skip to main content


Search for: All records

Creators/Authors contains: "Morris, A. G."

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. A<sc>bstract</sc>

    A comprehensive study of the local and nonlocal amplitudes contributing to the decayB0K*0(→K+π)μ+μis performed by analysing the phase-space distribution of the decay products. The analysis is based onppcollision data corresponding to an integrated luminosity of 8.4 fb1collected by the LHCb experiment. This measurement employs for the first time a model of both one-particle and two-particle nonlocal amplitudes, and utilises the complete dimuon mass spectrum without any veto regions around the narrow charmonium resonances. In this way it is possible to explicitly isolate the local and nonlocal contributions and capture the interference between them. The results show that interference with nonlocal contributions, although larger than predicted, only has a minor impact on the Wilson Coefficients determined from the fit to the data. For the local contributions, the Wilson Coefficient$$ {\mathcal{C}}_9 $$C9, responsible for vector dimuon currents, exhibits a 2.1σdeviation from the Standard Model expectation. The Wilson Coefficients$$ {\mathcal{C}}_{10} $$C10,$$ {\mathcal{C}}_9^{\prime } $$C9and$$ {\mathcal{C}}_{10}^{\prime } $$C10are all in better agreement than$$ {\mathcal{C}}_9 $$C9with the Standard Model and the global significance is at the level of 1.5σ. The model used also accounts for nonlocal contributions fromB0→ K*0[τ+τ→ μ+μ] rescattering, resulting in the first direct measurement of thebsττvector effective-coupling$$ {\mathcal{C}}_{9\tau } $$C9τ.

     
    more » « less
    Free, publicly-accessible full text available September 1, 2025
  2. A search for hidden-charm pentaquark states decaying to a range ofΣcD¯andΛc+D¯final states, as well as doubly charmed pentaquark states toΣcDandΛc+D, is made using samples of proton-proton collision data corresponding to an integrated luminosity of5.7fb1recorded by the LHCb detector ats=13TeV. Since no significant signals are found, upper limits are set on the pentaquark yields relative to that of theΛc+baryon in theΛc+pKπ+decay mode. The known pentaquark states are also investigated, and their signal yields are found to be consistent with zero in all cases.

    © 2024 CERN, for the LHCb Collaboration2024CERN 
    more » « less
    Free, publicly-accessible full text available August 1, 2025
  3. A<sc>bstract</sc>

    A search for the fully reconstructed$$ {B}_s^0 $$Bs0→ μ+μγdecay is performed at the LHCb experiment using proton-proton collisions at$$ \sqrt{s} $$s= 13 TeV corresponding to an integrated luminosity of 5.4 fb1. No significant signal is found and upper limits on the branching fraction in intervals of the dimuon mass are set$$ {\displaystyle \begin{array}{cc}\mathcal{B}\left({B}_s^0\to {\mu}^{+}{\mu}^{-}\gamma \right)<4.2\times {10}^{-8},& m\left({\mu}^{+}{\mu}^{-}\right)\in \left[2{m}_{\mu },1.70\right]\textrm{GeV}/{c}^2,\\ {}\mathcal{B}\left({B}_s^0\to {\mu}^{+}{\mu}^{-}\gamma \right)<7.7\times {10}^{-8},&\ m\left({\mu}^{+}{\mu}^{-}\right)\in \left[\textrm{1.70,2.88}\right]\textrm{GeV}/{c}^2,\\ {}\mathcal{B}\left({B}_s^0\to {\mu}^{+}{\mu}^{-}\gamma \right)<4.2\times {10}^{-8},& m\left({\mu}^{+}{\mu}^{-}\right)\in \left[3.92,{m}_{B_s^0}\right]\textrm{GeV}/{c}^2,\end{array}} $$BBs0μ+μγ<4.2×108,mμ+μ2mμ1.70GeV/c2,BBs0μ+μγ<7.7×108,mμ+μ1.70, 2.88GeV/c2,BBs0μ+μγ<4.2×108,mμ+μ3.92mBs0GeV/c2,

    at 95% confidence level. Additionally, upper limits are set on the branching fraction in the [2mμ,1.70] GeV/c2dimuon mass region excluding the contribution from the intermediateϕ(1020) meson, and in the region combining all dimuon-mass intervals.

     
    more » « less
    Free, publicly-accessible full text available July 1, 2025
  4. The production of 𝜂 and 𝜂′ mesons is studied in proton-proton and proton-lead collisions collected with the LHCb detector. Proton-proton collisions are studied at center-of-mass energies of 5.02 and 13TeV and proton-lead collisions are studied at a center-of-mass energy per nucleon of 8.16TeV. The studies are performed in center-of-mass (c.m.) rapidity regions 2.5<𝑦c.m.<3.5 (forward rapidity) and −4.0<𝑦c.m.<−3.0 (backward rapidity) defined relative to the proton beam direction. The 𝜂 and 𝜂′ production cross sections are measured differentially as a function of transverse momentum for 1.5<𝑝T<10GeV and 3<𝑝T<10GeV, respectively. The differential cross sections are used to calculate nuclear modification factors. The nuclear modification factors for 𝜂 and 𝜂′ mesons agree at both forward and backward rapidity, showing no significant evidence of mass dependence. The differential cross sections of 𝜂 mesons are also used to calculate 𝜂/𝜋0 cross-section ratios, which show evidence of a deviation from the world average. These studies offer new constraints on mass-dependent nuclear effects in heavy-ion collisions, as well as 𝜂 and 𝜂′ meson fragmentation. 
    more » « less
    Free, publicly-accessible full text available February 1, 2025
  5. Garisto, R (Ed.)
    The ratios of branching fractions R(D*)= B(B0 --> D*+tau- nu(bar))/ B(B0--> D*+mu- nu(bar)) and R(D)= B(B0 --> D0tau- nu(bar))/ B(B0 --> D0mu- nu(bar)) are measured, assuming isospin symmetry, using a sample of proton-proton collision data corresponding to 3.0 fb−1 of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode τ− → μ−ντν¯μ. The measured values are R*D*)= 0.281+/- 0.018+/- 0.024 and R(D0)=0.441+/- 0.060+/- 0.066, where the first uncertainty is statistical and the second is systematic. The correlation between these measurements is ρ= −0.43. The results are consistent with the current average of these quantities and are at a combined 1.9 standard deviations from the predictions based on lepton flavor universality in the standard model 
    more » « less