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+eD(*)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.
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)
Method of Reconstruction Additional primary Mesons 3.5 GeV e+ e- 8 GeV p K recoil D* D* recoil p p Mass- / Vertex Fit D „Inverse“ Fit D recoil e/µ p n K p p p
Method of Reconstruction 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*(n p/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.
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, D00 on tag side Current Statistics of D mln ( @152fb-1 , no bkg subtracted) reconstructed neutrino mass meson lepton K p e 380 80 µ 440 60 all 820 140 REAL DATA Kln mn² / GeV² pln mn² / GeV² F.Mandl
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 non-D bkg D hadronic Branching Ratio l, Kl : compatible with PDG mn² / GeV²
K/pln Analysis pln Analysis: q² distribution all preliminary Kln pln 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)) therefore no unfolding necessary MC DATA q² resolution REAL DATA raw q² distribution Kln q² / GeV² q²true -q²rec. / GeV² pln all preliminary q² / GeV²
K/pln Analysis pln Analysis: q² distribution all preliminary Kln pln shapes of bkg derived from MC except for non-D bkg (from D* side-band data) bkg subtracted according to bkg measurement presented before efficiency correction slightly rising with q² for K, rather flat for p q² signal & background Kln REAL DATA D pln non-D bkg MC DATA D Kln form factor f+(q²) single-pole model arbitrary normalization REAL DATA D hadronic 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
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*-0 and D*+D*-+- events D0 K-+ D0 K*(892)X Preliminary fit: 3 Gaussians 3rd order polynomial reflection of D0 K-+0 M(K+-)
Conclusion Plan 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