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Boosting long lived particles searches at $μ$TRISTAN

Daniele Barducci

TL;DR

The study assesses the potential of the proposed μTRISTAN facility, operating in the asymmetric $\mu^+e^-$ mode, to probe long-lived particles from exotic Higgs decays $h\to \phi\phi$. By exploiting boosted Higgs production via vector boson fusion at $\sqrt{s}\approx 346$–$775$ GeV and placing a far detector along the beam line, the authors show that a sizable fraction of the LLP flux can be captured, enabling 95% CL limits on ${\rm BR}(h\to \phi\phi)$ in regions of large $c\tau_\phi$ that can exceed HL-LHC projections for certain $\phi$ decays. However, the μTRISTAN reach does not generally surpass the capabilities of proposed LHC far detectors such as CODEX-b, ANUBIS, and MATHUSLA. Overall, the work demonstrates a complementary LLP search channel at a $\mu^+e^-$ collider and informs detector geometry choices for maximizing sensitivity to long-lived scenarios.

Abstract

We study the prospects of the proposed $μ$TRISTAN experiment, running in the energy asymmetric $μ^+ e^-$ mode, in probing long lived particles (LLPs) arising from the decay of the Standard Model Higgs boson. We focus on the proposed runs with $\{E_{μ^+}, E_{e^-}\} = \{1\,{\rm TeV},\,30\,{\rm GeV}\}$ and $\{E_{μ^+}, E_{e^-}\} = \{3\,{\rm TeV},\,50\,{\rm GeV}\}$ and we show that, owing to the boosted nature of the produced events, a far detector placed along the beam line can collect a large fraction of the LLP flux. This allows one to set bounds on the exotic Higgs branching ratio which, for specific $φ$ decay modes, can surpass those expected at the end of the High Luminosity LHC in the regime of large LLPs proper decay lengths. On the other hand, we find that the proposed strategy will not be able to further extend the limits that might be set by proposed LHC far detectors such as CODEX-b, ANUBIS and MATHUSLA.

Boosting long lived particles searches at $μ$TRISTAN

TL;DR

The study assesses the potential of the proposed μTRISTAN facility, operating in the asymmetric mode, to probe long-lived particles from exotic Higgs decays . By exploiting boosted Higgs production via vector boson fusion at – GeV and placing a far detector along the beam line, the authors show that a sizable fraction of the LLP flux can be captured, enabling 95% CL limits on in regions of large that can exceed HL-LHC projections for certain decays. However, the μTRISTAN reach does not generally surpass the capabilities of proposed LHC far detectors such as CODEX-b, ANUBIS, and MATHUSLA. Overall, the work demonstrates a complementary LLP search channel at a collider and informs detector geometry choices for maximizing sensitivity to long-lived scenarios.

Abstract

We study the prospects of the proposed TRISTAN experiment, running in the energy asymmetric mode, in probing long lived particles (LLPs) arising from the decay of the Standard Model Higgs boson. We focus on the proposed runs with and and we show that, owing to the boosted nature of the produced events, a far detector placed along the beam line can collect a large fraction of the LLP flux. This allows one to set bounds on the exotic Higgs branching ratio which, for specific decay modes, can surpass those expected at the end of the High Luminosity LHC in the regime of large LLPs proper decay lengths. On the other hand, we find that the proposed strategy will not be able to further extend the limits that might be set by proposed LHC far detectors such as CODEX-b, ANUBIS and MATHUSLA.

Paper Structure

This paper contains 5 sections, 6 equations, 3 figures.

Table of Contents

  1. Introduction
  2. $\mu$Tristan
  3. Boosted Higgs decay
  4. Expected sensitivity
  5. Conclusions

Figures (3)

  • Figure 1: Normalised flux of $\phi$ particles as a function of the polar angle $\theta_\phi$ for $m_\phi=0.5\,$GeV (solid lines) and $m_\phi=45\,$GeV (dashed lines) at $\mu$TRISTAN$_{\mu e}$ with $\sqrt s = 346\,$GeV (blue) and $\sqrt s = 775\,$GeV (red).
  • Figure 2: Fraction of the total $\phi$ flux that can be intercepted assuming a cylindrical detector subtending an angle $\theta_{\rm max}$ for $m_\phi=0.5\,$GeV (solid lines) and $m_\phi=45\,$GeV (dashed lines) at $\mu$TRISTAN$_{\mu e}$ with $\sqrt s = 346\,$GeV (blue) and $\sqrt s = 775\,$GeV (red).
  • Figure 3: Exclusion limits at 95% CL for the low-energy (blue) and high-energy (red) runs of $\mu$TRISTAN$_{\mu e}$ with a far detector along the beam line. We fix $D=100\,$m $(150\,$m), $r=10\,$m $(7.5\,$m) and $L=70\,$m $(125\,$m) for the low-energy (high-energy) runs respectively. The shaded areas represent current limits from LHC displaced vertices searches and the solid lines indicate their projected reach at the end of the HL-LHC with $3\,$ab$^{-1}$ of integrated luminosity. Also shown as an horizontal gray line is the limit on the invisible Higgs branching ratio expected with the same dataset. The dashed, dotted and dot-dashed lines represent the limits that could be obtained by the CODEX-b, ANUBIS and MATHUSLA experiments, respectively.