university of arizona physics colloquium, march 7, 2008 e prebys a muon to electron experiment at...

University of Arizona Physics Colloquium, March 7, 2008E Prebys

A Muon to Electron Experiment at FermilabA Muon to Electron Experiment at Fermilab

Eric Prebys*For the Mu2e Collaboration

1

*U of A ’84 (Eng. Phys.)

University of Arizona Physics Colloquium, March 7, 2008E Prebys 2

Mu2e CollaborationMu2e Collaboration

Currently: 50 Scientists 11 Institutions

*Co-contact persons

R.M. Carey, K.R. Lynch, J.P. Miller*, B.L. RobertsBoston University

Y. Semertzidis, P. YaminBrookhaven National Laboratory

Yu.G. KolomenskyUniversity 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. TatarIdaho State University

P.T. Debevec, D.W. Hertzog, P. KammelUniversity of Illinois, Urbana-Champaign

V. LobashevInstitute for Nuclear Research, Moscow, Russia

D.M. Kawall, K.S. KumarUniversity 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. SouderSyracuse University

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


AcknowledgementAcknowledgement

• This effort has benefited greatly (and plagiarized shamelessly) from over a decade of voluminous work done by the MECO collaboration, not all of whom have chosen to join the current collaboration.

3


OutlineOutline

• Theoretical Motivation• Experimental Technique• Making Mu2e work at Fermilab• Sensitivities• Future Upgrades• Conclusion

4


GeneralGeneral

• The study or rare particle decays allows us to probe mass scales far beyond those amenable to direct searches.

• Among these decays, rare muon decays offer the possibility of experimentally clean and unambiguous evidence of physics beyond the current Standard Model.

• Such searches are a natural part of the “Intensity Frontier”, which is being proposed for Fermilab after the end of the current collider program.

• In the case of muon conversion, we can take advantage of a great deal of work that has already been done in the planning of the Muon to Electron Conversion Experiment (MECO), which was proposed at Brookhaven.

5


Lepton Number ConservationLepton Number Conservation

• The concept of Lepton Number Conservation dates back to the earliest experiments and models for the Weak Interaction, originally involving only electrons and electron neutrinos. Example:

• After the discovery of the muon, it was discovered that Lepton number was separately conserved for each lepton generation:

• These conservation laws were an important constraint in formulating what is now the “Standard Model”

6


The Standard ModelThe Standard Model

• In the Standard Model, both quarks and leptons are arranged in generations.

• In weak eigenspace, the weak interaction causes transition within generations

• Because the mass eigenstates are superpositions of the weak eigenstates, transitions between physical generations can occur, iff The mixing element is nonzero The masses are nonzero (otherwise unitarity

will force the amplitude to sum to zero)

• Thus, to first order (where neutrinos are equally massless), generational transtions are Allowed for quarks Forbidden for leptons

7


->e CLFV in the SM->e CLFV in the SM

• Forbidden in Standard Model

• Observation of neutrino mixing shows this can occur at a very small rate

• Photon can be real (->e) or virtual (N->eN)

• Standard model B.R. ~O(10-50)

8

e

0Z

First Order FCNC: Higher order dipole “penguin”:

e

Virtual mixing

W


Beyond the Standard ModelBeyond the Standard Model

• Because extensions to the Standard Model couple the lepton and quark sectors, lepton number violation is virtually inevitable.

• Charged Lepton Flavor Violation (CLFV) is a nearly universal feature of such models, 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 to direct collider searches

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

9


Generic Beyond Standard Model PhysicsGeneric Beyond Standard Model Physics

?

?

?

Flavor Changing Neutral Current

e

?N N

• Mediated by massive neutral Boson, e.g.LeptoquarkZ’Composite

• Approximated by “four fermi interaction”

Dipole (penguin)• Can involve a real photon

• Or a virtual photon

?

?

?


Muon-to-Electron Conversion: Muon-to-Electron Conversion: +N+N e+Ne+N

• Similar to ewith important advantages: No combinatorial background Because the virtual particle can be a photon or heavy neutral

boson, this reaction is sensitive to a broader range of BSM physics

• Relative rate of eand NeNis the most important clue regarding the details of the physics

105 MeV e-

• When captured by a nucleus, a muon will have an enhanced probability of exchanging a virtual particle with the nucleus.

• This reaction recoils against the entire nucleus, producing the striking signature of a mono-energetic electron carrying most of the muon rest energy


e Conversion vs. e Conversion vs. ee

12

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 Violation SearchesHistory of Lepton Flavor Violation 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


Example Sensitivities*

CΛ = 3000 TeV

-4HH μμμeg =10 ×g

Compositeness

Second Higgs doublet

2Z

-17

M = 3000 TeV/c

B(Z μe) <10

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


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

•Examples with >>1 (no e signal):LeptoquarksZ-primeCompositenessHeavy 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)


Decay in Orbit (DIO) Backgrounds: Biggest IssueDecay in Orbit (DIO) Backgrounds: Biggest Issue

• Very high rate• Peak energy 52 MeV• Must design detector to be

very insensitive to these.

• Nucleus coherently balances momentum

• Rate approaches conversion (endpoint) energy as (Es-E)5

• Drives resolution requirement.

16

N

e

e

e

e

Ordinary: Coherent:


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


Mu2e (MECO) PhilosophyMu2e (MECO) Philosophy

• Eliminate prompt beam backgrounds by using a primary beam with short proton pulses with separation on the order of a muon life time

• Design a transport channel to optimize the transport of right-sign, low momentum muons from the production target to the muon capture target.

• Design a detector to strongly suppress electrons from ordinary muon decays

~100 ns ~1.5 s

Prompt backgrounds

live window

University of Arizona Physics Colloquium, March 7, 2008E Prebys19

SignalSignal

Single, monoenergetic electron with E=105 MeV, coming from the target, produced ~1 s (Al ~ 880ns) after the “” bunch hits the target foils

• Need good energy resolution: ≲ 0.200 MeV

• Need particle ID

• Need a bunched beam with less than 10-9 contamination between bunches


negligible 95.56 MeV10.08 MeV.0726 s

~0.8-1.5

Au(79,~197)

0.16

0.45

Prob decay >700 ns

104.18 MeV

104.97 MeV

Conversion Electron Energy

1.36 MeV.328 s1.7Ti(22,~48)

0.47 MeV.88 s1.0Al(13,27)

Atomic Bind. Energy(1s)

Bound lifetime

Re(Z) / Re(Al)

Nucleus

Aluminum is nominal choice for Mu2e

Choosing the Capture TargetChoosing the Capture Target• Dipole rates are enhanced for high-Z, but• Lifetime is shorter for high-Z

Decreases useful live window

• Also, need to avoid background from radiative muon capture

ee

NN Want M(Z)-M(Z-1) < signal energy


mu2e Muon Beam and Detectormu2e Muon Beam and Detector

MECO spectrometer design

for every incident proton 0.0025 ’s are stopped in the 17 0.2

mm Al target foils


Production RegionProduction Region

• Axially graded 5 T solenoid captures low energy backward and reflected pions and muons, transporting them toward the stopping target

• Cu and W heat and radiation shield protects superconducting coils from effects of 50kW primary proton beam

Superconducting coils

Production TargetHeat & Radiation Shield

Proton Beam

5 T2.5 T


Transport SolenoidTransport Solenoid

•Curved solenoid eliminates line-of-sight transport of photons and neutrons

•Curvature drift and collimators sign and momentum select beam

•dB/ds < 0 in the straight sections to avoid trapping which would result in long transit times

Collimators and pBar Window

2.5 T

2.1 T


Detector RegionDetector Region

1 T

1 T

2 T

• Axially-graded field near stopping target to sharpen acceptance cutoff.

• Uniform field in spectrometer region to simplify momentum analysis

• Electron detectors downstream of target to reduce rates from and neutrons Stopping Target Foils Straw Tracking Detector

Electron Calorimeter


Magnetic Field GradientMagnetic Field Gradient

25

Production

Solenoid

Transport Solenoid

Detector Solenoid


Transported ParticlesTransported Particles

26

E~3-15 MeV

Vital that e- momentum < signal

momentum


Tracking Detector/CalorimeterTracking Detector/Calorimeter

27

Coherent Decay-in-orbit, falls as (Ee-E)5


A long time comingA long time coming

1992 MELC proposed at Moscow Meson Factory

1997MECO proposed for the AGS at Brookhaven as part of RSVP (at this time, experiment incompatible with Fermilab)

1998-2005intensive work on MECO technical design: magnet system costed at $58M, detector at $27M

July 2005 RSVP cancelled for financial reasons

2006MECO subgroup + Fermilab physicists work out means to mount experiment at Fermilab

June 2007 mu2e EOI submitted to Fermilab

October 2007 LOI submitted to Fermilab

Fall 2008 mu2e submits proposal to Fermilab

2010 technical design approval: start of construction

2014 first beam


Enter FermilabEnter Fermilab

Fermilab Built ~1970

200 GeV proton beams Eventually 400 GeV

Upgraded in 1985 900GeV x 900 GeV p-pBar

collisions Most energetic in the world ever

since Upgraded in 1997

Main Injector-> more intensity 980 GeV x 980 GeV p-pBar

collisions Intense neutrino program

Will become second most energetic accelerator (by a factor of seven) when LHC comes on line ~2009

What next???


The Fermilab Accelerator ComplexThe Fermilab Accelerator Complex

Min

iBoo

NE/

BNB

NU

MI

University of Arizona Physics Colloquium, March 7, 2008E Prebys microBooNE, August 20th, 2007 - Prebys

31

Preac(cellerator) and LinacPreac(cellerator) and Linac

“Preac” - Static Cockroft-Walton

generator accelerates H- ions from 0 to 750

KeV. “Old linac”(LEL)- accelerate H- ions from 750

keV to 116 MeV

“New linac” (HEL)- Accelerate H- ions from

116 MeV to 400 MeV


BoosterBooster

• Accelerates the 400 MeV beam from the Linac to 8 GeV•Operates in a 15 Hz offset resonant circuit

•Sets fundamental clock of accelerator complex

•From the Booster, 8 GeV beam can be directed to

• The Main Injector

• The Booster Neutrino Beam (MiniBooNE)

• A dump.

•More or less original equipment


Main Injector/RecyclerMain Injector/Recycler

• The Main Injector can accept 8 GeV protons OR antiprotons from

• Booster

• The anti-proton accumulator

• The Recycler (which shares the same tunnel and stores antiprotons)

• It can accelerate protons to 120 GeV (in a minimum of 1.4 s) and deliver them to

• The antiproton production target.

• The fixed target area.

• The NUMI beamline.

• It can accelerate protons OR antiprotons to 150 GeV and inject them into the Tevatron.


Present Operation of Debuncher/AccumulatorPresent Operation of Debuncher/Accumulator

• Protons are accelerated to 120 GeV in Main Injector and extracted to pBar target

• pBars are collected and phase rotated in the “Debuncher”

• Transferred to the “Accumulator”, where they are cooled and stacked

• Not used for NOvA


Producing ~10Producing ~101818

6 batches x 4x1012 /1.33 s x 2x107 s/yr

= 3.6x1020 protons/yr

mu2e

Note: 8 GeV booster energy is the optimal energy for mu2e muon beam


Proposed LocationProposed Location

• Requires new building.

• Minimal wetland issues.

• Can tie into facilities at existing experimental hall.


What we GetWhat we Get

Proton flux 1.8x1013 p/s

Running time 2x107 s

Total protons 3.6x1020 p/yr

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


Three Types of BackgroundsThree Types of Backgrounds

•Muon decay in orbit: → e

• Ee < mc2 – ENR – EB

• N (E0 - Ee)5

• Fraction within 3 MeV of endpoint 5x10-15

• Defeated by good energy resolution

•Radiative muon capture: Al → Mg

• endpoint 102.5 MeV• 10-13 produce e- above 100 MeV

1. Stopped Muon Induced Backgrounds


Backgrounds (continued)Backgrounds (continued)

2. Beam Related Backgrounds•Suppressed by minimizing beam

between bunches– Need ≲ 10-9 extinction– Get 10-3 for free

•Muon decay in flight: → e

• Since Ee < mc2/2, p > 77 GeV/c

•Radiative capture:N →N*, Z → ee

•Beam electrons•Pion decay in flight:

→ ee3. Asynchronous Backgrounds• Cosmic rays

• suppressed by active and passive shielding


The Bottom LineThe Bottom Line

Roughly half of background is beam related, and half interbunch contamination related

Total background per 3.4x1020 protons, 2x107 s:0.43 events

Signal for Re = 10-16: 5 eventsSingle even sensitivity: 2x10-17

90% C.L. upper limit if no signal: 6x10-17

Blue text: beam related.


Possible Future: “Project X”Possible Future: “Project X”

• Three 5 Hz pulses every 1.4 s Main Injector cycle = 2.3MW at 120 GeV

• This leaves four pulses (~200 kW) available for 8 GeV physics• These will be automatically stripped and stored in the Recycler,

and can also be rebunched there.

41


Experimental Challenges for Increased FluxExperimental Challenges for Increased Flux

• Achieve sufficient extinction of proton beam. Current extinction goal directly driven by total protons

• Upgrade target and capture solenoid to handle higher proton rate Target heating Quenching or radiation damage to production solenoid

• Improve momentum resolution for the ~100 MeV electrons to reject high energy tails from ordinary DIO electrons. Limited by multiple scattering in target and detector planes Requirements at or beyond current state of the art.

• Operate with higher background levels. High rate detector

• Manage high trigger rates• All of these efforts will benefit immensely from the knowledge and

experience gained during the initial phase of the experiment.• If we see a signal a lower flux, can use increased flux to study in detail

Precise measurement of Re

Target dependence Comparison with e rate


However, the future has some uncertainty!However, the future has some uncertainty!

43

(from Dep. Director Y-K Kim)


ConclusionsConclusions

• We have proposed a realistic experiment to measure

• Single event sensitivity of Re=2x10-17

• 90% C.L. limit of Re<6x10-17

• ANY signal = Beyond Standard Model physics• This represents an improvement of more than four orders of

magnitude compared to the existing limit, or over a factor of ten in effective mass reach. For comparison

– TeV -> LHC = factor of 7– LEP 200 -> ILC = factor of 2.5

• Potential future upgrades could increase this sensitivity by one or two orders of magnitude

• ANY signal would be unambiguous proof of physics beyond the Standard Model

• The absence of a signal would be a very important constraint on proposed new models.

capture Al

AlAl

e

R e


Backup SlidesBackup Slides

45


Project X LinacProject X Linac

46β=1 β=1 β=1 β=1 β=1

Modulator

β=1 β=1 β=1 β=1

Modulator

36 Cavites / Klystron

ILC LINAC 8 Klystrons288 Cavities in 36 Cryomodules 1300 MHz β=1

β<1 ILC LINAC2 Klystrons

96 Elliptical Cavities12 Cryomodules

1300 MHz 0.1-1.2 GeV

β=1 β=1 β=1 β=1 β=1

Modulator

β=1 β=1 β=1 β=1

Modulator

β=1 β=1 β=1 β=1 β=1

Modulator

β=1 β=1 β=1 β=1

Modulator

β=1 β=1 β=1 β=1 β=1

Modulator

β=1 β=1 β=1 β=1

Modulator

10 MWILC

Multi-BeamKlystrons48 Cavites / Klystron

β=.81

Modulator

β=.81 β=.81 β=.81 β=.81 β=.81

8 Cavites / Cryomodule

0.5 MW Initial 8 GeV Linac11 Klystrons (2 types)

449 Cavities 51 Cryomodules

“PULSED RIA”Front End Linac

325 MHz 0-110 MeV H- RFQ MEBT RTSR SSR DSR

Single3 MW

JPARCKlystron

Multi-Cavity Fanout at 10 - 50 kW/cavityPhase and Amplitude Control w/ Ferrite Tuners

DSR

β=.47

Modulator

β=.47 β=.61 β=.61 β=.61 β=.61

or… 325 MHz Spoke Resonators

Elliptical Option

Modulator

10 MWILC

Klystrons


Helical Cooling ChannelHelical Cooling Channel

47

A helical cooling channel (similar to a “Siberian Snake”) provides transverse cooling of muon beam:

This, together with an ionizing degrader could allow the forward muons to be used, for a much higher efficiency.


The Big Picture: Goals of ExperimentThe Big Picture: Goals of Experiment

• Initial Phase: Exploit post-collider accelerator modifications at

Fermilab to mount a ->e conversion experiment patterned after proposed MECO experiment at BNL

• 4x1020 protons in ~2 years• Measure

• Single event sensitivity of Re=2x10-17

• 90% C.L. limit of Re<6x10-17

• ANY signal = Beyond Standard Model physics

• Ultimate goal Take advantage of intense proton source being

developed for Fermilab (“Project X”) as well as muon collider R&D

• If no signal: set limit Re<1x10-18

• If signal: measure target dependence, etc

capture Al

AlAl

e

R e


Beam Related RatesBeam Related Rates

• Cut ~700 ns after pulse to eliminate most serious prompt backgrounds.


Proton Timeline: Now and Post-ColliderProton Timeline: Now and Post-Collider

• In order to increase protons to the NOvA neutrino experiment after the collider program ends, protons will be “stacked” in the Recycler while the Main Injector is ramping, thereby eliminating loading time.

50

15 Hz Booster cycles

Present Operation:

“wasted” loading time


Available Protons: NOvA TimelineAvailable Protons: NOvA Timeline

Roughly 6*(4x1012 batch)/(1.33 s)*(2x107 s/year)=3.6x1020 protons/year available

MI uses 12 of 20 available Booster Batches per 1.33 second cycle

Preloading for NOvA

Available for 8 GeV program

Recycler

Recycler MI transfer

15 Hz Booster cyclesMI NuMI cycle (20/15 s)


Delivering Protons: “Boomerang” SchemeDelivering Protons: “Boomerang” Scheme

• Deliver beam to Accumulator/Debuncher enclosure with minimal beam line modifications and no civil construction.

Recycler(Main Injector

Tunnel)

MI-8 -> Recycler done

for NOvA

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


Momentum StackingMomentum Stacking

• Inject a newly accelerated Booster batch every 67 mS onto the low momentum orbit of the Accumulator

• The freshly injected batch is accelerated towards the core orbit where it is merged and debunched into the core orbit

• Momentum stack 3-6 Booster batches

T<133ms

T=134ms

T=0

Energy

1st batch is injected onto the injection orbit

1st batch is accelerated to the core orbit

T<66ms

2nd Batch is injected

T=67ms

2nd Batch is accelerated

3rd Batch is injected


Rebunching in Accumulator/DebuncherRebunching in Accumulator/Debuncher

Momentum stack 6 Booster batches directly in Accumulator (i.e. reverse direction)

Capture in 4 kV h=1 RF System.

Transfer to Debuncher

Phase Rotate with 40 kV h=1 RF in Debuncher

Recapture with 200 kV h=4 RF system

t~40 ns


Resonant ExtractionResonant Extraction

• Exploit 29/3 resonance• Extraction hardware similar to

Main Injector Septum: 80 kV/1cm x 3m Lambertson+C magnet ~.8T x

3m


Beam ExtinctionBeam Extinction

• Need 10-9

• Get at least ~10-3 from beam bunching• Remainder from AC Dipole in beam line

• Working with Osaka (FNAL+US-Japan funds) to develop AC dipole design, as well as explore measurement options


Expected Background (from MECO TDR)Expected Background (from MECO TDR)

For 4x1020 protons on target:Source Events Comments

decay in orbit 0.25 S/N = 20 for Re = 10-16

Tracking errors < 0.006

Radiative decay < 0.005

Beam e- < 0.04

decay in flight < 0.03 Without scattering in stopping target

decay in flight 0.04 With scattering in stopping target

decay in flight < 0.001

Radiative capture 0.07 From out of time protons

Radiative capture 0.001 From late arriving pions

Anti-proton induced 0.007 Mostly from

Cosmic ray induced 0.004 Assuming 10-4 CR veto inefficiency

Total Background 0.45 Assuming 10-9 inter-bunch extinction

Signal Events 5 For Re = 10-16


Cost and Time ScaleCost and Time Scale

• A detailed cost estimate of the MECO experiment had been done just before it was cancelled* Solenoids and cryogenics: $58M Remainder of experimental apparatus: $27M

• Additional Fermilab costs have not been worked out in detail, but are expected to be on the order of $10M.

• Hope to begin Accelerator work along with NOvA upgrades ~2010 (or 2011 if Run II extended)

• Based on the original MECO proposal, we believe the experiment could be operational within five years from the start of significant funding Driven by magnet construction. ~2014

• With the proposed beam delivery system, the experiment could collect the nominal 4x1020 protons on target in about one to two years, with no impact on NOvA NOvA rate limited by Main Injector

*Costs in 2005 dollars, including contingency


Tracking Detector/CalorimeterTracking Detector/Calorimeter

• 3000 2.6 m straws (r,) ~ 0.2 mm

• 17000 Cathode strips z) ~ 1.5 mm

• 1200 PBOW4 cyrstals in electron calorimeter E/E ~ 3.5%

• Resolution: .19 MeV/c

59

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