Observation of a State X ( 2600 ) in the π + π − η ′ System in the Process J / ψ → γ π + π − η ′
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Observation of an Isoscalar Resonance with Exotic J P C = 1 − + Quantum Numbers in J / ψ → γ η η ′
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Measurement of the Absolute Branching Fraction and Decay Asymmetry of Λ → n γ
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Study of the Semileptonic Decay Λ c + → Λ e + ν e
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Axial-Vector D 1 Hadrons in D * π Scattering from QCD
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Measurement of C P Violation in B 0 → K S 0 π 0 Decays at Belle II
We report a measurement of the C P -violating parameters C and S in B 0 → K S 0 π 0 decays at Belle II using a sample of 387 × 10 6 B B ¯ events recorded in e + e − collisions at a center-of-mass energy corresponding to the ϒ ( 4 S ) resonance. These parameters are determined by fitting the proper decay-time distribution of a sample of 415 signal events. We obtain C = − 0.0 4 − 0.15 + 0.14 ± 0.05 and S = 0.7 5 − 0.23 + 0.20 ± 0.04 , where the first uncertainties are statistical and the second are systematic. Published by the American Physical Society 2023
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Search for Λ ¯ − Λ Baryon-Number-Violating Oscillations in the Decay J / ψ → p K − Λ ¯ + c . c .
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Search for a τ + τ - Resonance in e + e - → μ + μ - τ + τ - Events with the Belle II Experiment
We report the first search for a nonstandard-model resonance decaying into $τ$ pairs in $e^+e^-$ → $μ^+μ^-τ^+τ^-$ events in the 3.6–10 GeV/c 2 mass range. We use a 62.8 fb -1 sample of $e^+e^-$ collisions collected at a center-of-mass energy of 10.58 GeV by the Belle II experiment at the SuperKEKB collider. The analysis probes three different models predicting a spin-1 particle coupling only to the heavier lepton families, a Higgs-like spin-0 particle that couples preferentially to charged leptons (leptophilic scalar), and an axionlike particle, respectively. We observe no evidence for a signal and set exclusion limits at 90% confidence level on the product of cross section and branching fraction into $τ$ pairs, ranging from 0.7 to 24 fb, and on the couplings of these processes. We obtain world-leading constraints on the couplings for the leptophilic scalar model for masses above 6.5 GeV/c 2 and for the axionlike particle model over the entire mass range.
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New constraints on heavy neutral leptons from Super-Kamiokande data
Abstract Heavy neutral leptons are predicted in many extensions of the Standard Model with massive neutrinos. If kinematically accessible, they can be copiously produced from kaon and pion decays in atmospheric showers, and subsequently decay inside large neutrino detectors. We perform a search for these long-lived particles using Super-Kamiokande multi-GeV neutrino data and derive stringent limits on the mixing with electron, muon and tau neutrinos as a function of the long-lived particle mass. We also present the limits on the branching ratio versus lifetime plane, which are helpful in determining the constraints in non-minimal models where the heavy neutral leptons have new interactions with the Standard Model.
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HEPfit: a code for the combination of indirect and direct constraints on high energy physics models
HEPfit is a flexible open-source tool which, given the Standard Model or any of its extensions, allows to (i) fit the model parameters to a given set of experimental observables; (ii) obtain predictions for observables. HEPfit can be used either in Monte Carlo mode, to perform a Bayesian Markov Chain Monte Carlo analysis of a given model, or as a library, to obtain predictions of observables for a given point in the parameter space of the model, allowing HEPfit to be used in any statistical framework. In the present version, around a thousand observables have been implemented in the Standard Model and in several new physics scenarios. In this paper, we describe the general structure of the code as well as models and observables implemented in the current release.
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The impact of the charge barrier height on Germanium (Ge) detectors with amorphous-Ge contacts for light dark matter searches
Germanium (Ge) detectors with ability of measuring a single electron–hole (e–h) pair are needed in searching for light dark matter (LDM) down to the MeV scale. We investigate the feasibility of Ge detectors with amorphous-Ge (a-Ge) contacts to achieve the sensitivity of measuring a single e-h pair, which requires extremely low leakage current. Three Ge detectors with a-Ge contacts are used to study the charge barrier height for blocking electrons and holes. Using the measured bulk leakage current and the Döhler–Brodsky model, we obtain the values for charge barrier height and the density of localized energy states near the Fermi energy level for the top and bottom contacts, respectively. We predict that the bulk leakage current is extremely small and can be neglected at helium temperature ( $$\sim $$ ~ 4 K). Thus, Ge detectors with a-Ge contacts possess the potential to measure a single e–h pair for detecting LDM particles.
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Quark structure of the $\chi _{\mathrm{c}}(3P)$ and X(4274) resonances and their strong and radiative decays
We calculate the masses of χc(3P) states with threshold corrections in a coupled-channel model. The model was recently applied to the description of the properties of χc(2P) and χb(3P) multiplets (Ferretti and Santopinto in Phys Lett B 789:550, 2019]. We also compute the open-charm strong decay widths of the χc(3P) states and their radiative transitions. According to our predictions, the χc(3P) states should be dominated by the charmonium core, but they may also show small meson-meson components. The X(4274) is interpreted as a cc¯ χc1(3P) state. More information on the other members of the χc(3P) multiplet, as well as a more rigorous analysis of the X(4274)’s decay modes, are needed to provide further indications on the quark structure of the previous resonance.
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Observation of X(2370) and search for X(2120) in $J/\psi \rightarrow \gamma K{\bar{K}} \eta '$: BESIII Collaboration
Using a sample of 1.31 × 10 9 J/ψ events collected with the BESIII detector, we perform a study of J/ψ → γKK¯η'. X(2370) is observed in the KK¯η' invariant-mass distribution with a statistical significance of 8.3σ. Its resonance parameters are measured to be M = 2341.6 ± 6.5(stat.) ± 5.7(syst.) MeV/c 2 and Γ = 117 ± 10(stat.) ± 8(syst.) MeV. The product branching fractions for J/ψ → γX(2370), X(2370) → K + K – η' and J/ψ → γX(2370), X(2370) → $K$ $^{0}_{S}$ $K$ $^{0}_{S}$η' are determined to be (1.79 ± 0.23(stat.) ± 0.65(syst.)) × 10 –5 and (1.18 ± 0.32(stat.) ± 0.39(syst.)) × 10 –5 , respectively. No evident signal for X(2120) is observed in the KK¯η' invariant-mass distribution. The upper limits for the product branching fractions of B(J/ψ → γX(2120) → γK + K – η') and B(J/ψ → γX(2120) → $K$ $^{0}_{S}$ $K$ $^{0}_{S}$η') are determined to be 1.49 × 10 –5 and 6.38 × 10 –6 at the 90% confidence level, respectively.
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Scaling properties of direct photon yields in heavy ion collisions
Abstract A recent analysis from the PHENIX collaboration of available direct photon measurement results in collisions of various systems such as Au+Au, Cu+Cu, and Pb+Pb, at different beam energies ranging from 39 to 2760 GeV, has shown a universal, within experimental uncertainties, multiplicity scaling, in which direct photon $$p_{T}$$ p T -spectra for transverse momenta up to 2 GeV/ c are scaled with charged hadron pseudorapidity density at midrapidity raised to power $$\alpha =1.25$$ α = 1.25 . On the other hand, those direct photon $$p_{T}$$ p T -spectra also exhibit geometrical scaling in the similar $$p_{T}$$ p T range. Assuming power-law dependence of the scaled photon spectra for both scaling laws, we formulate two independent conditions for the power $$\alpha $$ α , which overshoot experimental data by $$\sim 10\%$$ ∼ 10 % on average. We discuss possible sources that might improve this estimate.
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Characterization of high-purity germanium detectors with amorphous germanium contacts in cryogenic liquids
For the first time, planar high-purity germanium detectors with thin amorphous germanium contacts were successfully operated directly in liquid nitrogen and liquid argon in a cryostat at the Max-Planck-Institut für Physics in Munich. The detectors were fabricated at the Lawrence Berkeley National Laboratory and the University of South Dakota, using crystals grown at the University of South Dakota. They survived long-distance transportation and multiple thermal cycles in both cryogenic liquids and showed reasonable leakage currents and spectroscopic performance. Also discussed are the pros and cons of using thin amorphous semiconductor materials as an alternative contact technology in large-scale germanium experiments searching for physics beyond the Standard Model.
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Search for lepton flavour violating muon decay mediated by a new light particle in the MEG experiment
We present the first direct search for lepton flavour violating muon decay mediated by a new light particle X, μ + → e + X,X → γγ . This search uses a dataset resulting from 7.5 × 10 14 stopped muons collected by the MEG experiment at the Paul Scherrer Institut in the period 2009–2013. No significant excess is found in the mass region 20–45 MeV/c 2 for lifetimes below 40 ps, and we set the most stringent branching ratio upper limits in the mass region of 20–40 MeV/c 2 , down to O(10 –11 ) at 90% confidence level.
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Pulse-shape discrimination against low-energy Ar-39 beta decays in liquid argon with 4.5 tonne-years of DEAP-3600 data
The DEAP-3600 detector searches for the scintillation signal from dark matter particles scattering on a 3.3 tonne liquid argon target. The largest background comes from 39 Ar beta decays and is suppressed using pulse-shape discrimination (PSD). We use two types of PSD estimator: the prompt-fraction, which considers the fraction of the scintillation signal in a narrow and a wide time window around the event peak, and the log-likelihood-ratio, which compares the observed photon arrival times to a signal and a background model. We furthermore use two algorithms to determine the number of photons detected at a given time: (1) simply dividing the charge of each PMT pulse by the mean single-photoelectron charge, and (2) a likelihood analysis that considers the probability to detect a certain number of photons at a given time, based on a model for the scintillation pulse shape and for afterpulsing in the light detectors. The prompt-fraction performs approximately as well as the log-likelihood-ratio PSD algorithm if the photon detection times are not biased by detector effects. We explain this result using a model for the information carried by scintillation photons as a function of the time when they are detected.
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Probing the axion–nucleon coupling with the next generation of axion helioscopes
Abstract A finite axion–nucleon coupling, nearly unavoidable for QCD axions, leads to the production of axions via the thermal excitation and subsequent de-excitation of $$^{57}$$ 57 Fe isotopes in the sun. We revise the solar bound on this flux adopting the up to date emission rate, and investigate the sensitivity of the proposed International Axion Observatory IAXO and its intermediate stage BabyIAXO to detect these axions. We compare different realistic experimental options and discuss the model dependence of the signal. Already BabyIAXO has sensitivity far beyond previous solar axion searches via the nucleon coupling and IAXO can improve on this by more than an order of magnitude.
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