Post on 20-Mar-2016
description
Eric PrebysFermilab
For the Mu2e Collaboration
March 10, 2010
R.M. Carey, K.R. Lynch, J.P. Miller*, B.L. Roberts - Boston University
W.J. Marciano, Y. Semertzidis, P. Yamin - Brookhaven National Laboratory
Yu.G. Kolomensky - University of California, Berkeley
W. Molzon - University of California, Irvine
C.M. Ankenbrandt , R.H. Bernstein*, D. Bogert, S.J. Brice, D.R. Broemmelsiek, R.M. Coleman, D.F. DeJongh, S. Geer, D.A. Glezinski, D.F. Johnson, R.K. Kutsche, M.A. Martens, S. Nagaitsev, D.V. Neuffer, M. Popovic, E.J. Prebys, R.E. Ray,
V.L. Rusu, P. Shanahan, M.J. Syphers, R.S. Tschirhart, H.B. White Jr., K. Yonehara, C.Y. Yoshikawa – Fermi National Accelerator Laboratory
K.J. Keeter, E. Tatar - Idaho State University
P.T. Debevec, G.D. Gollin, D.W. Hertzog, P. Kammel - University of Illinois, Urbana-Champaign
V. Lobashev - Institute for Nuclear Research, Moscow, Russia
D.M. Kawall, K.S. Kumar - University of Massachusetts, Amherst
R.J. Abrams, M.A.C. Cummings, R.P. Johnson, S.A. Kahn, S.A. Korenev, T.J. Roberts, R.C. Sah - Muons, Inc.
A.L. de Gouvea - Northwestern University
F. Cervelli, R. Carosi, M. Incagli, T. Lomtadze, L. Ristori, F. Scuri, C. Vannini - Instituto Nazionale di Fisica Nucleare Pisa
M.D. Cororan - Rice
R.S. Holmes, P.A. Souder - Syracuse University
M.A. Bychkov, E.C. Dukes, E. Frlez, R.J. Hirosky, A.J. Norman, K.D. Paschke, D. Pocanic - University of Virginia
J. Kane – College of William and Mary
2March 10, 2010University of Maryland HEP Seminar
This effort has benefited greatly from over a decade of voluminous work done by the MECO collaboration, not all of whom have chosen to join the current collaboration.
3March 10, 2010University of Maryland HEP Seminar
Theoretical Motivation Experimental Technique Making Mu2e work at Fermilab Sensitivities Future Upgrades Conclusion
4March 10, 2010University of Maryland HEP Seminar
The study or rare particle decays allows us to probe mass scales far beyond those amenable to direct searches.
Among these decays, rare muon decays offer the possibility of experimentally clean and unambiguous evidence of physics beyond the current Standard Model.
Such searches are a natural part of the “Intensity Frontier”, which is being proposed for Fermilab after the end of the current collider program.
In the case of muon conversion, we can take advantage of a great deal of work that has already been done in the planning of the Muon to Electron Conversion Experiment (MECO), which was proposed at Brookhaven.
5March 10, 2010University of Maryland HEP Seminar
Forbidden in Standard Model Observation of neutrino mixing shows this can occur at a very small rate
Photon can be real (->e) or virtual (N->eN)
Standard model B.R. ~O(10-50)
e
0Z
First Order FCNC: Higher order dipole “penguin”:
e
Virtual mixing
W
6March 10, 2010University of Maryland HEP Seminar
Because extensions to the Standard Model couple the lepton and quark sectors, lepton number violation is virtually inevitable.
Charged Lepton Flavor Violation (CLFV) is a nearly universal feature of such models, and the fact that it has not yet been observed already places strong constraints on these models.
CLFV is a powerful probe of multi-TeV scale dynamics: complementary to direct collider searches
Among various possible CLFV modes, rare muon processes offer the best combination of new physics reach and experimental sensitivity
7March 10, 2010University of Maryland HEP Seminar
?
?
?
Flavor Changing Neutral Current
e
?N N
Mediated by massive neutral Boson, e.g. Leptoquark Z’ Composite
Approximated by “four fermi interaction”
Dipole (penguin)
Can involve a real photon
Or a virtual photon
?
?
?
8March 10, 2010University of Maryland HEP Seminar
Similar to ewith important advantages: No combinatorial background Because the virtual particle can be a photon or heavy neutral
boson, this reaction is sensitive to a broader range of BSM physics Relative rate of eand NeNis the most important clue
regarding the details of the physics
105 MeV e-
• When captured by a nucleus, a muon will have an enhanced probability of exchanging a virtual particle with the nucleus.
• This reaction recoils against the entire nucleus, producing the striking signature of a mono-energetic electron carrying most of the muon rest energy
9March 10, 2010University of Maryland HEP Seminar
Courtesy: A. de Gouvea
?
?
?
Sindrum IIMEGA
MEG proposal
We can parameterize the relative strength of the dipole and four fermi interactions.
This is useful for comparing relative rates for NeN and e
10March 10, 2010University of Maryland HEP Seminar
1
10-2
10-16
10-6
10-8
10-10
10-14
10-12
1940 1950 1960 1970 1980 1990 2000 2010
Initial mu2e Goal
- N e-N
+ e+ + e+ e+ e-
K0 +e-
K+ + +e-
SINDRUM II
Initial MEG Goal
10-4
10-16
11March 10, 2010University of Maryland HEP Seminar
Example Sensitivities*
CΛ = 3000 TeV
-4HH μμμeg =10 ×g
Compositeness
Second Higgs doublet
2Z
-17
M = 3000 TeV/c
B(Z μe) <10
Heavy Z’, Anomalous Z
coupling
Predictions at 10-15
Supersymmetry
2* -13μN eNU U = 8×10
Heavy Neutrinos
L
2μd ed
M =
3000 λ λ TeV/c
Leptoquarks
*After W. Marciano
12March 10, 2010University of Maryland HEP Seminar
Examples with >>1 (no e signal):LeptoquarksZ-primeCompositeness
SU(5) GUT Supersymmetry: << 1
Littlest Higgs: 1
Br(e)
Randall-Sundrum: 1
MEG
mu2e
10-12
10-14
10-16
10-1110-1310-15
R(TieTi)
10-13 10-11 10-9
Br(e)
10-16
10-10
10-14
10-12
10-10
R(TieTi)
13March 10, 2010University of Maryland HEP Seminar
Very high rate Peak energy 52 MeV Must design detector to be
very insensitive to these.
Nucleus coherently balances momentum
Rate approaches conversion (endpoint) energy as (Es-E)5
Drives resolution requirement.
N
e
e
e
e
Ordinary: Coherent:
14March 10, 2010University of Maryland HEP Seminar
Rate limited by need to veto prompt backgrounds!
>e Conversion: Sindrum II
12103.4capture
Ti
TieTiR e
11
12
11
2
102.72100.1102.1102.1
eeee
ee e
LFV Decay:
High energy tail of coherent Decay-in-orbit (DIO)
15March 10, 2010University of Maryland HEP Seminar
Eliminate prompt beam backgrounds by using a primary beam with short proton pulses with separation on the order of a muon life time
Design a transport channel to optimize the transport of right-sign, low momentum muons from the production target to the muon capture target.
Design a detector to strongly suppress electrons from ordinary muon decays
~100 ns ~1.5 s
Prompt backgrounds
live window
16March 10, 2010University of Maryland HEP Seminar
Single, monoenergetic electron with E=105 MeV, coming from the target, produced ~1 s (Al ~ 880ns) after the “” bunch hits the target foils
• Need good energy resolution: ≲0.200 MeV
• Need particle ID• Need a bunched beam with less
than 10-9 contamination between bunches
17March 10, 2010University of Maryland HEP Seminar
negligible 95.56 MeV10.08 MeV.0726 s~0.8-1.5Au(79,~197)
0.16
0.45
Prob decay >700 ns
104.18 MeV
104.97 MeV
Conversion Electron Energy
1.36 MeV.328 s1.7Ti(22,~48)
0.47 MeV.88 s1.0Al(13,27)
Atomic Bind. Energy(1s)
Bound lifetime
Re(Z) / Re(Al)
Nucleus
Aluminum is nominal choice for Mu2e
Dipole rates are enhanced for high-Z, but Lifetime is shorter for high-Z
Decreases useful live window Also, need to avoid background from radiative muon capture
ee
NN Want M(Z)-M(Z-1) < signal energy
18March 10, 2010University of Maryland HEP Seminar
MECO spectrometer design
for every incident proton 0.0025 ’s are stopped in the 17 0.2 mm Al target
foils
19March 10, 2010University of Maryland HEP Seminar
Production RegionProduction Region
• Axially graded 5 T solenoid captures low energy backward and reflected pions and muons, transporting them toward the stopping target
• Cu and W heat and radiation shield protects superconducting coils from effects of 50kW primary proton beam
Superconducting coils
Production TargetHeat & Radiation Shield
Proton Beam
5 T2.5 T
20March 10, 2010University of Maryland HEP Seminar
Transport SolenoidTransport Solenoid
• Curved solenoid eliminates line-of-sight transport of photons and neutrons
• Curvature drift and collimators sign and momentum select beam
• dB/ds < 0 in the straight sections to avoid trapping which would result in long transit times
Collimators and pBar Window
2.5 T
2.1 T
21March 10, 2010University of Maryland HEP Seminar
Detector RegionDetector Region
1 T1 T
2 T
• Axially-graded field near stopping target to sharpen acceptance cutoff.
• Uniform field in spectrometer region to simplify momentum analysis
• Electron detectors downstream of target to reduce rates from and neutrons
Stopping Target Foils Straw Tracking Detector
Electron Calorimeter
22March 10, 2010University of Maryland HEP Seminar
Production
Solenoid
Transport Solenoid
Detector Solenoid
23March 10, 2010University of Maryland HEP Seminar
E~3-15 MeV
Vital that e- momentum < signal momentum
24March 10, 2010University of Maryland HEP Seminar
3000 2.6 m straws (r,) ~ 0.2 mm
17000 Cathode strips z) ~ 1.5 mm
1200 PBOW4 cyrstals in electron calorimeter E/E ~ 3.5%
Resolution: .19 MeV/c
25March 10, 2010University of Maryland HEP Seminar
Re = 10-16 gives 5 events for 4x1020 protons on target
0.4 events background, half from out of time beam, assuming 10-9 extinction Half from tail of coherent
decay in orbit Half from prompt
Coherent Decay-in-orbit, falls as (Ee-E)5
26March 10, 2010University of Maryland HEP Seminar
1992 MELC proposed at Moscow Meson Factory
1997MECO proposed for the AGS at Brookhaven as part of RSVP (at this time, experiment incompatible with Fermilab)
1998-2005 intensive work on MECO technical design: magnet system costed at $58M, detector at $27M
July 2005 RSVP cancelled for financial reasons
2006 MECO subgroup + Fermilab physicists work out means to mount experiment at Fermilab
June 2007 mu2e EOI submitted to FermilabOctober 2007 LOI submitted to Fermilab
Fall 2008 mu2e submits proposal to FermilabNovember
2008 Stage 1 approval. Formal Project Planning begins
2010 technical design approval: start of construction2014? first beam
27March 10, 2010 University of Maryland HEP Seminar
Fermilab Built ~1970
200 GeV proton beams Eventually 400 GeV
Upgraded in 1985 900GeV x 900 GeV p-pBar collisions Most energetic in the world ever since
Upgraded in 1997 Main Injector-> more intensity 980 GeV x 980 GeV p-pBar collisions Intense neutrino program
Will become second most energetic accelerator (by a factor of seven) when LHC comes on line ~2009 What next???
28March 10, 2010University of Maryland HEP Seminar
MiniBo
oNE/
BNB
NUM
I
29March 10, 2010University of Maryland HEP Seminar
“Preac” - Static Cockroft-Walton generator
accelerates H- ions from 0 to 750 KeV.
“Old linac”(LEL)- accelerate H- ions from 750 keV to 116
MeV
“New linac” (HEL)- Accelerate H- ions from 116 MeV to 400 MeV
30March 10, 2010University of Maryland HEP Seminar
• Accelerates the 400 MeV beam from the Linac to 8 GeV
• Operates in a 15 Hz offset resonant circuit
• Sets fundamental clock of accelerator complex
•From the Booster, 8 GeV beam can be directed to
• The Main Injector
• The Booster Neutrino Beam (MiniBooNE)
• A dump.
•More or less original equipment
31March 10, 2010University of Maryland HEP Seminar
• The Main Injector can accept 8 GeV protons OR antiprotons from
• Booster
• The anti-proton accumulator
• The Recycler (which shares the same tunnel and stores antiprotons)
• It can accelerate protons to 120 GeV (in a minimum of 1.4 s) and deliver them to
• The antiproton production target.
• The fixed target area.
• The NUMI beamline.
• It can accelerate protons OR antiprotons to 150 GeV and inject them into the Tevatron.
32March 10, 2010University of Maryland HEP Seminar
Protons are accelerated to 120 GeV in Main Injector and extracted to pBar target
pBars are collected and phase rotated in the “Debuncher”
Transferred to the “Accumulator”, where they are cooled and stacked
Not used for NOvA
33March 10, 2010University of Maryland HEP Seminar
Roughly 6*(4x1012 batch)/(1.33 s)*(2x107 s/year)=3.6x1020 protons/year available
MI uses 12 of 20 available Booster Batches per 1.33 second cycle
Preloading for NOvA
Available for 8 GeV program
Recycler
Recycler MI transfer
15 Hz Booster cyclesMI NuMI cycle (20/15 s)
34March 10, 2010University of Maryland HEP Seminar
Deliver beam to Accumulator/Debuncher enclosure with minimal beam line modifications and no civil construction.
Recycler(Main Injector
Tunnel)
MI-8 -> Recycler done for NOvA
New switch magnet extraction to P150 (no need for kicker)
35March 10, 2010University of Maryland HEP Seminar
Inject a newly accelerated Booster batch every 67 mS onto the low momentum orbit of the Accumulator
The freshly injected batch is accelerated towards the core orbit where it is merged and debunched into the core orbit
Momentum stack 3-6 Booster batches
T<133ms
T=134ms
T=0
Energy
1st batch is injected onto the injection orbit
1st batch is accelerated to the core orbit
T<66ms
2nd Batch is injected
T=67ms
2nd Batch is accelerated
3rd Batch is injected
36March 10, 2010University of Maryland HEP Seminar
March 10, 201037 37
Booster-Era Beam Timelines for Mu2E Experiment
Base line scenario. Numerous other options being discussed.
University of Maryland HEP Seminar
Momentum stack 6 Booster batches directly in Accumulator (i.e. reverse direction)
Capture in 4 kV h=1 RF System.
Transfer to Debuncher
Phase Rotate with 40 kV h=1 RF in Debuncher
Recapture with 200 kV h=4 RF system t~40 ns
38March 10, 2010University of Maryland HEP Seminar
Exploit 29/3 resonance Extraction hardware similar to
Main Injector Septum: 80 kV/1cm x 3m Lambertson+C magnet ~.8T x
3m
39March 10, 2010University of Maryland HEP Seminar
RF noise, gas interaction, and intrabeam scattering cauase beam to “wander out” of the RF bucket.
D is the dispersion function: Transverse Offset = ΔE/E
× D
Anticipate installation of collimator in region with dispersion, removing off-momentum particles: Momentum scraping
University of Maryland HEP Seminar40March 10, 2010
Possible change from baseline in proposal: two stage collimation Dipoles at 0 and 360 Collimators at 90 and 180
University of Maryland HEP Seminar41
Baseline design, single collimator
March 10, 2010
Requires new building.
Minimal wetland issues.
Can tie into facilities at existing experimental hall.
42March 10, 2010University of Maryland HEP Seminar
Proton flux 1.8x1013 p/sRunning time 2x107 sTotal protons 3.6x1020 p/yr stops/incident proton 0.0025 capture probability 0.60Time window fraction 0.49Electron trigger efficiency 0.90Reconstruction and selection efficiency
0.19
Detected events for Re = 10-16 4.5
43March 10, 2010 University of Maryland HEP Seminar
Muon decay in orbit: → e
• Ee < mc2 – ENR – EB
• N (E0 - Ee)5
• Fraction within 3 MeV of endpoint 5x10-15
• Defeated by good energy resolution
Radiative muon capture: Al → Mg
• endpoint 102.5 MeV• 10-13 produce e- above 100 MeV
1. Stopped Muon Induced Backgrounds
44March 10, 2010University of Maryland HEP Seminar
2. Beam Related Backgrounds• Suppressed by minimizing beam
between bunches– Need ≲ 10-9 extinction– (see previous slides)
• Muon decay in flight: → e
• Since Ee < mc2/2, p > 77 GeV/c• Radiative capture:N →N*, Z → ee
• Beam electrons• Pion decay in flight: → ee
3. Asynchronous Backgrounds• Cosmic rays
• suppressed by active and passive shielding
45March 10, 2010University of Maryland HEP Seminar
Roughly half of background is beam related, and half interbunch contamination related
Total background per 4x1020 protons, 2x107 s: 0.43 events
Signal for Re = 10-16: 5 eventsSingle even sensitivity: 2x10-17
90% C.L. upper limit if no signal: 6x10-17
Blue text: beam related.
46March 10, 2010University of Maryland HEP Seminar
Beam delivery schemes Try to minimize charge in Accumulator at one time. Generally a trade-off that increases instantaneous rate.
Recalculating rates and backgrounds Models and data on low energy pion production have come a long way in
recent years. Optimizing magnet design
Original design based on SSC superconductor, which has since mysteriously vanished.
Is magnetic mirror worth it? New detector options
Investigating low pressure drift chamber Similar mass and less probability of fakes
Calibration schemes How can we convince the world we can measure something at a < 10-16
BR? Siting optimization and synergy with other programs
g-2 Muon collider R&D
47March 10, 2010University of Maryland HEP Seminar
One 5 Hz pulses every 1.4 s Main Injector cycle = 2.1MW at 120 GeV
This leaves six pulses (~860 kW) available for 8 GeV physics These will be automatically stripped and stored in the Recycler,
and can also be rebunched there.
48March 10, 2010University of Maryland HEP Seminar
Beam delivery Accumulator/Debuncher (like initial operation)?
How much beam can we put into the Accumulator and Debuncher and keep the beam stable?
Radiation issues (already a problem at initial intensities). Directly from Recycler?
Not enough aperture for conventional resonant extraction.
Investigating more clever ideas
49March 10, 2010University of Maryland HEP Seminar
Achieve sufficient extinction of proton beam. Current extinction goal directly driven by total protons
Upgrade target and capture solenoid to handle higher proton rate Target heating Quenching or radiation damage to production solenoid
Improve momentum resolution for the ~100 MeV electrons to reject high energy tails from ordinary DIO electrons. Limited by multiple scattering in target and detector planes Requirements at or beyond current state of the art.
Operate with higher background levels. High rate detector
Manage high trigger rates All of these efforts will benefit immensely from the knowledge and
experience gained during the initial phase of the experiment. If we see a signal a lower flux, can use increased flux to study in detail
Precise measurement of Re Target dependence Comparison with e rate
50March 10, 2010University of Maryland HEP Seminar
(from Dep. Director Y-K Kim)
51March 10, 2010University of Maryland HEP Seminar
We have proposed a realistic experiment to measure
Single event sensitivity of Re=2x10-17
90% C.L. limit of Re<6x10-17
This represents an improvement of more than four orders of magnitude compared to the existing limit, or over a factor of ten in effective mass reach. For comparison TeV -> LHC = factor of 7 LEP 200 -> ILC = factor of 2.5
Potential future upgrades could increase this sensitivity by one or two orders of magnitude
ANY signal would be unambiguous proof of physics beyond the Standard Model
The absence of a signal would be a very important constraint on proposed new models.
capture Al
AlAl
eR e
52March 10, 2010University of Maryland HEP Seminar
Eliminate prompt beam backgrounds by using a primary beam with short proton pulses with separation on the order of a muon life time
Design a transport channel to optimize the transport of right-sign, low momentum muons from the production target to the muon capture target.
Design a detector to strongly suppress electrons from ordinary muon decays
~100 ns ~1.5 s
Prompt backgrounds
live window
March 10, 2010 53University of Maryland HEP Seminar
Goal: make total backgrounds related to inter-bunch beam roughly equal to other backgrounds.
Need extinction at a level of 10-9 or better!
Blue text: beam related.
March 10, 2010 54University of Maryland HEP Seminar
In ring Momentum scraping Gap-clearing kicker 10-4 to 10-5?
In beam line System of AC dipoles and collimators
Think minature golf 10-5 to 10-6 (at least)
Monitoring Very important to measure extinction Big question
Can we measure inter-bunch contamination bunch by bunch, or only statistically?
March 10, 2010 55University of Maryland HEP Seminar
During h=4 capture, some beam may be captured in wrong bucket. Install gap cleaning kicker. Fire once per cycle, just prior to
extraction. RF noise or gas interactions
can cause beam to “wander” out of bucket, but tends to be driven well off momentum, as shown at right Noise set to 1% to exaggerate
effect.
March 10, 2010 56University of Maryland HEP Seminar
Animations courtesy of Mike Syphers
Momentum scraping in high dispersion sections can capture particles lost from bunches.
Still working to understand efficiency. In principle can be very high.
March 10, 2010 57University of Maryland HEP Seminar
Animations courtesy of Mike Syphers
Two matched dipoles at 180 phase separation Collimation channel at 90 Beam is transmitted at node
System resonant at half bunch frequency (~300 kHz)
Parameter Value CommentKinetic Energy 8 GeV
Emittance (95%) 20 -mm-mrErms 71 MeV
Beam line admittance 50 -mm-mr Set by collimators
March 10, 2010 58University of Maryland HEP Seminar
Consider it axiomatic that some beam may be present anywhere in the admittance of the beam line Historically very hard to predict or model.
Therefore, it’s important to have the beam admittance well defined by a collimation system, rather than rely on the limiting aperture of magnets, beam pipes, etc.
For the moment, assume that the defining admittance of the beam line is equal to the defining admittance of the collimation channel.
March 10, 2010University of Maryland HEP Seminar 59
*al la FNAL-BEAM-DOC-2925
Beam fully extinguished when deflection equals twice full admittance (A) amplitude
At collimator:
x
Af 2
At kicker:Full scale deflection
Fraction of FS to extinguish
March 10, 2010 60University of Maryland HEP Seminar
Phase space (live window ): Full amplitude:
Short live window -> large “extra” amplitude
March 10, 2010 61University of Maryland HEP Seminar
TLL
TAB
LgwBgwLBU
xx2/3
2/1
2/12/1
222
0
22
0
20
0
181
21
21
Falls with x
For a particular x, there is an optimum length L0: xx TL
0
For which the optimized parameters are:
2/5122/52
2
0min
22/32/12
3
2/12/12/1
2/12/1
1161
2
2
4
xx
xx
opt
xx
opt
xx
opt
ATABU
ATABB
AT
Ag
AA
w
March 10, 2010 62University of Maryland HEP Seminar
Parameter Value Commentx 50 m Typical beam line beta max
Effective length (L) 2 m
Full width (w) 5 cm
Vertical gap (g) 1 cm Scaled up for practicalityPeak field (B0) 600 Gauss
Peak stored energy (U) 1.43 J A little over twice the minimum
Recent analyses show that the pararameters are challenging Will probably go to larger , and longer magnets
March 10, 2010 63University of Maryland HEP Seminar
Symmetric about 2m collimator with x = 50m, y= 1m, x = .25 (at collimator center)
Shortest line which fits constraints (32 m) Small x (7.9 m) means small hole (x/y = 1.29 x 2.54 cm)
March 10, 2010 64University of Maryland HEP Seminar
Specified field and frequency leads to high voltages (few kV)
March 10, 2010University of Maryland HEP Seminar 65
The amount of beam transmitted (or which hits the target) is given by
This can be expressed in a generic way as
Where
dx
A95
Lateral displacement
Half-aperture
emittance
admittance
March 10, 2010 66University of Maryland HEP Seminar
March 10, 2010 67University of Maryland HEP Seminar
3 harmonic design of MECO 3 harmonics (1x, 2x, and 3x bunch rate) generate ~square
wave. Transmits at peak
Single harmonic designas in proposal Runs at half of bunch rate Transmits on the null
Modified sine wave Add high harmonic to reduce
slewing in transmission window. Important questions
Transmission during 200 ns live window
Magnet design Is second magnet necessary?
200 ns transmission window
March 10, 2010 68University of Maryland HEP Seminar
Normalized all waveforms to complete extinction at ±100 ns
March 10, 2010 69University of Maryland HEP Seminar
March 10, 2010 70University of Maryland HEP Seminar
Our baseline design has significant issues with transmission efficiency unless bunches are very short (~10ns).
The MECO design is markedly superior in this regard.
A new proposal involving a small amount of 4.8MHz harmonic looks very promising.
In comparing the two proposals, consideration will be given to Higher harmonic rate vs Reduced number of harmonics and lower magnetic field.
March 10, 2010University of Maryland HEP Seminar 71
It’s clear the original proposal parameters raise challenges for magnet and power supply design.
Analyzing switching to a lower field, longer magnet MECO design, for example was 6 m, 80 G Would required 250m
Working to balance practicalities of magnet and beam line design.
Also clear single harmonic is impractical unless pulse is extremely short (<10 ns)
Comparing MECO 3 harmonic design to modified sine wave design. Lower frequency vs. less harmonics and lower field.
In either case, is compensating dipole needed? Perhaps not.
March 10, 2010University of Maryland HEP Seminar 72
Challenge Measuring inter-bunch extinction requires a dynamic range (or
effective dynamic range) of at least 109. Options being considered
Statistical: use either a thin scatterer, or small acceptance target monitor
to count a small (10-7 or 10-8?) fraction of beam particles. Statistically measure inter-bunch beam. Pros: straightforward Cons: limited sensitivity to fluctuations in extinction (is that
important?) Single Particle
Measure inter-bunch beam at the single particle level Need something very fast (Cerenkov?) Probably have to “blind” detector at bunch time Pros: best picture of out of bunch beam Cons: hard
March 10, 2010 73University of Maryland HEP Seminar
Example Design to count ~10 protons/nominal bunch
~1 in 107
Can build up a 3s 10-9 measurement in 109 bunches ~30 minutes
March 10, 2010University of Maryland HEP Seminar 74
Primary beam
Scattered protons
target
Small acceptance
proton counter
Background rejection Need energy threshold
Sweeping magnet Calorimetric Cerenkov based
Rad hardness If placed after target, access could be difficult.
March 10, 2010University of Maryland HEP Seminar 75
Pros: Rad hard Variable light yield (pressure)
Cons: High pressure -> thick windows Scintillation? Difficult to gate
March 10, 2010University of Maryland HEP Seminar 76
Pros: Lots of light Coincidence to suppress scintillation Potentially gate light with Pockels cell during bunch
Cons: Beam scattering? Rad harness an issue (Grad ~ few days)
March 10, 2010University of Maryland HEP Seminar 77
Mu2e is working on all aspects of extinction and extinction measurement.
Still more questions than answers at this point.
March 10, 2010University of Maryland HEP Seminar 78