Extinction Eric Prebys Mu 2 e Extinction Technical
Extinction Eric Prebys Mu 2 e Extinction Technical Design Review 2 November 2015
Charged Lepton Flavor Violation Al • The Mu 2 e experiment will attempt to detect Charged Lepton Flavor Violation (CLFV) • CLFV is a process involving charged leptons (e , m , t ) that violates the conservation of the number of leptons of each flavor Ordinary muon decay is not CLFV e- - e. V M 5 0 1 - N e- N Lm : 1 0 DLm = -1 Le : 0 1 DLe = 1 Both Lm and Le are not conserved in this process 2 Lm : 1 0 0 1 Le : 0 1 -1 0 E. Prebys | Introduction and Overview If this is observed, it is evidence physics beyond the Standard Model 11/2/2015
Experimental Signature of m+N e+N • 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 a mono-energetic electron carrying most of the muon rest energy m ~105 Me. V e- • Similar to m eg with 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 new physics. • Relative rate of m eg and m. N e. N is the most important clue regarding the details of the physics 3 E. Prebys | Introduction and Overview 11/2/2015
What We (Plan to) Measure • We will measure the rate of m to e conversion… …relative to ordinary m capture • This is defined as 4 E. Prebys | Introduction and Overview 11/2/2015
History of Lepton Flavor Violation Searches 90% C. L. • Best Limits – Rme<7 x 10 -13 (Sindrum-II 2006) – Br(m eg) < 6 x 10 -13 (MEG 2013) – Br(m 3 e) < 1 x 10 -12 (Sindrum-I 1988) Not quite apples-toapples, R. Berstein but… Mu 2 e will measure: Goal: single event sensitivity of Rme=3 x 10 -17 5 E. Prebys | Introduction and Overview 11/2/2015
Just How Rare is that? ~90% C. L. goal Single event sensitivity of Mu 2 e 6 E. Prebys | Introduction and Overview 11/2/2015
The Problem m->e Conversion: Sindrum II Cosmic Backgrou nd DIO tail 7 E. Prebys | Introduction and Overview • Most backgrounds are prompt with respect to the beam – Mostly radiative pion capture • Previous experiments suppressed these backgrounds by vetoing all observed electrons for a period of time after the arrival of each proton. – This leads to a fundamental to a rate limitation. 11/2/2015
Pulsed Beams (first proposed for MELC) • Eliminate prompt beam backgrounds by using a primary beam consisting of short proton pulses with separation on the order of a muon life time ~200 ns ~1. 5 ms Prompt backgrounds “Nothing” between bunches ”Extinction” live window • 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 which is very insensitive to electrons from ordinary muon decays, and has excellent tracking resolution. 8 E. Prebys | Introduction and Overview 11/2/2015
Mu 2 e: The Big Picture • • 9 Production Target – Proton beam strikes target, producing mostly pions Production Solenoid – Contains backwards pions/muons and reflects slow forward pions/muons Transport Solenoid – Selects low momentum, negative muons Capture Target, Detector, and Detector Solenoid – Capture muons on target and wait for them to decay – Detector blind to ordinary (Michel) decays, with E ≤ ½mmc 2 – Optimized for E ~ mmc 2 E. Prebys | Introduction and Overview 11/2/2015
Prompt Backgrounds • Most significant backgrounds are “prompt” with respect to the incident proton beam: Most important – Radiative p- capture: p-N →N*g, g. Z → e+e– Muon decay in flight: m- → e-nn – Prompt electrons – Pion decay in flight p- → e-ne • These are suppressed by minimizing beam between bunches and waiting long enough for all pions to decay away. • Goal: prompt background ~equal to all other backgrounds ≤ 10 -10 extinction between bunches. 10 E. Prebys | Introduction and Overview 11/2/2015
Orientation 11 E. Prebys | Introduction and Overview 11/2/2015
Mu 2 e Proton Delivery Ø Two Booster “batches” are injected into the Recycler (8 Ge. V storage ring). Each is: • 4 x 1012 protons • 1. 7 msec long Main Injector/Recycle r Delivery Ring (formerly p. Bar Debuncher) Ø These are divided into 8 bunches of 1012 each Ø The bunches are extracted one at a time to the Delivery Ring • Period = 1. 7 msec Ø As the bunch circulates, it is resonantly extracted to produce the desired beam structure. • Bunches of ~3 x 107 protons each • Separated by 1. 7 msec Mu 2 e Booster 12 E. Prebys | Introduction and Overview Exactly what we need 11/2/2015
Final Product • The Mu 2 e experiment has very stringent limits on the amount of beam that appears between pulses • The extinction task is comprised of – Providing this level of extinction. – Monitoring to verify that we have achieved it. • We will address “Extinction” and “Extinction Monitoring” separately 13 E. Prebys | Introduction and Overview 11/2/2015
Extinction Requirements* • The total extinction requirement is < 1 every ~300 bunches • This is primarily driven by the need to eliminate radiative pion capture, as described in detail in Mu 2 e-DOC-1175 • Extinction will be achieved in two steps – Our beam delivery technique will “naturally” provide an extinction of ~10 - 4 -10 -5 • See talk by S. Werkema – An “External Extinction System” will consist of a set of resonant dipoles and collimation system, such that only in time beam will be transmitted to the production target ~almost two order of magnitude • Aiming for additional 10 -7 extinction. safety margin *extinction monitor requirements will be discussed shortly 14 E. Prebys | Introduction and Overview 11/2/2015
Goal: Combined Extinction Time distribution of extracted beam (S. Werkema’s talk) 15 E. Prebys | Introduction and Overview Time dependent transmission of beam line (my talks) 11/2/2015
Principle of Beam Line Extinction • A magnet is used to deflect out-of-time beam into a downstream collimator Betatron Phase advance Magnet Collimator • Ideally, we would use a square pulse to kick out-of-time beam out of (or in-time beam into) the transmission channel, but the 600 k. Hz bunch rate makes this impossible with present technology. • We will therefore focus on a system of resonant magnets or “AC Dipoles”. – Even this isn’t trivial 16 E. Prebys | Introduction and Overview 11/2/2015
Generic Analysis of AC Dipole System 17 • An angular deflection at the AC dipole cause a position displacement 90° later in phase advance • Define normalized deflection angle Admittance of collimator • In terms of this angle β at dipole location E. Prebys | Introduction and Overview 11/2/2015
Design Considerations • Generally, the cost and complexity of a magnet scale with maximum stored energy, so we want to minimize Pole gap in non-bend plane Length Aperture in bend plane • Clearly, we want a waist in the non-bend plane Minimize g 18 E. Prebys | Introduction and Overview 11/2/2015
Design Considerations (cont’d) • A bit more complicated in the bend plane. We need an integrated field given by • So the stored energy is Large bx, long weak magnets - Assume bx=250 m, L=6 m - Factor of 4 better than “typical” values of bx=50 m, L=2 m Driving consideration in beam line design! 19 E. Prebys | Introduction and Overview 11/2/2015
Optimization of Wave Form • The extinction specification is that less than 10 -10 of beam protons will be found outside of ± 125 ns of the nominal bunch. • We have considered three types of waveforms – Broadband square wave not practical – A combination of three harmonics to approximate a square wave (original MECO proposal). – A single sine wave, at half the bunch frequency (300 k. Hz) – A “modified sine wave”, in which a high frequency component is added to reduce slewing during the transmission time: • Considered 13 th through 17 th harmonic (3. 8 5. 1 Mhz) 20 E. Prebys | Introduction and Overview 11/2/2015
Evaluating Transmission • Two criteria – Maximize transmission of in-time beam • Want less than 1% beam loss – Minimize transmission of out-of-time beam • Want less than 10 -7 for beam outside of ± 125 ns • The first criteria was used to determine the optimum waveform. • This was an iterative process that began with purely mathematical models for bunch shape and collimator efficiency • What I’m presenting now is the final result, based on: – Accurate model of bunch shape (S. Werkema’s talk) – GEANT 4 model of beam transmission (E. Prebys’ second talk) • This didn’t change the conclusions 21 E. Prebys | Introduction and Overview 11/2/2015
Single Harmonic Case Phase space (live window t): Full amplitude: Transmission window Short live window -> large “extra” amplitude 22 E. Prebys | Introduction and Overview 11/2/2015
Problem with Sine Wave • Because a sine wave is linear over the bunch length, the window for good transmission is less than half the full transmission window. In time 50% transmission, sine wave 50% transmission, modified sine wave Complete extinction The addition of a higher harmonic reduces the slewing of in-time beam and extends the window for efficient beam transmission. 23 E. Prebys | Introduction and Overview 11/2/2015
Harmonic Optimization Peak field assumes: 3 m low frequency 3 m high frequency Efficiency too low Transmission window too wide 24 E. Prebys | Introduction and Overview 11/2/2015
Wave Form Comparison Maximize this time • Results – MECO: 95. 5% – Sine Wave: 81. 3% – Modified Sine Wave: 99. 5% 25 E. Prebys | Introduction and Overview Our Choice 11/2/2015
AC Dipole Insertion • The optical requirements drive the beam line design • The AC dipole system consists of 6 identical 1 m segments – 3 @ 300 k. Hz – 3 @ 4. 5 MHz 26 E. Prebys | Introduction and Overview 11/2/2015
Magnetic Specifications • System designed for 50 p-mm-mrad full normalized admittance • Aperture – Bend plane: 9 cm – Non-bend plane: 1. 8 cm (1. 2 required + head room for tails and optical mismatch) • Peak Integrated field (per 1 m segment) – 300 k. Hz: 140 Gauss-m – 4. 5 MHz: 13 Gauss-m • See talks by – A. Makarov: Magnet Design – H. Pfeffer: Power Supply Design 27 E. Prebys | Introduction and Overview 11/2/2015
Extinction Collimation: Two Separate Collimation Issues Phase space distribution of out of time beam at location of AC dipole Beam core: out of time beam will be steered into the collimator or collimators 90° downstream of the AC dipole shifts distribution along x’ axis in phase space 28 E. Prebys | Introduction and Overview Admittance of downstream collimation system High amplitude beam tails will be steered into the collimation channel, so they must be cleaned up 90° upstream of the AC dipole 11/2/2015
Additional Collimation: Slow Extraction Tails • Beam that strikes the electrostatic septum during slow extraction results in a large tail in phase space, which can result in beam being scattered into the transmission channel. X Phase space at exit from Delivery Ring Model used for downstream simulations This causes problems 29 E. Prebys | Introduction and Overview 11/2/2015
Summary: Collimator Needs and Locations Halo Collimator (-90°, 1 m Steel) Tail Collimator (1 m Steel) AC Dipole Extinction Collimator (+90°, 1 m Tungsten) Details: talk by V. Sidorov 30 E. Prebys | Introduction and Overview 11/2/2015
External (M 4) Beamline Layout Mu 2 e Fin al Fo cu s • g-2 project responsible for M 4/M 5 combined beamline section • Mu 2 e Project responsible for beamline downstream of V 907 Diagnostic Absorber Temp Shielding Extinction Dipole Modules MC-1 g-2 V 907 Delivery Ring M 5 Beamline M 4/M 5 Combined Beamline 31 E. Prebys | Introduction and Overview 11/2/2015
Why About Collimation in Y? • To first order, we don’t care about high amplitude beam in Y, but to second order… – Worst risk is out-of-time beam scraping the AC dipole in Y and scattering back into the transmission channel in X – Not a problem for diffuse, high amplitude particles, but could be a problem for non-Gaussian shoulders near the beam which scrape right at the edge of the magnet. • Unfortunately, because of the large phase advance across the AC dipole, cleaning these tails would require at least two Y collimators and tailored optic – Cannot accommodate in within the length of the beam line – Anything less does more harm than good. • Solution: Increase Y clearance of AC dipole – 1. 2 cm 1. 8 cm, A=50 p-mm-mrad A=130 p-mm-mrad – Keep rest of transport line clear. 32 E. Prebys | Introduction and Overview 11/2/2015
Extinction Monitor • Achieving 10 -10 extinction is hard, but it’s not useful unless we can verify it. • Must measure extinction to 10 -10 precision – Roughly 1 proton every 300 bunches! • Monitor sensitive to single particles not feasible – Would have to be blind to the 3 x 107 particles in the bunch. • Focus on statistical technique – Design a monitor to detect a small fraction of scattered particles from target • 10 -50 per in-time bunch – Good timing resolution – Statistically build up precision profile for in time and out of time beam. • Goal – Measure extinction to 10 -10 precision in a few hours 33 E. Prebys | Introduction and Overview 11/2/2015
Extinction Monitor Design Selection channel built into target dump channel • Spectrometer based on 8 planes of ATLAS pixels • Optimized for few Ge. V/c particles See afternoon talks 34 E. Prebys | Introduction and Overview 11/2/2015
A long time coming 1992 Proposed as “MELC” at Moscow Meson Factory 1997 Proposed as “MECO” at Brookhaven (at this time, experiment incompatible with Fermilab) 1998 -2005 Intensive work on MECO technical design July 2005 Entire rare-decay program canceled at Brookhaven 2006 MECO subgroup + Fermilab physicists work out means to mount experiment at Fermilab Fall 2008 Mu 2 e Proposal submitted to Fermilab November 2008 Stage 1 approval. Formal Project Planning begins November 2009 DOE Grants CD-0 E. Prebys | Introduction and Overview In DOE project-speak, this is the first “Critical Decision”: Statement of mission need = official existence 11/2/2015 35
Where we are in the Critical Decision Process Nov. 2009 DOE Grants CD-0 Approve mission need July 2012 CD-1 Approve alternative selection and cost scale July 2014 CD-3 a Approve purchase of superconductor Approve baseline, magnet procurement, and civil construction. March 2015 CD-2/3 b • Plan for CD-3 c (final CD-3) in early to mid-2016 – Approval of full construction Things are really happening now! 36 E. Prebys | Cost and Schedule 11/2/2015
Civil Construction 37 E. Prebys | Introduction and Overview 11/2/2015
The big picture: Mu 2 e Accelerator Schedule CD-3 c CD-2/3 b M 4 Enclosure BO Resonant Extraction Design Mu 2 e Complete Beam to Diagnostic Absorber Fabrication & Installation of Res. Extr. Magnets, Power Supplies, & Electronics Commission Res. Extr. Install ESS Fabricate ESS Extinction & M 4 DA Section Installation External (M 4) Beamline Design Hbend Section Installation Final Focus Section Installation Target Remote Handling Fabrication & Installation Target Fabrication Target Station Design HRS Installation HRS Procurement & Fabrication AC Dipole, Pwr Supply & Collimator Procurement, Fabrication & Install Extinction Design Extinction Monitor Procurement, Assembly & Install Instrumentation & Controls Implementation Instrumentation & Controls Design Radiation Safety Procurements, Fabrication & Installation Radiation Safety Design Delivery Ring RF Procurements, Fabrication & Installation Delivery Ring RF Design Q 3 Q 4 Q 1 Q 2 Q 3 Q 4 Q 1 Q 2 Q 3 M 4 Commissioning Q 4 Q 1 Q 2 Q 3 Q 4 Beam Operations: g-2 Beam Operations with single turn Beam FY 14 FY 15 FY 16 FY 17 FY 18 FY 19 FY 20 FY 21 38 E. Prebys | Cost and Schedule 11/2/2015
Risks • Both the extinction and extinction monitoring system are based on mature technology, so some risks from CD 1 have been transferred to operations Failure of extinction system to sufficiently eliminate out of time beam ACCEL-035 Threat ACCEL-036 Opportunity No need in internal extinction collimation Extinction monitor fails to perform to Threat requirements. ACCEL-037 transferred to operations realized! transferred to operations • Remaining risk at CD-2: ACEL-204 – We have budgeted for two collimators upstream of the AC dipole to remove high amplitude tails. It was considered that up to two additional collimators might be needed • Potential cost impact: $160 k • We consider this risk retired for CD-3 39 E. Prebys - Extinction Systems, Mu 2 e CD-2/3 b Review 10/22/14
Major Milestones 40 E. Prebys | Cost and Schedule 11/2/2015
Review Charge Note: cost has been removed from the charge completely 41 E. Prebys | Introduction and Overview 11/2/2015
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