[Paper Review] Simulated Detector Performance at the Muon Collider

N. Bartosik, K. Krizka+69 more|arXiv (Cornell University)|Mar 15, 2022

Particle Detector Development and Performance4 citations

TL;DR

This paper evaluates the performance of a detector design for a muon collider under intense beam-induced background (BIB) conditions, using full simulation and reconstruction with the Pandora algorithm. It demonstrates high reconstruction efficiency (>85% for pT > 80 GeV) and good momentum resolution, while proposing large-angle muon Bhabha scattering as a viable luminosity measurement method with a statistical uncertainty of 0.2% at 1.5 TeV.

ABSTRACT

In this paper we report on the current status of studies on the expected performance for a detector designed to operate in a muon collider environment. Beam-induced backgrounds (BIB) represent the main challenge in the design of the detector and the event reconstruction algorithms. The current detector design aims to show that satisfactory performance can be achieved, while further optimizations are expected to significantly improve the overall performance. We present the characterization of the expected beam-induced background, describe the detector design and software used for detailed event simulations taking into account BIB effects. The expected performance of charged-particle reconstruction, jets, electrons, photons and muons is discussed, including an initial study on heavy-flavor jet tagging. A simple method to measure the delivered luminosity is also described. Overall, the proposed design and reconstruction algorithms can successfully reconstruct the high transverse-momentum objects needed to carry out a broad physics program.

Motivation & Objective

• To assess the feasibility of high-precision particle reconstruction in a muon collider environment dominated by beam-induced background (BIB).
• To evaluate the performance of a detector design with shielding and particle flow reconstruction in mitigating BIB effects.
• To propose and validate a luminosity measurement method based on large-angle muon Bhabha scattering at high center-of-mass energy.
• To quantify reconstruction efficiency and momentum resolution for charged particles, jets, electrons, muons, and photons under realistic BIB conditions.
• To demonstrate the potential for tagging heavy-flavor jets and achieving precise luminosity measurement using simulated data.

Proposed method

• Simulated muon collider events at √s = 1.5 TeV using Pythia for initial state generation.
• Full detector simulation with detailed modeling of beamline components and shielding near the interaction point.
• Reconstruction of particles using the Pandora Particle Flow algorithm to reconstruct tracks, energy deposits, and jets.
• Application of a custom track reconstruction algorithm (CT) with optimized ∆Rt parameter to handle high-curvature tracks and barrel-endcap transition regions.
• Luminosity measurement via large-angle muon Bhabha scattering (µ⁺µ⁻ → µ⁺µ⁻) with angular and pT selection cuts: 30° < θ < 150°, pT > 130 GeV, ∆θ > 3.08 rad, and Mµµ ∈ (1440, 1560) GeV.
• Statistical uncertainty on luminosity estimated from 10⁷ seconds of data at L = 1.25×10³⁴ cm⁻²s⁻¹, assuming theoretical cross-section uncertainty is the dominant error source.

Experimental results

Research questions

• RQ1 Can a detector design with shielding effectively reconstruct key physics objects under extreme beam-induced background at a muon collider?
• RQ2 What is the achievable reconstruction efficiency and momentum resolution for muons and jets in the presence of BIB?
• RQ3 How does the beam-induced background affect track reconstruction, particularly in the barrel-endcap transition region?
• RQ4 Can large-angle muon Bhabha scattering serve as a precise luminosity measurement method at high-energy muon colliders?
• RQ5 What are the dominant sources of inefficiency in muon reconstruction at low transverse momentum, and how can they be mitigated?

Key findings

• Muon reconstruction efficiency exceeds 85% for transverse momentum above 80 GeV in the central region (15° < θ < 165°), with drops at low pT due to challenges in the barrel-endcap transition region.
• The muon transverse momentum resolution remains comparable to that achieved without BIB, with only a few percent degradation due to BIB in the endcaps.
• Track reconstruction efficiency shows dips at θ ≈ 52° and 132° due to mixed barrel-endcap hits, and at θ < 15° and >165° due to algorithmic limitations in the CT method.
• The large-angle muon Bhabha scattering method achieves a statistical uncertainty of 0.2% on luminosity at √s = 1.5 TeV over one year of data taking.
• Beam-induced background effects are negligible in the selected angular region (30° < θ < 150°), validating the use of muon Bhabha as a luminosity monitor.
• The method's total uncertainty depends critically on the theoretical precision of the high-energy, large-angle µ-Bhabha cross section, which requires further theoretical development.