mu-e conversion COMET at J-PARC Satoshi MIHARA KEK, Japan 23/Oct/2009ILC Seminar 2009

23/Oct/2009ILC Seminar 2009 Outline Introduction COMET at J-PARC – Proton/Muon beam at J-PARC – Detector – Sensitivity and Background – R&D Status – Schedule and Cost Summary

INTRODUCTION 23/Oct/2009ILC Seminar 2009

23/Oct/2009ILC Seminar 2009 Introduction Lepton Flavour Violation of Charged Leptons Neutrino Mixing (confirmed) Charged Lepton Mixing (not observed yet) Sensitive to new Physics beyond the Standard Model Very Small ( ) e     e ?? Soon!  e  e ~ B ~ mixing LFV diagram in SUSY Large top Yukawa coupling ~ LFV diagram in Standard Model µ e mixing  e W  (m /m W ) 4

23/Oct/2009ILC Seminar 2009 What is a  -e Conversion ? 1s state in a muonic atom Neutrino-less muon nuclear capture (=  -e conversion)    e  nucleus      ( A, Z )    ( A, Z  1) B(   N  e  N)   (   N  e  N)  (   N  N ' )    ( A, Z )  e   ( A, Z ) nuclear muon capture muon decay in orbit lepton flavors changes by one unit

23/Oct/2009ILC Seminar 2009  -e conversion Signal E  e ~ m  -B  – B  : binding energy of the 1s muonic atom Comparison with   e  (and   3e) from the view point of experimental technique Improvement of a muon beam is possible, both in purity (no pions) and in intensity (thanks to muon collider R&D). A higher beam intensity can be taken because of no accidentals. Potential to discriminate different models through studying the Z dependence R.Kitano, M.Koike, Y.Okada P.R. D66, (2002) BackgroundChallenge   e  and   3e AccidentalDetector performance resolution, high rate  -e conversion BeamBeam background

23/Oct/2009ILC Seminar 2009 Comparison between   e  and  -e Conversion (Physics Sensitivity) Photonic and non-photonic (SUSY) diagrams photonicnon-photonic   e  yes (on-shell)no  -e conversion yes (off-shell)yes

MEG at PSI Status Physics data production started in 2008 Current limit Br(   e  )<3.0x (at 90% C.L.) (MEGA world record 1.2x ) – Probability to obtain this limit given the average expected limit of 1.3x is 5% Will reach the MEGA limit with 2009 data and go further in /Oct/2009ILC Seminar 2009 Event Distribution in 90% Box

0  and  -e conversion V. Cirigliano et al. PRL 93, (04) R=B(   e)/B(   e  ) RPV-SUSY – R >> LRSM (Left-Right Symmetric Model) – R~O(1) Important to measure R to extract m 0  from  0  23/Oct/2009ILC Seminar 2009 RPV-SUSY LRSM

cLFV search and LHC 23/Oct/2009ILC Seminar 2009 Masiero et al. JHEP03 (2004) 046

History of  -e conversion search YearMuon sourceTargetUpper bound 1952Cosmic raysCu, Sn4×10 −2 1955Nevis cycl.Cu5×10 −4 1961Berkeley synchroc.Cu4×10 − CERN synchroc.Cu2.2×10 −7 1972Virginia SREL synchroc.Cu1.6×10 −8 1977SINS7×10 − TRIUMFPb Ti 4.9×10 −10 4.6×10 − PSIPb4.6×10 − (only in conference proc.)Ti6.1×10 − Au7×10 −13 23/Oct/2009ILC Seminar 2009

23/Oct/2009ILC Seminar 2009 The SINDRUM-II Experiment (at PSI) SINDRUM-II used a continuous muon beam from the PSI cyclotron. To eliminate beam related background from a beam, a beam veto counter was placed. Published Results

23/Oct/2009ILC Seminar 2009 The MELC and MECO Proposals The MECO Experiment at BNL Cancelled in 2005  Fermilab MELC (Russia) and then MECO (the US) To eliminate beam related background, beam pulsing was adopted (with delayed measurement) To increase a number of muons available, pion capture with a high solenoidal field was adopted For momentum selection, curved solenoid was adopted

23/Oct/2009ILC Seminar 2009 Fermilab Fermilab Accelerators The mu2e Experiment at Fermilab. – Proposal has been submitted. CD-0 – After the Tevatron shut-down uses the antiproton accumulator ring the debuncher ring to manipulate proton beam bunches

23/Oct/2009ILC Seminar 2009 cLFV Search Experiment cLFV search is as important as high-energy frontier experiments (and oscillation measurements) to find a clue to understand – SUSY-GUT – Neutrino See-saw MEG is expected to reach and go beyond the current limit pretty soon Need other experiment(s) to confirm it – Using “different” physics process (with better sensitivity)! COMET (COherent Muon Electron Transittion) – Submitted a proposal to J-PARC in 2008 and a CDR in 2009, – and obtained Stage-1 approval in July 2009

COMET An Experimental Search For Lepton Flavor Violating  - - e - Conversion at Sensitivity of /Oct/2009ILC Seminar 2009

23/Oct/2009ILC Seminar 2009 Collaboration as of Jul/2009 Y.G. Cui, R. Palmer Department of Physics, Brookhaven National Laboratory, USA Y. Arimoto, Y. Igarashi, S. Ishimoto, S. Mihara, T. Nakamoto, H. Nishiguchi, T. Ogitsu,C. Omori, N. Saito, M. Tomizawa, A. Yamamoto, K. Yoshimura High Energy Accelerator Research Organization (KEK), Tsukuba, Japan P. Dornan, P. Dauncey, U. Egede, A. Kurup, J. Pasternak, Y. Uchida, Imperial College London, UK Y. Iwashita Institute for Chemical Research, Kyoto University, Kyoto, Japan V. Kalinnikov, A. Moiseenko, D. Mzhavia, J. Pontecorvo, B. Sabirov, Z. Tsamaiaidze, and P. Evtukhouvich Joint Institute for Nuclear Research (JINR), Dubna, Russia M. Aoki, Md.I. Hossain, T. Itahashi, Y. Kuno ∗, E. Matsushita, N. Nakadozono, A. Sato, S. Takahashi, T. Tachimoto, M. Yoshida, Department of Physics, Osaka University, Osaka, Japan M. Koike, J. Sato, M. Yamanaka Department of Physics, Saitama University, Japan Y. Takubo Department of Physics, Tohoku University, Japan D. Bryman Department of Physics and Astronomy, University of British Columbia, Vancouver, Canada R. D’Arcy, M. Lancaster, M. Wing Department of Physics and Astronomy, University College London, UK E. Hungerford Department of Physics, University of Houston, USA T. Numao TRIUMF, Canada * Contact

23/Oct/2009ILC Seminar 2009 Overview of the COMET Experiment

PROTON BEAM 23/Oct/2009ILC Seminar 2009

23/Oct/2009ILC Seminar 2009 Requirements for the Muon Beam Backgrounds – Beam Pion Capture  - +(A,Z)  (A,Z-1)*   + (A,Z-1)   e + e - Prompt timing  good Extinction! –  - decay-in-flight, e - scattering, neutron streaming Requirements from the experiment – Pulsed – High purity – Intense and high repetition rate nuclei  Muon Capture(MC) Muon Decay in Orbit (MDO) SIGNAL

23/Oct/2009ILC Seminar 2009 Requirements for the Proton Beam Proton beam structure for the mu-e conversion search – 100nsec bunch width, 1.1  sec bunch-bunch spacing – 8GeV to suppress anti-proton background – < proton/bunch, limited by the detector performance – Repetition rate as high as possible within tolerable CR background Extinction – Residual protons in between the pulses should be <  s (584ns x 2) 0.7 second beam spill 1.5 second accelerator cycle 100ns N bg = NP R ext x Y  /P x A   x P  x A NP x R ext x Y  /P x A   x P  x A NP : total # of protons (~10 21 ) R ext : Extinction Ratio (10 -9 ) Y  /P :  yield per proton (0.015) A  :  acceptance (1.5 x ) P  : Probability of  from  (3.5x10 -5 ) A : detector acceptance (0.18) BR=10 -16, N bg < 0.12  Extinction < 10 -9

23/Oct/2009ILC Seminar 2009 Proton Acceleration at J-PARC Proton acceleration in – LINAC – Booster (RCS) – Main Ring Nominal scheme – RCS: h=2 – MR:h=9 8 buckets filled 1 empty bucket, used for kicker excitation MR RF cavities are designed for this scheme – h=18 optional by removing capacitors on cavities – Need long shutdown to change the configuration 8 filled buckets out of 9 buckets

23/Oct/2009ILC Seminar 2009 Proton Acceleration for COMET RCS: h=2 with one empty bucket MR:h=8(9) with 4(3) empty buckets Bunched slow extraction – Slow extraction with RF cavity ON Realization of an empty bucket in RCS by using the chopper in Linac Simple solution No need of hardware modification Heavier heat load in the scraper Possible leakage of chopped beam in empty buckets Simple solution No need of hardware modification Heavier heat load in the scraper Possible leakage of chopped beam in empty buckets

LINAC Chopper 池上雅紀 高エネルギーニュース vol.25 No.4 Two Cavities

RCS, MR Injection Acceleration and extraction in 20msec Bunch configurations – Micro bunch 324 MHz LINAC – Intermediate bunch ~1MHz Chopper – Macro bunch 25Hz RCS 池上雅紀 高エネルギーニュース vol.25 No.4 MLF RCS MR

MUON/PION PRODUCTION 23/Oct/2009ILC Seminar 2009

23/Oct/2009ILC Seminar 2009 Pion Production Target low-E pions – for low-E muons to stop – Backward extraction pion yield is proportional to T proton – pion yld is proportional to Beam Power High-Z Metal Rod like tungsten or gold – 12-mm  x 16-cm – 3-4 kW on the target – Water cooling 0.3mm water layer   T=56K 1.0mm water layer   T=42K

23/Oct/2009ILC Seminar 2009 Pion Capture 5 T at the target position – capture p t < 120 MeV/c Radiation Shield < 100 W on SC coil – 3-4 target – 35 W Shield – 2x10 -5 coil Yields – 0.05(  +  )/8-GeV-proton  -yield vs. B max MARS simulation

23/Oct/2009ILC Seminar 2009  -Capture Solenoid Heat-load density : 2 x W/g behind W shield Utilize Al stabilized SC cable to reduce a heat load to the cold mass. – Cable dimension: 15mm x 4.7mm Al-SC: one of world leading expertise of KEK Length(mm)Thickness (mm)  Current (A/mm2) Coil (6 layers)53.0 Coil (2 layers)53.0 Coil (2 layers)53.0 Coil (4 layers)62.9

MUON TRANSPORT 23/Oct/2009ILC Seminar 2009

23/Oct/2009ILC Seminar 2009 Muon Transport Guide  ’s until decay to  ’s Suppress high-p particles  ’s : p  < 75 MeV/c  ’s : p  < 75 MeV/c e’s : p e < 100 MeV/c e’s : p e < 100 MeV/c Beam collimator Beam Blocker

23/Oct/2009ILC Seminar 2009 A center of helical trajectory of charged particles in a curved solenoidal field is drifted by – This effect can be used for charge and momentum selection. This drift can be compensated by an auxiliary field parallel to the drift direction High-p Suppression See “Classical Electrodynamics”, J.D.Jackson Ch.12-Sec.4  p/  x = 1 MeV/c/cm

23/Oct/2009ILC Seminar 2009 Spectra at the End of the Muon Transport Preliminary beamline design – main magnetic field – compensation field – Inner radius of transport magnet cryostat (175 mm) Transport Efficiency Spectra at the end of the beamline ( top left) total momentum (top right)pt vs pL (bottom left) time of flight (bottom right) beam profile. # of  /proton # of stopped muons/proton # of muons with p>75MeV/c / proton Dispersion on the muon beam just before the collimator. 75 MeV/c

23/Oct/2009ILC Seminar 2009 The COMET Detector

23/Oct/2009ILC Seminar 2009 The COMET Detector to stop muons in the muon stopping target to eliminate low-energy beam particles and to transport only ~100 MeV electrons. to detect and identify 100 MeV electrons. under a solenoid magnetic field.

23/Oct/2009ILC Seminar 2009 Muon Stopping Target Light material for delayed measurement (1 st choice) – Aluminum :   - = 0.88  s Thin disks to minimize electron energy loss in the target – R = 100 mm, 200  m t, 17 disks, 50 mm spacing Graded B field for a good transmission in the downstream curved section. Good  -Stopping efficiency:  =0.66 – Muon rate 1.5x10 11 /sec – stopped-muon yields:~  ’ s/proton

23/Oct/2009ILC Seminar 2009 Curved Solenoid Spectrometer Torus drift for rejecting low energy DIO electrons. – rejection ~10 -6 : < 10kHz Good acceptance for signal electrons (w/o including event selection and trigger acceptance) – 20% 60-MeV/c DIO electrons 105-MeV/c  -e electron

23/Oct/2009ILC Seminar 2009 Electron Detectors Rate < 800 kHz Straw-tube tracker to measure electron momentum – 5 Planes with 48cm distance,  p = 230 keV/c One plane has 2 views (x and y) with 2 layers per view. A straw tube has 25mm thick, 5 mm diameter. – should work in vacuum and under a magnetic field. – <500  m position resolution. Crystal calorimeter for Trigger – GSO, PWO, or LYSO

Tracking Detector Main detector to measure Ee – Thickness should be about 0.01 radiation-length to suppress % backgrounds. – Spatial resolution < 0.5 mm – Hit multiplicity ~ 1 per plane per event Straw tube tracker – 5mm&, 208 tubes per sub-layer – four layers per station – anode readout (X, X’, Y, Y’) – five stations, 48 cm apart Amps and Digitizers (DRS) are in vacuum Optical-link to the outside of the vacuum vessel 23/Oct/2009ILC Seminar 2009

Trigger Calorimeter Trigger Source – Timing for Tracker Energy measurement – Better trigger condition – Redundancy to Ee measurement – E/p cut to cosmic muons Position measurement – Improve track recognition. – f = 92 kHz per crystal Possible Photon Detectors (operational in vacuum and magnet) – APD – MPPC 23/Oct/2009ILC Seminar 2009

23/Oct/2009ILC Seminar 2009 Cosmic Ray Shields Both passive and active shields are used Passive shields – 2 meter of concrete and 0.5 m thick of steel against skyshine neutron – Need additional passive study to protect CR veto counter from muon capture neutrons. Under investigation. Active shields – layers of scintillator veto counters (~1% inefficiency)

Experimental Space A possible layout Discussion in the task force – Target and beam dump outside the hall – Share the upstream proton transport line with the high p beam line – External extinction device in the switch yard 23/Oct/2009ILC Seminar 2009

23/Oct/2009ILC Seminar 2009 Signal Sensitivity 2x10 7 sec running Single event sensitivity – N  is a number of stopping muons in the muon stopping target. It is 2.0x10 18 muons. – f cap is a fraction of muon capture, which is 0.6 for aluminum. – A e is the detector acceptance, which is total protons muon yield per proton muon stopping efficiency 8.5x # of stopped muons2.0x10 18 Single event sensitivity 2.6 x Single event sensitivity 2.6 x % C.L. upper limit 6.0 x % C.L. upper limit 6.0 x

23/Oct/2009ILC Seminar 2009 Potential Background Events Background rejection is the most important in searches for rare decays. Types of backgrounds for  - +N  e - +N are, Intrinsic backgrounds originate from muons stopping in the muon stopping target. muon decay in orbit radiative muon capture muon capture with particle emission Beam-related backgrounds caused by beam particles, such as electrons, pions, muons, and anti-protons in a beam radiative pion capture muon decay in flight pion decay in flight beam electrons neutron induced antiproton induced Other backgrounds caused by cosmic rays cosmic-ray induced (pattern recognition error)

23/Oct/2009ILC Seminar 2009 Intrinsic Background (from muons) Muon Decay in Orbit – Electron spectrum from muon decay in orbit – Response function of the spectrometer included. – 0.05 events in the signal region of MeV (uncorrected). Radiative Muon Capture with Photon Conversion – Max photon energy MeV – < events Muon Capture with Neutron Emission Muon Capture with Charged Particle Emission – <0.001 events for both. Energy spectrum of electrons from decays in orbit in a muonic atom of aluminum, as a function of electron energy. The vertical axis shows the effective branching ratio of  -e conversion.

23/Oct/2009ILC Seminar 2009 DIO Background a number of events for 1.1 x10 18 stopped muons. <0.05 events

23/Oct/2009ILC Seminar 2009 Beam Related Background Rejection Rejection of beam related (prompt) backgrounds can be done by a combination of the following components. Momentum Selection at the Muon Transport (p  < 75 MeV/c) Timing Cut and Beam Extinction (10 -9 ) Electron Energy Cut ( MeV uncorrected) Electron Transverse Momentum Cut (p T > 52 MeV/c) Beam Channel Length (pion decay)

23/Oct/2009ILC Seminar 2009 Beam Related Backgrounds (and CR) Radiative Pion Capture – pion prod. rate : 1x10 -5 – pion survival : 2x10 -3 – E e >104 MeV with conversion : 6.3x10 -6 – beam extinction : – 0.12 events at Muon Decay in Flight – p  >77 MeV/c : 2x10 -4 /proton – muon decay prob. : 3x10 -2 – E e >104 MeV & p t > 52MeV/c : <10 -8 – beam extinction : – total is 0.02 events at Pion Decay in Flight –   e branching ratio : – p  >60MeV/c to make E e >104MeV:5x10 -6 / proton – E e >104 MeV & p t > 52MeV/c : 5x10 -6 – beam extinction : – <0.001 events at Beam Electrons – p e >100 MeV/c : /proton – scat. prob. : – beam extinction : – 0.08 events at Neutron induced – neutrons through beamline. – E n >100 MeV : 3x10 -7 /proton – E e >100 MeV : – beam extinction : – events at Antiproton induced – eliminate high-energy antiprotons by curved solenoid. – absorb low-energy antiprotons by 120  m beryllium foil placed in the middle of beamline. – eliminate backgrounds from antiproton annihilation above. – events at Cosmic ray Background – eliminate by passive and active shields. – veto inefficiency assumed. – 0.04 events for 2x10 7 sec (a duty factor 0.2) 8x10 20 protons

23/Oct/2009ILC Seminar 2009 Background Estimation Summary BackgroundEventsComments Radiative Pion Capture0.05 Beam Electrons<0.1MC stat limited Muon Decay in Flight< Pion Decay in Flight< Neutron Induced0.024For high E n Delayed-Pion Radiative Capture0.002 Anti-proton Induced0.007For 8 GeV p Muon Decay in Orbit0.15 Radiative Muon Capture<0.001 Muon Capture with n Emission<0.001 Muon Capture with Charged Part. Emission<0.001 Cosmic-Ray Muons0.002 Electrons from Cosmic-Ray Muons0.002 Total0.34 Assuming proton beam extinction < 10 -9

23/Oct/2009ILC Seminar 2009 R&D Status

23/Oct/2009ILC Seminar 2009 R&D Status Straw-tube tracker – Done by Osaka group for MECO Crystal calorimeter Transport Solenoid Extinction Measuring Device R&D – Gas Cherenkov + Gated PMT Extinction measurement at J-PARC MR

23/Oct/2009ILC Seminar 2009 Straw-tube Tracker R&D Seamless type tube (I.S.T.) – Thickness : 25  m – Diameter : 5mm – Material : polyimide+carbon – Resistance : 6M  /sq Prototype Straw-tube chamber Beam test using 2.0GeV/c pion beam in 2002

23/Oct/2009ILC Seminar 2009 Calorimeter R&D GSO crystal for PET use – Stack in 3D – Light loss across the connection Agreement btw data & MC Need further study – Stacking method – Readout – Radiation hardness? 30mm x 32mm x 120mm Stack of 5 x 8 x 4 crystals

23/Oct/2009ILC Seminar 2009 Transport Solenoid Design

R&D on the Transport Solenoid Transport Solenoid would be easier than the capture solenoid: – field magnitude ~ 2 T – smaller radiation load NbTi copper stabilized conductor, which is widely used in MRI magnets and commercially available, will be used. The solenoid will be constructed by arranging coil “pancakes” electrically and thermally connected in series along the curve. We are studying basic parameters by a prototype comprising of 3 pancakes. – cooling performance – electromagnetic forces between pancakes – quench back system A new high-Tc superconductor, MgB2, will be used for one of the coils for the first time. – MgB2 will be used for the electron-spectrometer and detector solenoids 23/Oct/2009ILC Seminar 2009

23/Oct/2009ILC Seminar 2009 Extinction Measuring Device Monitor extinction level online by using a Gas Cherenkov detector with gating PMTs – Blind to proton beam core, active only in between proton pulses (nsec) Aiming at Repetition ~1MHz On/off ratio <10 -6 Long-term operation 280V, 10kHz, fall t ~100nsec

23/Oct/2009ILC Seminar 2009 Extinction Measurement using Secondary Beam Measure secondary particle time structure relative to a reference signal from the MR – MR RF signal in the experimental area – Beam line hodoscope counters at the K1.8BR line Support by E15/E17 group – MR operation with empty buckets – Bunched slow extraction – Count the number of secondary particles as a function of time Particle identification – TOF Integration for ~10 3 seconds supposing 1MHz counting rate Delayed reference signalsCounter signal proton 

23/Oct/2009ILC Seminar 2009 Extinction Measurement Utilize beam monitor in the abort line Single bunch operation of the MR – Look at the empty bucket before the filled one – Detector that can count the number of protons Two layers of 2mmt scintillator hodoscopes – Support by thin carbon fiber plates – Read by Multi-anode PMT through optical fibers – Operated in the beam line vacuum

First Shot ! RCS single bunch operation Fast extraction to the abort line, First the empty bucket and then filled bucket Abort line monitor HV 300V Outside counter normal gain Kicker excitation signal Beam intensity monitor 23/Oct/2009ILC Seminar 2009

Chopper Phase Optimization Factor of 2.5 improvement  Extinction < 2 x – Estimated only from pulse height – Perhaps better than this because of scintillator saturation The chopper (two cavities) is currently driven by a single power supply. Operation with two independent power supply is planned. This is expected to improve. 23/Oct/2009ILC Seminar 2009

23/Oct/2009ILC Seminar 2009 Schedule and Construction Cost Funding starting 1st year design & order of SC wires 2nd year 3rd year 4th year 5th yearengineering run 6th yearphysics run

23/Oct/2009ILC Seminar 2009 Summary New experiment (COMET) to search for mu-e conversion at J- PARC COMET aims at achieving a sensitivity of – High-intensity, high-purity pulsed proton beam at J-PARC – Curved solenoid muon transport/spectrometer to suppress backgrounds efficiently R&D work in progress – Detector – Magnet – Proton beam Beam structure Extinction Do Join COMET Now!

Backup 23/Oct/2009ILC Seminar 2009

23/Oct/2009ILC Seminar 2009 High-frequency Chopper

23/Oct/2009ILC Seminar 2009 Additional Extinction Means Bunch Cleaner Bunch Cleaner in MR in MR tested at AGS for MECO tested at AGS for MECO AC-dipole primary primary beamline f extinction ~ 1/100 f extinction ~ 1/100 collaboration with mu2e collaboration with mu2e