515664 research outputs found
Sort by
Evidence for the dimuon decay of the Higgs boson in collisions with the ATLAS detector
No full textA search for the dimuon decay of the Higgs boson is presented based on collision data recorded by ATLAS during Run 3 of the Large Hadron Collider, corresponding to an integrated luminosity of at . To enhance the sensitivity, the results are combined with those from Run 2. An excess of events over the background is observed with a significance of ( expected). The best-fit signal strength is . This result provides evidence for the decay with ATLAS data and offers a direct probe of the Higgs-boson Yukawa coupling to second-generation fermions.A search for the dimuon decay of the Higgs boson is presented based on pp collision data recorded by ATLAS during Run 3 of the Large Hadron Collider, corresponding to an integrated luminosity of 165 fb-1 at s=13.6 TeV. To enhance the sensitivity, the results are combined with those from Run 2. An excess of events over the background is observed with a significance of 3.4σ (2.5σ expected). The best-fit signal strength is μ=1.4±0.4. This result provides evidence for the H→μμ decay with ATLAS data and offers a direct probe of the Higgs-boson Yukawa coupling to second-generation fermions.A search for the dimuon decay of the Higgs boson is presented based on pp collision data recorded by ATLAS during Run 3 of the Large Hadron Collider, corresponding to an integrated luminosity of 165 fb at TeV. To enhance the sensitivity, the results are combined with those from Run 2. An excess of events over the background is observed with a significance of ( expected). The best-fit signal strength is . This result provides evidence for the decay with ATLAS data and offers a direct probe of the Higgs-boson Yukawa coupling to second-generation fermions
Observation of a cross-section enhancement near the production threshold in TeV collisions with the ATLAS detector
No full textA measurement is presented of production in the invariant-mass region near the pair production threshold, , in final states with two charged leptons and multiple jets. The measurement is based on of proton–proton collision data collected at with the ATLAS detector. The data are compared to two models of production: a baseline model including only perturbative QCD (pQCD) predictions for the hard process, and an extended model that, in addition to the pQCD predictions, incorporates state-of-the-art Monte Carlo simulations of colour-singlet quasi-bound-state formation near the threshold. The agreement between the data and the models is quantified via a profile-likelihood fit to the reconstructed distributions, in bins of two angular observables sensitive to spin-correlations in the system. An excess of events is observed over the baseline pQCD prediction, with an observed significance of standard deviations. This excess is consistent with the formation of colour-singlet, -wave, quasi-bound states as predicted by non-relativistic QCD, and corresponds to an observed cross-section of
Examining the nucleosynthesis process and the inner nuclei structure with (anti)hypernuclei with ALICE at the LHC
No full textHypernuclei are bound states of nucleons and hyperons. The measurement of the production of hypernuclei with mass number A=3 and 4 in heavy-ion colli- sions is a powerful tool to investigate the mechanism of the nucleosynthesis. In the coalescence model, the production yields are sensitive to the interplay be- tween the spatial extension of the nucleus wavefunction and the baryon-emitting source size, whereas, in the statistical hadronization model, the nuclear struc- ture does not come into play in the production. Hypernuclei span over a wide range of wavefunction radii, from about 2 fm for A=4 hypernuclei to about 10 fm for the hypertriton, making them ideal probes to test such models. In addi- tion, the study of hypernuclei properties provides information on the nucleon- hyperon interactions, complementing the results obtained through femtoscopy correlation measurements. The strength of such interactions is a fundamen- tal input to calculate the equation-of-state of the high-density nuclear matter found inside neutron stars. This contribution presents recent measurements of the production and properties of 3ΛH, 4ΛH, and 4ΛHe based on the data samples collected by ALICE during the LHC Run 2 and Run 3. The measurement of A=4 (anti)hypernuclei using the LHC Run 2 data enabled also for the first evidence of the 4ΛHe. By comparing the yield measurements of these objects to the state-of-the-art production models, the production mechanisms can be investigated and by obtaining the properties such as their binding energy and lifetime, inputs to the equation-of-state can be delivered.
Refreshments will be served at 10h30
</p
Superadditivity at Large Charge
No full textThe weak gravity conjecture has been invoked to conjecture that the dimensions of charged operators in a CFT should obey a superadditivity relation (sometimes referred to as convexity). In this paper, we study superadditivity of the operator spectrum in theories expanded about the semi-classical saddle point that dominates correlators of large charge operators. We explore this in two contexts. The first is a model with two scalar fields that carry different charges, at a non-trivial Wilson-Fisher fixed point. A careful analysis of the semi-classics for this two field model demonstrates that ‘quantum’ violations of superadditivity (those not forbidden by the conjecture) persist in the large charge regime. We then turn to study the general properties of CFTs at large charge as bottom-up EFTs. By a trial and error procedure we come up with a seemingly consistent family of examples violating the conjecture. In so doing the presence of a genuine dilaton field appears necessary. On the one hand our result demonstrates that the superadditivity conjecture cannot be proven purely on the basis of a bottom-up analysis. On the other hand, the need for a dilaton, with the corresponding infinite fine tuning, indicates the conjecture-violating EFTs are unlikely to be UV completable.The weak gravity conjecture has been invoked to conjecture that the dimensions of charged operators in a CFT should obey a superadditivity relation (sometimes referred to as convexity). In this paper, we study superadditivity of the operator spectrum in theories expanded about the semi-classical saddle point that dominates correlators of large charge operators. We explore this in two contexts. The first is a model with two scalar fields that carry different charges, at a non-trivial Wilson-Fisher fixed point. A careful analysis of the semi-classics for this two field model demonstrates that 'quantum' violations of superadditivity (those not forbidden by the conjecture) persist in the large charge regime. We then turn to study the general properties of CFTs at large charge as bottom-up EFTs. By a trial and error procedure we come up with a seemingly consistent family of examples violating the conjecture. In so doing the presence of a genuine dilaton field appears necessary. On the one hand our result demonstrates that the superadditivity conjecture cannot be proven purely on the basis of a bottom-up analysis. On the other hand, the need for a dilaton, with the corresponding infinite fine tuning, indicates the conjecture-violating EFTs are unlikely to be UV completable
Preparing ATLAS for the high-luminosity LHC: system testing and performance evaluation of the ITk Strip detector
No full textThe new ATLAS Inner Tracker (ITk) will replace the current tracking system in ATLAS to cope with the challenging conditions during the high-luminosity phase of the Large Hadron Collider. ITk is an all-silicon detector consisting of a pixel inner tracker and a silicon microstrip outer tracker. This contribution focuses on the results of the large-scale system testing of the ITk Strip detector, which is the testbed for verifying the design and evaluating the performance of detector components prior to production. This setup is also being used to develop detector control and data acquisition systems required for the eventual operation of the ITk Strip detector.Two sets of experiments at CERN and DESY (Hamburg, Germany) target the design verification of the central barrel section around the interaction point and the end-cap section covering the forward region.In both setups, silicon sensors mounted on support structures are connected to electrical, optical and cooling services as realistic as possible as in the latter detector integration.As such, it is possible to validate the detector design, verify the detector DAQ and perform tests with the services, e.g. concerning the dual-phase CO2 cooling.This contribution gives an overview of the developed system tests for the ITk strip detector, summarizes the current status of the two sites, and shows a selection of performance measurements
Design and construction of an enhanced thermal conductivity measurement set-up in the temperature range of 1.8 K to 50 K at CERN
No full textWithin the goals of the High-Field Magnet (HFM) program at CERN, ongoing research focuses on achieving magnetic flux densities of up to 16 T using superconducting coils. Understanding the thermal properties of composite materials used as impregnation resins or insulation layers in superconducting magnets is crucial for the design of effective cooling methods. To this end, a new test stand was built at CERN in the Cryogenic Laboratory, to extend the investigation of thermal properties to a lower temperature range compared to the conventional cryocooler-based set-ups stopping at around 3 K, by linking a closed He II circuit to this system. This circuit enables to pre-cool helium gas, then gets it condensed by expansion through a Joule-Thomson valve before it gets pumped continuously via a roots pump, allowing to extend the measurement capabilities down to 1.8 K. The He II circuit is coupled to the cryocooler’s cold head via a gas-gap heat switch, enabling the He circuit to be thermally decoupled from the warmer cryocooler head for measurements at the lowest temperature. By varying base temperatures of the experimental platform, providing the cooling power either by the cryocooler or by the He circuit, a steady-state heat flux measurements can be ensured from 1.8 K up to 50 K. This work details the design and construction of this new enhanced test stand for thermal conductivity measurements at a lower temperature range, and its validation by measuring a reference sample
FCC-ee cavities RF power coupler: study on the optimal cooling strategy to boost the cryomodule energy efficiency
No full textThe RF fundamental power coupler (FPC) in SRF accelerating systems can have a major contribution to the cryogenic power consumption. In the framework of the FCC feasibility study, the focus on the energy saving is of primary importance given the size of the machine, with 264 cavities at 400 MHz and 488 cavities at 800 MHz for the collider, and 600 cavities at 800 MHz for the booster, at the ttbar working point. Additionally, this early stage of the design leaves freedom in exploring and comparing alternatives within a limited number of constraints. In this paper we present the comparison between active vapor cooling and fixed temperature heat interception for the FPC, with the aim of minimizing the heat loads to the helium bath - at 4.5K and 2K for the 400 MHz and 800 MHz cavities respectively – along with the overall cryogenic cost of the design solution. The choice for the FPC cooling method impacts the energy consumption, given the low efficiency of low-temperatures heat extraction, but it also affects the integration design of the coupler in the cryomodule, the cryogenic lines layout, and eventually the overall size of the cryomodule, with consequences on the tunnel space needs. In this paper, the results - concerning the temperature field on the FPC outer conductor, and the cryogenic cooling needs - are presented for the two cooling strategies and different coupler geometries. The data are derived with a semi-analytical model, describing the different heat transfer phenomena and the selected cooling strategy. The model is parametric with respect to the geometry and the RF inputs (RF power per cavity and electro-magnetic field across the outer conductor). In this way, it is possible to maintain flexibility towards the variations, in shape and heat loads, generated by integration choices, RF design constraints, and RF operating conditions across the four FCC working points. Additionally, the model serves as a tool to guide the design of the FPC, evaluating the direct impact of a choice on the final performances of the coupler in operation