1. 1    hadrons e  e  annihilation and  physics Michel Davier, Yuan Changzheng LAL-Orsay and IHEP-Beijing First France-China FCPPL Workshop January 15-18, 2008, Marseille davier@lal.in2p3.fr IHEP

2. 2 Collaboration IHEP-LAL a 20-year old tradition: agreement signed by Ye Minghan and MD in 1988 for collaborating in particle and accelerator physics many exchanges over the years: students, postdocs, engineers several visitors at LAL have now key positions in China present collaboration within FCPPL built over this foundation big contribution of Chinese physicists at LAL to ALEPH  physics Zhang Zhiqing, Chen Shaomin, Yuan Changzheng, all now leaders of FCPPL projects a lot of interest in BEPC/BES and the next facility BEPC2/BES3

3. 3 Present IHEP-LAL Project experiment and phenomenology in e  e  annihilation and  physics interest centered on vacuum polarization mostly and QCD studies provide the best experimental input and understanding of data 4 activities underway: (1) VP calculations and studies (2) evaluate potential and prepare for  physics at BES3 (3)  spectral functions and precision QCD studies (4) analysis of BaBar data for precision R measurement focus today on (1) and (4)

4. 4 The Actors at IHEP Yuan Changzheng Mo Xiaohu Wang Ping at LAL Michel Davier Wang Wenfeng Zhang Zhiqing Bogdan Malaescu PhD student in between Wang Liangliang PhD student joint supervision (French Embassy) at CERN Andreas Höcker

5. 5 Essentials of Hadronic Vacuum Polarization photon vacuum polarization function   (q 2 ) vacuum polarization modifies the interacting electron charge with : Leptonic  lep (s) calculable in QED. However, quark loops are modified by long-distance hadronic physics, cannot (yet) be calculated within QCD (!) Way out: Optical theorem (unitarity)... Im[ ]  | hadrons | 2... and subtracted dispersion relation for   (q 2 ) (analyticity)... and equivalently for a  [had]

6. 6 The Muonic (g –2)  Contributions to the Standard Model (SM) Prediction: Source (a)(a) Reference QED ~ 0.1  10 –10 [Schwinger ’48 &others (Kinoshita)] Hadrons ~ (15  4  3.5)  10 –10 [Eidelman-Jegerlehner ’95 & others] Z, W exchange ~ 0.2  10 –10 [Czarnecki et al. ‘95 & others] The Situation 1995 ”Dispersion relation“    hadhad had ... Dominant uncertainty from lowest order hadronic piece. Cannot be calculated from QCD (“first principles”) – but: we can use experiment (!)

7. 7 Improved Determinations of the Hadronic Contribution to (g –2)  and  (M Z )2 Energy [GeV]Input 1995Input after 1998 2m  - 1.8Data Data (e + e – &  ) (+ QCD) 1.8 – J/  DataQCD J/  -  DataData + QCD  - 40 DataQCD 40 -  QCD Eidelman-Jegerlehner’95, Z.Phys. C67 (1995) 585 Improvement in 4 Steps: Inclusion of precise  data using SU(2) (CVC) Extended use of (dominantly) perturbative QCD Theoretical constraints from QCD sum rules and use of Adler function Alemany-Davier-Höcker’97, + later works Martin-Zeppenfeld’95, Davier-Höcker’97, Kühn-Steinhauser’98, Erler’98, + others Groote-Körner-Schilcher-Nasrallah’98, Davier-Höcker’98, Martin-Outhwaite- Ryskin’00, Cvetič-Lee-Schmidt’01, Jegerlehner et al’00, Dorokhov’04 + others Since then: Improved determi- nation of the dispersion integral: better data extended use of QCD Better data for the e + e –   +  – cross section and multihadron channels CMD-2’02 (revised 03), KLOE’04, SND’05 (revised 06), CMD-2’06, BaBar’04-06

8. 8 Situation at ICHEP-2006 a  had [ee ]= (690.9 ± 4.4)  10 –10 a  [ee ]= (11 659 180.5 ± 4.4 had ± 3.5 LBL ± 0.2 QED+EW )  10 –10 Hadronic HO – ( 9.8 ± 0.1)  10 –10 Hadronic LBL + (12.0 ± 3.5)  10 –10 Electroweak (15.4 ± 0.2)  10 –10 QED (11 658 471.9 ± 0.1)  10 –10 inclu- ding: a  [exp ] – a  [SM ]= (27.5 ± 8.4)  10 –10  3.3 „standard deviations“ Observed Difference with Experiment (DEHZ) BNL E821 (2004): a  exp = (11 659 208.0  6.3) 10  10 Knecht-Nyffeler, Phys.Rev.Lett. 88 (2002) 071802 Melnikov-Vainshtein, hep-ph/0312226 Davier-Marciano, Ann. Rev. Nucl. Part. Sc. (2004) Kinoshita-Nio (2006)

9. 9 The Role of  Data through CVC – SU(2) hadrons   W  e+e+ e –e – CVC: I =1 & V W: I =1 & V,A  : I =0,1 & V Hadronic physics factorizes in Spectral Functions : Isospin symmetry connects I=1 e + e – cross section to vector  spectral functions: branching fractions mass spectrum kinematic factor (PS) fundamental ingredient relating long distance (resonances) to short distance description (QCD)

10. 10 SU(2) Breaking Corrections for SU(2) breaking applied to  data for dominant  –  + contrib.: Electroweak radiative corrections: dominant contribution from short distance correction S EW to effective 4-fermion coupling  (1 + 3  (m  )/4  )(1+2  Q  )log(M Z /m  ) subleading corrections calculated and small long distance radiative correction G EM (s) calculated [ add FSR to the bare cross section in order to obtain  –  + (  ) ] Charged/neutral mass splitting: m  –  m  0 leads to phase space (cross sec.) and width (FF) corrections  -  mixing (EM    –  + decay) corrected using FF model m  –  m  0 and   –    0 Electromagnetic decays, like:     ,    ,    ,   l + l – Electromagnetism does not respect isospin and hence we have to consider isospin breaking when dealing with an experimental precision of 0.5% Cirigliano-Ecker-Neufeld’ 02 Lopez-Castro et al ’06-07 Marciano-Sirlin’ 88 Braaten-Li’ 90 Alemany-Davier-Höcker’ 97, Czyż-Kühn’ 01

11. 11 e + e  -  Data Comparison: 2006  problems: overall normalization shape (especially above  )

12. 12 Achievements for VP calculations detailed cross-checks on existing e  e       data (one-month visit of Yuan C.Z. paid by French Embassy) small problem discovered (VP correction in KLOE)  /ee comparison completely revisited use new calculation for long-distance SU(2)-breaking question raised about the proper way to apply CVC  spectral function to be related to bare or dressed ee SF ? dressed ee SF would solve the discrepancy tests of procedure proposed, but found to be inconclusive unable for the moment to find theoretical proof (or disproof) results presented in muon g-2 workshop (Glasgow, Oct. 2007)

13. 13 Magnitude of the VP effect  (0)  (  )     1  2 (1+  FSR ) bare +FSR dressed VP FSR at s = m  2 leptonic VP 2.5% hadronic VP  1  4% mass shift from resonant VP: m R  m R (0)  3  R  ee / 2   1.4 MeV for 

14. 14 e + e  -  with dressed ee SF (tentative)  agreement in overall normalization shape much better still not perfect (region around 950 MeV, but small impact)

15. 15 Measuring R with BaBar (ISR) Precise measurements of cross section for all significant processes, e+e   hadrons, from threshold to ~4-5GeV Measure , K  K  channels with high precision Summing up exclusive cross sections ==>Improve the precision of R M. Davier et al., 2003 ss  ISR X = 2E  /E cm Pre-BaBar

16. 16 R Measurements with BaBar (ISR) exclusive multihadron channels essentially done results soon on precision     /     /K  K  (< 1%) Wang Wenfeng, Wang Liangliang (PhD), MD   g-2

17. 17 Conclusions we are engaged in a long-term collaboration effort in order to get the best e  e  annihilation and  decay data for vacuum polarization calculations and QCD studies most important involvement with ALEPH, BES2, and BaBar data long-standing ee/  discrepancy revisited: some improvement, some ideas, but more theoretical support needed short-term goal: precise determination of a  had using e  e  data to confirm/refute the present tantalizing 3.3  discrepancy with SM long-term goal: significantly improve  had (s) for EW tests at LHC and ILC (Higgs mass) the other topics will be pursued