This paper presents a search for exotic decays of the Higgs boson into a pair of new pseudoscalar particles, <math><mrow><mi>H</mi><mo>→</mo><mi>a</mi><mi>a</mi></mrow></math>, where one pseudoscalar decays into a <math><mi>b</mi></math>-quark pair and the other decays into a <math><mi>τ</mi></math>-lepton pair, in the mass range <math><mn>12</mn><mo>≤</mo><msub><mi>m</mi><mi>a</mi></msub><mo>≤</mo><mn>60</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>. The analysis uses <math><mi>p</mi><mi>p</mi></math> collision data at <math><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> collected with the ATLAS detector at the LHC, corresponding to an integrated luminosity of <math><mn>140</mn><mtext> </mtext><mtext> </mtext><msup><mi>fb</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></math>. No significant excess above the Standard Model (SM) prediction is observed. Assuming the SM Higgs boson production cross section, the search sets upper limits at 95% confidence level on the branching ratio of Higgs bosons decaying into <math><mi>b</mi><mover><mi>b</mi><mo>¯</mo></mover><msup><mi>τ</mi><mo>+</mo></msup><msup><mi>τ</mi><mo>−</mo></msup></math>, <math><mi>B</mi><mo>(</mo><mi>H</mi><mo>→</mo><mi>a</mi><mi>a</mi><mo>→</mo><mi>b</mi><mover><mi>b</mi><mo>¯</mo></mover><msup><mi>τ</mi><mo>+</mo></msup><msup><mi>τ</mi><mo>−</mo></msup></math>), between 2.2% and 3.9% depending on the pseudoscalar mass.

France

Norway

United States

United Arab Emirates

Germany

Morocco

Israel

Italy

Poland

United Kingdom

Türkiye

Spain

Romania

Canada

China

Sweden

Japan

CERN

Greece

Switzerland

Czechia

South Africa

Chile

Argentina

Brazil

Portugal

Search for decays of the Higgs boson into a pair of pseudoscalar particles decaying into <math><mi>b</mi><mover><mi>b</mi><mo>¯</mo></mover><msup><mi>τ</mi><mo>+</mo></msup><msup><mi>τ</mi><mo>−</mo></msup></math> using <math><mi>p</mi><mi>p</mi></math> collisions at <math><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> with the ATLAS detector