Search for Higgs boson decays to a Z boson and a photon in proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV
A. Tumasyan, W. Adam, Janik Walter Andrejkovic, T. Bergauer, S. Chatterjee, K. Damanakis, M. Dragicevic, A. Escalante Del Valle, R. Frühwirth, M. Jeitler, N. Krammer, L. Lechner, D. Liko, I. Mikulec, P. Paulitsch, F. M. Pitters, J. Schieck, R. Schöfbeck, D. Schwarz, S. Templ, W. Waltenberger, C.-E. Wulz, M. R. Darwish, E. A. De Wolf, X. Janssen, T. Kello, A. Lelek, Haifa Rejeb Sfar, P. Van Mechelen, S. Van Putte, N. Van Remortel, E. S. Bols, J. D’Hondt, A. De Moor, M. Delcourt, H. El Faham, S. Lowette, S. Moortgat, A. Morton, D. Müller, A. R. Sahasransu, S. Tavernier, W. Van Doninck, D. Vannerom, D. Beghin, B. Bilin, B. Clerbaux, G. De Lentdecker, L. Favart, A. K. Kalsi, K. Lee, M. Mahdavikhorrami, I. Makarenko, L. Moureaux, S. Paredes, L. Pétré, A. Popov, N. Postiau, E. Starling, L. Thomas, M. Vanden Bemden, C. Vander Velde, P. Vanlaer, T. Cornelis, D. Dobur, J. Knolle, Luka Lambrecht, Gianny Mestdach, M. Niedziela, César Rendón, C. Roskas, Amrutha Samalan, K. Skovpen, M. Tytgat, N. Van Den Bossche, A. Vermassen, L. Wezenbeek, A. Benecke, A. Bethani, G. Bruno, F. Bury, C. Caputo, P. David, C. Delaere, I. S. Donertas, A. Giammanco, K. Jaffel, Sa. Jain, V. Lemaitre, K. Mondal, J. Prisciandaro, A. Taliercio, M. Teklishyn, T. T. Tran, P. Vischia, S. Wertz, G. A. Alves, C. Hensel, A. Moraes, P. Rebello Teles
Abstract
A bstract Results are presented from a search for the Higgs boson decay H → Zγ, where Z → ℓ + ℓ − with ℓ = e or μ. The search is performed using a sample of proton-proton (pp) collision data at a center-of-mass energy of 13 TeV, recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 138 fb − 1 . Events are assigned to mutually exclusive categories, which exploit differences in both event topology and kinematics of distinct Higgs production mechanisms to enhance signal sensitivity. The signal strength μ , defined as the product of the cross section and the branching fraction $$ \left[\sigma \left(\textrm{pp}\to \textrm{H}\right)\mathcal{B}\left(\textrm{H}\to \textrm{Z}\upgamma \right)\right] $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mfenced><mml:mrow><mml:mi>σ</mml:mi><mml:mfenced><mml:mrow><mml:mi>pp</mml:mi><mml:mo>→</mml:mo><mml:mi>H</mml:mi></mml:mrow></mml:mfenced><mml:mi>B</mml:mi><mml:mfenced><mml:mrow><mml:mi>H</mml:mi><mml:mo>→</mml:mo><mml:mi>Zγ</mml:mi></mml:mrow></mml:mfenced></mml:mrow></mml:mfenced></mml:math> relative to the standard model prediction, is extracted from a simultaneous fit to the ℓ + ℓ − γ invariant mass distributions in all categories and is measured to be μ = 2 . 4 ± 0 . 9 for a Higgs boson mass of 125.38 GeV. The statistical significance of the observed excess of events is 2.7 standard deviations. This measurement corresponds to $$ \left[\sigma \left(\textrm{pp}\to \textrm{H}\right)\mathcal{B}\left(\textrm{H}\to \textrm{Z}\upgamma \right)\right]=0.21\pm 0.08 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mfenced><mml:mrow><mml:mi>σ</mml:mi><mml:mfenced><mml:mrow><mml:mi>pp</mml:mi><mml:mo>→</mml:mo><mml:mi>H</mml:mi></mml:mrow></mml:mfenced><mml:mi>B</mml:mi><mml:mfenced><mml:mrow><mml:mi>H</mml:mi><mml:mo>→</mml:mo><mml:mi>Zγ</mml:mi></mml:mrow></mml:mfenced></mml:mrow></mml:mfenced><mml:mo>=</mml:mo><mml:mn>0.21</mml:mn><mml:mo>±</mml:mo><mml:mn>0.08</mml:mn></mml:math> pb. The observed (expected) upper limit at 95% confidence level on μ is 4.1 (1.8), where the expected limit is calculated under the background-only hypothesis. The ratio of branching fractions $$ \mathcal{B}\left(\textrm{H}\to \textrm{Z}\upgamma \right)/\mathcal{B}\left(\textrm{H}\to \upgamma \upgamma \right) $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>B</mml:mi><mml:mfenced><mml:mrow><mml:mi>H</mml:mi><mml:mo>→</mml:mo><mml:mi>Zγ</mml:mi></mml:mrow></mml:mfenced><mml:mo>/</mml:mo><mml:mi>B</mml:mi><mml:mfenced><mml:mrow><mml:mi>H</mml:mi><mml:mo>→</mml:mo><mml:mi>γγ</mml:mi></mml:mrow></mml:mfenced></mml:math> is measured to be $$ {1.5}_{-0.6}^{+0.7} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mn>1.5</mml:mn><mml:mrow><mml:mo>−</mml:mo><mml:mn>0.6</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo><mml:mn>0.7</mml:mn></mml:mrow></mml:msubsup></mml:math> , which agrees with the standard model prediction of 0 . 69 ± 0 . 04 at the 1.5 standard deviation level.