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Study of e + e  collisions with a hard initial state photon at BaBar

Study of e + e  collisions with a hard initial state photon at BaBar. Michel Davier (LAL-Orsay) for the BaBar collaboration. TM. Initial state radiation (ISR) method.  ISR.

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Study of e + e  collisions with a hard initial state photon at BaBar

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  1. Study of e+e collisions with a hard initial state photon at BaBar Michel Davier (LAL-Orsay) for the BaBar collaboration TM

  2. Initial state radiation (ISR) method ISR • High PEP-II luminosity at s = 10.58 GeV precise measurement of the e+e- cross section0at low c.m. energies with BaBar. • Improved hadron spectroscopy • Input to (gm-2) and aemcalculations. • Few previous data in the 1.4-3.0 GeV range. • Comprehensive program at BaBar. • Today: results for +0, preliminary results for2+2, K+K+, 2K+2K from 89.3 fb-1

  3. ee 0  Event selection: Excited  states ? • Isolated ISR photon with ECM > 3 GeV • At least 2 good photons with E > 0.1 GeV • Two good, non-K tracks from IP Events/0.01 GeV/c2 Kinematic fit:  • Energy and momentum balance enforced • Mass of two soft photons constrained to 0 • 2 < 40 for fit in  0g hypothesis selects signal events • Reject events with extra photons if 2 < 40 for   0 0 g hypothesis J/

  4. Background for 3pg Most dangerous backgrounds: e+ e-  K+ K- 0 , e+ e-  qq  + - 0 0 Other backgrounds: e+e-  2, 4, 5, …, +-, 0 Two methods of background subtraction: • background mass distribution measured in data, subtracted bin-by-bin from signal mass distribution • taken from simulation, corrected to real experimentaldistribution MC Data Total background level: • (0.5 - 1.5)% in , regions • (15 - 50)% at higher masses • accuracy in background level ~25% up to 2 GeV

  5. Detection efficiency for 3 The detection efficiency (m): • determined from a Monte Carlo simulation that includes additional corrections extracted from special control event-samples • quite uniform in 0.5<m<3 GeV/c2 • systematic error currently ~4% - will be improved with more data

  6. Fit of the 0 mass spectrum • 3(m)- Born cross section of e+e-  + - 0 is a coherent sum of 4 resonances: , , , • R(m)~1 - radiative correction function from calculation • dL/dm - ISR luminosity taken from total integrated luminosity and photon radiator function W(s,x); (checked with mmgevents) • f(m,m) - detector resolutiontaken from simulation (with floating extra Gaussian smearing) • Fix, widths to PDG values • Fix -relative phase to experimental value(1637) • Fix-relative phase to180,  - to 0

  7. Fit results:  -  region  2/d.f.=146/148 consistent with known properties of these resonances (,  widths fixed to PDG values) f The resolution is about 6, 7, 9 MeV/c2 at , , J/ masses. Fitted resolution smearing is ~1 MeV/c2 BaBar PDG B(ee)B(3)=(6.700.06 0.27)10-5 (6.350.10)10-5 B(fee)B(f3) =(4.300.08 0.21)10-5(4.520.19)10-5

  8. Fit results: higher mass region   • Good fit obtained for the range up to 1.8 GeV/c2. • Extending the fit to masses above 1.8 GeV/c2 may require a more complicated fitting function taking into account non-resonant 3 production. • Mass and width parameters are dependent upon our assumed phases - interference effect is strong BaBar PDG B(ee)B(3)=(0.820.050.06)10-6 M()= 13502020 MeV/c21400 - 1450 ()= 4507070 MeV 180 - 250 B(ee)B(3)=(1.30.10.1)10-6 M()= 1660102 MeV/c21670  30 ()= 2303020 MeV 315  35

  9. e+ e-  + 0 cross section SND BaBar DM2 • coverage of wide region in this experiment - no point-to-point normalization problems • consistent with SND data EC.M. < 1.4 GeV • inconsistent with DM2 results • overall normalization error ~5% up to 2.5 GeV

  10. J/  3 decay • The J/ meson is narrow - clean signal • After sideband subtraction - NJ/ = 92034 • Detection efficiency - =(9.20.6)% • The result: (J/ ee)B(J/ 3)= 0.1220.0050.08 keV • We previously measured (mmg) (J/ ee)= (5.610.20) keV Events/0.004 GeV/c2 sideband sideband Phys. Rev. D69,011103 (2004) B(J/ 3) = (2.180.19)%BaBar (1.500.20)% PDG (2.100.12)%BES 2003

  11. ee 22, KK ,2K2K Event selection: • Isolated ISR photon with ECM > 3 GeV • At least four good tracks from IP Kinematic fit: • Energy and momentum balance enforced • Energy and angles of hard ISR photon are not used - 1C fit • Fit in 3 hypotheses: 4 for all events 2K2if 1 or 2 identified kaons 4K if 2, 3 or 4 identified kaons Background subtraction: • Other ISR processes (5, …) – using difference in 2 distributions • e+e-  qq – using JETSET simulation

  12. ee 22cross section BaBar Preliminary Systematic errors: • 12% for m4 < 1 GeV, • 5% for 1 < m4 < 3 GeV, • 16% for higher masses) • best measurement above 1.4 GeV Coverage of wide region in one experiment No point-to-point normalization problems Intermediate states: • a1(1260) - dominant, structure which may be f0(1370) final state is seen. • For detailed study, a simultaneous analysis of 2+2-and+-20 final states is required.

  13. ee 22cross section Good agreement with direct e emeasurements Most precise result above 1.4 GeV

  14.  substructures BaBar preliminary MC generator: • H.Czyz and J.H.Kuehn, Eur.Phys.J C18(2000)497-509 • Includes a1(1260)p and f0(1370)r • Does not include J/ a1(1260) J/ f0(1370) r(770)

  15. ee KK Systematic error – 15% (model dependence, kaon identification) Much more precise than previous measurement J/ Substantial resonance sub-structures observed: • K*(890)K dominant • f, KK contribute strongly • K*2(1430)K seen.

  16. KK substructures BaBar preliminary K*(890)Kp dominated No studies in previous e+e- experiments! K*Kpg MC generators are not available yet K* regions excluded r f No signal from ff0(980) yet Connection to f f0(980)g ? ff0(980)? Events from f band

  17. ee 2K2K BaBar preliminary First measurement Overall normalization systematic error – 25% (model dependence, kaon identification) J/ No clear mass structure in the two- or three-body subsystems No ’ s !

  18. J/ and (2S) decays +- J/ 2K+2K- K+K-+- 2+2- +- BaBar preliminaryPDG B(J/ +-+-)=(3.610.26 0.26)10-3(4.01.0) 10-3 B(J/ K+K-+-) =(6.090.50 0.53)10-3(7.22.3) 10-3 B(J/ K+K-K+K-) = (6.71.1 1.0)10-4(9.23.3) 10-4 B((2S)  J/ +-)=0.3610.015 0.028 0.3170.011

  19. Summary • Using ISR method the cross sections of e+e +0, 2+2, K+K+, 2K+2Kreactions have been measured from threshold to 4.5 GeV. • These are the most precise measurements to date for c.m. energies greater than 1.4 GeV. • Examples: contributions to ahad (1010) from 2+ 2 (0.56 – 1.8 GeV) from all e+ e exp. 14.21  0.87exp  0.23rad from all  data 12.35  0.96exp  0.40SU(2) fromBaBar 12.95  0.64exp  0.13rad from +  0 from all e+ e exp. 2.45  0.26exp  0.03rad fromBaBar 3.31  0.13exp  0.03rad • Several B(J/ -> X) measurements better than current world average • More modes to come; aim for systematic errors 1% (in +) Davier-Eidelman- Hoecker-Zhang 2003 total 696.37.2

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