Search for  -e Conversion in MECO at BNL Masaharu Aoki Osaka University 4th NuFact ’ 02 Workshop Neutrino Factories based on Muon Storage Rings Imperial College London, 1-6 July 2002

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop2 Outline Brief Introduction –Lepton Flavor Violation and SUSY-GUT –Muon-Electron Conversion (  N  e N) –  N  e N vs.   e  MECO –Learning from SINDRUM II –Potential Backgrounds –MECO features MECO muon beam line –Pulsed proton beam from AGS –Pion Production Target –Production Solenoid –Transport Solenoid –Detector Solenoid MECO Detector –Electron Tracker –Trigger Calorimeter MECO Sensitivity and Backgrounds Status of MECO and Summary Proton Beam Heat & Radiation Shield

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop3 Lepton Flavor Violation Lepton Flavor (L e, L  and L  ) Conservation is definitely violated at least for neutral lepton sector (neutrino). Extension of the Standard Model to include massive. Lepton Flavor Violation (LFV) in charged lepton sector could occur through intermediate states with mixing. However, the expected rate is far below the experimentally accessible range; (m 2 /M W 2 ) 2 ~ Many scenarios for physics beyond the SM predict sizable LFV processes in charged lepton sector. Charged LFVPhysics beyond the SM

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop4 SUSY-GUT and LFV Large top Yukawa couplings result in sizable off-diagonal components in a slepton mass matrix through radiative corrections, and that implies observable levels of LFV in some models of SUSY-GUT Barbieri and Hall, 1994 quark lepton (neutrino) slepton squark normal particlesSUSY particles ex. K-decays, B-decays ex. neutrino oscillation ex. charged lepton LFV Study of Charged LFV is almost equivalent to the study of slepton mass matrix in a framework of SUSY-GUT.

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop5 SU(5) SUSY-GUT Prediction only a few orders of magnitude below the current experimental limit. SO(10) SUSY-GUT Prediction enhanced by (m  /m  ) 2 (~100) from SU(5) prediction. SUSY-GUT Prediction Courtesy Hisano ProcessCurrent Limit SUSY-GUT level  N → e N  → e   →  MECO single event sensitivity

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop6 SUSY with RH Majorana neutrino a la Nomura and Hisano MECO single event sensitivity

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop7 History of LFV Searches Since 1948 E.P. Hincks and B. Pontecorvo, PR 73 (1948) 257 Two orders of magnitude per decade. Courtesy Kuno MECO Goal

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop8 Muon Electron Conversion Muonic atom (1s state) Neutrinoless muon nuclear capture –Single mono-energetic electron of E max = (M  - B  ) MeV (~105 MeV) –Rate is normalized to the kinematically similar weak capture process: R  e   (  - N  e - N) /  (  - N   N(Z-1)) muon decay in orbit nucleus  nuclear muon capture lepton flavors change by one unit. coherent process

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop9 Models for Muon-Electron Conversion SUSY-GUT –BR ~ Doubly Charged Higgs Boson –Logarithmic enhancement in a loop diagram for  - N  e - N, not for  e  –  ~ 1 PeV for MECO sensitivity M. Raidal and A. Santamaria, PLB 421 (1998) 250 SUSY with R-parity Violation W = ijk L i L j E c k + ’ ijk L i Q j D c k + ” ijk U c i D c j D c k -  i L i H 2 | ’ | < 2.6  for MECO sensitivity All other products measurable in  -e conversion will be more stringent than those from any other processes at MECO. Faessler et al., NPB 587 (2000) Leptquarks Heavy Z’ –M Z’ > (5-100) TeV for R  e ~ J. Bernabeu et al., NPB 409 (1993)69-86 Compositeness Multi-Higgs Models  q :model dependent combination of couplings, mixings, etc.  > 3000 TeV  q

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop10  - N  e - N vs.  e   - N  e - N Sensitive to non-photonic process   available for stopped experiment has been much less than that of   No accidental background. Rate-limited only in the sense that high detector rates will contaminate events and cause measurement errors.  e  B(  e  = 200  B(  - N  e - N) for photonic process Abundance of high intensity surface muons Rate-limited due to accidental background. Requires heroic efforts below level. The physics motivation is sufficiently strong for both Possibly different systematics, thus complementary each others. Both should be done to maximize discovery potential

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop11 MECO Collaboration Institute for Nuclear Research, Moscow V. M. Lobashev, V. Matushka, New York University R. M. Djilkibaev, A. Mincer, P. Nemethy, J. Sculli, A.N. Toropin Osaka University M. Aoki, Y. Kuno, A. Sato University of Pennsylvania W. Wales Syracuse University R. Holmes, P. Souder College of William and Mary M. Eckhause, J. Kane, R. Welsh Boston University J. Miller, B. L. Roberts, O. Rind Brookhaven National Laboratory K. Brown, M. Brennan, L. Jia, W. Marciano, W. Morse, Y. Semertzidis, P. Yamin University of California, Irvine M. Hebert, T. J. Liu, W. Molzon, J. Popp, V. Tumakov University of Houston E. V. Hungerford, K. A. Lan, L. S. Pinsky, J. Wilson University of Massachusetts, Amherst K. Kumar

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop12 Learning from SINDRUM II BR = 2 × (2000 Gold run) Major background sources were –Muon decay in orbit Requires much better resolution –Prompt   background Requires pulsed proton beam –Cosmic ray background

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop13 Potential Backgrounds I Muon Decay in Orbit –E max = E e –dN/dE e  (E max - E e ) 5 –Sets the scale for energy resolution required: N bg = 0.25 for R  e =2   E e =900 keV FWHM Radiative Muon Capture:   N   N(Z-1)  –E  max = MeV, P(E  > MeV) = 4  –P(   e + e -, E e > MeV) = 2.5  –(E e wrong measurement) < N bg < Radiative Pion Capture –BR(  emission) ~ 2% for E  > 105 MeV –P(   e + e -, < E e < MeV) = 3.5  –P(Pion stops at the muon stopping target) = 3  /proton = 1.2  /muon-stopped-in-the-target –Requires beam extinction < for N bg = 0.07, R  e =2  –Defines signal detection time window > 700 ns

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop14 Potential Backgrounds II Muon decay in flight + e - scattering in stopping target –Eliminated by using pulsed beam Beam e - scattering in stopping target –P(E e > 100 MeV) < high energy beam electron is suppressed by the curved solenoid. –N bg < 0.04 for R  e =2  Antiproton induced e - - new in MECO –Requires thin absorber to stop antiprotons in transport line Cosmic ray induced e - –Scales with running time, not beam intensity. –Requires the active and passive shielding

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop15 MECO Features Muon Intensity –1000 fold increase by using an idea from MELC at MMF   /P at 8 GeV (SINDRUM II = 10 -8, MELC = 10 -4, Muon Collider = 0.3) High Z target for improved pion production Graded solenoid field to maximize pion capture Muon Beam Quality Control –Muon transport in curved solenoid suppressing high momentum negatives and all positives and neutrals (new for MECO) Pulsed Beam A. Baertscher et al., NPA377(1982)406 –Beam pulse duration <<   –Pulse separation =   –Large duty cycle (50%) –Extinction between pulses < Detector –Graded solenoid field for improved acceptance, rate handling, background rejection (following MELC concept) –Spectrometer with nearly axial components and good resolution (new for MECO)

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop16 The MECO Apparatus Proton Beam 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 Heat & Radiation Shield

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop17 Pulsed Proton Beam from AGS BNL AGS at BNL –One of the most powerful pulsed proton drivers in the world today. 8 GeV with 4  protons per second - 50kW beam power –Below the transition energy of AGS –Suppress the antiproton production Cycle time of 1.0 sec with 50% duty factor Revolution time = 2.7  s with 6 RF buckets in which protons can be trapped and accelerated. Fill only 2 RF buckets for 1.35  s pulse spacing 2  protons/RF bucket – twice the current bunch intensity Requirement: the excellent beam extinction <10 -9 protons between bunches

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop18 The extinction = at AGS Quick test measurements –1st test 24 GeV with one RF bucket extinction < between buckets < in unfilled buckets –2nd test 7.4 GeV with one filled bucket extinction < How to improve extinction –40 kHz AC dipole and 740 kHz fast kicker magnets inside AGS ring and –RF modulated magnet and septum magnets in primary proton transport beam line. Filled bucket Unfilled bucket

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop19 Pion Production Target High Z target material Minimal material in bore to absorb  Cylinder with diameter 0.8 cm, length 16 cm About 5 kW of deposited energy Two target configurations being considered Radiation cooled tungsten –Requires high emissivity coating –Segmented into 40 disks –Maximum temperature ~ 2100K –Melting point = 3600K, evaporation = 2× mg/cm 2 s; not a problem –Thermal stresses near yield stress ; this is a problem –Requires a uniform proton beam profile on the target Raster p beam, or octopole magnet Water cooling in narrow channels in target –Required flow rate is reasonable –Temperature rise is below 100K –Detailed design and prototyping underway Temperature distribution in target segment

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop20 The MECO Superconducting Magnets Magnet Conceptual Design Report (CDR) from MIT Plasma Science and Fusion Center

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop21 Magnetic Field Specification Position along the beam path (m) B S (T) Production Solenoid T Mirror effect for maximizing pion capture acceptance Curved Transport Solenoid T Straight section : monotonically decreasing Curved section : gradient drift Detector Solenoid (muon target) T Maximize signal acceptance Detector Solenoid (spectrometer)1.0 T Uniform field

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop22 Production Solenoid Requirements –Capture most of pions and muons, and transport them toward detector –Stand up under high radiation and heat environment –50kW primary proton Proton beam Production target Toward Detector Superconducting coil Radiation and heat sheild MJ stored energy 150 W load on cold mass 15  W/g in superconductor 20 Mrad integrated dose Implementation –Axially graded magnetic field T –Cu and W heat and radiation shield

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop23 Transport Solenoid 2.5T 2.0T 2.2T 2.0T 2.3T Goals: Transport low energy   to the detector solenoid Minimize transport of positive particles and high energy particles Minimize transport of neutral particles Absorb anti-protons in a thin window Minimize long transit time trajectories Implementation –Curved solenoid eliminate line-of-sight transport of photons and neutrons. –Toroidal sections causes particles to drift out of plane; used to sign and momentum select beam. –dB/dS < 0 for straight section to avoid reflections which would cause long transit time trajectories.

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop24 Function of the Curved Solenoid Particle drifts in torus magnetic fields JD Jackson, Classical Electrodynamics D : drift distance B : magnetic field s/R : bend angle of the solenoid p s : perpendicular momentum p t : transverse momentum Curvature drift Gradient drift Charge and momentum selection

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop25 Beam Particles to Detector Limited maximum energy of beam particles Highly suppressed positive particles. Preserves pulsed beam structure –Long transit time particles are well suppressed. Signal window

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop26 Muon Yield Monte Carlo calculation –GEANT3 –Including original data models based on a measured pion production on similar targets at similar energy. –Decays, interactions, and magnetic transport included. Relative yield Muon Momentum [MeV/c] Total flux at stopping target Stopping Flux   stops/proton

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop27 Detector Solenoid 1T 2T Electron Calorimete r Tracking Detector Stopping Target: 17 layers of 0.2 mm Al Graded field in front section to increase acceptance and reduce cosmic ray background. Uniform field in spectrometer region to minimize corrections in momentum analysis. Tracking detector downstream of target to reduce rates from photons and neutrons.

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop28 Magnetic Spectrometer with Straw Tracker Goal Excellent momentum resolution, 900 keV FWHM (  p/p=0.3%) –Essential to eliminate muon decay in orbit background. High rate capability.500kHz in individual detector elements 2800 nearly axially aligned straw tubes in vacuum 5mm , 2.5m L, 25  m t Transverse direction:0.2mm(rms) by drift time measurement Axial direction:1.5mm(rms) by cathode pads on the exterior of the straws Electron starts upstream, reflects in field gradient

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop29 Spectrometer Performance GEANT3 Monte Carlo –Resolution dominated by Energy loss in muon stopping target –636 keV FWHM Tracker intrinsic resolution –353 keV FWHM 900 keV FWMH Background with Detector Response Full GEANT Simulation Signal

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop30 Trigger Calorimeter Provides prompt signal proportional to electron energy for use in online event selection Provides position measurement to confirm electron trajectory Energy resolution ~ 5% and spatial resolution ~1 cm Consists of 4 vanes extending radially from 0.39 m to 0.69 m and 1.5 m along the beam axis ~ cm x 3 cm x 12 cm (PbWO 4 or BGO) crystals

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop31 MECO Expected Sensitivity Contributions to 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 Fitting and selection criteria efficiency0.19 Single Event Sensitivity R  e = 2 

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop32 MECO Expected Background Background calculated for 10 7 s running with sensitivity of a single event for R  e = 2  SourceEventsComments  decay in orbit 0.25 S/N = 4 for R  e = 2  Tracking errors< Radiative  decay < Beam e - < 0.04  decay in flight < 0.03No scattering in target  decay in flight 0.04Scattering in target  decay in flight < 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 Sources of background will be determined directly from data.

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop33 Current Status Scientific approval status: Approved by BNL and by the NSF through level of the Director Approved (with KOPIO) by the NSB as an MREFC Project (RSVP) Endorsed by the recent HEPAP Subpanel on long-range planning Technical and management review status: Positively reviewed by many NSF and Laboratory appointed panels Some pieces (primarily magnet system) positively reviewed by external expert committees appointed by MECO leadership Funding status: Currently operating on R&D funds from the NSF Project start awaits Congressional action; RSVP (MECO + KOPIO) is not in the FY03 budget – efforts in Congress to improve NSF MRE funding Construction schedule Construction schedule driven by superconducting solenoids – estimate from the MIT Conceptual Design Study is 41 months from signing of contract for engineering design and construction until magnets are installed and tested More information at

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop34 Summary Muon-electron conversion is definitely a “must do” experiment. The discovery is right down there only a few orders of magnitude below. The physics output from the muon-electron conversion is very robust. Many different types of theoretical models beyond SM can be studied with this process. The discovery potential of MECO is MAXIMUM: –1000 fold increase of the  - stops in the target. –Well designed beam line, which minimizes the beam contamination while maintains maximum muon yield. –Large detector acceptance with good resolution. Get interested in MECO? We always Welcome you  - stops/proton R  e = 2 

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop35 End of Slides