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1. First Determination of the Spin-Parity of ${\mathrm{\Xi }}_c(3055{)}^{+,0}$ Baryons

   https://doi.org/10.1103/PhysRevLett.134.081901  

   Aaij, R; Abdelmotteleb, A_S W; Abellan_Beteta, C; Abudinén, F; Ackernley, T; Adefisoye, A A; Adeva, B; Adinolfi, M; Adlarson, P; Agapopoulou, C; et al (February 2025, Physical Review Letters)

   The ${\mathrm{\Xi }}_b^{0(-)}\to {\mathrm{\Xi }}_c\left(3055{)}^{+\left(0\right)}\right(\to D^{+\left(0\right)}\mathrm{\Lambda }){\pi }^{-}$ decay chains are observed, and the spin-parity of ${\mathrm{\Xi }}_c(3055{)}^{+\left(0\right)}$ baryons is determined for the first time. The measurement is performed using proton-proton collision data at a center-of-mass energy of $\sqrt{s}=13\mathrm{TeV}$ , corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{-1}$ , recorded by the LHCb experiment between 2016 and 2018. The spin-parity of the ${\mathrm{\Xi }}_c(3055{)}^{+\left(0\right)}$ baryons is determined to be $3/2^{+}$ with a significance of more than $6.5\sigma$ ( $3.5\sigma$ ) compared to all other tested hypotheses. The up-down asymmetries of the ${\mathrm{\Xi }}_b^{0(-)}\to {\mathrm{\Xi }}_c(3055{)}^{+\left(0\right)}{\pi }^{-}$ transitions are measured to be $-0.92\pm 0.10\pm 0.05$ ( $-0.92\pm 0.16\pm 0.22$ ), consistent with maximal parity violation, where the first uncertainty is statistical and the second is systematic. These results support the hypothesis that the ${\mathrm{\Xi }}_c(3055{)}^{+\left(0\right)}$ baryons correspond to the first $D$ -wave $\lambda$ -mode excitation of the ${\mathrm{\Xi }}_c$ flavor triplet. © 2025 CERN, for the LHCb Collaboration2025CERN 

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2. Search for Nuclear Modifications of $B^{+}$ Meson Production in $p$ -Pb Collisions at $\sqrt{s_{\mathrm{NN}}}=8.16\mathrm{TeV}$

   https://doi.org/10.1103/PhysRevLett.134.111903  

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

   Nuclear medium effects on $B^{+}$ meson production are studied using the binary-collision scaled cross section ratio between events of different charged-particle multiplicities from proton-lead collisions. Data, collected by the CMS experiment in 2016 at a nucleon-nucleon center-of-mass energy of $\sqrt{s_{\mathrm{NN}}}=8.16\mathrm{TeV}$ , corresponding to an integrated luminosity of $175{\mathrm{nb}}^{-1}$ , were used. The scaling factors in the ratio are determined using a novel approach based on the $Z\to {\mu }^{-}{\mu }^{+}$ cross sections measured in the same events. The scaled ratio for $B^{+}$ is consistent with unity for all event multiplicities, putting stringent constraints on nuclear modification for heavy flavor. © 2025 CERN, for the CMS Collaboration2025CERN 

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3. 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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4. 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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5. Observation of $t\overline{t}$ Production in Pb+Pb Collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$ with the ATLAS Detector

   https://doi.org/10.1103/PhysRevLett.134.142301  

   Aad, G; Aakvaag, E; Abbott, B; Abdelhameed, S; Abeling, K; Abicht, N J; Abidi, S H; Aboelela, M; Aboulhorma, A; Abramowicz, H; et al (April 2025, Physical Review Letters)

   Top-quark pair production is observed in lead–lead ( $\mathrm{Pb}+\mathrm{Pb}$ ) collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$ at the Large Hadron Collider with the ATLAS detector. The data sample was recorded in 2015 and 2018, amounting to an integrated luminosity of $1.9{\mathrm{nb}}^{-1}$ . Events with exactly one electron and one muon and at least two jets are selected. Top-quark pair production is measured with an observed (expected) significance of 5.0 (4.1) standard deviations. The measured top-quark pair production cross section is ${\sigma }_{t\overline{t}}=3.6{}_{-0.9}^{+1.0}\left(\mathrm{stat}\right){}_{-0.5}^{+0.8}\left(\mathrm{syst}\right)\mathrm{\mu }\mathrm{b}$ , with a total relative uncertainty of 31%, and is consistent with theoretical predictions using a range of different nuclear parton distribution functions. The observation of this process consolidates the evidence of the existence of all quark flavors in the preequilibrium stage of the quark-gluon plasma at very high energy densities, similar to the conditions present in the early Universe. © 2025 CERN, for the ATLAS Collaboration2025CERN 

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