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Semileptonic decay of D 0  l and form factors for the measurement of |V ub | at KEKB

Semileptonic decay of D 0  l and form factors for the measurement of |V ub | at KEKB Motivation, Method and preliminary results G.Leder, J.MacNaughton, F.Mandl and L.Widhalm Institute of High Energy Physics, Austrian Academy of Sciences

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Semileptonic decay of D 0  l and form factors for the measurement of |V ub | at KEKB

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  1. Semileptonic decay of D0 l and form factors for the measurement of |Vub| at KEKB Motivation, Method and preliminary results G.Leder, J.MacNaughton, F.Mandl and L.Widhalm Institute of High Energy Physics, Austrian Academy of Sciences Nikolsdorfer Gasse 18, A-1050 Vienna, Austria, Europe (BELLE Collaboration) Abstract When using the semileptonic decay B  l for a determination of |Vub| a form factor fB(q2) is needed. A corresponding form factor fD(q2) is measured in D0  l, since fB(q2) / fD(q2) has a smaller theoretical error. The analysis is based on about 152 fb-1 of data collected by BELLE at the e+e- assymetric collider KEKB. To get a significant number of D0  l decays events of the type e+eD(*)D(*) + i / K, i=0-5 are selected. Using a special tagging about 100 exclusive D0  l decays are obtained. Preliminary distributions fD(q2) are presented as well for the decay channel above as for D0  Klnu (the latter with about tenfold statistics). The aim of l < 10% is shown to be within reach even with currently available data. Several inclusive decays of the D0 can also be studied in view of the considerable number of D0’s.

  2. Measurement of Vub • via the decay B  pln • one has to use a form factor fB(q2) • an analogous form factor fD(q2) • can be measured in the decay • D  pln • the ratio fB / fD is well known by • numerical methods (lattice)

  3. K p recoil p K recoil Mass- / Vertex Fit „Inverse“ Fit p e/µ Method of Reconstruction Additional primary Mesons 3.5 GeV e+ e- 8 GeV D* D* p p D D recoil n K p p p

  4. There are more tasks which can be tackled by the Method of Reconstruction • semileptonic form factors • f+D(q²) for D  pln, ambitious aim: error < 10% • may be used to reduce systematic error on f+B(q²) for |Vub| measurement • high resolution q² distribution for D  Kln • cross sections for D*D*(np/K/p) • various channels: D*D*p, D*D*pp, D*D*KK, D*D*ppp, D*D*pppp, D*D*KKpp, ...., D*D*pp, …. • inclusive D decays BR • various channels, mostly poorly measured: • D  f, K*, , K±, e±, ± .... + anything • Particle searches in • D*, D*K, D*p, etc.

  5. Channels used for Reconstruction • D*+D*-, D*0D*0 (plus additional primary mesons) • mixed charged D*D* pairs ( i.e. D*0D*± ) • D+, D- on tag side • D*0 D0, D00 on tag side Current Statistics of D  mln (@152fb-1 , no bkg subtracted) reconstructed neutrino mass REAL DATA Kln mn² / GeV² pln mn² / GeV² F.Mandl

  6. Background Studies (work in progress) K/pln Analysis • Sources background for D  K/pln: • non-D events with fake D • hadronic D decays with fake lepton • fake kaon/pion in decay reconstructed neutrino mass REAL DATA MC DATA D pln D Kln D  hadronic non-D bkg Branching Ratio l, Kl : compatible with PDG mn² / GeV²

  7. pln Analysis: q² distribution K/pln Analysis • very good q² resolution(~0.01 GeV²) • small variation of resolution with q² between 0.006 and 0.012 GeV² • bin width limited by statistics to much larger values (0.100 (K) 0.333 (p)) • thereforeno unfolding necessary MC DATA q² resolution raw q² distribution REAL DATA Kln q² / GeV² q²true -q²rec. / GeV² pln all preliminary q² / GeV²

  8. form factor f+(q²) arbitrary normalization single-pole model single-pole model K/pln Analysis pln Analysis: q² distribution q² signal & background • shapes of bkg derived from MC except for non-D bkg (from D* side-band data) • bkg subtractedaccording to bkg measurement presented before • efficiency correctionslightly rising with q² for K, rather flat for p Kln REAL DATA D pln non-D bkg MC DATA D Kln D  hadronic REAL DATA pln Kln q² / GeV² all preliminary q² / GeV² • next step will be extraction of form factor f+(q²) • following BUTLER(Phys.Rev. D52, 2656), sf(q²) ~ spln (needs to be checked) • our advantage: comparatively clean, high resolution sample pln q² / GeV²

  9. Inclusive decay D0 K* (892) X (not in PDG list) K-+ effective masses of combinations of charged particles from kinematically selected D0 via recoil, tagging only D*+D*-, D*+D*-0and D*+D*-+- events D0 K-+ D0 K*(892)X Preliminary fit: 3 Gaussians 3rd order polynomial reflection of D0 K-+0 M(K+-)

  10. Conclusion • statistics of ~100 D  pln(@152fb-1) • have already been reached • aim of spln<10% within reach even with currently available data • very good statistics (~28k) available for inclusive D decays Plan • study systematics of form factor measurement • further background studies

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