Why Muon g-2 moved from BNL to FNAL

The driver is flux/statistics and infrastructure:

  1. Statistics. BNL's E821 final result (2004) was stats-limited at ~0.46 ppm. To push to ~0.14 ppm you need ~20× the muons. That requires a much more intense proton source than BNL's AGS delivered. FNAL's Booster → Recycler → Muon Campus chain produces dramatically more pions per cycle, hence more muons at 3.094 GeV/c.
  2. Beam purity. FNAL's long decay path (pion target → Delivery Ring → storage ring) lets almost all pions decay and removes the pion contamination that plagued BNL's shorter path. Cleaner injection, more uniform polarization.
  3. Repurposed Tevatron-era infrastructure. After Tevatron shutdown, the antiproton Debuncher ring became the Muon Campus "Delivery Ring" essentially for free. BNL would have had to build new beamlines from scratch.
  4. BNL priorities had shifted to RHIC and EIC planning; no appetite to build a new high-intensity proton source just for a g-2 upgrade.

The famous ~3000 mi "Big Move" in 2013 — the physical superconducting storage ring barged from Long Island around Florida up to Illinois — was cheaper than building a new ring. Keep the ring, change the beam feeding it.

Backlinks