Abstract We report measurements of the transverse diffusion of electrons in P-10 gas (90% Ar, 10% CH 4 ) in a laboratory-scale time projection chamber (TPC) utilizing a novel pixelated signal capture ...and digitization technique known as Q-Pix. The Q-Pix method incorporates a precision switched integrating transimpedance amplifier whose output is compared to a threshold voltage. Upon reaching the threshold, a comparator sends a 'reset' signal, initiating a discharge of the integrating capacitor. The time difference between successive resets is inversely proportional to the average current at the pixel in that time interval, and the number of resets is directly proportional to the total collected charge. We developed a 16-channel Q-Pix prototype fabricated from commercial off-the-shelf components and coupled them to 16 concentric annular anode electrodes to measure the spatial extent of the electron swarm that reaches the anode after drifting through the uniform field of the TPC. The swarm is produced at a gold photocathode using pulsed UV light. The measured transverse diffusion agrees with simulations in PyBoltz across a range of operating pressures (200–1500 Torr). These results demonstrate that a Q-Pix readout can successfully reconstruct the ionization topology in a TPC.
We report the status of a neural network regression model trained to extract new physics (NP) parameters in Monte Carlo (MC) simulation data. We utilize a new EvtGen NP MC generator to generate B → ...K*0µ+µ− events according to the deviation of the Wilson Coefficient C9 from its SM value, δC9. We train a three-dimensional ResNet regression model, using images built from the angular observables and the invariant mass of the di-muon system, to extract values of δC9 directly from the MC data samples. This work is intended for future analyses at the Belle II experiment but may also find applicability at other experiments.
We present a search for the direct production of a light pseudoscalar a decaying into two photons with the Belle II detector at the SuperKEKB collider. We search for the process e+e−→γa, a→γγ in the ...mass range 0.2<ma<9.7 GeV/c2 using data corresponding to an integrated luminosity of (445±3) pb−1. Light pseudoscalars interacting predominantly with standard model gauge bosons (so-called axionlike particles or ALPs) are frequently postulated in extensions of the standard model. We find no evidence for ALPs and set 95% confidence level upper limits on the coupling strength gaγγ of ALPs to photons at the level of 10−3 GeV−1. The limits are the most restrictive to date for 0.2<ma<1 GeV/c2.
Theories beyond the standard model often predict the existence of an additional neutral boson, the Z^{'}. Using data collected by the Belle II experiment during 2018 at the SuperKEKB collider, we ...perform the first searches for the invisible decay of a Z^{'} in the process e^{+}e^{-}→μ^{+}μ^{-}Z^{'} and of a lepton-flavor-violating Z^{'} in e^{+}e^{-}→e^{±}μ^{∓}Z^{'}. We do not find any excess of events and set 90% credibility level upper limits on the cross sections of these processes. We translate the former, in the framework of an L_{μ}-L_{τ} theory, into upper limits on the Z^{'} coupling constant at the level of 5×10^{-2}-1 for M_{Z^{'}}≤6 GeV/c^{2}.
We report the status of a neural network regression model trained to extract new physics (NP) parameters in Monte Carlo (MC) simulation data. We utilize a new EvtGen NP MC generator to generate B → ...K* 0 µ + µ − events according to the deviation of the Wilson Coefficient C 9 from its SM value, δ C 9 . We train a three-dimensional ResNet regression model, using images built from the angular observables and the invariant mass of the di-muon system, to extract values of δ C 9 directly from the MC data samples. This work is intended for future analyses at the Belle II experiment but may also find applicability at other experiments.
We report on a novel application of computer vision techniques to extract beyond the Standard Model (BSM) parameters directly from high energy physics (HEP) flavor data. We develop a method of ...transforming angular and kinematic distributions into "quasi-images" that can be used to train a convolutional neural network to perform regression tasks, similar to fitting. This contrasts with the usual classification functions performed using ML/AI in HEP. As a proof-of-concept, we train a 34-layer Residual Neural Network to regress on these images and determine the Wilson Coefficient \(C_{9}\) in MC (Monte Carlo) simulations of \(B \rightarrow K^{*}\mu^{+}\mu^{-}\) decays. The technique described here can be generalized and may find applicability across various HEP experiments and elsewhere.
Within the widely used EvtGen framework, we have added a new event generator
model for $B\to K^* \ell^+ \ell^-$ with improved standard model (SM) decay
amplitudes and possible BSM physics ...contributions, which are implemented in the
operator product expansion in terms of Wilson coefficients. This event
generator can then be used to investigate the experimental sensitivity to the
most general BSM signal resulting from dimension-six operators. We describe the
advantages and potential of the newly developed `Sibidanov Physics Generator'
in improving experimental sensitivity of searches for lepton non-universal BSM
physics and clarifying signatures. The new generator can properly simulate BSM
scenarios, interference between SM and BSM amplitudes, and correlations between
different BSM observables as well as acceptance bias. We show that exploiting
such correlations substantially improves experimental sensitivity. As a
demonstration of the utility of the MC generator, we examine the prospects for
improved measurements of lepton non-universality in angular distributions for
$B \to K^* \ell \ell$ decays from the expected 50 ab$^{-1}$ data set of the
Belle II experiment, using a four-dimensional unbinned maximum likelihood fit.
We describe promising experimental signatures and correlations between
observables. The use of lepton-universality violating $\Delta$-observables
significantly reduce uncertainties in the SM expectations due to QCD and
resonance effects, are ideally suited for Belle II with the large data sets
expected in the next decade. Our simulation studies also show that Belle II
should have excellent sensitivity to BSM physics in the Wilson coefficients
$C_7$ and $C_7'$, which appears at low $q^2$ in the di-electron channel.
Using Commercial Off-The-Shelf (COTS) Operational Amplifiers (OpAmps) and Complementary Metal-Oxide Semiconductor (CMOS) transistors, we present a demonstration of the Q-Pix front-end architecture, a ...novel readout solution for kiloton-scale Liquid Argon Time Projection Chamber (LArTPC) detectors. The Q-Pix scheme employs a Charge-Integrate/Reset process based on the Least Action principle, enabling pixel-scale self-triggering charge collection and processing, minimizing energy consumption, and maximizing data compression. We examine the architecture's sensitivity, linearity, noise, and other features at the circuit board level and draw comparisons to SPICE simulations. Furthermore, we highlight the resemblance between the Q-Pix front-end and Sigma-Delta modulator, emphasizing that digital data processing techniques for Sigma-Delta can be directly applied to Q-Pix, resulting in enhanced signal-to-noise performance. These insights will inform the development of Q-Pix front-end designs in integrated circuits (IC) and guide data collection and processing for future large-scale LArTPC detectors in neutrino physics and other high-energy physics experiments.
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