Michael Williams

Michael Williams

*This is an algorithmically generated author record based on publicly available information.

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Previous Organizations / Institutes

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Michael Williams has a total of 1000 co-authors. Here are the top co-authors by number of shared publications:


Latest Publications

  • Open Access

    Search for CP violation in D+ → ϕπ+ decays

    by R. Aaij, M. Abdelfatah, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, A. A. Adefisoye, B. Adeva, M. Adinolfi, P. Adlarson, et al.

    A bstract: A search for charge-parity ( CP ) violation in the Cabibbo-suppressed D + → ϕπ + decay is presented, using proton-proton collision data corresponding to an integrated luminosity of 6 fb − 1 , collected at a centre-of-mass energy of 13 TeV with the LHCb detector during Run 2. An abundant sample of $$ {D}^{+}\to {K}_{\mathrm{S}}^0{\pi}^{+} $$ D + → K S 0 π + decays is employed to correct for asymmetries arising from the production of the charmed meson and from detection effects associated with the charged pion accompanying the ϕ meson. Asymmetries induced by interference of multiple processes, such as neutral kaon mixing, regeneration of neutral kaons, and interference between the Cabibbo-favoured $$ {D}^{+}\to {\overline{K}}^0{\pi}^{+} $$ D + → K ¯ 0 π + and the doubly Cabibbo-suppressed D + → K 0 π + decay, are subtracted. The direct CP asymmetry in the D + → ϕπ + decay is measured to be $$ {a}_{CP}\left({D}^{+}\to \phi {\pi}^{+}\right)=\left(0.1\pm 4.9\left(\mathrm{stat}\right)\pm 2.4\left(\mathrm{syst}\right)\right)\times {10}^{-4}. $$ a CP D + → ϕ π + = 0.1 ± 4.9 stat ± 2.4 syst × 10 − 4 . For the first time at a hadron collider, the modulus of the ratio and the relative strong phase of the D + → K 0 π + to $$ {D}^{+}\to {\overline{K}}^0{\pi}^{+} $$ D + → K ¯ 0 π + decay amplitudes are also investigated. Two-dimensional confidence intervals are reported for these parameters.

  • Open Access

    Evidence for the decay $ {B}_s^0\to {\phi \eta}^{\prime } $

    by R. Aaij, M. Abdelfatah, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, A. A. Adefisoye, B. Adeva, M. Adinolfi, P. Adlarson, et al.

    A bstract: Using a dataset corresponding to an integrated luminosity of 9 fb − 1 collected in proton-proton collisions between 2011 and 2018 by the LHCb experiment, evidence is found for the decay $$ {B}_s^0\to {\phi \eta}^{\prime } $$ B s 0 → ϕη ′ with 3 . 5 σ significance. The branching ratio relative to the $$ {B}_s^0\to \phi \phi $$ B s 0 → ϕϕ decay is determined to be ℛ = (3 . 56 ± 0 . 79 ± 0 . 18 ± 0 . 06) × 10 − 2 . This corresponds to a branching fraction, $$ \mathcal{B}\left({B}_s^0\to {\phi \eta}^{\prime}\right)=\left(0.66\pm 0.15\pm 0.03\pm 0.02\right)\times {10}^{-6} $$ B B s 0 → ϕη ′ = 0.66 ± 0.15 ± 0.03 ± 0.02 × 10 − 6 where, in both cases, the first uncertainty is statistical, the second systematic, and the third due to external branching fractions.

  • Open Access

    Search for τ− → μ−μ+μ− decays at the LHCb experiment with Run 2 data

    by R. Aaij, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, A. A. Adefisoye, B. Adeva, M. Adinolfi, P. Adlarson, C. Agapopoulou, et al.

    A bstract: A search for the lepton-flavour-violating decay τ − → μ − μ + μ − is carried out using data collected by the LHCb experiment between 2016 and 2018 in proton-proton collisions at the LHC at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb − 1 . An upper limit of 1 . 9 (2 . 3) × 10 − 8 is set at the 90% (95%) confidence level on the branching fraction of the decay.

  • Open Access

    Measurement of the local and nonlocal amplitudes in B+ → K+μ+μ− decays

    by R. Aaij, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, A. A. Adefisoye, B. Adeva, M. Adinolfi, P. Adlarson, C. Agapopoulou, et al.

    A bstract: This paper presents a thorough study of the local and nonlocal amplitudes in B + → K + μ + μ − transitions through an amplitude analysis of the dimuon mass spectrum of the decay. The analysis is based on pp collision data corresponding to an integrated luminosity of 8.4 fb − 1 collected by the LHCb experiment during Run1 and Run2. This measurement employs a model that describes both one-particle and two-particle nonlocal amplitudes across the entirety of the dimuon mass spectrum, enabling the determination of both short- and long-distance contributions to the decay. The compatibility of the Wilson coefficient combinations $$ {C}_9+{C}_9^{\prime } $$ C 9 + C 9 ′ and $$ {C}_{10}+{C}_{10}^{\prime } $$ C 10 + C 10 ′ with the Standard Model prediction is found to vary between 1 . 6 σ and 4 σ , depending on the choice of local form factors.

  • Open Access

    Measurement of CP asymmetries in $ {\overline{B}}^0\to {D}_s^{-}{D}^{+} $ and $ {\overline{B}}_s^0\to {D}_s^{-}{D}^{-} $ decays

    by R. Aaij, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, A. A. Adefisoye, B. Adeva, M. Adinolfi, P. Adlarson, C. Agapopoulou, et al.

    A bstract: Measurements of the combined CP asymmetries in $$ {\overline{B}}^0\to {D}_s^{-}{D}^{+} $$ B ¯ 0 → D s − D + and $$ {\overline{B}}_s^0\to {D}_s^{-}{D}^{-} $$ B ¯ s 0 → D s − D − decays are made using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb − 1 . The measurements are found to be $$ {\displaystyle \begin{array}{l}{A}_{CP}\left({\overline{B}}^0\to {D}_s^{-}{D}^{+}\right)=0.0009\pm 0.0053\pm 0.0040,\\ {}{A}_{CP}\left({\overline{B}}_s^0\to {D}_s^{-}{D}^{-}\right)=0.103\pm 0.053\pm 0.010,\end{array}} $$ A CP B ¯ 0 → D s − D + = 0.0009 ± 0.0053 ± 0.0040 , A CP B ¯ s 0 → D s − D − = 0.103 ± 0.053 ± 0.010 , where the first and second uncertainties are statistical and systematic, respectively. This is the first measurement of this asymmetry in $$ {\overline{B}}_s^0 $$ B ¯ s 0 decays, and the most precise measurement to date for $$ {\overline{B}}^0 $$ B ¯ 0 decays. Both measurements are found to be consistent with CP symmetry.

  • Open Access

    Observation of the charmless purely baryonic decay $ {\Lambda}_b^0\to \Lambda p\overline{p} $

    by R. Aaij, M. Abdelfatah, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, A. A. Adefisoye, B. Adeva, M. Adinolfi, P. Adlarson, et al.

    A bstract: A search for the charmless purely baryonic decay $$ {\Lambda}_b^0\to \Lambda p\overline{p} $$ Λ b 0 → Λ p p ¯ is performed using proton-proton collision data recorded by the LHCb experiment at a centre-of-mass energy of $$ \sqrt{s}=13 $$ s = 13 TeV and corresponding to an integrated luminosity of 6 . 0 fb − 1 . The signal decay is observed with a significance of 5.1 standard deviations. Its branching fraction is measured for the first time, relative to that of the topologically similar decay $$ {\Lambda}_b^0\to \Lambda {K}^{+}{K}^{-} $$ Λ b 0 → Λ K + K − . Contributions from intermediate charmonium resonances decaying to the $$ p\overline{p} $$ p p ¯ and K + K − final states are explicitly excluded with a requirement on the invariant mass of the companion hadron system, $$ m\left(h\overline{h}\right)<2.85 $$ m h h ¯ < 2.85 GeV, where h stands for a proton or a charged kaon. The relative branching fraction is found to be $$ \frac{\mathcal{B}\left({\Lambda}_b^0\to \Lambda p\overline{p}\right)}{\mathcal{B}\left({\Lambda}_b^0\to \Lambda {K}^{+}{K}^{-}\right)}=\left(5.1\pm {1.3}_{\left(\mathrm{stat}\right)}\pm {0.3}_{\left(\mathrm{syst}\right)}\right)\times {10}^{-2}. $$ B Λ b 0 → Λ p p ¯ B Λ b 0 → Λ K + K − = 5.1 ± 1.3 stat ± 0.3 syst × 10 − 2 .

  • Open Access

    Measurement of γ using B± → DK± and B± → Dπ± decays with $ D\to {K}_{\mathrm{S}}^0{\pi}^{+}{\pi}^{-} $ and $ D\to {K}_{\mathrm{S}}^0{K}^{+}{K}^{-} $

    by R. Aaij, M. Abdelfatah, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, A. A. Adefisoye, B. Adeva, M. Adinolfi, P. Adlarson, et al.

    A bstract: A measurement of the CKM angle γ using the decay channels B ± → DK ± and B ± → Dπ ± , where the D meson decays to $$ D\to {K}_{\mathrm{S}}^0{\pi}^{+}{\pi}^{-} $$ D → K S 0 π + π − or $$ D\to {K}_{\mathrm{S}}^0{K}^{+}{K}^{-} $$ D → K S 0 K + K − , is performed with a data sample corresponding to an integrated luminosity of 5.8 fb − 1 , collected during 2024 by the upgraded LHCb experiment. CP violation is observed through a difference in the distributions of the Dalitz plot of the D decay between the B + and B − mesons. The CKM angle γ is determined to be γ = (68 . 1 ± 6 . 7) ° . Other parameters related to the examined B meson decay modes are also measured. This is the first measurement of the CKM angle γ using the upgraded LHCb detector.

  • Open Access

    Angular analysis of the B+ → π+μ+μ− decay

    by R. Aaij, M. Abdelfatah, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, A. A. Adefisoye, B. Adeva, M. Adinolfi, P. Adlarson, et al.

    A bstract: This paper presents the first measurement of the forward-backward asymmetry, A FB , and the flat term, F H , that parameterise the angular distribution of the B + → π + μ + μ − decay. The proton-proton collision dataset used in the analysis corresponds to an integrated luminosity of 9 fb − 1 , collected with the LHCb experiment between 2011 and 2018. The analysis is performed in two intervals of dimuon mass squared, one above and one below the region containing the J/ψ and ψ (2 S ) narrow charmonium resonances. The Standard Model predictions lie within the obtained 68% confidence level interval in the high-mass and within the 99% interval in the low-mass region.

  • Open Access

    Machine learning techniques for jet reconstruction at LHCb and application to the search for $ H\to b\overline{b} $ and $ H\to c\overline{c} $ in $ \sqrt{s}=13 $ TeV pp collisions

    by R. Aaij, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, A. A. Adefisoye, B. Adeva, M. Adinolfi, P. Adlarson, C. Agapopoulou, et al.

    A bstract: Two machine learning techniques for jet measurements at the LHCb experiment are presented: a regression-based method for jet-energy calibration and a deep neural network algorithm for jet flavour tagging, distinguishing between b -quark, c -quark, and light parton jets. These techniques are applied to a search for inclusive $$ H\to b\overline{b} $$ H → b b ¯ and $$ H\to c\overline{c} $$ H → c c ¯ decays using a LHCb dataset corresponding to an integrated luminosity of 1.6 fb − 1 . The observed (expected) 95% confidence level upper limits correspond to 6.6 (11.1) times the SM cross-section for the $$ H\to b\overline{b} $$ H → b b ¯ process, and 1003 (1834) times the SM cross-section for the $$ H\to c\overline{c} $$ H → c c ¯ process.

  • Open Access

    Improved branching-fraction measurements of $ {B}_{(s)}^0\to {K}_{\mathrm{S}}^0{h}^{+}h{\prime}^{-} $ decays and first observation of $ {B}_s^0\to {K}_{\mathrm{S}}^0{K}^{+}{K}^{-} $

    by R. Aaij, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, A. A. Adefisoye, B. Adeva, M. Adinolfi, P. Adlarson, H. Afsharnia, et al.