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Journal articleMorgan K, Azuma T, Baptista G, et al., 2026,
Transition-Edge Sensor Spectrometer for Precision Spectroscopy of Antiprotonic Atoms
, IEEE Transactions on Applied Superconductivity, Vol: 36, ISSN: 1051-8223antiProtonic Atom X-ray (PAX) spectroscopy is an experiment that aims to test strong-field quantum electrodynamics (QED) effects by performing high-precision X-ray spectroscopy of antiprotonic atoms. PAX will use a low-energy antiproton beam provided by the Extra Low ENergy Antiproton (ELENA) ring at the European Organization for Nuclear Research (CERN) to create antiprotonic atoms. A superconducting transition-edge sensor (TES) spectrometer will be used to measure the energy of transitions between circular Rydberg states in these atoms. The energy range of interest for the experiment spans 50 keV to 250 keV, and the desired precision for measuring the centroids of the emission lines is 10^{-5}. The spectrometer for PAX is intended to have four 96-pixel TES arrays and will be read out with a microwave superconducting quantum interference device (SQUID) multiplexer. As a step toward building the full instrument, we built a scaled-down version of the spectrometer that was installed at the TEst Line for Machine And Antimatter eXperiments (TELMAX) facility at ELENA in April 2025. The purpose of this deployment was to make an observation of X-ray emission by antiprotonic atoms and to better understand the effect of the pionic charged particle background due to antiproton annihilation on the performance of the TES array. This pilot spectrometer had an array of 60 TES pixels in a compact adiabatic demagnetization refrigerator cryostat. The sensors were read out with a microwave SQUID multiplexer. Each pixel consisted of a molybdenum/gold bilayer TES with a coplanar gold “landing pad” for a bulk tin absorber that was attached by an epoxy joint. We discuss the design of the TES pixels, the microwave SQUID readout, and the cryogenic platform. Finally, we present calibration data obtained at TELMAX using radioactive sources to assess the performance of the spectrometer in the antiproton beam-off condition.
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Journal articleHayrapetyan A, Makarenko V, Tumasyan A, et al., 2026,
Characterizing the initial state and dynamical evolution in XeXe and PbPb collisions using multiparticle cumulants
, Physics Letters Section B Nuclear Elementary Particle and High Energy Physics, Vol: 876, ISSN: 0370-2693For the first time, correlations among mixed-order moments of two or three flow harmonics —(v<inf>n</inf><sup>k</sup>,v<inf>m</inf><sup>l</sup>) and (v<inf>n</inf><sup>k</sup>,v<inf>m</inf><sup>l</sup>,v<inf>p</inf><sup>q</sup>), with k, l , and q denoting the respective orders—are measured in xenon–xenon (XeXe) collisions and compared with lead–lead (PbPb) results, providing a novel probe of collective behavior in heavy ion collisions. These measurements compare a nearly spherical, doubly-magic <sup>208</sup>Pb nucleus to a triaxially deformed <sup>129</sup>Xe nucleus, emphasizing the sensitivity to initial-state geometry fluctuations arising from nuclear deformation. The dependence of these results (v<inf>n</inf> , n=2,3,4) on the shape and size of the nuclear overlap region is studied. Comparisons between v <inf>2</inf>, v <inf>3</inf>, and v <inf>4</inf> demonstrate the importance of v <inf>3</inf> and v <inf>4</inf> in exploring the nonlinear hydrodynamic response of the quark-gluon plasma (QGP) to the initial spatial anisotropy. The results constrain initial-state model parameters that influence the evolution of the QGP. The CMS detector was used to collect XeXe and PbPb data at nucleon-nucleon center-of-mass energies of S<inf>NN</inf>=5.44 and 5.36 TeV, respectively. Correlations are extracted using multiparticle mixed-harmonic cumulants (up to eight-particle cumulants) with charged particles in the pseudorapidity range | η | ' 2.4 and transverse momentum range 0.5 ' p<inf>T</inf> ' 3 GeV/c.
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Journal articleAnchordoqui LA, Anders JK, Ariga A, et al., 2026,
The forward physics facility: Physics opportunities and conceptual design
, Nuclear Physics B, Vol: 1026, ISSN: 0550-3213The Forward Physics Facility (FPF) is a proposed extension of the HL-LHC program designed to exploit the unique scientific opportunities offered by the intense flux of high energy neutrinos, and possibly new particles, in the far-forward direction. Located in a well-shielded cavern 627 m downstream of one of the LHC interaction points, the facility will support a broad and ambitious physics program that significantly expands the discovery potential of the HL-LHC. Equipped with four complementary detectors—FLArE, FASER ν 2, FASER2, and FORMOSA—the FPF will enable breakthrough measurements that will advance our understanding of neutrino physics, quantum chromodynamics, and astroparticle physics, and will search for dark matter and other new particles. With this Letter of Intent, we propose the construction of the FPF cavern and the construction, integration, and installation of its experiments. We summarize the physics case, the facility design, the layout and components of the detectors, as well as the envisioned collaboration structure, cost estimate, and implementation timeline.
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Journal articleAaij R, Abdelmotteleb ASW, Abellan Beteta C, et al., 2026,
First Evidence of the B_{s}^{0}→K^{-}π^{+}γ Decay.
, Phys Rev Lett, Vol: 136The first search for the B_{s}^{0}→K^{-}π^{+}γ decay in the range 796<m(K^{-}π^{+})<1800 MeV/c^{2} is performed using data from proton-proton collisions collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb^{-1}. The photons are reconstructed through their conversion into an electron-positron pair, which significantly improves the mass resolution of the reconstructed decays with respect to decays with an unconverted photon. A signal excess with a significance of 3.5 standard deviations is measured, constituting the first experimental evidence for this decay. In the range 796<m(K^{-}π^{+})<996 MeV/c^{2}, the ratio R between the branching fractions of the signal decay and the favored B[over ¯]^{0}→K^{-}π^{+}γ decay is measured to be R=(3.7±1.2±0.4)×10^{-2} where the first uncertainty is statistical and the second is systematic. This measurement is consistent with the value predicted in the Standard Model. In the range 996<m(K^{-}π^{+})<1800 MeV/c^{2}, the ratio R=(0.2±2.7±1.3)×10^{-2} is measured.
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Journal articleHayrapetyan A, Makarenko V, Tumasyan A, et al., 2026,
Observation of Suppressed Charged-Particle Production in Ultrarelativistic Oxygen-Oxygen Collisions.
, Phys Rev Lett, Vol: 136A hot and dense state of nuclear matter, known as the quark-gluon plasma, is created in collisions of ultrarelativistic heavy nuclei. Highly energetic quarks and gluons, collectively referred to as partons, lose energy as they travel through this matter, leading to suppressed production of particles with large transverse momenta (p_{T}). Conversely, high-p_{T} particle suppression has not been seen in proton-lead collisions, raising questions regarding the minimum system size required to observe parton energy loss. Oxygen-oxygen (OO) collisions examine a region of effective system size that lies between these two extreme cases. The CMS detector at the CERN LHC has been used to quantify charged-particle production in inclusive OO collisions for the first time via measurements of the nuclear modification factor (R_{AA}). The R_{AA} is derived by comparing particle production to expectations based on proton-proton (pp) data and has a value of unity in the absence of nuclear effects. The data for OO and pp collisions at a nucleon-nucleon center-of-mass energy sqrt[s_{NN}]=5.36 TeV correspond to integrated luminosities of 6.1 nb^{-1} and 1.02 pb^{-1}, respectively. The R_{AA} is below unity with a minimum of 0.69±0.04 around p_{T}=6 GeV. The data exhibit better agreement with theoretical models incorporating parton energy loss as compared to baseline models without energy loss.
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Journal articleAaij R, Abdelmotteleb ASW, Abellan Beteta C, et al., 2026,
Precision Measurement of CP Violation and Branching Fractions in B^{±}→K_{S}^{0}h^{±} (h=π, K) Decays and Search for the Rare Decay B_{c}^{±}→K_{S}^{0}K^{±}.
, Phys Rev Lett, Vol: 136The decay B^{±}→K_{S}^{0}π^{±}, with a CP asymmetry expected to be close to zero in the standard model, is theoretically clean and sensitive to potential new physics. An analysis of the decays B^{±}→K_{S}^{0}π^{±} and B^{±}→K_{S}^{0}K^{±} is performed using proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb^{-1}. The CP asymmetries are determined to be A^{CP}(B^{±}→K_{S}^{0}π^{±})=-0.028±0.009±0.009 and A^{CP}(B^{±}→K_{S}^{0}K^{±})=0.118±0.062±0.031, and the branching fraction ratio is measured to be B(B^{±}→K_{S}^{0}K^{±})/B(B^{±}→K_{S}^{0}π^{±})=0.055±0.004±0.002, where the first uncertainties are statistical and the second are systematic. These results are the most precise measurements of these quantities to date. A search for the rare decay B_{c}^{±}→K_{S}^{0}K^{±} is also performed. No significant signal is observed, and the upper limit on the product of the branching fraction ratio B(B_{c}^{±}→K_{S}^{0}K^{±})/B(B^{±}→K_{S}^{0}π^{±}) and the fragmentation-fraction ratio f_{c}/f_{u} is set to be 0.015 (0.016) at the 90% (95%) confidence level.
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Journal articleHayrapetyan A, Makarenko V, Tumasyan A, et al., 2026,
Improving missing transverse momentum estimation with a deep neural network
, Physical Review D, Vol: 113, ISSN: 2470-0010<jats:p> At hadron colliders, the net transverse momentum of particles that do not interact with the detector (missing transverse momentum, <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:msubsup> <a:mover accent="true"> <a:mi>p</a:mi> <a:mo stretchy="false">→</a:mo> </a:mover> <a:mi mathvariant="normal">T</a:mi> <a:mrow> <a:mi>miss</a:mi> </a:mrow> </a:msubsup> </a:math> ) is a crucial observable in many analyses. In the standard model, <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" display="inline"> <f:msubsup> <f:mover accent="true"> <f:mi>p</f:mi> <f:mo stretchy="false">→</f:mo> </f:mover> <f:mi mathvariant="normal">T</f:mi> <f:mrow> <f:mi>miss</f:mi> </f:mrow> </f:msubsup> </f:math> originates from neutrinos. Many beyond-the-standard-model particles, such as dark matter candidates, are also expected to leave the experimental apparatus undetected. This paper presents a novel deep neural network based <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:ms
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Journal articleAlden N, Ali S, Allison P, et al., 2026,
Observation of In-Ice Askaryan Radiation from High-Energy Cosmic Rays
, Physical Review Letters, Vol: 136, ISSN: 0031-9007We present the first experimental evidence for in-ice Askaryan radiation—coherent charge-excess radio emission—from high-energy particle cascades developing in the Antarctic ice sheet. In 208 days of data recorded with the phased array instrument of the Askaryan Radio Array, a previous analysis has incidentally identified 13 events with impulsive radio frequency signals originating from below the ice surface. We here present a detailed reanalysis of these events. The observed event rate, radiation arrival directions, signal shape, spectral content, and electric field polarization are consistent with in-ice Askaryan radiation from cosmic ray air shower cores impacting the ice sheet. For the brightest events, the angular radiation pattern favors an extended cascadelike emitter over a pointlike source. An origin from the geomagnetic separation of charges in cosmic ray air showers is disfavored by the arrival directions and polarization. Considering the arrival angles, timing properties, and impulsive nature of the passing events, the event rate is inconsistent with the estimation of the combined background from thermal noise events and on-surface events at the level of 5.1σ.
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Journal articleChekhovsky V, Hayrapetyan A, Makarenko V, et al., 2026,
Search for light pseudoscalar boson pairs produced from Higgs boson decays using the 4τ and 2μ2τ final states in proton-proton collisions at $$ \sqrt{s}=13 $$ TeV
, Journal of High Energy Physics, Vol: 2026<jats:title> A <jats:sc>bstract</jats:sc> </jats:title> <jats:p> A search for a pair of light pseudoscalar bosons (a <jats:sub>1</jats:sub> ) produced in the decay of the 125 GeV Higgs boson is presented. The analysis examines decay modes where one a <jats:sub>1</jats:sub> decays into a pair of tau leptons and the other decays into either another pair of tau leptons or a pair of muons. The a <jats:sub>1</jats:sub> boson mass probed in this study ranges from 4 to 15 GeV. The data sample was recorded by the CMS experiment in proton-proton collisions at a center-of-mass energy of 13 TeV and corresponds to an integrated luminosity of 138 fb <jats:sup> <jats:italic>−</jats:italic> 1 </jats:sup> . No excess above standard model (SM) expectations is observed. The study combines the 4τ and 2μ2τ channels to set upper limits at 95% confidence level (CL) on the product of the Higgs boson production cross section and the branching fraction to the 4τ final state, relative to the Higgs boson production cross section predicted by the SM. In this interpretation, the a <jats:sub>1</jats:sub> boson is assumed to have Yukawa-like couplings to fermions, with coupling strengths proportional to the respective fermion masses. The observed (expected) upper limits range between 0.007 (0.011) and 0.079 (0.066) across the mass range considered. The results are also interpreted in the context of models with two Higgs doublets and an additional complex singlet field (2HD+S). The tightest constraints are obtained for the Type III 2HD+S mod
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Journal articleChekhovsky V, Hayrapetyan A, Makarenko V, et al., 2026,
Combination and interpretation of differential Higgs boson production cross sections in proton-proton collisions at $$ \sqrt{s}=13 $$ TeV
, Journal of High Energy Physics, Vol: 2026<jats:title> A <jats:sc>bstract</jats:sc> </jats:title> <jats:p> Precision measurements of Higgs boson differential production cross sections are a key tool to probe the properties of the Higgs boson and test the standard model. New physics can affect both Higgs boson production and decay, leading to deviations from the distributions that are expected in the standard model. In this paper, combined measurements of differential spectra in a fiducial region matching the experimental selections are performed, based on analyses of four Higgs boson decay channels (γγ, ZZ <jats:sup>(*)</jats:sup> , WW <jats:sup>(*)</jats:sup> , and ττ) using proton-proton collision data recorded with the CMS detector at <jats:inline-formula> <jats:alternatives> <jats:tex-math>$$ \sqrt{s}=13 $$</jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> <mml:mo>=</mml:mo> <mml:mn>13</mml:mn> </mml:math> </jats:alternatives> </jats:inline-formula> TeV, corresponding to an integrated luminosity of 138 fb <jats:sup> <jats:italic>−</jats:italic> 1 </jats:sup> . The differential measurements are extrapolated to the full phase space and combined to provide the differential spectra. A
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Journal articleHayrapetyan A, Makarenko V, Tumasyan A, et al., 2026,
Inclusive and differential measurements of the $$ \textrm{t}\overline{\textrm{t}}\upgamma $$ cross section and the $$ \textrm{t}\overline{\textrm{t}}\upgamma /\textrm{t}\overline{\textrm{t}} $$ cross section ratio in proton-proton collisions at $$ \sqrt{s}=13 $$ TeV
, Journal of High Energy Physics, Vol: 2026<jats:title> A <jats:sc>bstract</jats:sc> </jats:title> <jats:p> Inclusive and differential cross section measurements of top quark pair ( <jats:inline-formula> <jats:alternatives> <jats:tex-math>$$ \textrm{t}\overline{\textrm{t}} $$</jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>t</mml:mi> <mml:mover> <mml:mi>t</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> </jats:alternatives> </jats:inline-formula> ) production in association with a photon (γ) are performed as a function of lepton, photon, top quark, and <jats:inline-formula> <jats:alternatives> <jats:tex-math>$$ \textrm{t}\overline{\textrm{t}} $$</jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>t</mml:mi> <mml:mover> <mml:mi>t</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> </jats:alternatives> </jats:inline-formula> kinematic observables, using data from proton-proton collisions at <jats:inline-formula> <jats:alternatives> <jats:tex
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Journal articleTomalak O, Meyer AS, Wret C, et al., 2026,
Nucleon axial-vector form factor and radius from radiatively corrected antineutrino scattering data
, Physical Review D, Vol: 113, ISSN: 2470-0010<jats:p> The nucleon axial-vector form factor, <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:msub> <a:mi>G</a:mi> <a:mi>A</a:mi> </a:msub> </a:math> , is critical to determine the electroweak interactions of leptons with nucleons. Important examples of processes influenced by <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:msub> <c:mi>G</c:mi> <c:mi>A</c:mi> </c:msub> </c:math> are elastic (anti)neutrino-nucleon scattering and muon capture by the proton. Sparse experimental data results in a large uncertainty on the momentum dependence of <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:msub> <e:mi>G</e:mi> <e:mi>A</e:mi> </e:msub> </e:math> and has motivated the consideration of new experimental probes and first-principles lattice quantum chromodynamics (QCD) evaluations. The comparison of new and precise theoretical predictions for <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:msub> <g:mi>G</g:mi> <g:mi>A</g:mi> </g:msub> </g:math> with future experimental data necessitates the application of radiat
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Journal articleMiki S, Abe K, Abe S, et al., 2026,
Neutron-Multiplicity Measurement in Muon Capture on Oxygen Nuclei in the Gadolinium-Loaded Super-Kamiokande Detector.
, Phys Rev Lett, Vol: 136In recent neutrino detectors, neutrons produced in neutrino reactions play an important role. Muon capture on oxygen nuclei is one of the processes that produce neutrons in water Cherenkov detectors. We measured neutron multiplicity in the process using cosmic ray muons that stop in the gadolinium-loaded Super-Kamiokande detector. For this measurement, neutron detection efficiency is obtained with the muon capture events followed by gamma rays to be 50.2_{-2.1}^{+2.0}%. By fitting the observed multiplicity considering the detection efficiency, we measure neutron multiplicity in muon capture as P(0)=24±3%, P(1)=70_{-2}^{+3}%, P(2)=6.1±0.5%, P(3)=0.38±0.09%. This is the first measurement of the multiplicity of neutrons associated with muon capture on oxygen without neutron energy threshold.
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Journal articleAaij R, Abdelmotteleb ASW, Abellan Beteta C, et al., 2026,
Differential decay rate of B+→ J/ψK+ with the LHCb Upgrade I experiment
, Journal of High Energy Physics, Vol: 2026The normalised decay rate of B<sup>+</sup> → J/ψ(→ μ<sup>+</sup>μ<sup>−</sup>)K<sup>+</sup> is measured as a function of the lepton helicity angle using a data sample corresponding to an integrated luminosity of 1.1 fb<sup>−1</sup> collected during October 2024 with the upgraded (Upgrade I) LHCb detector. This angular distribution can be parameterised by two coefficients, the forward-backward asymmetry, A<inf>FB</inf>, and the flatness parameter, F<inf>H</inf>, whose values are constrained by conservation of angular momentum. These coefficients are measured both integrated and differentially across various kinematic and detector-response variables, and the results are found to be in good agreement with expectations. These measurements show that the detector response of the LHCb Upgrade I experiment is understood to the precision required to reliably extract the angular coefficients associated with rare b → sμ<sup>+</sup>μ<sup>−</sup> and b → dμ<sup>+</sup>μ<sup>−</sup> transitions, which are particularly sensitive to physics beyond the Standard Model.
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Journal articleSummers S, Tapper A, Årrestad TK, et al., 2026,
Roadmap on fast machine learning for science
, Machine Learning: Science and Technology, Vol: 7, Pages: 021501-021501<jats:title>Abstract</jats:title> <jats:p>The need for microsecond speed machine learning (ML) inference for particle physics experiments has emerged in recent years, in particular for the forthcoming upgrades to the experiments at the Large Hadron Collider at CERN. A community has grown around the need to develop the custom hardware platforms and tools required. The material presented in this report is drawn from the latest workshop held by the fast ML for science community and comprises of a collection of perspectives on the status of fast ML in different scientific domains, and the supporting technology.</jats:p>
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Journal articleHayrapetyan A, Makarenko V, Tumasyan A, et al., 2026,
High-level hadronic tau lepton triggers of the CMS experiment in proton-proton collisions at √s = 13.6 TeV
, Journal of Instrumentation, Vol: 21The trigger system of the CMS detector is pivotal in the acquisition of data for physics measurements and searches. Studies of final states characterized by hadronic decays of tau leptons require the reconstruction and the identification of genuine tau leptons against quark- and gluon-initiated jets at the trigger level. This is a difficult task, particularly as improvements to the LHC have resulted in an increased number of interactions per bunch crossing in recent years. To address this challenge, a series of machine-learning algorithms with high identification efficiency and low computational cost have been incorporated into the high-level trigger for hadronically decaying tau leptons. In this paper, these developments and the trigger performance are summarized using data collected by the CMS experiment in proton-proton collisions at √s = 13.6 TeV in 2022–2023, corresponding to an integrated luminosity of 62 fb<sup>−1</sup>
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Journal articleAnastopoulos C, Assmann R, Ball AH, et al., 2026,
LEP3: a high-luminosity e+e− Higgs and electroweak factory in the LHC tunnel**A possible back-up to the preferred option (FCC-ee and FCC-hh) for the next accelerator for CERN.
, Journal of Physics G Nuclear and Particle Physics, Vol: 53, ISSN: 0954-3899The 2020 European Strategy for Particle Physics (ESPP) emphasized the critical importance of completing the high-luminosity LHC (HL-LHC) upgrade of both the accelerator and experiments in a timely manner, identifying it as a top priority for the field. The strategy also established two key recommendations for future accelerator initiatives: (i) the realization of an electron–positron Higgs factory as the highest-priority next collider, and (ii) the investigation, in collaboration with international partners, of the technical and financial feasibility of a hadron collider at CERN with a centre-of-mass energy of at least 100 TeV, potentially preceded by an electron–positron Higgs and electroweak factory. In alignment with these objectives, the Future Circular Collider (FCC) programme—comprising FCC-ee and FCC-hh—represents the preferred path forward for CERN, offering both precision and energy-frontier capabilities. However, the 2025 ESPP update calls for the identification of prioritized alternative options should the preferred FCC pathway prove infeasible or non-competitive. In this context, we propose LEP3, an electron–positron collider reusing the existing LHC tunnel, as a strategic backup to FCC-ee. LEP3 would exploit much of the research and development already carried out for FCC-ee, enabling high-precision studies of the Z, W, and Higgs bosons below the top–antitop production threshold. Combining strong physics potential with reduced cost, LEP3 provides performance comparable or superior to other fallback options—such as linear, muon, or LHeC colliders—while maintaining the technological continuity essential for a future energy-frontier collider. Conceived as a contingency, LEP3 complements, rather than competes with, the FCC-ee proposal.
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Journal articleAkgül B, Fedar YE, Yüksel O, et al., 2026,
Development and implementation of a non-zero suppression system for HGCAL back-end electronics
, Journal of Instrumentation, Vol: 21In preparation for operations at the HL-LHC, the CMS Collaboration is upgrading its endcap calorimeters with a high granularity calorimeter (HGCAL). The HGCAL back-end electronics includes two Non-Zero Suppression (NZS) boards, which dynamically disable zero-suppression in designated regions of interest. This paper presents a detailed discussion of the principal components of the implemented NZS firmware and a comprehensive account of the hardware testing performed on the Serenity platform, including validation against a Python-based emulator. Each of the 48 DAQ (Data Acquisition) boards of a single endcap receives 432-bit NZS flags, which are generated non-zero-suppression control flags to disable zero suppression for designated regions of interest on the front-end sections and sent via high-speed output channels operating at 25 Gbps. The NZS firmware processes data from six EMTF input links operating at 25 Gbps, and produces the necessary non-zero suppression control flags for real-time selection and spatial mapping of up to 27 muon candidates per bunch crossing under a 360 MHz system clock constraint. To meet the stringent timing requirements, the design adopts a fully pipelined FPGA architecture, enabling deterministic latency while sustaining continuous high-throughput operation.
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Journal articleChekhovsky V, Hayrapetyan A, Makarenko V, et al., 2026,
Jet fragmentation function and groomed substructure of bottom quark jets in proton-proton collisions at 5.02 TeV
, Journal of High Energy Physics, Vol: 2026A measurement of the substructure of bottom quark jets (b jets) in proton-proton (pp) collisions is presented. The measurement uses data collected in pp collisions at s=5.02 TeV, with a low number of simultaneous interactions per bunch crossing, recorded by the CMS experiment in 2017, corresponding to an integrated luminosity of 301 pb<sup>−1</sup>. An algorithm to identify and cluster the charged decay daughters of b hadrons is developed for this analysis, which facilitates the exposure of the gluon radiation pattern of b jets using iterative Cambridge-Aachen declustering. The soft-drop-groomed jet radius, R<inf>g</inf>, and momentum balance, z<inf>g</inf>, of b quark jets are presented. These observables can be used to test perturbative quantum chromodynamics predictions that account for mass effects. Because the b hadron is partially reconstructed from its charged decay daughters, only charged particles are used for the jet substructure studies. In addition, a jet fragmentation function, z<inf>b,ch</inf>, is measured, which is defined as the distribution of the ratio of the transverse momentum (p<inf>T</inf>) of the partially reconstructed b hadron with respect to the charged-particle component of the jet p<inf>T</inf>. The substructure variable distributions are unfolded to the charged-particle level. The b jet substructure is compared to the substructure of jets in an inclusive jet sample that is dominated by light-quark and gluon jets in order to assess the role of the b quark mass. A strong suppression of emissions at small R<inf>g</inf> values is observed for b jets when compared to inclusive jets, consistent with the dead-cone effect. The measurement is also compared with theoretical predictions from Monte Carlo event generators. This is the first substructure measurement of b jets that clusters together the b hadron decay daughters independent of the b hadron species
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Journal articleAaij R, Abdelmotteleb ASW, Abellan Beteta C, et al., 2026,
A method for luminosity determination based on real-time hit reconstruction with the LHCb silicon pixel detector
, Journal of Instrumentation, Vol: 21The data acquisition system of the upgraded LHCb experiment includes the fast reconstruction of all hits in the vertex locator (VELO) pixel detector at the beam-crossing rate of 40 MHz, implemented as on-the-fly clustering embedded in the firmware of the readout board FPGAs. The availability of a high rate of reconstructed clusters in real time enables a new fast approach for measuring luminosity and monitoring the LHCb luminous region, directly at the detector readout level. This methodology has been implemented as an array of real-time cluster counters in the VELO readout FPGAs and has been in operation since the start of the 2024 physics run of LHCb. This paper describes the methodology and its features and performance, both on proton-proton and lead-lead collision data. The method shows a statistical resolution better than the percent level, and a sensitivity to variable running conditions of the same level. This is achieved with an intrinsic time granularity better than 100 ms, undersampled to 3 s for analysis purposes. Nonlinear behaviour is compatible with zero in a luminosity range including the LHCb Run 3 operating point.
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Journal articleAaij R, Abdelmotteleb ASW, Abellan Beteta C, et al., 2026,
Measurement of charged-hadron distributions in heavy-flavor jets in proton-proton collisions at s=13 TeV
, Journal of High Energy Physics, Vol: 2026Charged-hadron distributions in heavy-flavor jets are measured in proton-proton collisions at a center-of-mass energy of s=13 TeV collected by the LHCb experiment. Distributions of the longitudinal momentum fraction, transverse momentum, and radial profile of charged hadrons are measured separately in beauty and charm jets. The distributions are compared to those previously measured by the LHCb collaboration in jets produced back-to-back with a Z boson, which in the forward region are primarily light-quark-initiated, to compare the hadronization mechanisms of heavy and light quarks. The observed differences between the heavy- and light-jet distributions are consistent with the heavy-quark dynamics expected to arise from the dead-cone effect, as well as with a hard fragmentation of the heavy-flavor hadron as previously measured in single-hadron fragmentation functions. This measurement provides additional constraints for the extraction of collinear and transverse-momentum-dependent heavy-flavor fragmentation functions and offers another approach to probing the mechanisms that govern heavy-flavor hadronization.
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Journal articleAaij R, Abdelmotteleb ASW, Abellan Beteta C, et al., 2026,
Branching fraction measurement of the Λ→pμ−ν¯μ decay
, Journal of High Energy Physics, Vol: 2026A measurement of the branching fraction for the decay Λ→pμ−ν¯μ is presented using pp collision data collected by the LHCb experiment at a centre-of-mass energy of 13 TeV. The analysis is based on data recorded between 2016 and 2018, corresponding to an integrated luminosity of 5.4 fb<sup>−1</sup>. The result is obtained using Λ → pμ<sup>−</sup> decays as a normalisation channel. The measured branching fraction is BΛ→pμ−ν¯μ=1.462±0.016±0.100±0.011×10−4, where the uncertainties are statistical, systematic, and due to the limited knowledge of the normalisation mode branching fraction, respectively. This result improves the precision of the branching fraction measurement by a factor of two compared to the previous best measurement and sets a more stringent bound on lepton flavour universality in s → u quark transitions. It is consistent with previous measurements, and the extracted lepton flavour universality test observable, Rμe=ΓΛ→pμ−ν¯μΓΛ→pe−ν¯e=0.175±0.012, agrees with the Standard Model prediction.
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Journal articleAnfimov N, Branca A, Bürgi J, et al., 2026,
Cosmic ray measurements using charge and light readout in a pixelated liquid argon time projection chamber
, Journal of Instrumentation, Vol: 21Liquid argon time projection chambers have emerged as a competitive technology for detecting solar neutrinos. The SoLAr collaboration was formed to explore argon detectors with pixelated light and charge readout, aiming for high detection efficiency and improved energy resolution. Building on the success of an initial prototype, we present results obtained with a second SoLAr prototype (V2), a 30 × 30 × 30 cm<sup>3</sup> time projection chamber operated in a cryostat containing several hundred kilograms of liquid argon. We report measurements of cosmic-ray muons using both tracking and calorimetry from light and charge sensors, and we highlight the improved performance achieved through combined charge and light reconstruction. These results demonstrate the promise of dual-readout detectors and motivate future prototyping efforts toward kiloton-scale facilities.
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Journal articleCMS Collaboration, 2026,
High-precision measurement of the W boson mass with the CMS experiment.
, Nature, Vol: 652, Pages: 321-327In the standard model of particle physics, the masses of the W and Z bosons, the carriers of the weak interaction, are uniquely related. A precise determination of their masses is important because quantum loops of heavy, undiscovered particles could modify this relationship. Although the Z mass is known to the remarkable precision of 22 parts per million (2.0 MeV), the W mass is known much less precisely. A global fit to measured electroweak observables predicts the W mass with 6 MeV uncertainty1-3. Reaching a comparable experimental precision would be a sensitive and fundamental test of the standard model, made even more urgent by a recent challenge to the global fit prediction by a measurement from the CDF Collaboration at the Fermilab Tevatron collider4. Here we report the measurement of the W mass by the CMS Collaboration at the CERN Large Hadron Collider, based on a large data sample of W → μν events collected in 2016 at the proton-proton collision energy of 13 TeV. The measurement exploits a high-granularity maximum likelihood fit to the kinematic properties of muons produced in W decays. By combining an accurate determination of experimental effects with marked in situ constraints of theoretical inputs, we reach a precise measurement of the W mass, of 80,360.2 ± 9.9 MeV, in agreement with the standard model prediction.
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Journal articleAbdullahi AM, Abratenko P, Andrade Aldana D, et al., 2026,
First Search for Dark Sector e^{+}e^{-} Explanations of the MiniBooNE Anomaly at MicroBooNE.
, Phys Rev Lett, Vol: 136We present MicroBooNE's first search for dark sector e^{+}e^{-} explanations of the long-standing MiniBooNE anomaly. The MiniBooNE anomaly has garnered significant attention over the past 20 years including previous MicroBooNE investigations into both anomalous electron and photon excesses, but its origin still remains unclear. In this Letter, we provide the first direct test of dark sector models in which dark neutrinos, produced through neutrino-induced scattering, decay into missing energy and visible e^{+}e^{-} pairs comprising the MiniBooNE anomaly. Many such models have recently gained traction as a viable solution to the anomaly while evading past bounds. Using an exposure of 6.87×10^{20} protons-on-target in the Booster Neutrino Beam, we implement a selection targeting forward-going, coherently produced e^{+}e^{-} events. After unblinding, we observe 95 events, which we compare with the constrained background-only prediction of 69.7±17.3. This analysis sets the world's first direct limits on these dark sector models and, at the 95% confidence level, excludes the entirety of the single dark neutrino and majority of the dual dark neutrino, parameter space that is viable as a solution to the MiniBooNE anomaly.
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Journal articleChekhovsky V, Hayrapetyan A, Makarenko V, et al., 2026,
Measurement of D^{0} Meson Photoproduction in Ultraperipheral Heavy Ion Collisions.
, Phys Rev Lett, Vol: 136This Letter reports the first measurement of photonuclear D^{0} meson production in ultraperipheral heavy ion collisions. The study is performed using lead-lead collision data, with an integrated luminosity of 1.34 nb^{-1}, collected by the CMS experiment at a nucleon-nucleon center-of-mass energy of 5.36 TeV. Photonuclear events, where one of the colliding nuclei breaks up and the other remains intact, are selected based on breakup neutron emissions and by requiring no particle activity in a large rapidity interval in the direction of the photon-emitting nucleus. The D^{0} mesons are reconstructed via the D^{0}→K^{-}π^{+} decay channel, with the cross section measured as a function of D^{0} meson transverse momentum and rapidity. The results are compared with next-to-leading-order perturbative QCD calculations that employ recent parametrizations of the lead nuclear parton distribution functions, as well as with predictions based on the color glass condensate framework. This measurement is the first photonuclear collision study characterizing parton distribution functions of lead nuclei for parton fractional momenta x (relative to the nucleon) ranging approximately from a few 10^{-4} to 10^{-2} for different hard energy scale Q^{2} selections.
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Journal articleHayrapetyan A, Makarenko V, Tumasyan A, et al., 2026,
Characterization of the quantum state of top quark pairs produced in proton-proton collisions at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> <mml:mo>=</mml:mo> <mml:mn>13</mml:mn> <mml:mtext> </mml:mtext> <mml:mtext> </mml:mtext> <mml:mi>TeV</mml:mi> </mml:math> using the beam and helicity bases
, Physical Review D, Vol: 113, ISSN: 2470-0010<jats:p> Measurements of the spin correlation coefficients in the beam basis are presented for top quark-antiquark ( <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mi>t</a:mi> <a:mover accent="true"> <a:mi>t</a:mi> <a:mo stretchy="false">¯</a:mo> </a:mover> </a:math> ) systems produced in proton-proton collisions at <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:msqrt> <e:mi>s</e:mi> </e:msqrt> <e:mo>=</e:mo> <e:mn>13</e:mn> <e:mtext> </e:mtext> <e:mtext> </e:mtext> <e:mi>TeV</e:mi> </e:math> collected by the CMS experiment in 2016–2018, and corresponding to an integrated luminosity of <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:mn>138</g:mn> <g:mtext> </g:mtext> <g:mtext> </g:mtext> <g:msup> <g:mi>fb</g:mi> <g:mrow> <g:mo>−</g:mo> <g:mn>1</g:mn> </g:mrow> </g:msup> </g:math> . The <i:math xmlns
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Journal articleAbbaslu S, Abd Alrahman F, Abed Abud A, et al., 2026,
Identification of low-energy kaons in the ProtoDUNE-SP detector
, Physical Review D, Vol: 113, ISSN: 2470-0010<jats:p> The Deep Underground Neutrino Experiment (DUNE) is a next-generation neutrino experiment with a rich physics program that includes searches for the hypothetical phenomenon of proton decay. Utilizing liquid-argon time-projection chamber technology, DUNE is expected to achieve world-leading sensitivity in the proton decay channels that involve charged kaons in their final states. The first DUNE demonstrator, ProtoDUNE Single-Phase, was a 0.77 kt detector that operated from 2018 to 2020 at the CERN Neutrino Platform, exposed to a mixed hadron and electron test-beam with momenta ranging from 0.3 to <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mrow> <a:mn>7</a:mn> <a:mtext> </a:mtext> <a:mtext> </a:mtext> <a:mi>GeV</a:mi> <a:mo>/</a:mo> <a:mi mathvariant="normal">c</a:mi> </a:mrow> </a:math> . We present a selection of low-energy kaons among the secondary particles produced in hadronic reactions, using data from the 6 and <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline"> <d:mrow> <d:mn>7</d:mn> <d:mtext> </d:mtext> <d:mtext> </d:mtext> <d:mi>GeV</d:mi> <d:mo>/</d:mo> <d:mi mathvariant="normal">c</d:mi> </d:mrow> </d:math> beam runs. The selecti
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Journal articleHunter ED, Bumbar M, Amsler C, et al., 2026,
Optimizing antihydrogen production via slow plasma merging
, Physics of Plasmas, Vol: 33, ISSN: 1070-664XWe present advances in plasma control and diagnosis, leading to the production of exceptionally large quantities of neutral antimatter. We measure the time-dependent temperature and density distribution of antiprotons and positrons while slowly combining them to make antihydrogen atoms in a nested Penning–Malmberg trap. The total antihydrogen yield and the number of atoms escaping the trap as a beam are greatest when the positron temperature is lowest and when antiprotons enter the positron plasma at the smallest radius. We control these parameters by changing the rate at which we lower the electrostatic barrier between the antiproton and positron plasmas and by heating the positrons. With the optimal settings, we produce 2.3 × 10<sup>6</sup> antihydrogen atoms per 15-min run, surpassing the previous state of the art (3.1 × 10<sup>4</sup> atoms in 4 min) and the most recent advances in other experiments by factors of 20 and 5, respectively.
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Journal articleHayrapetyan A, Makarenko V, Tumasyan A, et al., 2026,
Search for low-mass hidden-valley dark showers with non-prompt muon pairs in proton-proton collisions at s=13 TeV
, Journal of High Energy Physics, Vol: 2026A search for signatures of a dark analog to quantum chromodynamics is performed. The analysis targets long-lived dark mesons that decay into standard-model particles, with a high branching fraction of the dark mesons decaying into muons. The dark mesons are formed by the hadronisation of dark partons, which are produced by a decay of the Higgs boson. The search is performed using a data set corresponding to an integrated luminosity of 41.6 fb<sup>−1</sup>, which was collected in proton-proton collisions at s=13 TeV by the CMS experiment at the CERN LHC in 2018 using non-prompt muon triggers. The search is based on resonant muon pair signatures. Machine-learning techniques are employed in the analysis, utilising boosted decision trees to discriminate between signal and background. No significant excess is observed above the standard model expectation. Upper limits on the branching fraction of the Higgs boson decaying to dark partons are determined to be as low as 10<sup>−4</sup> at 95% confidence level, surpassing and extending the existing limits on models with dark ω~ mesons for mean proper decay lengths of less than 500 mm and for ω~ masses down to 0.3 GeV. First limits are set for extended dark-shower models with two dark flavours that contain dark photons, probing their masses down to 0.33 GeV.
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