic evolution is included in the structure functions.

Isolated comma or corkscrew-shaped venular segments in the conjunctiva have been felt to be diagnostic of sickle cell disease. External eye examination of a 34-year-old black man with a two-year history of chronic granulocytic leukemia revealed multiple small and medium-sized isolated conjunctival venular segments. Laboratory findings at the time of examination included a white blood cell count of 132,000/mm3 with 87% eosinophils, a hematocrit reading of 30%, and hemoglobin AA. Since whole blood hyperviscosity can be present in chronic granulocytic leukemia as well as sickle cell disease, this may account for the similarly of the conjunctival changes.

In an experiment performed at Fermi National Accelerator Laboratory, the production of massive muon pairs in 225-GeV/c ${\ensuremath{\pi}}^{\ensuremath{-}}$-nucleus interactions has been studied for four nuclear targets. Comparison of the relative cross sections enables the dependence on atomic weight $A$ to be determined. If this dependence is parametrized such that the dimuon production cross section ${\ensuremath{\sigma}}_{\ensuremath{\mu}\ensuremath{\mu}}$ is proportional to ${A}^{\ensuremath{\alpha}}$ this experiment yields $\ensuremath{\alpha}=0.98\ifmmode\pm\else\textpm\fi{}0.04$ for $4&lt;{m}_{\ensuremath{\mu}\ensuremath{\mu}}&lt;8.5$ GeV/${\mathit{c}}^{2}$, where ${m}_{\ensuremath{\mu}\ensuremath{\mu}}$ is the invariant mass of the muon pair.

CMS will use silicon pixel as its innermost tracking device. Prototypes of these 150μm square pixels bump bonded to DMILL readout chips were tested at CERN in a pion beam. A silicon telescope consisting of 8 planes of silicon strips was used to interpolate tracks to the position of the pixel detector. Data were taken with the beam at different angles of incidence relative to the pixel sensors. Position resolutions between 10 and 20μm, depending on the hit position, were observed using charge sharing for the final configuration with unirradiated detectors. The observed resolution was as expected.

International Journal of Modern Physics AVol. 15, No. supp01a, pp. 307-332 (2000) Electroweak Interactions and BeyondNo AccessPRECISION ELECTROWEAK PHYSICS AT THE ZMORRIS L. SWARTZMORRIS L. SWARTZDepartment of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USAhttps://doi.org/10.1142/S0217751X00005206Cited by:1 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail You currently do not have access to the full text article. Recommend the journal to your library today! FiguresReferencesRelatedDetailsCited By 1The study of the contribution of the LHT model to couplingBingfang Yang, Xuelei Wang and Jinzhong Han1 Jun 2011 | Nuclear Physics B, Vol. 847, No. 1 Recommended Vol. 15, No. supp01a Metrics History PDF download

A new method for the extraction of the electric field in the bulk of heavily irradiated silicon pixel sensors is presented. It is based on the measurement of the Lorentz deflection and mobility of electrons as a function of depth. The measurements were made at the CERN H2 beam line, with the beam at a shallow angle with respect to the pixel sensor surface. The extracted electric field is used to simulate the charge collection and the Lorentz deflection in the pixel sensor. The simulated charge collection and the Lorentz deflection is in good agreement with the measurements both for non-irradiated and irradiated up to 1E15 neq/cm2 sensors.

The next upgrade of the Large Hadron Collider (LHC) is planned from 2026 when the collider will move to its High Luminosity phase (HL-LHC). The CMS detector needs to be substantially upgraded during this period to exploit the fourfold increase in luminosity provided by the HL-LHC. This upgrade is referred to as the CMS Phase-2 Upgrade. A program of laboratory and beam test measurements, and performance studies based on the detailed simulation of the detector was carried out to support the decision of the technology of the sensors to be adopted in the different regions of the detector for the Phase-2 Upgrade. Among the various options considered, CMS chose to use 3D sensors with a 25 $\times$ 100 $\mu$m$^2$ pixel cell in the innermost layer of the barrel and planar sensors with a 25 $\times$ 100 $\mu$m$^2$ pixel cell elsewhere. In this paper, we detail the simulation studies that were carried out to choose the best sensor design. These studies include a detailed standalone simulation of the sensors made with PixelAV and the expected performance on high level observables obtained with the simulation and reconstruction software of the CMS experiment.

The next upgrade of the Large Hadron Collider (LHC) is planned from 2026 when the collider will move to its High Luminosity phase (HL-LHC). The CMS detector needs to be substantially upgraded during this period to exploit the fourfold increase in luminosity provided by the HL-LHC. This upgrade is referred to as the CMS Phase-2 Upgrade. A program of laboratory and beam test measurements, and performance studies based on the detailed simulation of the detector was carried out to support the decision of the technology of the sensors to be adopted in the different regions of the detector for the Phase-2 Upgrade. Among the various options considered, CMS chose to use 3D sensors with a 25 $\times$ 100 $\mu$m$^2$ pixel cell in the innermost layer of the barrel and planar sensors with a 25 $\times$ 100 $\mu$m$^2$ pixel cell elsewhere. In this paper, we detail the simulation studies that were carried out to choose the best sensor design. These studies include a detailed standalone simulation of the sensors made with PixelAV and the expected performance on high level observables obtained with the simulation and reconstruction software of the CMS experiment.

This work describes the investigation of neuromorphic computing-based spiking neural network (SNN) models used to filter data from sensor electronics in high energy physics experiments conducted at the High Luminosity Large Hadron Collider. We present our approach for developing a compact neuromorphic model that filters out the sensor data based on the particle's transverse momentum with the goal of reducing the amount of data being sent to the downstream electronics. The incoming charge waveforms are converted to streams of binary-valued events, which are then processed by the SNN. We present our insights on the various system design choices - from data encoding to optimal hyperparameters of the training algorithm - for an accurate and compact SNN optimized for hardware deployment. Our results show that an SNN trained with an evolutionary algorithm and an optimized set of hyperparameters obtains a signal efficiency of about 91% with nearly half as many parameters as a deep neural network.

Highly granular pixel detectors allow for increasingly precise measurements of charged particle tracks. Next-generation detectors require that pixel sizes will be further reduced, leading to unprecedented data rates exceeding those foreseen at the High Luminosity Large Hadron Collider. Signal processing that handles data incoming at a rate of O(40MHz) and intelligently reduces the data within the pixelated region of the detector at rate will enhance physics performance at high luminosity and enable physics analyses that are not currently possible. Using the shape of charge clusters deposited in an array of small pixels, the physical properties of the traversing particle can be extracted with locally customized neural networks. In this first demonstration, we present a neural network that can be embedded into the on-sensor readout and filter out hits from low momentum tracks, reducing the detector's data volume by 54.4-75.4%. The network is designed and simulated as a custom readout integrated circuit with 28 nm CMOS technology and is expected to operate at less than 300 $\mu W$ with an area of less than 0.2 mm$^2$. The temporal development of charge clusters is investigated to demonstrate possible future performance gains, and there is also a discussion of future algorithmic and technological improvements that could enhance efficiency, data reduction, and power per area.

The combinatorics of track seeding has long been a computational bottleneck for triggering and offline computing in High Energy Physics (HEP), and remains so for the HL-LHC. Next-generation pixel sensors will be sufficiently fine-grained to determine angular information of the charged particle passing through from pixel-cluster properties. This detector technology immediately improves the situation for offline tracking, but any major improvements in physics reach are unrealized since they are dominated by lowest-level hardware trigger acceptance. We will demonstrate track angle and hit position prediction, including errors, using a mixture density network within a single layer of silicon as well as the progress towards and status of implementing the neural network in hardware on both FPGAs and ASICs.

The combinatorics of track seeding has long been a computational bottleneck for triggering and offline computing in High Energy Physics (HEP), and remains so for the HL-LHC. Next-generation pixel sensors will be sufficiently fine-grained to determine angular information of the charged particle passing through from pixel-cluster properties. This detector technology immediately improves the situation for offline tracking, but any major improvements in physics reach are unrealized since they are dominated by lowest-level hardware trigger acceptance. We will demonstrate track angle and hit position prediction, including errors, using a mixture density network within a single layer of silicon as well as the progress towards and status of implementing the neural network in hardware on both FPGAs and ASICs.

We have measured the atomic-mass dependence of the ${P}_{T}$ distribution of massive muon pairs produced in 225-GeV/c ${\ensuremath{\pi}}^{\ensuremath{-}}$-nucleus collisions at Fermilab. We find that $〈{P}_{T}^{2}〉$ is consistent with being independent of the atomic mass $A$, with the value of 1.69\ifmmode\pm\else\textpm\fi{}0.10 ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$ for muon pairs of mass between 4.0 and 8.5 GeV/${\mathit{c}}^{2}$. When the dependence of $〈{P}_{T}^{2}〉$ on $A$ is parametrized as $〈{P}_{T}^{2}〉=a+b{A}^{\frac{1}{3}}$, we find that $b=\ensuremath{-}0.079\ifmmode\pm\else\textpm\fi{}0.073$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$ which corresponds to an upper limit of 0.015 ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$ at the 90% confidence level.

In this paper a detailed simulation of irradiated pixel sensors was used to investigate the effects of radiation damage on the position determination and optimize the hit reconstruction algorithms. The simulation implements a model of radiation damage by including two defect levels with opposite charge states and trapping of charge carriers. The simulation shows that a position resolution below 15 μm along the CMS r–φ plane can be achieved after an irradiation fluence of 5.9×1014neq/cm2. In addition, we show that systematic errors in the position determination can be largely reduced by applying η corrections.

New techniques for the reconstruction of hits in the pixel detectors of the Compact Muon Solenoid (CMS) experiment are described. The techniques are based upon the use of pre-computed projected cluster shapes or templates. A detailed simulation called Pixelav that has successfully described the profiles of clusters measured in beam tests of radiation-damaged sensors is used to generate the templates. Although the reconstruction technique was originally developed to optimally estimate the coordinates of hits after the detector became radiation damaged, it also has superior performance before irradiation. The technique requires a priori knowledge of the track angle which makes it suitable for the second in a two-pass reconstruction algorithm. However, the same modest angle sensitivity allows the algorithm to determine if the sizes and shapes of the cluster projections are consistent with the input angles. This information is proved to be useful in suppressing spurious hits caused by secondary particles and in validating seeds used in track finding. In addition, the template technique improves the resolution on the track impact parameter and light quark background rejection in b-tagged jets. Finally, a new procedure that uses the templates to reweigh clusters generated by the CMS offline simulation is described.

A simulated dataset of silicon pixel clusters produced by charged particles (pions), where the particle kinematics are taken from fitted tracks in CMS Run 2 data. The interaction of the charged particles with a 100 micron thick silicon pixel detector is simulated using a time-sliced version of PixelAV. The pixel detector is taken to be a 21x13 array of pixels with 50x12.5 micron pitch, situated 30mm from the particle's origin point. The detector is immersed in a 3.8T magnetic field parallel to the sensor x coordinate. Positively and negatively charged particles are saved in the directories positive-charge and negative-charge, respectively. Truth properties of each particle are saved in the labels files, which include columns x-entry, y-entry, z-entry, n_x, n_y, n_z, number_eh_pairs, y-local, pt, cotAlpha, cotBeta, y-midplane, x-midplane. The particle impact point on the sensor surface is described by (x-entry, y-entry), and the impact point at the mid-plane of the sensor is (x-midplane, y-midplane). These impact points are in units of microns. The track direction is given by (n_x, n_y, n_z). The number of electron-hole pairs created in the silicon is number_eh_pairs. The y distance in mm between the center of the 21x13 pixel array and the center of a flat module is denoted by y-local (see included diagram). The particle transverse momentum ($p_T$) in GeV is stored in the pt variable, with the sign indicating the sign of the particle charge. The angle of incidence in the x-z plane is described by cotAlpha, and the angle of incidence in the y-z plane (the bending plane of the magnetic field) is described by cotBeta. The deposited charge per pixel per time slice is saved in the recon files. Reshaping each line as (8,13,21) gives the three dimensional cluster in (time, y, x). Each slice in time corresponds to a window of 200 ps. The combination of all files with index 16800+ yield a physical distribution. Files with lower indices are flattened at low $p_T$.

A 3500 wire drift chamber system has been built for a very large iron toroidal spectrometer which will be used at Fermilab. The chambers are trapezoidal, with each covering one-eighth of the face of an eight-foot-diameter toroid. The readout system was designed to give moderate resolution but provide excellent multi-hit capability.

The linac of the SLAC (Stanford Linear Accelerator Center) Linear Collider (SLC) must accelerate three high-intensity bunches on each linac pulse from 1.2 GeV to 50 GeV with minimal increase of small transverse emittance. The procedures and adjustments used to obtain this goal are outlined. Some of the accelerator parameters and components which interact are the beam energy, transverse position, component alignment, RF manipulation, feedback system, quadrupole lattice, BNS damping, energy spectra, phase space matching, collimation, instrumentation, and modeling. The method to bring these interdependent parameters collectively into specification has evolved over several years. The sequence which is sued to turn on the linac from a cold start and produce acceptable beams for the final focus and collisions is reviewed. Approximate time estimates for the various activities are given.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Charge collection measurements performed on heavily irradiated p-spray dofz pixel sensors with a grazing angle hadron beam provide a sensitive determination of the electric field within the detectors. The data are compared with a complete charge transport simulation of the sensor which includes signal trapping and charge induction effects. A linearly varying electric field based upon the standard picture of a constant type-inverted effective doping density is inconsistent with the data. A two-trap double junction model implemented in ISE TCAD software can be tuned to produce a doubly-peaked electric field which describes the data reasonably well at two different fluences. The modeled field differs somewhat from previous determinations based upon the transient current technique. The model can also account for the level of signal trapping observed in the data.

In this paper a detailed simulation of irradiated pixel sensors was used to investigate the effects of radiation damage on charge sharing and position determination. The simulation implements a model of radiation damage by including two defect levels with opposite charge states and trapping of charge carriers. We show that charge sharing functions extracted from the simulation can be parameterized as a function of the inter-pixel position and used to improve the position determination. For sensors irradiated to Φ=5.9×1014neq/cm2 a position resolution below 15μm can be achieved after calibration.

A review of the decade of Z-pole electroweak physics is presented. Although all experimental work has been completed, it represents a ``Golden Age'' in our understanding of the Minimal Electroweak Standard Model (MSM). The latest (and nearly final) results from the LEP and SLC experiments are presented. The remaining inconsistencies are discussed and and their effects upon the MSM interpretation are explored.

The CMS barrel pixel detector is the innermost tracking device, reconstructing the interaction vertices and charged particle trajectories. At the LHC design luminosity, 1034 cm−2 s−1, there will be 1000 charged particles per bunch crossing every 25 ns. In the innermost layer the pixel sensors will be exposed to a fluence of 3×1014neq/cm2/yr with consequent degradation of the silicon lattice structure and particle detection performances. Beam tests of irradiated pixel sensors were performed at CERN with the final front end electronics in a 3T magnetic field. We present the measurements of charge collection and radiation hardness, as well as spatial resolution.

Measurements of the production cross sections at large values of transverse momentum (${P}_{T}$) for ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$, ${K}^{\ifmmode\pm\else\textpm\fi{}}$, $p$, and $\overline{p}$ in 200- and 300-GeV/c ${\ensuremath{\pi}}^{\ensuremath{-}}p$ collisions are presented. The dependences of the cross section on ${P}_{T}$, the transverse scaling variable ${x}_{T}=\frac{2{P}_{T}}{\sqrt{s}}$, and the production angle are discussed. The cross sections are compared with those from $\mathrm{pp}$ collisions and with theoretical predictions. While the ${\ensuremath{\pi}}^{\ensuremath{-}}p$ and $\mathrm{pp}$ data are quite different, both agree qualitatively with hard-scattering calculations.

From an integrated luminosity of ∫Ldt = 116 nb-1, 10events are found which contain an electron pair of mass in the range 12 < Mee < 26 GeVc2 and electron transverse momenta pTe > 5 GeVc. THe sample are described, as well as some featruyres of the The production characteristics of this sample are described, as well as some features of the estimated to be 2.2±0.6 events. The production characteristics of this sample are described, as well as some features of the associated event topology. Comparisons are made with the expectations for such electron pair production from the Drell-Yan mechanism and from the semi-leptonic decay of heavy flavours.

We note that most experimental searches for rare phenomena actually measure the ratio of the number of event candidates to the number of some normalizing events. These measurements are most naturally interpreted within the framework of binomial or trinomial statistics. We present a general expression, based upon a classical treatment, that accounts for statistical normalization errors and incorporates expected background rates. The solutions of this expression converge to the standard Poisson values when the number of normalizing events is larger than a few hundred.

This paper reports on a current R&D activity for the sensor part of the CMS pixel detector. Devices featuring several design and technology options have been irradiated up to a proton fluence of 1 /spl times/ 10/sup 15/ n/sup eq//cm/sup 2/ at the CERN PS. Afterwards they have been bump bonded to unirradiated readout chips. The chips allow a non zero suppressed full analogue readout and therefore a good characterization of the sensors in terms of noise and charge collection properties. The samples have been tested using high energy pions in the H2 beam line of the CERN SPS in June and September 2003. The results of this test beam are presented and the differences between the sensor options are discussed.

A simulated dataset of silicon pixel clusters produced by charged particles (pions), where the particle kinematics are taken from fitted tracks in CMS Run 2 data. The interaction of the charged particles with a 100 micron thick silicon pixel detector is simulated using a time-sliced version of PixelAV. The pixel detector is taken to be a 21x13 array of pixels with 50x12.5 micron pitch, situated 30mm from the particle's origin point. The detector is immersed in a 3.8T magnetic field parallel to the sensor x coordinate. Positively and negatively charged particles are saved in the directories positive-charge and negative-charge, respectively. Truth properties of each particle are saved in the labels files, which include columns x-entry, y-entry, z-entry, n_x, n_y, n_z, number_eh_pairs, y-local, pt, cotAlpha, cotBeta, y-midplane, x-midplane. The particle impact point on the sensor surface is described by (x-entry, y-entry), and the impact point at the mid-plane of the sensor is (x-midplane, y-midplane). These impact points are in units of microns. The track direction is given by (n_x, n_y, n_z). The number of electron-hole pairs created in the silicon is number_eh_pairs. The y distance in mm between the center of the 21x13 pixel array and the center of a flat module is denoted by y-local (see included diagram). The particle transverse momentum ($p_T$) in GeV is stored in the pt variable, with the sign indicating the sign of the particle charge. The angle of incidence in the x-z plane is described by cotAlpha, and the angle of incidence in the y-z plane (the bending plane of the magnetic field) is described by cotBeta. The deposited charge per pixel per time slice is saved in the recon files. Reshaping each line as (8,13,21) gives the three dimensional cluster in (time, y, x). Each slice in time corresponds to a window of 200 ps. The combination of all files with index 16800+ yield a physical distribution. Files with lower indices are flattened at low $p_T$.

The electroweak theory of Glashow, Weinberg, and Salam (GWS) has become one of the twin pillars upon which our understanding of all particle physics phenomena rests. It is a brilliant achievement that qualitatively and quantitatively describes all of the vast quantity of experimental data that have been accumulated over some forty years. Note that the word quantitatively must be qualified. The low energy limiting cases of the GWS theory, Quantum Electrodynamics and the V-A Theory of Weak Interactions, have withstood rigorous testing. The high energy synthesis of these ideas, the GWS theory, has not yet been subjected to comparably precise scrutiny. The recent operation of a new generation of proton-antiproton (p{bar p}) and electron-positron (e{sup +}e{sup {minus}}) colliders has made it possible to produce and study large samples of the electroweak gauge bosons W{sup {plus minus}} and Z{sup 0}. We expect that these facilities will enable very precise tests of the GWS theory to be performed in the near future. In keeping with the theme of this Institute, Physics at the 100 GeV Mass Scale, these lectures will explore the current status and the near-future prospects of these experiments.

We show that doubly peaked electric fields are necessary to describe grazing-angle charge collection measurements of irradiated silicon pixel sensors. A model of irradiated silicon based upon two defect levels with opposite charge states and the trapping of charge carriers can be tuned to produce a good description of the measured charge collection profiles in the fluence range from 0.5×10 14 neq/cm 2 to 5.9×10 14 neq/cm 2 . The model correctly predicts the variation in the profiles as the temperature is changed from 10 ◦ C to 25 ◦ C. The measured charge collection profiles are inconsistent with the linearly-varying electric fields predicted by the usual description based upon a uniform effective doping density. This observation calls into question the practice of using effective doping densities to characterize irradiated silicon. The model is now being used to calibrate pixel hit reconstruction algorithms for CMS.

Charge collection measurements performed on heavily irradiated p-spray dofz pixel sensors with a grazing angle hadron beam provide a sensitive determination of the electric field within the detectors. The data are compared with a complete charge transport simulation of the sensor which includes signal trapping and charge induction effects. A linearly varying electric field based upon the standard picture of a constant type-inverted effective doping density is inconsistent with the data. A two-trap double junction model implemented in ISE TCAD software can be tuned to produce a doubly-peaked electric field which describes the data reasonably well at two different fluences. The modeled field differs somewhat from previous determinations based upon the transient current technique. The model can also account for the level of signal trapping observed in the data.

We show that doubly peaked electric fields are necessary to describe grazing-angle charge collection measurements of irradiated silicon pixel sensors. A model of irradiated silicon based upon two defect levels with opposite charge states and the trapping of charge carriers can be tuned to produce a good description of the measured charge collection profiles in the fluence range from 0.5x10^{14} Neq/cm^2 to 5.9x10^{14} Neq/cm^2. The model correctly predicts the variation in the profiles as the temperature is changed from -10C to -25C. The measured charge collection profiles are inconsistent with the linearly-varying electric fields predicted by the usual description based upon a uniform effective doping density. This observation calls into question the practice of using effective doping densities to characterize irradiated silicon. The model is now being used to calibrate pixel hit reconstruction algorithms for CMS.

A new method for the extraction of the electric field in the bulk of heavily irradiated silicon pixel sensors is presented. It is based on the measurement of the Lorentz deflection and mobility of electrons as a function of depth. The measurements were made at the CERN H2 beam line, with the beam at a shallow angle with respect to the pixel sensor surface. The extracted electric field is used to simulate the charge collection and the Lorentz deflection in the pixel sensor. The simulated charge collection and the Lorentz deflection is in good agreement with the measurements both for non-irradiated and irradiated up to 1E15 neq/cm2 sensors.

The structure of e{sup +}e{sup {minus}}{r_arrow}b{bar b}g events was studied using Z{sup 0} decays recorded in the SLC Large Detector experiment at SLAC. Three-jet final states were selected and the charge-coupled device-based vertex detector was used to identify two of the jets as {ital b} or {bar b}. Distributions of the gluon energy and polar angle were measured over the full kinematic range for the first time, and compared with perturbative QCD predictions. The energy distribution is potentially sensitive to an anomalous {ital b} chromomagnetic moment {kappa}. We measured {kappa} to be consistent with zero and set the first limits on its value: {minus}0.17{lt}{kappa}{lt}0.11 at 95{percent} C.L. {copyright} {ital 1999} {ital The American Physical Society}

A review of the decade of Z-pole electroweak physics is presented. Although all experimental work has been completed, it represents a ``Golden Age'' in our understanding of the Minimal Electroweak Standard Model (MSM). The latest (and nearly final) results from the LEP and SLC experiments are presented. The remaining inconsistencies are discussed and and their effects upon the MSM interpretation are explored.

The SLAC Linear Collider (SLC) was constructed in the years 1983--1987 for two principal reasons: to develop the accelerator physics and technology that are necessary for the construction of future linear electron-positron colliders; and to produce electron-positron collisions at the Z{sup 0} pole and to study the physics of the weak neutral current. To date, the SLC program has been quite successful at achieving the first goal. The machine has produced and collided high energy electron and positron beams of three-micron transverse size. The problems of operating an open geometry detector in an environment that is more akin to those found in fixed-target experiments than in storage rings have largely been solved. As a physics producing venture, the SLC has been less successful than was originally hoped but more successful than is commonly believed. Some of the results that have been produced by the Mark II experiment with a very modest data sample are competitive with those that have been produced with much larger samples by the four LEP collaborations. At the current, time, SLAC is engaged in an ambitious program to upgrade the SLC luminosity and to exploit one of its unique features, a spin polarized electron beam. Thesemore » lectures are therefore organized into three sections: a brief description of the SLC; a review of the physics results that have been achieved with the Mark II detector; a description of the SLC's future: the realization and use of a polarized electron beam.« less

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation Morris L. Swartz; Electroweak radiative corrections and measurements of Rhad. AIP Conf. Proc. 5 January 1996; 349 (1): 270–284. https://doi.org/10.1063/1.49265 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search

The production of massive muon pairs in 225 GeV/c $\pi^-$-nucleus interactions has been studied for four nuclear targets. The dependence of the integrated cross section on atomic mass A was measured by comparing the relative cross sections for the targets. If one assumes that the cross section is proportional to $A^{\alpha}$, a value of a= 1.00±0.06 for muon pair masses between 4.0 GeV/$c^2$ and 8.5 GeV/$c^2$ was obtained. The Drell-Yan model predicts an additional dependence of the cross section on the proton fraction Z/A. If one parametizes the integrated cross I section as a(Z/A)$A^{\alpha}$ where $\sigma$(Z/A) is a function of the proton fraction that includes the effects of the Drell-Yan model, Fermi Motion, and secondary pion production, a value of $\alpha$ = 0.97±0.06 was obtained. The dependence of the muon pair transverse momentum distribution on nuclear size was also investigated. The second moment of the distribution <$P^2_T$> was found to be consistent with being independent of nuclear size. If the dependence of <$P^2_T$> on nuclear size is parametized as <$P^2_T$> = a + b $A^{1/3}$ the coefficient b was found to be less than 0.015 $GeV^2$/$c^2$ with 90% confidence.

It is pointed out that the MSM still must be tested at heavy particle loops. Searches for Z[prime] are discussed as are lineshape parameters of gauge bosons. (AIP)

The SLAC Linear Collider (SLC) has recently been upgraded to produce, accelerate, and collide a spin polarized electron beam. The average beam polarization during the 1992 run was (22.4 {plus_minus} 0.7)%. The SLD Collaboration used the polarized beam to perform the first measurement of the left-right cross section asymmetry (A{sub LR}) for Z boson production by e{sup +}e{sup {minus}} collisions. The measurement was performed at a center-of-mass energy of 91.55 GeV with a sample of 10,224 Z decays. The measured value of A{sub LR} is 0.100 {plus_minus} 0.044(stat.) {plus_minus} O.004(syst.) which determines the effective weak mixing angle to be sin{sup 2}{theta}{sub W}{sup eff} = 0.2378 {plus_minus} 0.0056(stat.) {plus_minus} 0.0005(syst.).

Abstract

The SLAC Linear Collider (SLC) was constructed in the years 1983–1987 for two principal reasons:

The SLAC Linear Collider has been designed to readily accomodate polarized electron beams. Considerable effort has been made to implement a polarized source, a spin rotation system, and a system to monitor the beam polarization. Nearly all major components have been fabricated. At the current time, severa1 source and polarimeter components have been installed. The installation and commissioning of the entire system will take place during available machine shutdown periods as the commissioning of SLC progresses. It is expected that a beam polarization of 45% will be achieved with no loss in luminosity.