p' 117

1
The Status of the (g-2) Theory
B. Lee Roberts Department of Physics Boston
University
roberts_at_bu.edu http//physics.bu.edu/robert
s.html
2
Matrix Element for MDM and EDM

• MDM (g-2) chirality changing
• EDM

3
Dirac Pauli moment
4
Standard Model Value for (g-2)
5
QED Summary

• using the latest value of a from CODATA
• and the latest Kinoshita-Nio higher order QED
• This value comes from de Rafael (private
  communication) and also from M. Passera,
• hep-ph/0411168 v2, to be published in J. Phys. G.
• With slightly different a, Kinoshita-Nio obtained

uncertainties from (a4 term) (a5 term) (a )
6
Which value of a ?

• CODATA (NIST compilation by B.Taylor and P.
  Moore)
• Kinoshita used a from atom interferometry
  measurements

7
Two Hadronic Issues

• Lowest order hadronic contribution
• Hadronic light-by-light

8
Lowest Order Hadronic from ee- annihilation
9
Evaluating the Dispersion Integral
Agreement between Data (BES) and pQCD (within
correlated systematic errors)
use data
Better agreement between exclusive and inclusive
(??2) data than in 1997-1998 analyses
use QCD
use QCD
from A. Höcker ICHEP04
10
a(had) from hadronic t decay?

• Must assume CVC, no second-class currents, make
  the appropriate isospin breaking corrections.
  decay has no isoscalar piece, while ee- does
• Lets look at the branching ratio and Fp
  from the two data sets

11
Tests of CVC (A. Höcker ICHEP04)
12
Shape of Fp from ee- and hadronic t decay
Comparison between t data and ee- data from CDM2
(Novosibirsk)
zoom
New precision data from KLOE confirms CMD2
13
A. Höcker at ICHEP04
14
Hadronic light-by-light

• This contribution must be determined by
  calculation.
• the knowledge of this contribution limits
  knowledge of theory value.

Marciano M/V
Melnikov/Vainshtein
15
Electroweak

• a? (weak) (154 3) ? 10 10

16
Where we came from
17
am from E821
18
Discrepancy with ee- based theory

• Recent reviews
• Passera - pushed the Russian group which got
  such a different answer on a(had) to find their
  mistake, so the agree with everyone else on the
  dispersion integral. Uses latest value of a.
• de Rafael - taking a close look at all aspects of
  the theory

19
on the horizon

• CMD2 has a new data set
• same total error as before, role of systematic
  and statistical errors is reversed.
• expect final results by mid-summer
• These new data should improve the r region by
• BaBar is measuring R across the full energy range
  
• Daphne also has data with half the error