Precise Measurement of the D0 and D+ Lifetimes at Belle II

We report a measurement of the D0 and D+ lifetimes using D0→K-π+ and D+→K-π+π+ decays reconstructed in e+e-→cc¯ data recorded by the Belle II experiment at the SuperKEKB asymmetric-energy e+e- collider. The data, collected at center-of-mass energies at or near the (4S) resonance, correspond to an integrated luminosity of 72 fb-1. The results, τ(D0)=410.5±1.1(stat)±0.8(syst) fs and τ(D+)=1030.4±4.7(stat)±3.1(syst) fs, are the most precise to date and are consistent with previous determinations. © 2021 authors

Combined analysis of Belle and Belle II data to determine the CKM angle ϕ 3 using B + → D(KS0 h + h −)h + decays

We present a measurement of the Cabibbo-Kobayashi-Maskawa unitarity triangle angle ϕ3 (also known as γ) using a model-independent Dalitz plot analysis of B+ → D (KS0h+h−)h+, where D is either a D0 or D¯ 0 meson and h is either a π or K. This is the first measurement that simultaneously uses Belle and Belle II data, combining samples corresponding to integrated luminosities of 711 fb−1 and 128 fb−1, respectively. All data were accumulated from energy-asymmetric e+e− collisions at a centre-of-mass energy corresponding to the mass of the Υ(4S) resonance. We measure ϕ3 = (78.4 ± 11.4 ± 0.5 ± 1.0)°, where the first uncertainty is statistical, the second is the experimental systematic uncertainty and the third is from the uncertainties on external measurements of the D-decay strong-phase parameters. [Figure not available: see fulltext.] © 2022, The Author(s)

Search for Axionlike Particles Produced in e+e- Collisions at Belle II

We present a search for the direct production of a light pseudoscalar a decaying into two photons with the Belle II detector at the SuperKEKB collider. We search for the process e+e-→γa, a→γγ in the mass range 0.

Search for axionlike particles produced in e(+)e(-) collisions at Belle II

We present a search for the direct production of a light pseudoscalar α decaying into two photons with the Belle II detector at the SuperKEKB collider. We search for the process e⁺e⁻→γα, α→γγ in the mass range 0.2<mₐ<9.7  GeV/c² using data corresponding to an integrated luminosity of (445±3)  pb⁻¹. Light pseudoscalars interacting predominantly with standard model gauge bosons (so-called axionlike particles or ALPs) are frequently postulated in extensions of the standard model. We find no evidence for ALPs and set 95% confidence level upper limits on the coupling strength gₐγγ of ALPs to photons at the level of 10⁻³  GeV⁻¹. The limits are the most restrictive to date for 0.2<mₐ<1  GeV/c².F. Abudinén … P. Jackson … et al. [The Belle II Collaboration

Improved measurement of CP violation parameters in Bs0→J/ψK+K− decays in the vicinity of the ϕ(1020) resonance

The decay-time-dependent C P asymmetry in B 0 s → J / ψ ( → μ + μ − ) K + K − decays is measured using proton-proton collision data, corresponding to an integrated luminosity of 6     fb − 1 , collected with the LHCb detector at a center-of-mass energy of 13 TeV. Using a sample of approximately 349 000 B 0 s signal decays with an invariant K + K − mass in the vicinity of the ϕ ( 1020 ) resonance, the C P -violating phase ϕ s is measured, along with the difference in decay widths of the light and heavy mass eigenstates of the B 0 s − ¯ B 0 s system, Δ Γ s , and the difference of the average B 0 s and B 0 meson decay widths, Γ s − Γ d . The values obtained are ϕ s = − 0.039 ± 0.022 ± 0.006     rad , Δ Γ s = 0.0845 ± 0.0044 ± 0.0024     ps − 1 , and Γ s − Γ d = − 0.005 6 + 0.0013 − 0.0015 ± 0.0014     ps − 1 , where the first uncertainty is statistical and the second systematic. These are the most precise single measurements to date and are consistent with expectations based on the Standard Model and with the previous LHCb analyses of this decay. These results are combined with previous independent LHCb measurements. The phase ϕ s is also measured independently for each polarization state of the K + K − system and shows no evidence for polarization dependence

Measurement of τL using the B0s→J/ψη decay mode

Using a proton–proton collision data sample collected by the LHCb detector and corresponding to an integrated luminosity of 5.7 fb−1 , the lifetime of the light B0s mass eigenstate, τL , is measured using the B0s→J/ψη decay mode to be τL=1.445±0.016(stat)±0.008(syst)ps. A combination of this result with a previous LHCb analysis using an independent dataset corresponding to 3 fb−1 of integrated luminosity gives τL=1.452±0.014±0.007±0.002ps, where the first uncertainty is statistical, the second due to the uncorrelated part of the systematic uncertainty and the third due to the correlated part of the systematic uncertainty

Helium identification with LHCb

The identification of helium nuclei at LHCb is achieved using a method based on measurements of ionisation losses in the silicon sensors and timing measurements in the Outer Tracker drift tubes. The background from photon conversions is reduced using the RICH detectors and an isolation requirement. The method is developed using pp collision data at √(s) = 13 TeV recorded by the LHCb experiment in the years 2016 to 2018, corresponding to an integrated luminosity of 5.5 fb-1. A total of around 105 helium and antihelium candidates are identified with negligible background contamination. The helium identification efficiency is estimated to be approximately 50% with a corresponding background rejection rate of up to Script O(1012). These results demonstrate the feasibility of a rich programme of measurements of QCD and astrophysics interest involving light nuclei

Momentum scale calibration of the LHCb spectrometer

For accurate determination of particle masses accurate knowledge of the momentum scale of the detectors is crucial. The procedure used to calibrate the momentum scale of the LHCb spectrometer is described and illustrated using the performance obtained with an integrated luminosity of 1.6 fb-1collected during 2016 in pp running. The procedure uses large samples of J/ψ → μ+μ- and B+ → J/ψK+ decays and leads to a relative accuracy of 3 × 10-4 on the momentum scale

J/ψ and D0 production in sNN−−−√=68.5GeV PbNe collisions

The first measurement of J/ψ and D0 production in PbNe collisions by the LHCb experiment in its fixed-target configuration is reported. The production of J/ψ and D0 mesons is studied with a beam of lead ions with an energy of 2.5TeV per nucleon colliding on gaseous neon targets at rest, corresponding to a nucleon-nucleon centre-of-mass energy of sNN−−−√=68.5GeV. The J/ψ/D0 production cross-section ratio is studied as a function of rapidity, transverse momentum and collision centrality. These data are compared with measurements from pNe collisions at the same energy and show no difference in the observed J/ψ suppression trend when comparing pNe and PbNe peripheral collisions with PbNe central collisions