# High Energy Physics Phenomenology

###### Featured Researches

## ? polarization from thermalized jet energy

We examine the formation of vortical "smoke rings" as a result of thermalization of energy lost by a jet. We simulate the formation and evolution of these rings using hydrodynamics and define an observable that allows to probe this phenomenon experimentally. We argue that observation of vorticity associated with jets would be an experimental confirmation of the thermalization of the energy lost by quenched jets, and also a probe of shear viscosity.

Read more## ?-meson lepto-production near threshold and the strangenessD-term

We present a model of exclusive?-meson lepto-productionep??e??p???near threshold which features the strangeness gravitational form factors of the proton. We argue that the shape of the differential cross sectiond?/dtis a sensitive probe of the strangeness D-term of the proton.

Read more## ?B=2neutron decay into antiproton moden??p¯e+ν(ν¯)

We discuss the unique baryon number violation by two units neutron decay moden??p¯e+?, with?being the standard model (SM) neutrinoνor antineutrinoν¯or any beyond SM light fermion, in the framework of effective field theory. This mode is kinematically allowed but rarely discussed theoretically or searched for experimentally. We estimate the lower bound on its partial lifetime from that of the dinucleon decaynp??e+?per oxygen nucleus16O set by the Super-Kamiokande experiment, with a conservative bound???n??p¯e+?>5.7?1039 yrs. We also discuss its characteristic signature for the future experimental search and astrophysical implications.

Read more## ?exchange contribution to neutrinoless double beta decay

We consider?meson contributions to neutrinoless double beta decay amplitude stemming from the hadronization of the short distance quark-electron currents. These contributions are evaluated within vacuum dominance approximation. The one and two?exchange contributions affect the Fermi transition nuclear matrix element in a way that lead to near cancellations in the same chirality, left-left and right-right, short range amplitudes when these new contributions are combined with the conventional short range amplitudes, while the left-right amplitude almost triples. This then necessitates the inclusion of?exchange amplitudes in any phenomenological study, like in left-right theories.

Read more## A Living Review of Machine Learning for Particle Physics

Modern machine learning techniques, including deep learning, are rapidly being applied, adapted, and developed for high energy physics. Given the fast pace of this research, we have created a living review with the goal of providing a nearly comprehensive list of citations for those developing and applying these approaches to experimental, phenomenological, or theoretical analyses. As a living document, it will be updated as often as possible to incorporate the latest developments. A list of proper (unchanging) reviews can be found within. Papers are grouped into a small set of topics to be as useful as possible. Suggestions and contributions are most welcome, and we provide instructions for participating.

Read more## A New Approach to Probe Non-Standard Interactions in Atmospheric Neutrino Experiments

We propose a new approach to explore the neutral-current non-standard neutrino interactions (NSI) in atmospheric neutrino experiments using oscillation dips and valleys in reconstructed muon observables, at a detector like ICAL that can identify the muon charge. We focus on the flavor-changing NSI parameterεμ?, which has the maximum impact on the muon survival probability in these experiments. We show that non-zeroεμ?shifts the oscillation dip locations inL/Edistributions of the up/down event ratios of reconstructedμ??andμ+in opposite directions. We introduce a new variable?drepresenting the difference of dip locations inμ??andμ+, which is sensitive to the magnitude as well as the sign ofεμ?, and is independent of the value of?m232. We further note that the oscillation valley in the (E,cosθ) plane of the reconstructed muon observables bends in the presence of NSI, its curvature having opposite signs forμ??andμ+. We demonstrate the identification of NSI with this curvature, which is feasible for detectors like ICAL having excellent muon energy and direction resolutions. We illustrate how the measurement of contrast in the curvatures of valleys inμ??andμ+can be used to estimateεμ?. Using these proposed oscillation dip and valley measurements, the achievable precision on|εμ?|at 90% C.L. is about 2% with 500 kt??yr exposure. The effects of statistical fluctuations, systematic errors, and uncertainties in oscillation parameters have been incorporated using multiple sets of simulated data. Our method would provide a direct and robust measurement ofεμ?in the multi-GeV energy range.

Read more## A No-Lose Theorem for Discovering the New Physics of(g??)μat Muon Colliders

We perform a model-exhaustive analysis of all possible beyond Standard Model (BSM) solutions to the(g??)μanomaly to study production of the associated new states at future muon colliders, and formulate a no-lose theorem for the discovery of new physics if the anomaly is confirmed and weakly coupled solutions below the GeV scale are excluded. Our goal is to find the highest possible mass scale of new physics subject only to perturbative unitarity, and optionally the requirements of minimum flavour violation (MFV) and/or naturalness. We prove that a 3 TeV muon collider is guaranteed to discover all BSM scenarios in which?aμis generated by SM singlets with masses above??GeV; lighter singlets will be discovered by upcoming low-energy experiments. If new states with electroweak quantum numbers contribute to(g??)μ, the minimal requirements of perturbative unitarity guarantee new charged states belowO(100TeV), but this is strongly disfavoured by stringent constraints on charged lepton flavour violating (CLFV) decays. Reasonable BSM theories that satisfy CLFV bounds by obeying Minimal Flavour Violation (MFV) and avoid generating two new hierarchy problems require the existence of at least one new charged state below??0TeV. This strongly motivates the construction of high-energy muon colliders, which are guaranteed to discover new physics: either by producing these new charged states directly, or by setting a strong lower bound on their mass, which would empirically prove that the universe is fine-tuned and violates the assumptions of MFV while somehow not generating large CLFVs. The former case is obviously the desired outcome, but the latter scenario would perhaps teach us even more about the universe by profoundly revising our understanding of naturalness, cosmological vacuum selection, and the SM flavour puzzle.

Read more## A Phenomenological analysis on isospin-violating decay ofX(3872)

In a molecular scenario, we investigate the isospin-breaking hidden charm decay processes ofX(3872), i.e.,X(3872)???+???J/?,X(3872)???+????0J/?, andX(3872)???0?cJ. We assume that the source of the strong isospin violation comes from the different coupling strengths ofX(3872)to its charged componentsD??D??and neutral componentsD??D¯0as well as the interference between the charged meson loops and neutral meson loops. The former effect could fix our parameters by using the measurement of the ratio?[X(3872)???+????0J/?]/?[X(3872)???+???J/?]. With the determined parameter range, we find that the estimated ratio?[X(3872)???0?c1/?[X(3872)???+???J/?]is well consistent with the experimental measurement from the BESIII collaboration. Moreover, the partial width ratio of?0?cJforJ=0,1,2is estimated to be1.77??.65:1:1.09??.43, which could be tested by further precise measurements of BESIII and Belle II.

Read more## A Standard Model Explanation for the "ATOMKI Anomaly"

Using thee+e??pair spectrometer at the 5 MV Van de Graaff accelerator at the Institute for Nuclear Research, Hungarian Academy of Sciences (ATOMKI), Krasznahorkay et al. have claimed a 6.8?excess at highe+e??opening angles in the internal pair creation isoscalar transition8Be(18.15)??8Bee+e??. A hypothetical gauge boson with the mass circa17MeV, "X17", has been proposed as an explanation for the excess. We show that the observed experimental structure can be reproduced within the Standard Model by adding the full set of second-order corrections and the interference terms to the Born-level decay amplitudes considered by Krasznahorkay et al. We implement a detailed model of the ATOMKI detector, and also show how experimental selection and acceptance bias exacerbate the apparent difference between the experimental data and the Born-level prediction.

Read more## A composite solution to the EDGES anomaly

Subcomponent millicharged dark matter that cools baryons via Coulomb interactions has been invoked to explain the EDGES anomaly. However, this model is in severe tension with constraints from cosmology and stellar emissions. In this work, we consider the consequences of these millicharged particles existing in composite blobs. The relevant degrees of freedom at high temperature are minuscule elementary charges, which fuse at low temperatures to make up blobs of larger charge. These blobs serve as the degrees of freedom relevant in cooling the baryons sufficiently to account for the EDGES anomaly. In such a model, cosmology and stellar constraints (which involve high-temperature processes) apply only to the feebly-interacting elementary charges and not to the blobs. This salvages a large range of parameter space for millicharged blobs that can explain the EDGES anomaly. It also opens up new parameter space for direct detection, albeit at low momentum transfers.

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