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Search for the pair production of long-lived supersymmetric partners of the tau lepton in proton-proton collisions at sqrt{s}=13 TeV
No full textGauge-mediated supersymmetry breaking models provide a strong motivation to search for a supersymmetric partner of the tau lepton (stau) with a macroscopic lifetime.
Long-lived stau decays produce tau leptons that are displaced from the primary proton-proton interaction vertex, leading to unconventional signatures in the detector.
This study presents the first search for the direct production of long-lived staus decaying within the tracker volume in proton-proton collisions at TeV, performed with a dedicated graph network-based identification algorithm for displaced tau leptons.
The data sample used, corresponding to an integrated luminosity of 138 fb, was recorded with the CMS experiment at the CERN LHC between 2016 and 2018.
This search excludes at confidence level stau masses in the () GeV range for mm in the maximally mixed (mass degenerate) scenario, while for GeV, stau proper lifetimes are excluded in the range () mm
Multi-loop spectra in general scalar EFTs and CFTs
No full textWe consider the most general effective field theory (EFT) Lagrangian with scalar fields and derivatives, and renormalise it to substantially higher loop order than existing results in the literature. EFT Lagrangians have phenomenological applications, for example by encoding corrections to the Standard Model from unknown new physics. At the same time, scalar EFTs capture the spectrum of Wilson--Fisher conformal field theories (CFTs) in dimensions. Our results are enabled by a more efficient version of the method for renormalisation, in which the IR divergences are subtracted via a small-momentum asymptotic expansion. In particular, we renormalise the most general set of composite operators up to engineering dimension six and Lorentz rank two. We exhibit direct applications of our results to Ising (), , and hypercubic () CFTs, relevant for a plethora of real-world critical phenomena. The computed scaling dimensions agree well with known non-perturbative results, and they lead to new predictions where such results do not yet exist. We thereby expand the understanding of generic EFTs and open new possibilities in diverse fields, such as the numerical conformal bootstrap
Decommissioning and Post-Irradiation Examination of the LHC Beam Dumps
No full textThe LHC beam dumps are responsible for the safe absorption of the Large Hadron Collider (LHC) particle beams. In 2018, the two 6.4-tonne beam dumps that had been in operation since the LHC’s startup in 2008 were removed and replaced with upgraded versions. Endoscopic inspections of these beam dumps and experimental high-intensity proton-beam irradiation of material samples raised concerns about the structural integrity of the carbon-based materials in their cores. It was therefore decided to undertake an accelerated project of dismantling and postirradiation examination of the removed dumps as part of a wider program of work to ensure the safe operation of the LHC beam dumps in the coming years. This paper describes the decommissioning process for the two beam dumps carried out at CERN between 2021 and 2023, covering the preparatory studies, practical challenges encountered, and solutions implemented. It details the establishment of an operational framework, including the preparation of the working environment, the development of a method for cutting the irradiated 12-mm-thick duplex stainless-steel vessel, and the cut sequencing. Additionally, the paper presents the findings derived from the postirradiation examination of the different carbon-based core materials subjected to deposited energy densities up to 1.5 kJ/g. The extruded graphite plates within the vessel exhibited a cracking pattern, which was likely due to the dynamic response of the device upon beam impact, and their retaining rings were found to be displaced. Despite minor signs of surface deterioration, the expanded graphite sheets were intact, and the isostatic graphite blocks showed no evidence of material degradation. These findings were consistent across both beam dumps. Finally, this manuscript discusses the implications of these results for the safe operation of the beam dumps during LHC Run 3 (2022–2026) and for the design and construction of Run 3 operational spares.The LHC beam dumps are responsible for the safe absorption of the Large Hadron Collider (LHC) particle beams. In 2018, the two 6.4-tonne beam dumps that had been in operation since the LHC's startup in 2008 were removed and replaced with upgraded versions. Endoscopic inspections of these beam dumps and experimental high-intensity proton-beam irradiation of material samples raised concerns about the structural integrity of the carbon-based materials in their cores. It was therefore decided to undertake an accelerated project of dismantling and post-irradiation examination of the removed dumps as part of a wider program of work to ensure the safe operation of the LHC beam dumps in the coming years. This paper describes the decommissioning process for the two beam dumps carried out at CERN between 2021 and 2023, covering the preparatory studies, practical challenges encountered, and solutions implemented. It details the establishment of an operational framework, including the preparation of the working environment, the development of a method for cutting the irradiated 12-mm-thick duplex stainless-steel vessel, and the cut sequencing. Additionally, the paper presents the findings derived from the post-irradiation examination of the different carbon-based core materials subjected to deposited energy densities up to 1.5 kJ/g. The extruded graphite plates within the vessel exhibited a cracking pattern, which was likely due to the dynamic response of the device upon beam impact, and their retaining rings were found to be displaced. Despite minor signs of surface deterioration, the expanded graphite sheets were intact, and the isostatic graphite blocks showed no evidence of material degradation
High-Precision Engineering for the ATLAS Inner Tracker Outer Endcap
No full textThe Large Hadron Collider will be upgraded to increase the machine luminosity. The ATLAS experiment has developed an all-silicon inner tracker (ITk) to operate with much higher density of tracks while improving the performance of the tracking system. To withstand this harsh high luminosity environment, both a low material budget and radiation hardness are critical. Within the ITk pixel system, the outer endcap local supports are three differently sized double loaded half-rings. These structures provide mechanical support and cooling for the silicon pixel modules. The placement of the silicon modules and the local supports is paramount for the optimal reconstruction of the tracks of the particles produced on each collision. These half-ring assemblies feature carbon sandwich structures and radiation-hard polymer inserts, which are hand-assembled using radiation-hard glue. The machining tolerances of the carbon composite structures are typically tighter than expected due to the material’s anisotropic nature and are even tight by metallic standards. To meet the required specifications, extremely precise tooling is needed, testing the limits of CNC technologies. Positional tolerances of hole features in assembly plates are as low as 35 µm. Achieving this requires a precisely flat surface over an area as large as 0.3 m². This is only achievable by using extremely stable CNC machines and software capable of compensating for environmental temperature variations. In addition to these plates, custom fixings are required, produced to fit within these hole features with a clearance of less than 10 µm. Producing these parts is only the first stage. Next, advanced precision metrology is required to verify that the tooling has been made within these specified tolerances. A combination of mechanical, optical and laser metrology techniques is necessary for this. After extensive iterations and skilled technical effort, we have passed the pre-production requirements for these hand-fabricated carbon sandwich structures and are now undergoing full-scale production. In this contribution, all the challenges faced during the R&D and prototyping phases that enabled us to comply with the project specifications will be presented
Differential measurement of the Higgs boson production with two jets in the WW decay channel
No full textA measurement of the differential production cross section of the Higgs boson decaying into two W bosons, with two jets produced in association, is presented. The analysis is based on proton-proton collision data collected by the CMS detector from 2016 to 2018. A novel approach based on adversarial neural networks is employed to reduce model dependence and enable reinterpretability. Constraints on several Wilson coefficients are also derived
Higgs boson property measurements (mass, width, CP) in ATLAS
No full textStudying the Higgs boson properties is essential for probing the Standard Model (SM) with high precision, as any deviations from expectations could be signs of new physics. In addition, some Beyond the SM theories predict effects on the mass, width, and Charge-Parity (CP) of the Higgs boson. This talk will highlight the most recent ATLAS results on Higgs mass, width, and CP measurements
CERN-LHC seminar
No full textThe study of CP violation in charm mesons provides a complementary probe for possible interactions beyond the Standard Model with respect to beauty mesons, and allows the exploration of even higher energy scales. The LHCb experiment collected the largest sample of charm hadrons ever, order of billions of decays, and reported the first observation of CP violation in D0→K+K- and D0→pi+pi- decays in 2019, marking a milestone in flavour physics. However, the compatibility of the observation with the Standard Model is still debated, and providing complementary experimental results is a crucial step towards clarifying the physics picture. In this seminar, a new measurement of the time-integrated CP asymmetry in the decay D0->KsKs will be presented. The analysis has been performed using data collected by the LHCb experiment in 2024. This dataset marks the beginning of a new era for LHCb, enabled by an upgraded detector featuring enhanced tracking, improved vertex resolution, and a software-based trigger system. Thanks to these improvements, unprecedented precision in charm physics can now be achieved
The Rise of Particle Physics
No full textDiscovery of the J Particle at Brookhaven National Laboratory and the Physics of Electrons and Positrons; The Standard Model Yesterday, Today and Tomorrow; The Rise of Gauge Theories: From Many Models to One Theory; From Charm to CP Violation; When the Standard Model Was Ignored; The Discovery of the W and Z Bosons at the CERN Proton-Antiproton Collider; A Personal History of CERN Particle Colliders (1972-2022); The Age of Gravitational Wave Astronomy; Precision Physics in the Era of (HL)LHC; Recent Developments in Flavor Physics, the Unitary Triangle Fit, Anomalies and All That; About BSM Physics, with Emphasis on Flavour; The Discovery of the Antiproton between Rome and Berkeley; Raoul Gatto and Bruno Touschek: the Rise of Physics; From ADONE's Multi-Hadron Production to the J/ Discovery; From Bjorken Scaling to Scaling Violation
Frustrated Bose ladder with extended range density-density interaction
No full textWhen hard-core bosons on a two-leg ladder get frustrated by ring exchange interactions, the elusive d-wave Bose liquid (DBL) can be stabilized, a bosonic analog of a correlated metal. Here, we analyze the effect of extended Hubbard interactions on the DBL phase. Strikingly, these interactions are found to act in favor of the exotic Bose liquid. This observation is of immediate relevance for physical systems in which nonlocal exchange processes occur as a consequence of extended range density-density interactions. Our observation also helps to achieve DBL physics in a synthetic-dimension ladder, where on-site interactions translate into nonlocal interactions along a synthetic rung. In this context, we also consider the extreme limit, in which the local hard-core constraint is elevated to an effective rung blockade. In addition to the enhancement of DBL physics due to extended range density-density interactions, we also find signatures of an interesting intermediate phase between the superfluid and the DBL regime. This phase, called the density-modulated s-wave pairing phase, combines features of density wave and s-wave pairing. Our results offer insights into the physics of frustrated bosons by highlighting the influence of density-density interaction and rung blockade.When hard-core bosons on a two-leg ladder get frustrated by ring exchange interactions, the elusive d-wave Bose liquid (DBL) can be stabilized, a bosonic analog of a correlated metal. Here, we analyze the effect of extended Hubbard interactions on the DBL phase. Strikingly, these interactions are found to act in favor of the exotic Bose liquid. This observation is of immediate relevance for physical systems in which non-local exchange processes occur as a consequence of extended-range density-density interactions. Our observation also helps to achieve DBL physics in a synthetic-dimension ladder, where on-site interactions translate into non-local interactions along a synthetic rung. In this context, we also consider the extreme limit, in which the local hardcore constraint is elevated to an effective rung blockade. In addition to the enhancement of DBL physics due to extended-range density-density interactions, we also find signatures of an interesting intermediate phase between the superfluid and the DBL regime. This phase, labeled as the density modulated s-wave paired (DMSP) phase, combines features of density wave and s-wave pairing. Our results offer new insights into the physics of frustrated bosons by highlighting the influence of density-density interaction and rung-blockade