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SHiP experiment at the SPS Beam Dump Facility
No full textAbstract In 2024, the SHiP experiment, together with the associated Beam Dump Facility (BDF) un- der the auspices of the High Intensity ECN3 (HI-ECN3) project, was selected for the future physics exploitation of the ECN3 experimental facility at the SPS. The SHiP experiment is a general-purpose intensity-frontier setup designed to search for physics beyond the Standard Model in the domain of Feebly Interacting Particles at the GeV-scale. It comprises a multi- system apparatus that provides discovery sensitivity to both decay and scattering signatures of models with feebly interacting particles, such as dark-sector mediators, both elastic and inelastic light dark matter, as well as millicharged particles. The experiment will also be able to perform both Standard Model measurements and Beyond Standard Model searches with neutrino interactions. In particular, it will have access to unprecedented statistics of tau and anti-tau neutrinos. The construction plan foresees commissioning of the facility and detector, and start of operation in advance of Long Shutdown 4, with a programme of exploration for 15 years of data taking. By exploring unique regions of parameter space for feebly interacting particles in the GeV/c2 mass range, the SHiP experiment will complement ongoing searches at the LHC and searches at future colliders. Document submitted to European Strategy for Particle Physics Update 202
Impact of the circuit layout on the charge collection in a monolithic pixel sensor
No full textCERN's strategic R&D programme on technologies for future experiments recently started investigating the TPSCo 65nm ISC CMOS imaging process for monolithic active pixels sensors for application in high energy physics. In collaboration with the ALICE experiment and other institutes, several prototypes demonstrated excellent performance, qualifying the technology. The Hybrid-to-Monolithic (H2M), a new test-chip produced in the same process but with a larger pixel pitch than previous prototypes, exhibits an unexpected asymmetric efficiency pattern. This contribution describes a simulation procedure combining TCAD, Monte Carlo and circuit simulations to model and understand this effect. It proved able to reproduce measurement results and attribute the asymmetric efficiency drop to a slow charge collection due to low amplitude potential wells created by the circuitry layout and impacting efficiency via ballistic deficit
OPECST
No full textvisite de l’Office parlementaire des choix scientifiques et technologiques représenté par Madame Dominique Voynet, Députée (ancienne ministre de l’Environnement), République française et Madame Anne-Catherine Loisier, Sénatric
Search for jet quenching with dijets from high-multiplicity pPb collisions at 8.16 TeV
No full textThe first measurement of the dijet transverse momentum balance in proton-lead (pPb) collisions at a nucleon-nucleon center-of-mass energy of 8.16 TeV is presented. The observable, defined as the ratio of the subleading over leading jet transverse momentum in a dijet pair, is used to search for jet quenching effects. The data, corresponding to an integrated luminosity of 174.6 nb, were collected with the CMS detector in 2016. The distributions and their average values are studied as functions of the charged-particle multiplicity of the events and for various dijet rapidity selections. The latter enables probing hard scattering of partons carrying distinct nucleon momentum fractions in the proton- and lead-going directions. The former, aided by the high-multiplicity triggers, allows probing for potential jet quenching effects in high-multiplicity events (with up to 400 charged particles), for which collective phenomena consistent with quark-gluon plasma (QGP) droplet formation were previously observed. The ratios of distributions for high- to low-multiplicity events are used to quantify the possible medium effects. These ratios are consistent with simulations of the hard-scattering process that do not include QGP production. These measurements set an upper limit on medium-induced energy loss of the subleading jet of 1.26% of its transverse momentum at the 90% confidence level in high multiplicity pPb events.The first measurement of the dijet transverse momentum balance in proton-lead (pPb) collisions at a nucleon-nucleon center-of-mass energy of = 8.16 TeV is presented. The observable, defined as the ratio of the subleading over leading jet transverse momentum in a dijet pair, is used to search for jet quenching effects. The data, corresponding to an integrated luminosity of 174.6 nb, were collected with the CMS detector in 2016. The distributions and their average values are studied as functions of the charged-particle multiplicity of the events and for various dijet rapidity selections. The latter enables probing hard scattering of partons carrying distinct nucleon momentum fractions \x in the proton- and lead-going directions. The former, aided by the high-multiplicity triggers, allows probing for potential jet quenching effects in high-multiplicity events (with up to 400 charged particles), for which collective phenomena consistent with quark-gluon plasma (QGP) droplet formation were previously observed. The ratios of distributions for high- to low-multiplicity events are used to quantify the possible medium effects. These ratios are consistent with simulations of the hard-scattering process that do not include QGP production. These measurements set an upper limit on medium-induced energy loss of the subleading jet of 1.26% of its transverse momentum at the 90% confidence level in high multiplicity pPb events
Search for a heavy resonance produced in association with and decaying to a tt pair in the single lepton final state in proton-proton collisions at sqrt s= 13 TeV with the CMS detector
No full textA search for a top-philic boson in the final state with one electron or muon and jets is presented. The boson is produced in association with and decays to a top quark-antiquark pair, coupling exclusively to top quarks. The analysis aims to identify a heavy boson that results in Lorentz-boosted top quarks, whose hadronic decay products are merged into large-radius jets. We employ a machine learning algorithm (ParticleNet) to identify such jets. The distribution of invariant mass for the two most energetic top quark candidates is used to search for a boson in the mass range of 0.5 to 3 TeV with decay widths of , , , and relative to its mass. They are found to be in agreement with the standard model background prediction. Upper limits at confidence level are set on the production cross section of the boson as a function of its mass, for each of the considered decay widths.
These results represent the most stringent constraints to date on the existence of the boson in the scenario where the boson exclusively couples to top quarks. The data were recorded by the CMS experiment at the CERN LHC in proton-proton collisions at TeV and correspond to an integrated luminosity of 138 fb
Search for charged-lepton flavour violation in top quark interactions with an up-type quark, a muon, and a lepton in proton-proton collisions at 13 TeV
No full textA search for charged-lepton flavour violation (CLFV) in top quark (t) production and decay is presented. The search uses proton-proton collision data corresponding to 138 fb collected with the CMS experiment at 13 TeV. The signal consists of the production of a single top quark via a CLFV interaction or top quark pair production followed by a CLFV decay. The analysis selects events containing a pair of oppositely charged muon and hadronically decaying lepton and at least three jets, where one has been identified to originate from the fragmentation of a bottom quark. Machine learning classification techniques are used to distinguish signal from standard model background events. The results of this search are consistent with the standard model expectations. The upper limits at 95% confidence level on the branching fraction for CLFV top quark decays to a muon, a lepton, and an up or a charm quark are set at (0.040, 0.078, and 0.118) 10, and (0.810, 1.710, and 2.052) 10 for scalar, vector, and tensor-like operators, respectively.A search for charged-lepton flavour violation (CLFV) in top quark (t) production and decay is presented. The search uses proton-proton collision data corresponding to 138 fb collected with the CMS experiment at = 13 TeV. The signal consists of the production of a single top quark via a CLFV interaction or top quark pair production followed by a CLFV decay. The analysis selects events containing a pair of oppositely charged muon and hadronically decaying lepton and at least three jets, where one has been identified to originate from the fragmentation of a bottom quark. Machine learning classification techniques are used to distinguish signal from standard model background events. The results of this search are consistent with the standard model expectations. The upper limits at 95% confidence level on the branching fraction for CLFV top quark decays to a muon, a lepton, and an up or a charm quark are set at (t u) (0.040, 0.078, and 0.118) 10, and (t c) (0.810, 1.710, and 2.052) 10 for scalar, vector, and tensor-like operators, respectively
ATLAS Event Displays: 2025 Beam Splashes
No full textFirst beams of 2025 splash in the ATLAS Experiment, 14 April 2025
Search for Higgs boson pair production in the two photons plus two bottom quarks final state using partial Run-3 proton-proton collision data with the ATLAS detector
No full textA search for the Standard Model (SM) Higgs boson pair production in the final state is presented, using data from Run-II (2015–2018, TeV, 140 fb) and partial Run-III (2022–2023, TeV, 59 fb) collected with the ATLAS detector at the LHC. Despite its small branching ratio (0.26), the channel benefits from excellent diphoton invariant mass resolution (), a smooth background, and a high branching fraction (59), making it a golden channel for searches. The analysis includes the development and implementation of a Kinematic Fit Tool that, assuming transverse-plane balance between and , calibrates the system and improves the invariant mass () resolution by leveraging precise photon information through per-event log-likelihood minimization. The is the most discriminating input variable for the Boosted Decision Tree used to separate signal from background, after events are selected and categorized to retain sensitivity to the signal strength and variations of the trilinear Higgs self-coupling modifier . The parameter remains largely unconstrained by direct experimental measurements. The statistical results are interpreted in terms of the expected upper limits on the signal strength and an exclusion interval for . A 95 confidence level (CL) expected upper limit of 3.96 is set on the signal strength, assuming no di-Higgs production. Furthermore, a 95 CL expected allowed range for is found to be , assuming SM production