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1. First Measurement of νe and νμ Interaction Cross Sections at the LHC with FASER’s Emulsion Detector

   https://doi.org/10.1103/PhysRevLett.133.021802  

   Abraham, Roshan Mammen ; Anders, John ; Antel, Claire ; Ariga, Akitaka ; Ariga, Tomoko ; Atkinson, Jeremy ; Bernlochner, Florian U ; Boeckh, Tobias ; Boyd, Jamie ; Brenner, Lydia ; et al ( July 2024 , Physical Review Letters)

   The first results of the study of high-energy electron neutrino (${\nu }_e$) and muon neutrino (${\nu }_{\mu }$) charged-current interactions in the$\mathrm{FASER}\nu$emulsion-tungsten detector of the FASER experiment at the LHC are presented. A 128.8 kg subset of the$\mathrm{FASER}\nu$volume was analyzed after exposure to$9.5{\mathrm{fb}}^{-1}$of$\sqrt{s}=13.6\mathrm{TeV}$$pp$data. Four (eight)${\nu }_e$(${\nu }_{\mu }$) interaction candidate events are observed with a statistical significance of$5.2\sigma$($5.7\sigma$). This is the first direct observation of${\nu }_e$interactions at a particle collider and includes the highest-energy${\nu }_e$and${\nu }_{\mu }$ever detected from an artificial source. The interaction cross section per nucleon$\sigma /E_{\nu }$is measured over an energy range of 560–1740 GeV (520–1760 GeV) for${\nu }_e$(${\nu }_{\mu }$) to be$({1.2}_{-0.7}^{+0.8})\times {10}^{-38}{\mathrm{cm}}^2{\mathrm{GeV}}^{-1}$[$(0.5\pm 0.2)\times {10}^{-38}{\mathrm{cm}}^2{\mathrm{GeV}}^{-1}$], consistent with standard model predictions. These are the first measurements of neutrino interaction cross sections in those energy ranges.

   Published by the American Physical Society2024 

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2. First Measurement of R(Xτ/ℓ) as an Inclusive Test of the b→cτν Anomaly

   https://doi.org/10.1103/PhysRevLett.132.211804  

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

   We measure the tau-to-light-lepton ratio of inclusive$B$-meson branching fractions$R(X_{\tau /\ell })\equiv \mathcal{B}(B\to X\tau \nu )/\mathcal{B}(B\to X\ell \nu )$, where$\ell$indicates an electron or muon, and thereby test the universality of charged-current weak interactions. We select events that have one fully reconstructed$B$meson and a charged lepton candidate from$189{\mathrm{fb}}^{-1}$of electron-positron collision data collected with the Belle II detector. We find$R(X_{\tau /\ell })=0.228\pm 0.016(\mathrm{stat})\pm 0.036(\mathrm{syst})$, in agreement with standard-model expectations. This is the first direct measurement of$R(X_{\tau /\ell })$.

   Published by the American Physical Society2024 

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3. Search for a μ+μ− resonance in four-muon final states at Belle II

   https://doi.org/10.1103/PhysRevD.109.112015  

   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 report on a search for a resonance$X$decaying to a pair of muons in$e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}X$events in the$0.212–9.000\mathrm{GeV}/c^2$mass range, using$178{\mathrm{fb}}^{-1}$of data collected by the Belle II experiment at the SuperKEKB collider at a center of mass energy of 10.58 GeV. The analysis probes two different models of$X$beyond the standard model: a$Z^{\prime }$vector boson in the$L_{\mu }-L_{\tau }$model and a muonphilic scalar. We observe no evidence for a signal and set exclusion limits at the 90% confidence level on the products of cross section and branching fraction for these processes, ranging from 0.046 fb to 0.97 fb for the$L_{\mu }-L_{\tau }$model and from 0.055 fb to 1.3 fb for the muonphilic scalar model. For masses below$6\mathrm{GeV}/c^2$, the corresponding constraints on the couplings of these processes to the standard model range from 0.0008 to 0.039 for the$L_{\mu }-L_{\tau }$model and from 0.0018 to 0.040 for the muonphilic scalar model. These are the first constraints on the muonphilic scalar from a dedicated search.

   Published by the American Physical Society2024 

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4. First Measurement of the |t| Dependence of Incoherent J/ψ Photonuclear Production

   https://doi.org/10.1103/PhysRevLett.132.162302  

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

   The first measurement of the cross section for incoherent photonuclear production of$J/\psi$vector mesons as a function of the Mandelstam$|t|$variable is presented. The measurement was carried out with the ALICE detector at midrapidity,$|y|<0.8$, using ultraperipheral collisions of Pb nuclei at a center-of-mass energy per nucleon pair of$\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$. This rapidity interval corresponds to a Bjorken-$x$range$(0.3–1.4)\times {10}^{-3}$. Cross sections are given in five$|t|$intervals in the range$0.04<|t|<1{\mathrm{GeV}}^2$and compared to the predictions by different models. Models that ignore quantum fluctuations of the gluon density in the colliding hadron predict a$|t|$dependence of the cross section much steeper than in data. The inclusion of such fluctuations in the same models provides a better description of the data.

   © 2024 CERN, for the ALICE Collaboration2024CERN 

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5. Observation of the J/ψ→μ+μ−μ+μ− decay in proton-proton collisions at s=13  TeV

   https://doi.org/10.1103/PhysRevD.109.L111101  

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

   The$J/\psi \to {\mu }^{+}{\mu }^{-}{\mu }^{+}{\mu }^{-}$decay has been observed with a statistical significance in excess of five standard deviations. The analysis is based on an event sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment in 2018 and corresponding to an integrated luminosity of$33.6{\mathrm{fb}}^{-1}$. Normalizing to the$J/\psi \to {\mu }^{+}{\mu }^{-}$decay mode leads to a branching fraction of$[{10.1}_{-2.7}^{+3.3}(\mathrm{stat})\pm 0.4(\mathrm{syst})]\times {10}^{-7}$, a value that is consistent with the standard model prediction.