Resolving combinatorial ambiguities in dilepton $t\overline{t}$ event topologies with constrained $M_2$ variables

Journal Article · 09 October 2017 · Physical Review D

DOI: https://doi.org/10.1103/physrevd.96.076005 · OSTI ID:1398745

Debnath, Dipsikha ^[1]; Kim, Doojin ^[2]; Kim, Jeong Han ^[3]; Kong, Kyoungchul ^[4]; Matchev, Konstantin T. ^[1]

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1. Univ. of Florida, Gainesville, FL (United States). Physics Dept.
2. European Organization for Nuclear Research (CERN), Geneva (Switzerland). Theory Dept.
3. Univ. of Kansas, Lawrence, KS (United States). Dept. of Physics and Astronomy
4. Univ. of Kansas, Lawrence, KS (United States). Dept. of Physics and Astronomy; Univ. of Pittsburgh, PA (United States). Pittsburgh Particle Physics, Astrophysics, and Cosmology Center. Dept. of Physics and Astronomy

We advocate the use of on-shell constrained $${M}_{2}$$ variables in order to mitigate the combinatorial problem in supersymmetry-like events with two invisible particles at the LHC. We show that in comparison to other approaches in the literature, the constrained $${M}_{2}$$ variables provide superior ansätze for the unmeasured invisible momenta and therefore can be usefully applied to discriminate combinatorial ambiguities. We illustrate our procedure with the example of dilepton $$t\overline{t}$$ events. We critically review the existing methods based on the Cambridge $${M}_{T2}$$ variable and MAOS reconstruction of invisible momenta, and show that their algorithm can be simplified without loss of sensitivity, due to a perfect correlation between events with complex solutions for the invisible momenta and events exhibiting a kinematic endpoint violation. Then we demonstrate that the efficiency for selecting the correct partition is further improved by utilizing the $${M}_{2}$$ variables instead. Finally, we also consider the general case when the underlying mass spectrum is unknown, and no kinematic endpoint information is available.

• Research Organization: Univ. of Kansas, Lawrence, KS (United States); Univ. of Florida, Gainesville, FL (United States); European Organization for Nuclear Research (CERN), Geneva (Switzerland)
• Sponsoring Organization: USDOE Office of Science (SC), High Energy Physics (HEP); USDOE
• Grant/Contract Number: SC0007863; FG02-12ER41809; SC0010296
• OSTI ID: 1398745
• Alternate ID(s): OSTI ID: 1498897
• Journal Information: Physical Review D, Vol. 96, Issue 7; ISSN 2470-0010
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English