Search for Higgs boson decays to a photon and a Z boson in pp collisions at $\sqrt{s}=7$ and 8 TeV with the ATLAS detector

A search is reported for a neutral Higgs boson in the decay channel <math altimg="si2.gif" xmlns="http://www.w3.org/1998/Math/MathML"><mi>H</mi><mo stretchy="false">→</mo><mi>Z</mi><mi>γ</mi></math> , <math altimg="si3.gif" xmlns="http://www.w3.org/1998/Math/MathML"><mi>Z</mi><mo stretchy="false">→</mo><msup><mrow><mi>ℓ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>ℓ</mi></mrow><mrow><mo>−</mo></mrow></msup></math> ( <math altimg="si4.gif" xmlns="http://www.w3.org/1998/Math/MathML"><mi>ℓ</mi><mo>=</mo><mi>e</mi><mo>,</mo><mi>μ</mi></math> ), using 4.5 fb −1 of pp collisions at <math altimg="si5.gif" xmlns="http://www.w3.org/1998/Math/MathML"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>7</mn><mtext> TeV</mtext></math> and 20.3 fb −1 of pp collisions at <math altimg="si6.gif" xmlns="http://www.w3.org/1998/Math/MathML"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>8</mn><mtext> TeV</mtext></math> , recorded by the ATLAS detector at the CERN Large Hadron Collider. The observed distribution of the invariant mass of the three final-state particles, <math altimg="si7.gif" xmlns="http://www.w3.org/1998/Math/MathML"><msub><mrow><mi>m</mi></mrow><mrow><mi>ℓ</mi><mi>ℓ</mi><mi>γ</mi></mrow></msub></math> , is consistent with the Standard Model hypothesis in the investigated mass range of 120–150 GeV. For a Higgs boson with a mass of 125.5 GeV, the observed upper limit at the 95% confidence level is 11 times the Standard Model expectation. Upper limits are set on the cross section times branching ratio of a neutral Higgs boson with mass in the range 120–150 GeV between 0.13 and 0.5 pb for <math altimg="si6.gif" xmlns="http://www.w3.org/1998/Math/MathML"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>8</mn><mtext> TeV</mtext></math> at 95% confidence level.