Snapshots of a molecular swivel in action

Members of the serine family of site-specific recombinases exchange DNA strands via 180° rotation about a central protein-protein interface. Modeling of this process has been hampered by the lack of structures in more than one rotational state for any individual serine recombinase. Here we report crystal structures of the catalytic domains of four constitutively active mutants of the serine recombinase Sin, providing snapshots of rotational states not previously visualized for Sin, including two seen in the same crystal. Normal mode analysis predicted that each tetramer's lowest frequency mode (i.e. most accessible large-scale motion) mimics rotation: two protomers rotate as a pair with respect to the other two. Our analyses also suggest that rotation is not a rigid body movement around a single symmetry axis but instead uses multiple pivot points and entails internal motions within each subunit

Observation of sizeable ω\omega contribution to χc1(3872)→π+π−J/ψ\chi_{c1}(3872) \to \pi^+\pi^- J/\psi decays

Resonant structures in the dipion mass spectrum from $\chi_{c1}(3872)\to\pi^+\pi^- J/\psi$ decays, produced via $B^+\to K^+\chi_{c1}(3872)$ decays, are analyzed using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb$^{-1}$. A sizeable contribution from the isospin conserving $\chi_{c1}(3872)\to\omega J/\psi$ decay is established for the first time, $(21.4\pm2.3\pm2.0)\%$, with a significance of more than $7.1\sigma$. The amplitude of isospin violating decay, $\chi_{c1}(3872)\to\rho^0 J/\psi$, relative to isospin conserving decay, $\chi_{c1}(3872)\to\omega J/\psi$, is properly determined, and it is a factor of six larger than expected for a pure charmonium state.Resonant structures in the dipion mass spectrum from χc1(3872)→π+π-J/ψ decays, produced via B+→K+χc1(3872) decays, are analyzed using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9  fb-1. A sizeable contribution from the isospin conserving χc1(3872)→ωJ/ψ decay is established for the first time, (21.4±2.3±2.0)%, with a significance of more than 7.1σ. The amplitude of isospin violating decay, χc1(3872)→ρ0J/ψ, relative to isospin conserving decay, χc1(3872)→ωJ/ψ, is properly determined, and it is a factor of 6 larger than expected for a pure charmonium state.Resonant structures in the dipion mass spectrum from $\chi_{c1}(3872)\to\pi^+\pi^- J/\psi$ decays, produced via $B^+\to K^+\chi_{c1}(3872)$ decays, are analyzed using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 $fb^{-1}$. A sizeable contribution from the isospin conserving $\chi_{c1}(3872)\to\omega J/\psi$ decay is established for the first time, $(21.4\pm2.3\pm2.0)\%$, with a significance of more than $7.1\sigma$. The amplitude of isospin violating decay, $\chi_{c1}(3872)\to\rho^0 J/\psi$, relative to isospin conserving decay, $\chi_{c1}(3872)\to\omega J/\psi$, is properly determined, and it is a factor of six larger than expected for a pure charmonium state

Search for the rare hadronic decay Bs0→ppˉB_s^0\to p \bar{p}

A search for the rare hadronic decay Bs0→pp¯ is performed using proton-proton collision data recorded by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6  fb-1. No evidence of the decay is found and an upper limit on its branching fraction is set at B(Bs0→pp¯)&lt;4.4(5.1)×10-9 at 90% (95%) confidence level; this is currently the world’s best upper limit. The decay mode B0→pp¯ is measured with very large significance, confirming the first observation by the LHCb experiment in 2017. The branching fraction is determined to be B(B0→pp¯)=(1.27±0.15±0.05±0.04)×10-8, where the first uncertainty is statistical, the second is systematic and the third is due to the external branching fraction of the normalization channel B0→K+π-. The combination of the two LHCb measurements of the B0→pp¯ branching fraction yields B(B0→pp¯)=(1.27±0.13±0.05±0.03)×10-8.A search for the rare hadronic decay $B_s^0\to p \bar{p}$ is performed using proton-proton collision data recorded by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6 fb$^{-1}$. No evidence of the decay is found and an upper limit on its branching fraction is set at ${\cal B}(B_s^0\to p \bar{p}) < 4.4~(5.1) \times 10^{-9}$ at 90% (95%) confidence level; this is currently the world's best upper limit. The decay mode $B^0\to p \bar{p}$ is measured with very large significance, confirming the first observation by the LHCb experiment in 2017. The branching fraction is determined to be ${\cal B}(B^0\to p \bar{p}) = \rm (1.27 \pm 0.15 \pm 0.05 \pm 0.04) \times 10^{-8}$, where the first uncertainty is statistical, the second is systematic and the third is due to the external branching fraction of the normalization channel $B^0\to K^+\pi^-$. The combination of the two LHCb measurements of the $B^0\to p \bar{p}$ branching fraction yields ${\cal B}(B^0\to p \bar{p}) = \rm (1.27 \pm 0.13 \pm 0.05 \pm 0.03) \times 10^{-8}$

Measurement of CP asymmetries in D(s)+→ηπ+ {D}_{(s)}^{+}\to \eta {\pi}^{+} and D(s)+→η′π+ {D}_{(s)}^{+}\to {\eta}^{\prime }{\pi}^{+} decays

Searches for CP violation in the decays ${D}_{(s)}^{+}\to \eta {\pi}^{+}$ and ${D}_{(s)}^{+}\to {\eta}^{\prime }{\pi}^{+}$ are performed using pp collision data corresponding to 6 fb$^{−1}$ of integrated luminosity collected by the LHCb experiment. The calibration channels ${D}_{(s)}^{+}\to \phi {\pi}^{+}$ are used to remove production and detection asymmetries. The resulting CP-violating asymmetries are${\displaystyle \begin{array}{l}{\mathcal{A}}^{CP}=\left({D}^{+}\to \eta {\pi}^{+}\right)=\left(0.34\pm 0.66\pm 0.16\pm 0.05\right)\%,\\ {}{\mathcal{A}}^{CP}=\left({D}_s^{+}\to \eta {\pi}^{+}\right)=\left(0.32\pm 0.51\pm 0.12\right)\%,\\ {}\begin{array}{l}{\mathcal{A}}^{CP}=\left({D}^{+}\to {\eta}^{\prime }{\pi}^{+}\right)=\left(0.49\pm 0.18\pm 0.06\pm 0.05\right)\%,\\ {}{\mathcal{A}}^{CP}=\left({D}_s^{+}\to {\eta}^{\prime }{\pi}^{+}\right)=\left(0.01\pm 0.12\pm 0.08\right)\%,\end{array}\end{array}}$where the first uncertainty is statistical, the second is systematic and the third, relevant for the D$^{+}$ channels, is due to the uncertainty on ${\mathcal{A}}^{CP}=\left({D}^{+}\to \phi {\pi}^{+}\right)$. These measurements, currently the most precise for three of the four channels considered, are consistent with the absence of CP violation. A combination of these results with previous LHCb measurements is presented.[graphic not available: see fulltext]Searches for $CP$ violation in the decays $D^+_{(s)}\rightarrow \eta \pi^+$ and $D^+_{(s)}\rightarrow \eta^{\prime} \pi^+$ are performed using $pp$ collision data corresponding to 6 fb$^{-1}$ of integrated luminosity collected by the LHCb experiment. The calibration channels $D^+_{(s)}\rightarrow \phi \pi^+$ are used to remove production and detection asymmetries. The resulting $CP$-violating asymmetries are $A^{CP}(D^+ \rightarrow \eta \pi^+) = (0.34 \pm 0.66 \pm 0.16 \pm 0.05)\%$, $A^{CP}(D^+_s \rightarrow \eta \pi^+) = (0.32 \pm 0.51 \pm 0.12)\%$, $A^{CP}(D^+ \rightarrow \eta^{\prime} \pi^+) = (0.49 \pm 0.18 \pm 0.06 \pm 0.05)\%$, $A^{CP}(D^+_s \rightarrow \eta^{\prime} \pi^+) = (0.01 \pm 0.12 \pm 0.08)\%$, where the first uncertainty is statistical, the second is systematic and the third, relevant for the $D^+$ channels, is due to the uncertainty on $A^{CP}(D^+ \to \phi \pi^+)$. These measurements, currently the most precise for three of the four channels considered, are consistent with the absence of $CP$ violation. A combination of these results with previous LHCb measurements is presented

Nuclear modification factor of neutral pions in the forward and backward regions in ppPb collisions

The nuclear modification factor of neutral pions is measured in proton-lead collisions collected at a center-of-mass energy per nucleon of $8.16$ TeV with the LHCb detector. The $\pi^0$ production cross section is measured differentially in transverse momentum ($p_{T}$) for 1.5π0 production cross section is measured differentially in transverse momentum (pT) for 1.5<pT<10.0  GeV and in center-of-mass pseudorapidity (ηc.m.) regions 2.5<ηc.m.<3.5 (forward) and -4.0<ηc.m.<-3.0 (backward) defined relative to the proton beam direction. The forward measurement shows a sizable suppression of π0 production, while the backward measurement shows the first evidence of π0 enhancement in proton-lead collisions at the LHC. Together, these measurements provide precise constraints on models of nuclear structure and particle production in high-energy nuclear collisions.The nuclear modification factor of neutral pions is measured in proton-lead collisions collected at a center-of-mass energy per nucleon of 8.16~{\rm TeV}$with the LHCb detector. The$\pi^0$production cross section is measured differentially in transverse momentum ($p_{\rm T}$) for$1.5<p_{\rm T}<10.0~{\rm GeV}$and in center-of-mass pseudorapidity ($\eta_{\rm c.m.}$) regions$2.5<\eta_{\rm c.m.}<3.5$(forward) and$-4.0<\eta_{\rm c.m.}<-3.0$(backward) defined relative to the proton beam direction. The forward measurement shows a sizable suppression of$\pi^0$production, while the backward measurement shows the first evidence of$\pi^0$ enhancement in proton-lead collisions at the LHC. Together, these measurements provide precise constraints on models of nuclear structure and particle production in high-energy nuclear collisions

Amplitude analysis of the Λc+→pK−π+\Lambda^+_c\to pK^-\pi^+ decay and Λc+\Lambda^+_c baryon polarization measurement in semileptonic beauty hadron decays

An amplitude analysis of $\Lambda^+_c \to pK^-\pi^+$ decays together with a measurement of the $\Lambda^+_c$ polarization vector in semileptonic beauty hadron decays is presented. A sample of $400\,000$ candidates is selected from proton-proton collisions recorded by the LHCb detector at a center-of-mass energy of 13 TeV. An amplitude model is developed and the resonance fractions as well as two- and three-body decay parameters are reported. The mass and width of the $\Lambda(2000)$ state are also determined. A significant $\Lambda^+_c$ polarization is found. A large sensitivity of the $\Lambda^+_c \to pK^-\pi^+$ decay to the polarization is seen, making the amplitude model suitable for $\Lambda^+_c$ polarization measurements in other systems.An amplitude analysis of Λc+→pK-π+ decays together with a measurement of the Λc+ polarization vector in semiōleptonic beauty hadron decays is presented. A sample of 400 000 candidates is selected from proton-proton collisions recorded by the LHCb detector at a center-of-mass energy of 13 TeV. An amplitude model is developed and the resonance fractions as well as two- and three-body decay parameters are reported. The mass and width of the Λ(2000) state are also determined. A significant Λc+ polarization is found. A large sensitivity of the Λc+→pK-π+ decay to the polarization is seen, making the amplitude model suitable for Λc+ polarization measurements in other systems.An amplitude analysis of $\Lambda^+_c \to pK^-\pi^+$ decays together with a measurement of the $\Lambda^+_c$ polarization vector in semileptonic beauty hadron decays is presented. A sample of $400\,000$ candidates is selected from proton-proton collisions recorded by the LHCb detector at a center-of-mass energy of 13 TeV. An amplitude model is developed and the resonance fractions as well as two- and three-body decay parameters are reported. The mass and width of the $\Lambda(2000)$ state are also determined. A significant $\Lambda^+_c$ polarization is found. A large sensitivity of the $\Lambda^+_c \to pK^-\pi^+$ decay to the polarization is seen, making the amplitude model suitable for $\Lambda^+_c$ polarization measurements in other systems

Search for CPCP violation using T^\hat{T}-odd correlations in B0→ppˉK+π−B^{0} \to p \bar p K^{+} \pi^{-} decays

A search for $CP$ and $P$ violation in charmless four-body $B^{0} \to p \bar p K^{+} \pi^{-}$ decays is performed using triple-product asymmetry observables. It is based on proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of $7$, $8$ and $13$ TeV, corresponding to a total integrated luminosity of $8.4$ fb$^{-1}$. The $CP$- and $P$-violating asymmetries are measured both in the integrated phase space and in specific regions. No evidence is seen for $CP$ violation. $P$-parity violation is observed at a significance of 5.8 standard deviations.A search for CP and P violation in charmless four-body B0→pp¯K+π- decays is performed using triple-product asymmetry observables. It is based on proton-proton collision data collected by the LHCb experiment at center-of-mass energies of 7, 8 and 13 TeV, corresponding to a total integrated luminosity of 8.4  fb-1. The CP- and P-violating asymmetries are measured both in the integrated phase space and in specific regions. No evidence is seen for CP violation. P-parity violation is observed at a significance of 5.8 standard deviations.A search for $CP$ and $P$ violation in charmless four-body $B^{0} \to p \bar p K^{+} \pi^{-}$ decays is performed using triple-product asymmetry observables. It is based on proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of $7$, $8$ and $13$ TeV, corresponding to a total integrated luminosity of $8.4$ fb$^{-1}$. The $CP$- and $P$-violating asymmetries are measured both in the integrated phase space and in specific regions. No evidence is seen for $CP$ violation. $P$-parity violation is observed at a significance of 5.8 standard deviation

Search for the doubly heavy baryon Ξbc+\it{\Xi}_{bc}^{+} decaying to J/ψΞc+J/\it{\psi} \it{\Xi}_{c}^{+}

A first search for the decay is performed by the LHCb experiment with a data sample of proton-proton collisions, corresponding to an integrated luminosity of 9 fb$^{−1}$ recorded at centre-of-mass energies of 7, 8, and 13 TeV. Two peaking structures are seen with a local (global) significance of and standard deviations at masses of 6571 and 6694 MeV/, respectively. Upper limits are set on the baryon production cross-section times the branching fraction relative to that of the decay at centre-of-mass energies of 8 and 13 TeV, in the and in the rapidity and transverse-momentum ranges from 2.0 to 4.5 and 0 to , respectively. Upper limits are presented as a function of the mass and lifetime.A first search for the $\it{\Xi}_{bc}^{+}\to J/\it{\psi}\it{\Xi}_{c}^{+}$ decay is performed by the LHCb experiment with a data sample of proton-proton collisions, corresponding to an integrated luminosity of $9\,\mathrm{fb}^{-1}$ recorded at centre-of-mass energies of 7, 8, and $13\mathrm{\,Te\kern -0.1em V}$. Two peaking structures are seen with a local (global) significance of $4.3\,(2.8)$ and $4.1\,(2.4)$ standard deviations at masses of $6571\,\mathrm{Me\kern -0.1em V\!/}c^2$ and $6694\,\mathrm{Me\kern -0.1em V\!/}c^2$, respectively. Upper limits are set on the $\it{\Xi}_{bc}^{+}$ baryon production cross-section times the branching fraction relative to that of the $B_{c}^{+}\to J/\it{\psi} D_{s}^{+}$ decay at centre-of-mass energies of 8 and $13\mathrm{\,Te\kern -0.1em V}$, in the $\it{\Xi}_{bc}^{+}$ and in the $B_{c}^{+}$ rapidity and transverse-momentum ranges from 2.0 to 4.5 and 0 to $20\,\mathrm{Ge\kern -0.1em V\!/}c$, respectively. Upper limits are presented as a function of the $\it{\Xi}_{bc}^{+}$ mass and lifetime

Observation of the Bs0 ⁣→D∗+D∗−B^0_s\!\to D^{*+}D^{*-} decay

International audienceThe first observation of the ${B}_s^0$→ D$^{∗+}$D$^{∗−}$ decay and the measurement of its branching ratio relative to the B$^{0}$→ D$^{∗+}$D$^{∗−}$ decay are presented. The data sample used corresponds to an integrated luminosity of 9 fb$^{−1}$ of proton-proton collisions recorded by the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV between 2011 and 2018. The decay is observed with more than 10 standard deviations and the time-integrated ratio of branching fractions is determined to be$\frac{\mathcal{B}\left({B}_s^0\to {D}^{\ast +}{D}^{\ast -}\right)}{\mathcal{B}\left({B}^0\to {D}^{\ast +}{D}^{\ast -}\right)}=0.269\pm 0.032\pm 0.011\pm 0.008,$where the first uncertainty is statistical, the second systematic and the third due to the uncertainty of the fragmentation fraction ratio f$_{s}$/f$_{d}$. The ${B}_s^0$→ D$^{*+}$D$^{*−}$ branching fraction is calculated to be$\mathcal{B}\left({B}_s^0\to {D}^{\ast +}{D}^{\ast -}\right)=\left(2.15\pm 0.26\pm 0.09\pm 0.06\pm 0.16\right)\times {10}^{-4},$where the fourth uncertainty is due to the B$^{0}$→ D$^{*+}$D$^{*−}$ branching fraction. These results are calculated using the average ${B}_s^0$ meson lifetime in simulation. Correction factors are reported for scenarios where either a purely heavy or a purely light ${B}_s^0$ eigenstate is considered.[graphic not available: see fulltext