Search For New Physics Research Articles

Parton distributions and new physics searches: the Drell–Yan forward–backward asymmetry as a case study

We discuss the sensitivity of theoretical predictions of observables used in searches for new physics to parton distributions (PDFs) at large momentum fraction x. Specifically, we consider the neutral-current Drell–Yan production of gauge bosons with invariant masses in the TeV range, for which the forward–backward asymmetry of charged leptons from the decay of the gauge boson in its rest frame is a traditional probe of new physics. We show that the qualitative behaviour of the asymmetry depends strongly on the assumptions made in determining the underlying PDFs. We discuss and compare the large-x behaviour of various different PDF sets, and find that they differ significantly. Consequently, the shape of the asymmetry observed at lower dilepton invariant masses, where all PDF sets are in reasonable agreement because of the presence of experimental constraints, is not necessarily reproduced at large masses where the PDFs are mostly unconstrained by data. It follows that the shape of the asymmetry at high masses may depend on assumptions made in the PDF parametrization, and thus deviations from the traditionally expected behaviour cannot be taken as a reliable indication of new physics. We demonstrate that forward–backward asymmetry measurements could help in constraining PDFs at large x and discuss the accuracy that would be required to disentangle the effects of new physics from uncertainties in the PDFs in this region.

Methodology for the Application of Deep Neural Networks in Searches for New Physics at Colliders and Statistical Interpretation of Expected Results

Methodology for the Application of Deep Neural Networks in Searches for New Physics at Colliders and Statistical Interpretation of Expected Results

The search for new physics gets a new partner: the Sun

The search for new physics gets a new partner: the Sun

Search for New Physics in Ultraperipheral Collisions at the Large Hadron Collider

Search for New Physics in Ultraperipheral Collisions at the Large Hadron Collider

Room-temperature emission of muonium from aerogel and zeolite targets

Novel emitters of muonium ($\mathrm{Mu}={\ensuremath{\mu}}^{+}+{e}^{\ensuremath{-}}$) with high conversion efficiencies can enhance the precision of muonium spectroscopy experiments and enable next-generation searches for new physics. At the Paul Scherrer Institute (PSI), we investigate muonium production at room-temperature as well as in cryogenic environment using a superfluid helium converter. In this paper, we describe the development of compact detection schemes which resulted in the background-suppressed observation of atomic muonium in vacuum, and can be adapted for cryogenic measurements. Using these setups, we compared the emission characteristics of various muonium production targets at room temperature using low momentum (${p}_{\ensuremath{\mu}}=11--13\phantom{\rule{4pt}{0ex}}\mathrm{MeV}/c$) muons, and observed muonium emission from zeolite targets into vacuum. For a specific laser-ablated aerogel target, we determined a muon-to-vacuum-muonium conversion efficiency of $7.23\ifmmode\pm\else\textpm\fi{}0.05{\text{(stat)}}_{\ensuremath{-}0.76}^{+1.06}\text{(sys)}\phantom{\rule{0.16em}{0ex}}%$, assuming thermal emission of muonium. Moreover, we investigated muonium-helium collisions and from it we determined an upper temperature limit of 0.3 K for the superfluid helium converter.

The Upgrade of the LHCb RICH detector

LHCb is one of the four main experiments operating at the LHC and it is dedicated to measurements of CP violation and to the search for new physics beyond Standard Model in the rare decays of hadrons containing heavy quarks. LHCb is currently undergoing a major upgrade in order to increase the operating luminosity to 2 × 1033 cm-2 sec-1 from the start of Run 3 in 2022. The strategy of reading out the detectors at the full rate of 40 MHz without a hardware trigger requires a complete renewal of the data acquisition system.

Mass-energy equivalence in gravitationally bound quantum states of the neutron

Gravitationally bound neutrons have become an important tool in the experimental searches for new physics, such as modifications to Newton's force or candidates for dark matter particles. Here we include the relativistic effects of mass-energy equivalence into the model of gravitationally bound neutrons. Specifically, we investigate a correction in a gravitationally bound neutron's Hamiltonian due to the presence of an external magnetic field. We show that the neutron's additional weight due to mass-energy equivalence will cause a small shift in the neutron's eigenenergies and eigenstates, and examine how this relativistic correction would affect experiments with trapped neutrons. We further consider the ultimate precision in estimating the relativistic correction to the precession frequency and find that, at short times, a joint measurement of both the spin and motional degrees of freedom provides a metrological enhancement as compared to a measurement of the spin alone.

Detector design for a multi-TeV muon collider

The design of a feasible multi-TeV muon collider facility is the mandate of the International Muon Collider Collaboration based at CERN and is considered with great interest along the presently on-going US Snowmass 2021 process. The physics potential of such a novel future collider is overwhelming, ranging from precision measurements to direct searches for new Physics. Despite the machine-design challenges, it gives access to the uncharted territory of leptonic collisions at a center-of-mass energy of 10 TeV or higher with an instantaneous luminosity up to a few 1035 cm−2 s−1. The experiment design, the detector technology choices, and the event reconstruction tools are strongly affected by the presence of the beam-induced background, generated by the interactions of the muon decay products with the machine elements. Full simulation studies at s=1.5 TeV and 3 TeV, adopting the CLIC experiment technologies, represent the starting point to optimize the detector design and propose future dedicated R&D.

First constraints on axionlike particles from Galactic sub-PeV gamma rays

Experimental refinements and technical innovations in the field of extensive air shower telescopes have enabled measurements of Galactic cosmic-ray interactions in the sub-PeV range, providing new avenues for the search for new physics and dark matter. For the first time, we exploit sub-PeV (1 TeV -- 1 PeV) observations of Galactic diffuse gamma rays by HAWC and Tibet AS$\gamma$ to search for an axion-like-particle (ALP) induced gamma-ray signal directly linked to the origin of the IceCube extragalactic high-energy neutrino flux. Indeed, the production of high-energy neutrinos in extragalactic sources implies the concomitant production of gamma rays at comparable energies. Within the magnetic field of the neutrino emitting sources, gamma rays may efficiently convert into ALPs, escape their host galaxy un-attenuated, propagate through intergalactic space, and reconvert into gamma rays in the magnetic field of the Milky Way. Such a scenario creates an all-sky diffuse high-energy gamma-ray signal in the sub-PeV range. Accounting for the guaranteed Galactic astrophysical gamma-ray contributions from cosmic-ray interactions with gas and radiation and from sub-threshold sources, we set competitive upper limits on the photon-ALP coupling constant $g_{a\gamma\gamma}$. We find $g_{a\gamma\gamma} < 2.1\times10^{-11}$ GeV$^{-1}$ for ALP masses $m_a \leq 2\times10^{-7}$ eV at a 95\% confidence level. Our results are comparable to previous limits on ALPs derived from the TeV gamma-ray domain and progressively close the mass gap towards ADMX limits. The code and data to reproduce the results of this study are available on GitHub \url{https://github.com/ceckner/subPeVALPs}.

Impact of ligand deformation on the P,T-violation effects in the YbOH molecule.

Ytterbium monohydroxide is a promising molecule in the search for new physics. It is well known that levels of opposite parity, separated by energy split, the so-called l-doublets, define the experimental electric field strength required for molecule polarization. In addition, in our previous paper [Phys. Rev. A 105, L050801 (2022)], we have shown that the value of l-doubling directly influences the sensitivity of linear triatomic molecules toward the P,T-odd effects. In our work [J. Chem. Phys. 155, 164301 (2021)], we have calculated the value of l-doubling for YbOH molecules with the approximation of fixed O-H bond length. Taking the importance of this property into account, in the present study, we consider the additional degree of freedom corresponding to ligand (OH) deformation.

Entanglement-enhanced matter-wave interferometry in a high-finesse cavity

An ensemble of atoms can operate as a quantum sensor by placing atoms in a superposition of two different states. Upon measurement of the sensor, each atom is individually projected into one of the two states. Creating quantum correlations between the atoms, that is entangling them, could lead to resolutions surpassing the standard quantum limit1–3 set by projections of individual atoms. Large amounts of entanglement4–6 involving the internal degrees of freedom of laser-cooled atomic ensembles4–16 have been generated in collective cavity quantum-electrodynamics systems, in which many atoms simultaneously interact with a single optical cavity mode. Here we report a matter-wave interferometer in a cavity quantum-electrodynamics system of 700 atoms that are entangled in their external degrees of freedom. In our system, each individual atom falls freely under gravity and simultaneously traverses two paths through space while entangled with the other atoms. We demonstrate both quantum non-demolition measurements and cavity-mediated spin interactions for generating squeezed momentum states with directly observed sensitivity 3,.,{4}_{-0.9}^{+1.1} dB and 2,.,{5}_{-0.6}^{+0.6} dB below the standard quantum limit, respectively. We successfully inject an entangled state into a Mach–Zehnder light-pulse interferometer with directly observed sensitivity 1,.,{7}_{-0.5}^{+0.5} dB below the standard quantum limit. The combination of particle delocalization and entanglement in our approach may influence developments of enhanced inertial sensors17,18, searches for new physics, particles and fields19–23, future advanced gravitational wave detectors24,25 and accessing beyond mean-field quantum many-body physics26–30.

Search for New Physics in Electronic Recoil Data from XENONnT.

We report on a blinded analysis of low-energy electronic recoil data from the first science run of the XENONnT dark matter experiment. Novel subsystems and the increased 5.9ton liquid xenon target reduced the background in the (1, 30)keV search region to (15.8±1.3) events/(ton×year×keV), the lowest ever achieved in a dark matter detector and ∼5 times lower than in XENON1T. With an exposure of 1.16ton-years, we observe no excess above background and set stringent new limits on solar axions, an enhanced neutrino magnetic moment, and bosonic dark matter.

Event-Based Anomaly Detection for Searches for New Physics

This paper discusses model-agnostic searches for new physics at the Large Hadron Collider using anomaly-detection techniques for the identification of event signatures that deviate from the Standard Model (SM). We investigate anomaly detection in the context of a machine-learning approach based on autoencoders. The analysis uses Monte Carlo simulations for the SM background and several selected exotic models. We also investigate the input space for the event-based anomaly detection and illustrate the shapes of invariant masses in the outlier region which will be used to perform searches for resonant phenomena beyond the SM. Challenges and conceptual limitations of this approach are discussed.

Robust new physics searches with unknown backgrounds

Searches for new physics often face unknown backgrounds, causing false detections or weakened upper limits. This paper introduces the ``deficit hawk'' technique, which mitigates unknown backgrounds by testing multiple options for data cuts, such as fiducial volumes or energy thresholds. Combining the power of likelihood ratios with the robustness of the interval-searching techniques, deficit hawks could improve mean upper limits on new physics by a factor 2 for experiments with partial or speculative background knowledge. Deficit hawks are well suited to analyses that use machine learning or other multidimensional discrimination techniques and can be extended to permit discoveries in regions without unknown background.

CMS improved resistive plate chamber studies in preparation for the high luminosity phase of the LHC

The high luminosity expected from the HL-LHC will provide a great opportunity for precise physics measurements and searches for new physics. Nevertheless, the increased rate of particles coming from the collisions will pose a challenge for the CMS detectors. To prepare the muon system for the challenging conditions during the high luminosity phase, several upgrades have been planned and are being developed. Thanks to their fast time and space resolution, resistive plate chambers form part of the trigger system and are installed both in the barrel and endcap regions as a subsystem of the muon detector. As part of the upgrades, the muon forward region will be enhanced with two stations, called RE3/1 and RE4/1, equipped with improved Resistive Plate Chambers (iRPCs). These detectors use thinner electrodes, a narrower gas gap (1.4 mm compared to 2 mm in the current design) and improved front-end electronics. These features allow them to withstand particle rates up to a few kHz/cm2. Furthermore, they will extend the geometrical acceptance of the RPCs from a pseudorapidity of 1.9 to 2.4. In this work we present different studies related to the iRPC prototypes in preparation for the high luminosity phase of the LHC.

The GALPROP Cosmic-ray Propagation and Nonthermal Emissions Framework: Release v57

The past decade has brought impressive advances in the astrophysics of cosmic rays (CRs) and multiwavelength astronomy, thanks to the new instrumentation launched into space and built on the ground. Modern technologies employed by those instruments provide measurements with unmatched precision, enabling searches for subtle signatures of dark matter and new physics. Understanding the astrophysical backgrounds to better precision than the observed data is vital in moving to this new territory. A state-of-the-art CR propagation code, called GalProp, is designed to address exactly this challenge. Having 25 yr of development behind it, the GalProp framework has become a de facto standard in the astrophysics of CRs, diffuse photon emissions (radio to γ-rays), and searches for new physics. GalProp uses information from astronomy, particle physics, and nuclear physics to predict CRs and their associated emissions self-consistently, providing a unifying modeling framework. The range of its physical validity covers 18 orders of magnitude in energy, from sub-keV to PeV energies for particles and from μeV to PeV energies for photons. The framework and the data sets are public and are extensively used by many experimental collaborations and by thousands of individual researchers worldwide for interpretation of their data and for making predictions. This paper details the latest release of the GalProp framework and updated cross sections, further developments of its initially auxiliary data sets for models of the interstellar medium that grew into independent studies of the Galactic structure—distributions of gas, dust, radiation, and magnetic fields—as well as the extension of its modeling capabilities. Example applications included with the distribution illustrating usage of the new features are also described.

Astrophysical, phenomenological and experimental predictions of neutrino masses, traces of new physics

The crucial phenomenological and experimental predictions for new physics are outlined, where the number of problems of the Standard Model (neutrino masses and oscillations, dark matter, baryon asymmetry of the Universe, leptonic CP-violation) could find their solutions. The analogies between the cosmological neutrino mass scale from the early universe data and laboratory probes are discussed and the search for new physics and phenomena. It will be impossible to directly measure the masses of individual neutrinos from cosmology, but the discovery of a nonzero total neutrino mass in a future review is inevitable, as is the case with the neutrino mass hierarchy. Now neutrino physics has entered the era of precise measurements. The KATRIN experiment is known for directly measuring the neutrino mass until 2025 if its mass exceeds 0.20 eV. Several experiments are currently underway to observe double beta decay without neutrinos. In the future, if cosmological data indicate a smaller neutrino mass or a smaller sum of neutrino masses than the minimum allowed by the oscillations, this discrepancy will become an important argument in favor of new physics. A careful comparison of cosmological and laboratory results should always be made before combining them for a joint analysis.

Relativistic exact two-component coupled-cluster calculations of electronic g-factors for heavy-atom-containing molecules pertinent to search of new physics

Exact two-component (X2C) coupled-cluster calculations of electronic g-factors for heavy-atom-containing small molecules pertinent to search of new physics beyond the standard model (BSM) is reported. A magnetic-field-dependent unitary transformation of the Dirac Hamiltonian has been adopted to enable a simple inclusion of the quantum electrodynamics correction to the free-electron g-factor in the four-component formulation. The X2C transformation is subsequently employed to eliminate the positronic degrees of freedom to enhance computational efficiency without significant loss of accuracy. The relationship of the present scheme to alternative four- and two-component formulations is discussed. To demonstrate the accuracy and usefulness of the present X2C scheme, we report coupled-cluster calculations for electronic g-factors of representative heavy-metal-containing small molecules including those relevant to precision spectroscopic search of BSM physics.

Review of noble-gas spin amplification via the spin-exchange collisions

Due to isolation from the environment with the protection of the full electronic shells, nuclear spins of noble gas typically feature extraordinary long coherence times, high polarization and good chemical inertness, which makes themselves attractive in extensive scientific applications. Recently, the noble-gas spin amplification via the spin-exchange collisions between overlapping noble-gas spins and alkali-atom spins has been theoretically and experimentally demonstrated in various quantum techniques including maser, Floquet maser, spin-based amplifier, and Floquet spin amplifier. The noble-gas spin amplification can enhance the external oscillating magnetic field by a factor of more than 100 and realize ultrasensitive magnetometry, which is important for the detection of weak electromagnetic fields and hypothetical particles. Based on the spin amplification, experiments have been conducted to search for axion-like dark matter and exotic spin-dependent forces and new constraints have been established. This review summarizes the recent progress on noble-gas spin amplification, including the basic principles, methods, different types, the related applications ranging from magnetic-field sensing to searches for new physics, and prospects for further improvements.

Exploring the SMEFT at dimension eight with Drell-Yan transverse momentum measurements

Effective field theories (EFTs) are used to parameterize searches for new physics in a largely model-independent way. Here, the authors study Drell-Yan processes at the LHC including terms up to dimension 8 in the EFT expansion. They find that these higher-dimension operators can be probed in the future and are potentially important in distinguishing different models.