Search for -e Conversion in MECO at BNL Masaharu Aoki Osaka University 4th NuFact ’ 02 Workshop Neutrino Factories based on Muon Storage Rings Imperial

Search for -e Conversion in MECO at BNL

Masaharu AokiOsaka University

4th NuFact ’02 WorkshopNeutrino Factories based on Muon Storage Rings

Imperial CollegeLondon, 1-6 July 2002

July 1-7, 2002Masaharu Aoki, Osaka University 4th NuFact '02 Workshop 2

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


Lepton Flavor Violation

• Lepton Flavor (Le, 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 experimentallyaccessible range; (m

2/MW2)2~10-47

• Many scenarios for physics beyond the SM predict sizable LFV processes in charged lepton sector.

Charged LFV Physics beyond the SM

∝ ( mν/ m

W)4

≈ 10− 26


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

LFV diagram in SUSY-GUTLFV diagram in Standard Modelmixing in massive neutrinosµeµeBmixingµemixing e Wlarge top Yukawa coupling

md

ms

mb

⎛

⎝

⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟

mνe

mνμ

mν τ

⎛

⎝

⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟

m˜ d

m s

m˜ b

⎛

⎝

⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟

m e e 2 Δm e μ

2 Δm e τ

2

Δm μ e

2 m μ μ

2 Δm˜ μ τ

2

Δm τ e

2 Δm τ μ

2 m˜ τ τ

2

⎛

⎝

⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟

quark

lepton (neutrino) slepton

squarknormal particles SUSY 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.


• SU(5) SUSY-GUT Predictiononly a few orders of magnitude below the current experimental limit.

• SO(10) SUSY-GUT Predictionenhanced by (m/m)2(~100) from SU(5) prediction.

SUSY-GUT Prediction

Courtesy Hisano

Process CurrentLimit

SUSY-GUTlevel

N → e N 10-13 10-16

→ e 10-11 10-14

→ 10-6 10-9

MECO single event sensitivity


SUSY with RH Majorana neutrino

a la Nomura and HisanoMECO single event sensitivity


History of LFV Searches

• Since 1948E.P. Hincks and B. Pontecorvo, PR 73 (1948) 257

• Two orders of magnitude per decade.

10-1410-1210-1010-810-610-410-2

1940195019601970198019902000Year

KL0→eK+→πeA→eA→eee→e

Courtesy Kuno MECO Goal


Muon Electron Conversion

• Muonic atom (1s state)

• Neutrinoless muon nuclear capture

– Single mono-energetic electron of Emax = (M - B) MeV (~105 MeV)

– Rate is normalized to the kinematically similar weak capture process:

Re (-Ne-N) / (-NN(Z-1))

muon decay in orbit

nucleus

−→ e−ν ν −+ (A,Z) → ν μ + (A,Z −1)

nuclear muon capture

−+ (A,Z) → e− + (A,Z )

lepton flavors change by one unit.

coherent process


Models for Muon-Electron Conversion

•SUSY-GUT– BR ~ 10-15

•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 ViolationW = ijkLiLjEc

k + ’ijkLiQjDck

+ ”ijkUciDc

jDck - iLiH2

•|’211212| < 2.6 10-11

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) 25-44

•Leptquarks

•Heavy Z’– MZ’ > (5-100) TeV for Re~10-16

• J. Bernabeu et al., NPB 409 (1993)69-86

•Compositeness

•Multi-Higgs Models

q:model dependent combination of

couplings, mixings, etc.

> 3000 TeV q


-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 10-14 level.

The physics motivation is sufficiently strong for both

Possibly different systematics, thus complementary each others.Both should be done to maximize discovery potential


MECO Collaboration

Institute for Nuclear Research, Moscow

V. M. Lobashev, V. Matushka,

New York UniversityR. M. Djilkibaev, A. Mincer,

P. Nemethy, J. Sculli, A.N. Toropin

Osaka UniversityM. Aoki, Y. Kuno, A. Sato

University of PennsylvaniaW. Wales

Syracuse University R. Holmes, P. Souder

College of William and MaryM. Eckhause, J. Kane, R. Welsh

Boston UniversityJ. Miller, B. L. Roberts,

O. RindBrookhaven National Laboratory

K. Brown, M. Brennan, L. Jia, W. Marciano, W. Morse,

Y. Semertzidis, P. YaminUniversity of California, Irvine

M. Hebert, T. J. Liu, W. Molzon, J. Popp, V. Tumakov

University of HoustonE. V. Hungerford, K. A. Lan,

L. S. Pinsky, J. Wilson

University of Massachusetts, AmherstK. Kumar


Learning from SINDRUM II

• BR = 2 × 10-13 (2000 Gold run)• Major background sources were

– Muon decay in orbit• Requires much better resolution

– Prompt π background• Requires pulsed proton beam

– Cosmic ray background


Potential Backgrounds I

• Muon Decay in Orbit– Emax = Ee

– dN/dEe (Emax - Ee)5

– Sets the scale for energy resolution required:

• Nbg = 0.25 for Re=2 10-17 Ee=900 keV FWHM

• Radiative Muon Capture: N N(Z-1) – E

max = 102.5 MeV, P(E > 100.5 MeV) = 4 10-9

– P( e+e-, Ee > 100.5 MeV) = 2.5 10-5

– (Ee wrong measurement) < 10-6

• Nbg < 0.005

• Radiative Pion Capture– BR( emission) ~ 2% for E > 105 MeV

– P( e+e-, 103.5 < Ee < 105.0 MeV) = 3.5 10-5

– P(Pion stops at the muon stopping target) = 3 10-7/proton= 1.2 10-4/muon-stopped-in-the-target

– Requires beam extinction < 10-9 for Nbg = 0.07, Re=2 10-17

– Defines signal detection time window > 700 ns


Potential Backgrounds II

• Muon decay in flight + e- scattering in stopping target– Eliminated by using pulsed beam

• Beam e- scattering in stopping target

– P(Ee > 100 MeV) < 10-7

•high energy beam electron is suppressed by the curved solenoid.

– Nbg < 0.04 for Re=2 10-17

• 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


MECO Features

• Muon Intensity– 1000 fold increase by using an idea from MELC at MMF

10-2 /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 < 10-9

• 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)


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


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 1013 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 1013 protons/RF bucket– twice the current bunch intensity

• Requirement:the excellent beam extinction<10-9 protons between bunches


The extinction = 10-9 at AGS

• Quick test measurements– 1st test

24 GeV with one RF bucketextinction < 10-6 between buckets

< 10-3 in unfilled buckets

– 2nd test7.4 GeV with one filled bucketextinction < 10-7

• 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


Pion Production Target

• High Z target material• Minimal material in bore to absorb π• 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 = 2×10-12 mg/cm2s ; 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


The MECO Superconducting Magnets

• Magnet Conceptual Design Report (CDR)from MIT Plasma Science and Fusion Center


Magnetic Field Specification

Position along the beam path (m)

Position along the beam path (m)

B S (T)

•Production Solenoid 5.0 - 2.5 T•Mirror effect for maximizing pion capture acceptance

•Curved Transport Solenoid 2.5 - 2.0 T•Straight section : monotonically decreasing•Curved section : gradient drift

•Detector Solenoid (muon target) 2.0 - 1.0 T•Maximize signal acceptance

•Detector Solenoid (spectrometer) 1.0 T•Uniform field


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 DetectorToward Detector

Superconducting coil

Radiation and heat sheild

•109.20 MJ stored energy•150 W load on cold mass•15 W/g in superconductor•20 Mrad integrated dose

•Implementation– Axially graded magnetic field

• 5 - 2.5 T

– Cu and W heat and radiation shield


Transport Solenoid

2.5T

2.5T

2.0T

2.2T2.0T

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.


Function of the Curved Solenoid

• Particle drifts in torus magnetic fieldsJD Jackson, Classical Electrodynamics

D : drift distanceB : magnetic fields/R : bend angle of the

solenoidps : perpendicular

momentumpt : transverse momentum

Curvature drift

Gradient drift

Charge and momentum selection


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


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.

Rel

ativ

e yi

eld

Muon Momentum [MeV/c]0 50 100

Total flux at stopping

target

Stopping Flux

0.0025 stops/proton


Detector Solenoid

1T

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 minimizecorrections in momentum analysis.

• Tracking detector downstream oftarget to reduce rates from

photons and neutrons.


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, 2.5mL, 25mt

•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


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


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

• ~2000 3 cm x 3 cm x 12 cm (PbWO4 or BGO) crystals


MECO Expected Sensitivity

Contributions to 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

Fitting and selection criteria efficiency 0.19

Single Event Sensitivity Re = 2 10-17


MECO Expected Background

• Background calculated for 107 s running with sensitivity of a single

event for Re= 2 10-17

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

Tracking errors < 0.006

Radiative decay < 0.005

Beam e- < 0.04

decay in flight < 0.03 No scattering in target

decay in flight 0.04 Scattering in target

π decay in flight < 0.001

Radiative π capture 0.07 From out of time protons

Radiative π capture 0.001 From late arriving pions

Anti-proton induced 0.007 Mostly from π

Cosmic ray induced 0.004 10-4 CR veto inefficiency

Total Background 0.45 With 10-9 inter-bunch extinction

Sources of background will be determined directly from data.


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 planningTechnical 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 leadershipFunding 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 http://meco.ps.uci.edu


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.

0.0025- stops/proton

Re = 2 10-17


End of Slides

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Search for -e Conversion in MECO at BNL Masaharu Aoki Osaka University 4th NuFact ’ 02 Workshop Neutrino Factories based on Muon Storage Rings Imperial