Search

Measurements of the differential production cross-sections of prompt and non-prompt J / ψ and ψ (2 S) mesons with transverse momenta between 8 and 360 GeV and rapidity in the range | y | < 2 are reported. Furthermore, measurements of the non-prompt fractions of J / ψ and ψ (2 S) , and the prompt and non-prompt ψ (2 S) -to- J / ψ production ratios, are presented. The analysis is performed using 140 fb - 1 of s = 13 TeV pp collision data recorded by the ATLAS detector at the LHC during the years 2015–2018. [ABSTRACT FROM AUTHOR]

The elliptic flow (v 2) of D 0 mesons from beauty-hadron decays (non-prompt D 0) was measured in midcentral (30–50%) Pb–Pb collisions at a centre-of-mass energy per nucleon pair s NN = 5.02 TeV with the ALICE detector at the LHC. The D 0 mesons were reconstructed at midrapidity (| y | < 0.8) from their hadronic decay D 0 → K - π + , in the transverse momentum interval 2 < p T < 12 GeV/c. The result indicates a positive v 2 for non-prompt D 0 mesons with a significance of 2.7 σ . The non-prompt D 0 -meson v 2 is lower than that of prompt non-strange D mesons with 3.2 σ significance in 2 < p T < 8 GeV / c , and compatible with the v 2 of beauty-decay electrons. Theoretical calculations of beauty-quark transport in a hydrodynamically expanding medium describe the measurement within uncertainties. [ABSTRACT FROM AUTHOR]

The very rare D ∗ (2007) 0 → μ + μ - decay is searched for by analysing B - → π - μ + μ - decays. The analysis uses a sample of beauty mesons produced in proton–proton collisions collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of 9 \,fb - 1 . The signal signature corresponds to simultaneous peaks in the μ + μ - and π - μ + μ - invariant masses. No evidence for an excess of events over background is observed and an upper limit is set on the branching fraction of the decay at B (D ∗ (2007) 0 → μ + μ -) < 2.6 × 10 - 8 at 90 % confidence level. This is the first limit on the branching fraction of D ∗ (2007) 0 → μ + μ - decays and the most stringent limit on D ∗ (2007) 0 decays to leptonic final states. The analysis is the first search for a rare charm-meson decay exploiting production via beauty decays. [ABSTRACT FROM AUTHOR]

We report on the results of the first search for the production of axion-like particles (ALPs) via Primakoff production on nuclear targets, γ A → a A , in the "SRC-CT" experiment using the GlueX detector at Jefferson Lab. This search uses an integrated luminosity of 100 pb ⋅ − 1 nucleon on a 12C target with a real photon beam of energies 6 < E γ < 10.8 GeV, and explores the mass region of 200 < m a < 450 MeV via the decay a → γ γ. This mass range is between the π 0 and η meson masses, which enables the use of the measured η meson production rate to obtain absolute bounds on the ALP production with reduced sensitivity to experimental luminosity and detection efficiency. We find no evidence for an ALP, consistent with previous searches in the quoted mass range, and present limits on the effective photon coupling scale of O (1 TeV − 1). We further find that the ALP production limit we obtain is hindered by the peaking structure of the non-target-related dominant background the in GlueX spectrometer, which we treat by using data on 4He to estimate and subtract it. We comment on how this search can be improved in a future higher-statistics dedicated measurement. [ABSTRACT FROM AUTHOR]

A method for reconstructing spectra of short-range charged particles in experimental investigations of stopped-pion absorption by nuclei is described. This approach is based on the use of a monitor system, which consists of two Si detectors, and a "live" target, which is also a Si detector. By simultaneously analyzing data from the monitor detectors and the live target, it is possible to determine the depth at which a pion stops inside the target. It is shown that the use of the presented "aiming" method with targets ∼0.1 g/cm2 thick makes it possible to correctly reconstruct the energy spectra of 3He and 4He isotopes in the energy range of 16−35 MeV. [ABSTRACT FROM AUTHOR]

We present a search for the charged lepton-flavor-violating decays ϒ(1S) →ℓ±ℓ′∓ and radiative charged lepton-flavour-violating decays ϒ(1S) → γℓ±ℓ′∓ [ℓ,ℓ′ = e, μ, τ] using the 158 million ϒ(2S) sample collected by the Belle detector at the KEKB collider. This search uses ϒ(1S) mesons produced in ϒ(2S) → π+π− ϒ(1S) transitions. We do not find any significant signal, so we provide upper limits on the branching fractions at the 90% confidence level. [ABSTRACT FROM AUTHOR]

Cosmic ray muon has strong penetrating power and no ionizing radiation hazards, which makes it an ideal probe for detecting special nuclear materials (SNMs). In this article, a high spatial resolution muon tomography system based on Micromegas detectors is proposed to optimize the imaging time and quality. The proposed system includes eight Micromegas detectors based on the thermal bonding technique and a scalable readout system. In addition, a multiplexing method based on position encoding is developed to reduce the number of electronics channels by order of magnitude. The spatial resolution of the proposed system with encoding readout can reach a value of hundred micrometers. Finally, a tomography test is performed, and test results show that this proposed system can image 2-cm objects and distinguish different materials. [ABSTRACT FROM AUTHOR]

We present a field-programmable gate array (FPGA)-based technique for the on-line identification of highly ionizing particles in a liquid xenon (LXe) detector. The method was developed and successfully exploited to select $\alpha $ particles emitted by 241Am sources submerged in LXe in an overwhelming, mostly beam-related, $\gamma $ -ray background. After revising the main features of xenon and other liquid noble gases as ultra-violet (UV) scintillating media, we describe the algorithm idea and its firmware implementation. We then present the results in terms of efficiency and background suppression for the real-time $\alpha $ -particle tagging and the limits of the MEG trigger configuration. Finally, we show that in MEG II we are going to overcome the main issues and further improve the performances. [ABSTRACT FROM AUTHOR]

Using a data sample corresponding to an integrated luminosity of 2.93 b-1 collected at a center-of-mass energy √s=3.773  GeV by the BESIII detector, the decay D0→ωϕ is observed for the first time. The branching fraction is measured to be (6.48±0.96±0.40)×10-4 with a significance of 6.3σ, where the first and second uncertainties are statistical and systematic, respectively. An angular analysis reveals that the ϕ and ω mesons from the D0→ωϕ decay are transversely polarized. The 95% confidence level upper limit on longitudinal polarization fraction is set to be less than 0.24, which is inconsistent with current theoretical expectations and challenges our understanding of the underlying dynamics in charm meson decays. [ABSTRACT FROM AUTHOR]

The pT-differential cross sections of prompt charm-strange baryons Ξ0c and Ξ+c were measured at midrapidity (|y|<0.5) in proton-proton (pp) collisions at a center-of-mass energy √s=13  TeV with the ALICE detector at the LHC. The Ξ0c baryon was reconstructed via both the semileptonic decay (Ξ-e+νe) and the hadronic decay (Ξ-π+) channels. The Ξ+c baryon was reconstructed via the hadronic decay (Ξ-π+π+) channel. The branching-fraction ratio BR(Ξ0c→Ξ-e+νe)/BR(Ξ0c→Ξ-π+)=1.38±0.14(stat)±0.22(syst) was measured with a total uncertainty reduced by a factor of about 3 with respect to the current world average reported by the Particle Data Group. The transverse momentum (pT) dependence of the Ξ0c- and Ξ+c-baryon production relative to the D0 meson and to the Σ0,+,++c- and Λ+c-baryon production are reported. The baryon-to-meson ratio increases toward low pT up to a value of approximately 0.3. The measurements are compared with various models that take different hadronization mechanisms into consideration. The results provide stringent constraints to these theoretical calculations and additional evidence that different processes are involved in charm hadronization in electron-positron (e+e-) and hadronic collisions. [ABSTRACT FROM AUTHOR]