A semiconductor laser system for the production of antihydrogen

Laser-controlled charge exchange is a promising method for producing cold antihydrogen. Caesium atoms in Rydberg states collide with positrons and create positronium. These positronium atoms then interact with antiprotons, forming antihydrogen. Las er excitation of the caesium atoms is essential to increase the cross section of the charge-exchange collisions. This method was demonstrated in 2004 by the ATRAP collaboration by using an available copper vapour laser. For a second generation of charge-e xchange experiments we have designed a new semiconductor laser system that features several improvements compared to the copper vapour laser. We describe this new laser system and show the results from the excitation of caesium atoms to Rydberg states wit hin the strong magnetic fields in the ATRAP apparatus

Common, low-frequency, rare, and ultra-rare coding variants contribute to COVID-19 severity

The combined impact of common and rare exonic variants in COVID-19 host genetics is currently insufficiently understood. Here, common and rare variants from whole-exome sequencing data of about 4000 SARS-CoV-2-positive individuals were used to define an interpretable machine-learning model for predicting COVID-19 severity. First, variants were converted into separate sets of Boolean features, depending on the absence or the presence of variants in each gene. An ensemble of LASSO logistic regression models was used to identify the most informative Boolean features with respect to the genetic bases of severity. The Boolean features selected by these logistic models were combined into an Integrated PolyGenic Score that offers a synthetic and interpretable index for describing the contribution of host genetics in COVID-19 severity, as demonstrated through testing in several independent cohorts. Selected features belong to ultra-rare, rare, low-frequency, and common variants, including those in linkage disequilibrium with known GWAS loci. Noteworthily, around one quarter of the selected genes are sex-specific. Pathway analysis of the selected genes associated with COVID-19 severity reflected the multi-organ nature of the disease. The proposed model might provide useful information for developing diagnostics and therapeutics, while also being able to guide bedside disease management. © 2021, The Author(s)

Searches for rare B-s(0) and B-0 decays into four muons

Searches for rare B-s(0) and B-0 decays into four muons are performed using proton-proton collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 9 fb(-1). Direct decays and decays via light scalar and J/psi resonances are considered. No evidence for the six decays searched for is found and upper limits at the 95% confidence level on their branching fractions ranging between 1.8 x 10(-10) and 2.6 x 10(-9) are set

A measurement of ∆Γs

Using a dataset corresponding to 9 fb−1 of integrated luminosity collected with the LHCb detector between 2011 and 2018 in proton-proton collisions, the decay-time distributions of the decay modes Bs 0→J/ψη′ and Bs 0→J/ψπ+π− are studied. The decay-width difference between the light and heavy mass eigenstates of the Bs 0 meson is measured to be ∆Γs = 0.087 ± 0.012 ± 0.009 ps−1, where the first uncertainty is statistical and the second systematic

Study of charmonium and charmonium-like contributions in B+ -> J/psi eta K+ decays

A study of B+ -> J/psi eta K+ decays, followed by J/psi -> mu(+)mu(-) and eta -> gamma gamma, is performed using a dataset collected with the LHCb detector in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fb(-1). The J/psi eta mass spectrum is investigated for contributions from charmonia and charmonium-like states. Evidence is found for the B+ -> (psi(2)(3823) -> J/psi eta)K+ and B+ -> (psi(4040) -> J/psi eta)K+ decays with significance of 3.4 and 4.7 standard deviations, respectively. This constitutes the first evidence for the psi(2)(3823) -> J/psi eta decay

Test of Lepton Flavor Universality with B+→K+π+π−l+l− Decays

The first test of lepton flavor universality between muons and electrons using Bþ → Kþπþπ−lþl− (l 1⁄4 e, μ) decays is presented. The measurement is performed with data from proton-proton collisions collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb−1. The ratio of branching fractions between Bþ → Kþπþπ−eþe− and Bþ → Kþπþπ−μþμ− decays is measured in the dilepton invariant-mass-squared range 1.1 < q2 < 7.0 GeV2=c4 and is found to be R−1 Kππ 1⁄4 1.31þ0.18 −0.17 ðstatÞ þ0.12 −0.09 ðsystÞ, in agreement with the standard model prediction. The first observation of the Bþ → Kþπþπ−eþe− decay is also reporte

Measurement of the CKM angle γ in B± → DK*(892)± decays

Measurements of CP observables and the CKM angle γ are performed in B± → DK∗ (892)± decays, where D represents a superposition of D0 and D 0 states, using the LHCb dataset collected during Run 1 (2011–2012) and Run 2 (2015–2018). A study of this channel is presented with the D meson reconstructed in two-body fnal states K±π ∓, K+K− and π +π −; four-body fnal states K±π ∓π ±π ∓ and π +π −π +π −; and threebody fnal states K0 S π +π − and K0 SK+K−. This analysis includes the frst observation of the suppressed B± → [π ±K∓]DK∗± and B± → [π ±K∓π ±π ∓]DK∗± decays. The combined result gives γ = (63 ± 13)◦

Measurement of CP Violation Observables in D+→K−K+π+ Decays

A search for violation of the charge-parity (CP) symmetry in the D+→K-K+π+ decay is presented, with proton-proton collision data corresponding to an integrated luminosity of 5.4 fb-1, collected at a center-of-mass energy of 13 TeV with the LHCb detector. A novel model-independent technique is used to compare the D+ and D- phase-space distributions, with instrumental asymmetries subtracted using the Ds+→K-K+π+ decay as a control channel. The p value for the hypothesis of CP conservation is 8.1%. The CP asymmetry observables ACP|Sφπ+=(0.95±0.43stat±0.26syst)×10-3 and ACP|SK̄∗0K+=(-0.26±0.56stat±0.18syst)×10-3 are also measured. These results show no evidence of CP violation and represent the most sensitive search performed through the phase space of a multibody decay

Observation of the doubly charmed baryon decay Xi(++)(cc) -> Xi(c)'(+)pi(+)

The Xi(++)(cc) -> Xi('+)(c)pi(+) decay is observed using proton-proton collisions collected by the LHCb experiment at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb(-1). The Xi(++)(cc) -> Xi('+)(c)pi(+) decay is reconstructed partially, where the photon from the Xi('+)(c) -> Xi(+)(c)gamma decay is not reconstructed and the pK(-)pi(+) final state of the Sc+ baryon is employed. The Xi(++)(cc) -> Xi('+)(c)pi(+) branching fraction relative to that of the Xi(++)(cc) -> Xi('+)(c)pi(+) decay is measured to be 1.41 +/- 0.17 +/- 0.10, where the first uncertainty is statistical and the second systematic

Measurement of D0−D ̄0 mixing and search for CP violation with D0→K+π− decays

A measurement of the time-dependent ratio of the D0→K+π- to D ̄0→K+π- decay rates is reported. The analysis uses a sample of proton-proton collisions corresponding to an integrated luminosity of 6 fb-1 recorded by the LHCb experiment from 2015 through 2018 at a center-of-mass energy of 13 TeV. The D0 meson is required to originate from a D∗(2010)+→D0π+ decay, such that its flavor at production is inferred from the charge of the accompanying pion. The measurement is performed simultaneously for the K+ π- and K- π+ final states, allowing both mixing and CP-violation parameters to be determined. The value of the ratio of the decay rates at production is determined to be RKπ=(343.1±2.0)×10-5. The mixing parameters are measured to be cKπ=(51.4±3.5)×10-4 and cKπ′=(13±4)×10-6, where RKπcKπ is the linear coefficient of the expansion of the ratio as a function of decay time in units of the D0 lifetime, and cKπ′ is the quadratic coefficient, both averaged between the K+ π- and K- π+ final states. The precision is improved relative to the previous best measurement by approximately 60%. No evidence for CP violation is found