Intensity Frontier Research Articles

Reappraisal of the minimal flavoured Z′ scenario

Recent results from the intensity frontier indicate the tantalizing possibility of violation in lepton flavour universality. In light of this we revisit the minimal phenomenological Z′ model taking in account both vectorial and axial-vectorial flavour violating couplings to the charged leptons. We make a systematic study to identify the minimal framework that can simultaneously explain the recent results on anomalous magnetic moment of muon and electron while remaining in consonance with RK(⁎), Bs0−Bs0¯ mixing and angular observables in the B+→K+⁎μ+μ− channel reported by the LHCb collaboration. We demonstrate that the neutrino trident data imply a further SU(2)L violation in the leptonic couplings of the exotic Z′.

Towards large calorimeters based on Lanthanum Bromide or LYSO crystals coupled to silicon photomultipliers: A first direct comparison for future precision physics

Two very promising materials as the BrilLanCe (Cerium doped Lanthanum Bromide, LaBr3(Ce) and the LYSO (Lutetium Yttrium OxyorthoSilicate, Lu2(1−x) Y2x SiO5 (Ce)) coupled to Silicon photomultipliers (MPPC/SiPM) could represent an appealing option for the future calorimetry. The response of both LaBr3(Ce) and LYSO detectors having MPPC as photosensors have been studied via detailed Monte Carlo (MC) simulations. The impinging gammas are in the range of 50–100 MeV. The MC simulations are based on GEANT4, including the full electronic chain up to the waveform digitizer and finally the reconstruction algorithms.The results have been obtained are very promising. For a detector based on a (radius R = 4.45 cm, length L = 20.3 cm) LaBr3(Ce) crystal an energy resolution of σE/E[%]=2.3(1) and a timing resolution of σt[ps] = 35(1) have been predicted. The energy resolution can be further improved by using larger crystals (either R = 6.35 cm or R = 7.6 cm, L = 20.3 cm) approaching respectively a σE/E[%]=1.20(3) or a σE/E[%]=0.91(1). Detector based on LYSO crystal of similar size performs even better, thanks to the shorter LYSO Moliere radius compared to the LaBr3(Ce) one. For a detector based on a (R = 3.5 cm, L = 16 cm) LYSO crystal an energy resolution of σE/E[%]=1.7(1)% can be obtained, and that can be further improved using bigger crystals (R = 6.5 cm, L = 25 cm, σE/E[%]=0.74(1)%. Energy resolution approaching σE/E[%]=0.3(1)% can be addressed for both crystals with ultimate sizes (R = 20–23 cm, L = 17–32 cm), complemented by timing and position resolutions in the range of O(30) ps and O(a few mm) respectively. Such results put these future high energy calorimeters at the detector forefront at intensity frontiers.

Preface

These are the proceedings of the “New Scientific Opportunities at the TRIUMF ARIEL e-linac” workshop, which took place at TRIUMF laboratory, in Vancouver, Canada, May 25-27, 2022. The workshop was a hybrid of in-person and online attendance via Zoom, gathering together theorists and experimentalists with shared interests in MeV-scale physics at the intensity frontier, in order to stimulate ideas and collaboration for novel applications of new, high-intensity, modest-energy accelerators like the ARIEL e-Linac.While the LHC and its large detector collaborations continue to seek BSM physics at the energy frontier, and increasingly large subterranean detectors probe neutrino and dark matter signals with greater and greater sensitivities, the increasing scale of these experiments represents a substantial undertaking, in terms of cost and timeline. These have yielded important results, confirming the existence of the Higgs and furthering our understanding of neutrino dynamics, but they have not yet provided a clear view of what lies beyond the Standard Model. The prevailing expectations of the previous decades—minimal supersymmetry, WIMP-based dark matter—have not yet been observed.A complementary experimental thrust in the quest for new physics is to probe lower energy scales at the intensity and precision frontiers. Such experiments can be mounted more nimbly, and in parallel, to focus on different reported anomalies as lampposts, to improve precision in places where new physics may lurk, and to test new classes of BSM physics that may arise at those energies. With no definitive guidance on the form an underlying theory must take, this is an increasingly appealing approach to the search.Modern accelerator designs can provide higher and higher beam currents, achieving high luminosities without the need for thick targets, unlocking new experimental avenues. Energy Recovery Linacs (ERLs) at the sub-GeV scale are a particularly exciting emerging platform, with a series of machines at various levels of development, including the planned upgrade for ARIEL, the MESA accelerator complex currently under construction, and the planned PERLE facility.The articles in these proceedings showcase the experimental avenues now being explored, or which could be undertaken at ARIEL and similar-scale accelerators, as well as theoretical studies in these regimes, and the status of accelerators that will enable these and future experiments that aim to address current anomalies and outstanding questions in particle and nuclear physics.The workshop was funded by the Gordon and Betty Moore Foundation, to which the organizing committee give their sincere thanks.Jan Bernauer (CFNS, Stony Brook University and RIKEN BNL Research Center)Ross Corliss (CFNS, Stony Brook University)Michael Hasinoff (University of British Columbia)Rituparna Kanungo (Saint Mary’s University)Jeffery Martin (University of Winnipeg)Richard Milner (Massachusetts Institute of Technology)Katherine Pachal (TRIUMF)Stanley Yen (TRIUMF)

Forecasting dark showers at Belle II

Dark showers from strongly interacting dark sectors that confine at the GeV scale can give rise to novel signatures at e+e− colliders. In this work, we study the sensitivity of B factory experiments to dark showers produced through an effective interaction arising from a heavy off-shell mediator. We show that a prospective search for displaced vertices from GeV-scale long-lived particles at Belle II can improve the sensitivity to dark showers substantially compared to an existing search at BaBar. We compare the sensitivity of searches for displaced signals to searches for promptly produced resonances at BaBar and KLOE and calculate sensitivity projections for a single-photon search at Belle II to invisible dark showers produced through an effective interaction. The underlying structure of the effective interaction can be resolved at higher-energy experiments, where the mediator can be produced on-shell. To study the resulting constraints, we update electroweak precision bounds on kinetically mixed Z′ bosons and reinterpret a search for low-mass di-muon resonances at LHCb in terms of dark showers. We find that LHCb and Belle II are most sensitive to different particle decay lengths, underscoring the complementarity of LHC and intensity frontier experiments.

Chiral Z′ in FASER, FASER2, DUNE, and ILC beam dump experiments

The origin of neutrino mass is a big unsolved problem of the Standard Model (SM) that motivate us to consider beyond the SM (BSM) scenarios where SM-singlet right-handed neutrinos (RHNs) are introduced to explain the origin of the light neutrino masses through the seesaw mechanism. There is a variety of ways which could lead us to this goal and one of them is a general U$(1)$ extension of the SM. In this scenario, three SM-singlet RHNs are introduced to cancel the gauge and mixed gauge gravity anomalies. After anomaly cancellation, we notice that the left- and right-handed charged fermions are differently charged under the general U$(1)$ gauge group evolving a chiral scenario. After the breaking of the general U$(1)$ symmetry, a neutral BSM gauge boson $(Z^\prime)$ acquires mass and it is a free parameter. Such $Z^\prime$, being lighter than $5$ GeV, could be probed at the intensity and lifetime frontiers like FASER, FASER2, DUNE, and ILC beam dump experiments. The estimated bounds are needed to be compared with the existing bounds. We find that existing constraints from Orsay, Nomad, PS191, KEK, LSND, CHARM experiments, and cosmological scenario like SN1987A can be compared in our case once estimated for chiral scenarios. Finally, we compare the parameter spaces showing viable ones that could be probed by FASER, FASER2, DUNE, and ILC beam dump experiments and already excluded regions from Orsay, Nomad, PS191, KEK, LSND, CHARM, and SN1987A for a chiral scenario.

Fast and Radiation Hard Inorganic Scintillators for Future HEP Experiments

Future HEP experiments at the energy and intensity frontiers require fast and ultrafast inorganic scintillators with excellent radiation hardness to face the challenges of unprecedented event rate and severe radiation environment. We report recent progress in fast and ultrafast inorganic scintillators for future HEP experiments. Examples are LYSO crystals and LuAG ceramics for an ultra-compact shashlik sampling calorimeter for the HL-LHC and the proposed FCC-hh, and yttrium doped BaF2 crystals for the proposed Mu2e-II experiment. Applications for GHz hard X-ray imaging will also be discussed.

Towards a Large Calorimeter Based on Lyso Crystals for Future High Energy Physics

The state-of-the-art research at the intensity frontier of particle physics aims to find evidence for new physics beyond the Standard Model by searching for faint signals in a vast amount of background. To this end, detectors with excellent resolution in all kinematic variables are required. For future calorimeters, a very promising material is LYSO, due to its short radiation length, fast decay time and good light yield. In this article, the simulation of a calorimeter assembled from multiple large LYSO crystals is presented. Although there is still a long way to go before crystals of that size can be produced, the results suggest an energy resolution of 1%, a position resolution around 5 mm and a time resolution of about 30 ps for photons and positrons with an energy of 55 MeV. These results would put such a calorimeter at the technology forefront in precision particle physics.

Lepton beam facilities at the intensity frontier

The Thomas Jefferson National Accelerator Facility (JLab) is a national laboratory in the United States. It houses the Continuous Electron Beam Accelerator Facility (CEBAF), with energies up to 12 GeV and currents up to 100 μA. JLab studies hadron physics in fixed target experiments. Downstream of the target, electrons are absorbed into a Beam-Dump (BD). Particles produced in the BD can originate secondary beams that can be used to explore new physics frontiers in parallel to the current physics program. Secondary beams include neutrinos, muons and (if it exist) light dark matter.

Tapir: A tool for topologies, amplitudes, partial fraction decomposition and input for reductions

The demand for precision predictions in the field of high energy physics has dramatically increased over recent years. Experiments conducted at the LHC, as well as precision measurements at the intensity frontier such as Belle II require equally precise theoretical predictions to make full use of the acquired data. To match the experimental precision, second-, third- and, for certain quantities, even higher-order calculations in perturbative quantum field theory are required.To facilitate such calculations, computer software automating as many steps as possible is required. Yet, each calculation poses different challenges and thus, a high level of configurability is required. In this context we present tapir: a tool for identification, manipulation and minimization of Feynman integral families. It is designed to integrate in toolchains based on the computer algebra system FORM, the use of which is common practice in the field. tapir can be used to reduce the complexity of multi-loop problems with cut-filters, topology mapping, partial fraction decomposition and alike. Program summaryProgram Title:tapirCPC Library link to program files:https://doi.org/10.17632/ptc9t46xyn.1Developer's repository link:https://gitlab.com/tapir-devs/tapirLicensing provisions: GPLv3Programming language:python 3, C++Nature of problem: Multi-loop computations require the automatization of a large number of different tasks related to Feynman integral topologies. Among them are the identification and minimization of integral topologies, partial fraction decomposition of topologies in the case of linearly dependent propagators as well as mapping scalar products of loop momenta to scalar functions.Solution method: The minimization of topologies is performed by comparison of their respective Nickel indices [1], even further minimization utilizes Pak's algorithm [2]. To efficiently map scalar products of loop momenta to scalar functions FORM [3] code is generated.Additional comments including restrictions and unusual features: Minimization based on Pak's algorithm slows down for many lines and scales. A coarser minimization using the Nickel indices, however, is still possible.

New bounds on axion-like particles from MicroBooNE

Neutrino experiments lie at the edge of the intensity frontier and therefore can be exploited to search for new light particles weakly coupled to the visible sector. In this work we derive new constraints on axion-like particles (ALPs) using data from the MicroBooNE experiment, from a search for e+e− pairs pointing in the direction of the NuMI absorber. In particular, we consider the addition of higher-dimensional effective operators coupling the ALP to the electroweak gauge bosons. These would induce K → πa from kaon decay at rest in the NuMI absorber, as well as ALP decays into pairs of leptons or photons. We discuss in detail and compare various results obtained for the decay width K → πa in previous literature. For the operator involving the Higgs, MicroBooNE already sets competitive bounds (comparable to those of NA62) for ALP masses between 100 and 200 MeV. We also compute the expected sensitivities from the full NuMI dataset recorded at MicroBooNE. Our results show that a search for a a → γγ signal may be able to improve over current constraints from beam-dump experiments on the operator involving the ALP coupling to the W.

DIS physics at the EIC and LHeC and connections to the future LHC and $\nu$A programs

Deeply-inelastic scattering (DIS) stands to enter a golden age with the prospect of precision programs at the Electron-Ion Collider (EIC) and Large Hadron-electron Collider (LHeC). While these programs will be of considerable importance to resolving longstanding issues in (non)perturbative QCD as well as hadronic and nuclear structure, they will also have valuable implications for a wider range of physics at the Energy and Intensity Frontiers, including at the High-Luminosity LHC (HL-LHC) and future \nu AνA facilities. In this plenary contribution, we highlight a number of salient examples of the potential HEP impact from the complementary EIC and LHeC programs drawn from their respective Yellow Report and Whitepaper. Interested readers are encouraged to consult the extensive studies and literature from which these examples are taken for more detail.

Production of Chern–Simons bosons in decays of mesons

We consider the effective interaction of quarks with a new GeV-scale vector particle that couples to electroweak gauge bosons by the so-called effective Chern–Simons (CS) interaction. We call this particle the CS boson. We construct effective Lagrangian of the CS boson interaction with quarks of two different flavors. This interaction is given by a divergent loop diagram, however, it turns out that the divergent part is equal to zero as a consequence of the CKM matrix unitarity in the SM. Therefore, we are able to predict effective interaction of the CS boson with quarks of different flavors without introducing new unknown parameters to the model, using only parameters of the initial effective Lagrangian. Our result shows that the effective interaction of the CS boson with down-type quarks is sufficiently stronger compared with up-type quarks. Based on our results, we give a prediction for the production of CS bosons in mesons decays. Branching fractions were obtained for the main reactions of the CS production in meson decays. The results obtained will be useful for searching for the long-lived GeV-scale CS boson in intensity frontier experiments.

Challenges of Future Accelerators for Particle Physics Research

For over half a century, high-energy particle accelerators have been a major enabling technology for particle and nuclear physics research as well as sources of X-rays for photon science research in material science, chemistry and biology. Particle accelerators for energy and intensity Frontier research in particle and nuclear physics continuously push the accelerator community to invent ways to increase the energy and improve the performance of accelerators, reduce their cost, and make them more power efficient. The accelerator community has demonstrated imagination and creativity in developing a plethora of future accelerator ideas and proposals. The technical maturity of the proposed facilities ranges from shovel-ready to those that are still largely conceptual. At this time, over 100 contributed papers have been submitted to the Accelerator Frontier of the US particle physics decadal community planning exercise known as Snowmass’2021. These papers cover a broad spectrum of topics: beam physics and accelerator education, accelerators for neutrinos, colliders for Electroweak/Higgs studies and multi-TeV energies, accelerators for Physics Beyond Colliders and rare processes, advanced accelerator concepts, and accelerator technology for Radio Frequency cavities (RF), magnets, targets and sources. This paper provides an overview of the present state of accelerators for particle physics and gives a brief description of some of the major facilities that have been proposed, their perceived advantages and some of the remaining challenges.

XYZ states: An experimental point-of-view

Since 2003, a new family of states without a clear theoretical interpretation has been measured in the heavy quarkonium spectrum, the so-called X Y Z states. While the nature of these states is so far unclear, the experimental search is one of the most active fields in the intensity frontier. In this review, the most important and representative results obtained in this field in recent years are going to be illustrated, providing insights into the nature of these exotic states. The focus will be on the experimental side, describing how it is possible to investigate their exotic nature with respect to the conventional quarkonium states.

High Activity Earthquake Swarm Event Monitoring and Impact Analysis on Underground High Energy Physics Research Facilities

A seismic swarm is a series of earthquakes that occur in a small area over a short period of time. A sequence of earthquakes of this magnitude is unusual in Switzerland, and it is impossible to anticipate how it may unfold in the future.The seismic activity of such an event usually fades after a few days or weeks. Significantly greater earthquakes are likely to occur during the next several days, with up to a chance of 5 to 10%. For these reasons, the underground research facilities need tools to provide data on the impact of these events on their experiments. The paper presents the techniques implemented at The European Organization for Nuclear Research (CERN) to allow the tracking and monitoring of these unusual events. Additionally, the real effect of such an unusual event is presented together with the statistical approach to monitoring and effect evaluation. Considering the collision energy of the beams at 14 TeV, the energy stored in the magnets at 10 GJ (2400 kg of TNT), and the energy carried by the two beams at 724 MJ (173 kg of TNT), prolonged exposure to vibration close to or above the set alarm levels may result in serious safety issues. The presented evaluation of earthquake swarm impact on underground facilities together with the approach for data evaluation can be used for the design of future detectors and accelerators. Additionally, it provides tools for facilities users to present the data in an easy to understand way. This includes the Future Circular Collider, whose purpose is to significantly expand the energy and intensity frontiers of planned particle colliders, with the goal of reaching collision energies of 100 TeV in the quest for novel physics. As a result, even greater standards for beam size and stability will be required.

Toward deconstructing the simplest seesaw mechanism

The triplet or type-II seesaw mechanism is the simplest way to endow neutrinos with mass in the Standard Model (SM). Here we review its associated theory and phenomenology, including restrictions from $S$, $T$, $U$ parameters, neutrino experiments, charged lepton flavour violations as well as collider searches. We also examine restrictions coming from requiring consistency of electroweak symmetry breaking, i.e. perturbative unitarity and stability of the vacuum. Finally, we discuss novel effects associated to the scalar mediator of neutrino mass generation namely, (i) rare processes, e.g. $l_\alpha \to l_\beta \gamma$ decays, at the intensity frontier, and also (ii) four-lepton signatures in colliders at the high-energy frontier. These can be used to probe neutrino properties in an important way, providing a test of the absolute neutrino mass and mass-ordering, as well as of the atmospheric octant. They may also provide the first evidence for charged lepton flavour violation in nature. In contrast, neutrino non-standard interaction strengths are found to lie below current detectability.

High-energy colliders as a probe of neutrino properties

The mediators of neutrino mass generation can provide a probe of neutrino properties at the next round of high-energy hadron (FCC-hh) and lepton colliders (FCC-ee/ILC/CEPC/CLIC). We show how the decays of the Higgs triplet scalars mediating the simplest seesaw mechanism can shed light on the neutrino mass scale and mass-ordering, as well as the atmospheric octant. Four-lepton signatures at the high-energy frontier may provide the discovery-site for charged lepton flavor non-conservation in nature, rather than low-energy intensity frontier experiments.

Analytical estimations of the chromaticity and corrections to the spin precession frequency in weak focusing magnetic storage rings

Understanding beam and spin dynamics are fundamental in accelerator-based experiments concerning polarized beams. And there has been growing interest in having more precise estimations of the beam and spin dynamics variables, as more high precision particle physics experiments in the intensity frontier appear. This paper provides analytical estimations of some of the important variables such as beam transverse chromaticities and corrections to the spin precession frequency in the simplest type of particle accelerator: a circular magnetic storage ring with weak vertical focusing. We attempt to precisely obtain the next order approximations from the small betatron oscillations or the momentum dispersion, verified by high precision spin tracking simulation. We also discuss a potential way to suppress the corrections to the spin precession frequency, which relevant experiments may find beneficial.

Magnetic Field Dynamics and Shock Physics at the High Intensity Frontier of Laser Plasma Interactions

Magnetic Field Dynamics and Shock Physics at the High Intensity Frontier of Laser Plasma Interactions

Reconciling resonant leptogenesis and baryogenesis via neutrino oscillations

Right-handed neutrinos offer an elegant solution to two well established phenomena beyond the Standard Model (SM) - masses and oscillations of neutrinos, as well as the baryon asymmetry of the Universe. It is also a minimalistic solution since it requires only singlet Majorana fermions to be added to the SM particle content. If these fermions are nearly degenerate, the mass scale of right-handed neutrinos can be very low and accessible by the present and planned experiments. There are at least two well studied mechanisms of the low-scale leptogenesis: baryogenesis via oscillations and resonant leptogenesis. These two mechanisms were often considered separate, but they can in fact be understood as two different regimes of one and the same mechanism, described by a unique set of quantum kinetic equations. In this work we show, using a unified description based on quantum kinetic equations, that the parameter space of these two regimes of low-scale leptogenesis significantly overlap. We present a comprehensive study of the parameter space of the low-scale leptogenesis with the mass scale ranging from $0.1$ GeV to $\sim 10^6$ GeV. The unified perspective of this work reveals the synergy between intensity and energy frontiers in the quest for heavy Majorana neutrinos.