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e -. e +. 8GeV. 3.5GeV. = 0.425. bg. Form Factors and Absolute BRs for D 0 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
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e- e+ 8GeV 3.5GeV = 0.425 bg Form Factors and Absolute BRs for D0p n / Kn 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 D0p n / Kn 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
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