MUSE: The MUon proton Scattering Experiment
Evangeline J. Downie
On behalf of the MUSE Collaboration
The George Washington University
Washington DC, USA
Award DE-SC0012485
Awards PHY-1309130 & 1314148
Motivation for Muon Scattering
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Previous e-μ Scattering Comparisons

1970's & 80's several scattering ep & mp tests


Supported universality at 10% level
Insufficient precision to test proton radius issues
Ellsworth et al. Phys. Rev. 165
(1968): form factors from elastic μp
Kostoulas et al. PRL 32 (1974) parameterization
of μp vs. ep elastic differences
no difference
3
3
Two-photon exchange tests in μp elastics
Camilleri et al. PRL 23: No evidence for two-photon exchange effects,
but very poor constraints by modern standards.

No difference between μ+p and
μ-p elastic scattering
Rosenbluth plot is linear.
4
4
MUSE Experiment
rp(fm)
ep
ratom
(fm)
p
0.8779ep
± 0.0094
(Pohl)
0.877±0.007
spectroscop
y
scattering
scattering
0.879
± 0.008
0.875±0.006
(Mainz)
0.875 ± 0.009
(JLab)
mp
mp ±
0.84087
0.00039
0.841±0.0004
(Antognini)
?
?
Simultaneous measurement of e+/μ+ e-/μ- at beam momenta of
115, 153, 210 MeV/c in πM1 channel at PSI allows:

➔
Determination of two-photon effects
➔
Test of lepton universality
Simultaneous determination of proton radius in both ep and
μp scattering
➔
5
Paul Scherrer Institute πM1 Beam

590 MeV proton beam, 2.2mA, 1.3 MW beam, 50.6 MHz RF frequency

World's most powerful proton beam
➔ Secondary e±, m±, p± in piM1 beamline

Separate out particle species by timing relative to beam RF

Cut as many pions as possible, trigger on e±, m±
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6
MUSE Experiment
θ ≈ 20o – 100o
Q2 ≈ 0.002 - 0.07 GeV2
3.3 MHz total beam
flux
≈ 2-15% μ's
≈ 10-98% e's
≈ 0-80% π's

Low beam flux
➔

Secondary beam
➔

Large angle, non-magnetic detectors
Tracking of beam particles to target
Mixed beam
➔
Identification of beam particle in trigger
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Beam Particle Tracking / Identification
Scintillating SiPM Detector Array (Tel Aviv, Rutgers, PSI)

Thin, fast, scint., double-ended SiPM readout

Beam PID by RF timing diff. (~50 ps RMS)

Beam flux, TOF for beam p & reaction ID

Position & time for correlations with GEMS.
GEM Chambers (Hampton)

Built for OLYMPUS

2 mr instrinsic resolution

< 10 mr resolution with mult. scattering

Already used in PiM1 beam tests
8
Liquid Hydrogen Target (GWU) & Veto Detector (USC)
Veto Detector (USC)

Annular 8-element veto detector (target-mounted)

Eliminate upstream scattering & beam decays
Liquid Hydrogen Target (GWU)

Advanced conceptual design (below), 6cm “coffee can”

Geant 4 implementation (lower right)
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(Un)Scattered Particle Tracking / Identification
Straw Tube Tracker (HUJI & Temple)

Position/angular res. 140μm/1mr

2850 straws, directly mounted readout

First half-chamber tested
Trigger Scintillators (USC)

Two planes on each side of beam

92 bars, double-ended readout

55 ps achieved
Forward Beam Monitor Scintillators (USC)

Array of 32 thin scintillators

Read out by SiPMs

Flanked by large scintillators

Double-ended read out
10
Back Wall Scintillator Time Resolution
55 ps average resolution
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Readout
TRB3: trb.gsi.de
DAQ system (GWU & Montgomery College)
Measured timing differences
from 2014 PSI test beam time

3000 TDC, 500 ADC chanels

TRB3-based read-out

Mesytec MQDC-32 ADCs mostly for timing correction
Trigger (Rutgers)

TRB3 FPGA-based, accept e±, m±, reject p±

SiPM PID && Scattered Particle (LUT) && NOT(veto)

PID determined by time between RF pulse and SiPM
See Poster by I. Lavrukhin & C. Collicot
Relative timing test,
s = 32 ps
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Mechanical Assembly (ANL & PSI)

Rotating table

Retractable beam tracker

Dedicated alignment procedures
13
MUSE Test Beam Times
12 MUSE Test Runs
✔ to
characterize piM1 beam
✔ to
test detector prototypes (scintillators, Cerenkov, straw tubes)
✔ to
study and optimize GEM performance
➔ Oct 2012
➔ May 2013
➔ July 2013
➔ Oct 2013 (Cosmics)
➔ Dec 2013
➔ June 2014
➔ Dec 2014
➔ Feb 2015 (Cosmics)
➔ June-July 2015
➔ Dec 2015
➔ May 2016

Representation from 13 institutions

12th run scheduled for June-July 2016
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First Beam Tests
Time of flight
relative to RF time
(Fall 2012)
Beam spot with GEM – May 23, 2013
15
Composition of the πM1 secondary beam
Beam test results from
December 2013
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3D Beam Tomography
17
Simulations (USC)

Particle vertex and scattering angle
reconstruction meet MUSE
requirements

Background from target walls and
windows can be cleanly eliminated or
subtracted

Simulations verified by test data
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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
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TOF Beam Momentum Measurement
Consistent beam momenta
were extracted from muon
and pion spectra
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
20
Simulations (USC)

Muon decays in flight can be removed
with time-of-flight measurements

Moeller/Bhabba events can be
effectively suppressed with veto from
the beamline monitor detector
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Recent Results
Top:

Geant 4 sims tuned to match
measured beam parameters
Left:

Neural net seperates muon
scattering from muon decay
reactions
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MUSE Error Budget
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.

Have six settings and two independent detectors, consistency check

Multiple calibration measurements / simulations planned
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Projected sensitivity for MUSE

Cross sections to < 1% stat. for backward μ, <<1% for forward e and μ,
absolute 2%, point-to-point realtive uncertainties to a few x 10-3

Individual radius extractions from e±, μ± each to 0.01 fm
+Q4
+Q6
linear
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Projected sensitivity for MUSE

Compare e± xsecs and μ± xsecs for TPE. Charge average to eliminate
TPEeach to 0.01 fm

From e/μ xsec ratios: extract e-μ radius difference with minimal truncation
error to 0.005 fm

If no difference, extract radius to 0.007 fm (2nd-order fit)
*Note: MUSE point arbitrarily put at rp=0.875 fm
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Projected sensitivity for MUSE

Charge radius extraction limited by systematics, fit uncertainties

Many uncertainties are common to all extractions in the experiments,
cancel in e+/e-, μ+/μ-, and μ/e comparisons

MUSE suited to verify 5.6σ effect (CODATA 2014) with even higher
significance

Re - Rμ = 0.034±0.006 fm (5.6σ), MUSE: δr = 0.005 fm (~7σ)
Uncertainties on radius difference
~0.005 fm (stat.) ~0.1 fm (syst.)
*Note: Difference in MUSE determined entirely by MUSE. Other
differences are taken with respect to Antognini muonic hydrogen radius.
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MUon proton Scattering Experiment - MUSE

55 MUSE collaborators from 24 institutions in 5 countries
A. Afanasev, A. Akmal, J. Arrington, H. Atac, C. Ayerbe-Gayoso, F. Benmokhtar, N.
Benmouna, J. Bernauer, A. Blomberg, E. Brash, W.J. Briscoe, E. Cline, D. Cohen,
E.O. Cohen, C. Collicott, K. Deiters, J. Diefenbach, B. Dongwi, E.J. Downie, L. El
Fassi, S. Gilad, R. Gilman, K. Gnanvo, R. Gothe, D. Higinbotham, Y. Ilieva, L. Li,
M. Jones, N. Kalantarians, M. Kohl, G. Kumbartzki, I. Lavrukhin, J. Lichtenstadt,
W. Lin, A. Liyanage, N. Liyanage, Z.-E. Meziani, P. Monaghan, K.E. Mesick, P.
Moran, J. Nazeer, C. Perdrisat, E. Piasetzsky, V. Punjabi, R. Ransome, D.
Reggiani, P.E. Reimer, A. Richter, G. Ron, T. Rostomyan, A. Sarty, Y. Shamai, N.
Sparveris, S. Strauch, V. Sulkosky, A.S. Tadepalli, M. Taragin, and L. Weinstein
George Washington University, Montgomery College, Argonne National Lab,
Temple University, College of William & Mary, Duquesne University, Massachusetts
Institute of Technology, Christopher Newport University, Rutgers University, Hebrew
University of Jerusalem,Tel Aviv University, Paul Scherrer Institut, Johannes
Gutenberg-Universität, Hampton University, University of Virginia, University of
South Carolina, Jefferson Lab, Los Alamos National Laboratory, Norfolk State
University, Technical University of Darmstadt, St. Mary’s University, Soreq Nuclear
Research Center, Weizmann Institute, Old Dominion University
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Ron consulted closely with wise, experienced project managers...
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MUon proton Scattering Experiment - MUSE

Since initial proposal in February 2012, 12 beam tests, and counting...
➔ Determine
beam line properties
➔ Prototyped
most of needed technology for the experiment

Series of NSF funding reviews: R & D funding from NSF, DOE, BSF

Successful funding and project management review concluded May 2016

NSF mid-scale funding should enable:
➔ Funding
& construction 2016–2017
➔ Production

running 2018–2019 (2x 6 months)
MUSE will be the first muon scattering measurement with the
required precision to address the PRP!
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Backup Slides
30
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
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George Washington & Rutgers work very closely together...
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