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1. Quantum Semidefinite Programming with the Hadamard Test and Approximate Amplitude Constraints

   https://doi.org/10.48550/arXiv.2206.14999  

   Patti, T.L. ; Kossaifi, J. ; Anandkumar, A. ; Yelin, S.F. ( July 2022 , ArXivorg)

   Semidefinite programs are optimization methods with a wide array of applications, such as approximating difficult combinatorial problems. We introduce a variational quantum algorithm for semidefinite programs that uses only n qubits, a constant number of circuit preparations, and O(n2) expectation values in order to solve semidefinite programs with up to N=2n variables and M=2n constraints. Efficient optimization is achieved by encoding the objective matrix as a properly parameterized unitary conditioned on an auxilary qubit, a technique known as the Hadamard Test. The Hadamard Test enables us to optimize the objective function by estimating only a single expectation value of the ancilla qubit, rather than separately estimating exponentially many expectation values. Similarly, we illustrate that the semidefinite programming constraints can be effectively enforced by implementing a second Hadamard Test, as well as imposing ∼n2/2 Pauli string amplitude constraints. We demonstrate the effectiveness of our protocol by devising an efficient quantum implementation of the Goemans-Williamson algorithm, which is a useful approximation for various NP-hard problems, such as MaxCut. Our method exceeds the performance of analogous classical methods on a diverse subset of well-studied MaxCut problems from the GSet library. 

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2. Test of lepton flavor universality in B±→K±μ+μ− and B±→K±e+e− decays in proton-proton collisions at s=13TeV

   https://doi.org/10.1088/1361-6633/ad4e65  

   CMS_Collaboration, The ( July 2024 , Reports on Progress in Physics)

   A test of lepton flavor universality in${\text{B}}^{\pm }\to {\text{K}}^{\pm }{\mu }^{+}{\mu }^{-}$and${\text{B}}^{\pm }\to {\text{K}}^{\pm }{\text{e}}^{+}{\text{e}}^{-}$decays, as well as a measurement of differential and integrated branching fractions of a nonresonant${\text{B}}^{\pm }\to {\text{K}}^{\pm }{\mu }^{+}{\mu }^{-}$decay are presented. The analysis is made possible by a dedicated data set of proton-proton collisions at$\sqrt{s}=13\text{TeV}$recorded in 2018, by the CMS experiment at the LHC, using a special high-rate data stream designed for collecting about 10 billion unbiased b hadron decays. The ratio of the branching fractions$B({\text{B}}^{\pm }\to {\text{K}}^{\pm }{\mu }^{+}{\mu }^{-})$to$B({\text{B}}^{\pm }\to {\text{K}}^{\pm }{\text{e}}^{+}{\text{e}}^{-})$is determined from the measured double ratio$R(\text{K})$of these decays to the respective branching fractions of the${\text{B}}^{\pm }\to \text{J}/\text{ψ}{\text{K}}^{\pm }$with$\text{J}/\text{ψ}\to {\mu }^{+}{\mu }^{-}$and${\text{e}}^{+}{\text{e}}^{-}$decays, which allow for significant cancellation of systematic uncertainties. The ratio$R(\text{K})$is measured in the range$1.1<q^2<6.0{\text{GeV}}^2$, whereqis the invariant mass of the lepton pair, and is found to be$R(\text{K})={0.78}_{-0.23}^{+0.47}$, in agreement with the standard model expectation$R(\text{K})\approx 1$. This measurement is limited by the statistical precision of the electron channel. The integrated branching fraction in the sameq²range,$B({\text{B}}^{\pm }\to {\text{K}}^{\pm }{\mu }^{+}{\mu }^{-})=(12.42\pm 0.68)\times {10}^{-8}$, is consistent with the present world-average value and has a comparable precision.

    

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3. Photoproduction of K+K− Pairs in Ultraperipheral Collisions

   https://doi.org/10.1103/PhysRevLett.132.222303  

   Acharya, S ; Adamová, D ; Aglieri_Rinella, G ; Agnello, M ; Agrawal, N ; Ahammed, Z ; Ahmad, S ; Ahn, S U ; Ahuja, I ; Akindinov, A ; et al ( May 2024 , Physical Review Letters)

   $K^{+}{K}^{-}$pairs may be produced in photonuclear collisions, either from the decays of photoproduced$\varphi (1020)$mesons or directly as nonresonant$K^{+}{K}^{-}$pairs. Measurements of$K^{+}{K}^{-}$photoproduction probe the couplings between the$\varphi (1020)$and charged kaons with photons and nuclear targets. The kaon-proton scattering occurs at energies far above those available elsewhere. We present the first measurement of coherent photoproduction of$K^{+}{K}^{-}$pairs on lead ions in ultraperipheral collisions using the ALICE detector, including the first investigation of direct$K^{+}{K}^{-}$production. There is significant$K^{+}{K}^{-}$production at low transverse momentum, consistent with coherent photoproduction on lead targets. In the mass range$1.1<M_{KK}<1.4\mathrm{GeV}/c^2$above the$\varphi (1020)$resonance, for rapidity$|y_{KK}|<0.8$and$p_{T,KK}<0.1\mathrm{GeV}/c$, the measured coherent photoproduction cross section is$\mathrm{d}\sigma /\mathrm{d}y=3.37\pm 0.61(\text{stat})\pm 0.15(\mathrm{syst})\mathrm{mb}$. The center-of-mass energy per nucleon of the photon-nucleus (Pb) system$W_{\gamma \mathrm{Pb},n}$ranges from 33 to 188 GeV, far higher than previous measurements on heavy-nucleus targets. The cross section is larger than expected for$\varphi (1020)$photoproduction alone. The mass spectrum is fit to a cocktail consisting of$\varphi (1020)$decays, direct$K^{+}{K}^{-}$photoproduction, and interference between the two. The confidence regions for the amplitude and relative phase angle for direct$K^{+}{K}^{-}$photoproduction are presented.

   © 2024 CERN, for the ALICE Collaboration2024CERN 

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4. Evidence for B+→K+νν¯ decays

   https://doi.org/10.1103/PhysRevD.109.112006  

   Adachi, I ; Adamczyk, K ; Aggarwal, L ; Ahmed, H ; Aihara, H ; Akopov, N ; Aloisio, A ; Anh_Ky, N ; Asner, D M ; Atmacan, H ; et al ( June 2024 , Physical Review D)

   We search for the rare decay$B^{+}\to K^{+}\nu \overline{\nu }$in a$362{\mathrm{fb}}^{-1}$sample of electron-positron collisions at the$\mathrm{\Upsilon }(4S)$resonance collected with the Belle II detector at the SuperKEKB collider. We use the inclusive properties of the accompanying$B$meson in$\mathrm{\Upsilon }(4S)\to B\overline{B}$events to suppress background from other decays of the signal$B$candidate and light-quark pair production. We validate the measurement with an auxiliary analysis based on a conventional hadronic reconstruction of the accompanying$B$meson. For background suppression, we exploit distinct signal features using machine learning methods tuned with simulated data. The signal-reconstruction efficiency and background suppression are validated through various control channels. The branching fraction is extracted in a maximum likelihood fit. Our inclusive and hadronic analyses yield consistent results for the$B^{+}\to K^{+}\nu \overline{\nu }$branching fraction of$[2.7\pm 0.5(\mathrm{stat})\pm 0.5(\mathrm{syst})]\times {10}^{-5}$and$[{1.1}_{-0.8}^{+0.9}(\mathrm{stat}{)}_{-0.5}^{+0.8}(\mathrm{syst})]\times {10}^{-5}$, respectively. Combining the results, we determine the branching fraction of the decay$B^{+}\to K^{+}\nu \overline{\nu }$to be$[2.3\pm 0.5(\mathrm{stat}{)}_{-0.4}^{+0.5}(\mathrm{syst})]\times {10}^{-5}$, providing the first evidence for this decay at 3.5 standard deviations. The combined result is 2.7 standard deviations above the standard model expectation.

   Published by the American Physical Society2024 

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5. Observation of the Ξb−→ψ(2S)Ξ− decay and studies of the Ξb(5945)0 baryon in proton-proton collisions at s=13  TeV

   https://doi.org/10.1103/PhysRevD.110.012002  

   Hayrapetyan, A ; Tumasyan, A ; Adam, W ; Andrejkovic, J W ; Bergauer, T ; Chatterjee, S ; Damanakis, K ; Dragicevic, M ; Hussain, P S ; Jeitler, M ; et al ( July 2024 , Physical review)

   The first observation of the decay${\mathrm{\Xi }}_b^{-}\to \psi (2S){\mathrm{\Xi }}^{-}$and measurement of the branching ratio of${\mathrm{\Xi }}_b^{-}\to \psi (2S){\mathrm{\Xi }}^{-}$to${\mathrm{\Xi }}_b^{-}\to J/\psi {\mathrm{\Xi }}^{-}$are presented. The$J/\psi$and$\psi (2S)$mesons are reconstructed using their dimuon decay modes. The results are based on proton-proton colliding beam data from the LHC collected by the CMS experiment at$\sqrt{s}=13\mathrm{TeV}$in 2016–2018, corresponding to an integrated luminosity of$140{\mathrm{fb}}^{-1}$. The branching fraction ratio is measured to be$\mathcal{B}({\mathrm{\Xi }}_b^{-}\to \psi (2S){\mathrm{\Xi }}^{-})/\mathcal{B}({\mathrm{\Xi }}_b^{-}\to J/\psi {\mathrm{\Xi }}^{-})=0.84_{-0.19}^{+0.21}(\mathrm{stat})\pm 0.10(\mathrm{syst})\pm 0.02(\mathcal{B})$, where the last uncertainty comes from the uncertainties in the branching fractions of the charmonium states. New measurements of the${\mathrm{\Xi }}_b(5945{)}^0$baryon mass and natural width are also presented, using the${\mathrm{\Xi }}_b^{-}{\pi }^{+}$final state, where the${\mathrm{\Xi }}_b^{-}$baryon is reconstructed through the decays$J/\psi {\mathrm{\Xi }}^{-}$,$\psi (2S){\mathrm{\Xi }}^{-}$,$J/\psi \mathrm{\Lambda }{K}^{-}$, and$J/\psi {\mathrm{\Sigma }}^0{K}^{-}$. Finally, the fraction of${\mathrm{\Xi }}_b^{-}$baryons produced from${\mathrm{\Xi }}_b(5945{)}^0$decays is determined.