Session J07: Beyond the Standard Model III

Experiments That can Determine Whether Pions and Kaons are Spin-0 Vector Particles

I am going to discuss experiments with the potential to prove that the pion and kaon are vector particles. The motivation is intriguing results of several experiments conducted during the late 1950s and early 1960s that strongly imply that pions and kaons carry directional information. These experiments were performed by five distinct research groups and demonstrated that pions possess directional attributes with a statistical uncertainty of less than 1 in 2500 in each experiment. During the 1950s and 1960s, the prevailing scientific consensus held that a particle could only be classified as a vector particle if it exhibited spin equal to 1.  However, it was firmly established that pions possess spin equal to 0, leading many scientists to overlook the observed pi-mu asymmetry results. More recently, it has been shown that a spin-0 particle can indeed be a vector [1]. The proposed pion experiments depart from those conducted in the 1950s and 1960s because they involve the variation of the angle between the pion's polarization vector and its momentum vector using a magnetic field (which does not affect the polarization direction due to the pion's spin zero). One observes how the muon distribution changes as the pion's direction is varied. Additionally, given the compelling evidence of directional information in kaons, it is imperative to investigate potential asymmetries in the decay process K+ -> mu+ + neutrino.

 

[1] W. A. Perkins, "Massive vector particles with spin zero," EPL (Europhysics Letters) 114 (2016) 41002.   

QCD-Collapsed Domain Walls: QCD Phase Transition and Gravitational Wave Spectroscopy

For a discrete symmetry that is anomalous under QCD, the domain walls produced in the early universe from its spontaneous breaking can naturally annihilate due to QCD instanton effects. The gravitational waves generated from wall annihilation have their amplitude and frequency determined by both the discrete symmetry-breaking scale and the QCD scale. The evidence of stochastic gravitational waves at nanohertz observed by pulsar timing array experiments suggests that the discrete-symmetry-breaking scale is around 100 TeV, assuming the domain-wall explanation. The annihilation temperature is about 100 MeV, which could naturally be below the QCD phase transition temperature. We point out that the QCD phase transition within some domains with an effective large QCD theta angle could be a first-order one. To derive the phase diagram in theta and temperature, we adopt a phenomenological linear sigma model with three quark flavors. The domain-wall explanation for the NANOGrav, EPTA, PPTA, and CPTA results hints at a first-order QCD phase transition, which predicts additional gravitational waves at higher frequencies. If the initial formation of domain walls is also a first-order process, this class of domain-wall models predicts an interesting gravitational wave spectroscopy with frequencies spanning more than ten orders of magnitude, from nanohertz to 100 Hz.   

Search for Anomalous Couplings to dimension-6 operators of the SMEFT in W boson pair production

A bottom-up approach is used to look for the effects of beyond-standard model (BSM) physics on the pair production of W bosons while measuring its inclusive cross section with the Compact Muon Solenoid experiment on the LHC at CERN. Preliminary expected limits are set on the strengths of anomalous couplings to the dimension-6 operators of the Standard Model Effective Field theory. There are eight such operators sensitive to this channel in the Warsaw basis. Expected limits are set using the Asimov data set corresponding to 137 $\text{fb}^{-1}$ of simulated integrated luminosity, in preparation for the unblinding of Run II data.   

Search for a doubly charged Higgs decaying to muons or electrons: Prospects for CMS Run 3

A variety of exotic models predict a doubly charged Higgs-like particle that can be pair-produced in hadronic interactions via a Drell-Yan-like mechanism. The H++ and H-- can each decay to a pair of like-sign leptons (muons or electrons in this study) with TeV-scale mass, providing a distinctive event signature.  We present preliminary studies for the sensitivity of the CMS experiment during Run 3 and compare to the sensitivity in Run II.   

Weak Effective Theory Treatment of Electric Dipole Moments

A fully generic treatment of electric dipole moments (EDMs) will be presented in the CP-violating and flavour conserving weak effective field theory (WET) with five flavours. We systematically analyze leading contributions to EDMs originating due to the QCD and/or QED renormalization group running up to two-loop level between the electroweak and low energy scale O(1GeV) as well as the threshold corrections at bottom and charm mass. This allows us to derive a master formula for various EDM observables in the space of generic WET. As an application, we interpret the EDM constraints on the CP-violating Higgs and Z-boson couplings in the scenarios with linear and non-linear realizations of electroweak symmetry breaking.   

Search for dark photons decaying to lepton jets: Prospects for CMS Run 3

Production of dark photons with GeV-scale mass is predicted in many dark sector models. A distinctive signature is the presence of two pairs of oppositely charged leptons (muons only, in this study) where the angle between the leptons in a pair is small so that they form a lepton jet. We present preliminary studies for the sensitivity of a model-independent search for dark photons at the CMS experiment during Run 3 and compare to the sensitivity in Run II. This update includes event selection and the use of a boosted decision tree to identify lepton jets from dark photons.   

Search for new physics using unsupervised machine learning for anomaly detection in \sqrt(s) = 13 TeV p p collisions recorded by the ATLAS detector at the LHC

Searches for new resonances in two-body invariant mass distributions are performed using an unsupervised anomaly detection technique in events produced in ? ? collisions at a center of mass energy of 13 TeV recorded by the ATLAS detector at the LHC. Studies are conducted in data containing at least one isolated lepton. An autoencoder network is trained with 1% randomly selected collision events and anomalous regions are then defined which contain events with high reconstruction losses from the decoder. Nine invariant mass distributions are inspected which contain pairs of one light jet (or one ?-jet) and one lepton (?, ?), photon, or a second light jet (?-jet). The 95% confidence level upper limits on contributions from generic Gaussian signals are reported for the studied invariant mass distributions. The obtained model-independent limits show strong potential to exclude generic heavy states with complex decays.   

Search for very high magnetic charges with the CMS Beam-Pipe via the Schwinger effect

The Schwinger mechanism predicts the production of an electron-positron pair through the decay of an extremely strong electric field. Magnetic Monopoles (MMs) - if they exist - would be produced in sufficiently strong magnetic fields via the electromagnetic dual of this process. In this talk, we report on a search for magnetic monopoles produced in ultraperipheral Pb-Pb collisions during the LHC Run-1. The beryllium beampipe surrounding the interaction region of the CMS experiment was exposed to 174.29 \textmu b$^{-1}$ of Pb-Pb collisions at $\sqrt{S_{NN}}$ = 2.76 TeV in December 2011. The ultraperipheral collisions produced very strong magnetic fields -- several orders of magnitude greater than the critical field strength in quantum electrodynamics. This made possible the production of composite and elementary MMs via the Schwinger effect, a process that is calculable nonperturbatively via semi-classical methods. The beampipe was scanned by the MoEDAL experiment using a SQUID magnetometer to search for trapped MMs. The closeness of the Beryllium trapping volume to the collision point greatly increases the acceptance to high magnetic charges. These advantages allowed us to search for very high magnetic charges, sizeably extending previous search set by the collider experiments.