# Physics Beyond Colliders Kickoff Workshop

Sep 6 – 7, 2016
CERN
Europe/Zurich timezone
There is a live webcast for this event.
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## Prospects for an experiment to measure BR(K_L to pi0nubarnu) at the CERN SPS

Sep 7, 2016, 11:40 AM
20m
500/1-001 - Main Auditorium (CERN)

72
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### Speaker

Matthew Moulson (Istituto Nazionale Fisica Nucleare Frascati (IT))

### Description

Precise measurements of the branching ratios (BRs) for the flavor-changing
neutral current decays $K\to\pi\nu\bar{\nu}$ can provide unique constraints
on CKM unitarity and, potentially, evidence for new physics. It is important
to measure both decay modes, $K^+\to\pi^+\nu\bar{\nu}$ and
$K_L\to\pi^0\nu\bar{\nu}$, since different new physics models affect the rates
for each channel differently. The NA62 experiment at the CERN SPS is currently
collecting data and should measure BR($K^+\to\pi^+\nu\bar{\nu}$) to within 10%
by 2018; there are plans to measure BR($K_L\to\pi^0\nu\bar{\nu}$) with similar
precision at a successor to the KOTO experiment at J-PARC using a low-energy
secondary beam, but no official proposal has yet been made. We are investigating
the feasibility of performing a measurement of BR($K_L\to\pi^0\nu\bar{\nu}$)
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 measurement technique is
complementary to that of KOTO Step 2 and would provide comparable sensitivity.
The mean momentum of $K_L$s decaying in the fiducial volume is 70 GeV.
This causes decay products to be 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 $K_L$
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, with an emphasis on the design challenges faced and
the sensitivity obtainable for the measurement of
BR($K_L\to\pi^0\nu\bar{\nu}$).

### Primary author

Matthew Moulson (Istituto Nazionale Fisica Nucleare Frascati (IT))