We present first estimates of NICA sensitivity to Standard Model extensions with light hypothetical particles singlet under the known gauge transformations. Our analysis reveals that NICA can explore new regions in the parameter spaces of models with a hidden vector and models with an axion-like particle of masses about 30-500 MeV. Some of these regions seem unreachable by other ongoing and approved future projects. NICA has good prospects in discovery (5σ) of the new physics after 1 year of data taking.

Russia

Dmitry Gorbunov

Dmitry Kalashnikov

NICA prospects in searches for light exotics from hidden sectors: The cases of hidden photons and axion-like particles

Hypothetical particles with tiny electric charges (millicharged particles or MCPs) can be produced in electron-positron annihilation if kinematically allowed. Typical searches for them at <math><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup></math> colliders exploit a signature of a single photon with missing energy carried away by the undetected MCP pair. We put forward an idea to look alternatively for MCP energy deposits inside a tracker, which is a direct observation. The new signature is relevant for non-relativistic MCPs, and we illustrate its power on the example of the c-τ factory, where we argued that the corresponding searches may be background-free. We find that it can probe the MCP charge down to <math><mn>3</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>3</mn></mrow></msup></math> of the electron charge for the MCP masses in <math><mi>O</mi><mrow><mo>(</mo><mn>5</mn><mo>)</mo></mrow></math> MeV vicinity of each energy beam value where the factory will collect a luminosity of 100 fb$^{−1}$ in one year. This mass region is unreachable with the searches for missing energy and single photon.

Pavel Pakhlov

Timofey Uglov

On direct observation of millicharged particles at - Factories and Other -colliders

Future <math><mrow><mi>c</mi><mtext>−</mtext><mi>τ</mi></mrow></math> factories are natural places to study extensions of the Standard Model (SM) of particle physics with new long-lived feebly interacting particles light enough to be produced in electron-positron collisions. We investigate prospects of these machines in exploring such extensions emphasizing the role of polarized beams in getting rid of the SM irreducible background for the missing energy signature. We illustrate this on the example of the <math><mrow><mi>c</mi><mtext>−</mtext><mi>τ</mi></mrow></math> project in Novosibirsk, where the electron beam is designed to be polarized to achieve much higher sensitivity to hadronic resonances and <math><mi>τ</mi></math> leptons. We investigate models with hidden photons, with millicharged particles (fermions and scalars), with <math><msup><mi>Z</mi><mo>′</mo></msup></math> bosons and with axionlike particles. We find that the electron beam polarization of 80% significantly improves the chances to observe the signal, especially with large statistics. We outline the regions of the model parameter space which can be reached at this factory in one year and in ten years of operation according with the scientific schedule of tuning the energy of colliding beams.

Probing light exotics from a hidden sector at <math><mrow><mi>c</mi><mtext>−</mtext><mi>τ</mi></mrow></math> factories with polarized electron beams

Millicharged particles (MCPs) arise in many well-motivated extensions of the Standard Model and are a popular subject for experimental searches. We investigate the attenuation of the MCP flux produced at accelerator experiments due to their interactions in the media and demonstrate that it can significantly affect the final sensitivity to the MCP parameter space, leaving its essential part still unexplored. Applying our analysis to the SLACmQ experiment [A. A. Prinz et al., Phys. Rev. Lett. 81, 1175 (1998)], we correct their published exclusion bounds; the obtained results are numerically in a good accordance with A. A. Prinz [Report No. SLAC-R-569]. We also show that this newly reopened area with the MCP masses in the range <math><mrow><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>4</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>eV</mi><mi>–</mi><mn>1</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math> and charges <math><mrow><mo>≳</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>5</mn></mrow></msup><mi>e</mi></mrow></math> can be effectively probed by the <math><mrow><mi>NA</mi><mn>64</mn><mi>e</mi></mrow></math> experiment at the CERN SPS. Light MCPs are mostly produced by a virtual photon in electron scattering off nuclei. The main source of heavy MCP is decays of vector mesons, produced by the electrons on nuclei.

Nataliya Arefyeva

Sergei Gninenko

Dmitry Kirpichnikov

Passage of millicharged particles in the electron beam-dump: Refining constraints from SLACmQ and estimating sensitivity of <math><mrow><mi>NA</mi><mn>64</mn><mi>e</mi></mrow></math>

We investigate FASER@LHC perspectives in searches for light (0.1–5 GeV) sgoldstinos in models with low energy (10–104 TeV) supersymmetry breaking. We consider flavor conserving and flavor violating couplings of sgoldstinos to Standard Model fermions and find the both options to be testable at FASER. Even the first FASER run allows one to probe interesting patches in the model parameter space, while the second run, FASER-II, with significantly larger detector fiducial volume, gives a possibility to thoroughly explore a wide class of supersymmetric extensions of particle physics complementary to those probed at LHC with ATLAS and CMS detectors.

Sergey Demidov

Sgoldstino signal at FASER: prospects in searches for supersymmetry

We perform Monte Carlo simulations of the sterile neutrino signal at the fixed target experiment PS191 operated on a proton beam of 19.2GeV at CERN in the eighties. We find that the strongest bounds the PS191 could obtain are significantly lower than what they published, and now are obsolete being surpassed by recent T2K, NA62, E949, TRIUMF and PIENU experiments.

Igor Krasnov

France

Sergey Suvorov

Revisiting PS191 limits on sterile neutrinos

Recently, the Baksan Experiment on Sterile Transitions (BEST) has presented results [1] confirming the gallium anomaly—a lack of electron neutrinos <math><mrow><msub><mrow><mi>ν</mi></mrow><mrow><mi>e</mi></mrow></msub></mrow></math> at calibrations of SAGE [2,3] and GALLEX [4]—at the statistical significance exceeding <math><mrow><mn>5</mn><mi>σ</mi></mrow></math>. This result is consistent with explanation of the gallium anomaly as electron neutrino oscillations into a sterile neutrino, <math><msub><mi>ν</mi><mi>s</mi></msub></math>. Within this explanation, the BEST experiment itself provides the strongest evidence for the sterile neutrino among all the previous anomalous results in the neutrino sector. We combine the results of gallium experiments with searches for sterile neutrinos in reactor antineutrino experiments (assuming <math><mi>C</mi><mi>P</mi><mi>T</mi></math> conservation in the <math><mn>3</mn><mo>+</mo><mn>1</mn></math> neutrino sector). While the “gallium” best-fit point in the model parameter space (sterile neutrino mass squared <math><msubsup><mi>m</mi><msub><mi>ν</mi><mi>s</mi></msub><mn>2</mn></msubsup><mo>≈</mo><mn>1.25</mn><mtext> </mtext><mtext> </mtext><msup><mrow><mi>eV</mi></mrow><mrow><mn>2</mn></mrow></msup></math>, sterile-electron neutrino mixing <math><msup><mi>sin</mi><mn>2</mn></msup><mn>2</mn><mi>θ</mi><mo>≈</mo><mn>0.34</mn></math>) is excluded by these searches, a part of the BEST-favored <math><mrow><mn>2</mn><mi>σ</mi></mrow></math> region with <math><msubsup><mi>m</mi><msub><mi>ν</mi><mi>s</mi></msub><mn>2</mn></msubsup><mo>&gt;</mo><mn>5</mn><mtext> </mtext><mtext> </mtext><msup><mrow><mi>eV</mi></mrow><mrow><mn>2</mn></mrow></msup></math> is consistent with all of them. Remarkably, the regions advertised by anomalous results of the NEUTRINO-4 experiment [5] overlap with those of the BEST experiment: the best-fit point of the joint analysis is <math><msup><mi>sin</mi><mn>2</mn></msup><mn>2</mn><mi>θ</mi><mo>≈</mo><mn>0.38</mn></math>, <math><msubsup><mi>m</mi><msub><mi>ν</mi><mi>s</mi></msub><mn>2</mn></msubsup><mo>≈</mo><mn>7.3</mn><mtext> </mtext><mtext> </mtext><msup><mrow><mi>eV</mi></mrow><mrow><mn>2</mn></mrow></msup></math>, and the favored region will be explored by the KATRIN experiment [6]. The sterile neutrino explanation of the BEST results would suggest not only the extension of the Standard Model of particle physics but also either serious modifications of the Standard Cosmological Model and Solar Model, or a specific modification of the sterile sector needed to suppress the sterile neutrino production in the early Universe and in the Sun.

Vladislav Barinov

BEST impact on sterile neutrino hypothesis

We calculate the production of hypothetical millicharged particles (MCPs) of sub-GeV masses by the J-PARC proton beam in the framework of T2K and future T2HK neutrino oscillation experiments. Concentrating on the region of model parameter space, where an MCP can hit the near neutrino detector twice, we adopt this background-free signature to estimate the sensitivity of T2K and T2HK experiments to MCPs. We find that a previously inaccessible in direct searches region of charges 5×<math><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>4</mn></mrow></msup></math>-<math><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>2</mn></mrow></msup></math> e for MCP masses 0.1-0.5 GeV can be probed.

Yury Kudenko

Double-hit signature of millicharged particles in 3D segmented neutrino detector

The recent confirmation by FNAL of the <math><msub><mrow><mo>(</mo><mi>g</mi><mo>−</mo><mn>2</mn><mo>)</mo></mrow><mrow><mi>μ</mi></mrow></msub></math> muon anomaly gives strong evidence for the possible existence of new physics beyond the Standard Model in the muon sector. Thus it is worthy to revisit the existing experimental constraints on models suggesting theoretically consistent explanations of the anomaly. In this work, we point out that accounting for the loss of coherence between the wave packets (mass states) of solar neutrinos is important for setting limits on any model with new flavor-sensitive couplings in the neutrino sector. By taking into account this effect and considering more accurately the experimental constraints from the BOREXINO measurement of the $^{7}$Be solar neutrino interaction rate we corrected the limits previously placed on the coupling of the light <math><msup><mrow><mi>Z</mi></mrow><mrow><mo>′</mo></mrow></msup></math> to <math><msub><mrow><mi>L</mi></mrow><mrow><mi>μ</mi></mrow></msub></math>-<math><msub><mrow><mi>L</mi></mrow><mrow><mi>τ</mi></mrow></msub></math> current in the parameter space relevant to the muon <math><msub><mrow><mo>(</mo><mi>g</mi><mo>−</mo><mn>2</mn><mo>)</mo></mrow><mrow><mi>μ</mi></mrow></msub></math>.

Refining constraints from Borexino measurements on a light ′-boson Coupled to - Current

We argue that the fixed target experiment PS191 operating on a proton beam of 19.2 GeV at CERN in the eighties was sensitive to hypothetical light scalars produced by mesons and decaying to charged particles. The experiment was dedicated to searches for sterile neutrinos produced in weak meson decays and decaying into final states with pairs of charged particles: electrons and muons. Two charged tracks from the same point have been adopted as the signal signature. Exploiting the same signature we use the negative results of searches at PS191 and place new limits on the light scalars coupled to the Standard Model (SM) particles via mixing with the Higgs boson. In particular, previously allowed region of masses 100–150 MeV and mixing above <math><mn>4</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>4</mn></mrow></msup></math> is disfavored. Our analysis can be extended straightforwardly to models with other patterns of scalar couplings to SM particles.