high energy physics seminar, princeton university, april 15, 2009 e prebys a muon to electron...

High Energy Physics Seminar, Princeton University, April 15, 2009E Prebys

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

Eric PrebysFermilab

For the Mu2e Collaboration


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

W.J. Marciano, Y. Semertzidis, P. Yamin - Brookhaven National Laboratory

Yu.G. Kolomensky - University of California, Berkeley

W. Molzon - University of California, Irvine

C.M. Ankenbrandt , R.H. Bernstein*, D. Bogert, S.J. Brice, D.R. Broemmelsiek, R.M. Coleman, D.F. DeJongh, S. Geer, D.A. Glezinski, D.F. Johnson, R.K. Kutsche, M.A. Martens, S. Nagaitsev, D.V. Neuffer, M. Popovic, E.J. Prebys, R.E. Ray,

V.L. Rusu, P. Shanahan, M.J. Syphers, R.S. Tschirhart, H.B. White Jr., K. Yonehara, C.Y. Yoshikawa – Fermi National Accelerator Laboratory

K.J. Keeter, E. Tatar - Idaho State University

P.T. Debevec, G.D. Gollin, 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.

A.L. de Gouvea - Northwestern University

F. Cervelli, R. Carosi, M. Incagli, T. Lomtadze, L. Ristori, F. Scuri, C. Vannini - Instituto Nazionale di Fisica Nucleare Pisa

M.D. Cororan - Rice

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

J. Kane – College of William and Mary

Mu2e CollaborationMu2e Collaboration

2


AcknowledgementAcknowledgement

• This effort has benefited greatly 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


->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)

e

0Z

First Order FCNC: Higher order dipole “penguin”:

e

Virtual mixing

W

6


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

7


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

?

?

?

8


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

9


e Conversion vs. e Conversion vs. ee

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

10


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

11


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

12


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

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

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)

13


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.

N

e

e

e

e

Ordinary: Coherent:

14


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)

15


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

16


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

17


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

18


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

19


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

20


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

21


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

22


Magnetic Field GradientMagnetic Field Gradient

Production

Solenoid

Transport Solenoid

Detector Solenoid

23


Transported ParticlesTransported Particles

E~3-15 MeV

Vital that e- momentum < signal

momentum

24


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

25


SensitivitySensitivity

• Re = 10-16 gives 5 events for 4x1020 protons on target

• 0.4 events background, half from out of time beam, assuming 10-9 extinction Half from tail of

coherent decay in orbit Half from prompt

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

26


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

November 2008

Stage 1 approval. Formal Project Planning begins

2010 technical design approval: start of construction

2014? first beam

27


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???

28


The Fermilab Accelerator ComplexThe Fermilab Accelerator Complex

Min

iBoo

NE/

BNB

NU

MI

29


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

30


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

31


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.

32


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

33


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)

34


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)

35


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

36

High Energy Physics Seminar, Princeton University, April 15, 2009E Prebys June 3, 20083737

Booster-Era Beam Timelines for Mu2E Experiment

Base line scenario. Numerous other options being discussed.


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

38


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

39


Extinction in the RingsExtinction in the Rings

• RF noise, gas interaction, and intrabeam scattering cauase beam to “wander out” of the RF bucket.

• D is the dispersion function: Transverse Offset =

ΔE/E × D

• Anticipate installation of collimator in region with dispersion, removing off-momentum particles: Momentum scraping

Mu2e/PAC Meeting - 5 March 2009

40


External Extinction (AC-Dipole Scheme)External Extinction (AC-Dipole Scheme)

• Possible change from baseline in proposal: two stage collimation Dipoles at 0 and 360 Collimators at 90 and 180

Mu2e/PAC Meeting - 5 March 2009

41

Baseline design, single collimator


Proposed LocationProposed Location

• Requires new building.

• Minimal wetland issues.

• Can tie into facilities at existing experimental hall.

42


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

43


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

44


Backgrounds (continued)Backgrounds (continued)

2. Beam Related Backgrounds•Suppressed by minimizing beam

between bunches– Need ≲ 10-9 extinction– (see previous slides)

•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

45


The Bottom LineThe Bottom Line

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

Total background per 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.

46


Present areas of researchPresent areas of research• Beam delivery schemes

Try to minimize charge in Accumulator at one time. Generally a trade-off that increases instantaneous rate.

• Recalculating rates and backgrounds Models and data on low energy pion production have come a long

way in recent years.

• Optimizing magnet design Original design based on SSC superconductor, which has since

mysteriously vanished. Is magnetic mirror worth it?

• New detector options Investigating low pressure drift chamber

• Similar mass and less probability of fakes• Calibration schemes

How can we convince the world we can measure something at a < 10-16 BR?

• Siting optimization and synergy with other programs g-2 Muon collider R&D

47


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

• One 5 Hz pulses every 1.4 s Main Injector cycle = 2.1MW at 120 GeV

• This leaves six pulses (~860 kW) available for 8 GeV physics• These will be automatically stripped and stored in the Recycler,

and can also be rebunched there.

48


Accelerator Challenges for using Project X beamAccelerator Challenges for using Project X beam

• Beam delivery Accumulator/Debuncher (like initial operation)?

• How much beam can we put into the Accumulator and Debuncher and keep the beam stable?

• Radiation issues (already a problem at initial intensities).

Directly from Recycler?

• Not enough aperture for conventional resonant extraction.

• Investigating more clever ideas

49


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

50


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

(from Dep. Director Y-K Kim)

51


ConclusionsConclusions

• We have proposed a realistic experiment to measure

• Single event sensitivity of Re=2x10-17

• 90% C.L. limit of Re<6x10-17

• 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

52

high energy physics seminar, princeton university, april 15, 2009 e prebys a muon to electron...

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