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 = GeV and at  (4S) test of QCD, hadronization models, scaling conclusions and perspectives

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

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

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

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: % f

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

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/ BABAR Preliminary ~70000 events

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

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

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:

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.

Fabio Anulli 12 April 1, 2004 BABAR can provide precise measurements of inclusive spectra in e + e  events at  s = 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

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: fb-1 off-resonance 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

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

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 ± 0.01 K+K ± 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

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 ± ± ± K+K ± ± ± p/p ± ± ±  0.276±0.002± ±0.04 ± continuum (B A B AR :  s = GeV) B A B AR         p/p PR D 31, 2161Z. Phys C62, 371

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)

Fabio Anulli 18 April 1, 2004 BACKUP SLIDES

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

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

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.