Prospects for an experiment to measure at the CERN SPS

M Moulson

doi:10.1088/1742-6596/800/1/012037

Abstract

Precise measurements of the branching ratios for the decays can provide unique constraints on CKM unitarity and, potentially, evidence for new physics. It is important to measure both decay modes, and , since different new physics models affect the rates for each channel differently. We are investigating the feasibility of performing a measurement of using a high-energy secondary neutral beam at the CERN SPS in a successor experiment to NA62. The planned experiment would reuse some of the NA62 infrastructure, including possibly the NA48 liquid-krypton calorimeter. The mean momentum of mesons decaying in the fiducial volume is 70 GeV; the decay products are boosted forward, so that less demanding performance is required from the large-angle photon veto detectors. On the other hand, the layout poses particular challenges for the design of the small-angle vetoes, which must reject photons from decays escaping through the beam pipe amidst an intense background from soft photons and neutrons in the beam. We present some preliminary conclusions from our feasibility studies, summarizing the design challenges faced and the sensitivity obtainable for the measurement of .

Highlights

The K → πννdecays are flavor-changing neutral current (FCNC) processes that probe the s → dννtransition via the Z-penguin and box diagrams shown in figure 1
We are evaluating the feasibility of an experiment at the CERN SPS to measure branching ratios (BRs)(KL0 → π0νν) using a high-energy beam
The possibility of adding charged-particle tracking to the experiment, which would provide more complete final-state reconstruction for efficiency estimation and systematic control, and which would allow significant expansion of the physics program, is under investigation

Summary

Introduction

The K → πννdecays are flavor-changing neutral current (FCNC) processes that probe the s → dννtransition via the Z-penguin and box diagrams shown in figure 1. By the end of 2015, the beam power reached 42 kW; it is expected to gradually increase to 100 kW If this can be done, the experiment should reach single-event sensitivity for the SM BR by about 2019. We are evaluating the feasibility of an experiment at the CERN SPS to measure BR(KL0 → π0νν) using a high-energy beam. This makes photon vetoing significantly easier, but increases considerably the size of the detector, and in particular, the volume to be covered with photon vetoes. Running with an intensity this high would require comprehensive upgrades to the current beamline cavern and experimental area, as well as the nearly 2 km long beam transport from the extraction point in the SPS to the production target of the experiment.

LKr Cold bore

IRC SAC

Findings

Conclusions