May William 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 William 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/ v1.pdfarxiv.org/PS_cache/hep-ex/pdf/0409/ v1.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 resultMuLan result Measurement of muon capture on protons – nucleon axial form factor −Relatively low intensity  - beam −Currently being done at PSI −MuCap ResultsMuCap Results Probably none of these are good candidates for Fermilab, but might be done parasitically at a flexible muon facility

May William 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 resultJPARC LOI ~10 12 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 ~ ecm (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_LOIJPARC_LOI NP 2 = 1.5x10 17 where N is the number of stored muons, P is the polarization Beam based on PRISM approach (see later discussion on LFV) −BNL white paperBNL white paper 1.5x10 15 detected decay electrons 3x 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 William 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 −Limited by backgrounds S/N proportional to Rate x  E   x  Ee x  t x    Rate dependence of background limits stop rate to <10 8 Hz −Possibility of pushing MEG to 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 < −Probably best done at PSI – surface muon beam with enough intensity is available

May William 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: R  e < 6x −MECO proposal at BNL was a single event sensitivity of , 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 ~10 11 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 (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 William Molzon, UC Irvine Muon Physics at Fermilab 6 Current Limits on Muon Number Violating Processes  G=0  G=1 Mass limit B(K + →  +  + e - ) < 1.3 x TeV/c 2 50 TeV/c TeV/c 2 21 TeV/c 2 86 TeV/c 2

May William Molzon, UC Irvine Muon Physics at Fermilab 7  - N→e - N Sensitivity to Different Physics Processes Compositeness Second Higgs doublet Heavy Z’, Anomalous Z coupling Predictions at Supersymmetry Heavy Neutrinos Leptoquarks After W. Marciano

May William Molzon, UC Irvine Muon Physics at Fermilab 8 Supersymmetry Predictions for LFV Processes From Hall and Barbieri Possibly observable levels of LFV in supersymmetric grand unified models Extent of lepton flavor violation in grand unified supersymmetry related to quark mixing Original ideas extended by Hisano, et al. Process Current Limit SUSY level  N→eN single event sensitivity goal ReRe PSI  →e  single event sensitivity Current SINDRUM2 bound Current MEGA bound B (   e  )

May William Molzon, UC Irvine Muon Physics at Fermilab 9 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 large angle Just so Possible interpretations of solar  deficit MEG  →e  goal Goal of new  - N→e - N experiment Just so MSW small angle MSW large angle MSW small angle  m 2 [eV 2 ] M R2 [GeV/c 2 ] BR(  →e  ) sin 2 (2  ) MEGA  →e  limit

May William Molzon, UC Irvine Muon Physics at Fermilab 10 Why  - N  e - 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.  e  decay 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 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  - N  e - 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  e  at PSI – rates for other LFV processes will be needed to understand the underlying mechanism. −MEG may set a limit of to – 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 William 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 running time 10 7 s detection efficiency0.1 macro duty cycle1 stop rate10 8 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 running time10 7 s detection efficiency0.2 macro duty cycle0.5 stop rate10 11 decay rate of Hz, instantaneous intensity higher with pulsed beam even higher fluxes from neutrons, photons from muon capture −Muon conversion experiment is unique in ability to use very high stopping rates

May William Molzon, UC Irvine Muon Physics at Fermilab 12 The MEG Experiment at PSI E e / E max E  / E max Experiment limited by accidental backgrounds: e + from Michel decay,  from radiative decay or annihilation in flight. S/N proportional to 1/Rate. –  E e : 0.8% (FWHM)  E  : 4.5% (FWHM) –  e  : 18 mrad (FWHM)  t e  : 141ps (FWHM) MEG uses the PSI cyclotron (1.8 mA at ~600 MeV) to produce 10 8   per second (surface muon beam) Partial engineering run this autumn First physics run Spring 2007 Sensitivity of with 2 years running (c.f. MEGA 1.2x ) Possibility of detector improvements to reach in subsequent 2 year run

May William 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 the best limit on this process: Expected signal Cosmic ray background Prompt background Experimental signature is105 MeV e - originating in a thin stopping target. Muon decay

May William 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  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 < 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 William 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 10 8 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 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 William Molzon, UC Irvine Muon Physics at Fermilab 16 Comparison of Potential Muon Beam Sources 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 idea PSI 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 William 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 PRISM/PRIME at JPARC −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 >10 5 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 (< ) −Uses proton (and muon) beam similar to MECO −Retains electron transport system and detector system from PRIME

May William 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 William 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, costedMECO proposalMECO part of RSVP proposal −Draft technical proposal existsDraft technical proposal −Extensive reference design documents existExtensive reference design −Detailed conceptual design of the superconducting magnet system completedDetailed conceptual design −Many project and physics reviews have been doneMany project and physics reviews 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 collaborationLoosely coupled group

May William Molzon, UC Irvine Muon Physics at Fermilab 20 Expected Signal and Background with 4x GeV Protons Sources of background will be determined directly from data. Background SourceEventsComments  decay in orbit 0.25 S/N = 4 for R  e = 2  Tracking errors< Beam e - < 0.04  decay in flight < 0.03No scattering in target  decay in flight 0.04Scattering in target Radiative  capture 0.07From out of time protons Radiative  capture 0.001From late arriving pions Anti-proton induced0.007 Mostly from   Cosmic ray induced CR veto inefficiency Total Background0.45With inter-bunch extinction Background calculated for 10 7 s running time at intensity giving 5 signal event for R  e = Factors affecting the Signal RateFactor Running time (s)10 7 Proton flux (Hz) (50% duty factor, 740 kHz  pulse)4   entering transport solenoid / incident proton  stopping probability 0.58  capture probability 0.60 Fraction of  capture in detection time window 0.49 Electron trigger efficiency0.90 Geometrical acceptance, fitting and selection criteria efficiency0.19 Detected events for R  e = signal events with 0.5 background events in 10 7 s running if R  e =

May William 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