Session KK01: V: Particle Physics III

Dark Matter Searches at Coherent CAPTAIN-Mills

Coherent CAPTAIN-Mills (CCM) experiment is a 10 ton Liquid Argon scintillation detector experiment located at the Los Alamos National Laboratory (LANL). The Los Alamos Neutron Science Center (LANSCE) provides an 800 MeV proton beam on a tungsten target which is a copious source of neutrinos from stopped pions, as well as, possibly, new particles belonging to the Dark Sector of particle physics with masses in the range of keV to MeV. This sub-GeV Dark Matter then undergoes both elastic and inelastic scattering off the Ar nuclei and produces scintillation light. The CCM detector is equipped with photomultiplier tubes (PMTs) to capture the scintillation light. A prototype detector instrumented with 120 PMTs, CCM120 operated between 2018 and 2019, demonstrating the potential of such a detector for the search of Sub-GeV dark matter. The upgraded CCM200 detector, with 200 PMTs and improved shielding is now taking beam data. In this talk the status of the experiment, as well as results from CCM200 for elastic and inelastic scattering of dark matter with LAr and expected sensitivity to new physics with CCM200 will be presented.   

Faster Global Fitting of Neutrino Experiments with Machine Learning

The global fitting of experimental results from neutrino observatories worldwide is an integral part of sterile neutrino searches. Since Wilks' theorem does not hold in the statistical treatment of these data, the Feldman-Cousins algorithm is instead considered to be the correct approach to joint analyses. This algorithm, however, introduces a catastrophic computing-time bottleneck, preventing physicists from employing the algorithm on more than a couple of experiments at a time. In this contribution, we present a novel machine learning procedure which approximates Feldman-Cousins fits on one or more experiments simultaneously. We demonstrate this method's performance potential on real experimental data and discuss ways in which this can overhaul existing approaches to global fits.   

Efficient Neutrino Oscillation Parameter Inference with Gaussian Process

The unified approach of Feldman and Cousins allows for estimating confidence intervals for datasets with small statistics that commonly arise in high energy physics. It has gained widespread use, for instance, in measurements of neutrino oscillation parameters in long-baseline experiments. However, the approach is computationally intensive as it is typically done in a grid-based fashion over the entire parameter space. In this talk, I will discuss a more efficient algorithm for the Feldman-Cousins approach using Gaussian processes to construct confidence intervals iteratively. I'll show that in the neutrino oscillation context, one can obtain confidence intervals fives times faster in one dimension and ten times faster in two dimensions, while maintaining an accuracy above 99.5%. I'll also discuss the next steps for implementing the NOvA FC framework at NERSC.   

Cherenkov Light Identification at CCM

The Coherent CAPTAIN-Mills (CCM) experiment is a 10 ton liquid argon scintillation detector located at Los Alamos National Lab studying neutrino and beyond Standard Model physics. The detector is located 23m downstream from the Lujan Facility's stopped pion source which will receive 2.25 x 10²² POT in the ongoing 3 year run cycle. CCM is instrumented with 200 8-inch PMTs, 80% of which are coated in wavelength shifting tetraphenyl-butadiene, and 40 optically isolated 1-inch veto PMTs. The combination of PMTs coated in wavelength shifter and uncoated PMTs allows CCM to resolve both scintillation and Cherenkov light. Argon scintillation light peaks at 128nm, which requires the use of wavelength shifters into the visible spectrum for detection by the PMTs. The uncoated PMTs, however, will be more sensitive to the broad-spectrum Cherenkov light and less sensitive to the UV scintillation light produced in argon. This combination of coated and uncoated PMTs, along with our 2 nsec timing resolution, enables event by event identification of Cherenkov light. This event by event identification of Cherenkov light is a powerful tool in rejecting neutron backgrounds – enabling improved sensitivities to dark sector and beyond Standard Model physics searches.   

Measuring Charged Current Electron Neutrino - Argon scattering cross section with the CCM detector

The next generation of large-scale detectors employing liquid argon (LAr) demands a detailed understanding of the neutrino interaction cross-sections with this element. In particular, the first measurement of the charged current scattering of electron neutrinos with argon at low energies has not yet been made. This absence of data represents a challenge for future experiments, such as those that aim to detect supernovae neutrinos via this interaction, like DUNE. To carry out this crucial measurement, a facility that generates a substantial flux of neutrinos of an energy of tens of MeV is required, such as LANSCE-Lujan at Los Alamos National Laboratory. It consists of an 800 MeV, short-pulsed 20 Hz proton beam on a tungsten target neutron source, which is a prolific source of neutrinos from stopped pions and muon decay. Located 23 m from the target, the Coherent Captain Mills (CCM) detector is a 10 ton cryostat filled with Liquid LAr instrumented with 200 photomultiplier tubes that capture scintillation light, and has the necessary conditions to perform this measurement. In this talk, the progress and status of the ongoing data analysis will be presented.   

Cross Section Measurements with the Accelerator Neutrino Neutron Interaction Experiment

The Accelerator Neutrino Neutron Interaction Experiment (ANNIE) is a 26-ton gadolinium-doped water Cherenkov detector on-axis at the Booster Neutrino Beam (BNB) at Fermilab. ANNIE's experimental goals include cross section and neutron multiplicity measurements of neutrino-nucleus interactions in water, and test new detector technologies. Among the cross section measurements, the experiment seeks to measure CC Inclusive and CC0pi cross sections which are relevant toward oscillation experiments. These measurements may be used in a joint analysis with Liquid Argon Time Projection Chamber (LArTPC) experiments, such as MicroBooNE and SBND, also on the BNB line for multi-nuclear-target measurements. This would provide unique constraints on nuclear modeling relevant to next generation liquid argon experiments.   

On charged-current elastic neutrino-nucleon scattering

The (anti)neutrino-nucleon charged-current elastic scattering cross sections are parametrized by vector and axial form factors at leading order in weak and electromagnetic couplings. On the other hand, radiative corrections in the Standard Model, and potential new physics contributions beyond the Standard Model, can generate additional operators with corresponding invariant amplitudes. We review the definition of these amplitudes in a general framework and study various constraints from existing experimental data. We explore the impact of modern and future cross section measurements, considering both unpolarized cross sections and polarization observables, on constraining these amplitudes. We also discuss the effects of radiative corrections on the observables of interest.   

Beyond standard model: axial electric potential of elementary particle structures made of elementary charges +- e/3

It is suggested that elementary particles are made of basic elementary charges +e/3 and -e/3. Equations for axial electric potentials and electric fields of some charged as well as neutral structures (neutrinos n) are derived. It is shown that an electric attraction between different quarks of opposite charge signs (such as d-quark and u-quark) can change for repulsion at short distances between the quarks resulting in the equilibrium distance between the quarks in structures made of them. It is shown that the electric potential of a neutrino is not zero at small distances from it, resulting in possible interaction of neutrinos with charged particles. Equations for the axial potentials allow to suggest that both the strong and the weak interactions have an electromagnetic origin. On the examples of beta decays, it is suggested that the neutrino-antineutrino pairs should be added as reagents in the decays so the total numbers of +e/3 and -e/3 basic charges would be conserved through the reaction. It is suggested for the first time that the neutrino-antineutrino pairs are essential participants in fusion reactions. The neutral neutrino-antineutrino pairs can be a bank of basic elementary +- e/3 charges, for being used in many nuclear reactions.   

DUNE potential as a New Physics probe

Neutrino experiments, in the next years, aim to determine with precision all the six parameters of the three-neutrino standard paradigm. The complete success of the experimental program is, nevertheless, attached to the non-existence (or at least smallness) of Non-Standard Interactions (NSI). In this work, anticipating the data taken from long-baseline neutrino experiments, we map all the weakly coupled theories that could induce sizable NSI, with the potential to be determined in these experiments, in particular DUNE. Once present constraints from other experiments are taken into account, in particular charged-lepton flavor violation, we find that only models containing leptoquarks (scalar or vector) and/or neutral isosinglet vector bosons are viable. We provide the explicit matching formulas connecting weakly coupled models and NSI, both in propagation and production. Departing from the weakly coupled completion with masses at TeV scale, we also provide a global fit on all NSI for DUNE, finding that NSI smaller than $10^{-2}$ cannot be probed even in the best-case scenario.   

Observations of the Radiation Amplitude Zero effect and of the Diboson Longitudinal-Longitudinal Interactions in high $p_T^Z$ phase space using $W^{\pm}Z$ Production with the ATLAS Detector

In the standard model of particle physics, the spontaneous symmetry breaking of the complex Higgs field gives rise to the massive Higgs boson and three Goldstone bosons. These Goldstone bosons give the longitudinal degree of freedom to the W and Z bosons. In the production of WZ from the proton-proton collision in the ATLAS experiment of the Large Hadron Collider, it is critical to study the longitudinal-longitudinal interactions of W and Z. This analysis studies diboson polarization states in $WZ$ production. The dominant contribution of both bosons being transversely polarized nearly vanishes at tree-level if the bosons are produced centrally, which effectively enhances the longitudinal-longitudinal $WZ$ contribution. As high jet multiplicity skews this Radiation Amplitude Zero (RAZ) effect, only events with lower $p_T^{WZ}$ ($<20, 40, 70$ GeV) are selected. We measure RAZ as the depth in the central region of the distributions of the rapidity differences between the $W$ lepton and the $Z$ boson and between the $W$ boson and the $Z$ boson. A high $p_T^Z$ cut also enhances the $W_0Z_0$ contribution. A BDT variable is trained to distinguish different diboson polarization states in two high $p_T^Z$ exclusive regions: $100 < p_T^Z \leq 200$ GeV and $p_T^Z > 200$ GeV. A maximum log-likelihood fit is then executed, yielding an observation of a non-zero longitudinal-longitudinal polarization fraction ($f_{00}$). Notably, this analysis marks the first observations of the Radiation Amplitude Zero Effect and of the longitudinal-longitudinal $WZ$ production in the high-$p_T^Z$ phase space.