MUSE Status Report
Evangeline J. Downie
On behalf of the MUSE Collaboration
The George Washington University
Washington DC, USA
Award DE-SC0012485
Awards PHY-1309130 & 1314148
The Proton Charge Radius

2010: Muonic hydrogen spectroscopy

Inconsistent with the electron measurements

Charge radius 7σ smaller than CODATA value
Uncertainty on μ / e radius difference
~0.005 fm
 New experiments planned / underway:
➔Excitation spectrum 3,4He (CREMA)
➔Low q2 e- scattering Jlab / Mainz
➔Muon scattering on proton (MUSE) at PSI
(μ+/μ-, e+e-)
MUSE Experiment
rp(fm)
ep
spectroscopy
0.877±0.007
scattering
0.875±0.006
mp
0.841±0.0004
?
Simultaneous measurement of e+/μ+ e-/μ- at beam momenta of
115, 153, 210 MeV/c in πM1 channel at PSI allows:

➔Determination
➔Test
of two-photon effects
of lepton universality
➔Simultaneous
scattering
determination of proton radius in both ep and μp
MUSE Experiment
θ ≈ 20o – 100o
Q2 ≈ 0.002 - 0.07 GeV2
5 MHz total beam flux
≈ 2-15% μ's
≈ 10-98% e's
≈ 0-80% π's

Low beam flux
➔ Large

angle, non-magnetic detectors
Secondary beam
➔ Tracking

of beam particles to target
Mixed beam
➔ Identification
of beam particle in trigger
Timeline Since BVR 46

February 9-11, 2015: BVR 46

Three test runs: June; July/Aug; December 2015

July 2, 2015: Internal review at JLab

July 22 & 24, 2015: Workshop at PSI with Peter Kammel,
Klaus Kirch, Alexey Stoykov, Ueli Straumann

Oct 8-9, 2015: MUSE collaboration meeting, GWU

Nov 13, 2015: NSF proposal submitted

January 7, 2016: revised TDR to NSF

Feb 1-2, 2016: NSF Technical Review

Feb 8-10, 2016: BVR 47
Silicon PM Scintillator Detector (TAU / Rutgers)
→
+
beam Cerenkov
(Albrow et al
Fermilab design)
for timing
SciFi for
triggering &
GEM correlation
SiPM plus thin
plastic scintillator
PSI readout
(prototype)

Thanks to advice and assistance by Alexey Stoykov

Timing almost as good as beam Cerenkov

Spatial resolution almost as good as SciFi

Replaces both with less material in beam
Silicon PM Scintillator Detector
Setup in pM1for initial prototype tests
Silicon PM Scintillator Detector

99.9 % efficiency achieved

<100 ps time resolution achieved

Multiple configurations tested

Work with Alexey Stoykov
Beam & Scattered Particle Tracking / Identification
GEM Chambers (Hampton)

Demonstrated > 98% efficiency in πM1
beam tests
Target (GWU)

Conceptual designs completed

Enhanced target cell design in progress
Straw Tube Tracker (HUJI / Temple)

First half-chamber completed

Noise suppression in progress
Trigger Scintillators (USC)

55 ps resolution achieved

Final full-sized configuration tested
Back Wall Scintillator Time Resolution
55 ps average resolution
Readout
● after splitting
 without splitting
 copy resolution
Relative timing test,
s = 32 ps
DAQ system (GWU & MC)

Multiple TRB3s running in synch with VMEs

Inter-TRB3 synch issues resolved
Trigger (Rutgers, Krakow, GW)

Trigger splitter time resolution tested

No significant difference in time resolution
Recent Results
Top:

Geant 4 sims tuned to match
measured beam parameters
Left:

Neural net seperates muon
scattering from muon decay
reactions
TOF Beam Momentum Measurement
tsimulation – texperiment = D(tXcm - t0cm)
In the simulation
✔ Use
realistic beam profile
✔ Match
to experimental time resolution
✔ Match
to experimental particle flux
TOF Beam Momentum Measurement
Consistent beam momenta
were extracted from muon
and pion spectra
e
μ
Good agreement between simulation and data,
no evidence of beam tail from collimation
p(p) ≈ p(μ) with dp / p < 0.3%
Preliminary results meet specifications
π
Simulated Empty Target Subtraction
Simulated Empty Target Subtraction
Physics

Uncertainty on radius difference
~0.005 fm

Extract radius from ep and
μp form factors
MUSE will:
➔ Verify
➔ Compare
form factors
➔ Compare
cross sections
➔ Measure
two-photon
effects
➔ Solve
Uncertainty on radius with
m & e combined ~0.007 fm
1
the effect
the PRP?
Thank you to PSI & all of our expert consultants!
1
Thank you for your attention!
1
MUSE Main Systematic Uncertainties
Scintillator efficiency
0.1%
Solid angle
0.1%
Beam momentum
offset
0.1%
Theta offset
0.2%
Multiple scattering
0.15%
Muon decay in flight
Radiative corrections
0.1%
0.1% m; 0.5% e
Target wall subtraction
0.3%
Beam PID mis-ID
0.1%

MUSE measuring relative cross sections

Point-to-point uncertainties most important

Uncertainties mostly well controlled: largest from angle and radiative
corrections.

3 mom. x 2 pol. x 2 independent detectors → consistency check

Multiple calibration measurements / simulations planned