Abstract
Despite no new physics so far at the LHC, a $Z'$ boson with $m_{Z'} \sim 100$ GeV could still emerge via Drell-Yan (DY) production, $q \bar q \to Z' \to \mu^+ \mu^-$, in the next few years. To unravel the nature of the $Z'$ coupling, we utilize the $c$- and $b$-tagging algorithms developed by ATLAS and CMS to investigate $cg \to c Z'$ at 14 TeV LHC. While light-jet contamination can be eliminated, mistagged $b$-jets cannot be rejected in any of the tagging schemes we adopt. On the other hand, for nonzero $bbZ'$ coupling, far superior $b$-tagging could discover the $bg \to b Z'$ process, where again light-jet mistag can be ruled out, but mistagged $c$-jets cannot yet be excluded. Provided that DY production is discovered soon enough, we find that a simultaneous search for $c g \to c Z'$ and $b g \to b Z'$ can conclusively discern the nature of $Z'$ couplings involved.
Highlights
A Z0 boson with a mass of a few hundred GeV could still emerge via the Drell-Yan (DY) process, qq → Z0 → μþμ−, for qqZ0 couplings that are weaker than analogous Standard Model (SM) couplings
If a Z0 is discovered via the DY process in the few years, by combining the cZ0 and bZ0 signatures together with current limits from heavy resonance searches one can conclusively infer the nature of Z0 couplings
If a Z0 is discovered first via the pp → Z0 þ X → μþμ− þ X DY production, one could discover cg → cZ0 and bg → bZ0 processes at the HL-LHC
Summary
A Z0 boson with a mass of a few hundred GeV could still emerge via the Drell-Yan (DY) process, qq → Z0 → μþμ−, for qqZ0 couplings that are weaker than analogous Standard Model (SM) couplings. As qqZ0 coupling is constrained by searches for heavy resonances in the DY process [1], our analysis shows that in certain c-tagging schemes one can completely rule out the possibility of fake cZ0’s from light jets. In case the Z0 couples instead to b quarks (bbZ0 coupling), pp → bZ0 þ X → bμþμ− þ X (the bZ0 process) would emerge after the discovery in the DY process This process could be observed by the well-developed b-tagging algorithms [5,7,8], which provide excellent discrimination against light and c jets while maintaining high b-tagging efficiency. The analysis for the DY process is detailed in Appendix A, while normalized kinematic distributions for the signal and backgrounds of the cZ0 process are provided in Appendix B
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