ABSTRACT 1. ANALYSIS METHOD AND CUTS

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1 . SEMILEPTONIC CHARM DECAY* SLACPUB4753 November, 1988 Pm Joseph M. Izen University of Illinois at Urbana/Champaign Urbana, Illinois Representing the MARK III Collaboration at the Stanford Linear Accelerator Center Stanford University, Stanford, California ABSTRACT Semileptonic branching ratios for Do + ae+v,, Ice+v, and li p+ve are presented, leading to a measurement of &d/j&. Seven additional exclusive Do and D+ semileptonic branching ratios and a first inclusive 0: measurement are given. _.... L, _Y_ 1. ANALYSIS METHOD AND CUTS Semileptonic decays are searched for using 3329 DoDo decays tagged with 1(r+, IGr+Tr+7r, I( n+~ and li7r+7r and 1777 D+D decays tagged with I<rr+r+, I( r+ and I(vr+n+7r ( Fi g. 1). These are found in 9.56 pb of +(3770) data. Both TOF and shower information is used to identify leptons. The kinematic variable U = Emissing I@miss;ngI is sensitive particle misidentification (Fig. 2). Redundant kinematic and TOF hadron identification is required. Mvasible < 1.7 GeV rejects hadronic decays, and we require that there be no extra isolated photons in an event. U is sensitive to the presence of an undetected r (Fig. 3); we require IUI < GeV. Invited talk presented at the 1988 Meeting of the Division of Particles and & Fields of the American Physical Society, Storrs, Connecticut, August 1518, a L _ * This work was supported in part by the Department of Energy, under contracts DEACOS 76SF00515, DEAC0276ER01195, DEAC0381ER40050, and DEAM0376SF00034 and by the National Science Foundation.

2 i. 2. CABIBBOSUPPRESSED SEMILEPTONIC DECAYS AND Vcd Semileptonic decays of charm mesons provide an excellent laboratory for studying the weak KobayashiMaskawa (KM) coupling of the charm quark to down and strange quarks because the interference effects and final state interactions present in hadronic decays are absent. An indirect measurement of the charmdown coupling has been obtained from neutrino induced charm productionf but it depends on an estimate of the relative abundance of produced charm species, the total semimuonic branching ratios of each species, and it assumes that phase space and form factors do not differ significantly between Cabibbofavoured and Cabibbosuppressed decays. We obtain it directly by measuring semileptonic branching PI ratios and using the relation: B(D + 7rr e+ ue) 13(D + K e+ ue) = l86 * IKd/vcs12 [f;(o)/f+k(o)]2 Recent calculations for the ratio of form factors f;/f, at q2 = 0 give values around 0.69/0.76! Branching ratios may be found in Table I. Mark III s re+, events (Fig. 2b) constitute the first measurement of an exclusive Cabibbosuppressed semileptonic decay, and they have a statistical significance of By forming the ratio of branching ratios, we eliminate any systematic dependence on charm cross sections, efficiency and the number of tags, and we find: IKdlv,,12 = [f+k(o)/.fj(o)] 2(0.051f;:;;; f 0.010) 3. MORE SEMILEPTONIC BRANCHING RATIOS Exclusive semileptonic decays with more complex final states have been found as evidenced by the U distributions of Fig. 4. Table I lists individual branching ratios and averages which have been computed using lepton universality, isospin symmetry and Poisson statistics. E measurements have been included for comparison. There is good agreement between experiments. Inclusive semileptonic branching ratios I51 suggest that the list of D+ decays is not complete. Mark III places the following 90% C.L. limits: B(D+ + p e+v,) < 0.5% and B(D+ + Kr r e v,) < 3.0%. The resonant (I<*) fraction of ICreu decays is measured to be 0.68 f (Fig. 5).

3 4. SEARCH FOR SEMILEPTONIC 0, DECAYS i.,s A similar analysis is performed on 6.3 pb of & = 4.14 GeV data containing D,DB events. 73 f 10 D, events are tagged by &r, I(* I(+ and K l<+, and nine correct sign (three wrong sign) electrons are counted among the recoiling tracks (Fig. 6). C orrections are made for misidentified pions, and the charge symmetric background is subtracted to give B(o$ + e+x) = 0.09+~$ f The expectation from D lifetimes[61 and B(D,D+ + e+x)15] is f Since the statistical significance of this signal is only 1.2a, we can express it as the upper limit B(ot + e+x) < % C.L. REFERENCES 1. H. Abramowicz et al., 2. Phys. C 15, 19 (1982); K. Kleinknecht and B. Renk, 2. Phys. C 34, 209 (1987). 2. The numerical value of 1.86 in this formula is: S[4l*l(4P t)12 (E; m;)3/2 dt / j&;,/(m$;. t)12 (E; n&)3/2 dt. 3. See, for example: M. Wirbel et al., 2. Phys. C29, 637 (1985); C. Dominguez and N. Paver, Phys. Lett. 20 7, 499 (1988). 4. J.C. Anjos et al. A Study of the Semileptonic Decay Mode Do + Ke+ve and An Experimental Study of the Semileptonic Decay D+ + lc* e+v, submitted to the 24th Int..Conf. on High Energy Physics, Munich, West Germany, August 410, R.M. Baltrusaitis et al., Phys. Rev. Lett. 54, 1976 (1985). 6. J.C. Anjos et al. Phys. Rev. D37, 2391 (1988).. FIGURE CAPTIONS 1. Beam constrained mass of Do and D+ tags. 2. U distribution for re+v, events (shaded), K!+vf events (histogram) where the I( is intentionally interpreted as a r. Overlayed curves are Monte Carlo for these two classes of events. 3.~ Monte Carlo U distribution for lire+v, and ICr e+y, events interpreted as I(e+v,. 4. U distributions for additional Do and D+ decays. Arrows mark the IUI < GeV cut. Overlayed curves are Monte Carlo shapes. 5. Invariant li r mass from D + Ic7rev events. Fit is to li * plus nonresonant. ;c Swave. _ 6. Mass distribution of D, tags (bold curve, left scale), wrongsign electrons (solid, right scale) and rightsign electrons (light curve, right scale) plotted at the mass of its tag.

4 i.,c Table I. Preliminary Mark III Semileptonic Branching Ratios Decay mode Signal Branching Ratio (%) Events Mark III DO k ne+u, y;~ f 0.08 Do + I(e+v, f 0.7 f 0.4 Do + Iip+v, f 1.0 f 0.9 D + I(e+v, (avg.) 4.2 f 0.6 f f 0.5 f 0.6 Do + li 0 r+ev e T.i f 0.5 Do + x ~+pvp 6 2.6t f.i f 1.0 DO + I7r eu e 5 1.s$; f 0.2 o DO + [I{7r0 + I< 7rr]e+u, 5.9y; f 0.9 D C exclusive 10.5 f 1.8 f 1.3 DO inclusive 7.5 f 1.1 f 0.4 D+ + peve fT.i f 0.5 D+ + lil pv, f 3.1 f 1.7 D+ + frl e+v, (avg.) D + Krev, 7.1:;:; f :;:;: f D+ + K lroev e :.; f 0.6 D+ + [KT+ +?+r ]e+ve 4.2 ;:; f f 0.5 f 1.1 D+ C exclusive 11.3 f 2.3 f 1.6 D+ inclusive 17.0 f 1.9 f 0.7

5 Do aool n D+ 600 c vj s w L I 0 c J Beam Constrained Mass (GeV) 6,95A, Fig. I.

6 12 10 a VI 2 6 g w KB+v U (ne% hypothesis) (GeV) 6195A2 Fig. 2

7 i,p..cw U (Ke% hypothesis) (GeV) 6195A3 Fig. 3

8 i&&i$ 3 F d D'+Kr'e+v 1 U (GeV) I ll I,,. ti I AL U (GeV) ES 4 D++Kn+e+v b U (GeV) U (GeV) U (GeV) 1 l68 U (GeVl 6195A4 Fig. 4

9 a _..r Mass(Kn) (GeV) 6195A5 Fig. 5

10 n 2 El 15 M 2 =1 cr n CD lr d r lo 5 r 0 q i Mass (GeV) A6