Il g2 del Muone nel

1
Il g-2 del Muone nel Modello Standard
Massimo Passera Università and INFN Padova
Road-Map INFN Fisica ee- a LNF Riunione 1
Milano, 4 Novembre 2005
2
The current world average value
0.5 parts per million !!
3
E821 Homepage
4
a? (116592080 50stat 40sys) 10-11
5
The Anomalous Magnetic Moment Theory
i
The Dirac theory predicts

i
QED predicts deviations from the Dirac result
i
Study the photon lepton vertex
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The QED Contribution to a?
a?QED (1/2)(?/?)
Schwinger 1948 0.765857410
(27) (?/?)2
Sommerfield, Petermann, Suura, Wichmann, Elend,
MP 04 24.05050964 (43)
(?/?)3
Barbieri, Laporta, Remiddi, , Czarnecki,
Skrzypek, MP 04
130.992 (8) (?/?)4 In progress
Kinoshita Lindquist 81, ,
Kinoshita Nio July 05
677 (40) (?/?)5 In progress

Kinoshita et al. 90, Yelkhovsky, Milstein,
Kataev, Starshenko,
Broadhurst, Karshenboim, Laporta,
Ellis et al., , Kinoshita 04
Adding up I get
a?QED 116584718.7 (0.3) (0.4) x 10-11 MP
05 with a 1/137.03599911 (46) 3.3 ppb PDG04
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The Electron g-2 and (the best determination of)
Alpha
aeth (1/2)(?/?) - 0.328 478 444 002
90(60) (?/?)2
Schwinger 1948 Sommerfield, Petermann
57, Suura, Wichmann 57, Elend 66, MP 05
1.181 234 016 827 (19) (?/?)3
Barbieri, Laporta,
Remiddi, , Czarnecki, Skrzypek, MP 05
- 1.7283 (35) (?/?)4 In progress
Kinoshita Lindquist
81, , Kinoshita Nio July 05
0.0 (3.8) (?/?)5 In progress
(12672 mass-indep. diagrams!)
Mohr Taylor 05 (CODATA 2002)
Kinoshita Nio, in progress.
1.671 (19) x 10-12 Hadronic
Mohr Taylor 05 (CODATA
2002), Davier Hoecker 98, Krause 97, Knecht
03 0.0297 (5) x 10-12
Electroweak Mohr
Taylor 05 (CODATA 2002)
a-1 137.035 998 83 (50) 3.6 ppb
Kinoshita Nio 05, MP 05
versus a-1
137.036 000 10 (110) 7.7 ppb Wicht et al.
2002 ?-1 137.035 999 11 (46) 3.3 ppb
CODATA 02 PDG 04

Check of QED at 4 loop level !
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Back to a? The Electroweak Contribution
i
One-Loop Term
1972 Jackiv, Weinberg Bars, Yoshimura
Altarelli, Cabibbo, Maiani Bardeen, Gastmans,
Lautrup Fujikawa Lee, Sanda.
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Hadronic contributions - I
Bouchiat Michel 1961
i
e e- Data (CMD2 after 8-2003)
amHLO 6934 (64) x 10-11 Hoecker
10-04 6948 (86) x 10-11 Jegerlehner
10-03 6934 (92) x 10-11 Ezhela et
al. 1-05 6924 (64) x 10-11
Hagivara et al 12-03 6944 (49) x
10-11 de Troconiz et al 2-04

• Are all Radiative Corr. under control
• (Luminosity, ISR, Vac. Pol. and FSR) ??
• New CMD2 pp- data presented at HEP
• in July agree well with their earlier ones.
• New SND pp- data released in June
• some hint of discrepancy with the
• CMD2 pp- data (See Logashenko at HEP05).

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Hadronic contributions - II
i
e e- Data from Radiative Return (KLOE BABAR)

• KLOE The collider operates at fixed energy but
  sp can vary
• continuously between upper and lower
  thresholds. This is
• an important independent method!
• Some discrepancies between KLOEs and CMD2s
  results,
• although their integrated contributions to
  amHLO are similar.
• SNDs new result (June 05) is significantly
  higher than
• KLOEs one above the r peak.
• Comparison in the range (0.37 lt sp lt 0.93) GeV2
  

a?pp (3786 27stat 23systh) 10-11 CMD2
8/03 PLB578 (2004) 285
a?pp (3756 8stat 48systh) 10-11
KLOE Venanzoni_at_ ICHEP04
a?pp (3856 52) 10-11
SND hep-ex/0506076
a?pp (3823 19stat 31systh 10calc)
10-11 New CMD2 Eidelman, Logashenko


(July 2005 Preliminary)
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Hadronic contributions - III
i
Tau Data (ALEPH, CLEO, OPAL)

• Significant discrepancy between t and CMD2
  (8-2003) ee-
• data above 0.85 GeV. KLOE confirms this
  deviation.
• The new SND result agrees with the
  cross-section
• calculated from the tau spectral function data
  within the
• accuracy of the measurements (SND,
  hep-ex/0506076).
• Inconsistencies in the ee- or tau data? Are
  all possible
• isospin-breaking effects properly taken into
  account??
• (Marciano Sirlin 1988 Cirigliano, Ecker,
  Neufeld 2001-02, )
• Latest value (Davier,Eidelman, Hoecker, Zhang,
  August 2003)

amHLO 7110 (58) x 10-11
12
Hadronic contributions - IV
Davier, Hoecker, Zhang, hep-ph/0507078
13
The Hadronic Contribution to a(MZ2)

• The effective fine-structure constant at the
  scale s is given by
• The light quarks part is determined by
• Progress due to significant improvement
• of the data (mostly CMD-2 and BES)

Dahad(5) (Mz2) 0.02800 (70)
Eidelman, Jegerlehner95 0.02761 (36)
Burkhardt, Pietrzyk 2001 0.02755 (23)
Hagivara et al., 2004 0.02758 (35)
Burkhardt, Pietrzyk 6-05
Hagivara et al., PRD69 (2004) 093003
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Higher-order Hadronic contributions
O(a3) contribution of diagrams containing hadronic
vacuum polarization insertions
amHLO(vp) -98 (1) x 10-11
Krause96, Alemany et al.98, Hagivara et al.03
The contribution of the O(a3) hadronic
light-by-light diagram had a troubled life. The
latest vales are
amHLO(lbl) 80 (40) x 10-11 Knecht
Nyffeler 2002 amHLO(lbl) 136 (25) x 10-11
Melnikov Vainshtein 2003

Hayakawa, Kinoshita 2001 Bijnens, Pallante,
Prades 2001 Knecht, Nyffeler 2001, This term
is likely to become the ultimate limitation of
the Standard Model prediction.
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Standard Model vs. Experiment
Adding up all the above contribution we get the
following SM predictions for am and comparisons
with the measured value
amHLO(lbl) 80 (40) x 10-11 amHLO(lbl) 136
(25) x 10-11
1 A. Hoecker, October 2004 2 F.
Jegerlehner, October 2003 3 Ezhela, Lugovsky,
Zenin, January 2005 4 Hagivara, Martin,
Nomura, Teubner, Dec 03 5 de Troconiz
Yndurain, February 2004 6 Davier, Eidelman,
Hoecker, Zhang, Aug 03
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Conclusions
The future
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The End
18

Backup Slides
19
R current status (Logashenko_at_HEP05)
VEPP-2M energy region
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CMD2 vs. SND KLOE Logashenko_at_HEP05
With SND data
With KLOE data
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KLOE vs. SND CMD2 D. Leone_at_HEP05

• above the r mass a significant
  difference btw SND and KLOE
• is out of discussion, but not btw
• CMD-2 and KLOE
• (at least within errors)