1. Initial State Radiation and Inclusive Hadron Production at B A B AR Fabio Anulli University of Perugia, INFN – Laboratori Nazionali di Frascati On behalf of the B A B AR Collaboration XXXIXth Rencontres de Moriond - March 28th-April 4th 2004 QCD and Hadronic Interactions at High Energy Outline ISR studies in B A B AR hadron spectroscopy measurement of R =  had /   in the energy region ~1-4 GeV lineshape for J/  →  tot  and  ee measurement inclusive hadron production studies K ,  ±, p/p,  production at  s = 10.54 GeV and at  (4S) test of QCD, hadronization models, scaling conclusions and perspectives

2. Fabio Anulli 2 April 1, 2004 precise measurements of e  e  cross sections at low c.m. energy hadron spectroscopy for 1 <  s < 4 GeV measurement of the ratio R(s) allow the calculation of hadronic contribution to Anomalous magnetic moment of the muon Running Fine Structure Constant at Z 0 -mass by means of dispersion integrals: Initial State Radiation: motivations ISR studies at the  (4S) can yield the same observables as the low energy e  e   experiments Hadronic Vacuum Polarization     q q main contribution from low energy region ~ 1  s 2 M f 2 < s

3. Fabio Anulli 3 April 1, 2004 R measurement: work in progress perspectives on R measurements by BABAR: comparable accuracy w.r.t. CMD-2 and KLOE for  s < 1 GeV few % accuracy for 1 <  s < 3 GeV relative contributions to the error on  em by energy range CMD-2 and KLOE recently measured  (e  e  →      at ~1% level very few data with large errors for  s > 1.4 GeV  R ~ 10-15% data from different experiments and different systematics a  had and  em will benefit of precise hadronic cross section measurements also at energies > 1 GeV highest uncertainties for  em from energy region 1 <  s < 5 GeV

4. Fabio Anulli 4 April 1, 2004 ISR studies program in BABAR Many analysis in progress:     pion form factor              0  0  resonance recurrences           0  resonance recurrences 5 ,7  6  structures between 1 and 3 GeV K + K -    K + K - K + K - K + K -, K S K L kaon form factor K + K - ,    resonance recurrences K 0 K    4-quark state? p p proton form factor The ratio R will be measured from the sum of cross sections of all exclusive channels J/  and  s  production via ISR Shown here

5. Fabio Anulli 5 April 1, 2004 ISR cross section ISR Cross Section ( Born approximation for  f ) cross section for final state f (normalized to  final state) energy in c.m. of the radiated photon “radiator function at lowest order” detection efficiencies corrections for final state radiation “effective c.m. energy squared” ISR equivalent luminosity f can be a hadronic state or     photon tagging acceptance at BABAR: 10 -15% f

6. Fabio Anulli 6 April 1, 2004 ISR equivalent luminosity experimentally measured from topology: “hard”  + 2 charged tracks +  ID  statistically very competitive sample  uniform data all-over the energy range limits of ISR techniques: resolution on invariant mass: (limits the width of the narrowest resonances which can be measured) BABAR 89.3 fb -1 equivalent e  e  luminosity L : 0.7  3.6 pb -1 /0.1GeV M  1  4 GeV a 1C kinematics fit (E and p conservation) improve the mass resolution (  J   ~ 16 MeV/c 2 before fit)  ~ 8 MeV/c 2 J/  mass after fit GeV/c 2

7. Fabio Anulli 7 April 1, 2004 e  e  →         BABAR 89.3 fb -1 events/0.025 GeV 4  invariant mass distribution data ISR bkgd non-ISR bkgd very competitive statistical uncertainties estimated total systematic error: 5% (1 <  s < 3 GeV ) no point-to-point normalization problem BABAR is the only experiment which covers whole energy range ISR photon + 4 charged hadrons 1C fit in 4  hypothesis topology preliminary evaluation of a  hadr (  s < 1.8 GeV): using BABAR data all previous data Davier, Edelman, Höcker, Zang Eur. Phys. J. C31 (2003) 503 Davier (2003) hep-ex/0312063 BABAR Preliminary ~70000 events

8. Fabio Anulli 8 April 1, 2004 K-ID required for 1 or 2 tracks systematic errors dominate acceptance corrections K-ID calibration K-ID required for 3 or 4 tracks systematic errors dominate acceptance corrections K-ID calibration first measurement ever

9. Fabio Anulli 9 April 1, 2004 Mass substructures in          no evidence of  in the  band (C-parity conservation)  no evidence so far for “expected”  f 0 events events not in K* bands no MC generators available yet BABAR preliminary K* events in  band

10. Fabio Anulli 10 April 1, 2004 BABAR 89.3 fb -1 J/  production in e  e  →     for a narrow state such as the J/  : W(s,x  ) can be calculated with < 1% accuracy J/  cross section (i.e. number of selected events) proportional to : use the PDG values of to get  J/  obtained from the ratio of     events from J/  peak to continuum compute the product:

11. Fabio Anulli 11 April 1, 2004 Results on  J/  →e  e  and  J/  BABAR measurementcombine with PDG values: improved measurements w.r.t. PDG values comparison of  J  measurements with previous results Accepted for publication: Phys. Rev. D – Rapid Comm.

12. Fabio Anulli 12 April 1, 2004 BABAR can provide precise measurements of inclusive spectra in e + e  events at  s = 10.54 GeV  so far, have studied    K , p/p and   measurements also done at  (4S) Inclusive hadronic spectra at  s ~ 10 GeV Hadronization: not yet understood quantitatively described by several models many recent high-energy results improved low-energy measurements would be useful recently little theoretical progress check consistency with fragmentation models test scaling predictions test QCD predictions data at  (4S) will contribute to the understanding of B decays

13. Fabio Anulli 13 April 1, 2004    K , p/p spectra cross sections given: - excellent particle-ID system - tracking, photon, PID efficiencies calibrated from data BABAR can reach few % precision level data samples used in these analysis: - 0.9 fb-1 off-resonance - 3.6 fb-1 on-resonance BABAR cover the full kinematics range  precision comparable to that from measurements at  s = 91 GeV test cross section scaling properties up to very high values of Scaled momentum x p = 2p cm /E cm   p/p BABAR Preliminary

14. Fabio Anulli 14 April 1, 2004    K , p/p spectra pions cross sections scaling Hadronization should be scale invariant except for “small” effects of hadron masses, running of  S,… scaling violations at low x p, due to masses are well known and modeled adequately (here JETSET is shown for comparison) expect substantial scaling violations at high x p seen clearly in  data; reproduced by models NOT seen in p/p data! Wrong model predictions observed violations in K,  data, also smaller than in models protons important experimental input for tuning fragmentation models BABAR Preliminary

15. Fabio Anulli 15 April 1, 2004    K , p/p : test QCD In the Modified Leading Logarithmic Approximation (MLLA ), distributions versus ξ = -ln(x p ) should be Gaussian near the peak. Gaussian fit to cross section distributions π+π+ 2.36 ± 0.01 K+K+ 1.64 ± 0.01 p 1.61 ± 0.01  1.44 ± 0.02 peak position  from symmetric gaussian fits QCD prediction is that  falls monotonically with increasing particle mass. while it is observed  * p   * K p/p   BABAR Preliminary

16. Fabio Anulli 16 April 1, 2004    K , p/p : test QCD s (GeV 2 )  peak position All data are consistent with the expected logarithm dependence with the center-of-mass energy but, different slopes, protons data above kaons… peak position vs E cm total number of particles produced per event extrapolated using fit to dσ/dξ distribution BABARARGUSCLEOJETSETUCLA π+π+ 6.40 ± 0.176.38 ± 0.128.3 ± 0.46.22 6.44 K+K+ 0.910 ± 0.0180.888 ± 0.0301.3 ± 0.20.934 1.01 p/p 0.235 ± 0.0120.271 ± 0.0180.40 ± 0.060.3360.217  0.276±0.002±0.0170.19±0.04 ±0.04---0.410 continuum (B A B AR :  s = 10.54 GeV) B A B AR         p/p PR D 31, 2161Z. Phys C62, 371

17. Fabio Anulli 17 April 1, 2004 Conclusions lots of hadron physics at B A B AR ! ISR has been proven to be an effective tools to study low energy e  e  processes very rich program in the energy range  s < 4 GeV precise e  e  cross section measurements will improve the accuracy on the hadronic contribution to (g-2)  and  QED (M Z ) many interesting results in hadron spectroscopy expected precise measurements  ee and  tot for J/  to be published inclusive spectra of    K , p/p and  have been measured, with competitive precision produced both in e  e   annihilation and  (4S) events test of predictions of QCD, models of jet fragmentation and B hadron decays clear discrepancies between models and data for protons (also for kaons and etas)

18. Fabio Anulli 18 April 1, 2004 BACKUP SLIDES

19. Fabio Anulli 19 April 1, 2004 The B A B AR Detector

20. Fabio Anulli 20 April 1, 2004 Study of  e  e   →     topology: “hard”  + 2 charged tracks + NO  -ID ratio (bin-by-bin) cancels: luminosity radiative corrections efficiencies: photon, trigger, tracking relatively large background from e  e     and     hard work! less than 1% systematic errors needed for (g-2)  hope to have results soon

21. Fabio Anulli 21 April 1, 2004  →  spectrum similar analysis to measure inclusive production of  in continuum and in  (4S) decays 35.5 fb-1 on-resonance data 3.8 fb-1 off-resonance data use dominant decay  →  fit the γγ mass with an asymmetric function for the signal. selection slightly different on- and off-peak very good agreement with JETSET at high x p overestimation by JETSET at low momentum clear scaling violation.