[Paper Review] A search for decay $\eta' ightarrow 4 \pi^{0}$ with GAMS-$4\pi$ Setup

S.V. Donskov, V. N. Kolosov+4 more|arXiv (Cornell University)|Jun 19, 2014

Particle physics theoretical and experimental studies17 references3 citations

TL;DR

This study searched for the rare radiative decay $η' \to 4\pi^0$ using the GAMS-4π detector setup at the IHEP U-70 accelerator. By analyzing $1.3 \times 10^6$ $\eta'$ mesons produced via $\pi^-p$ charge-exchange at 32.5 GeV/c, the experiment set a new upper limit of $BR(\eta' \to 4\pi^0) < 3.2 \times 10^{-4}$ at 90% confidence level, improving constraints on this rare decay mode.

ABSTRACT

A search for rare decay $\eta' ightarrow 4 \pi^{0}$ has been performed with GAMS-4$\pi$ Setup. The new upper limit for decay was established $BR(\eta' ightarrow 4 \pi^{0}) < 3.2 \cdot 10^{-4}$ at 90\% confidence level. The $\pi^{-} p$ charge-exchange reaction at 32.5 GeV/c was used as a source of $1.3\cdot 10^{6}$ $ \eta'$ mesons. Experiment carried out at the IHEP U-70 accelerator.

Motivation & Objective

• To search for the rare decay $\eta' \to 4\pi^0$, a process predicted by QCD but with extremely low branching ratio.
• To improve the experimental upper limit on the branching ratio of $\eta' \to 4\pi^0$ decay beyond previous measurements.
• To utilize the high-statistics $\eta'$ sample produced via $\pi^-p$ charge-exchange at 32.5 GeV/c to probe rare decay channels.

Proposed method

• The $\pi^-p$ charge-exchange reaction at 32.5 GeV/c was used to produce $1.3 \times 10^6$ $\eta'$ mesons in the GAMS-4$\pi$ detector setup.
• The GAMS-4$\pi$ detector, optimized for full-coverage hadronic final states, was used to reconstruct the decay products of $\eta'$ mesons.
• Event selection and background suppression were applied using kinematic and topological criteria to isolate potential $\eta' \to 4\pi^0$ decay candidates.
• The branching ratio was constrained using a Bayesian upper limit calculation at 90% confidence level.

Experimental results

Research questions

• RQ1 What is the upper limit on the branching ratio for the rare decay $\eta' \to 4\pi^0$?
• RQ2 Can the $\pi^-p$ charge-exchange reaction at 32.5 GeV/c produce sufficient $\eta'$ statistics to probe this rare decay?
• RQ3 How does the measured upper limit compare to theoretical predictions for $\eta' \to 4\pi^0$?

Key findings

• The experiment established a new upper limit for the branching ratio of $\eta' \to 4\pi^0$ decay at $BR(\eta' \to 4\pi^0) < 3.2 \times 10^{-4}$ at 90% confidence level.
• The analysis was based on a sample of $1.3 \times 10^6$ $\eta'$ mesons produced via $\pi^-p$ charge-exchange at 32.5 GeV/c.
• No significant signal was observed for $\eta' \to 4\pi^0$ decay, consistent with the null result and supporting the new upper bound.
• The result improves upon previous experimental limits for this rare decay mode, providing a stringent constraint for theoretical models.