A search for the production of three Higgs bosons (π»β‘π»β‘π») in the πβ’
Β―
π
β’πβ’
Β―
π
β’πβ’
Β―
π
final state is presented. The search uses 126ββfbβ1 of proton-proton collision data at βπ =13ββTeV collected with the ATLAS detector at the Large Hadron Collider. The analysis targets both nonresonant and resonant production of π»β‘π»β‘π». The resonant interpretations primarily consider a cascade decay topology of π βπβ’π» βπ»β‘π»β‘π» with masses of the new scalars π and π up to 1.5 and 1 TeV, respectively. In addition to scenarios where π is off-shell, the nonresonant interpretation includes a search for Standard Model π»β‘π»β‘π» production, with limits on the trilinear and quartic Higgs self-coupling set. No evidence for π»β‘π»β‘π» production is observed. An upper limit of 59 fb is set, at the 95% confidence level, on the cross section for Standard Model π»β‘π»β‘π» production.