Search for A′→μ+μ− Decays

Abstract

Searches are performed for both promptlike and long-lived dark photons, A 0 , produced in proton-proton collisions at a center-of-mass energy of 13 TeV. These searches look for A 0 → μ þ μ − decays using a data sample corresponding to an integrated luminosity of 5.5 fb −1 collected with the LHCb detector. Neither search finds evidence for a signal, and 90% confidence-level exclusion limits are placed on the γ-A 0 kinetic mixing strength. The promptlike A 0 search explores the mass region from near the dimuon threshold up to 70 GeV and places the most stringent constraints to date on dark photons with 214 < mðA 0 Þ ≲ 740 MeV and 10.6 < mðA 0 Þ ≲ 30 GeV. The search for long-lived A 0 → μ þ μ − decays places world-leading constraints on low-mass dark photons with lifetimes Oð1Þ ps.

Self-interacting dark matter without prejudice

“…5 The relevant bounds on dark photon production from the SM sector reproduced in Fig. 4 are taken from [119,[124][125][126][127][128]. Bounds from a freeze-in production of V at T > 1 MeV derived in [121] are not applied, in accordance with our assumptions.…”

“…Summary of existing constraints of the dark photon ½ϵ; m V parameter space. The various labels summarize principal detection strategies, astrophysical constraints from stellar energy loss ("stellar") [119], and diffuse γ-ray background ("diffuse") [120], from cooling of the proto-neutron star of SN1987A ("SN") [124], from beam-dump and collider experiments; see e.g., [125,126] and references therein. Hatched regions show recent exclusions derived from gamma-ray signatures from SN [127] (blue) and energy-transfer argument inside SN [128] (pink).…”

Split SIMPs with decays

“…Finally, searches in the + − final states (with = e or µ) at lepton and hadron colliders [64][65][66] rival EWPT for the best current sensitivity in the m A 8 GeV region, despite the strongly-suppressed branching ratio to SM particles of our dark photon. BaBar searched for e + e − → γA , A → ee, µµ in the mass range 0.02 GeV < m A < 10.2 GeV, using 514 fb −1 of data [64], whereas LHCb has recently searched for qq → A → µµ in the range 2m µ < m A < 70 GeV [65]. In our scenario these analyses are only competitive for m A 8 GeV, as the BaBar monophoton constraint is far stronger for smaller masses.…”

“…in the rather steep shape of the NA64 and LDMX curves. Finally, we show the current constraints derived from A → at BaBar [64] (dark yellow), as well as from A → µµ at LHCb [65] (dark red) and CMS [66] (light green). Although σ × BR ∝ ε 4 , as opposed to ε 2 for invisible final states, the strong sensitivity of the dilepton searches compensates for the suppression.…”

Reinterpretation of LHC Results for New Physics: Status and recommendations after Run 2

“…NA62 and NA64) experiments. The LHC searches include dark photon resonance searches via data scouting methods [110][111][112] with future projections [113,114], and Higgs-produced dark photon decays into prompt [115][116][117] and displaced [118] lepton-jet final states, as well as lepton-jet projections for the HL-LHC [119,120]. Along similar lines, the DarkEFT package can be used to place limits on light dark sectors interacting with the SM through a heavier off-shell mediator in an effective "fermion portal" approach [104].…”