Hertzog / Experiment DOE Intensity Frontier Review The g-2 Experimental Essentials David Hertzog University of Illinois  University of Washington Beam / Ring Magnetic Field Detectors / Electronics / DAQ A word on Systematics Momentum Spin e

The key ingredients to measure a  to high precision (1) Polarized muons ~97% polarized for forward decays (2) Precession proportional to ( g -2) (3) P  magic momentum = GeV/c E field doesn’t affect muon spin when  = 29.3 (4) Parity violation in the decay gives average spin direction     µ

ParameterFNAL/BNL p / fill0.25  / p 0.4  survive to ring 0.01  at magic P 50 Net0.05 The 900-m long decay beam: reduced flash; more store  /p Stored muons / POT Parameter BNL FNAL Gain FNAL/BNL Flash compared to BNL See also, M. Syphers

Benefits of a longer beamline n Reduced pion fraction that survive to ring n Permits “forward” decays (BNL was “off forward”) n Collects “all” forward muons n Eliminates “lost muon” systematic from muons born at the end of the channel having a different phase

The anomaly is obtained from three well- measured quantities

The Storage Ring exists. It will be moved to FNAL Talk by C. Polly

The Storage Ring components affect muon storage incoming muons Superconducting inflector magnet Fast Kickers Electrostatic Quadrupoles

Muons enter the ring in short bunch and spread out in predictable manner yielding key storage parameters: e + at 1 Detector  s  s “Early” “Later” g-2 Distribution of equilibrium radii

The present inflector magnet has closed ends which scatter away ~half the incoming muon beam Length = 1.7 m; Central field = 1.45 T Open end prototype, built and tested  x2 increase in stored muons As-used Closed-ended Prototype Open-ended 

Improvements in the kicker are planned because present one underkicks and pulse lasts too long. This kick affects the storage efficiency IDEAL kick  8% REAL kick  <3 % ?? 149 ns cyclotron period Kicker waveform Kicker Amplitude

We have developed a new simulation tool to guide our improvements. It includes all major subsystems Vacuum vessel Inflector Kickers Quadrupoles Collimators

Example: Collective beam motion for stored muons is reproduced The predicted horizontal and vertical betatron oscillation frequencies match measured values from E821 at the percent level.

We can simulate modified kicker pulse shapes to predict storage improvements Real LCR Kick Ideal Square Kick % stored

The  p (field) Measurement

The ± 1 ppm uniformity in the average field is obtained with special shimming tools. The dipole, quadrupole sextupole are shimmed independently 6 – 9 months required with cryogenics and ring on / off and in stable operating mode

Improvement of Field by Shimming shimming At this level, one hardly needs to know the muon distribution

Absolute Calibration Probe: a Spherical Water Sample Electronics, Computer & Communication Position of NMR Probes The magnetic field is measured and controlled using pulsed NMR and the free-induction decay Fixed Probes in the walls of the vacuum tank Trolley with matrix of 17 NMR Probes

The  a (precession) and EDM Measurements

An “event” is an isolated positron above a threshold. e+e+ digitized samples N A NA 2 =0.4

An “event” is an isolated positron above a threshold. e+e+ digitized samples

Traditional method of determining  a is to plot Number of events above threshold vs. Time Event Method Geant N A NA 2 =0.4 Here, Asym is the average asymmetry of events above energy threshold cut

A complementary (integrating) method of determining  a is to plot Energy vs. Time Event Method Geant Energy Method Same GEANT simulation We will operate this mode in parallel to above

Parasitic Muon EDM Measurement using straw tube arrays The EDM tips the precession plane, producing an up-down oscillation with time (out of phase with  a ) BNL statistics limited u 1 tracking station u Late turn-on time u Small acceptance u Ran 2 out of 3 years FNAL: many stations, long runs, expect ~10,000 x the events See: B. Casey in “extra” materials Technique: Measure up-going / down-going tracks vs. time, (modulo g-2):

Detector systems n Calos: time and energy of decays n Hodoscopes: beam profiles, calo seeds, muon loss monitor n In-vacuum Straws: stored muon profile & independent EDM measurement Hodoscope hodoscope CALO e+e+ X E821

New W/SciFi calorimeter development aimed at transverse segmentation, high density and fast response Original prototype encouraging, results in NIM New 25-channel array built and tested in beam Magnetically immune SiPMs* used on 1 channel –Excellent performance, comparable to PMTs GEANT 4 and neural-net modeling mature Lead tungstate crystal alternative being explored *a.k.a, Silicon Photomultipliers, “Geiger mode APDs, Multi-Pixel Photon Counter, …

Hertzog / Experiment DOE Intensity Frontier Review W/SciFi Calorimeter Development 17 X 0 12 cm 6 x 6 mm 2 SiPM array used on 1 channel 15 cm Brendan Chris Mandy MTest with many young physicists and students

Hertzog / Experiment DOE Intensity Frontier Review Early analysis shows promising performance of large array 1 R M = 1.7 cm  2 GeV  of elements 8.5%

Hertzog / Experiment DOE Intensity Frontier Review SiPM readout using Paul Rubinov’s custom digitizer board prototypes time Pulse area 2 GeV Example with pileup time Simple, single pulse Energy resolution same as with PMTs

Systematic error projections are in-line with statistical goal Precession Improvement vs time  Magnetic field For more details, Lee has a few slides More details in slides posted at the end of this talk To here, requires “no” improvements. To 0.07 requires some R&D

Conclusions: The experimental method is mature New challenges: –Increased rate and total data volume –Systematic error demands on “stability” –The “ring” must be put back together –It must be shimmed to even higher uniformity R&D efforts –Calorimeters –SiPMs –NMR Probe placement –Kicker waveform –Inflector opening –In-vacuum straws Simulations efforts –End-to-end beam transport –Ring dynamics –Calorimeter optimization Many young people are enjoying these development opportunities and, like us, look forward to the experiment

Backup materials

Hertzog / Experiment DOE Intensity Frontier Review Digitizers and DAQ: Basic Plan 500 MHz, 8 – 12 bit, continuous digitization on all calorimeter channels –For SiPMs, includes onboard voltage control 24 frontend computers each service one of the detector stations –High-level language control of event acceptance and formatting Built-in pileup control and diagnostic histograms We have considerable experience with these data rates and volumes for similar precision experiments (g-2, MuLan, MuCap, …)

Error due to gain shifts in the calorimeters Systematic error on  a previously ~ 0.13 ppm., goal <0.03 ppm –Gain was controlled to ~0.25%; shifts partially caused by ‘flash’ and / or PMT gating (or rate changes) –Laser calibration system was not sufficiently pulse height stable, so electron data early-to-late were used. –If gain does not oscillate at g-2 frequency, it does not correlate very much to  a –Presence of CBO leads to larger correlation to gain shift Solutions: –Reduce CBO –Lower average rates –Reduce flash –Better laser monitoring system (already demonstrated in MuLan experiment at PSI)

Coherent betatron oscillations (CBO) Focusing and defocusing of stored muon beam can lead to a systematic error in  a. –The horizontal aperture of the inflector is narrow, so the beam is focused in the horizontal direction at the time of injection. The full-aperture ‘kick’ is not fully efficient, so the average radius is off-center. As a result, the average radial position of the beam, at a fixed location in the ring, oscillates: –The acceptance of electrons depends on radius, therefore an oscillation with frequency near f CBO appears in the electron time spectrum. This leads to an error when the spectrum is fit; the closer to 2f a, the larger the error. Potential improvements: –Improve the efficiency of the full-aperture kick, so that beam does not ‘wobble –RF to reduce CBO amplitude –Add higher multipoles to wash out the CBO more rapidly –Adjust the quadrupole E-field to keep f CBO as far away from 2f a as possible.

3 categories of pileup systematics Uncertainty in pileup fraction, –~ 8% for E821, ppm error on  a. –Decreases with more statistics available to construct the pileup spectrum Uncertainty in the constructed pileup phase: –0.036 ppm –Decreases with increased statistics ‘Unseen’ pileup: (from pulses too small to be seen) –~0.026 ppm –Reduce backgrounds and use lower thresholds for pileup spectrum reconstruction In general: –A more highly segmented detector will reduce errors by about a factor of 2 – 3, and with the same rate/burst we get a similar reduction in pileup. –Increased number of beam pulses minimizes the instantaneous rate –New digitizers will operate with lower threshold and longer sampling, which greatly improves correction algorithm

What drives the detector choice? n Compact based on fixed space n Non-magnetic to avoid field perturbations Resolution is not critical for  a u Useful for pileup & gain monitoring u E821 “8%”; We propose 10% for tungsten-based calorimeter n Pileup depends on signal speed and shower separation u 4/5 events separated was goal u GEANT sim work in good shape Many more details and studies available. See also,

How was event rate obtained? Proton complex parameters and plans Compared to achieved BNL stored muon per proton rate and detailed factors for beamline differences Monte Carlo and simple calculations This is the key factor. We have calculated 11.5 so far, so we have included a “100% contingency” in estimating the beam time request to allow for something to go wrong. MARS15 model of target, beamline simulation to capture / decay pions

Electrons from g-2 ring strike calo at energy-dependent angle. T/he energy vs. average striking angle

Positron entrance angle depends on energy: low-E showers are “wider” vacuum  central radius High E Low E TOP DOWN VIEW

The New Muon (g-2) Collaboration, DOE – HEP – 5 February 2010 Precision field improvements:

Calibration of the trolley probes: 0.09 → 0.06 Issues: –position of the probes inside the trolley –uniformity of the field at the place where the trolley probes are calibrated –position of the plunging probe that transfers the calibration Solutions –better shimming of the field in the calibration point. –an indexing scheme needs to be developed that will permit us to know more accurately where the active part of the probes are inside of the trolley

The New Muon (g-2) Collaboration, DOE – HEP – 5 February 2010 Interpolation with the fixed probes: 0.07 → 0.05 Only 150 of the 370 fixed probes gave useful signals because they were near pole boundaries Need to move probes, or shim at pole boundaries, so that we have more points constantly monitoring the field. vacuum chamber pole piece beam fixed probe