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1. First Measurement of the $\left|t\right|$ Dependence of Incoherent $J/\psi$ 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 $\left|t\right|$ variable is presented. The measurement was carried out with the ALICE detector at midrapidity, $\left|y\right|<0.8$ , 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 $\left(0.3–1.4\right)\times {10}^{-3}$ . Cross sections are given in five $\left|t\right|$ intervals in the range $0.04<\left|t\right|<1{\mathrm{GeV}}^2$ and compared to the predictions by different models. Models that ignore quantum fluctuations of the gluon density in the colliding hadron predict a $\left|t\right|$ 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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2. Search for New Resonances Decaying to Pairs of Merged Diphotons in Proton-Proton Collisions at $\sqrt{s}=13\mathrm{TeV}$

   https://doi.org/10.1103/PhysRevLett.134.041801  

   Hayrapetyan, A; Tumasyan, A; Adam, W; Andrejkovic, J W; Bergauer, T; Chatterjee, S; Damanakis, K; Dragicevic, M; Hussain, P S; Jeitler, M; et al (January 2025, Physical Review Letters)

   A search is presented for an extended Higgs sector with two new particles, $X$ and $\varphi$ , in the process $X\to \varphi \varphi \to \left(\gamma \gamma \right)\left(\gamma \gamma \right)$ . Novel neural networks classify events with diphotons that are merged and determine the diphoton masses. The search uses LHC proton-proton collision data at $\sqrt{s}=13\mathrm{TeV}$ collected with the CMS detector, corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$ . No evidence of such resonances is seen. Upper limits are set on the production cross section for $m_X$ between 300 and 3000 GeV and $m_{\varphi }/m_X$ between 0.5% and 2.5%, representing the most sensitive search in this channel. © 2025 CERN, for the CMS Collaboration2025CERN 

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3. Measurement of the branching fraction and $CP$ -violating asymmetry of the decay $B^0\to {\pi }^0{\pi }^0$ using 387 million $\mathrm{\Upsilon }\left(4S\right)$ decays in Belle II data

   https://doi.org/10.1103/PhysRevD.111.L071102  

   Adachi, I; Aggarwal, L; Ahmed, H; Aihara, H; Alhakami, M; Aloisio, A; Althubiti, N; Anh_Ky, N; Asner, D M; Atmacan, H; et al (April 2025, Physical Review D)

   We measure the branching fraction and $CP$ -violating flavor-dependent rate asymmetry of $B^0\to {\pi }^0{\pi }^0$ decays reconstructed using the Belle II detector in an electron-positron collision sample containing $387\times {10}^6\mathrm{\Upsilon }\left(4S\right)$ mesons. Using an optimized event selection, we find $125\pm 20$ signal decays in a fit to background-discriminating and flavor-sensitive distributions. The resulting branching fraction is $(1.25\pm 0.23)\times {10}^{-6}$ and the $CP$ -violating asymmetry is $0.03\pm 0.30$ . Published by the American Physical Society2025 

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4. 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 $\varphi \left(1020\right)$ mesons or directly as nonresonant $K^{+}{K}^{-}$ pairs. Measurements of $K^{+}{K}^{-}$ photoproduction probe the couplings between the $\varphi \left(1020\right)$ 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 $\varphi \left(1020\right)$ resonance, for rapidity $\left|y_{KK}\right|<0.8$ and $p_{T,KK}<0.1\mathrm{GeV}/c$ , the measured coherent photoproduction cross section is $\mathrm{d}\sigma /\mathrm{d}y=3.37\pm 0.61\left(\text{stat}\right)\pm 0.15\left(\mathrm{syst}\right)\mathrm{mb}$ . 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 $\varphi \left(1020\right)$ photoproduction alone. The mass spectrum is fit to a cocktail consisting of $\varphi \left(1020\right)$ 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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5. Search for Nearly Mass-Degenerate Higgsinos Using Low-Momentum Mildly Displaced Tracks in $pp$ Collisions at $\sqrt{s}=13\mathrm{TeV}$ with the ATLAS Detector

   https://doi.org/10.1103/PhysRevLett.132.221801  

   Aad, G; Aakvaag, E; Abbott, B; Abeling, K; Abicht, N J; Abidi, S H; Aboelela, M; Aboulhorma, A; Abramowicz, H; Abreu, H; et al (May 2024, Physical Review Letters)

   Higgsinos with masses near the electroweak scale can solve the hierarchy problem and provide a dark matter candidate, while detecting them at the LHC remains challenging if their mass splitting is $\mathcal{O}\left(1\mathrm{GeV}\right)$ . This Letter presents a novel search for nearly mass-degenerate Higgsinos in events with an energetic jet, missing transverse momentum, and a low-momentum track with a significant transverse impact parameter using $140{\mathrm{fb}}^{-1}$ of proton-proton collision data at $\sqrt{s}=13\mathrm{TeV}$ collected by the ATLAS experiment. For the first time since LEP, a range of mass splittings between the lightest charged and neutral Higgsinos from 0.3 to 0.9 GeV is excluded at 95% confidence level, with a maximum reach of approximately 170 GeV in the Higgsino mass. © 2024 CERN, for the ATLAS Collaboration2024CERN 

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