Search for Light Long-Lived Particles in pp Collisions at sqrt[s]=13  TeV Using Displaced Vertices in the ATLAS Inner...

Area of Science:

• High Energy Physics
• Particle Physics
• Collider Physics

Background:

• The Standard Model of particle physics allows for new phenomena beyond its predictions.
• Long-lived particles (LLPs) are hypothetical particles that travel a detectable distance before decaying.
• Searches for LLPs can probe new physics models, including those involving exotic Higgs boson decays and axion-like particles (ALPs).

Purpose of the Study:

• To search for long-lived particles (LLPs) decaying hadronically within the ATLAS inner detector.
• To investigate benchmark models featuring LLP pair production from exotic Higgs boson decays.
• To explore models with long-lived axion-like particles (ALPs) produced in association with vector bosons and in top quark decays.

Main Methods:

• Analysis of 140 fb^{-1} of proton-proton collision data at 13 TeV center-of-mass energy collected by the ATLAS experiment.
• Targeting LLPs with masses between 5 and 55 GeV that decay hadronically.
• Utilizing sophisticated background estimation techniques to compare observed data with theoretical predictions.

Main Results:

• No significant excess of events above the expected background was observed in the analyzed data.
• Upper limits were placed on the branching ratio of the Higgs boson to pairs of LLPs.
• Upper limits were set on the cross section for ALPs produced with a vector boson and, for the first time, on the top quark branching ratio to an ALP and a light quark.

Conclusions:

• The search provides stringent constraints on models predicting the existence of long-lived particles.
• The results exclude certain parameter spaces for exotic Higgs boson decays and axion-like particle production.
• This study contributes to the ongoing quest for physics beyond the Standard Model by constraining new particle properties and interactions.