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Solenoid Siberian snakes have successfully maintained polarization in particle rings below 1 GeV, but never in multi-GeV rings, because the spin rotation by a solenoid is inversely proportional to the beam momentum. High energy rings, such as Brookhaven’s 255 GeV Relativistic Heavy Ion Collider (RHIC), use only odd multiples of pairs of transverse B-field Siberian snakes directly opposite each other. When it became impractical to use a pair of Siberian Snakes in Fermilab’s 120GeV/c Main Injector, we searched for a new type of single Siberian snake that could overcome all depolarizing resonances in the 8.9–120GeV/c range. We found that a snake made of one 4-twist helix and 2 dipoles could maintain the polarization. This snake design could solve the long-standing problem of significant polarization loss during acceleration of polarized protons from a few GeV to tens of GeV, such as in the AGS, before injecting them into multi-hundred GeV rings, such as RHIC.

The fundamental building blocks of the proton—quarks and gluons—have been known for decades. However, we still have an incomplete theoretical and experimental understanding of how these particles and their dynamics give rise to the quantum bound state of the proton and its physical properties, such as its spin 1 . The two up quarks and the single down quark that comprise the proton in the simplest picture account only for a few per cent of the proton mass, the bulk of which is in the form of quark kinetic and potential energy and gluon energy from the strong force 2 . An essential feature of this force, as described by quantum chromodynamics, is its ability to create matter–antimatter quark pairs inside the proton that exist only for a very short time. Their fleeting existence makes the antimatter quarks within protons difficult to study, but their existence is discernible in reactions in which a matter–antimatter quark pair annihilates. In this picture of quark–antiquark creation by the strong force, the probability distributions as a function of momentum for the presence of up and down antimatter quarks should be nearly identical, given that their masses are very similar and small compared to the mass of the proton 3 . Here we provide evidence from muon pair production measurements that these distributions are considerably different, with more abundant down antimatter quarks than up antimatter quarks over a wide range of momenta. These results are expected to revive interest in several proposed mechanisms for the origin of this antimatter asymmetry in the proton that had been disfavoured by previous results 4 , and point to future measurements that can distinguish between these mechanisms. Quark–antiquark annihilation measurements provide a precise determination of the ratio of down and up antiquarks within protons as a function of momentum, which confirms the asymmetry between the abundance of down and up antiquarks.

A first search for [Formula omitted] violation in the Cabibbo-suppressed [Formula omitted] decay is performed using both a binned and an unbinned model-independent technique in the Dalitz plot. The studies are based on a sample of proton-proton collision data, corresponding to an integrated luminosity of [Formula omitted], and collected by the LHCb experiment at centre-of-mass energies of 7 and [Formula omitted]. The data are consistent with the hypothesis of no [Formula omitted] violation.

In the Introduction section of the original article [1].

Using a data sample corresponding to an integrated luminosity of 2.0 [Formula omitted], collected by the LHCb experiment, the production of the [Formula omitted] state in proton-proton collisions at a centre-of-mass energy of [Formula omitted] [Formula omitted] is studied in the rapidity range [Formula omitted] and in the transverse momentum range [Formula omitted]. The cross-section for prompt production of [Formula omitted] mesons relative to that of the [Formula omitted] meson is measured using the [Formula omitted] [Formula omitted] decay mode and is found to be [Formula omitted]. The quoted uncertainties are, in order, statistical, systematic and due to uncertainties on the branching fractions of the [Formula omitted] and [Formula omitted] decays. The prompt [Formula omitted] production cross-section is determined to be [Formula omitted], where the last uncertainty includes that on the [Formula omitted] meson cross-section. The ratio of the branching fractions of [Formula omitted]-hadron decays to the [Formula omitted] and [Formula omitted] states is measured to be [Formula omitted], where the last uncertainty is due to those on the branching fractions of the [Formula omitted] and [Formula omitted] decays. The difference between the [Formula omitted] and [Formula omitted] masses is also determined to be [Formula omitted], which is the most precise single measurement of this quantity to date.

The cross-sections of [Formula omitted] meson production in proton-proton collisions at [Formula omitted] are measured with a data sample collected by the LHCb detector corresponding to an integrated luminosity of [Formula omitted]. The production cross-sections for prompt [Formula omitted] mesons and those for [Formula omitted] mesons from b-hadron decays ( [Formula omitted]) are determined as functions of the transverse momentum, [Formula omitted], and the rapidity, y, of the [Formula omitted] meson in the kinematic range [Formula omitted] and [Formula omitted]. The production cross-sections integrated over this kinematic region are [sigma](prompt[psi](2S),13TeV)=1.430±0.005(stat)±0.099(syst)[mu]b,[sigma]([psi](2S)-from-b,13TeV)=0.426±0.002(stat)±0.030(syst)[mu]b.A new measurement of [Formula omitted] production cross-sections in pp collisions at [Formula omitted] is also performed using data collected in 2011, corresponding to an integrated luminosity of [Formula omitted]. The integrated production cross-sections in the kinematic range [Formula omitted] and [Formula omitted] are [sigma](prompt[psi](2S),7TeV)=0.471±0.001(stat)±0.025(syst)[mu]b,[sigma]([psi](2S)-from-b,7TeV)=0.126±0.001(stat)±0.008(syst)[mu]b.All results show reasonable agreement with theoretical calculations.

A search for the doubly-charmed-baryon decay $$ {\\Xi}_{cc}^{++}\\to {\\Xi}_c^0{\\pi}^{+}{\\pi}^{+} $$ Ξ cc + + → Ξ c 0 π + π + is performed using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 5 . 4 fb − 1 . A significant structure consistent with the $$ {\\Xi}_{cc}^{++} $$ Ξ cc + + baryon is observed in the $$ {\\Xi}_c^0{\\pi}^{+}{\\pi}^{+} $$ Ξ c 0 π + π + invariant-mass spectrum. Using the $$ {\\Xi}_{cc}^{++}\\to {\\Lambda}_c^{+}{K}^{-}{\\pi}^{+}{\\pi}^{+} $$ Ξ cc + + → Λ c + K − π + π + decay as the normalisation channel, the branching fraction ratio, $$ \\frac{\\mathcal{B}\\left({\\Xi}_{cc}^{++}\\to {\\Xi}_c^0{\\pi}^{+}{\\pi}^{+}\\right)}{\\mathcal{B}\\left({\\Xi}_{cc}^{++}\\to {\\Lambda}_c^{+}{K}^{-}{\\pi}^{+}{\\pi}^{+}\\right)} $$ B Ξ cc + + → Ξ c 0 π + π + B Ξ cc + + → Λ c + K − π + π + , is measured to be 1 . 37 ± 0 . 18 (stat) ± 0 . 09 (syst) ± 0 . 35 (ext). This measurement provides critical input for testing QCD factorisation methods in the weak decays of doubly-heavy baryons, particularly in quantifying nonperturbative effects such as final-state interactions and resonance contributions to the hadronisation process.

Branching fraction ratios between the decays $$ {B}_{(s)}^0\\to J/\\psi {\\eta}^{\\left(\\prime \\right)} $$ B s 0 → J / ψ η ′ are measured using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fb − 1 . The measured ratios of these branching fractions are $$ {\\displaystyle \\begin{array}{c}\\frac{\\mathcal{B}\\left({B}^0\\to J/{\\psi \\eta}^{\\prime}\\right)}{\\mathcal{B}\\left({B}^0\\to J/\\psi \\eta \\right)}=0.48\\pm 0.06\\pm 0.02\\pm 0.01,\\\ {}\\frac{\\mathcal{B}\\left({B}_s^0\\to J/{\\psi \\eta}^{\\prime}\\right)}{\\mathcal{B}\\left({B}_s^0\\to J/\\psi \\eta \\right)}=0.80\\pm 0.02\\pm 0.02\\pm 0.01,\\end{array}} $$ B B 0 → J / ψη ′ B B 0 → J / ψη = 0.48 ± 0.06 ± 0.02 ± 0.01 , B B s 0 → J / ψη ′ B B s 0 → J / ψη = 0.80 ± 0.02 ± 0.02 ± 0.01 , where the uncertainties are statistical, systematic and related to the precision of the η (′) branching fractions, respectively. They are used to constrain the η/η ′ mixing angle, ϕ P , and to probe the presence of a possible glueball component in the η ′ meson, described by the gluonic mixing angle ϕ G . The obtained results are $$ {\\displaystyle \\begin{array}{c}{\\phi}_{\\textrm{P}}={\\left({41.6}_{-1.2}^{+1.0}\\right)}^{\\circ },\\\ {}{\\phi}_{\\textrm{G}}={\\left({28.1}_{-4.0}^{+3.9}\\right)}^{\\circ },\\end{array}} $$ ϕ P = 41.6 − 1.2 + 1.0 ∘ , ϕ G = 28.1 − 4.0 + 3.9 ∘ , where the uncertainties are statistically dominated. While the value of ϕ P is compatible with existing experimental determinations and theoretical calculations, the angle ϕ G differs from zero by more than four standard deviations, which points to a substantial glueball component in the η ′ meson and/or unexpectedly large contributions from gluon-mediated processes in these decays. The absolute branching fractions are also measured relative to that of the well-established $$ {B}_s^0\\to J/\\psi \\phi $$ B s 0 → J / ψϕ decay, which serves as the normalisation channel. These results supersede the previous LHCb measurements and are the most precise to date.

A time-integrated angular analysis of the decay $$ {B}_s^0\\to J/\\psi {\\overline{K}}^{\\ast }{(892)}^0 $$ B s 0 → J / ψ K ¯ ∗ 892 0 , with J / ψ → μ + μ − and $$ {\\overline{K}}^{\\ast }{(892)}^0\\to {K}^{-}{\\pi}^{+} $$ K ¯ ∗ 892 0 → K − π + , is presented. The analysis employs a sample of proton-proton collision data collected by the LHCb experiment during 2015–2018 at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6 fb − 1 . A simultaneous maximum-likelihood fit is performed to the angular distributions in bins of the K − π + mass. This fit yields measurements of the CP -averaged polarisation fractions and CP asymmetries for the P-wave component of the K − π + system. The longitudinal and parallel polarisation fractions are determined to be f 0 = 0.534 ± 0.012 ± 0.009 and f || = 0.211 ± 0.014 ± 0.005, respectively, where the first uncertainty is statistical and the second is systematic. The CP asymmetries are measured with 3–7% precision and are found to be consistent with zero. These measurements, along with an updated determination of the branching fraction relative to the B 0 → J / ψK *0 decay, are combined with previous LHCb results, providing the most precise values for these observables to date.

A study of $$ {\\Lambda}_b^0 $$ Λ b 0 and $$ {\\Xi}_b^0 $$ Ξ b 0 baryon decays to the final states $$ p{K}_{\\textrm{S}}^0{\\pi}^{-} $$ p K S 0 π − and $$ p{K}_{\\textrm{S}}^0{K}^{-} $$ p K S 0 K − is performed using pp collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb − 1 . The decays $$ {\\Lambda}_b^0\\to p{K}_{\\textrm{S}}^0{K}^{-} $$ Λ b 0 → p K S 0 K − and $$ {\\Xi}_b^0\\to p{K}_{\\textrm{S}}^0{K}^{-} $$ Ξ b 0 → p K S 0 K − are observed for the first time, with significances reaching eight standard deviations. The branching fractions and integrated CP asymmetries are measured for the $$ {\\Lambda}_b^0\\to p{K}_{\\textrm{S}}^0{\\pi}^{-} $$ Λ b 0 → p K S 0 π − , $$ {\\Lambda}_b^0\\to p{K}_{\\textrm{S}}^0{K}^{-} $$ Λ b 0 → p K S 0 K − , and $$ {\\Xi}_b^0\\to p{K}_{\\textrm{S}}^0{K}^{-} $$ Ξ b 0 → p K S 0 K − decays. For the decay $$ {\\Lambda}_b^0\\to p{K}_{\\textrm{S}}^0{\\pi}^{-} $$ Λ b 0 → p K S 0 π − , the CP asymmetries are measured in different regions of the Dalitz plot. No evidence of CP violation is observed.