Exclusive displaced hadronic signatures in the LHC forward region

Abstract

The LHCb detector provides accurate vertex reconstruction and hadronic particle identification, which make the experiment an ideal place to look for light long-lived particles (LLP) decaying into Standard Model (SM) hadrons. In contrast with the typical search strategy relying on energetic jets and a high multiplicity of tracks from the LLP decay, LHCb can identify LLPs in exclusive, specific hadronic final states. To illustrate the idea, we study the sensitivity of LHCb to an exotic Higgs decay h → SS, followed by the displaced decay of GeV-scale scalars into charged kaons S → K + K − . We show that the reconstruction of kaon vertices in narrow invariant mass windows can efficiently eliminate the combinatorial backgrounds from B-meson decays. While the same signal is extremely difficult to probe in the existing displaced jet searches at ATLAS/CMS, the LHCb search we propose can probe the branching ratio BR(h → SS) down to 0.1% (0.02%) level with 15 (300) fb −1 of data. We also apply this projected bound to two scenarios with Higgs portal couplings, where the scalar mediator S either couples to a) the SM quarks only, or b) to both quarks and leptons in the minimal flavor violation paradigm. In both scenarios we compare the reach of our proposed search with the expected constraints from ATLAS and CMS on the invisible Higgs width and with the constraints from rare B-decays studies at LHCb. We find that for 1 GeV < m S < 2 GeV and 0.5 mm cτ 10 mm our proposed search will be competitive with the ATLAS and CMS projections, while at the same time providing crucial information of the hadronic interactions of S, which can not be obtained from the indirect measurement of the Higgs invisible width.

Feebly-interacting particles: FIPs 2020 workshop report

“…This is studied in more detail in Ref. [984], where the sensitivity of LHCb to reconstruct such FIPs, produced through exotic decays of the SM Higgs boson, is studied. The main results of this study are summarized in Fig.…”

“…LHCb prospects for model independent limits on B(H → SS), assuming B(S → K + K − ) = 100% for different lifetimes and masses of the scalar S, which is the FIP in this case. Figure taken from Ref [984]…”

Prospects on searches for baryonic Dark Matter produced in $${\varvec{b}}$$-hadron decays at LHCb

“…With this, and following Refs. [19,20], we determine the smallest distance of closest approach (DOCA) to our candidates and use that to measure the isolation. The distribution of this quantity, DOCA ISO will peak at smaller quantities for background than for signal.…”

Multi-track displaced vertices at B-factories

“…LHCb only have sensitivity for LLP masses above approximately 20 GeV [101,102] because the large vertex mass can be used to efficiently reject B backgrounds, although the reconstruction of displaced resonances is possible at lower masses [51]. While it is possible for LHCb to improve on low-mass exclusive and inclusive signatures [103,104] and this merits further study, we nevertheless expect Belle II to have a unique role in covering intermediate-lifetime hidden sectors in an inclusive manner.…”