Form Factors and Absolute BRs for D 0  p  n / K  n

e- e+ 8GeV 3.5GeV = 0.425 bg Form Factors and Absolute BRs for D0p n / Kn Belle in a nutshell q² • located at KEK / Japan • KEKB Collider • B-Factory at (4s) resonance • peak luminosity 16.270 1/nb/s • integrated luminosity 600 1/fb(as of June 2006; 280 1/fb used in this analysis) • main physics goal: observation of CPV in B meson Decays Laurenz Widhalm HEPHY Vienna Belle Collaboration KEK 高エネルギ

Why are semileptonic decays interesting? q² • single form factor fD(q2) • calcuable in LQCD, but • needs checking from data • D-System ideal for experimental input • results can be applied in B-physics (extraction of CKM parameters)

K p recoil p D*- K recoil pslow D0 „inverse“ fit recoil K/p+ e/µ- n p p Method of Reconstruction (Event Topology)  additional primary mesons IP 3.5 GeV e+ e- 8 GeV D* g p mass-constrained vertex fits D • note: • all possible combinations tried in parallel • cuts after complete reconstruction • equal weight for remaining combinations •  no event loss due to particle exchanges! Ktag p  signal side  tag side

D0 Signal and Background* * from decays without a D0 , or combinatorial background • cuts • all mass-constr. fits CL >0.1%(released on D0 fit for righthand plot) • same charge Ktag/pslow control region signal region same sign Ktag/pslow s=0.0006 GeV! signal D0 invariant mass opposite sign Ktag/pslow note: data used for bkg subtraction, MC shown only for comparison data (normalized) B0 charm (D°) MC MC charm, no D° uds MC MC wrong sign D° B± MC MC

D0  K/plnSignal and Background • additional cuts • same charge pslow / lepton • extra g energy < 700 MeV • no excess charge • En > 100 MeV recoil neutrino mass D0 Kln • Backgroundsources • fake D0 • other semileptonic channels • hadronic channels mn² / GeV² D0 pln signal region note high resolution s(m²n)=0.016 GeV²

hadronic background same sign µ/pslow opposite sign µ/pslow signal region D0  K/plnSignal and Backgrounds (for pmn)* semileptonic background control region for K*/r bkg measurement signal region recoil neutrino mass for D0 pln note: data used for bkg subtraction, crosschecked by MC bkg from misidentified kaons fake-D0 bkg data data bkg from Kmn bkg from misidentified pions data data * smaller background for pen and Kln handled likewise bkg from K*/rmn MC data

Summary of Signal / Background Decomposition D0 Ken D0 pen remaining signal data fake-D0 bkg data D0 Kmn D0 pmn hadronic bkg data Kln bkg data K*/rln bkg MC mn² / GeV² * error dominated by MC stats ** error dominated by fit errors & bias special bkg sample

Absolute Branching Ratios • ratio to total number of recoil D0 tags • efficiency correction • corrected for bias due to differences data/MC • (1.9%±3.9%)

Form Factors – q² distribution D0 Ken D0 pen signal q² non-D bkg hadronic bkg semileptonic bkg s(q²) = 0.0145 GeV²/c² (width of red line)  no unfolding necessary! D0 Kmn D0 pmn background shapes from data

f+(q²)= 1-q²/m²  •  f+(0) m......pole mass = m D*s 2.11 GeV (Kln) = m D*  2.01 GeV (pln) Form Factors - Theory • in principle, two form factors f+(q²) and f-(q²) • kinematically only f+(q²) relevant, f-(q²) suppressed by ml² • three differentmodels that are frequently discussed in literature: simple pole modified pole f+(q²)= (1-q²/m²) (1-aq²/m²)  0.50 (Kln) atheor.  G. Armoros, S. Noguera, J. Portoles, Eur. Ph. J. C27, 243 (2003)  0.44 (pln) ISGW2 f+(q²)= (1-a(q²-q²max))²  N. Isgur and D. Scora, Phys. Lett. B 592 1(2004)

Form Factors – Comparison with Models modified pole model D0 Kln lattice calculation ISGW2 model fit results simple pole D0 pln modified pole (poles fixed at theo. values)

Form Factors and Absolute BRs for D0p n / Kn Summary & Conclusion • events searched in e+e-D(*)D*cX (X=np/K) • new full-reconstruction-recoil method: 56k D0 in 282 fb-1 of BELLE data • high resolution neutrino s(m²n)=0.016 GeV² • background <5%(<27%) for K/p • absolute BRs of better accuracy than previous experiments, in good agreement with recent CLEO measurements • good agreement with relative measurements done by BES and FOCUS • high q² resolution, no unfolding necessary • absolute multi-bin measurement of f+(q²) • measured form factorin good agreement with theoretical predictions and other experiments • competitative with recent CLEO-c measurements Laurenz.Widhalm@oeaw.ac.at preprint hep-ex/0604049, submitted to PRL

Spares

K p p K p e/µ p p Method of Reconstruction (Event Topology) • tag side: • reconstruction & fit of D0,± Kp, K2p, K3p • reconstruction & fit of D*0,± Dp, Dg • use either D or D* as primary meson • signal side: • reconstruction & fit of inclusive D*0,± via recoil from e+e-  D(*) D*np/K • reconstruction & fit of inclusive D0 via recoil from D*  Dp • reconstruction & fit of neutrino via recoil from D  mpn additional primary mesons e+ e- ( ) D* D* D g p p D n p K tag signal

D*-sig m/GeV D*+tag D0sig D*0 tag m/GeV m/GeV Method of Reconstruction (Event Topology)

stable particle selection: • gammas: • p > 40 MeV • charged tracks (general): • p > 100 MeV • trk_fit.nhits(3) > 0 • dr < 2 cm, dz < 4 cm • electron: • p > 500 MeV • eid.prob(3,-1,5) > 0.9 • muon: • p > 500 MeV • prerejection != 1 • Muon_likelihood > 0.9 • kaon / pion: • atc_pid (3,1,5,3,2) • prob*(1-prob_e-prob_mu) > 0.5 • for meson in hlnu: > 0.9 List of Cuts • unstable particle selection: • pi0: • PDG mass ± 10 MeV • fit CL > 0.1 • K0: • only via decay pi+pi- • PDG mass ± 25 MeV • D_tag: • channels Knpi, n=1-3 • PDG mass ± 20 MeV • D*_tag: • channel Dpi, Dg • PDG mass ± 5 MeV • mass/vertex fit CL > 0 • D*_signal: • via recoil from D*_tag+n pi/K, n=0-5 • mass/vertex fit CL > 0.001 • D_signal: • via recoil from D*_signal  Dpi • mass/vertex fit CL > 0.001 • n: • via recoil from D_signal  hlnu • |m²| < 0.05 GeV² • mass/vertex fit CL > 0 • additional Klnu / pilnu cuts: • E_leftover < 700 MeV, no leftover charge • E_nu > 100 MeV • right charges of slow pions & lepton

Bias by mass-constrained Fits on Background? no real D0   with real D0 after fit of D* before fit of D*  D0 invariant mass • very sharp mass peak after fit • no bias on background 

D0 Signal and Background* * from decays without a D0 , or combinatorial background • cuts • confidence level of all mass-constrained vertex fits >0.1%(released on D0 fit for righthand plot) • right charge correlation between slow pion and tag side kaon (right sign, RS) control region same sign Ktag/pslow signal D0 invariant mass • procedure to measure background: • select wrong charge correlation data (WS) to get shape of background • correct for small WS signal component • normalize to RS data in region 1.84-1.85 GeV signal region opposite sign Ktag/pslow B0 MC data (normalized) charm MC charm, no D° uds MC wrong sign true D° B± MC

Measurement of Semileptonic Background (for pln)* • procedure to measure background: • 1. crosstalk from Kln: • prepare special background sample, with K intentionally misidentified as p • normalize to standard Kln sample • then reweight the sample using known** efficiencies / fake rates (in p,) • 2. background from vector mesons: • get shapes for K*ln and rlnfrom MC (simulated ratio K*/r from PDG) • normalize to data in region m²n > 0.3 GeV² recoil neutrino mass control region for K*/r bkg measurement D0 pln signal region data non-D° bkg (measured as described previously) * background for Kln is very small, and is handled the same way ** measured independently in data measured bkg from Kln measured bkg from K*ln measured bkg from rln

Measurement of Hadronic Background (for pmn)* • procedure to measure background: • prepare special background samples, with K(p) intentionally misidentifiedas m(subtract fake D0 background in these samples with the method described above) • separate into same sign (SS) and opposite sign (OS) samples, with respect to the charges of the lepton and the slow pion • semileptonic channels are highly suppressed in OS  clean sample of hadronic background • perform a 2-parameter fit in the standard OS sample, using the shapes from the OS background samples for K and p, to measure the effective fake rates • then apply these fake rates in the background SS sample to obtain the backgrounds in the signal sample same sign SS signal: D*  D0p+  p-m+n SS both signs D*  D0p+  p-p+p0/K0 p-m± n opposite sign OS D*  D0p+  K-p+p0 p+m-n SS OS OS D*  D0p+  K-p+p0/K0 p-m+ n * significant background only for this channel; other channels are handled likewise

use result of fit here   fit in this sample Fit ofHadronic Background (for pmn)* D0 pmn comparison with MC MC true composition SS green = particle seen in recoil mass D0 p-p+p0 D0 K0p-p+ D0 K-p+p0 OS signal region bkg from misidentified kaons bkg from Kmn bkg from misidentified pions bkg from K*/rmn * background for pen and Kln are much smaller remaining events in signal region fake-D0 bkg

Measured Absolute Form Factors as function of q² D0 Ken D0 pen D0 pmn D0 Kmn • extracted by dividing q² distribution by kinematical factor • no unfolding necessary due to very good q² resolution

Kmn Ken f+ kinematical factor f+ kinematical factor f- kinematical factor f- kinematical factor f+(q²)= 1-q²/m² q² / GeV² q² / GeV²  •  f+(0) m......pole mass pen pmn f+ kinematical factor f+ kinematical factor = mass D*s 2.11 GeV (Kln) = mass D*  2.01 GeV (pln) f- kinematical factor f- kinematical factor Form Factor Theory • in principle, two form factors f+(q²) and f-(q²) • kinematically only f+(q²) relevant, f-(q²) suppressed by ml² • applying certain boundary conditions, theory* suggests model-independently a pole-structure for the form factor: * G. Amoros et al., hep-ph/0109169

Form Factors and Absolute BRs for D 0  p  n / K  n