# Presentation: 542066

## AAC Meeting

- Chuck Ankenbrandt                         Muon Collider Design Workshop

- A Mu2e Upgrade Plan for the Project X Era

- Chuck Ankenbrandt
- Muons, Inc. and Fermilab
- February 4, 2009

## Introduction

- Synergies among NFs, MCs, and a Mu2e Upgrade:
- All three need an intense proton source.
- At Fermilab, Project X (initially 1 MW @ 8 GeV).
- Project X needs an 8-GeV “customer”.
- That could be the Mu2e experiment (upgraded).
- The same 8-GeV ring(s) could be used for all three.
- All three (or two!) will benefit from muon cooling.
- Cooling may be provided by a helical cooling channel.
- The Mu2e application is easier than that of the MC.
- The Mu2e need is earlier than that of the MC.
- Multiple uses of bright muons build HEP support.
- Muon cooling technology will enable a diverse program.
- The other kind of lepton collider is a one-trick pony.
- We should come to praise spinoffs, not bury them.

- February 4, 2009

- Chuck Ankenbrandt                 Muons, Inc. and Fermilab

## MANX and Mu2e

- MANX proposes to test a helical cooling channel.
- The same kind of HCC might be used to upgrade the Mu2e experiment.
- Mu2e plans to use ~ 25 kW of beam power from the Booster.
- HEP community would like sensitivity of 10-18 instead of 10-16
- Can we find a way to use 1 MW of beam from Project X?
- Probably we’ll need to rethink everything.
- Bob Bernstein, co-spokesperson for Mu2e, said I could use some of the slides he prepared for this meeting.
- Jim Miller, the other Mu2e co-spokesperson, said I could use some of his slides from the PAC meeting.

- February 4, 2009

- Chuck Ankenbrandt                 Muons, Inc. and Fermilab

## Structure of this talk

- Introduction
- Mu2e Baseline Design
- A Mu2e Upgrade Plan
- Summary/Conclusions

- February 4, 2009

- Chuck Ankenbrandt                 Muons, Inc. and Fermilab

## Delivers 0.0025 stopped

**Production**
**Solenoid**

**Transport**
**Solenoid**
**Selects low momentum **********
**Avoids straight line from production target to detectors**

**Detector**
**Solenoid**

**Proton**
**Target**

**Target**
**Shielding**

**Muon Beam**
**Collimators**

**Tracker**

**Calorimeter**

**Pions**

**Electrons**

**Muons**

**Muon **
**Stopping Target**

**Mu2e Muon Beamline- follows MECO design**

**Muons are collected, transported, and**
** ****detected in superconducting solenoidal magnets**

**Delivers 0.0025 stopped**
**muons per 8 GeV proton**

**Proton Beam**

**Jim Miller**

## Two Classes of  Backgrounds

|  | Prompt | Decay-In-Orbit |
| --- | --- | --- |
| Source | Mostly π’s produced in target | Physics Background nearly indistinguishable from signal |
| Solution | Design of Muon Beam, 
formation, transport, and time structure  | Spectrometer Design:
resolution and pattern recognition |

**R. Bernstein, FNAL                                                              AAC Seminar Jan 2009**

## Prompt Backgrounds

- Particles produced by proton pulse which interact almost immediately when they enter the detector:  π, neutrons, pbars
*Radiative pion capture*
* **π-+A(N,Z) →γ +X. *
*γ *up to* m**π**, *peak at 110 MeV*;  γ→ e+e- ; *
- if one electron ~ 100 MeV in the target, looks like signal: limitation in best existing experiment,  SINDRUM II?

**R. Bernstein, FNAL                                                                  AAC Seminar Jan 2009**

**Notes:**
76 MeV from relativistic kinematics

## Radiative π vs. Time

** ****This is a main reason why we have to wait 700 nsec**
** ****would be really nice to eliminate pions another way!!**

**R. Bernstein, FNAL                                                                  AAC Seminar Jan 2009**

**Gain 10****11**** in ********rejection by waiting 700 nsec**

**Upgrade alert!**

## Beam Flash

- Beam electrons: incident on the stopping target and scatter into the detector region.
- Need to suppress e- with E>100 MeV near 105 MeV signal

**electrons**

**muons**

**R. Bernstein, FNAL                                                                  AAC Seminar Jan 2009**

**Upgrade alert!**

## Other Backgrounds

**R. Bernstein, FNAL                                                                  AAC Seminar Jan 2009**

**Upgrade alert!**

## Backgrounds from Stopped Muons(Cont’d) 

- Backgrounds from Stopped Muons(Cont’d)

- Ordinary muon capture on the nucleus
- In aluminum, 40% capture, 60% decay, lifetime = 864 ns
- n, p are low energy,  are mostly low energy, well below conversion electron energy: create high rate background in detectors, potential track recognition errors
- Neutral background (n, ) is reduced by displacing detectors downstream from the stopping target
- Protons are reduced by placing thin absorbers in their path
- Muon radiative decay,  near conversion energy, prob ~ few x 10-5; endpoint for aluminum 102.4 MeV, 2.5 MeV below conversion electron energy. Smaller event rate but still significant compared to DIO.
- In-flight muon decay
- p>75 MeV/c can decay to >100 MeV electron

**Upgrade alert!**

**Jim Miller**

## Long Transit Time Background

- Particles with low longitudinal velocity can take a long time to traverse the beam line, arriving at the stopping target during the measurement period
- Antiprotons and radiative pion capture:
- Antiprotons are stopped by a thin window in middle of transport
- Adjust measure start time until most long-transit time pions decay
- Example of a potential problem
- Pion decays into a muon early in the transport solenoid
- Muon can have small pitch and progress very slowly downstream
- Muon can decay after a long time into an electron
- Decay electron can be >100 MeV if p>75 MeV/c
- Electron could scatter in collimators, arriving at the target late during the measurement period, where it could scatter into the detector acceptance
- To suppress this...
- Straight sections of solenoids have dBs/ds<0.02 T/m
- Greatly reduces number of particles (e.g) with small pitch
- Gradient criterion not necessary in curved solenoid sections, low pitch particles are swept away vertically by dBs/dr field gradient.

** ****PAC Meeting - Nov. 3 2008**

**Upgrade alert!**

**Jim Miller**

## Choice of Stopping Material:rate vs wait

- Choice of Stopping Material:rate vs wait

- Stop muons in target (Z,A)
- Physics sensitive to Z: with signal, can switch target to probe source of new physics
- Why start with Al?

**R. Bernstein, FNAL                                                                  AAC Seminar Jan 2009**

**Upgrade alert!**

## Prompt Background and Choice of Z

**R. Bernstein, FNAL                                                                  AAC Seminar Jan 2009                                   **

- Prompt Background and Choice of Z

- choose Z based on tradeoff between rate and lifetime: longer lived reduces prompt backgrounds

| Nucleus | Rμe(Z) / Rμe(Al) | Bound Lifetime | Conversion Energy | Fraction >700 ns |
| --- | --- | --- | --- | --- |
| Al(13,27) | 1.0 | 864 nsec  | 104.96 MeV | 0.45 |
| Ti(22,~48) | 1.7 | 328 nsec | 104.18 MeV | 0.16 |
| Au(79,~197) | ~0.8-1.5 | 72.6 nsec | 95.56   MeV | negligible |

## R. Bernstein, FNAL                                                                  AAC Seminar Jan 2009                                   

**R. Bernstein, FNAL                                                                  AAC Seminar Jan 2009                                   **

## Previous Data, NeN

- Rate limited by need to veto prompt backgrounds! pulsed beam

**High energy tail of  Decay-in-orbit (DIO) electrons. ****Simulated conversion peak**

** ****PAC Meeting - Nov. 3 2008**

**From SINDRUM Experiment**

**DC beam**

## Mu2e Upgrades

**Yes**

**No**

**1. Probe additional two orders of magnitude made possible by Project X**
**2. Need upgrades to muon transport and detector**

**R. Bernstein, FNAL                                                                  AAC Seminar Jan 2009                                   **

## Upgrade Plans...

**Yes**

**No**

**1. Both Prompt and DIO backgrounds must drop to measure**
**R****μe**** ****~ ****10****-18**
**2. Detector, Muon Transport, Cosmic Ray Veto, Calorimeter**

**R. Bernstein, FNAL                                                                  AAC Seminar Jan 2009**

## Upgrade Challenges

- If we want higher Z targets, must shorten the 700 nsec wait time, perhaps 700 → 70 nsec
- Beam flash
- Radiative pi capture
- But without a signal, *also* need to improve resolution from decay-in-orbit background
- Just the beam improvements are not enough: would only reduce background x2
- Resolution of spectrometer and pattern recognition algorithms; new hardware?
- Extinction: need ~x100 better

**R. Bernstein, FNAL                                                                  AAC Seminar Jan 2009**

**Upgrade alert!**

## Conclusions (upgrade)

- Resolution and background issues are critical
- Project X will get at least x10 in statistics,
*With a signal*
- Explore different targets
- Reduce radiative pion background
- Decrease time spread of muons
*And with a limit, *the beam related sources are only 1⁄2 of background – resolution becomes the limiting problem

**R. Bernstein, FNAL                                                                  AAC Seminar Jan 2009**

**Upgrade alert!**

## Structure of this talk

- Introduction
- Mu2e Baseline Design
- A Mu2e Upgrade Plan (rethink everything)
- Summary/Conclusions

- February 4, 2009

- Chuck Ankenbrandt                 Muons, Inc. and Fermilab

## Major components of the plan

**Accumulate protons from linac into bunches**
**No. bunches can be optimized vs Z of the target.**
**!st ring: accumulate and form N bunches**
**Bunch rotate into shorter bunches**
**Transfer M bunches at a time to 2****nd**** ring and extract**
**Two-stage slow extraction to mitigate losses**
**Produce pions in dipole plus wedge system**
**Transmit muons to stopping target**
**Match quasi-monochromatic pion beam into HCC**
**(matching section is also decay volume)**
**Cool and degrade muons in HCC**
**Match into stopping target solenoid**
**Use S-bend a la MECO to transport e’s to detector**

- February 4, 2009

- Chuck Ankenbrandt                 Muons, Inc. and Fermilab

## Project X

- Chuck Ankenbrandt                 Muons, Inc. and Fermilab

- Parameters
- 8-GeV H- Linac
- 1 MW of beam power initially
- 5 Hz repetition rate
- ~1.3 msec beam pulse
- ~20 mA beam current during pulse
- Upgrade Path to 4 MW for NF/MC
- 10 Hz?
- 2.5 msec?
- Must “repackage” the beam to meet NF/MC needs.
- Can use the same bunching rings for Mu2e.

## Providing p Bunches for a  Factory or a  Collider

- Chuck Ankenbrandt                 Muons, Inc. and Fermilab

**Providing p Bunches for a ******** Factory or a ******** Collider**

**Accumulate protons from linac into N bunches**

## Two-stage resonant extraction

- Extraction loss fraction ~ septum width/step size ~ 1%
- Losses of 10 kW in ring would be serious.
- Protons hitting wires get partial deflection by E field
- Worse than interactions and multiple scattering
- Those protons are likely to hit the Lambertson septum
- Brute force: reduce width, increase step size
- New concept: two-stage extraction
- Move Lambertson ~ 270 degrees downstream from 1st septum
- Add second electrostatic device ~ 90 degrees from 1st septum
- Second device has two wire septa, with E field in between
- Circulating and extracting protons are undeflected
- “Damaged” protons are deflected by second device to dump or to test beam area

- February 4, 2009

- Chuck Ankenbrandt                 Muons, Inc. and Fermilab

## Stopping Muon Beams 101

- Chuck Ankenbrandt	Fermilab

- p + A ->  + X
- ~One charged pion of each sign per 8-GeV proton
- Pion decay length is 7.8 meters for p = mc
-   decay kinematics in lab:
- There’s less than 29 MeV/c of transverse momentum.
- Momentum distribution of relativistic muons is uniform between about 60% and about 100% of pion momentum.
- Polarization is completely correlated with longitudinal momentum.
- Where the pions are: cf. next slide.
- Passing the muons through material causes the momentum spread to grow significantly. (dE/dx causes longitudinal heating.) cf. following slide.

**(Taken from Talk At Project X Physics Workshop)**

- Momentum vs. Cosine of production angle (from C. Yoshikawa)

**p**

**Cos theta**

- Momentum vs. Cosine of production angle (from C. Yoshikawa)

- MECO

- Alt.A

- Alt. B

## Momentum vs Range in LiH

- February 4, 2009

- Chuck Ankenbrandt                 Muons, Inc. and Fermilab

## Concepts

- Chuck Ankenbrandt	Fermilab

- (a) production
-     (b) momentum
-            evolution
- SBIR Cooling Concept:
- 6D particle density
-     increase
- Absorber density
-     decrease

- MECO acceptance

- HCC acceptance

- a)

- b)

- (From Mary Anne Cummings)

## SBIR: Stopping Muon Beams

- February 4, 2009

- Chuck Ankenbrandt                 Muons, Inc. and Fermilab

## However, ...

- Chuck Ankenbrandt	Fermilab

- Above example used collider target solenoid (20 T)
- Not a fair comparison with MECO (5 T)
- Perhaps not affordable for mu2e
- Also, Mu2e collaborators don’t want proton beam pointed at detector.
- Ergo, explore other concepts:

## Target + Wedge @ Dipole Edge

- Chuck Ankenbrandt	Fermilab

- Followed by low-Z absorber in HCC to cool the beam and reduce its energy**.**

## Dipole + Wedge Results

- February 4, 2009

- Chuck Ankenbrandt                 Muons, Inc. and Fermilab

## Transmit muons to stopping target 

**Match quasi-monochromatic pion beam into HCC**
**(matching section is also pion decay volume)**
**Cool and degrade muons in HCC**
**Match into stopping target in solenoid**

- February 4, 2009

- Chuck Ankenbrandt                 Muons, Inc. and Fermilab

## Reconfigure stopping target/detector 

**Use S-bend a la MECO to transport e’s to detector.**
**Perhaps can reuse muon transport solenoid from Phase I.**
**Remove proton catcher around stopping target.**
**Many advantages result...**

- February 4, 2009

- Chuck Ankenbrandt                 Muons, Inc. and Fermilab

## Advantages

- Much higher proton flux is available (thanks to Project X) and _usable_.
- The production target configuration is easily shielded.
- The coils of the production dipole are shielded by iron pole tips.
- The pions are produced forward, so we don’t need a small-radius target.
- So it’s easier to handle ~ 1 MW of beam power.
- Wrong-sign particles from the production target are eliminated.
- Hi-Z wedge suppresses electrons from production target.
- There’s much less straggling in flight times of muons and pions.
- Angles in beam are smaller, so don’t need precise fields to avoid trapping.
- Hadronic “flash” is suppressed; they stop upstream, in the degrader.
- The protons from muon capture are eliminated in the S-bend solenoid.
- (5 MeV protons have p~100 MeV/c.)
- Since we don’t need a proton catcher around the stopping target, the energy resolution for the signal electrons is better.
- Helps suppress background from muon decay in orbit.
- (Can make polarized muon beam for other applications.)

- February 4, 2009

- Chuck Ankenbrandt                 Muons, Inc. and Fermilab

## In conclusion:

- Chuck Ankenbrandt                 Muons, Inc. and Fermilab

- A promising Mu2e Upgrade concept has emerged.
- The concept seems to have many advantages.
- No disadvantages are obvious to the naked eye.
- The ideas are synergistic with the Project X initial configuration and with the subsequent evolution of the facility for a neutrino factory and/or a muon collider.
- Support for the development of the concept is requested.
- Extensive design and simulation work is needed.
- Experimental testing of the muon transport and cooling is essential.

## Backup slides

- Chuck Ankenbrandt                 Muons, Inc. and Fermilab

## Detector and Solenoid

**Production****: Magnetic mirror reflects ****π’s**** into acceptance**

**Decay**** into muons and transport to stopping target**

**S-curve eliminates backgrounds and sign-selects**

**Tracking and Calorimeter**

**Pictures from G4Beamline/MuonsInc**

**R. Bernstein, FNAL                                                                  AAC Seminar Jan 2009**

## Production Solenoid:

**Protons leave through thin window**
** ****π’****s are captured, spiral around and decay**
**muons exit to right**

**Protons enter opposite to outgoing muons**

**4 m ****× ****0.30 m**

**Pions**

**Proton Target**

**Target Shielding**

**Protons enter here**

**R. Bernstein, FNAL                                                                  AAC Seminar Jan 2009**

## Transport Solenoid

- Curved solenoid eliminates                     line-of-sight transport of photons  and neutrons
- Curvature drift and collimators sign and momentum select beam

**occasional ****μ****+**

**13.1 m along axis ****×**** ~0.25 m**

**R. Bernstein, FNAL                                                                  AAC Seminar Jan 2009**

## Separation of  from 

** ****PAC Meeting - Nov. 3 2008**

- Separation of  from 

********

********

**cm**

**cm**

## Detector Solenoid

**low momentum particles and almost all DIO background passes down center**

**signal events pass ****through**** octagon of tracker**
**and produce hits **

**Al foil stopping target**

**octagonal tracker surrounding central region:**
**radius of helix proportional to momentum**

**10 m ****× ****0.95 m**

**R. Bernstein, FNAL                                                                  AAC Seminar Jan 2009**

**Notes:**
so background goes down center and signal spirals out to tracker

##  Pulsed Beam Structure

-  Pulsed Beam Structure

- Tied to prompt rate and machine: FNAL near-perfect
- Want pulse duration <<       , pulse separation ≥
- FNAL Debuncher has circumference 1.7sec !
- Extinction between pulses < 10-9  needed
-  = # protons out of pulse/# protons in pulse

**10****-9**** based on simulation of prompt backgrounds**

**R. Bernstein, FNAL                                                                  AAC Seminar Jan 2009**

## Extinction Scheme

- Eliminate protons in beam in-between pulses:
- “Switch” dipole timing to switch signal and background:  accept only out-of-time protons for direct measurement of extinction
- Continuous Extinction monitoring techniques under study
- Cerenkov light with gated PMT for beam flash

**CDR under development**

**achieving 10****-9**** is hard; normally get 10****-2***** – *****10****-3**

**R. Bernstein, FNAL                                                                  AAC Seminar Jan 2009**

## Project X Timing

- Must run and analyze Mu2e Phase I
- We will continue to refine our existing design and look for new ideas
- solenoid?  tracking?  time structure?
- Finish analysis Phase I around 2020 then
- Project X makes a program possible, improving as we learn

**R. Bernstein, FNAL                                                                  AAC Seminar Jan 2009**

**Notes:**
in principle, we could run at project x without significant upgrades -- run longer, and can take instantaneous rates x4 higher.  So that would get about an order of magnitude right away.  Getting additional x10 is hard and requires redesign.  

## Advantages of Wedge@edge

- Chuck Ankenbrandt	Fermilab

**Advantages of Wedge@edge**

- Hard momentum cutoff at ~ 150 MeV/c
- Eliminates wrong-sign particles
- Full width of target magnet is used: magnetic field volume is not wasted
- Particles heavier than muons stop in degrader, not in stopping target;
-            thus much better hadron background rejection than in MECO design
- Electrons get eaten by high-Z wedge, thus probably not a problem.
- Better background suppression means might live with higher intensity
- Little dispersion in muon arrival times
- May have better mu/proton ratio:
- 	Uses pions at peak of momentum distribution
- 	Uses pions produced near zero degrees
- May be less expensive than MECO (maybe even fly under P5 radar?)
- Probably can operate with shorter deadtime after proton arrival
- 		=>More usable muons per proton
- 		=>Could use titanium or other material having Z greater than Aluminum
- Proton beam points away from experiment and is easily dumped.
- Produces polarized stopping muon beam
- Polarization can be varied by changing the thickness of the degrader