Mu2e experiment at Fermilab Yuri Davydov DLNP, JINR, Dubna
Erevan, March 2015
Slide 2
Introduction What is Mu2e? A search for Charged-Lepton Flavor
Violation via Will use current Fermilab accelerator complex to
reach a sensitivity 10 000 better than current worlds best Will
have discovery sensitivity over broad swath of New Physics
parameter space 2 - N e - N March 2015
Slide 3
Flavor Violation Weve known for a long time that quarks mix
(Quark) Flavor Violation In last 15 years weve come to know that
neutrinos mix Lepton Flavor Violation (LFV) Why not Charged Lepton
Flavor Violation (CLFV)? 3March 2015
Slide 4
CLFV in the Standard Model Strictly speaking, forbidden in the
SM Even in -SM, extremely suppressed (rate ~ m 2 / M w 2 < 10
-50 ) However, most all NP models predict rates observable at next
generation CLFV experiments 4 q q e-e- W e March 2015
Slide 5
5 Mu2e : SM prediction and New Physics The BR of CLFV processes
in the Standard Model Flavour Physics of Leptons and Dipole
Moments, Eur.Phys.J.C57:13-182,2008 NP Sensitive to mass scales up
to O(10,000 TeV) Mu2e sensitivity is 6*10 -17 March 2015
Slide 6
Mu2e High Priority for U.S. HEP In the 2008 P5 report Mu2e was
strongly supported: Mu2e should be pursued in all budget scenarios
considered by the panel In 2010 P5 reiterated their support of the
2008 plan and the priorities specified therein. In 2013 the
Facilities Panel gave Mu2e the highest endorsement: The science of
Mu2e is Critical to the DOE OHEP mission and is Ready to Construct.
In the 2014 P5 report Mu2e is strongly supported: Recommendation
14, Complete the Muon (g-2) and Mu2e Projects. March 20156
Slide 7
How does Mu2e work? March 20157
Slide 8
8 Mu2e Concept Generate a beam of low momentum muons ( Stop the
muons in a target Mu2e plans to use aluminum Sensitivity goal
requires ~10 18 stopped muons The stopped muons are trapped in
orbit around the nucleus In orbit around aluminum: Al = 864 ns
Large N important for discriminating background Look for events
consistent with N eN March 2015
Slide 9
9 Mu2e Signal The process is a coherent one The nucleus is kept
intact Experimental signature is an electron and nothing else
Energy of electron: E e = m - E recoil - E 1S-B.E. For aluminum: E
e =104.96 MeV Important for discriminating background March
2015
Slide 10
Mu2e Sensitivity Design goal: single-event-sensitivity 2.4 x 10
-17 Requires about 10 18 stopped muons Requires about 10 20 protons
on target Requires extreme suppression of backgrounds Expected
limit: R e < 6 x 10 -17 @ 90% CL Factor 10 4 improvement
Discovery sensitivity: all R e > 1 x 10 -16 Covers broad range
of new physics theories March 201510
Slide 11
The great-grandparents of the Mu2e ( MELC, 1992; MECO, 1997)
V.M. Lobashev and R.M. Djilkibaev 11March 2015 -e conversion
experiment concept
Slide 12
Baseline Mu2e Apparatus Particles produced from tungsten target
Muons stop on Al target, which emits an electron isotropically 12
Tracker/calorimeter detect electron signature S-shaped solenoid:
transports particles to detector area, and allows remaining pions
to decay to muons collimator selects negatively-charged particles
8-GeV protons from delivery ring 4.6 T 2.5 T 2.0 T 1.0 T Detector
Region: Uniform Field 1T Graded B for most of length ( about 25
meters end-to-end March 2015
Slide 13
13 The Measurement Method E e = m - E recoil - E 1S-B.E. E e
=104.96 MeV
Slide 14
Some Mu2e numbers Every 1 second Mu2e will Send
7,000,000,000,000 protons to theProduction Solenoid Send
26,000,000,000 s through the Transport Solenoid Stop
13,000,000,000, s in the Detector Solenoid By the time Mu2e is done
Total number of stopped muons 1,000,000,000,000,000,000 March
201514
Slide 15
15 Mu2e Proton Beam Mu2e will use a pulsed proton beam and a
delayed live gate to suppress prompt backgrounds 0 500 1000 1500
2000 2500 3000 3500 Time (ns) Proton pulse on Production target
Muons at Stopping target 1700 ns 700 ns900 ns Live Window March
2015
Slide 16
The Mu2e Tracker Will employ straw technology Low mass Can
reliably operate in vacuum Robust against single-wire failures 16 5
mm diameter straw Spiral wound Walls: 12 m Mylar + 3 m epoxy + 200
Au + 500 Al 25 m Au-plated W sense wire 33 117 cm in length 80/20
Ar/CO2 with HV < 1500 V March 2015
Slide 17
The Mu2e Tracker Self-supporting panel consists of 100 straws 6
panels assembled to make a plane 2 planes assembled to make a
station Rotation of panels and planes improves stereo information
>20k straws total 17 panel planestation March 2015
Slide 18
The Mu2e Tracker 18-20 stations with straws transverse to beam
Naturally moves readout and support to large radii, out of active
volume 18 3 meters 38 cm 70 cm March 2015
Slide 19
The Mu2e Tracker Inner 38 cm is purposefully un-instrumented
Blind to beam flash Blind to >99% of DIO spectrum 19 Escape thru
center of Tracker Fully fiducial March 2015
Slide 20
Mu2e Calorimeter Crystal calorimeter Compact Radiation hard
Good timing and energy resolution 20March 2015
Slide 21
Mu2e Calorimeter Baseline design : Barrium Flouride (BaF 2 )
Radiation hard, very fast, non-hygroscopic 21 BaF 2 Density
(g/cm3)4.89 Radiation length (cm)2.03 Moliere Radius (cm)3.10
Interaction length (cm)30.7 dE/dX (MeV/cm)6.52 Refractive index1.50
Peak luminescence (nm)220 (300) Decay time (ns)1 (650) Light yield
(rel. to NaI)5% (42%) Variation with temperature0.1% (-1.9)% /
deg-C March 2015
Slide 22
Mu2e Calorimeter Will employ 2 disks ( radius = 36-70 cm) ~2000
crystals with hexagonal cross-section ~3 cm diameter, ~20 cm long
(10 X 0 ) Two photo-sensors/crystal on back (APDs or SiPMs) 22 Disk
1 Disk 2 March 2015
Slide 23
Mu2e Cosmic-Ray Veto Veto system covers entire DS and half TS
23 PS TS Without the veto system, ~1 cosmic-ray induced background
event per day March 2015
Slide 24
Mu2e Cosmic-Ray Veto Will use 4 overlapping layers of
scintillator Each bar is 5 x 2 x ~450 cm 3 2 WLS fibers / bar
Read-out both ends of each fiber with SiPM Have achieved > 99.4%
(per layer) in test beam 24March 2015
Slide 25
Backgrounds Stopped Muon induced Muon decay in orbit (DIO) Out
of time protons or long transit-time secondaries Radiative pion
capture; Muon decay in flight Pion decay in flight; Beam electrons
Anti-protons Secondaries from cosmic rays 25 Mitigation: Excellent
momentum resolution Excellent extinction plus delayed measurement
window Thin window at center of TS absorbs anti-protons Shielding
and veto March 2015
Slide 26
CategorySourceEvents Decay in Orbit 0.20 Intrinsic Radiative
Capture
27 Mu2e Intrinsic Backgrounds Once trapped in orbit, muons
will: 1)Decay in orbit (DIO): N --> e - e N For Al. DIO fraction
is 39% Electron spectrum has tail out to 104.96 MeV Accounts for
~55% of total background March 2015
Slide 28
28 Mu2e Intrinsic Backgrounds Once trapped in orbit, muons
will: 2)Capture on the nucleus: For Al. capture fraction is 61%
Ordinary Capture N Z --> N * Z-1 Used for normalization
Radiative capture N Z --> N * Z-1 + (# Radiative / # Ordinary) ~
1 / 100,000 E kinematic end-point ~102 MeV Asymmetric -->e + e -
pair production can yield a background electron March 2015
Slide 29
670 ns 925 ns 1695 ns Prompt Background Suppression Prompt
background Happens around the time, when the beam arrives at the
target. Sources beam electrons, muon decay in flight, pion decay in
flight, radiative pion capture May create electrons with energies
in the signal region Prompt background can be suppressed by not
taking data during the first 670 ns after the peak of the proton
pulse. However, this prompt background cannot be eliminated
entirely, since some of the protons arrive out of time. A ratio of
10 -10 is required for the beam between pulses vs. the beam
contained in a pulse. 29 The lifetime of a muon in an Al orbit is
864 ns March 2015
Slide 30
30 Mu2e Late Arriving Backgrounds Contributions from Radiative
Capture N Z --> N * Z-1 + For Al. R C fraction: 2% E extends out
to ~m Asymmetric e + e - pair production can yield background
electron Beam electrons Originating from upstream and decays
Electrons scatter in stopping target to get into detector
acceptance Muon and pion Decay-in-Flight Taken together these
backgrounds account for ~10% of the total background and scale
linearly with the number of out-of- time protons March 2015
Slide 31
SourceEventsComment decay in orbit (DIO)0.20 0.06 Anti-proton
capture0.10 0.06 Radiative - capture*0.04 0.02From protons during
detection time Beam electrons*0.001 0.001 decay in flight*0.010
0.005With e - scatter in target Cosmic ray induced0.050
0.013Assumes 10 -4 veto inefficiency Total0.4 0.1 * scales with
extinction: values in table assume extinction = 10 -10 All values
preliminary; some are stat error only. Backgrounds for 3 Year Run
31March 2015
Slide 32
32 Mu2e Miscellaneous Backgrounds Several additional
miscellaneous sources can contribute background - most importantly:
Anti-protons Proton beam is just above pbar production threshold
These low momentum pbars wander until they annihilate A thin mylar
window in beamline absorbs most of them Annihilations produce high
multiplicity final states e.g. can undergo R C to yield a
background electron Cosmic rays Suppressed by passive and active
shielding DIF or interactions in the detector material can give an
e - or that yield a background electron Background listed assumes
veto efficiency of 99.99% March 2015
Slide 33
Signal Sensitivity for 3 Year Run Reconstructed e - Momentum ~
4x10 20 protons on target (3 year run @ 8 KW) Stopped : 10 18 N e =
3.94 0.03 For R = 10 -16 N DIO = 0.20 0.06 N Other = 0.2 SES = (2.5
0.1) 10 -17 Errors are stat only 33March 2015
Slide 34
34 LYSO 5x5 matrix beam tests
Slide 35
JINR CONTRIBUTION (1) March 201535 Mu2e Electromagnetic
calorimeter Evaluation of crystal samples including LGSO, LSO,
LYSO, BaF2 and CsI. Tests of the crystals on the gamma sources,
cosmic muons and accelerator beams. Tests of the optical
uniformity, scintillation yield and yield collection uniformity.
Upgrade of the facility for the crystal testing at DLNP JINR.
Simulation of the electromagnetic calorimeter elements and
calorimeter in whole. Participation in the radiation hardness of
the crystal and front-end electronic tests on the neutron sources
of JINR and/or collaborator institutes. Participation in the
production of crystals for the experiment in cooperation with
Kharkov. Participation in quality control of the crystals by
testing their performance. Participation in calorimeter
construction and integration in the full detector on the
experimental site. Maintenance of the calorimeter during the data
taking period to ensure efficient operation.
Slide 36
JINR CONTRIBUTION (2) March 201536 Mu2e Cosmic Ray Veto system
Participation in the simulation activity of Mu2e experiment to
define the final demands to Cosmic Ray Veto system and choose the
optimal geometry of this system. Upgrade of the facility for
scintillation counters tests at DLNP JINR and Fermilab. Design,
build and test the prototype scintillation counters for Cosmic Ray
Veto system at the created stands. Participation in the prototype
scintillator counters tests on the neutron facilities of JINR
and/or collaborator institutes to define sensitivity of neutron
registration and radiation hardness. Participation in the mass
production and tests of the scintillation counters for Cosmic Ray
Veto system in the cooperation with Kharkov, Fermilab and
University of Virginia (UVA). Participation in the CRV test stand
construction at Fermilab. Participation in the CRV construction and
integration in the full detector on the experimental site.
Maintenance of this system during the data taking period to provide
its efficient operation.
Slide 37
JINR CONTRIBUTION (3) 37March 2015
Slide 38
Experimental setups for crystals and strips tests March
201538
Slide 39
LYSO SICCAS: 22 Na, coincidence Two left frames: linear scales,
the bottom frame shows 1275 keV and 511+1275 keV sum peaks Right
bottom frame shows spectrum in log scale along with peaks fitted
with Gaussian 39
Slide 40
JINR Mu2e: Comparison of 3 crystals - Energy resolution and
Linearity of the energy response
Slide 41
Sample from ISMA NASU * with triangular cross-section and inner
hole 41 Geometry for the our strip sample: Base:33 mm Height:17 mm
Length:2000 mm * ISMA NASU Institute for Scintillation Materials,
National Academy of Sciences of Ukraine For water-filling holes
were drilled in the side faces of the sample and plugs are made
(see photo). The triangle scintillation strips with a hole in the
center (diam. 2.6 mm) are similar to those developed for MINERvA
Water-filling hole plug Fiber end
Slide 42
42 T EST CONDITIONS M EASUREMENTS OF THE LIGHT YIELDS FOR THE
SAME SAMPLE OF THE SCINTILLATION STRIP WITH / WITHOUT DISTILLED
WATER INSIDE WERE DONE ; L IGHT COLLECTED BY USING D = 1.2 MM K
URARAY WLS FIBER. T HE STRIP S FAR END WAS COVERED BY A LUMINUM
FOIL, NEAR END WAS CLOSED BY BLACK PLASTIC CAP FOR LIGHT ISOLATION.
J UST HOLE LEFT FOR COUPLING THE WLS FIBER TO THE PMT; T HE WLS
FIBER WAS INSERTED INTO THE HOLE AND FIXED BY GLUE ON BOTH ENDS ; D
ISTILLED WATER PUMPED THROUGH THE SAMPLE, NO AIR BUBBLES WERE
OBSERVED. PMT EMI 9814B WAS USED, HV= 2200 V. F OUR PAIRS OF
TRIGGER COUNTERS WERE USED ; A BSOLUTE CALIBRATION METHOD WAS USED
TO CALCULATE THE LIGHT YIELD 2 2 4
Slide 43
Results: comparison of the light collected of the same sample
using the wls fiber with/without water 43 Fit function f(x)=exp
p0+p1*x Measuring points () : 71.5 111.5 151.5 191.5 Increase of
the yield of light (%) : 51 54 53 44
Slide 44
Some publications March 201544 L. Bartoszek et al., Mu2e
Technical Design Report, arXiv:1501.05241 (2015). K. Afanaciev et
al., Response of LYSO:Ce scintillation crystals to low energy
gamma- rays, Particles and Nuclei, Letters, 2015, issue 2. G.
Pezzullo et al., Progress status for the Mu2e calorimeter system,
Journal of Physics: Conference Series 587(2015), 012047. G.
Pezzullo et al., The LYSO crystal calorimeter for the Mu2e
experiment, 2014 JINST 9 C03018. O. Sidletskiy et al., Evaluation
of LGSO:Ce scintillator for high energy physics experiments, Nucl.
Instr.&Meth. A735(2014) 620-623. J. Budagov et al., The
calorimeter project for the Mu2e experiment, Nucl. Instr.&Meth.
A718(2013) 56-59. Z. Usubov, Light output simulation of LYSO single
crystal, arXiv:1305.3010 (2013). Z. Usubov, Electromagnetic
calorimeter simulation for future e conversion experiments,
arXiv:1212.4322 (2012).arXiv:1212.4322 R.J. Abrams et al., Mu2e
Conceptual Design Report, arXiv:1211.7019
(2012).arXiv:1211.7019
Slide 45
March 201545 CD-1 CD-3a CD-2/3 Superconductor R&D Solenoid
Infrastructure Solenoid Installation Install Detector Fabricate and
QA Superconductor Solenoid Design Solenoid Fabrication and QA Mu2e
Technical Schedule FY13 FY14 FY15 FY16 FY17 FY18 FY19 FY20
Accelerator and Beamline Detector Construction Field Mapping
Detector Hall Design Site Work Detector Hall Construction
Operations
Slide 46
What next? A next-generation Mu2e experiment makes sense in all
scenarios Push sensitivity or Study underlying new physics Will
need more protons upgrade accelerator 46 Precision Measurement if
necessary Measure conversion rate as a function of Z Higher
Sensitivity search Mu2e Signal? Yes No Accelerator Upgrade
Accelerator Upgrade March 2015
Slide 47
Summary The Mu2e experiment: Improves sensitivity by a factor
of 10 4 Provides discovery capability over wide range of New
Physics models Is complementary to LHC, heavy-flavor, and neutrino
experiments 47March 2015
Slide 48
48 BACKUP March 2015
Slide 49
49
Slide 50
Mu2e / COMET comparisonMu2eCOMET approval/ funding ranked among
the very top priorities for the U.S. HEP program P5 Report 2014
Complete the Mu2e and g-2 projects. Mu2e is fully funded in all
budget scenarios The DOE is committed to completing Mu2e COMET
phase-II funding has not been identified and Japan has clearly
stated that their top priorities are Belle-II, long baseline
neutrinos, and ILC OperationCondition Mu2e will run simultaneously
with NOvA and the short-baseline neutrino program at Fermilab COMET
cannot run simultaneously with the JPARC neutrino program. It
forces COMET to plan for higher beam power in order to minimize the
amount of required beam time Detector Straight Solenoid with
gradient field Tracker and Calorimeter C-shape Solenoid with
gradient field Tracker and Calorimeter Because the Mu2e DS is
straight, it is equally sensitive to e- and e+ and thus have an
additional physics channel - N e + N and will be able to measure in
situ some background components (e.g. - N N e - e + N) the COMET
solenoids, particularly their production solenoid, is more
technically risky (e.g. they will use a 9 (!) layer coil, Mu2e is 3
layer). March 201550
Slide 51
51March 2015
Slide 52
Mu2e / COMET comparison Mu2e has consistently been ranked among
the very top priorities for the U.S. HEP program P5 Report 2008
Facilities Report 2012 P5 Report 2014 Complete the Mu2e and g-2
projects. Mu2e is fully funded in all budget scenarios The DOE is
committed to completing Mu2e COMET phase-II funding has not been
identified and Japan has clearly stated that their top priorities
are Belle-II, long baseline neutrinos, and ILC Mu2e solenoids are
technically less risky and employ fabrication and cooling
techniques that have been used before the COMET solenoids,
particularly their production solenoid, is more technically
challenging (e.g. they will use a 9 (!) layer coil, Mu2e is 3
layer). March 201552