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hadrons

. e  e  annihilation and  physics. Michel Davier, Yuan Changzheng LAL-Orsay and IHEP-Beijing. IHEP. First France-China FCPPL Workshop January 15-18 , 200 8 , Marseille. . . . hadrons. davier@lal.in2p3.fr. Collaboration IHEP-LAL.

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hadrons

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

  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. 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. 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. Essentials of Hadronic Vacuum Polarization vacuum polarization modifies the interacting electron charge with: photon vacuum polarization function (q2) 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) ... ... and subtracted dispersion relation for (q2) (analyticity) Im[ ]  | hadrons |2 ... and equivalently for a [had]

  6. The Muonic (g–2) Contributions to the Standard Model (SM) Prediction: Dominant uncertainty from lowest order hadronic piece. Cannot be calculated from QCD (“first principles”) – but:we can use experiment (!) The Situation 1995 had  ”Dispersion relation“  had   ...

  7. Improved Determinations of the Hadronic Contribution to (g–2) and (MZ ) 2 Eidelman-Jegerlehner’95, Z.Phys. C67 (1995) 585 • Since then: Improved determi-nation of the dispersion integral: • better data • extended use of QCD • Inclusion of precise  data using SU(2) (CVC) Alemany-Davier-Höcker’97, + later works • Extended use of (dominantly) perturbative QCD Martin-Zeppenfeld’95, Davier-Höcker’97, Kühn-Steinhauser’98, Erler’98, + others Improvement in 4 Steps: • Theoretical constraints from QCD sum rules and use of Adler function Groote-Körner-Schilcher-Nasrallah’98, Davier-Höcker’98, Martin-Outhwaite-Ryskin’00, Cvetič-Lee-Schmidt’01, Jegerlehner et al’00, Dorokhov’04 + others • 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. Situation at ICHEP-2006 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: Knecht-Nyffeler,Phys.Rev.Lett. 88 (2002) 071802 Melnikov-Vainshtein, hep-ph/0312226 Davier-Marciano, Ann. Rev. Nucl. Part. Sc. (2004) Kinoshita-Nio (2006) BNL E821 (2004): aexp = (11 659 208.0  6.3) 1010 Observed Difference with Experiment (DEHZ)

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

  10. SU(2) Breaking Electromagnetism does not respect isospin and hence we have to consider isospin breaking when dealing with an experimental precision of 0.5% • Corrections for SU(2) breaking applied to  data for dominant  – + contrib.: • Electroweak radiative corrections: • dominant contribution from short distance correction SEW to effective 4-fermion coupling  (1 + 3(m)/4)(1+2Q)log(MZ /m) • subleading corrections calculated and small • long distance radiative correction GEM(s) calculated [ add FSR to the bare cross section in order to obtain  – + () ] • Charged/neutral mass splitting: • m–  m0leads 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 – Marciano-Sirlin’ 88 Braaten-Li’ 90 Cirigliano-Ecker-Neufeld’ 02 Lopez-Castro et al ’06-07 Alemany-Davier-Höcker’ 97, Czyż-Kühn’ 01

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

  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. 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: mRmR(0)  3 Ree / 2  1.4 MeV for 

  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. Measuring R with BaBar (ISR) 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 X = 2E /Ecm Pre-BaBar Ös

  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. 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

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