Search for pair production of heavy resonances in final states with a photon and large-radius jets in proton-proton collisions at $\sqrt{s}$ = 13 TeV

Abstract

A search for the pair production of heavy spin-1/2 or spin-3/2 resonances (t$^*$) in proton-proton collisions at $\sqrt{s}$ = 13 TeV is presented. Data collected with the CMS detector at the CERN LHC from 2016 to 2018 corresponding to an integrated luminosity of 138 fb$^{-1}$ are used. The analysis targets benchmark signal scenarios where one t$^*$ decays into a top quark (t) and a photon ($γ$), and the other into a t quark and a gluon (g), i.e., pp $\to$ t$^*\bar{\mathrm{t}}^*$ $\to$ tt$γ$g. All-hadronic final states from the t pair decay chain are selected using jet substructure techniques. The signal is probed as a function of the t$^*$ candidate mass, which is reconstructed using the photon and a top quark candidate jet. No significant deviation from the background-only hypothesis is found. Observed (expected) upper limits on the signal cross section at 95% confidence level are set, excluding masses of spin-1/2 t$^*$ particles below 930 (930) GeV and spin-3/2 t$^*$ particles below 1330 (1390) GeV. This analysis marks the first search for heavy resonances in the $\mathrm{t\bar{t}}γ$g channel. Exploiting the high-energy photon to reduce the backgrounds, this search achieves sensitivity competitive with pp $\to$ t$^*\mathrm{\bar{t}}^*$ $\to$ $\mathrm{t\bar{t}}γ$g searches for spin-1/2 t$^*$ despite the small expected t$^*$ $\to$ t$γ$ branching fraction.

Figures (5)

• Figure 1: Representative LO Feynman diagram for pair production of $\mathup{{{{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {*}}}$ in the ${ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{ \overline{ {{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\upgamma}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{g}}{} _{ {}} ^{ {}}} }\xspace$ channel.
• Figure 2: Shape comparison of the $m_{{ \mathup{{{\upgamma}}{} _{ {}} ^{ {}}} }\xspace\text{j}_{1}}$ distribution for $\mathup{{{{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {*}}} \xspace \mathup{{ \overline{ { \mathup{{{{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {*}}} \xspace}}}{} _{ {}} ^{ {}}} \xspace\xspace$ signal events generated at different $m_{ \mathup{{{{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {*}}} \xspace}$, for the spin-$1/2$ (solid) and spin-$3/2$ (dashed) cases.
• Figure 3: The photon (left) and j$_1$ (right) $p_{\mathrm{T}}$ distributions in SR (upper), VR1 (middle), and VR2 (lower) are presented for data and expected backgrounds. Statistical and systematic uncertainties in the expected background yields are depicted by the hatched bands. Additionally, the simulated signal distributions for spin-$1/2$ and spin-$3/2$$\mathup{{{{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {*}}} \xspace$ with a mass of 900$\,\text{Ge\spaceV}$ are overlaid for comparison, with both samples normalized to a cross section of 10$\text{\,fb}$. The last bins include the overflow. The lower panels show the ratio of the data to the total SM background, with the total uncertainties indicated by the shaded gray band.
• Figure 4: The background-only postfit $m_{{ \mathup{{{\upgamma}}{} _{ {}} ^{ {}}} }\xspace\text{j}_{1}}\xspace$ distributions for the SR (left) and VR1 (right) are shown. Notations are as in Fig. \ref{['kin1']}.
• Figure 5: The expected (red solid lines) and the observed (black solid lines) 95% $\text{CL}$ upper limits on the cross section of the ${ \mathup{{{p}}{} _{ {}} ^{ {}}} }\xspace { \mathup{{{p}}{} _{ {}} ^{ {}}} }\xspace \to \mathup{{{{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {*}}} \xspace \mathup{{ \overline{ { \mathup{{{{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {*}}} \xspace}}}{} _{ {}} ^{ {}}} \xspace \to { \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{ \overline{ {{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\upgamma}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{g}}{} _{ {}} ^{ {}}} }\xspace\xspace$ process as functions of the $m_{ \mathup{{{{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {*}}} \xspace}$ for a spin-$1/2$ (left) and spin-$3/2$ (right) $\mathup{{{{ \mathup{{{t}}{} _{ {}} ^{ {}}} }\xspace}}{} _{ {}} ^{ {*}}} \xspace$. The blue (inner) and yellow (outer) bands indicate the 68% and 95% coverage of the expected upper limits. The black dashed lines indicate the theoretical expectations Alhazmi:2018whk