Search for new physics beyond the Standard Model at the LHC with the ATLAS detector

Stage numéro : M2-1920-AT-01
Laboratoire :Centre de Physique des Particules de Marseille Case 902
 163 avenue de Luminy - 13288 Marseille Cedex 9
Directeur :Cristinel Diaconu - 04.91.82.72.01 - diaconu@cppm.in2p3.fr
Correspondant :William Gillard - 04.91.82.72.67 - gillard@cppm.in2p3.fr
Groupe d'accueil :Atlas
Chef de groupe :Marlon Barbero - 04.91.82.76.58 - barbero@cppm.in2p3.fr
Responsable de stage :Lorenzo Feligioni - 04 91 82 76 21 - lorenzo@cppm.in2p3.fr

Thématique : Physique des particules

While CERN experiments are still working on analysing the data produced by proton-proton collisions at the unprecedented center of mass energy of √s=13 TeV, delivered during the last Run 2 data taking period, the predictivity of the Standard Model (SM) of particle physics remains unchallenged by experimental results. So far the measurements of the Higgs boson properties, such as its spin, parity and couplings with other SM particles have confirmed its SM-like nature.

While new physics close to the electroweak (EW) scale is theoretically well-motivated, current direct searches all gave null results.

Indeed, the excellent performance of the LHC, in terms of delivered luminosity, allowed the ATLAS and CMS experiments to set stringent limits on the presence of new particles

well beyond the EW scale, thus worsening the naturalness problem.

The so far nearly SM properties of the 125 GeV Higgs

boson and the absence of direct signs of TeV physics beyond the SM

go hand in hand, if the new physics scale lies well

above the present experimentally probed energies.

If so, one would be left with the sole experimental perspective

of searching for small deviations within the SM, and with

no theoretical explanation of why the new physics should be so

unnaturally heavy. There is, however, another logical possibility:

new physics may be hidden at lower energies, if sufficiently weakly coupled to the SM.

As a matter of fact,

given the limited experimental improvements expected at the energy frontier promised in Run 3,

the time has come to reconsider theories that address some of the fundamental questions

associated with the EW scale. We aim to explore more in depth their low energy spectrum, that is,

the possible new resonances with mass below the EW scale, and couplings

with the SM of EW size or smaller. Those are predicted by a variety of SM extensions, i.e. composite models, supersymmetry, axions, dark matter models, to cite

few.

The aim of the proposed stage is on one side to analyse signal and background samples, produced with fast simulation of the detector response, to assess the LHC capabilities for various final states for the low mass range at Run 3, on the other to help finalizing the data analysis aimed at searching for new physics with the data collected by ATLAS during Run 2 [1,2].

During its longstanding participation to the ATLAS experiment, the CPPM group has been a key player in the design, construction and commissioning of the trigger system, the tracking and calorimeter detectors, with a recognized leadership of collaboration-wide projects dedicated to τ, photon, and hBcjet reconstruction and calibration, both offline and at trigger level, to di-photon searches beyond the SM, and measurements of the Yukawa Higgs couplings to bottom and top quarks.

[1] S. Diglio, L. Feligioni and G. Moultaka,

Stashing the stops in multijet events at the LHC,"

Phys. Rev. D 96, no. 5, 055032 (2017)

[arXiv:1611.05850 [hep-ph]].

[2] ATLAS Collaboration,

Search for the Standard Model Higgs boson decaying into bb produced in association with top quarks decaying hadronically in pp collisions at √s=8 TeV with the ATLAS detector,"

JHEP 1605, 160 (2016)

[arXiv:1604.03812 [hep-ex]].