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We report on an analysis of the decay J/ψ→γπ0η′ using a sample of (1310.6±7.0)× 106 J/ψ events collected with the BESIII detector. We search for the CP-violating process ηc→π0η′ and a dark gauge boson U′ in J/ψ→U′η′, U′→γπ0, π0→γγ. No evidence of an ηc signal is observed in the π0η′ invariant-mass spectrum and the upper limit of the branching fraction is determined to be 7.2× 10−5 at the 90\% confidence level. We also find no evidence of U′ production and set upper limits at the 90\% confidence level on the product branching fraction B(J/ψ→U′η′)×B(U′→π0γ) in the range between (0.8−6.5)×10−7 for 0.2 ≤mU′≤2.1GeV/c2. In addition, we study the process J/ψ→ωη′ with ω→γπ0. The branching fraction of J/ψ→ωη′ is found to be (1.87±0.09±0.12)×10−4, where the first uncertainty is statistical and the second is systematic, with a precision that is improved by a factor of 1.4 over the previously published BESIII measurement.
Using a 2.93 fb−1 data sample of electron-positron collisions taken with the BESIII detector at a center-of-mass energy of 3.773 GeV, which corresponds to (8296±31±64)×103D+D− pairs, we search for the baryon and lepton number violating decays D+→Λ¯(Σ¯0)e+ and D+→Λ(Σ0)e+. No obvious signals are found with the current statistics and upper limits on the branching fractions of these four decays are set at the level of 10−6 at 90% confidence level.
By analyzing a 2.93~fb−1 data sample of e+e− collisions, recorded at a center-of-mass energy of 3.773 GeV with the BESIII detector operated at the BEPCII collider, we have searched for the semileptonic D+ transition into the axial-vector meson K¯1(1270)0. The D+→K¯1(1270)0e+νe decay is observed for the first time with a statistical significance greater than 10σ. Its decay branching fraction is determined to be B[D+→K¯1(1270)0e+νe]=(2.30±0.26±0.18±0.25)×10−3, where the first and second uncertainties are statistical and systematic, respectively, and the third originates from the input branching fraction of K¯1(1270)0→K−π+π0.
Using an e+e− annihilation data sample corresponding to an integrated luminosity of 2.93fb−1 collected at the center-of-mass energy of 3.773\,GeV with the BESIII detector, we measure the absolute branching fractions of D+→ηηπ+, D+→ηπ+π0, and D0→ηπ+π− to be (2.96±0.24±0.13)×10−3, (2.23±0.15±0.11)×10−3, and (1.20±0.07±0.04)×10−3, respectively, where the first uncertainties are statistical and the second ones systematic. The D+→ηηπ+ decay is observed for the first time and the branching fractions of D+(0)→ηπ+π0(−) are measured with much improved precision. In addition we test for CP asymmetries in the separated charge-conjugate branching fractions; no evidence of CP violation is found.
Using a data sample of (448.1±2.9)×106 ψ(3686) decays collected by the BESIII detector at the Beijing Electron Positron Collider (BEPCII), we observe the decays χcJ→ϕϕη (J=0, 1, 2), where the χcJ are produced via the radiative processes ψ(3686)→γχcJ. The branching fractions are measured to be B(χc0→ϕϕη)=(8.41±0.74±0.62)×10−4, B(χc1→ϕϕη)=(2.96±0.43±0.22)×10−4, and B(χc2→ϕϕη)=(5.33±0.52±0.39)×10−4, where the first uncertainties are statistical and the second are systematic. We also search for intermediate states in the ϕϕ or ηϕ combinations, but no significant structure is seen due to the limited statistics.
We report the first observation of D+→τ+ντ with a significance of 5.1σ. We measure B(D+→τ+ντ)=(1.20±0.24stat.±0.12syst.)×10−3. Taking the world average B(D+→μ+νμ)=(3.74±0.17)×10−4, we obtain Rτ/μ=Γ(D+→τ+ντ)/Γ(D+→μ+νμ)=3.21±0.64stat.±0.43syst., which is consistent with the Standard Model expectation of lepton flavor universality. Using external inputs, our results give values for the D+ decay constant fD+ and the CKM matrix element |Vcd| that are consistent with, but less precise than, other determinations.
A search for the rare radiative leptonic decay D+s→γe+νe is performed for the first time using electron-positron collision data corresponding to an integrated luminosity of 3.19 fb−1, collected with the BESIII detector at a center-of-mass energy of 4.178 GeV. No evidence for the D+s→γe+νe decay is seen and an upper limit of B(D+s→γe+νe)<1.3×10−4 is set on the partial branching fraction at a 90\% confidence level for radiative photon energies E∗γ>0.01~GeV.
The new class of microbial rhodopsins, called xenorhodopsins (XeRs),[1] extends the versatility of this family by inward H+ pumps.[2–4] These pumps are an alternative optogenetic tool to the light-gated ion channels (e.g. ChR1,2), because the activation of electrically excitable cells by XeRs is independent from the surrounding physiological conditions. In this work we functionally and spectroscopically characterized XeR from Nanosalina (NsXeR).[1] The photodynamic behavior of NsXeR was investigated on the ps to s time scale elucidating the formation of the J and K and a previously unknown long-lived intermediate. The pH dependent kinetics reveal that alkalization of the surrounding medium accelerates the photocycle and the pump turnover. In patch-clamp experiments the blue-light illumination of NsXeR in the M state shows a potential-dependent vectoriality of the photocurrent transients, suggesting a variable accessibility of reprotonation of the retinal Schiff base. Insights on the kinetically independent switching mechanism could furthermore be obtained by mutational studies on the putative intracellular H+ acceptor D220.
Rhodopsins are the most universal biological light-energy transducers and abundant phototrophic mechanisms that evolved on Earth and have a remarkable diversity and potential for biotechnological applications. Recently, the first sodium-pumping rhodopsin KR2 from Krokinobacter eikastus was discovered and characterized. However, the existing structures of KR2 are contradictory, and the mechanism of Na+ pumping is not yet understood. Here, we present a structure of the cationic (non H+) light-driven pump at physiological pH in its pentameric form. We also present 13 atomic structures and functional data on the KR2 and its mutants, including potassium pumps, which show that oligomerization of the microbial rhodopsin is obligatory for its biological function. The studies reveal the structure of KR2 at nonphysiological low pH where it acts as a proton pump. The structure provides new insights into the mechanisms of microbial rhodopsins and opens the way to a rational design of novel cation pumps for optogenetics.