g-2 accelerator and cryo needs

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

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

4. Measuring g-2 g > 2 g = 2 • Polarized muons in magnetic field precess with Larmor spin precession frequency • Measure g-2 using cyclotron • Requires precise measurements of and of the magnetic field

5. Magic momentum • One more trick: • Polarized muons in storage ring with vertical focusing by electrical quadrupole field • At magic momentum pm = 3.094 GeV/c (g = 29.3), g-2 precession frequency wa independent of electric field

6. Measuring • Distribution of decay electrons as function of time Intensity at a single detector station shortly after injection Phys. Rev. D73 (2006) 072003

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

8. 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

9. 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 2016

10. Protons on target 4x1020 POT in two-year running period in order to detect at least 1.8x1011 e+ from m+ decay in the g-2 storage ring Minimize pile-up of multiple e+ in a single detector channel by keeping single pulse <~1012 POT Time between beam pulses > 10ms for DAQ Bunch length less than revolution time of muons around storage ring (149ns)

11. Estimation of POT needed 4 2

12. Secondary beam • Create 3.1 GeV secondary pions off a target • forward decay kinematics require pp=1.005pm • Capture 3.094 GeV (“magic momentum” muons) • Increase muon flux by accepting pions with momentum ±2%, small b 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) • Beamlinelong enough for ~all pions to decay in order to maximize number of muons • Aim for beamline acceptance of 40p mm mrad

13. 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

14. Systematic effects 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

15. 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 vstime 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!”

16. Differential decay systematic effect • Low momentum muons decay earlier on average than high momentum muons • tlab= gt0 • 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

17. Summary table of accelerator requirements

18. g-2 storage ring magnet

19. g-2 ring superconducting coils / cryostats

20. g-2 expectations for cryogenics 1000 liter Liquid Helium dewar from BNL 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

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

22. Cryogenic system requirements

23. Cryogenic heat leaks in the BNL system

24. 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

25. 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