May 2 2007William Molzon, UC Irvine Muon Physics at Fermilab 1

Muon Physics at Fermilab

• Will the physics be important in a global context when the experiment is done?

• Can it be done at Fermilab with reasonable resources in a reasonable time?

• Can it be done uniquely or substantially better at Fermilab than at other labs?

• Is the experiment unique in its physics reach?

May 2 2007William Molzon, UC Irvine Muon Physics at Fermilab 2

Possible Muon Physics Experiments 1

• Study of Michel decays of muons – test of precision electroweak physics− Stopping + beam (very low rate)− Currently being done at TRIUMF− First result arxiv.org/PS_cache/hep-ex/pdf/0409/0409063v1.pdf− Best done at low energy facilities, no special muon beam properties

• Measurement of muon lifetime – precise measurement of Fermi coupling constant− Low intensity positive muon beam – no special beam characteristics − MuLan result

• Measurement of muon capture on protons – nucleon axial form factor− Relatively low intensity - beam− Currently being done at PSI − MuCap Results

• Probably none of these are good candidates for Fermilab, but might be done parasitically at a flexible muon facility

May 2 2007William Molzon, UC Irvine Muon Physics at Fermilab 3

Possible Muon Physics Experiments 2

• Measurement of muon g-2 – search for non-SM physics − Potential contributions from any kinds of loop, in particular supersymmetry − ~3 GeV + and - beams – magic − Best result from BNL – hint of non-SM value− Used large fraction of BNL intensity (~100kW)− Limited by experiment and theory of the SM contributions – improvements possible− Next generation needs 100X muon flux (10x precision) – higher power, more efficient beam− JPARC LOI – 5-10 improvement over current BNL result

• ~1012 detected muon decays • Large fraction of JPARC beam power with many very short pulses

− Fermilab at 8 GeV probably not competitive if limited to a fraction of the full beam power (energy too low for 3 GeV pion production, but should be checked)

• Measurement of muon electric dipole moment – non-SM CP violation− Goal of ~10-24 e•cm (well above the SM expectation)− Uses short pulses proton pulses at few x 10 Hz− Momentum select pions (~600 MeV/c) to produce polarized muons to store in a ring− JPARC_LOI

• NP2 = 1.5x1017 where N is the number of stored muons, P is the polarization • Beam based on PRISM approach (see later discussion on LFV)

− BNL white paper • 1.5x1015 detected decay electrons • 3x1013 24-GeV protons per second (~100 kW)

− Candidate for Fermilab facility • 600 MeV pion yield with 8 GeV protons should be checked• Possible problem with getting multiple pulses per store out of debuncher (not studied)

May 2 2007William Molzon, UC Irvine Muon Physics at Fermilab 4

Possible Muon Physics Experiments 3: Muon and Electron Number Violation

• →e+ − Currently being done at PSI – MEG experiment− First phase goal of 10-13

− Limited by backgrounds • S/N proportional to Rate x E

x Ee x t x

• Rate dependence of background limits stop rate to <108 Hz

− Possibility of pushing MEG to 10-14 will depend on performance − Background limitations will be hard to overcome much beyond this− Probably not a good candidate for Fermilab – best done at PSI

• Accelerator produces enough beam with semi-transparent target parasitic with neutron source

• Proton energy is high enough to produce positive pions with relatively high efficiency

• →e-e+e-

− Best result from very old experiment: B < 10-12

− Probably best done at PSI – surface muon beam with enough intensity is available

May 2 2007William Molzon, UC Irvine Muon Physics at Fermilab 5

Possible Muon Physics Experiments 3: Muon and Electron Number Violation

• -N→e-N− Best result from SINDRUM2 at PSI: Re < 6x10-13

− MECO proposal at BNL was a single event sensitivity of 10-17, motivated by• Predictions of models (e.g. good coverage of supersymmetry predictions)• Reach greater than that of MEG experiment

− Requires pulsed muon beam (~1 MHz) intensity of ~1011 Hz− Best done with ~8 GeV proton source

• Near turn-on of anti-proton production: anti-proton induced backgrounds rise sharply above 8 GeV

• Maximize pion yield per beam power: little increase in muon yield/kW above this

− Uniquely capable of using very intense muon source− Limited by backgrounds around 10-17 (energy resolution from straggling and

scattering in detectors and rate effects, some muon beam backgrounds)• Slow and expensive improvement in background limit with improved technology• Completely different technology (PRISM/PRIME) proposes reduced background

− Best candidate for a flagship Fermilab muon program • Negative result from MEG will make conversion experiment probably the only hope for

seeing muon number violation• Positive result from MEG will motivate additional experiments to clarify the source of LFV

May 2 2007William Molzon, UC Irvine Muon Physics at Fermilab 6

Current Limits on Muon Number Violating Processes

0 12LB(K e ) < 4.7 10

0 0 10LB(K e ) 3.2 10

+ + - -12B( e e e ) < 1×10

+ 11B( e ) < 1.2 10

-13( A e A) < 6.1 10

( A A )

G=0

G=1

Mass limit

B(K+ → + + e-) < 1.3 x 10-11

150 TeV/c2

50 TeV/c2

50 TeV/c2

365 TeV/c2

21 TeV/c2

86 TeV/c2

May 2 2007William Molzon, UC Irvine Muon Physics at Fermilab 7

-N→e-N Sensitivity to Different Physics Processes

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

May 2 2007William Molzon, UC Irvine Muon Physics at Fermilab 8

Supersymmetry Predictions for LFV Processes • From Hall and Barbieri

Possibly observable levels of LFV insupersymmetric grand unified models

• Extent of lepton flavor violation in grand unified supersymmetry related to quark mixing

• Original ideas extended by Hisano, et al.

ProcessCurrent

LimitSUSY level

10-12 10-15

10-11 10-13

10-6 10-9

+ e

- -N e N

100 200 300 100 200 300

Rem (GeV)

Rem (GeV)

N→eN single event sensitivity goal

10 -11

10 -13

10 -15

10 -19

10 -17

10 -21

Re

10 -10

10 -12

10 -14

10 -18

10 -16

10 -20

PSI →e single event sensitivity

Current SINDRUM2 boundCurrent MEGA

bound

B(

e

)

May 2 2007William Molzon, UC Irvine Muon Physics at Fermilab 9

10

(GeV)M R2

141312101010

bound

Experimental

-1-2-3 11010

MSW small angle

MSW large anglesmall mass

J ust so

MSW large angle

sin 22

m

2(e

V )2

e

)

Br(

10

10

10

10

10

10

10

10

-3

-4

-5

-6

-7

-8

-9

-10

10

-11

10

10

10

10

10

10

-10

-11

-12

-13

-14

-15

Rates for LFV Processes Linked to Oscillations

From the model of J. Hisano and D. Nomura, Phys. Rev. D59 (1999): SU(5) grand unified model with heavy, right-handed neutrinos

MSW la

rge a

ngle

Just

soPossible interpretations of solar deficit

MEG →egoal

Goal of new -N→e-N experiment

Just so

MSW small angle

MSW large angle

MSW sm

all an

gle

m2

[eV

2 ]

MR2 [GeV/c2]

BR

(→

e)

sin2(2)

MEGA →elimit

May 2 2007William Molzon, UC Irvine Muon Physics at Fermilab 10

Why -Ne-N Conversion Experiment?

• Rate for LFV processes might be significantly higher, but reaching equivalent sensitivity in popular models is very difficult, requiring new accelerator and very large improvement in experimental techniques – significant progress is unlikely to be made in next decade

• Improvements in kaon processes appear very difficult, and rates are not higher in most model predictions.

• edecay is more sensitive at same branching fraction for the most popular extensions to the Standard Model, but is less sensitive for other modes and appears to be limited by background considerations at 1000-10000 times larger branching fraction than could be achieved in next generation conversion experiment. Conversion experiment has possibility of both helicity changing and helicity conserving amplitudes.

• Most robust channel for discovering LFV in charged sector (funding and other non-technical considerations aside) appears to be in -Ne-N experiment. This is the only channel that can be pushed to significantly higher sensitivity due to backgrounds in other modes.

• Things are likely to change before a new conversion experiment is done: − MEG may see eat PSI – rates for other LFV processes will be needed to understand the

underlying mechanism. − MEG may set a limit of 10-13 to 10-14 – more sensitive experiments will be needed, probably not

possible with e− LHC my discover supersymmetric particles or evidence of other new physics at the TeV scale –

experiments to probe the flavor structure of new physics will be equally as important as without such new results.

May 2 2007William Molzon, UC Irvine Muon Physics at Fermilab 11

Limitations: Detector Rates, Rate Induced Physics Backgrounds

For LFV experiments, stop muons and look at decay or conversion processes− Detector rates from Michel decays (e) decays

− Detector rates from other beam particles, muon capture processes, etc

− For most processes, physics backgrounds dominated by accidentals at useful rates• Example: + e+

sensitivity goal 10-14

running time 107 sdetection efficiency 0.1

macro duty cycle 1stop rate 108

background dominated by accidental coincidences of Michel positron, photon from radiative decay or positron annihilation in flight

− Without some care, detector rates are too high• Example: muon conversion on a nucleus -N e-N

sensitivity goal 10-17

running time 107 sdetection efficiency 0.2macro duty cycle 0.5stop rate 1011

decay rate of 1011 Hz, instantaneous intensity higher with pulsed beameven higher fluxes from neutrons, photons from muon capture

− Muon conversion experiment is unique in ability to use very high stopping rates

May 2 2007William Molzon, UC Irvine Muon Physics at Fermilab 12

The MEG Experiment at PSI

Ee / Emax

0.90 0.95 1.00

0.90

0.95

1.0

0

E

/ E

ma

x

• Experiment limited by accidental backgrounds: e+ from Michel decay, from radiative decay or annihilation in flight. S/N proportional to 1/Rate.

–Ee : 0.8% (FWHM) E : 4.5% (FWHM)–e : 18 mrad (FWHM) te : 141ps (FWHM)

• MEG uses the PSI cyclotron (1.8 mA at ~600 MeV) to produce 108 per second (surface muon beam)

• Partial engineering run this autumn• First physics run Spring 2007• Sensitivity of 10-13 with 2 years running (c.f. MEGA 1.2x10-11)• Possibility of detector improvements to reach 10-14 in subsequent 2 year run

May 2 2007William Molzon, UC Irvine Muon Physics at Fermilab 13

What Drives the Design of the Next-Generation Conversion Experiment?

Considerations of potential sources of fake backgrounds specify much of the design of the beam and experimental apparatus.

SINDRUM2 currently has thebest limit on this process:

Expected signal

Cosmic raybackground

Prompt background

Experimental signature is105 MeV e- originating in a thin stopping target.

Muon decay

May 2 2007William Molzon, UC Irvine Muon Physics at Fermilab 14

Pulsed Proton Beam Requirement for -N→e-N Experiment

• Subsequent discussion focuses on accelerator operating at 8 GeV with 2 1013 protons per second and 90% duty cycle – 25 kW beam power at 8 GeV

• Pulsed proton beam generated using RF structure of appropriate accelerator or storage ring

• To eliminate prompt backgrounds, we require < 10-9 protons between bunches for each proton in bunch. We call this the beam extinction.

• Gap between proton pulse and start of detection time

largely set by pion lifetime (~25

Alternate beam strategy (PRISM + PRIME) – use very short proton pulses at low frequency (100 Hz), very long muon storage time to eliminate beam backgrounds, very different detector geometry to reduce detector rates.

Set by

May 2 2007William Molzon, UC Irvine Muon Physics at Fermilab 15

Existing and Possible Muon Sources

• Available muon beams at TRIUMF(500MeV, 0.3MW) and PSI (590MeV, 1MW)− DC beams with intensity up to 108 per second, less for -

− Limitations of low energy machines• Muons per watt of beam power low due to low pion production cross section at low energy• Fewer negative muons• Fewer options to make pulsed beam• More difficulty with beam power on target (wrt higher energy accelerators)

• Potential muon beam sources− BNL proton synchrotron

• few to 24 GeV proton beam • low frequency RF for acceleration – relatively easy pulsing • available slow extraction• beam power 20-50 kW at 8 GeV

− JPARC• Few to 40 (50) GeV proton beam• Relatively low frequency RF• Slow extraction being developed• Beam power 1 MW at 50 GeV

− Fermilab• 8 to 120 GeV• No existing slow spill• Few 10s of kW at 8 GeV, few 100 kW at 120 GeV

May 2 2007William Molzon, UC Irvine Muon Physics at Fermilab 16

Comparison of Potential Muon Beam SourcesFacility BNL PSI JPARC FermilabAccelerator Synchrotron Cyclotron Synchrotron Synchrotron

+ stretcher

Proton energy [GeV] 8.0 0.59 40.0 8.0Duty cycle 0.5 1.0 0.19 0.9Proton intensity [THz]

average 20 9400 40 20instantaneous 40 9400 210 22

Proton interaction fraction 0.8 0.04 0.8 0.8Power [kW] 26 >1000 256 26Average muon intensity [GHz] 100 0.1 100 50Pulse spacing [ns] 1350 0 1130 1650

Fermilab• Essentially best duty cycle • Best micro structure – nearly ideal match to muon lifetime in orbit• Sufficient intensity is available, compatible with a simultaneous neutrino program

JPARC• micropulse frequency is at (perhaps beyond) the limit set by backgrounds• duty cycle is bad – for equivalent muon rate, JPARC will have 5X instantaneous rate,

perhaps compensated by detector ideaPSI

• Highest beam power, but can only use thin production target and fraction of beam• Can only be pulsed by chopping beam (reducing intensity)• Negative muon yield not saturated

May 2 2007William Molzon, UC Irvine Muon Physics at Fermilab 17

Possible Muon Conversion Experiments 1

• PRISM/PRIME at JPARC – ambitious program based on cooled muon beam with very low duty cycle and sensitivity of order 10-18

− Uses essentially full JPARC power (>1 MW) − Pulse proton beam at ~100 Hz, few ns pulse width– limited by maximum cycling rate

of the FFAG− Phase rotate (exchange energy spread for time spread) in FFAG accelerator

• Allows very thin stopping target to minimize electron straggling – improve electron energy resolution and reduce background

− Instantaneous muon decay intensity >105 times that of MECO− Use a novel electron transport and detector system (born of necessity)

• passively momentum select high energy electrons using a curved solenoid with large aperture to reduce instantaneous rate to acceptable level.

− Not in approved JPARC program − My understanding is that this is now deferred indefinitely

• New LOI for JPARC conversion experiment− Not publicly available (I’ll request a copy for our use)− Goal similar to MECO (< 10-16)− Uses proton (and muon) beam similar to MECO− Retains electron transport system and detector system from PRIME

May 2 2007William Molzon, UC Irvine Muon Physics at Fermilab 18

MECO: A Model Muon Beam and Conversion Experiment

Straw Tracker

Crystal Calorimeter

Muon Stopping Target

Muon Beam Stop

Superconducting Production Solenoid

(5.0 T – 2.5 T)

Superconducting Detector Solenoid

(2.0 T – 1.0 T)

Superconducting Transport Solenoid

(2.5 T – 2.1 T)

Collimators

May 2 2007William Molzon, UC Irvine Muon Physics at Fermilab 19

Possible Muon Conversion Experiments 2: MECO at Fermilab

• Could build on the MECO experiment proposed for BNL− MECO proposal and MECO part of RSVP proposal have been well reviewed, costed− Draft technical proposal exists − Extensive reference design documents exist − Detailed conceptual design of the superconducting magnet system completed− Many project and physics reviews have been done

• Potential beam advantages− Pulse spacing marginally better due to circumference of debuncher ring− Duty cycle would be nearly 100% (c.f. ~50% for BNL)− Increased running time per year

• Required accelerator modifications under study − Upgrades to booster intensity, transfer to and stacking in accumulator, store in

debuncher− Rebunching scheme− Slow extraction− Secondary beam extinction ideas from MECO

• Loosely coupled group is planning LOI, forming a collaboration

May 2 2007William Molzon, UC Irvine Muon Physics at Fermilab 20

Expected Signal and Background with 4x1020 8 GeV Protons

Sources of background will be determined directly from data.

Background Source Events Comments decay in orbit 0.25 S/N = 4 for Re = 2 10-17

Tracking errors < 0.006

Beam e- < 0.04

decay in flight < 0.03 No scattering in target

decay in flight 0.04 Scattering in target

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 10-4 CR veto inefficiencyTotal Background 0.45 With 10-9 inter-bunch extinction

Background calculated for 107 s running time at intensity giving 5 signal event for Re = 10-16.

Factors affecting the Signal Rate FactorRunning time (s) 107

Proton flux (Hz) (50% duty factor, 740 kHz pulse) 4 1013

entering transport solenoid / incident proton 0.0043

stopping probability 0.58

capture probability 0.60

Fraction of capture in detection time window 0.49

Electron trigger efficiency 0.90

Geometrical acceptance, fitting and selection criteria efficiency 0.19

Detected events for Re = 10-16 5.0

5 signal events with0.5 background events in 107 s running if Re = 10-16

May 2 2007William Molzon, UC Irvine Muon Physics at Fermilab 21

Summary• For muon conversion experiment

− Will the physics be important in a global context when the experiment is done?• Yes, independent of results of + e+experiment, independent of discovery (or not) of

supersymmetry at Tevatron, LHC− Can it be done at Fermilab with reasonable resources in a reasonable time?

• Yes, pending some studies and how much money is considered reasonable for the physics.

– No problems yet seen with technical implementation, more study needed.– Experiment resources of order $100M including contingency, inflation, fully loaded,

based on MECO costing– Accelerator modifications, proton transport, civil construction uncosted.– Running time of 3-4 years at full intensity, realistic startup, reaction to first results.

− Can it be done uniquely or substantially better at Fermilab than at other labs?• Certainly yes

– Claimed improved sensitivity of PRISM/PRIME is not thoroughly studied, requires new technology, probably substantially increased costs (in U.S. cost accounting)

– More comparable (in terms of technical implementation) experiment at JPARC suffers from significant disadvantages, is not approved

− Is the experiment unique in its physics reach?• Yes, other LFV experiments are of lower sensitivity, narrower in scope, more difficult to

upgrade.• For other muon experiments

− Probably not flagship experiments, could be done elsewhere or parasitically at Fermilab