The Mu2e Experiment The Mu2e Experiment at Fermilabat Fermilab

Jim MillerJim Miller

Boston UniversityBoston University

for the Mu2e Collaborationfor the Mu2e CollaborationJune 6, 2008June 6, 2008

Mu2e Collaboration• R.M. Carey, K.R. Lynch, J.P. Miller*, B.L. Roberts• Boston University

• Y. Semertzidis, P. Yamin• Brookhaven National Laboratory

• Yu.G. Kolomensky• University of California, Berkeley

• C.M. Ankenbrandt , R.H. Bernstein*, D. Bogert, S.J. Brice, D.R. Broemmelsiek,D.F. DeJongh, S. Geer, • M.A. Martens, D.V. Neuffer, M. Popovic, E.J. Prebys, R.E. Ray, H.B. White, K. Yonehara, C.Y. Yoshikawa• Fermi National Accelerator Laboratory

• D. Dale, K.J. Keeter, J.L. Popp, E. Tatar• Idaho State University

• P.T. Debevec, D.W. Hertzog, P. Kammel• University of Illinois, Urbana-Champaign

• V. Lobashev• Institute for Nuclear Research, Moscow, Russia

• D.M. Kawall, K.S. Kumar• University of Massachusetts, Amherst

• R.J. Abrams, M.A.C. Cummings, R.P. Johnson, S.A. Kahn,• S.A. Korenev, T.J. Roberts, R.C. Sah• Muons, Inc.

• R.S. Holmes, P.A. Souder• Syracuse University

• M.A. Bychkov, E.C. Dukes, E. Frlez, R.J. Hirosky, A.J. Norman, K.D. Paschke, D. Pocanic• University of Virginia

50 Scientists

11 Institutes

Recent LOI for Stage I measurement favorably reviewed by the Fermilab PAC

What is the measurement?What is the measurement?► Detect charged lepton flavor non-conservation in the coherent, Detect charged lepton flavor non-conservation in the coherent,

neutrinoless conversion of a muon to an electron in the field of neutrinoless conversion of a muon to an electron in the field of a nucleus:a nucleus:

► Measure the ratio of conversion relative to ordinary muon Measure the ratio of conversion relative to ordinary muon capture on the nucleus:capture on the nucleus:

(where ‘X’=(A, Z-1); or (A’,Z’)+ (where ‘X’=(A, Z-1); or (A’,Z’)+ protons, neutrons, protons, neutrons, gammas)gammas)

► Current limits: R<4.3x10Current limits: R<4.3x10-12-12 (Ti), R<7x10 (Ti), R<7x10-13-13 (Au) ( (Au) (SINDRUM IISINDRUM II at at PSI)PSI)

► Goals of Goals of Mu2eMu2e: : Stage I: R<6x10Stage I: R<6x10-17 -17 (Al, 90% c.l.). An improvement over (Al, 90% c.l.). An improvement over

existing limit by four orders of magnitude!existing limit by four orders of magnitude! Stage II: (Project X) R<10Stage II: (Project X) R<10-18 -18 (Al).(Al).

( , ) ( , )A Z e A Z

( , ) ( , )

( , )

A Z e A ZR

A Z X

Beyond the Standard Model► Charged Lepton Flavor Violation (CLFV) is a nearly universal

feature of extensions to the Standard Model, and the fact that it has not yet been observed already places strong constraints on these models.

► CLFV is a powerful probe of multi-TeV scale dynamics: complementary and in some cases more powerful than direct collider searches

► Among various possible CLFV modes, rare muon processes offer the best combination of new physics reach and experimental sensitivity.

► Muon to electron conversion offers ultimate in LFV sensitivity because of experimental

advantages over other reactions

► Detection of muon to electron conversion is an unmistakable signal of new physics

The MethodThe Method► Muon beam line: Low energy pions decay to low energy Muon beam line: Low energy pions decay to low energy

muonsmuons► Muon stops in an appropriate target, quickly forming a muonic Muon stops in an appropriate target, quickly forming a muonic

atom with muon in 1s stateatom with muon in 1s state► Bohr radius (1s) much less than 1s orbit of Bohr radius (1s) much less than 1s orbit of

innermost atomic electronsinnermost atomic electrons► Bohr energy (1s) which is ~470 keV for AlBohr energy (1s) which is ~470 keV for Al► 3 muon interactions can occur3 muon interactions can occur

1 Muon to electron conversion Muon to electron conversion Conversion electron is monoenergeticConversion electron is monoenergetic

2 muon can decaymuon can decay► Endpoint of bound muon same as conversion energy:Endpoint of bound muon same as conversion energy:

3 muon can capture on nucleusmuon can capture on nucleus

► For muonic Aluminum, muon lifetime is 0.86 For muonic Aluminum, muon lifetime is 0.86 s; partial decay s; partial decay lifetime=2.2 lifetime=2.2 s, partial capture lifetime=1.5 s, partial capture lifetime=1.5 ss

0 eB

a mr

Z m

2(13.6 )Be

mE eV Z

m

( , ) ( , )A Z e A Z ( ) 105.0ceE Al MeV

[ ( , )] [ ( , )]eA Z e A Z (max) 105.0e ceE E MeV

p n ( , ) ( ', ') 'A Z A Z protons neutrons s

Some potential backgroundsSome potential backgrounds1 Electrons from decay of muon bound in atomic orbit: max Electrons from decay of muon bound in atomic orbit: max

energy is same as conversion electron energy energy is same as conversion electron energy Probability falls rapidly near endpoint,Probability falls rapidly near endpoint, This background can be separated from conversion electrons with This background can be separated from conversion electrons with

good electron energy resolutiongood electron energy resolution: Require <1 MeV FWHM for : Require <1 MeV FWHM for Mu2e, R<6x10Mu2e, R<6x10-17-17

Vast majority of decay electrons are < 53 MeV, well below Vast majority of decay electrons are < 53 MeV, well below conversion electron energy- big experimental advantage over conversion electron energy- big experimental advantage over

This is an example of a ‘Delayed’ backgroundThis is an example of a ‘Delayed’ background

2 Radiative pion capture, followed by photon conversionRadiative pion capture, followed by photon conversion

, E, E up to 140 MeV up to 140 MeV This is an example of a ‘Prompt’ backgroundThis is an example of a ‘Prompt’ background Possibility of ~105 MeV conversion electrons strong Possibility of ~105 MeV conversion electrons strong

suppression of pions suppression of pions is requiredis required3 Flux of low energy protons, neutrons, gammas from ordinary Flux of low energy protons, neutrons, gammas from ordinary

muon capture on stopping target nuclei- can lead to tracking muon capture on stopping target nuclei- can lead to tracking errors.errors.

4 Beam electrons ~105 MeVBeam electrons ~105 MeV5 Cosmic rays- suppress with shielding and 4Cosmic rays- suppress with shielding and 4 veto veto

(max) 105e ceE E MeV 5( )eE E

( , ) ( , 1)A Z A Z

e

SINDRUM II Experimental MethodSINDRUM II Experimental Method

► Low energy beamline collects muons from pion decay; Low energy beamline collects muons from pion decay; beam line length is large enough so that most pions beam line length is large enough so that most pions decaydecay

► Pass beam through material to degrade energy: range Pass beam through material to degrade energy: range out pions, muons continue on to stop in targetout pions, muons continue on to stop in target

► Use a scintillator to detect charged particles entering Use a scintillator to detect charged particles entering stopping target.stopping target.

► Detect electrons Detect electrons delayeddelayed relative to incident particle- relative to incident particle- Conversion electrons + background from muon Conversion electrons + background from muon interactionsinteractions

► Reject Reject promptprompt electrons- could be from beam electrons- could be from beam radiative capture or beam electronradiative capture or beam electron

► ‘‘One-at-a-time’ method limits rates to ~10One-at-a-time’ method limits rates to ~1077/s:/s:

It would take ~ 100 years to get the statistics necessary It would take ~ 100 years to get the statistics necessary to approach Mu2e goal of R<10to approach Mu2e goal of R<10-16-16

8

Previous muon decay/conversion limits Previous muon decay/conversion limits (90% C.L.)(90% C.L.)

• Rate limited by need to veto prompt backgrounds!

>e Conversion: Sindrum II

124.3 10capture

e

Ti e TiR

Ti

11

12

11

2

102.72

100.1

102.1

102.1

e

eee

e

e e

LFV Decay:

High energy tail of coherent Decay-in-orbit (DIO)

After background suppression, thereare no counts in the region of interest.

The New ApproachThe New Approach► Based on the proposed MELC and MECO approachBased on the proposed MELC and MECO approach► Go to a temporally narrow pulsed primary proton beam. Go to a temporally narrow pulsed primary proton beam.

Delay beginning of measurement period after proton Delay beginning of measurement period after proton injection pulse until almost all pions have decayed and injection pulse until almost all pions have decayed and other beam particles have dissipated (after about 700 other beam particles have dissipated (after about 700 ns).ns).

► Establish high level of between-burst beam suppression Establish high level of between-burst beam suppression (extinction ~10(extinction ~10-9-9) to avoid ) to avoid or e production leading to or e production leading to false conversion electrons during the measurement false conversion electrons during the measurement period.period.

► Select a stopping target having a muon lifetime which is Select a stopping target having a muon lifetime which is matched to this delay time (Aluminum is a good choice: matched to this delay time (Aluminum is a good choice: lifetime = 0.86 lifetime = 0.86 s).s).

► Beam pulse spacing of ~1.7 Beam pulse spacing of ~1.7 s is a good match for Al: s is a good match for Al: collect data from .7-1.7 collect data from .7-1.7 s after muon injection pulses after muon injection pulse

► Ideally, there would be a continuous stream of muon Ideally, there would be a continuous stream of muon pulses, ~100% duty factorpulses, ~100% duty factor

6/3/2008 10

Production Solenoid

Transport Solenoid

DetectorSolenoid

ProtonTarget

TargetShielding

Muon BeamCollimators

Tracker

Calorimeter

Pions ElectronsMuons

Muon Stopping Target

Mu2e Muon BeamlineSimulations with G4beamline

(Code developed by Muons Inc)

6/3/2008 11

Proton Target andSuperconducting

Production Solenoid

ProtonTarget

TargetShielding(Copper)

Pions

Muons

TargetShielding

(Tungsten)

Protons enter here

B=5T

B=2.5T

6/3/2008 12

Transport Solenoid

+

- Collimator 3(Copper)

Collimator 3(Copper)

(Showing muons only)

6/3/2008 13

Detector Solenoid

TrackerCalorimeter

105 MeV/cElectronsMuons

Muon Stopping Target

B=2 T

B=2T

B=1T

B=1T

Stopping Target and DetectorsStopping Target and Detectors► Solenoid, 1m radius, B=2 T-> 1T from 0 to 4 m, B=1 T from 4 to 10 mSolenoid, 1m radius, B=2 T-> 1T from 0 to 4 m, B=1 T from 4 to 10 m► Negative field gradient at target creates mirror increasing detector Negative field gradient at target creates mirror increasing detector

acceptance. acceptance. ► Stopping target: thin to reduce energy loss and loss of energy Stopping target: thin to reduce energy loss and loss of energy

resolutionresolution► Tracker measures momentum of electrons to <1MeV FWHM: 2.6 m long, Tracker measures momentum of electrons to <1MeV FWHM: 2.6 m long,

0.5 cm0.5 cm► Copious low energy charged particles (e.g. electrons from in-orbit muon Copious low energy charged particles (e.g. electrons from in-orbit muon

decays) spiral down the hollow axis of the tracker, missing it entirely.decays) spiral down the hollow axis of the tracker, missing it entirely.► Calorimeter after the tracker: provides fast trigger, confirms energy and Calorimeter after the tracker: provides fast trigger, confirms energy and

position information on tracks.position information on tracks.

15

Delivering Protons: “Boomerang” Delivering Protons: “Boomerang” SchemeScheme

► Deliver beam to Accumulator/Debuncher enclosure with minimal beam line modifications and minimal civil construction.

► Use Booster batches which would not otherwise be used for NoVA

Recycler(Main Injector

Tunnel)

MI-8 -> Recycler done

for NOvA

New switch magnet extraction to P150 (no need for kicker)

Proton flux, per second

muon stopping rate, per second

1.8x1013

4x1010

Running time 2x107 s

Total protons per year 3.6x1020

stops/incident proton 0.0025

capture probability 0.60

Time window fraction 0.49

Electron trigger efficiency 0.90

Reconstruction and selection efficiency

0.19

Detected events for Re = 10-16 4.5

Event Rates (Stage I, from Booster)

Time ScaleTime Scale► Stage I, Booster-era, ~20-25 kW proton beamStage I, Booster-era, ~20-25 kW proton beam

MECO proposal is baseline design, vetted in several reviewsMECO proposal is baseline design, vetted in several reviews Readiness determined primarily by the four to five years to Readiness determined primarily by the four to five years to

construct the solenoidal beam line after funding is availableconstruct the solenoidal beam line after funding is available Commissioning + data collection, ~3-4 yearsCommissioning + data collection, ~3-4 years LOI in Fall 2007, strong physics stamp of approval from PACLOI in Fall 2007, strong physics stamp of approval from PAC Full proposal being prepared now for Fall 2008 PACFull proposal being prepared now for Fall 2008 PAC Plan for a reasonable upgrade path to Stage IIPlan for a reasonable upgrade path to Stage II

► Stage II, Project X, 200 kW proton beam, R<10Stage II, Project X, 200 kW proton beam, R<10-18-18

Depends on Project X schedule and lessons learned in Stage IDepends on Project X schedule and lessons learned in Stage I Extensive upgrade studies will be needed:Extensive upgrade studies will be needed:

► Primary target upgrade to handle increased heat loadPrimary target upgrade to handle increased heat load► Production solenoid upgrade to handle increased heat and Production solenoid upgrade to handle increased heat and

radiation loads on superconducting magnet.radiation loads on superconducting magnet.► Improved extinctionImproved extinction► Improved detector to handle higher rates with improved energy Improved detector to handle higher rates with improved energy

resolution resolution

Tasks► Tracker: two candidates, need R&D (simulations, prototypes) to choose► Calorimeter: Lead tungstate is baseline- limited initial prototype work-

need to evaluate new crystal materials, new photo-sensitive devices► Cosmic ray veto system- candidate system has been proposed- needs to

be developed- a challenge to get to 99.9% efficiency, 4 coverage► Simulations:

Have GEANT3, working; full GEANT4 simulation being developed, > manpower Beam line optimization, background studies

► Calibration systems for all detectors► Extinction monitor(p beam)- ideas exist- needs to be developed and built► Muon stopping rate monitor- Measure xray rate from muonic aluminum► Solenoid magnets (big project): joint effort of physicists and engineers.

Initial design work done, needs further development for full design.► Develop readout electronics for calorimeter, tracker, cosmic veto,…► Identify a viable upgrade path to get to R<10-18 with Project X.► Develop the proton source, with needed extinction► …radiation shielding, building siting,…► If you might be interested in working on some of these tasks, let’s talk!Contact persons: Jim Miller: miller@bu.edu Bob Bernstein:

rhbob@fnal.gov

End

Conclusions

►Muon to electron conversion is a powerful probe of new physics, complementary to LHC

►A baseline design exists on paper. It needs to be updated and holes filled in. Need prototypes; much development work remains

►P5 has given a strong endorsement, and FNAL is gearing up to do this experiment.

Example Sensitivities*

CΛ = 3000 TeV

-4HH μμμeg =10 ×g

Compositeness

Second Higgs doublet

2

ZM = 3000 TeV / c

Heavy Z’,

Anomalous Z

coupling

Predictions at 10-15

Supersymmetry

2* -13μN eNU U = 8×10

Heavy Neutrinos

L

2μd ed

M =

3000 λ λ TeV/c

Leptoquarks

*After W. Marciano

High Flux Muon BeamHigh Flux Muon Beam

► Following the idea from the MELC and MECO proposals, use a negative gradient Following the idea from the MELC and MECO proposals, use a negative gradient solenoid, 5 T to 2.5 T, around the production target to mirror upstream-going solenoid, 5 T to 2.5 T, around the production target to mirror upstream-going low energy pions and muons back downstream into the beam line.low energy pions and muons back downstream into the beam line.

► Negative gradient causes p(longtudinal) to increase as particle moves Negative gradient causes p(longtudinal) to increase as particle moves downstreamdownstream

► Use an ‘S’ shaped solenoid to transport the beam to the aluminum stopping Use an ‘S’ shaped solenoid to transport the beam to the aluminum stopping targettarget Avoids line-of-sight between detectors and production target: eliminate Avoids line-of-sight between detectors and production target: eliminate

neutral bkg.neutral bkg. Curved (toroidal) solenoid sections move beam vertically depending on Curved (toroidal) solenoid sections move beam vertically depending on

charge and momentum: select low energy negative particles, attenuate charge and momentum: select low energy negative particles, attenuate everything else.everything else.

► Rates- Booster Era: 8 GeV protons, 23 kW average current, 4x10Rates- Booster Era: 8 GeV protons, 23 kW average current, 4x101010 stopped stopped muons/s, (Project X: 10 times more beam)muons/s, (Project X: 10 times more beam)

Mu2e Muon Beam Line and Mu2e Muon Beam Line and DetectorDetector

Toroidal section: vertical separation of + and -

Production Solenoid: pions, muons, electrons

Mu2e Solenoids

e Conversion vs. e Conversion vs. ee

34

Courtesy: A. de Gouvea

?

?

?

Sindrum IIMEGA

MEG proposal

► We can parameterize the relative strength of the dipole and four fermi interactions.

► This is useful for comparing relative rates for NeN and e

History of Lepton Flavor History of Lepton Flavor Violation SearchesViolation Searches1

10-2

10-

16

10-6

10-8

10-

10

10-

14

10-

12

1940 1950 1960 1970 1980 1990 2000 2010

Initial mu2e Goal

- N e-N

+ e+ + e+ e+ e-

K0 +e-

K+ + +e-

SINDRUM II

Initial MEG Goal

10-4

10-

16

36

Previous muon decay/conversion Previous muon decay/conversion limits (90% C.L.)limits (90% C.L.)

► Rate limited by need to veto prompt backgrounds!

>e Conversion: Sindrum II

12103.4capture

Ti

TieTiR e

11

12

11

2

102.72

100.1

102.1

102.1

e

eee

e

e e

LFV Decay:

High energy tail of coherent Decay-in-orbit (DIO)

37

Sensitivity (cont’d)Sensitivity (cont’d)

►Examples with >>1 (no e signal): Leptoquarks Z-prime Compositeness Heavy neutrino

SU(5) GUT Supersymmetry: << 1

Littlest Higgs: 1

Br(e)

Randall-Sundrum: 1

MEG

mu2e

10-12

10-14

10-16

10-1110-1310-15

R(TieTi)

10-13 10-11 10-9

Br(e)

10-16

10-10

10-14

10-12

10-10

R(TieTi)