g-2 accelerator and cryo needs Mary Convery Muon Campus Review 1/23/13

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The anomolous magnetic moment and g-2 g  2 but higher-order corrections – QED, EW, hadronic, new physics? 3 proposed exp. precision Currently ~3  discrepancy between theory and experiment New muon g-2 experiment at Fermilab expected precision could yield ~5 

Measuring g-2 4 g = 2 g > 2

5 Magic momentum One more trick: – Polarized muons in storage ring with vertical focusing by electrical quadrupole field – At magic momentum p  = GeV/c (  = 29.3), g-2 precession frequency  a independent of electric field

6 Distribution of decay electrons as function of time Intensity at a single detector station shortly after injection Phys. Rev. D73 (2006)

g-2 apparatus Reusing storage ring from BNL g-2 experiment New calorimeters and straw-tube tracking 7

Planned improvements Rebunch high-intensity beam into multiple bunches to lower the instantaneous rate Increase the detector segmentation to reduce the instantaneous rate in a given cell Modify secondary beamlines to store as many muons from pion decays as possible Remove pions and protons from muon beam to prevent hadronic flash in calorimeters – Allows analysis of more (earlier) decay e+ – Longer beamline for pion decay – Let heavier protons separate in time from pions/muons and kick them out Improve beam dynamics in storage ring Improve storage ring field uniformity and the measurement and calibration system 8

g-2 schedule Preparing for CD1 review this spring MC1 building complete early FY14 g-2 storage ring ships early FY14 Ring reassembly starting FY14 Cryo ready to cool ring early FY15 Ring magnetic field shimming starting mid FY15 Recycler and Muon beamline work FY14-15 New beamline enclosure beneficial occupancy mid FY15 Beam to g-2 early

Protons on target 4x10 20 POT in two-year running period in order to detect at least 1.8x10 11 e + from  + decay in the g-2 storage ring Minimize pile-up of multiple e + in a single detector channel by keeping single pulse <~10 12 POT Time between beam pulses > 10ms for DAQ Bunch length less than revolution time of muons around storage ring (149ns) 10

Estimation of POT needed

Secondary beam Create 3.1 GeV secondary pions off a target – forward decay kinematics require p  =1.005p  Capture GeV (“magic momentum” muons) Increase muon flux by accepting pions with momentum ±2%, small  functions to reduce pion beam size so that muons with larger decay angles accepted – Needed in decay region, i.e. most important in beamline immediately downstream of target (M2 line) Beamline long enough for ~all pions to decay in order to maximize number of muons Aim for beamline acceptance of 40  mm mrad 12

Hadronic flash Long enough beamline for ~all pions to decay in order to minimize pions into storage ring Prevent secondary protons from making it into storage ring 13

Correlation between spin angle and muon momentum Pion decays in straight sections give no correlations, by symmetry Pion decays in regions with non-zero dispersion do give correlations Want to minimize and/or be able to calculate systematic effects Limit momentum spread of beam Systematic effects 14

Lost muons systematic effect Muons in g-2 storage ring may be lost before decaying, depending on where they are in phase space If average spin direction of “lost muon” sample is different than that of “muon decay” sample, this introduces a systematic error on the measurement 1) If muons born in the Delivery Ring fill phase space differently from straight section born muons, different lost muon vs time in the muon storage ring for DR and straight-section born muons 2) Muons born in the DR have different average spin direction because the muon spin precesses in the DR, but the pion spin doesn’t (no spin) Effect = 1) x 2) “Average bending field of DR is about one tenth that of the muon storage ring dipole magnetic field. This helps a lot. In fact, skipping the DR might give a larger lost muon systematic error, due to more pion decays in the muon storage ring!” 15

Differential decay systematic effect 16 Low momentum muons decay earlier on average than high momentum muons –  lab =  0 If high and low momentum muons have different average spin direction, then average spin direction changes with time in storage ring, which leads to a mis-measurement of the spin precession rate Correct for effect due to turns in Delivery Ring, estimates suggest ~10 turns is small enough effect

Summary table of accelerator requirements 17

g-2 storage ring magnet 18

g-2 ring superconducting coils / cryostats 19

Cryo Refrigeration plant will be built by Fermilab Accelerator Division using AIP funds Design should provide two dedicated refrigeration systems for g-2 AD Cryo system design should include a method to trap contamination AD to provide Transfer Line for LHe and LN2 to the g-2 Hall liter Liquid Helium dewar from BNL g-2 expectations for cryogenics

21 Compressor System Refrigeration Plant Experimental Hall g-2 cryogenic system at BNL

g-2 Cryo Requirements FLUIDPRESSURESTATE FLOWRATE normal operations Liquid Helium28 psiasaturated liquid25 g/s Helium Vapor Return21 psiacold vapor23.6 g/s Helium Gas Return - compressor suction 16 psia assumedwarm gas1.4 g/s Helium Gas - compressor discharge compressor discharge pressure warm gasincidental use Liquid Nitrogen20-25 psigsaturated liquid1.6 g/s Nitrogen Gas20-25 psigwarm gasincidental use 22 Cryogenic system requirements

23 Cryogenic heat leaks in the BNL system

Cryo schedule Cryogenics for g-2 storage ring is on critical path for g-2 Need to have ring cold in FY15 to allow ~9 months for field shimming 24

g-2 schedule priorities Critical path: – MC-1 building complete – Ship ring – Cool ring – Field shimming Advantages to completing Recycler extraction and primary beamline improvements early to commission in stages Secondary beamline, DR, extraction line work less priority 25