B. Kilminster

We present results of a dark matter search performed with a 0.6 kg d exposure of the DAMIC experiment at the SNOLAB underground laboratory.We measure the energy spectrum of ionization events in the bulk silicon of charge-coupled devices down to a signal of 60 eV electron equivalent.The data are consistent with radiogenic backgrounds, and constraints on the spin-independent WIMPnucleon elastic-scattering cross section are accordingly placed.A region of parameter space relevant to the potential signal from the CDMS-II Si experiment is excluded using the same target for the first time.This result obtained with a limited exposure demonstrates the potential to explore the low-mass WIMP region (<10 GeV c -2 ) with the upcoming DAMIC100, a 100 g detector currently being installed in SNOLAB.

A direct dark matter search is performed using fully-depleted high-resistivity CCD detectors. Due to their low electronic readout noise (R.M.S. ∼7 eV) these devices operate with a very low detection threshold of 40 eV, making the search for dark matter particles with low masses (∼5 GeV) possible. The results of an engineering run performed in a shallow underground site are presented, demonstrating the potential of this technology in the low mass region.

The CONNIE detector prototype is operating at a distance of 30 m from the core of a 3.8 GW$_{\rm th}$ nuclear reactor with the goal of establishing Charge-Coupled Devices (CCD) as a new technology for the detection of coherent elastic neutrino-nucleus scattering. We report on the results of the engineering run with an active mass of 4 g of silicon. The CCD array is described, and the performance observed during the first year is discussed. A compact passive shield was deployed for the detector, producing an order of magnitude reduction in the background rate. The remaining background observed during the run was stable, and dominated by internal contamination in the detector packaging materials. The {\it in-situ} calibration of the detector using X-ray lines from fluorescence demonstrates good stability of the readout system. The event rates with the reactor on and off are compared, and no excess is observed coming from nuclear fission at the power plant. The upper limit for the neutrino event rate is set two orders of magnitude above the expectations for the standard model. The results demonstrate the cryogenic CCD-based detector can be remotely operated at the reactor site with stable noise below 2 e$^-$ RMS and stable background rates. The success of the engineering test provides a clear path for the upgraded 100 g detector to be deployed during 2016.

We present measurements of radioactive contamination in the high-resistivity silicon charge-coupled devices (CCDs) used by the DAMIC experiment to search for dark matter particles. Novel analysis methods, which exploit the unique spatial resolution of CCDs, were developed to identify $\alpha$ and $\beta$ particles. Uranium and thorium contamination in the CCD bulk was measured through $\alpha$ spectroscopy, with an upper limit on the $^{238}$U ($^{232}$Th) decay rate of 5 (15) kg$^{-1}$ d$^{-1}$ at 95% CL. We also searched for pairs of spatially correlated electron tracks separated in time by up to tens of days, as expected from $^{32}$Si-$^{32}$P or $^{210}$Pb-$^{210}$Bi sequences of $\beta$ decays. The decay rate of $^{32}$Si was found to be $80^{+110}_{-65}$ kg$^{-1}$ d$^{-1}$ (95% CI). An upper limit of $\sim$35 kg$^{-1}$ d$^{-1}$ (95% CL) on the $^{210}$Pb decay rate was obtained independently by $\alpha$ spectroscopy and the $\beta$ decay sequence search. These levels of radioactive contamination are sufficiently low for the successful operation of CCDs in the forthcoming 100 g DAMIC detector.

Pixelated low-gain avalanche diodes (LGADs) can provide both precision spatial and temporal measurements for charged particle detection; however, electrical termination between the pixels yields a no-gain region, such that the active area or fill factor is not sufficient for small pixel sizes. Trench-isolated LGADs (TI-LGADs) are a strong candidate for solving the fill-factor problem, as the p-stop termination structure is replaced by isolated trenches etched in the silicon itself. In the TI-LGAD process, the p-stop termination structure, typical of LGADs, is replaced by isolating trenches etched in the silicon itself. This modification substantially reduces the size of the no-gain region, thus enabling the implementation of small pixels with an adequate fill factor value. In this article, a systematic characterization of the TI-RD50 production, the first of its kind entirely dedicated to the TI-LGAD technology, is presented. Designs are ranked according to their measured inter-pixel distance, and the time resolution is compared against the regular LGAD technology.

The reconstruction of the invariant mass of τ lepton pairs is important for analyses containing Higgs and Z bosons decaying to τ+τ−, but highly challenging due to the neutrinos from the τ lepton decays, which cannot be measured in the detector. In this paper, we demonstrate how artificial neural networks can be used to reconstruct the mass of a di-τ system and compare this procedure to an algorithm used by the CMS Collaboration for this purpose. We find that the neural network output shows a smaller bias and better resolution of the di-τ mass reconstruction and an improved discrimination between a Higgs boson signal and the Drell–Yan background with a much shorter computation time.

We describe the filtering and analysis software running in the Collider Detector at Fermilab (CDF) Run II Level-3 trigger, as well as the client- and event-driven data hub system. These systems constitute critical components of the data acquisition system of the CDF detector. The Level-3 trigger is responsible for reconstructing the events and forming the final trigger decision. The consumer-server/logger (CSL) system receives the accepted physics events from multiple connections and writes them to disk in multiple streams, while distributing them to online analysis programs (consumers). Since 2001, the system has been running successfully at high throughput rates: the Level-3 trigger reduces the event rate from 350 Hz to about 100 Hz with an average event size of 150 kB, while the CSL is able to process up to 22 MB/s of constant event logging. We describe these systems in detail and report on their current performance. We briefly outline upgrade plans for the remainder of Tevatron Run II.

Minerals are solid state nuclear track detectors - nuclear recoils in a mineral leave latent damage to the crystal structure. Depending on the mineral and its temperature, the damage features are retained in the material from minutes (in low-melting point materials such as salts at a few hundred degrees C) to timescales much larger than the 4.5 Gyr-age of the Solar System (in refractory materials at room temperature). The damage features from the $O(50)$ MeV fission fragments left by spontaneous fission of $^{238}$U and other heavy unstable isotopes have long been used for fission track dating of geological samples. Laboratory studies have demonstrated the readout of defects caused by nuclear recoils with energies as small as $O(1)$ keV. This whitepaper discusses a wide range of possible applications of minerals as detectors for $E_R \gtrsim O(1)$ keV nuclear recoils: Using natural minerals, one could use the damage features accumulated over $O(10)$ Myr$-O(1)$ Gyr to measure astrophysical neutrino fluxes (from the Sun, supernovae, or cosmic rays interacting with the atmosphere) as well as search for Dark Matter. Using signals accumulated over months to few-years timescales in laboratory-manufactured minerals, one could measure reactor neutrinos or use them as Dark Matter detectors, potentially with directional sensitivity. Research groups in Europe, Asia, and America have started developing microscopy techniques to read out the $O(1) - O(100)$ nm damage features in crystals left by $O(0.1) - O(100)$ keV nuclear recoils. We report on the status and plans of these programs. The research program towards the realization of such detectors is highly interdisciplinary, combining geoscience, material science, applied and fundamental physics with techniques from quantum information and Artificial Intelligence.

Charge-coupled devices (CCDs) are a leading technology in direct dark matter searches because of their eV-scale energy threshold and high spatial resolution. The sensitivity of future CCD experiments could be enhanced by distinguishing nuclear recoil signals from electronic recoil backgrounds in the CCD silicon target. We present a technique for event-by-event identification of nuclear recoils based on the spatial correlation between the primary ionization event and the lattice defect left behind by the recoiling atom, later identified as a localized excess of leakage current under thermal stimulation. By irradiating a CCD with an $^{241}$Am$^{9}$Be neutron source, we demonstrate $>93\%$ identification efficiency for nuclear recoils with energies $>150$ keV, where the ionization events were confirmed to be nuclear recoils from topology. The technique remains fully efficient down to 90 keV, decreasing to 50$\%$ at 8 keV, and reaching ($6\pm2$)$\%$ at 1.5--3.5 keV. Irradiation with a $^{24}$Na $\gamma$-ray source shows no evidence of defect generation by electronic recoils, with the fraction of electronic recoils with energies $<85$ keV that are spatially correlated with defects $<0.1$$\%$.

In extended Higgs sectors, heavy Higgs bosons can decay via cascades to a light Higgs boson plus $W$ and $Z$ bosons. We study signals of such sectors at the Tevatron and LHC that result from resonant production of a heavy ${H}^{0}$ followed by the decay ${H}^{0}\ensuremath{\rightarrow}{H}^{\ifmmode\pm\else\textpm\fi{}}{W}^{\ensuremath{\mp}}$ with ${H}^{+}\ensuremath{\rightarrow}{W}^{+}{h}^{0}\ensuremath{\rightarrow}{W}^{+}b\overline{b}$ or ${H}^{+}\ensuremath{\rightarrow}t\overline{b}\ensuremath{\rightarrow}{W}^{+}b\overline{b}$. The final states have the same particle content as that of $t\overline{t}$ production, but with a resonant structure that can be used to distinguish signal events from background events. We propose analysis techniques and estimate the experimental sensitivity of the Tevatron and LHC experiments to these signals.

Both the current upgrades to accelerator-based HEP detectors (e.g. ATLAS, CMS) and also future projects (e.g. CEPC, FCC) feature large-area silicon-based tracking detectors. We are investigating the feasibility of using CMOS foundries to fabricate silicon radiation detectors, both for pixels and for large-area strip sensors. A successful proof of concept would open the market potential of CMOS foundries to the HEP community, which would be most beneficial in terms of availability, throughput and cost. In addition, the availability of multi-layer routing of signals will provide the freedom to optimize the sensor geometry and the performance, with biasing structures implemented in poly-silicon layers and MIM-capacitors allowing for AC coupling. A prototyping production of strip test structures and RD53A compatible pixel sensors was recently completed at LFoundry in a 150nm CMOS process. This presentation will focus on the characterization of pixel modules, studying the performance in terms of charge collection, position resolution and hit efficiency with measurements performed in the laboratory and with beam tests. We will report on the investigation of RD53A modules with 25x100 mu^2 cell geometry.

The characterization of spacial and timing resolution of the novel Trench Isolated LGAD (TI-LGAD) technology is presented. This technology has been developed at FBK with the goal of achieving 4D pixels, where an accurate position resolution is combined in a single device with the precise timing determination for Minimum Ionizing Particles (MIPs). In the TI-LGAD technology, the pixelated LGAD pads are separated by physical trenches etched in the silicon. This technology can reduce the interpixel dead area, mitigating the fill factor problem. The TI-RD50 production studied in this work is the first one of pixelated TI-LGADs. The characterization was performed using a scanning TCT setup with an infrared laser and a $^{90}$Sr source setup.

The level-3 trigger system for the CDF experiment runs on a farm of Linux PCs. Events that pass this trigger system are collected and logged to disk by a logger process running on an SGI Origin 200 GIGAchannel server. The system must support data logging at 75 Hz for 250 KB events. In addition, some of the events are sent to remote consumer processes for online monitoring. The Consumer-server/logger system inherently behaves like an intelligent hardware hub, maintaining connectivity between these large numbers (/spl sim/200) of Level-3 farm nodes, consumer processes, and the logging hardware. The farm nodes and the consumer processes are networked using multiple Fast Ethernet interfaces while the disk subsystem of 0.5-1 TB capacity is connected via dual fibre channel arbitrated loops. Different functions of the consumer-server/logger are implemented as distinct state machines to keep each section of the code as simple and robust as possible. In this paper, we describe the first implementation of the system and present initial performance results conducted at CDF.

The structure of the tbW vertex is probed by measuring the polarization of the W in t → W + b → l + v + b. The invariant mass of the lepton and b quark measures the W decay angle which in turn allows a comparison with polarizations expected from different possible models for the spin properties of the tbW interaction. We measure the fraction by rate of Ws produced with a V + A coupling in lieu of the Standard Model V-A to be fV + A = [special characters omitted] (stat) ± 0.21 (sys). We assign a limit of fV + A < 0.80 @ 95% Confidence Level (CL). By combining this result with a complementary observable in the same data, we assign a limit of fV + A < 0.61 @ 95% CL. We find no evidence for a non-Standard Model tbW vertex.

The CMS MIP Timing Detector, proposed for the HL-LHC upgrade, will be instrumented with O(10) square meters of ultra-fast Silicon detectors (UFSD) in the forward region.These UFSDs are aimed at measuring the time of passage of each track with a precision of about 30 ps.The sensor that will be used for this task is the low gain avalanche detectors (LGAD).In this contribution, we will present the latest results from laboratory measurements on 50 and 35 µm thick LGADs fabricated by CNM, in the framework of the AIDA-2020 project.We will concentrate on the timing performance of the sensors.Additionally the electrical characterisation of the sensor will be discussed.

The consistency of the spin correlation strength in top quark pair production with the standard model (SM) prediction is tested in the muon+jets final state. The events are selected from pp collisions, collected by the CMS detector, at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.7fb$^{−1}$. The data are compared with the expectation for the spin correlation predicted by the SM and with the expectation of no correlation. Using a template fit method, the fraction of events that show SM spin correlations is measured to be 0.72 ± 0.08 (stat)$^{+0.15} _{−0.13}$(syst), representing the most precise measurement of this quantity in the muon+jets final state to date.

We introduce the fully-depleted charge-coupled device (CCD) as a particle detector. We demonstrate its low energy threshold operation, capable of detecting ionizing energy depositions in a single pixel down to 50 eVee. We present results of energy calibrations from 0.3 keVee to 60 keVee, showing that the CCD is a fully active detector with uniform energy response throughout the silicon target, good resolution (Fano ~0.16), and remarkable linear response to electron energy depositions. We show the capability of the CCD to localize the depth of particle interactions within the silicon target. We discuss the mode of operation and unique imaging capabilities of the CCD, and how they may be exploited to characterize and suppress backgrounds. We present the first results from the deployment of 250 um thick CCDs in SNOLAB, a prototype for the upcoming DAMIC100. DAMIC100 will have a target mass of 0.1 kg and should be able to directly test the CDMS-Si signal within a year of operation.

A search is presented for narrow resonances decaying to dijet final states in proton–proton collisions at s√=13TeV using data corresponding to an integrated luminosity of 12.9 $fb{−1}$. The dijet mass spectrum is well described by a smooth parameterization and no significant evidence for the production of new particles is observed. Upper limits at 95% confidence level are reported on the production cross section for narrow resonances with masses above 0.6 TeV. In the context of specific models, the limits exclude string resonances with masses below 7.4 TeV, scalar diquarks below 6.9 TeV, axigluons and colorons below 5.5 TeV, excited quarks below 5.4 TeV, color-octet scalars below 3.0 TeV, W′ bosons below 2.7 TeV, Z′ bosons below 2.1 TeV and between 2.3 and 2.6 TeV, and RS gravitons below 1.9 TeV. These extend previous limits in the dijet channel. Vector and axial-vector mediators in a simplified model of interactions between quarks and dark matter are excluded below 2.0 TeV. The first limits in the dijet channel on dark matter mediators are presented as functions of dark matter mass and are compared to the exclusions of dark matter in direct detection experiments.

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <?Pub Dtl=""?>The CDF II detector uses dedicated hardware to identify charged tracks that are used in an important class of level 1 trigger decisions. Until now, this hardware identified track segments based on patterns of hits on only the axial sense wires in the tracking chamber and determined the transverse momentum of track candidates from patterns of track segments. This identification is efficient but produces trigger rates that grow rapidly with increasing instantaneous luminosity. High trigger rates are a consequence of the large numbers of low momentum tracks produced in inelastic <formula formulatype="inline"> <tex>$p\bar p$</tex></formula> collisions which generate overlapping patterns of hits that match those expected for high-momentum tracks. A recently completed upgrade to the level 1 track trigger system makes use of information from stereo wires in the tracking chamber to reduce the rate of false triggers while maintaining high efficiency for real high momentum particles. We describe the new electronics used to instrument the additional sense wires, identify track segments and correlate these with the track candidates found by the original track trigger system. The performance of this system is characterized in terms of the efficiency for identifying charged particles and the improved rejection of axial track candidates that do not correspond to real particles. </para>

We present a readout chip prototype for future pixel detectors with timing capabilities. The prototype is intended for characterizing 4D pixel arrays with a pixel size of $100\times100~\mu \text{m}^2$, where the sensors are Low Gain Avalanche Diodes (LGADs). The long-term focus is towards a possible replacement of disks in the extended forward pixel system (TEPX) of the CMS experiment during the High Luminosity LHC (HL-LHC). The requirements for this ASIC are the incorporation of a Time to Digital Converter (TDC) within each pixel, low power consumption, and radiation tolerance up to $5\times10^{15}~n_\text{eq}\text{~cm}^{-2}$ to withstand the radiation levels in the innermost detector modules for $3000 \text{fb}^{-1}$ of the HL-LHC (in the TEPX). A prototype has been designed and produced in 110~nm CMOS technology at LFoundry and UMC with different versions of TDC structures, together with a front end circuitry to interface with the sensors. The design of the TDC will be discussed, with the test set-up for the measurements, and the first results comparing the performance of the different structures.

We present CDF and D0 searches for a Standard Model Higgs boson produced associatively with a W or Z boson at {radical}s = 1.96 TeV using up to 1 fb{sup -1} of analyzed Tevatron data collected from February 2002 to February 2006. For Higgs masses less than 135 GeV/c{sup 2}, as is favored by experimental and theoretical constraints, W{sup {+-}} H {yields} {ell}{sup {+-}}{nu}b{bar b}, ZH {yields} {ell}{sup +}{ell}{sup -} b{bar b}, and ZH {yields} {nu}{bar {nu}}b{bar b} are the most sensitive decay channels to search for the Higgs boson. Both CDF and D0 have analyzed these three channels and found no evidence for Higgs production, and therefore set upper limits on the Higgs production cross-section. While the analyses are not yet sensitive to Standard Model Higgs production, improvements in analysis techniques are increasing sensitivity to the Higgs much faster than added luminosity alone.

The CDF II detector uses dedicated hardware to identify charged tracks that are used in an important class of Level 1 trigger decisions. Until now, this hardware identified track segments based on patterns of hits on only the axial sense wires in the tracking chamber and determined the transverse momentum of track candidates from patterns of track segments. This identification is efficient but produces trigger rates that grow rapidly with increasing instantaneous luminosity. High trigger rates are a consequence of the large numbers of low momentum tracks produced in inelastic pp macr collisions which generate overlapping patterns of hits that match those expected for high-momentum tracks. A recently completed upgrade to the Level 1 track trigger system makes use of information from stereo wires in the tracking chamber to reduce the rate of false triggers while maintaining high efficiency for real high momentum particles. We describe the new electronics used to instrument the additional sense wires, identify track segments and correlate these with the track candidates found by the original track trigger system. The performance of this system is characterized in terms of the efficiency for identifying charged particles and the improved rejection of axial track candidates that do not correspond to real particles.

The CDF II eXtremely Fast Tracker is the trigger track processor which reconstructs charged particle tracks in the transverse plane of the CDF II central outer tracking chamber. The system is now being upgraded to perform a three dimensional track reconstruction. A review of the upgrade is presented here.

The cross sections for the production of $t\overline{t}b\overline{b}$ and $t\overline{t}jj$ events and their ratio $\sigma_{t\overline{t}b\overline{b}} / \sigma_{t\overline{t}jj}$ are measured using data corresponding to an integrated luminosity of 2.3 $fb^{−1}$collected in pp collisions at $\sqrt{s}$ = 13TeV with the CMS detector at the LHC. Events with two leptons (e or μ) and at least four reconstructed jets, including at least two identified as b quark jets, in the final state are selected. In the full phase space, the measured ratio is $0.022 \pm 0.003(stat) \pm 0.006(syst)$, the cross section $\sigma_{t\overline{t}b\overline{b}}$ is $4.0 \pm 0.6(stat) \pm 1.3(syst)pb$ and $\sigma_{t\overline{t}jj}$ is $184 \pm 6(stat) \pm 33(syst)pb$. The measurements are compared with the standard model expectations obtained from a powheg simulation at next-to-leading-order interfaced with pythia.

We present CDF and D0 searches for a Standard Model Higgs boson produced associatively with a W or Z boson at {radical}s = 1.96 TeV using up to 1 fb{sup -1} of analyzed Tevatron data collected from February 2002 to February 2006. For Higgs masses less than 135 GeV/c{sup 2}, as is favored by experimental and theoretical constraints, W{sup {+-}} H {yields} {ell}{sup {+-}}{nu}b{bar b}, ZH {yields} {ell}{sup +}{ell}{sup -} b{bar b}, and ZH {yields} {nu}{bar {nu}}b{bar b} are the most sensitive decay channels to search for the Higgs boson. Both CDF and D0 have analyzed these three channels and found no evidence for Higgs production, and therefore set upper limits on the Higgs production cross-section. While the analyses are not yet sensitive to Standard Model Higgs production, improvements in analysis techniques are increasing sensitivity to the Higgs much faster than added luminosity alone.

Commodity hardware running the Linux operating system will serve various roles in the next few years at Fermilab. We discuss several applications of Linux to distributed systems with real time or other performance constraints. First, we describe the level-3 trigger of the CDF experiment. In Run II, starting in the year 2000, this trigger will consist of hundreds of Intel-based PC's and will be responsible for filtering events arriving via ATM at up to 250 MBytes/sec. The events will be distributed via fast ethernet to subfarms providing at least 45000 MIPS of computational power for the online reconstruction codes. Second, we discuss investigations of commodity hardware applied to lattice-gauge calculations, requiring hundreds of systems coupled via very low latency, high bandwidth networks. Third, we describe a high performance shared file system running on a cluster of Linux systems attached via fibre channel to a common disk pool.

We construct the first comprehensive radioactive background model for a dark matter search with charge-coupled devices (CCDs). We leverage the well-characterized depth and energy resolution of the DAMIC at SNOLAB detector and a detailed {\tt GEANT4}-based particle-transport simulation to model both bulk and surface backgrounds from natural radioactivity down to 50~eV$_{\text{ee}}$. We fit to the energy and depth distributions of the observed ionization events to differentiate and constrain possible background sources, for example, bulk $^{3}$H from silicon cosmogenic activation and surface $^{210}$Pb from radon plate-out. We observe the bulk background rate of the DAMIC at SNOLAB CCDs to be as low as $3.1 \pm 0.6$ counts kg$^{-1}$ day$^{-1}$ keV$_{\text{ee}}^{-1}$, making it the most sensitive silicon dark matter detector. Finally, we discuss the properties of a statistically significant excess of events over the background model with energies below 200~eV$_{\text{ee}}$.

Both the current upgrades to accelerator-based HEP detectors (e.g. ATLAS, CMS) and also future projects (e.g. CEPC, FCC) feature large-area silicon-based tracking detectors. We are investigating the feasibility of using CMOS foundries to fabricate silicon radiation detectors, both for pixels and for large-area strip sensors. A successful proof of concept would open the market potential of CMOS foundries to the HEP community, which would be most beneficial in terms of availability, throughput and cost. In addition, the availability of multi-layer routing of signals will provide the freedom to optimize the sensor geometry and the performance, with biasing structures implemented in poly-silicon layers and MIM-capacitors allowing for AC coupling. A prototyping production of strip test structures and RD53A compatible pixel sensors was recently completed at LFoundry in a 150nm CMOS process. This presentation will focus on the characterization of pixel modules, studying the performance in terms of charge collection, position resolution and hit efficiency with measurements performed in the laboratory and with beam tests. We will report on the investigation of RD53A modules with 25x100 mu^2 cell geometry.

For Run II, the CDF Level-3 trigger must provide a sustained input bandwidth of at least 45 MBytes/set and will require processing power of at least 45000 MIPS to perform the necessary reconstruction and filtering of events. We present a distributed, scalable architecture using commod- ity hardware running the Linux operating system. I/O and CPU intensive functions are separated into two types of nodes; �converter� nodes receive event fragments via ATM from Level 2 computers and distribute complete events to �processor� nodes via multiple fast ethernets. We present re- sults from a small-scale prototype roughly equivalent to a 1/16th vertical slice of the final system. With this hardware we have demonstrated the capability of sustained I/O rates of 15 MBytes/set, more then three times the required baseline performance. We discuss PC hardware and Linux software issues and modifications for real time performance.