PSIでのミューオン実験 - 大阪大学sato/100223muonWS/...PSI Proton Cyclotron The cyclotron facility contains a cascade of three accelerators that deliver a proton beam of

RCNP研究会「ミューオン科学と加速器研究」, 23-24.Feb.2010, 大阪大学RCNP

PSIでのミューオン実験西口創, KEK素核研

Muon Experiment at the PSI

Contents✤ PSI ?✤ Muon Beam Line in PSI✤ Muon Experiment in PSI

✤ past / present (MEG)✤ Future Prospects in PSI

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Hajime NISHIGUCHI (KEK) “Muon Experiment at PSI” 「RCNP研究会: ミューオン科学と加速器研究」, 23-24.Feb.2010, RCNP

PSI ?

PSI : Paul Scherrer Institut✤ Largest Swiss Federal Institute for a lot of Scientific research activities.

✤ Mainly based on “proton cyclotron” and “nuclear reactor” because this institute was merged by two institutes in 1988:

✤ SIN : Swiss Institute for Nuclear Research

✤ EIR : Federal Institute for Reactor Research

✤ something similar with combination of KEK and JAEA in Japan

✤ PSI is a member of ETH domain (ETHZ, EPFL); for not only Particle-Nuclear but also Structure of Matter, Energy & Environment, and Health.

✤ However, according to its prestigious history of powerful cyclotron, PSI is still referred as “Mecca of Meson Factory” like TRIUMF, LAMPF, RAL.

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PSI


PSI and its Cyclotron Facility5


PSI Proton Cyclotron✤ The cyclotron facility contains a

cascade of three accelerators that deliver a proton beam of 590 MeV energy at a current up to 2 mA (1.2 MW).

✤ Pre-accelerated in a C-W column to an energy of 870 keV, secondary-accelerated in the 4-sector Injector 2 cyclotron up to 72 MeV.

✤ Final acceleration of the main beam to 590 MeV occurs in the large 8-sector Ring Cyclotron, from which the beam is transported through the experimental hall in a shielded tunnel.

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Experimental Facility with 2nd-beamlines✤ The main beam passes through

two pion production targets whereby the proton energy is reduced to 570 MeV.

✤ Target-M (5mm C)

✤ Target-E (40mm C)

✤ After passing through the targets the beam can either be dumped in a beam stopper or can be recaptured and bent downwards through a sloping drift tube for onward transport to the SINQ-facility.

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proton therapy

isotope prod.

πM1

πM3 πE5

πE1

πE3

μE1

μE4


Muon Beamline

As a “Meson Factory”✤ PSI provides beam time for particle physics and other experiments. Its

unique specialty is very high intensity pion and muon beams of momenta up to a few hundred MeV/c.

✤ Each beam line is designed for “surface”, “subsurface”, “cloud”, and “low-E μSR” muons, except for πM1.

✤ The world most intense DC muon beam (~108 muon/sec) is available.

✤ Two target station, M (thin, 5 mm C) and E (thick, 40/60 mm C), are equipped; Two beam lines are attached with Target-M and Five beam lines are attached with Target-E.

✤ One beam line is used for test beam purpose, Three beam lines are exclusively used for μSR, and Three beam lines are used for Particle/Nuclear Physics experiments.

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Target-M; πM1 and πM3✤ πM1 beam line

✤ High resolution pion beam line with a momentum range between 100 and 500 MeV/c.

✤ The beam line contains an electrostatic separator built at CERN, which can reduce the proton contamination in a π+ beam from 400% to about 5% at 300 MeV/c momentum.

✤ No "surface" muons available.✤ Mainly used for the test-beam

purposes.

✤ πM3 beam line✤ Currently the only beam line

dedicated exclusively to μSR experiments with "surface" muons

✤ A 3 m long crossed-field separator can be used either as an electron/muon separator or as a muon spin rotator.

✤ After the separator the beam can be steered into one of two experimental areas; Low temperature facility LTF and a general purpose system GPS for μSR studies is installed.

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Target-E; πE1, πE3, πE5, μE1 and μE4 11

Secondary Beam lines with Thick Target Station “E”Secondary Beam lines with Thick Target Station “E”Secondary Beam lines with Thick Target Station “E”

πE1 High intensity pi/mu with momentum ranging 10-500 MeV/c. Surface muon is available.

Was used by PiBeta.Is being used by PEN.

πE3 High intensity pi/mu with momentum ranging 10-250 MeV/c. Surface and Cloud muons.

Was used by Many muon programs.Is being used by MuSun, and being

modified for high-B muSR.

πE5 High intensity low momenta pi/mu ranging 10-120 MeV/c. The most intense surface muon.

Was used by SINDRUM.Is being used by MEG/LambShift

μE1 For an intense medium energy polarized muon beam, very low pion/electron contamination. Dedicated for μSR

μE4 Large acceptance beam line for low momenta muon (<40MeV/c), specially designed for Low-E μSR Dedicated for μSR


μ Experiments

Past Pion/Muon Experiments in PSI✤ PSI has born the burden of fundamental physics for many decades; in

particular precise measurement of pion and muon properties.✤ Recently completed programs:

✤ Muonium-AntiMuonium conversion (MM)✤ Search for Heavy Neutral Particle (KARMEN)✤ Muon-Electron Conversion (SINDRUM-II)✤ Improved Measurement of Charged Pion Mass✤ T-violation in Muon decay✤ Pion Beta-decay (PiBeta)✤ Pionic Hydrogen✤ (developments) Large Acceptance Detector System (LADS)✤ (developments) F/B muon spectrometer at L3✤ (developments) Central Silicon Tracker at H1

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Active Particle Physics Experiments in PSI✤ MEG and nEDM : Flagship Projects in Particle Physics Division

✤ MuCap : Singlet Muon Capture on the Proton

✤ nTRV : Decay of Free Polarized Neutron

✤ LambShift in Muonic Hydrogen : to eliminate the contribution of the proton charge radius

✤ MuLan : τμ measurement (Improving the precision of GF)

✤ FAST : τμ measurement (Improving the precision of GF)

✤ PEN : Improving the accuracy of the π→eν branching ratio.

✤ MuSun : Muon Capture on the Deuterium

✤ Detector Developments : Pixel barrel and ECAL for CMS

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MEG Experiment✤ Search Experiment for “μ→eγ”

✤ μ→eνν ～ 100% (normal muon decay in SM)

✤ μ→eγ violates Lepton Flavour Conservation

✤ Even assuming “SM” + “Neutrino-Oscillation” B(μ→eγ) is assumed < 10-50

✤ Many models of beyond SM, however, predicts large B(μ→eγ) ～ 10-15～-11

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✤ New experiment with a Sensitivity of B ~ 10-13 was proposed at PSI

✤ Two orders of magnitude better than current best limit (1.2×10-11)

✤ Cover the most of theoretically predicted region

✤ Physics data-taking started 2008 and is currently running.


Hunting for μ→eγ ✤ Signal and Backgrounds

✤ Clear 2-body kinematics (Ee=Eγ=52.8MeV, θeγ=180°, Time Coincidence)

✤ Sensitivity is Limited by “Accidental Overlap”

✤ DC muon is the Best Solution

✤ Good Resolution (Energy, Spacial and Timing) under Very High Rate

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Sign

al

Prom

pt B

G.

Accid

enta

l BG.

How about in MUSIC ???


Hajime NISHIGUCHI @ Univ. of Tokyo

Lepton Flavour Violating Muon Decay at MEG

05-09 Jun. 2008, MelbourneHQ&L2008

Positron Spectrometer - Overview

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Solenoid

superconducting solenoid

gradient B-field (0.5-1.7 T)

very thin conductor and

cryostat wall (0.2X0)

Drift Chamber

segmented radially (16 sectors)

helium:ethane (50:50)

opened-frame

very thin cathode foil with pads

Timing Counter

2-layers of scintillators

- scintillator bars (outer)

- scintillator fibres (inner)

Features of MEG✤ The world most intense DC muon beam

✤ ~ 108 muon/sec at πE5

✤ Liquid-Xenon photon detector✤ Excellent Resolutions (E: 2%, T: ~70ps, X: ~5mm)✤ Fast Response (Good for pile-ups)✤ Uniform, Segment is not necessary

✤ Specially Degraded Magnetic Spectrometer✤ Possible in 108 /sec intensity✤ Very Light Tracker (0.002X0 in total) ✤ Very Fast Hodoscope array (~120ps)

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Hajime NISHIGUCHI @ Univ. of Tokyo

Lepton Flavour Violating Muon Decay at MEG

05-09 Jun. 2008, MelbourneHQ&L2008

MEG Liquid Xe Detector

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Active Volume ~ 800 l is surrounded

by PMTs on all faces

846 PMTs in the liquid

No segmentation

Energy

• All PMT outputs

• σE/E = 2 % (@52.8MeV)

Position

• PMTs on the inner face

• σx = 4~5 mm (@52.8MeV)

Timing

• Averaging of signal arrival time of

selected PMTs

• σT = 65 ps (@52.8MeV)1m

verified by

prototype

γ-ray from

muon decay


The 1st Physics Run, Run2008✤ Proposal was approved 1999, Construction was completed 2007.

✤ The 1st Physics Run 12/Sep. to 23/Dec. 2008.

✤ Right after the detector maintenance period, physics data taking started

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✤ Several Sever Problems;

✤ Inefficient and Unstable operation of Spectrometer due to DC-HV discharge.

✤ Lower Light yield of Calorimeter due to Impurity in Liquid Xenon.

✤ Lower Trigger Rate due to lack of triggering counter (fibre counter).

✤ i.e. Lower Statistics than expected.

Integrated Stopped Muon on Target


Run2008 : Analysis (Blinding)✤ “Eγ-ΔTeγ“ plane was

used to determine Pre-selection, Analysis Box, and Blind Box.

✤ 16% of triggered events are pre-selected and 0.2% of events are blinded.

✤ Performances are estimated by Side-band.

✤ Reprocess was repeated several times with improved calibrations and algorithms.

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✤ Final blinding box: ±1ns around Time-Zero


Run2008 : Analysis (Likelihood)20

✤ 1189 events in Analysis Box✤ Best Fit : 0 < Nsignal < 14.7


The 1st Results of MEG✤ Single Event Sensitivity :

5×10-12

✤ Expected NBG : 0.5

✤ Evaluated by Sideband

✤ Average Sensitivity : 1.3×10-11

✤ ToyMC with obtained PDF

✤ Best Fit : UL(Nsignal)=14.7

✤ Obtained by Likelihood

✤ Upper Limit (90% C.L.) : B(μ+→e+γ)<2.8×10-11

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✤ Preliminary Result of Run2008 was Published in hep-ex/0908.2594 , and the final result of Run2008 will come soon in NPB.


Current Status of MEG✤ 2009, the 2nd Physics Run was performed successfully

✤ Spectrometer Problem was solved !! Full Efficiency and Better Resolution.

✤ nb. All Digitizer replaced, Blighter Xenon, Still missing fibre counters

✤ Even Shorter Run period than 2008, the data amount is 2.2 times more than that we took 2008 because of recovered detector efficiency !

✤ Analysis & Detector Maintenance is Ongoing.

✤ The 2nd result will be published this summer.

✤ Aiming to finish Maintenance works by the end of April.

✤ Run-2010 will start ~May (after several commissioning and calibration runs), and will continue by Christmas shutdown. (First Long-term Run)

✤ MEG will continue to collect further more data (at least) 3 years in order to achieve 10-13 sensitivity.

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Future Prospects

Next Flagship Projects in PSI (particle physics)

✤ Active muon experiments (only for particle physics!) are “MEG”, “MuLAN/FAST”, “LambShift” and “MuCap/Sun”

✤ Flagship project, MEG, will continue by 2012 at least.

✤ Recently the discussion has been arising for the future flagship project.

✤ Next flagship project should be discussed by following points:

✤ Should contribute for “New Physics”, not for just an “Improvement”

✤ Should be utilized for using the world most intense DC muon beam✤ PSI cyclotron is still upgrading (2.2mA @ 2010, aiming 2.5-3mA)

✤ Currently there are three major discussions:

✤ “New Muon EDM”, “MEG upgrades” and “μ→eee”

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New Muon-EDM experiment✤ Compact Storage Ring (<1m dia.) with adapting the frozen spin method✤ Aiming dμ ~ 5×10-23 e cm, and confirm the tech. to achieve 10-25 in future✤ cf. hep-ex/0606034 (experiment idea), PRL93.p052001 (frozen spin meth.)

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MEG Upgrades (“Sensitive MEG” & “Polarized MEG”)✤ It is possible to improve the current MEG sensitivity

✤ Xenon; High QE, Finer Granularity by using Smaller PMT (MPPC?)✤ Spectrometer; Reduce Material more, Double Acceptance✤ Expected Improvements; 10 times better sensitivity is possible

✤ Using Polarized Muon is very attractive✤ Plastic target is currently used, thus ~100% depolarized✤ Using Metal target can provide full polarization because πE5 is surface-

muon beam line.✤ Measuring angular asymmetry of e+ emission wrt. muon polarization

will tell us the useful information to understand the New Physics.✤ Asymmetry is distinguishable with 68% C.L. assuming B(μ→eγ)>10-12.5

✤ cf. Several Ideas for future improvement were presented in Workshop on Precision Measurements at Low Energy, 18-19.Jan.2007 at PSI

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Search for “μ→3e” with a Sensitivity of 10-16 ✤ “μ→3e“ has many more diagrams than “μ→eγ“

✤ Present Upper limit; B(μ→3e) < 1.2×10-12 (SINDRUM-I, 22 years old!)✤ Signature

✤ total energy, total momentum✤ phase space distribution gives additional information if observed.✤ in a constant B field the acceptance is defined by the pt threshold.

✤ Background

✤ accidental background involves low invariant mass e+e- pairs produced by photons or by Bhabha scattering

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Physik-Instituta µ→ 3e search at 10−16 ? ETHZ, November 17 2008andries van der schaaf, Zurich

2 signature µ→ 3e at rest

- total energy, total momentum (→ coplanarity).

- Phase space distribution gives additional information if observed.

- In a constant B field the acceptance is defined by the pt threshold.

3 backgroundSINDRUM I

µ→ 3e2ν

accidentals

Accidental backgroundinvolves low invariant mass e+e− pairs produced by photons or by Bhabha scattering.

7/16

SINDRUM I

Dominated by Accidental

DC muon is BEST

How about in MUSIC ???


PSI2010

✤ Physics of fundamental Symmetries & Interactions✤ Oct. 11-14, 2010 at PSI

✤ Continuation of the past Workshop; Precision Measurements at Low Energy, Jan. 18-19, 2007 at PSI✤ as a contribution to an evaluation

of the Future Particle Physics Research at PSI

✤ Future Particle Physics Research at PSI will be discussed in detail !!

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Summary✤ PSI has a powerful proton cyclotron and has been contributing to the

fundamental particle physics as a “Meson Factory”

✤ The world most intense DC muon beam is available.

✤ Presently, 2.2mA (1.2MW) proton current and 108 muon/sec is provided.

✤ MEG experiment started 2008 and currently running in order to discover the first event of “charged lepton flavour violation”.

✤ In addition, several muon-experiment programs are running.

✤ Recently, the next particle physics program is being discussed.

✤ New muon EDM ?, MEG upgrades (improved sensitivity and using polarized muon) ?, μ→3e search experiment with a sensitivity of 10-16

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Documents

PSIでのミューオン実験 - 大阪大学sato/100223muonWS/...PSI Proton Cyclotron The cyclotron facility contains a cascade of three accelerators that deliver a proton beam of