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    Search for a scalar partner of the top quark in the all-hadronic tt¯ plus missing transverse momentum final state at √s=13 TeV with the ATLAS detector

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    Author
    Aad, G; Abbott, B; Abbott, DC; Abud, AA; Abeling, K; Abhayasinghe, DK; Abidi, SH; AbouZeid, OS; Abraham, NL; Abramowicz, H; ...
    Date
    2020-08-01
    Source Title
    European Physical Journal C: Particles and Fields
    Publisher
    Springer Science and Business Media LLC
    University of Melbourne Author/s
    Urquijo, Phillip; Barberio, Luigia; Taylor, Geoffrey; Milesi, Marco; Ungaro, Francesca Consiglia; Shojaii, Seyed Ruhollah
    Affiliation
    School of Physics
    Metadata
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    Document Type
    Journal Article
    Citations
    Aad, G., Abbott, B., Abbott, D. C., Abud, A. A., Abeling, K., Abhayasinghe, D. K., Abidi, S. H., AbouZeid, O. S., Abraham, N. L., Abramowicz, H., Abreu, H., Abulaiti, Y., Acharya, B. S., Achkar, B., Adam, L., Adam Bourdarios, C., Adamczyk, L., Adamek, L., Adelman, J. ,... Arcangeletti, C. (2020). Search for a scalar partner of the top quark in the all-hadronic tt¯ plus missing transverse momentum final state at √s=13 TeV with the ATLAS detector. European Physical Journal C, 80 (8), pp.737-. https://doi.org/10.1140/epjc/s10052-020-8102-8.
    Access Status
    Open Access
    URI
    http://hdl.handle.net/11343/252155
    DOI
    10.1140/epjc/s10052-020-8102-8
    Abstract
    <jats:title>Abstract</jats:title> <jats:p>A search for direct pair production of scalar partners of the top quark (top squarks or scalar third-generation up-type leptoquarks) in the all-hadronic <jats:inline-formula><jats:alternatives><jats:tex-math>$$t{\bar{t}}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>t</mml:mi><mml:mover><mml:mrow><mml:mi>t</mml:mi></mml:mrow><mml:mrow><mml:mo>¯</mml:mo></mml:mrow></mml:mover></mml:mrow></mml:math></jats:alternatives></jats:inline-formula> plus missing transverse momentum final state is presented. The analysis of 139 <jats:inline-formula><jats:alternatives><jats:tex-math>$$\hbox {fb}^{-1}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mtext>fb</mml:mtext><mml:mrow><mml:mo>-</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msup></mml:math></jats:alternatives></jats:inline-formula> of <jats:inline-formula><jats:alternatives><jats:tex-math>$${\sqrt{s}=13}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msqrt><mml:mi>s</mml:mi></mml:msqrt><mml:mo>=</mml:mo><mml:mn>13</mml:mn></mml:mrow></mml:math></jats:alternatives></jats:inline-formula> TeV proton–proton collision data collected using the ATLAS detector at the LHC yields no significant excess over the Standard Model background expectation. To interpret the results, a supersymmetric model is used where the top squark decays via <jats:inline-formula><jats:alternatives><jats:tex-math>$${\tilde{t}} \rightarrow t^{(*)} {\tilde{\chi }}^0_1$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover><mml:mi>t</mml:mi><mml:mo>~</mml:mo></mml:mover><mml:mo>→</mml:mo><mml:msup><mml:mi>t</mml:mi><mml:mrow><mml:mo>(</mml:mo><mml:mrow /><mml:mo>∗</mml:mo><mml:mo>)</mml:mo></mml:mrow></mml:msup><mml:msubsup><mml:mrow><mml:mover><mml:mi>χ</mml:mi><mml:mo>~</mml:mo></mml:mover></mml:mrow><mml:mn>1</mml:mn><mml:mn>0</mml:mn></mml:msubsup></mml:mrow></mml:math></jats:alternatives></jats:inline-formula>, with <jats:inline-formula><jats:alternatives><jats:tex-math>$$t^{(*)}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mi>t</mml:mi><mml:mrow><mml:mo>(</mml:mo><mml:mrow /><mml:mo>∗</mml:mo><mml:mo>)</mml:mo></mml:mrow></mml:msup></mml:math></jats:alternatives></jats:inline-formula> denoting an on-shell (off-shell) top quark and <jats:inline-formula><jats:alternatives><jats:tex-math>$${\tilde{\chi }}^0_1$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mover><mml:mi>χ</mml:mi><mml:mo>~</mml:mo></mml:mover></mml:mrow><mml:mn>1</mml:mn><mml:mn>0</mml:mn></mml:msubsup></mml:math></jats:alternatives></jats:inline-formula> the lightest neutralino. Three specific event selections are optimised for the following scenarios. In the scenario where <jats:inline-formula><jats:alternatives><jats:tex-math>$$m_{{\tilde{t}}}&gt; m_t+m_{{\tilde{\chi }}^0_1}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>m</mml:mi><mml:mover><mml:mi>t</mml:mi><mml:mo>~</mml:mo></mml:mover></mml:msub><mml:mo>&gt;</mml:mo><mml:msub><mml:mi>m</mml:mi><mml:mi>t</mml:mi></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>m</mml:mi><mml:msubsup><mml:mrow><mml:mover><mml:mi>χ</mml:mi><mml:mo>~</mml:mo></mml:mover></mml:mrow><mml:mn>1</mml:mn><mml:mn>0</mml:mn></mml:msubsup></mml:msub></mml:mrow></mml:math></jats:alternatives></jats:inline-formula>, top squark masses are excluded in the range 400–1250 GeV for <jats:inline-formula><jats:alternatives><jats:tex-math>$${\tilde{\chi }}^0_1$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mover><mml:mi>χ</mml:mi><mml:mo>~</mml:mo></mml:mover></mml:mrow><mml:mn>1</mml:mn><mml:mn>0</mml:mn></mml:msubsup></mml:math></jats:alternatives></jats:inline-formula> masses below 200 GeV at 95% confidence level. In the situation where <jats:inline-formula><jats:alternatives><jats:tex-math>$$m_{{\tilde{t}}}\sim m_t+m_{{\tilde{\chi }}^0_1}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>m</mml:mi><mml:mover><mml:mi>t</mml:mi><mml:mo>~</mml:mo></mml:mover></mml:msub><mml:mo>∼</mml:mo><mml:msub><mml:mi>m</mml:mi><mml:mi>t</mml:mi></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>m</mml:mi><mml:msubsup><mml:mrow><mml:mover><mml:mi>χ</mml:mi><mml:mo>~</mml:mo></mml:mover></mml:mrow><mml:mn>1</mml:mn><mml:mn>0</mml:mn></mml:msubsup></mml:msub></mml:mrow></mml:math></jats:alternatives></jats:inline-formula>, top squark masses in the range 300–630 GeV are excluded, while in the case where <jats:inline-formula><jats:alternatives><jats:tex-math>$$m_{{\tilde{t}}}&lt; m_W+m_b+m_{{\tilde{\chi }}^0_1}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>m</mml:mi><mml:mover><mml:mi>t</mml:mi><mml:mo>~</mml:mo></mml:mover></mml:msub><mml:mo>&lt;</mml:mo><mml:msub><mml:mi>m</mml:mi><mml:mi>W</mml:mi></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>m</mml:mi><mml:mi>b</mml:mi></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>m</mml:mi><mml:msubsup><mml:mrow><mml:mover><mml:mi>χ</mml:mi><mml:mo>~</mml:mo></mml:mover></mml:mrow><mml:mn>1</mml:mn><mml:mn>0</mml:mn></mml:msubsup></mml:msub></mml:mrow></mml:math></jats:alternatives></jats:inline-formula> (with <jats:inline-formula><jats:alternatives><jats:tex-math>$$m_{{\tilde{t}}}-m_{{\tilde{\chi }}^0_1}\ge 5$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>m</mml:mi><mml:mover><mml:mi>t</mml:mi><mml:mo>~</mml:mo></mml:mover></mml:msub><mml:mo>-</mml:mo><mml:msub><mml:mi>m</mml:mi><mml:msubsup><mml:mrow><mml:mover><mml:mi>χ</mml:mi><mml:mo>~</mml:mo></mml:mover></mml:mrow><mml:mn>1</mml:mn><mml:mn>0</mml:mn></mml:msubsup></mml:msub><mml:mo>≥</mml:mo><mml:mn>5</mml:mn></mml:mrow></mml:math></jats:alternatives></jats:inline-formula> GeV), considered for the first time in an ATLAS all-hadronic search, top squark masses in the range 300–660 GeV are excluded. Limits are also set for scalar third-generation up-type leptoquarks, excluding leptoquarks with masses below 1240 GeV when considering only leptoquark decays into a top quark and a neutrino.</jats:p>

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