Muon g-2 Precision Precession Steve Maxfield University of - - PowerPoint PPT Presentation

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Muon g-2 Precision Precession Steve Maxfield University of - - PowerPoint PPT Presentation

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Muon g-2 Precision Precession Steve Maxfield University of Liverpool sjm@hep.ph.liv.ac.uk 1 Stephen Maxfield Seminar Birmingham Oct2013 OUTLINE What is it? Why measure it (again)? How? Goals and how to achieve them:

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Stephen Maxfield Seminar Birmingham Oct2013

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Muon g-2

Precision Precession

Steve Maxfield University of Liverpool sjm@hep.ph.liv.ac.uk

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  • What is it?
  • Why measure it (again)?
  • How?
  • Goals and how to achieve them:
  • Brief recap of technique
  • Upgrades!
  • Beam, detectors, field
  • Status and Conclusions

† The material for this talk has been shamelessly stolen from many including:

  • B. Lee Roberts, Leah Welty-Reiger, Mark Lancaster, Thomas Teubner, Chris

Polly, Andreas Kronfeld, Ruth Van de Water……

OUTLINE

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  • Magnetic moment of elementary particles related

to their spin by the “g-factor”

2

S

Qe g S m  

1924 Stern-Gerlach Magnetic moment of silver atom in it’s ground state is 1 Bohr magneton. (10%) …but not understood as spin 1/2 A little history…

B    

Larmor frequency

Magnetic Moments

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1925/26 Uhlenbeck And Goldschmidt proposed electron spin to explain fine structure…. …but prediction off by factor of 2! Rescued by Thomas precession (1926)

  • relativistic kinematics effect

(successive non-collinear boosts give rotation).

Spin ½?

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g=2

 

 

i ieA m

  

     

Non-relativistic reduction

2

1 2 2 2 p e i L S B t m m                  

2

S

g 

1

L

g 

1928

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…1947 (Nafe, Nelson, Rabi)Hyperfine structure of H and D did not fit g=2…(It was a 5 sigma effect) 1948 Kusch and Foley : A precision measurement: ge=2(1.00119±0.00005) An anomaly! Define

2 2 g a  

It takes QED to begin to explain the anomaly…

0.001161 2

e

a    

Greater Experimental Precision...

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1

1 2 g C          

Laporta,, Rameddi Kinoshita et al. Even analytically… Some very weird diagrams!

More QED…

4 5 4 5

C C                   

2 3 2 3

C C                  

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Together with a succession of experiments 

exp 12

1159652180.73(28) 10

e

a

 

12

1159652181.78(77) 10

thy e

a

 

 

12

1.05 0.82 10

e

a

   

Status of electron g-2

Ultra-precise agreement Gives best value of E

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Standard Model Physics predicts electron magnetic moment anomaly at ppt level!

But the story is different for the muon… More sensitive to more contributions…

(Hadronic corrections

  • nly enter around 12th

decimal place in ae)

+ + + …

a

It’s heavier

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  • QED well known
  • EW contributions also understood (only couple of loop accuracy needed)
  • Hadronic contributions are significant and the biggest source of

uncertainty. Non-perturbative - cannot be calculated. Determined from experiment Low energy e+e-  hadrons. + some lattice QCD for L-by-L contribution

QCD

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 K+K-  Older e+e- data new new PHIPSI13 Rome, 2013

e+e-  hadrons

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HLMNT DHMZ

How the contributions stack up:

Determination of hadronic contribution to muon g-2 has become an industry Paralleled by g-2 measurements…

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Experimental Determination of a .

…Details to follow!

A succession of improving measurements FNAL GOES HERE

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Muon anomalous magnetic moment is sensitive to most of the standard model… and to new physics. Not same precision as the electron but compensated by higher mass. A tantalising but inconclusive 3.3-3.6 s discrepancy

The current state of the art:

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There is no shortage of interest in this intriguing result! Were it to persist…

  • Strong indicator of BSM physics…

Loop contributions sensitive to new particles running round loop…

2

40,000

e

m m

      

 better than e

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e.g. SUSY But broad spectrum of sensitivity in TeV mass range… a related to m Generically:

 

2 2

1

NP NP NEW

m m a M m

   

                  O

highly model dependent

C

 flavour-conserving, CP-conserving, chirality flipping, loop-induced

NP

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a provides discriminating power…

NP

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…also can inform, low mass, below LHC reach…

e.g. Dark photons:

NP

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How do we measure g-2?

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First make your muons… Parity violation delivers conveniently polarised muons: …from pions.

Fortune of nature number 1

 beam of polarised muons Fortunes of Nature

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inject into a (very) uniform magnetic field…

Muon momentum turns with cyclotron frequency

C

QeB m    

Spin turns with frequency

 

1 2

S

QeB QeB g m m        2 2

a S C

g QeB QeB a m m

  

               

Fortune of nature number 2:

Direct dependence on the anomaly: an immediate 3 orders of magnitude gain

  • ver measuring  in at-rest

experiments!

We need to measure and B

a

…and know very accurately?

m Fortunes of Nature

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Actually measure:

a p a p p

a

       

Normalise magnetic field to Larmor frequency of proton

p 

   

Measured from hyperfine structure of muonium: currently known to 120ppb†

†JPARC expt. to reduce this to ppb level

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E821 at BROOKHAVEN

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Inflector Kicker Modules Central orbit Injection orbit

Pions

π

p=3.1GeV/c

E821 21 Experimental erimental Te Technique chnique

B 

  • Muon polarization
  • Muon storage ring
  • injection & kicking
  • focus with Electric Quadrupoles
  • 24 electron calorimeters

R=711.2cm d=9cm

(1.45T)

Electric Quadrupoles

xc ≈ 77 mm q ≈ 10 mrad B·dl ≈ 0.1 Tm

xc

R R q

Target 25ns bunch of 5 X 1012 protons from AGS

Storage ring

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Magic 

  • Vertical magnetic field – need vertical focussing to stop muons spiralling
  • ut of ring
  • Achieve using electrostatic dipoles
  • The E-field modifies the precession frequency:

2

1 1

a

e aB a E mc                    

  • Unwelcome source of additional systematics
  • Can be made to vanish for ‘magic’ . Extremely lucky that size of a makes

this possible!

29.3 3.09

magic

GeV p    

…but sadly, not every  will be magic! Method pioneered by 3rd CERN g-2

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But how to measure a?

Parity violation again!

  • Highest energy e+ emitted

along direction of + spin

  • Use calorimeters to count e+

above an energy threshold vs. t

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…an iconic plot

E 821

   

/

1 cos

t a

N t N e A t



 

      

“5-parameter fit”

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Measuring a …some reality

High frequency modulation because muon bunch initially doesn’t fill ring…decays as bunch

  • spreads. This is good – can get p

distribution of muons a

Expected for E989: c 149ns Bunch length 120ns at injection

Simulated for E989

   

/

1 cos

t a

N t N e A t



 

      

N,A depend on energy

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Many sources of systematic error.

Particularly insidious are ‘early-to-late’ errors

Example: Effect of pile up.

 

at

  

Time dependence in phase:

   

 

2

cos cos(( ) )

a a

t t t t t t t                     

…but why should  change? Things which change early to late in the fill can lead to a phase change in the accepted events  direct bias to extracted a.

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Higher energy positrons come from further away. spin  If we get the energy wrong, we get the phase wrong. If we have pile-up, two low energy positrons fake a high energy positron. More pile-up early in the fill.

Beam relaxation Vertical breathing 3 CBO terms Muons lost from ring

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…strong incentive to repeat the measurement with increased precision:

E989 Muon g-2 at FNAL aims to:

Build on BNL result and: increase number of muons by factor ~21 reduce total systematics by factor ~3

           

11 821

10 116592089 54 33 54 33 11 11 0.54 0.14

ppm ppm

E stat sys stat sys stat sys

a      

11

16 10 a 

  

3.5 5 s s 

i.e.

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How these goals will be achieved:

Move the entire E821 storage ring to FNAL!

Use the same experimental technique as E821 but:

  • exploit the unique FNAL facilities to deliver more

muons Reduce systematics by improving and refining

  • the detectors
  • the stored beam dynamics
  • Uniformity and measurement of magnetic field
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Fermilab Muon Campus

  • B. Lee Roberts - Ultra Slow Muon Microscope – 9 August 2013
  • p. 33

g-2 Mu2e Multipurpose Building designed for future experiments as well

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At FNAL…

Get more and cleaner beam: ~21 times statistics of E821 and Use beam transfer and delivery as 1900m decay line  no pion background, no hadronic flash

11

1.8 10 

Detected decays Goal is Systematic errors of better than: ±0.07ppm on a ±0.07ppm on p

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Factor ~3 reduction in systematics built from large number

  • f individual improvements:

a

calorimeter beam tracker

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Beam injection, beam dynamics

INFLECTOR

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Improved acceptance, improved matching between delivery and ring leading to more muons and reduced beam oscillations  possible factor ~4 in storage efficiency. Possible redesign of inflector Replace with open ended design and larger aperture. Shielding challenging.

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Beam Injection and Ring

Numerous Improvements in collimation, beam tune etc. New inflector, New kickers. Reduction in muon loss Better control of coherent betatron oscillations and their impact on a .

vertical and horizontal oscillations Avoid this E821 feature! Muons not all magic, not all perpendicular to B,E Pitch corrections needed.

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Calorimeters

New for E989:

  • Segmented: 6x9 PbF2 crystals with SiPM
  • readout. Attack pileup systematic.
  • Pileup: muon phase correlated with e+ energy
  • verlapping pulses wrong phase shifts
  • varying fraction of pileup within fill

produces earlylate shift in average phasedirect impact on a.

  • ne pulse should not affect gain of

subsequent pulse on same channel. Should be able to separate at 5ns level

  • Fills ~ 700s long
  • Gain variations and time shifts over this

period feed into systematics. G(t) < 0.1% 0.05 ppm systematic budget for a

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Calorimeters II

  • Determine arrival time
  • Determine energy
  • Pileup separation
  • Laser calibration system

Continuous distribution of muons with random decay probability  Wave Form Digitisation Improvements: Gain changes 0.12  0.02ppm Pileup: 0.08  0.04ppm

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Tracking detectors

  • Measure beam profile at several locations as function of time in fill.
  • Convolute  spatial distribution with field to determine effective field seen

by ’s 0.03  0.01ppm

  • Momentum spread and betatron oscillations lead to ppm corrections to

 from non-magic muons - E-field and pitch corrections… Beam dynamics corrections 0.05  0.03ppm

  • Pileup identification.

0.08  0.04ppm

  • Independent momentum measurement. Verify calorimeter gain
  • Correct for acceptance changes in calorimeters from betatron
  • scillations. Validate calorimeter based determinations of pileup

corrections, gain, muon loss. 0.120.02ppm

  • EDM measure positron vertical angle – asymmetry.

Design will allow a factor ~200/month increase in statistics over Brookhaven measurement  factor of 10 on EDM very quickly and ~100 eventually.

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New Tracking detectors

  • Straw chambers
  • In vacuum
  • 2-3 locations

round ring

  • Need: long lever arm ~1mm determination of muon decay up to 10m away
  • Continuously distributed decay points, muon momenta distributed detector
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Straws do the trick:

  • Low mass ~0.1Xo per station, non-magnetic, OK in vacuum
  • 5mm diameter, 12cm long straws. Mylar coated with Al+Au.
  • 25 gold-plated tungsten wires
  • Based on Mu2e straws.
  • 80:20 Argon:CO2 gas
  • ±7.5º UV layers to give vertical resolution
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What about p ?

A lot of shimming Goal is to get this to 0.07ppm accuracy… A lot of measuring and monitoring

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p

Field measured with set of NMR probes

  • fixed probes
  • plunging probes
  • trolley probes

Again, requires concerted attack to beat down systematics. Improvements from reduced position uncertainties, more frequent measurements, better electronics etc. e.g. Absolute Calibration Dedicated 1.45T calibration magnet, more probes. Possibility of using 3He as well as water-based NMR probes.

Average muon orbits ~400 times sampling toroidal region

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The move…

But first…Vital bits of E821 have to get from BNL to FNAL

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Disassembly September 2012

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May 2013 : Yoke pieces arriving at FNAL

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Building support structure…

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"Yeah, We can move that "

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Big barge to limit pitch, roll and heave…

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5 nights sheltering from Storm near Norfolk Virginia. Tennessee-Tombigbee Waterway Mississippi, Illinois and Des Plaines rivers. 25th June - July 20th

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Miss Katie

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Lemont, IL. …safely ashore

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It fits…

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‘Overdaying’ at Costco’s supermarket!

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…after 3200 mile journey.

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CONCLUSIONS/Timeline

 Important bits of E821 now at Fermilab

 coils, ~2/3 steel

 Building under construction

 expect beneficial occupancy February 2014

 Arduous series of CD-1 reviews this year nearly over

 (then CD-2,… next year!)

 Many upgrades well-underway  On-schedule for:  Magnet powered 2015  Beam in 2016 or 2017

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Thank You