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Initial State Radiation and Inclusive Hadron Production at B A B AR

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. Outline ISR studies in B A B AR hadron spectroscopy

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Initial State Radiation and Inclusive Hadron Production at B A B AR

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  1. Initial State Radiation and Inclusive Hadron Production atBABAR Fabio Anulli University of Perugia, INFN – Laboratori Nazionali di Frascati On behalf of the BABARCollaboration Outline • ISR studies in BABAR • hadron spectroscopy • measurement of R = shad/smmin the energy region ~1-4 GeV • lineshape for J/y →mm Gtotand Gee measurement • inclusive hadron production studies • K±, p±, p/p, h production at s = 10.54 GeV and at (4S) • test of QCD, hadronization models, scaling • conclusions and perspectives XXXIXth Rencontres de Moriond - March 28th-April 4th 2004 QCD and Hadronic Interactions at High Energy

  2. q · q · · HadronicVacuum Polarization Initial State Radiation: motivations ISR studies at the(4S) can yield the same observables as the low energye+e-experiments • 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 Z0-mass by means of dispersion integrals: Mf2 < s ~ 1/ s2 main contribution from low energy region Fabio Anulli

  3. R measurement: work in progress • CMD-2and KLOE recently measured s(e+e- → p+p-) at ~1% level • very few data with large errors for s > 1.4 GeV • DR ~ 10-15% • data from different experiments and different systematics • amhad and Daem will benefit of precise hadronic cross section measurements also at energies > 1 GeV highest uncertainties for aem from energy region 1 < s < 5 GeV 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 aem by energy range Fabio Anulli

  4. ISR studies program in BABAR • Many analysis in progress: • p+p- pion form factor • p+p- p+p- • p+p- 0 0 r resonance recurrences • p+p- h • p+p- 0 w resonance recurrences • 5,7 • 6 structures between 1 and 3 GeV • K+K-p+p, K+K-K+K- • K+K- , KSKLkaon form factor • K+K- h, f hfresonance recurrences • K0K  • f p04-quark state? • p p proton form factor • The ratio R will be measured from the sum of cross sections of all exclusive channels • J/yandy(2s) production via ISR Shown here Fabio Anulli

  5. “effective c.m. energy squared” corrections for final state radiation detection efficiencies ISR cross section ISR Cross Section ( Born approximation for sf ) f can be a hadronic state orm+m- f energy in c.m. of the radiated photon “radiator function at lowest order” photon tagging acceptance at BABAR: 10 -15% cross section for final state f (normalized to mmg final state) ISR equivalent luminosity Fabio Anulli

  6. BABAR 89.3 fb-1 equivalent e+e- luminosity L : 0.7  3.6 pb-1/0.1GeV Mmm : 1  4 GeV ISR equivalent luminosity • experimentally measured from • topology: “hard” g + 2 charged tracks + m-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) J/y mass after fit s ~ 8 MeV/c2 a 1C kinematics fit (E and p conservation) improve the mass resolution (sJ/y~ 16 MeV/c2 before fit) Fabio Anulli GeV/c2

  7. 4p invariant mass distribution events/0.025 GeV data ISR bkgd non-ISR bkgd e+e-→ g + p+ p- p+ p- • ISR photon + 4 charged hadrons • 1C fit in 4p hypothesis topology ~70000 events • 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 BABAR Preliminary preliminary evaluation of amhadr (s < 1.8 GeV): BABAR 89.3 fb-1 using BABAR data Davier (2003) hep-ex/0312063 all previous data Davier, Edelman, Höcker, Zang Eur. Phys. J. C31 (2003) 503 Fabio Anulli

  8. first measurement ever • 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 Fabio Anulli

  9. K* Mass substructures in K+ K- p+ p- f BABAR preliminary no MC generators available yet events not in K* bands r no evidence so far for “expected”f f0 events no evidence of rin the f band (C-parity conservation) events in f band Fabio Anulli

  10. BABAR 89.3 fb-1 J/y production in e+e-→ g m+ m- W(s,x0) can be calculated with < 1% accuracy • for a narrow state such as the J/y: • J/ycross section (i.e. number of selected events) proportional to : use the PDG values of to get • sJ/Y obtained from the ratio of m+m- events from J/Y peak to continuum • compute the product: Fabio Anulli

  11. Results on GJ/y→e+e- and GJ/y • combine with PDG values: • BABAR measurement Accepted for publication: Phys. Rev. D – Rapid Comm. • improved measurements w.r.t. PDG values comparison of GJ/ymeasurements with previous results Fabio Anulli

  12. 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 BABAR can provide precise measurements of inclusive spectra in e+e- events at s = 10.54 GeV so far, have studied p±, K±, p/p and h measurements also done at(4S) Fabio Anulli

  13. p±, K±, p/p spectra BABAR Preliminary cross sections • data samples used in these analysis: • 0.9 fb-1 off-resonance • 3.6 fb-1 on-resonance p± • given: • - excellent particle-IDsystem • - tracking, photon, PID efficiencies • calibrated from data • BABAR can reach few % precision level K± 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 p/p Scaled momentum xp = 2pcm/Ecm Fabio Anulli

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

  15. p/p p±, K±, p/p : test QCD Gaussian fit to cross section distributions • In the Modified Leading Logarithmic Approximation (MLLA ), distributions versus ξ = -ln(xp) should be Gaussian near the peak. p± peak position x* from symmetric gaussian fits K± BABAR Preliminary • QCD prediction is that x* falls monotonically with increasing particle mass. while it is observed x*p x*K Fabio Anulli

  16. p±, K±, p/p : test QCD peak position vsEcm • All data are consistent with the expected logarithm dependence with the center-of-mass energy • but, different slopes, protons data above kaons… • p± • K± • p/p x* peak position • total number of particles produced per event extrapolated using fit to dσ/dξ distribution BABAR s (GeV2) continuum (BABAR : s = 10.54 GeV) Z. Phys C62, 371 PR D 31, 2161 Fabio Anulli

  17. Conclusions • 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)m and aQED(MZ) • many interesting results in hadron spectroscopy expected • precise measurements Gee and Gtot for J/Y to be published • lots of hadron physics at BABAR ! • inclusive spectra of p±, K±, p/p and h 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. BACKUP SLIDES Fabio Anulli

  19. The BABAR Detector Fabio Anulli

  20. Study ofe+e-→ p+p- • topology: “hard” g + 2 charged tracks + NO m-ID • ratio (bin-by-bin) cancels: • luminosity • radiative corrections • efficiencies: photon, trigger, tracking • relatively large background from e+e-, m+m-andK+K- hard work! less than 1% systematic errors needed for (g-2)m hope to have results soon Fabio Anulli

  21. h → gg spectrum • similar analysis to measure inclusive production of h in continuum and in (4S) decays • 35.5 fb-1 on-resonance data • 3.8 fb-1 off-resonance data • use dominant decay h → gg • fit the γγmass with an asymmetric function for the signal. • selection slightly different on- and off-peak • very good agreement with JETSET at high xp • overestimation by JETSET at low momentum • clear scaling violation. Fabio Anulli

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