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Muon g-2: Where have all the muons gone? David Hertzog Bunce Symposium Gerry Collaboration: Boston, BNL, Budker, Cornell, Heidelberg, Illinois, KVI, KEK, Minnesota, Tokyo, Yale Outline g-2 impact today How is g-2 measured? Gerry and g-2 The Future B u N c e 2 0 0 8

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muon g 2 where have all the muons gone
Muon g-2:Where have all the muons gone?

David Hertzog

Bunce Symposium

Gerry

Collaboration:

Boston, BNL, Budker, Cornell, Heidelberg, Illinois,

KVI, KEK, Minnesota, Tokyo, Yale

outline
Outline
  • g-2 impact today
  • How is g-2 measured?
  • Gerry and g-2
  • The Future

BuNce 2008

particle physicists ask
Particle Physicists Ask

Why spin?

  • Why matter?
      • CP Violation
  • Why mass?
      • Higgs field
  • Why this standard model?
      • SUSY or other extensions
g 2 experiment theory comparison
Standard Model

BNL Expt.

g-2 experiment / theory comparison
  • Key points:
    • Theory: 0.48 ppm
    • Experimental 0.54 ppm (statistics limited!)
  • Dam(expt-thy) = (297±88) x 10-11 (3.4 s)

deRafael, Glasgow MDM

Arguably, strongest experimental evidence of Physics Beyond Standard Model

in 2001 the muon was in the news
In 2001, the muon was in the news…

Time called the muon “a winner !”

slide8
Compare to Theory

“I will spare you the long, checkered, sometimes amusing history of the theory here, with it’s sign flips, and “gotcha” corrections, and them there radiative corrections, and hard-to-figure-out loops with those pions and other stuff that goes on kinda’ quick when you aren’t really looking to see if it’s so and such …” (S.P.)

“Look you guys, put the damn number on the table !”

T. Kirk (BNL) New York Times, August, 2002

Just tell the theorists:

g 2 because of virtual loops many of which can be calculated very precisely
p

p

g

m

Z

m

p

p

B

Good shape

Not so good shape

Weak

Had LbL

Had VP

Had VP

QED

2006 plot

KEY REGION

g ≠ 2 because of virtual loops, many of which can be calculated very precisely

A significant amount has happened in 2008 … some confirming … some unnerving

hadronic light by light is settling down finally
g

m

Z

m

p

p

p

p

B

Weak

Had LbL

Had LbL

QED

Had VP

Had VP

Hadronic light-by-light is settling down (finally)

This is new, based on combined work by three leading groups

new physics enters through loops e g susy
New physics enters through loops … e.g., SUSY

R-parity conserving Supersymmetry (vertices have pairs)

And the diagrams are amplified by powers of tanb(here linearly)

slide12
Typical CMSSM 2D space showing g-2 effectHere and in next slides, we also project a reduced uncertainty on expt/thy from 88 to 39 in 10-11 units based on a next-generation expt.

Present:

Dam = 297 ± 88 x 10-11

Future

Dam = 297 ± 39 x 10-11

scalar mass

2s

1s

Excluded for neutral dark matter

gaugino mass

With new experimental and theoretical precision and same Dam

This CMSSM calculation: Ellis, Olive, Santoso, Spanos. Plot update: K. Olive

slide13
Expt

The Snowmass Points and Slopes give reasonable benchmarks to test observables with model predictionsMuon g-2 is a powerful discriminatorno matter where the final value lands!!

Future?

Model Version

slide14
Suppose the MSSM reference point SPS1a* is realized and parameters determined by global fit (from LHC results)
  • sgn(m) can’t be obtained from the collider
  • tanbcan’t be pinned down by collider

Possible future “blue band” plot, where tan β is determined from aμ.

D. Stockinger

* SPS1a is a ``Typical '' mSUGRA point with intermediate tanb = 10

*Snowmass Points and Slopes:

http://www.ippp.dur.ac.uk/~georg/sps/sps.html

muon g 2 is determined from 3 measurements
BMuon g-2 is determined from 3 measurements

(1) Precession frequency

(2) Muon distribution

(3) Magnetic field map

and 4 miracles make it happen
And, 4 miracles make it happen
  • Polarized muons

n p+ m+

1997 first evidence that muons are stored
1997: First evidence that muons are stored!

Matthias has found the electrons !

149 ns

e821 used forward decay beam which permitted a large p component to enter ring
Far Side

Near Side

A tough reality and delicate balancing act

E821 used forward decay beam, which permitted a large p component to enter ring

DP ~ 1.7%

Pions @ 3.115 GeV/c

Decay muons @ 3.094 GeV/c

and 4 miracles make it happen21
And, 4 miracles make it happen
  • Polarized muons
  • Precession proportional to (g-2)

n p+ m+

µ

slide22
e

Momentum

Spin

amis proportional to the difference between the spin precession and the rotation rate

and 4 miracles make it happen23
And, 4 miracles make it happen
  • Polarized muons
  • Precession proportional to (g-2)
  • Pm The magic momentum

E field doesn’t affect muon spin when g = 29.3

n p+ m+

µ

bnl storage ring
100

kV

KICK

0 500 ns

incoming muons

Quads

BNL Storage Ring

Only a few percent get stored!

magnetic field
2001

1 ppm contours

0.05

0.09

0.05

0.07

0.10

0.17

Magnetic Field

Measured in situ using an NMR trolley

Continuously monitored using 150 fixed probes mounted above and below the storage region

and 4 miracles make it happen26
And, 4 miracles make it happen
  • Polarized muons
  • Precession proportional to (g-2)
  • Pm The magic momentum

E field doesn’t affect muon spin when g = 29.3

  • Parity violation in the decay

n p+ m+

µ

measuring the difference frequency w a
2.5 ns samples

Counts

TIME

Measuring the difference frequency “wa”

e+

< 20 ps shifts

< 0.1% gain change

1 st plot showing muon precession signal the money plot
1st Plot showing muon precession signal … the “money” plot

But, Gerry got all of us who were awake then to sign it too

Plot made by Prisca Cushman

slide29
Components do

not pull g-2

Data can “almost” be fit using a simple 5-parameter function

N(t) = N0e-t/t[1+Acos(wat + f)]

Few billion events

Getting a good c2requires understanding beam motions

a double blind analysis culture
A double-blind analysis culture

Magnetic Field

Secret Offsets

Secret Offsets

UIUC

UIUC

Data Production

BU

Yale

(Each year had different divisions of labor)

e821 complete and published
E821 Complete and Published

14 Individual analyses independent and consistent

Bennett et al, PRD 73, 072003 (2006)

where have all the muons gone
Where have all the muons gone?*
  • Where have all the protons gone?
    • Gone to pions, every one …
  • Where have all the pions gone?
    • Gone to muons, every one …
  • Where have all the muons gone?
    • Gone to electrons, every one …
  • Where have all the spokesmen gone?
    • Gone to coffee, every one …

The “Gang of Four”

*Apologies to Pete Seeger.

The complete set of our lyrics, once sung on Gerry’s deck at a pool party, remain locked unto the year 2050

slide33
Gerry and g-2

Chapter III

slide34
S

Gerry Bunce, Bill Morse, Vernon Hughes, Gordon Danby + hosts of others

  • The rings have great power
  • The rings can consume you
  • The rings will corrupt you
gerry a respected counting house leader
Gerry, a respected counting house leader …

Gerry, like MacArthur, has returned !!

Now we will stabilize our beam and

Gotham will be safe once again … (Ofer, 1997)

lots of highly cited papers
Lots of highly cited papers

Gerry got us all to sign this too

gerry s world
Gerry’s World

Secret passage way into the castle

g-2 Quiz: Name that part

slide42
The Future

g-2FiNALe

Goal: 0.14 ppm; 21 x statistics

Move ring to FNAL

Chapter IV

slide43
Then, to accept the higher rate, changes in the experiment are required; e.g.,

4

Segmented detectors

For BNL E969, we identified some obvious places to improve the muon transmission and to prepare for higher rate

Open inflector

2

1

Beamline changes

3

Improve kicker

the g 2 f i nal e next generation experiment aiming at 4x improved precision
Gives 18 Hz of ring fills

BNL was 4.4 Hz

Intensity being studied, but expect 1year run will achieve the x21 statistics goal

Most items are costed

Including moving the ring

Goal is < $20 M

Target area least understood

The g-2FiNALe “next-generation” experiment aiming at >4x improved precision
use pbar complex as an 800 m long dogbone beamline
pbar target

8 GeV/c protons

not 120 GeV as is now

s(p) & 3.1 GeV/c

Not 24 GeV (~3 lower)

Li lens

Pion to muon decay line optics

New building required for ring

Use pbar complex as an 800 m long “dogbone” beamline
slide47
Final Thought from the Lord(s) of the Ring(s)
  • to store muons
  • to observe positrons
  • to connect muons to new physics quantum loops

One Ring to rule them all,

One Ring to find them,

One Ring to bring them all and in the darkness bind them

THANKS GERRY !!!!!

slide49
“Muon Anomalous Magnetic Moment—The Last Word”Robert W. WilliamsNew Frontiers in High-Energy Physics, 1978

“I conclude that a super effort might lead to a determination of am to between 1 and 2 parts per million …”

“It is the end of an era; the muon g-2 worker is no longer a Kit Carson blazing a trail in the wilderness, but more like a J. Edgar Hoover keeping a watchful eye on the imaginative excesses of theorists.”

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