Search for rare or forbidden decays of the D0 meson

We present a search for nine lepton-number-violating and three lepton-flavor-violating neutral charm decays of the type D0→h'−h−ℓ'+ℓ+ and D0→h'−h+ℓ'±ℓ∓, where h and h′ represent a K or π meson and ℓ and ℓ′ an electron or muon. The analysis is based on 468 fb−1 of e+e− annihilation data collected at or close to the Υ(4S) resonance with the BABAR detector at the SLAC National Accelerator Laboratory. No significant signal is observed for any of the twelve modes, and we establish 90% confidence level upper limits on the branching fractions in the range (1.0–30.6)×10−7. The limits are between 1 and 3 orders of magnitude more stringent than previous measurements.publishedVersio

Light meson spectroscopy from Dalitz plot analyses of ηc decays to η0 K+K− , η0 π + π − , and ηπ + π − produced in two-photon interactions

We study the processes γγ→ηc→η′K+K−, η′π+π−, and ηπ+π− using a data sample of 519  fb−1 recorded with the BABAR detector operating at the SLAC PEP-II asymmetric-energy e+e− collider at center-of-mass energies at and near the Υ(nS) (n=2, 3, 4) resonances. This is the first observation of the decay ηc→η′K+K− and we measure the branching fraction Γ(ηc→η′K+K−)/(Γ(ηc→η′π+π−)=0.644±0.039stat±0.032sys. Significant interference is observed between γγ→ηc→ηπ+π− and the nonresonant two-photon process γγ→ηπ+π−. A Dalitz plot analysis is performed of ηc decays to η′K+K−, η′π+π−, and ηπ+π−. Combined with our previous analysis of ηc→K¯Kπ, we measure the K∗0(1430) parameters and the ratio between its η′K and πK couplings. The decay ηc→η′π+π− is dominated by the f0(2100) resonance, also observed in J/ψ radiative decays. A new a0(1700)→ηπ resonance is observed in the ηc→ηπ+π− channel. We also compare ηc decays to η and η′ final states in association with scalar mesons as they relate to the identification of the scalar glueball.publishedVersio

Measurements of the absolute branching fractions of B± →k±Xc c

A study of the two-body decays B±→Xc¯cK±, where Xc¯c refers to one charmonium state, is reported by the BABAR Collaboration using a data sample of 424 fb−1. The absolute determination of branching fractions for these decays are significantly improved compared to previous BABAR measurements. Evidence is found for the decay B+→X(3872)K+ at the 3σ level. The absolute branching fraction B[B+→X(3872)K+]=[2.1±0.6(stat)±0.3(syst)]×10−4 is measured for the first time. It follows that B[X(3872)→J/ψπ+π−]=(4.1±1.3)%, supporting the hypothesis of a molecular component for this resonance.publishedVersio

Measurement of the F2 structure function in deep inelastic e+^{+}p scattering using 1994 data from the ZEUS detector at HERA

We present measurements of the structure function \Ft\ in e^+p scattering at HERA in the range 3.5\;\Gevsq < \qsd < 5000\;\Gevsq. A new reconstruction method has allowed a significant improvement in the resolution of the kinematic variables and an extension of the kinematic region covered by the experiment. At \qsd < 35 \;\Gevsq the range in x now spans 6.3\cdot 10^{-5} < x < 0.08 providing overlap with measurements from fixed target experiments. At values of Q^2 above 1000 GeV^2 the x range extends to 0.5. Systematic errors below 5\perc\ have been achieved for most of the kinematic urray, W

Measurement of Elastic ϕ\phi Photoproduction at HERA

The production of $\phi$ mesons in the reaction $e^{+}p \rightarrow e^{+} \phi p$ ($\phi \rightarrow K^{+}K^{-}$) at a median $Q^{2}$ of $10^{-4} \ \rm{GeV^2}$has been studied with the ZEUS detector at HERA. The differential$\phi$photoproduction cross section$d\sigma/dt$has an exponential shape and has been determined in the kinematic range$0.1<|t|<0.5 \ \rm{GeV^2}$and$60 < W < 80 \ \rm{GeV}$. An integrated cross section of$\sigma_{\gamma p \rightarrow \phi p} = 0.96 \pm 0.19^{+0.21}_{-0.18}$$\rm{\mu b}$has been obtained by extrapolating to {\it t} = 0. When compared to lower energy data, the results show a weak energy dependence of both$\sigma_{\gamma p \rightarrow \phi p}$and the slope of the$t$distribution. The$\phi$decay angular distributions are consistent with$s$-channel helicity conservation. From lower energies to HERA energies, the features of$\phi$ photoproduction are compatible with those of a soft diffractive process.Comment: 23 pages, including 6 post script figure

Comparison of ZEUS data with standard model predictions for e+p→e+Xe^+ p \rightarrow e^+ X scattering at high xx and Q2Q^2

Using the ZEUS detector at HERA, we have studied the reaction e(+)p --> e(+)X for Q(2) > 5000 GeV2 with a 20.1 pb(-1) data sample collected during the years 1993 to 1996. For Q(2) below 15000 GeV2, the data are in good agreement with Standard Model expectations. For Q(2) > 35000 GeV2. two events are observed while 0.145 +/- 0.013 events are expected, A statistical analysis of a large ensemble of simulated Standard Model experiments indicates that with probability 6.0%, an excess at least as unlikely as that observed would occur above some Q(2) cut. For x > 0.55 and y > 0.75, four events are observed where 0.91 +/- 0.08 events are expected, A statistical analysis of the two-dimensional distribution of the events in x and y yields a probability of 0.72% for the region x > 0.55 and y > 0.25 and a probability of 7.8% for the entire Q(2) > 5000 GeV2 data sample. The observed excess above Standard Model expectations is particularly interesting because it occurs in a previously unexplored kinematic region

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century