Dark photons from charm mesons at LHCb

• Main Authors: Thaler, Jesse (Contributor), Xue, Wei (Contributor), Ilten, Philip James (Contributor), Williams, Michael (Contributor)
• Other Authors: Massachusetts Institute of Technology. Center for Theoretical Physics (Contributor), Massachusetts Institute of Technology. Department of Physics (Contributor), Massachusetts Institute of Technology. Laboratory for Nuclear Science (Contributor)
• Format: Article
• Language: English
• Published: American Physical Society, 2016-01-07T03:03:08Z.
• Subjects: Article
• Online Access: Get fulltext

 We propose a search for dark photons A[superscript '] at the LHCb experiment using the charm meson decay D[superscript *](2007)[superscript 0] → D[superscript 0]A[superscript ']. At nominal luminosity, D[superscript *0] → D[superscript 0]γ decays will be produced at about 700 kHz within the LHCb acceptance, yielding over 5 trillion such decays during Run 3 of the LHC. Replacing the photon with a kinetically mixed dark photon, LHCb is then sensitive to dark photons that decay as A[superscript '] → e[superscript +]e[superscript -]. We pursue two search strategies in this paper. The displaced strategy takes advantage of the large Lorentz boost of the dark photon and the excellent vertex resolution of LHCb, yielding a nearly background-free search when the A[superscript '] decay vertex is significantly displaced from the proton-proton primary vertex. The resonant strategy takes advantage of the large event rate for D[superscript *0] → D[superscript 0]A[superscript '] and the excellent invariant-mass resolution of LHCb, yielding a background-limited search that nevertheless covers a significant portion of the A[superscript '] parameter space. Both search strategies rely on the planned upgrade to a triggerless-readout system at LHCb in Run 3, which will permit the identification of low-momentum electron-positron pairs online during data taking. For dark photon masses below about 100 MeV, LHCb can explore nearly all of the dark photon parameter space between existing prompt-A[superscript '] and beam-dump limits.