RSVP Simulation Review MECO Overview

1
RSVP Simulation Review MECO Overview
W. MolzonUniversity of California,
Irvine January 12, 2005

• Very brief physics overview
• Critical performance issues and challenges
• Producing required muon intensity
• Producing required time structure
• Detector performance (resolution and rates)
• Significant simulation challenges
• Predicting muon yield (soft)
• Predicting beam time structure (hard)
• Predicting magnet environment (hard)
• Predicting detector environment (soft)
• Predicting detector performance (hard)
• Simulation and calculation toolkit
• GEANT 3 and 4 with modifications
• MARS
• TOSCA
• Beam simulation packages
• Integrated simulation and analysis package

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What Will Observation of ?-N ? e-N Teach Us?

• Discovery of ?-N ? e-N or a similar charged
  lepton flavor violating (LFV) process will be
  unambiguous evidence for physics beyond the
  Standard Model.
• For non-degenerate neutrino masses, n
  oscillations can occur. Discovery of neutrino
  oscillations required changing the Standard Model
  to include massive ?.
• Charged LFV processes occur through intermediate
  states with n mixing. Small n mass differences
  and mixing angles ? expected rate is well below
  what is experimentally accessible.
• Charged LFV processes occur in nearly all
  scenarios for physics beyond the SM, in many
  scenarios at a level that MECO or PSIMEG will
  detect.
• Effective mass reach of sensitivesearches is
  enormous, well beyondthat accessible with direct
  searches.

One example of new physics, with leptoquarks
lmd
led
?
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Supersymmetry Predictions for LFV Processes

• From Hall and Barbieri
• Large t quark Yukawa couplingsimply observable
  levels of LFV insupersymmetric grand unified
  models
• Extent of lepton flavor violation in grand
  unified supersymmetry related to quark mixing
• Original ideas extended by Hisano, et al.

MEGA bound
SINDRUM2 bound
B(? ? e g)
R?e
MEG phase 2goal (start 2006)
MECO goal (start 2011)
100 200
300 100
200 300
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History of Lepton Flavor Violation Searches
1
?- N ? e-N ? ? e? ? ? e e e-
10-2
10-4
10-6
Branching Fraction Upper Limit
10-8
MEGA
10-10
SINDRUM2
10-12
K0?? ?e- K?? ? ?e-
PSI-MEG goal
10-14
MECO goal
10-16
1940 1950 1960 1970 1980
1990 2000 2010
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Coherent Conversion of Muon to Electrons
(?-N?e-N) ?

• Muons stop in matter and form a muonic atom.
• They cascade down to the 1S state in less than
  10-16 s.
• They coherently interact with a nucleus (leaving
  the nucleus in its ground state) and convert to
  an electron, without emitting neutrinos ? Ee
  Mm - ENR - EB.
• Experimental signature is an electron with
  Ee105.1 MeV emerging from stopping target, with
  no incoming particle near in time.
• More often, they are captured on the nucleus
  or decay in the Coulomb
  bound orbit
• (?? 2.2 ?s in vacuum,
  0.9 ?s in Al)
• Rate is normalized to the kinematically similar
  weak capture process
• MECO goal is to detect ?-N?e-N if R?e is at least
  2 X 10-17 ,
• with one event providing compelling evidence of a
  discovery.

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What Drives the Design of the MECO Experiment?
Considerations of potential sources of fake
backgrounds specify much of the design of the
beam and experimental apparatus.
Cosmic raybackground
Prompt background
SINDRUM2 currently has thebest limit on this
process
Expected signal
Muon decay
Experimental signature is105 MeV e- originating
in a thin stopping target.
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Potential Sources of Background
Muon decay in vacuum Ee lt m?c2/2 Muon
decay in bound orbit Ee lt m?c2 - ENR -
EB

• Muon Decay in Orbit
• Emax Econversion when neutrinos have zero
  energy
• dN/dEe ? (Emax Ee)5
• Sets required energy resolution 200 keV
  Tracker talk following
• Radiative Muon Capture ?- N ? ?? N(Z-1) ?
• For Al, Egmax 102.5 MeV/c2, P(Eg gt 100.5
  MeV/c2) 4 ? 10-9
• P(g ? ee-, Ee gt 100.5 MeV/c2) 2.5 ? 10-5
• Restricts choice of stopping targets Mz-1 gt Mz
• Radiative Pion Capture
  - Extinction talk following
• Branching fraction 1.2 for Eg gt 105 MeV/c2
• P(g ? ee-, 103.5 lt Eelt 100.5 MeV/c2) 3.5 ?
  10-5
• Limits allowed pion contamination in beam during
  detection time

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Other Potential Sources of Backgrounds

• Muon decay in flight e- scattering in
  stopping target
• Beam e- scattering in stopping target
  Extinction talk following
• Limits allowed electron flux in beam
• Antiproton induced e-
• Annihilation in stopping target or beamline
• Requires thin absorber to stop antiprotons in
  transport line
• Cosmic ray induced e- seen in earlier
  experiments CR talk following
• Primarily muon decay and interactions
• Scales with running time, not beam luminosity
• Requires the addition of active and passive
  shielding

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Features of the MECO Experiment

• 1000 fold increase in muon intensity Muon yield
  talk following
• High Z target for improved pion production
• Graded solenoidal field to maximize pion capture
• Produce ?10-2 m-/p at 8 GeV (SINDRUM2 ?10-8, MELC
  ?10-4,Muon Collider ?0.3)
• Muon transport in curved solenoid suppressing
  high momentum negatives and all positives and
  neutrals (new for MECO)
• Pulsed beam to eliminate prompt backgrounds
  following PSI method (A. Badertscher, et al.
  1981) - Extinction talk following
• Beam pulse duration ltlt tm
• Pulse separation ? tm
• Large duty cycle (50)
• Extinction between pulses lt 10-9
• Improved Detector Resolution and Rate Capability
• Detector in graded solenoid field for improved
  acceptance, rate handling, background rejection
  following MELC concept
• Spectrometer with nearly axial components and
  very high resolution (new for MECO) Tracker
  talk following
• Calorimeter for trigger and crude energy
  confirmation Calorimeter talk following

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The MECO Apparatus
Straw Tracker
Muon Stopping Target
Muon Beam Stop
Superconducting Transport Solenoid
(2.5 T 2.1 T)
Crystal Calorimeter
Superconducting Detector Solenoid (2.0 T
1.0 T)
Superconducting Production Solenoid (5.0
T 2.5 T)
Collimators
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Simulation and Calculation Tools

• AGS
• Simulations planned using matrix tools
  supplemented by stochastic processes for
  scattering, space charge, etc. (Kevin Brown)
• Will give some information on expected effects of
  internal extinction devices (extinction talk)
• Will not allow calculations of time dependence of
  circulating beam at 109 dynamic range
• Secondary proton beam
• Beam optics codes to design beamline primarily
  responsibility of AGS (P. Pile, K. Brown)
• Secondary beam also simulated in GEANT3 useful
  for ray tracing, scattering effects, radiation
  loads under normal and fault conditions
  (production solenoid environment talk)
• Magnetic and electric field calculations
• TOSCA used to design and study superconducting
  solenoids (magnetic tolerance talk)
• TOSCA and ELECTRA used to design and study pulsed
  and RF magnets (extinction talk)
• Finite element stress, thermal, fluid flow
  analysis (heat shield, water-cooled target)
• Many codes for magnet development at MIT
  (structural, thermal, quench)
• GEANT3 and GEANT4 simulation codes
• Most work done in GEANT3
• Modifications and bug fixes for a variety of
  effects (e.g. negative muon capture)
• Variety of hadron codes (FLUKA, GHEISHA, GCALOR,
  others in GEANT4) compared
• Now developing model in GEANT4 yet more new
  features to deal with
• Relatively extensive verification/comparison with
  data for low energy effects in hadron codes
• Used for most calculations of radiation
  environment, beam properties, detector
  performance

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Integrated Simulation and Analysis Tools

• Goal is an integrated simulation and analysis
  tool that allows easy, collaboration-wide
  development and use of GEANT simulation tools and
  MECO analysis tools first implementation of
  this (GMC) currently used
• Common geometrical description of full experiment
  from the front end of the proton beamline
• User interface to GEANT that simplifies geometry
  and kinematic definitions
• Implementations of a variety of tools useful for
  simulation of experiment to search for rare
  processes
• Simple way to allow users to easily reproduce
  very rare events
• Simple way to distribute large statistics jobs
  across many computers
• Integrated event and numerical display of rare
  events
• Code development supported by CVS, running on
  Unix and Linux platforms
• Currently running primarily in FORTRAN, being
  ported to C
• Many (but not all) results shown today use this
  structure
• Plan to modernize tools and extend usage of this
  package to all simulation and analysis work
  (integrated simulation and analysis plans talk
  following)

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MIT Plasma Science and Fusion Center Conceptual
Design of MECO Magnet System
5 T
2.5 T

• Very detailed CDR completed (300 pages)
• Complete 3D drawing package prepared
• TS and SOW for commercial procurement developed
• Industrial studies contracts let and completed

1 T
2 T
1 T

• 150 MJ stored energy
• 5T maximum field
• Uses surplus SSC cable
• Can be built in industry

Magnet tolerance talk following
This field implemented in simulation codes
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Muons Production and Capture in Graded Magnetic
Field

• Pions produced in a target located in an axially
  graded magnetic field
• 50 kW beam incident on gold target
• Charged particles are trapped in 5 2.5 T,
  axial magnetic field
• Pions and muons moving away from the experiment
  are reflected
• Superconducting magnet is protected by Cu and W
  heat and radiation shield

Production solenoid environment talk following
150 W load on cold mass15 ?W/g in
superconductor20 Mrad integrated dose
mW/gm in coil
2.5T
Superconducting coil
5T
Azimuthal position
Productiontarget
Heat Shield
Axial position
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Production Target for Large Muon Yield

• Production target region designed for high yield
  of low energy muons
• High Z target material
• Little extraneous material in bore to absorb p/m
• Diameter 0.6 - 0.8 mm, length 160 mm
• 5 kW of deposited energy
• Water cooling in 0.3 mm cylindrical
  shellsurrounding target
• Simulated with 2D and 3D thermal and turbulent
  fluid flow finite element analysis
• Target temperature well below 100? C
• Pressure drop is acceptable ( 10 Atm)
• Prototype built, tested for pressure and flow
  

Fully developed turbulent flow in 300 mm water
channel
Preliminary cooling testsusing induction heating
completed
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Muon Beam Transport with Curved Solenoid

• Curved sections eliminate line of site transport
  of photons and neutrons.
• Toroidal sections causes particles to drift out
  of planeused to sign and momentum select beam.
• dB/dS lt 0 to avoid reflections

2.5T
2.4T

• Goals
• Transport low energy m-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 transittime trajectories

2.4T
2.1T
2.1T
2.0T
Extinction talk following
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Sign and Momentum Selection in the Curved
Transport Solenoid
Transport in a torus results in charge and
momentum selection positive particles and low
momentum particles absorbed in collimators.
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Stopping Target and Experiment in Detector
Solenoid

• 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
• Polyethylene with lithium/boron to absorb
  neutrons
• Thin absorber to absorb protons
• Cosmic ray active and passive shield not shown

1T
Electron Calorimeter
1T
Tracking Detector
2T
Stopping Target 17 layers of 0.2 mm Al or Ti
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Magnetic Spectrometer to Measure Electron Momentum

• Measures electron momentum with precision of
  about 0.3 (RMS) essential to eliminate muon
  decay in orbit background

Electron starts upstream, reflects in field
gradient

• Must operate in vacuum and at high rates 500
  kHz rates in individual detector elements
• Energy resolution dominated by multiple
  scattering
• Implemented in straw tube detectors
• Vanes and octants, each nearly axial, and each
  with 3 close-packed layers of straws
• 2800 detectors, 2.6 m long, 5 mm diameter, 0.025
  mm wall thickness issues with straightness,
  wire supports, low mass end manifolds, mounting
  system
• r-f position resolution of 0.2 mm per straw from
  drift time
• axial resolution of 1.5 mm from induced charge on
  cathode pads requires resistive straws,
  typically carbon loaded polyester film
• High resistivity to maximize induced signal
• Low resistivity to carry cathode current in high
  rates
• Alternate implementation in straw tubes
  perpendicular to magnet axis has comparable
  performance

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Tracking Detector Rates vs. Time
Rate MHz
Rate kHz
Full time between proton pulses
Detection time interval
25 20 15 10 5 0
800 700 600 500 400 300 200 100 0
m-capture protons
beam electrons
m- decay in flight
0 400 800
1200 700 900
1100 1300
time with respect to proton pulse ns

• Very high rate from beam electrons at short times
  potential problems with chamber operation
• Protons from m capture are very heavily ionizing
  potential problems with noise, crosstalk

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Proton Contribution to Tracker Rates
105 103 10

• Protons are very heavily ionizing up to 50
  times minimum ionizing
• Protons below 18 MeV absorbed in target and
  proton shield
• Rate hitting tracker reduced by absorbers
  further optimization possible
• Studies of response of chambers to low energy
  protons planned at TUNL at Duke University

all generated protons
100 10 1
protons hitting tracker
0 20 40 60
80 100
Proton energy MeV
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Energy Load in Electron Calorimeter
Energy per trigger gate keV/cell/100ns
Energy per micropulse MeV/cell/mpulse

• Total rate dominated by bremsstrahlung of beam
  electrons during the flash protected by thin
  skin on upstream face
• During trigger gate (assumed to be 100 ns), rate
  is from a variety of sources, but typically small

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Expected Signal and Background in MECO Experiment

• Background calculated for 107 s running time at
  intensity giving 5 signal events for Rme 10-16
  
• Sources of background will be determined directly
  from data.

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Expected Signal and Background in MECO Experiment
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Running Scenario

• Estimated 107 seconds of running at full
  intensity to reach design goal
• 4 x 1013 protons per pulse
• 90 efficiency on 120 scheduled hours and 30
  weeks/year 0.9 year after 1(?) year of
  commissioning
• Original goal was to have machine operating at
  nearly nominal intensity, since machine
  modifications were not the critical path and
  pre-operations funding was envisaged
• Also anticipated to have much of the detector
  system operational prior to commissioning of
  superconducting magnets, which were the critical
  path
• Goal was a relatively fast turn-on
• Such early goals are not often realized
• What has changed, and how does that affect
  running?
• Perhaps only 2.5 x 1013 protons per second, only
  80 scheduled hours, only 25 weeks per year (none
  definitive, but perhaps best guess now)
• 0.9 years becomes 2.5 years of dedicated MECO
  running after 1(?) years of commissioning
• Running with Ti gains back a bit (15 improvement
  in sensitivity)
• Very important to work to improve above
  pessimistic estimate of running

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Reacting to Problems 1

• Rate handling difficulties important to
  identify early and modify running
• Ti and Al have different fractions of decays and
  capture Ti has higher sensitivity, but Al has
  fewer captures and flatter time dependence of
  rates
• Detector tradeoffs could decrease some rates,
  e.g. increased proton absorbers at the expense of
  slightly worse resolution
• High rates very near inner edge of detectors
  could be ameliorated by moving to slightly (1-2
  cm) larger radius with small loss in efficiency
• Could increase duty factor of machine and reduce
  intensity as last resort
• If problems at fixed times (e.g. just before
  spill) adjust extinction device(s) or change the
  measurement interval. Ti target is not very
  sensitive to small changes in length of detection
  interval
• Muon yield is less than expected
• Most things are optimized for yield
• If we have administrative limits (e.g. ALARA
  limits on radiation), can work to reduce losses,
  increase shielding
• Higher than expected radiation heat load on PS
• Additional shielding is possible in current
  design with small loss in yield
• Important to be conservative in design

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Reacting to Problems 2

• Backgrounds important to identify them early
• Extinction
• Monitor the extinction in real time
• If problems at fixed times (e.g. just before
  spill) adjust extinction device(s) or change the
  measurement interval. Ti target is not very
  sensitive to small changes in length of detection
  interval
• Measure each background from the data examples
  given
• Radiative pion decay has characteristic energy
  extending to above 130 MeV, should have
  characteristic pion lifetime dependence if from
  long latency, possibility of monitoring with pion
  cascade X-rays
• Beam electrons backgrounds will be forward peaked
  (pitch angle), only slightly above DIO endpoint
  due to transport properties
• Monitor CR backgrounds in real time (triggers off
  spill) carefully control detector efficiency
• Antiproton induced will have totally flat time
  dependence
• Reaction will depend on details examples given
• Increased secondary extinction can be had for
  money (stronger pulsed magnets)
• Increased DIO background rejection can be had
  with marginal loss in efficiency really a final
  analysis issue, but important to recognize early