Muon g-2 and SLAC Detector TestT-519

Momentum

Spin

e

David HertzogUniversity of Washington

wa Subset of g-2 Collaboration*

2/20

University of Washington

Cornell

University of Kentucky

University Illinois

University of VirginiaJames Madison

Shanghai Jiao Tong

*38 Institutes, 150 members

Frascati

Naples

Trieste

Pisa

Roma II

Udine

At SLAC

Three sigma is not enough to claim a discovery

BNL E821

2012 e+e- Thy

3.6 s

x10-11

Future Goals

Goal: 140 ppb

Expected Improvement

Expect to turn on in late 2016

a P5 priority

4

Ring moved to FNAL and Magnet being assembled

g-2

Why SLAC is importantWe measure muon decay to electrons 0 – 3.1 GeVDetectors must measure Energy and its Time and we must optimize them

e+

Calorimeter

Electronics

Events above threshold

Software threshold

5

Muon g-2

• Read out by SiPMs• (pixelated avalanche photodiodes run in Geiger mode)

Compact, non-magnetic calorimeters made of 54 Lead-Fluoride Cherenkov Crystals

Muon g-2

Last November: SLAC T-512

7

• 2.5 – 4 GeV e-

• SiPMs (cooled), augmented by PMTs on sides

• Digitizers for pulse shapes

3.5 GeV

Linearity

Measured resolution with limited size array

Learned how to use the beam effectively

Muon g-2

July 2014: T-519 Test 4x7 array of PbF2 crystals with SiPM readout using 2.2 – 4.5 GeV beam

8

Muon g-2

Calibration System Set Absolute Gains

Tested in Seattle 2 weeks ago and also at SLAC

9

• Laser Filter Wheel 10:90 Splitter– Source Monitor (pin diode) & PMT– Sphere or Diffuser

• 4 monitors (pin diodes, PMT)• Fiber Bundle (60; 800 mm id)

– Front plate + Focusing Lens» Crystals / SiPMs

Pulse shape

pe from laser pulses

Typical beam on detector

0 1 2 3 4 5

electrons per pulse

Usually Good small spot

But, not always so …

Linearity Beam Energy Selection

There remains an ambiguity between “requested” energy and delivered energy and an independent system that can calibrate the beam true energy (i.e., not the detector under “test”)

Now a selection of the good findings in what should be a publishable set of results

dE/E = 2.2%

3.27 GeV

1500 pe/GeV

Resolution 2.7% at 2 GeVEnergy resolution exceeds our goal by a factor of 2

Position scanning using high-quality pencil-like beam and remote XY table

Horizontal Scan (no gain correction)

Comment: Only possible with steady and high-quality beam conditions(takes many hours)

Gain stability very important for g-2Measured over 8 hours: (1.0 ± 1.4) x 10-4 / hour

Data corrected by concurrent laser calibration system

Summary• Important for g-2• Beam setup and quality critical• Great results to far

• Hope to come again with complete calorimeter and all onboard electronics and DAQ. Possibly also Straw Tracker system

• Thanks