arXiv subjects

Matthew Moulson

Publications and source records attributed to Matthew Moulson.

At least 19 recordsLinked to original sources

arXiv2025

High-Precision Alignment Techniques for Realizing an Ultracompact Electromagnetic Calorimeters Using Oriented high-Z Scintillator Crystals

Electromagnetic calorimeters used in high-energy physics and astrophysics rely heavily on high-Z inorganic scintillators, such as lead tungstate (PbWO4 or PWO). The crystalline structure and lattice orientation of inorganic scintillators are frequently underestimated in detector design, even though it is known that the crystalline lattice strongly modifies the features of the electromagnetic processes inside the crystal. A novel method has been developed for precisely bonding PWO crystals with aligned atomic planes within 100 {\mu}rad, exploiting X-ray diffraction (XRD) to accurately measure miscut angles. This method demonstrates the possibility to align a layer of crystals along the same crystallographic direction, opening a new technological path towards the development of next-generation electromagnetic calorimeters.

physics.ins-det↗

arXiv2025

Proposal of the KOTO II experiment

The KOTO II experiment is proposed to measure the branching ratio of the decay $K_L\to\pi^0\nu\bar{\nu}$ at J-PARC. With a beamline to extract long-lived neutral kaons at 5 degrees from a production target, the single event sensitivity of the decay is $8.5\times 10^{-13}$, which is much smaller than the Standard Model prediction $3\times 10^{-11}$. This allows searches for new physics beyond the Standard Model and the first discovery of the decay with a significance exceeding $5\sigma$. As the only experiment proposed in the world dedicated to rare kaon decays, KOTO II will be indispensable in the quest for a complete understanding of flavor dynamics in the quark sector. Moreover, by combining efforts from the kaon community worldwide, we plan to develop the KOTO II detector further and expand the physics reach of the experiment to include measurements of the branching ratio of the $K_L\to\pi^0\ell^+\ell^-$ decays, studies of other $K_L$ decays, and searches for dark photons, axions, and axion-like particles. KOTO II will therefore obtain a comprehensive understanding of $K_L$ decays, providing further constraints on new physics scenarios with existing $K^+$ results.

hep-ex↗

arXiv2024

Particle identification capability of a homogeneous calorimeter composed of oriented crystals

Recent studies have shown that the electromagnetic shower induced by a high-energy electron, positron or photon incident along the axis of an oriented crystal develops in a space more compact than the ordinary. On the other hand, the properties of the hadronic interactions are not affected by the lattice structure. This means that, inside an oriented crystal, the natural difference between the hadronic and the electromagnetic shower profile is strongly accentuated. Thus, a calorimeter composed of oriented crystals could be intrinsically capable of identifying more accurately the nature of the incident particles, with respect to a detector composed only of non-aligned crystals. Since no oriented calorimeter has ever been developed, this possibility remains largely unexplored and can be investigated only by mean of numerical simulations. In this work, we report the first quantitative evaluation of the particle identification capability of such a calorimeter, focusing on the case of neutron-gamma discrimination. We demonstrate through Geant4 simulations that the use of oriented crystals significantly improves the performance of a Random Forest classifier trained on the detector data. This work is a proof that oriented calorimeters could be a viable option for all the environments where particle identification must be performed with a very high accuracy, such as future high-intensity particle physics experiments and satellite-based gamma-ray telescopes.

hep-ex↗

arXiv2024

Strong Enhancement of Electromagnetic Shower Development in Oriented Scintillating Crystals and Implications for Particle Detectors

A particle traversing a crystal aligned with one of its crystallographic axes experiences a strong electromagnetic field that is constant along the direction of motion over macroscopic distances. For $e^\pm$ and $\gamma$-rays with energies above a few $\mathrm{GeV}$, this field is amplified by the Lorentz boost, to the point of exceeding the Schwinger critical field $\mathcal{E}_0 \sim 1.32 \times 10^{16}~\mathrm{V/cm}$. In this regime, nonlinear quantum-electrodynamical effects occur, such as the enhancement of intense electromagnetic radiation emission and pair production, so that the electromagnetic shower development is accelerated and the effective shower length is reduced compared to amorphous materials. We have investigated this phenomenon in lead tungstate (PbWO$_4$), a high-$Z$ scintillator widely used in particle detection. We have observed a substantial increase in scintillation light at small incidence angles with respect to the main lattice axes. Measurements with $120$-$\mathrm{GeV}$ electrons and $\gamma$-rays between $5$ and $100~\mathrm{GeV}$ demonstrate up to a threefold increase in energy deposition in oriented samples. These findings challenge the current models of shower development in crystal scintillators and could guide the development of next-generation accelerator- and space-borne detectors.

hep-ex↗

arXiv2023

New Physics Searches at Kaon and Hyperon Factories

Rare meson decays are among the most sensitive probes of both heavy and light new physics. Among them, new physics searches using kaons benefit from their small total decay widths and the availability of very large datasets. On the other hand, useful complementary information is provided by hyperon decay measurements. We summarize the relevant phenomenological models and the status of the searches in a comprehensive list of kaon and hyperon decay channels. We identify new search strategies for under-explored signatures, and demonstrate that the improved sensitivities from current and next-generation experiments could lead to a qualitative leap in the exploration of light dark sectors.

hep-ph↗

arXiv2023

Scrutinizing CKM unitarity with a new measurement of the $K_{μ3}/K_{μ2}$ branching fraction

Precision tests of first-row unitarity of the Cabibbo-Kobayashi-Maskawa matrix currently display two intriguing tensions, both at the $3σ$ level. First, combining determinations of $V_{ud}$ from superallowed $β$ decays with $V_{us}$ from kaon decays suggests a deficit in the unitarity relation. At the same time, a tension of similar significance has emerged between $K_{\ell 2}$ and $K_{\ell 3}$ decays. In this Letter, we point out that a measurement of the $K_{\mu3}/K_{μ2}$ branching fraction at the level of $0.2\%$ would have considerable impact on clarifying the experimental situation in the kaon sector, especially in view of tensions in the global fit to kaon data as well as the fact that the $K_{\mu2}$ channel is currently dominated by a single experiment. Such a measurement, as possible for example at NA62, would further provide important constraints on physics beyond the Standard Model, most notably on the role of right-handed vector currents.

hep-ph↗

arXiv2022

HIKE: High Intensity Kaon Experiments at the CERN SPS

The availability of high intensity kaon beams at the CERN SPS North Area gives rise to unique possibilities for sensitive tests of the Standard Model in the quark flavor sector. Precise measurements of the branching ratios for the flavor-changing neutral current decays $K\toπν\barν$ can provide unique constraints on CKM unitarity and, potentially, evidence for new physics. Building on the success of the NA62 experiment, plans are taking shape at CERN for a comprehensive program that will include experimental phases to measure the branching ratio for $K^+\toπ^+ν\barν$ to ~5% and to $K_L\toπ^0ν\barν$ to ~20% precision. These planned experiments will also carry out lepton flavor universality tests, lepton number and flavor conservation tests, and perform other precision measurements in the kaon sector, as well as searches for exotic particles in kaon decays. We overview the physics goals, detector requirements, and project status for the next generation of kaon physics experiments at CERN.

hep-ex↗

arXiv2019

KLEVER: An experiment to measure BR($K_L\toπ^0ν\barν$) at the CERN SPS

Precise measurements of the branching ratios for the flavor-changing neutral current decays $K\toπν\barν$ can provide unique constraints on CKM unitarity and, potentially, evidence for new physics. It is important to measure both decay modes, $K^+\toπ^+ν\barν$ and $K_L\toπ^0ν\barν$, since different new physics models affect the rates for each channel differently. The NA62 experiment at the CERN SPS will measure the BR for the charged channel to better than 20%. The BR for the neutral channel has never been measured. We are designing the KLEVER experiment to measure BR($K_L\toπ^0ν\barν$) to $\sim$20% using a high-energy neutral beam at the CERN SPS. The boost from the high-energy beam facilitates the rejection of background channels such as $K_L\toπ^0π^0$ by detection of the additional photons in the final state. On the other hand, the layout poses particular challenges for the design of the small-angle vetoes, which must reject photons from $K_L$ decays escaping through the beam exit amid an intense background from soft photons and neutrons in the beam. We present findings from our design studies, with an emphasis on the challenges faced and the potential sensitivity for the measurement of BR($K_L\toπ^0ν\barν$).

hep-ex↗

arXiv2018

KLEVER: An experiment to measure BR($K_L\toπ^0ν\barν$) at the CERN SPS

Precise measurements of the branching ratios for the flavor-changing neutral current decays $K\toπν\barν$ can provide unique constraints on CKM unitarity and, potentially, evidence for new physics. It is important to measure both decay modes, $K^+\toπ^+ν\barν$ and $K_L\toπ^0ν\barν$, since different new physics models affect the rates for each channel differently. The goal of the NA62 experiment at the CERN SPS is to measure the BR for the charged channel to within 10%. For the neutral channel, the BR has never been measured. KOTO, an experiment at J-PARC, should have enough data for the first observation of the decay by about 2021. We are designing the KLEVER experiment to measure BR($K_L\toπ^0ν\barν$) to $\sim$20% using a high-energy neutral beam at the CERN SPS starting in Run 4. The boost from the high-energy beam facilitates the rejection of background channels such as $K_L\toπ^0π^0$ by detection of the additional photons in the final state. On the other hand, the layout poses particular challenges for the design of the small-angle vetoes, which must reject photons from $K_L$ decays escaping through the beam pipe amidst an intense background from soft photons and neutrons in the beam. Background from $Λ\to nπ^0$ decays in the beam must also be kept under control. We present findings from our design studies, with an emphasis on the challenges faced and the potential sensitivity for the measurement of BR($K_L\toπ^0ν\barν$).

physics.ins-det↗

arXiv2017

Summary of the CKM 2016 working group on rare decays

Rare $B$, $D$, and $K$ decays offer unique opportunities to probe for evidence of new particles from physics beyond the Standard Model at mass scales extending from the electroweak scale to well above those directly accessible at the LHC. We review a selection of theoretical and experimental results on rare $B$, $D$, and $K$ decays illustrating the progress made during the past two years.

hep-ph↗

arXiv2017

Experimental determination of $V_{us}$ from kaon decays

The status of the experimental determination of $V_{us}$ from $K_{\ell3}$ and $K_{\mu2}$ decays is reviewed. Factors currently limiting the precision of the evaluation of $V_{us}$ from kaon decays and prospects for new measurements within the next few years are discussed.

hep-ex↗

arXiv2016

Search for $K^+\toπ^+ν\barν$ at NA62

hep-ex↗

arXiv2014

Experimental determination of $V_{us}$ from kaon decays

During the last few years, new experimental and theoretical results have allowed ever-more-stringent tests of the Standard Model to be performed using kaon decays. This overview of recent progress includes updated results for the evaluation of the CKM matrix element $V_{us}$ and related tests of CKM unitarity from experimental data on kaon decays.

hep-ex↗

arXiv2013

Searches for rare and forbidden kaon decays at the NA62 experiment at CERN

The decay $K^+ \to π^+ν\barν$ is highly suppressed in the Standard Model (SM), while its rate can be predicted with minimal theoretical uncertainty. The branching ratio (BR) for this decay is thus a sensitive probe of the flavor sector of the SM; its measurement, however, is a significant experimental challenge. The primary goal of the NA62 experiment is to measure ${\rm BR}(K^+ \to π^+ν\barν)$ with $\sim$10% precision. This will require the observation of $10^{13}$ $K^+$ decays in the experiment's fiducial volume, as well as the use of high-performance systems for precision tracking, particle identification, and photon vetoing. These aspects of the experiment will also allow NA62 to carry out a rich program of searches for lepton flavor and/or number violating $K^+$ decays. Part of the experimental apparatus was commissioned during a technical run in 2012; installation continues and data taking is expected to begin in late 2014. The physics prospects and the status of the NA62 experiment are reviewed.

hep-ex↗

arXiv2013

Forbidden Kaon and Pion Decays in NA62

NA62, an experiment at the CERN SPS to measure the branching ratio for the decay K+ -> pi+ nu nu-bar with ~10% precision, will observe ~10^13 K+ decays in its fiducial volume, and will thus also be able to carry out a rich program to search for forbidden K+ and pi0 decays, including in particular K+ decays that violate the conservation of lepton flavor and/or number. NA62's potential performance in searches for a number of forbidden K+ and pi0 decays is discussed, with initial sensitivity estimates.

hep-ex↗

arXiv2013

V_us from kaon decays

During the last few years, new experimental and theoretical results have allowed ever-more-stringent tests of the Standard Model to be performed using kaon decays. This overview of recent progress includes updated results for the evaluation of the CKM matrix element V_us from kaon decay data and related tests of CKM unitarity and gauge and lepton universality.

hep-ex↗

arXiv2012

Testing the Standard Model with Kaon Decays

During the last few years, new experimental and theoretical results have allowed ever more stringent tests of the Standard Model to be performed using kaon decays. This overview of recent progress includes an updated evaluation of the CKM matrix element Vus. Tests of CKM unitarity and gauge universality and lepton universality tests with Kl2 and Kl3 decays are discussed.

hep-ex↗

arXiv2009

Recent KLOE results on radiative kaon decays

While measuring the ratio R_K = Γ(K+e2(γ))/Γ(K+\mu2(γ)), the KLOE Collaboration has studied the radiative process Ke2γ. The ratio of the width for the Ke2γdecay with a positively polarized photon from structure-dependent radiation to the inclusive K\mu2(γ) width is found to be 1.484(68) 10-5. The observed radiation spectrum agrees with predictions from chiral perturbation theory and is in contrast with predictions based on the light front quark model. This result reduces the contribution to systematic uncertainties on measurements of R_K. In a separate study, KLOE has measured the ratio of the radiative Ke3γdecay width to the inclusive Ke3(γ) width to be 924(28) 10-5. The distribution in energy and angle of the radiative photon has been analyzed in an attempt to isolate the signature from interference of the inner-bremsstrahlung and structure-dependent amplitudes.

hep-ex↗