Extinction Eric Prebys Mu2e Extinction Technical Design Review 2 November 2015

Charged Lepton Flavor Violation The Mu2e experiment will attempt to detect Charged Lepton Flavor Violation (CLFV) CLFV is a process involving charged leptons ( e ,  ,   ) that violates the conservation of the number of leptons of each flavor 11/2/2015E. Prebys | Introduction and Overview2  - N  e - N L  :L  = -1 L  :10  L  = -1 L e :L e  = 1 L e :01  L e  = 1 Both L   and L e are not conserved in this process L  : L  :1001 L e : L e :01-10 Ordinary muon decay is not CLFV If this is observed, it is evidence physics beyond the Standard Model  - - - - e-e-e-e-Al 105 MeV

Experimental Signature of  +N  e+N Similar to  e  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  e  and  N  eN  is 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 a mono-energetic electron carrying most of the muon rest energy 11/2/20153E. Prebys | Introduction and Overview

What We (Plan to) Measure We will measure the rate of  to e conversion… …relative to ordinary  capture This is defined as 11/2/2015E. Prebys | Introduction and Overview4

History of Lepton Flavor Violation Searches Best Limits –R  e <7x (Sindrum-II 2006) –Br(   e  ) < 6x (MEG 2013) –Br(   3e) < 1x (Sindrum-I 1988) 11/2/2015E. Prebys | Introduction and Overview5 Mu2e will measure: Not quite apples-to- apples, but… Goal: single event sensitivity of R  e =3x % C.L. R. Berstein

Just How Rare is that? 11/2/2015E. Prebys | Introduction and Overview6 Single event sensitivity of Mu2e ~90% C.L. goal

The Problem 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.  >e Conversion: Sindrum II DIO tail 11/2/20157E. Prebys | Introduction and Overview Cosmic Backgrou nd

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 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. ~200 ns ~1.5  s Prompt backgrounds live window 11/2/20158E. Prebys | Introduction and Overview “Nothing” between bunches  ”Extinction”

Mu2e: The Big Picture 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 ≤ ½m  c 2 – Optimized for E ~ m  c 2 11/2/2015E. Prebys | Introduction and Overview9

Prompt Backgrounds Most significant backgrounds are “prompt” with respect to the incident proton beam: – Radiative  - capture:   N → N* ,  Z → e  e  – Muon decay in flight:   → e  – Prompt electrons – Pion decay in flight   → e  e 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  ≤ extinction between bunches. 11/2/2015E. Prebys | Introduction and Overview10 Most important

Orientation 11/2/2015E. Prebys | Introduction and Overview11

Mu2e Proton Delivery 12 Booster Main Injector/Recycle r Delivery Ring (formerly pBar Debuncher) Mu2e  Two Booster “batches” are injected into the Recycler (8 GeV storage ring). Each is: 4x10 12 protons 1.7  sec long  These are divided into 8 bunches of each  The bunches are extracted one at a time to the Delivery Ring Period = 1.7  sec  As the bunch circulates, it is resonantly extracted to produce the desired beam structure. Bunches of ~3x10 7 protons each Separated by 1.7  sec Exactly what we need 11/2/2015E. Prebys | Introduction and Overview

Final Product The Mu2e 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 11/2/2015E. Prebys | Introduction and Overview13

Extinction Requirements* The total extinction requirement is This is primarily driven by the need to eliminate radiative pion capture, as described in detail in Mu2e-DOC-1175 Extinction will be achieved in two steps – Our beam delivery technique will “naturally” provide an extinction of ~ 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 Aiming for additional extinction. 11/2/2015E. Prebys | Introduction and Overview14 *extinction monitor requirements will be discussed shortly < 1 every ~300 bunches ~almost two order of magnitude safety margin

Goal: Combined Extinction 11/2/2015E. Prebys | Introduction and Overview15 Time distribution of extracted beam (S. Werkema’s talk) Time dependent transmission of beam line (my talks)

Principle of Beam Line Extinction A magnet is used to deflect out-of-time beam into a downstream 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 kHz 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 11/2/2015E. Prebys | Introduction and Overview16 Magnet Collimator Betatron Phase advance

Generic Analysis of AC Dipole System An angular deflection at the AC dipole cause a position displacement 90° later in phase advance Define normalized deflection angle In terms of this angle 11/2/2015E. Prebys | Introduction and Overview17 Admittance of collimator β at dipole location

Design Considerations Generally, the cost and complexity of a magnet scale with maximum stored energy, so we want to minimize Clearly, we want a waist in the non-bend plane 11/2/2015E. Prebys | Introduction and Overview18 Pole gap in non-bend plane Aperture in bend plane Length Minimize g 

Design Considerations (cont’d) A bit more complicated in the bend plane. We need an integrated field given by So the stored energy is 11/2/2015E. Prebys | Introduction and Overview19  Large  x, long weak magnets - Assume  x =250m, L=6m - Factor of 4 better than “typical” values of  x =50m, L=2m Driving consideration in beam line design!

Optimization of Wave Form The extinction specification is that less than 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 kHz) – 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) 11/2/2015E. Prebys | Introduction and Overview20

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 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) – GEANT4 model of beam transmission (E. Prebys’ second talk) This didn’t change the conclusions 11/2/2015E. Prebys | Introduction and Overview21

Single Harmonic Case Phase space (live window  ): Full amplitude: Short live window -> large “extra” amplitude 11/2/201522E. Prebys | Introduction and Overview Transmission window

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. 11/2/2015E. Prebys | Introduction and Overview23 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.

Harmonic Optimization 11/2/2015E. Prebys | Introduction and Overview24 Transmission window too wide Efficiency too low Peak field assumes: 3 m low frequency 3 m high frequency

Wave Form Comparison Results – MECO: 95.5% – Sine Wave: 81.3% – Modified Sine Wave: 99.5% 11/2/2015E. Prebys | Introduction and Overview25 Maximize this time Our Choice

AC Dipole Insertion The optical requirements drive the beam line design The AC dipole system consists of 6 identical 1 m segments – 300 kHz – 4.5 MHz 11/2/2015E. Prebys | Introduction and Overview26

Magnetic Specifications System designed for 50  -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 1m segment) – 300 kHz: 140 Gauss-m – 4.5 MHz: 13 Gauss-m See talks by – A. Makarov: Magnet Design – H. Pfeffer: Power Supply Design 11/2/2015E. Prebys | Introduction and Overview27

Extinction Collimation: Two Separate Collimation Issues 11/2/2015E. Prebys | Introduction and Overview28 AC dipole shifts distribution along x’ axis in phase space Beam core: out of time beam will be steered into the collimator or collimators 90° downstream of the AC dipole 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 Phase space distribution of out of time beam at location of AC dipole

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. 11/2/2015E. Prebys | Introduction and Overview29 X Phase space at exit from Delivery Ring Model used for downstream simulations This causes problems

Summary: Collimator Needs and Locations 11/2/2015E. Prebys | Introduction and Overview30 Extinction Collimator (+90°, 1m Tungsten) AC Dipole Halo Collimator (-90°, 1m Steel) Tail Collimator (1m Steel) Details: talk by V. Sidorov

External (M4) Beamline Layout 11/2/2015E. Prebys | Introduction and Overview31 MC-1g-2 Delivery Ring Diagnostic Absorber Final Focus Mu2e Extinction Dipole Modules M5 Beamline M4/M5 Combined Beamline V907 g-2 project responsible for M4/M5 combined beamline section Mu2e Project responsible for beamline downstream of V907 Temp Shielding

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  -mm-mrad  A=130  -mm-mrad – Keep rest of transport line clear. 11/2/2015E. Prebys | Introduction and Overview32

Extinction Monitor Achieving extinction is hard, but it’s not useful unless we can verify it. Must measure extinction to precision – Roughly 1 proton every 300 bunches! Monitor sensitive to single particles not feasible – Would have to be blind to the 3x10 7 particles in the bunch. Focus on statistical technique – Design a monitor to detect a small fraction of scattered particles from target per in-time bunch – Good timing resolution – Statistically build up precision profile for in time and out of time beam. Goal – Measure extinction to precision in a few hours 11/2/2015E. Prebys | Introduction and Overview33

Extinction Monitor Design 11/2/2015E. Prebys | Introduction and Overview34 Selection channel built into target dump channel Spectrometer based on 8 planes of ATLAS pixels Optimized for few GeV/c particles See afternoon talks

A long time coming 1992Proposed as “MELC” at Moscow Meson Factory 1997 Proposed as “MECO” at Brookhaven (at this time, experiment incompatible with Fermilab) Intensive work on MECO technical design July 2005Entire rare-decay program canceled at Brookhaven 2006 MECO subgroup + Fermilab physicists work out means to mount experiment at Fermilab Fall 2008Mu2e Proposal submitted to Fermilab November 2008Stage 1 approval. Formal Project Planning begins November 2009DOE Grants CD-0 In DOE project-speak, this is the first “Critical Decision”: Statement of mission need = official existence 11/2/2015 E. Prebys | Introduction and Overview 35

Where we are in the Critical Decision Process Nov. 2009DOE Grants CD-0Approve mission need July 2012CD-1Approve alternative selection and cost scale July 2014CD-3aApprove purchase of superconductor March 2015CD-2/3b Approve baseline, magnet procurement, and civil construction. 11/2/2015E. Prebys | Cost and Schedule36 Plan for CD-3c (final CD-3) in early to mid-2016 – Approval of full construction Things are really happening now!

Civil Construction 11/2/2015E. Prebys | Introduction and Overview37

M4 Enclosure BO The big picture: Mu2e Accelerator Schedule Q3Q4Q1Q2Q3Q4Q1Q2Q3Q4Q1Q2Q3Q4Q1Q2Q3Q4Q1Q2Q3Q4Q1Q2Q3Q4Q1Q2Q3Q4Q1Q2Q3Q4 FY14 FY15 FY16 FY17 FY18 FY19 FY20 FY21 CD-3c CD-2/3b Resonant Extraction Design g-2 Beam Operations Extinction Design AC Dipole, Pwr Supply & Collimator Procurement, Fabrication & Install External (M4) Beamline Design Target Station Design HRS Procurement & Fabrication Instrumentation & Controls Implementation Delivery Ring RF Procurements, Fabrication & Installation 11/2/2015 E. Prebys | Cost and Schedule38 Fabrication & Installation of Res. Extr. Magnets, Power Supplies, & Electronics Fabricate ESS Target Fabrication Instrumentation & Controls Design Radiation Safety Design Delivery Ring RF Design Beam to Diagnostic Absorber Mu2e Complete M4 Commissioning with single turn Beam Extinction Monitor Procurement, Assembly & Install HRS Installation Final Focus Section Installation Hbend Section Installation Extinction & M4DA Section Installation Install ESS Radiation Safety Procurements, Fabrication & Installation Commission Res. Extr. Beam Operations: Target Remote Handling Fabrication & Installation

Risks Both the extinction and extinction monitoring system are based on mature technology, so some risks from CD1 have been 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: $160k We consider this risk retired for CD-3 10/22/14E. Prebys - Extinction Systems, Mu2e CD-2/3b Review39 ACCEL-035Threat Failure of extinction system to sufficiently eliminate out of time beam ACCEL-036OpportunityNo need in internal extinction collimation ACCEL-037Threat Extinction monitor fails to perform to requirements. realized! transferred to operations

Major Milestones 11/2/2015E. Prebys | Cost and Schedule40

Review Charge 11/2/2015E. Prebys | Introduction and Overview41 Note: cost has been removed from the charge completely