- Email: [email protected]
Recent results in B and D decays from CLEO
UCLEAR PHYSICS
PROCEEDINGS SUPPLEMENTS ELSEVIER
Nuclear Physics B (Proc. Suppl.) 115 (2003) 98-102
www.elsevier.com/locate/npe
Recent Results in B and D Decays from CLEO Todd K. Pedlar a, for the CLEO Collaboration a Department of Physics The Ohio State University Columbus, OH 43210 We present three new results in the physics of B and D decays obtained by the CLEO Collaboration. These axe new measurements of B--.-~DTr branching ratios and subsequent evaluation of the strong phase in these decays, a first measurement of the decay B--~K%-, and an update on D meson mixing results.
1. Introduction On June 26, 2001, the CLEO experiment took its last data at the T(4S). Since its advent, CLEO has written or re-written most of the initial chapters in the story of heavy meson spectroscopy. While the lead has been handed off to the B-factories, CLEO continues to produce significant results in the field. In this paper we present the results of three recent analyses by CLEO in the realm of B and D decays. All of the data used in the analyses presented in this talk were obtained using CLEO II a n d / o r II.V detector configurations, which have been described in detail elsewhere [1,2]. The data were taken in symmetric e+e - collisions at energies near v ~ = 10 GeV, provided by the Cornell Electron-positron Storage Ring (CESR). The hadronic B results utilize the full CLEO data set of 9.7 million B B pairs, while the D mixing result is based on the 9 fb -1 sample of e+e - collisions observed by the CLEO II.V detector. 2. T h e D e c a y s B--~DT~ and M e a s u r e m e n t o f the Strong Phase 6i In this section we present the results of measurements of the branching fractions for B - - + D ° r - and -JB°-+D+r- and the extraction of the strong phase difference 51 between the I = 1/2 and I = 3/2 isospin amplitudes in the D r system. These decays are an excellent testing ground for the theoretical description of hadronic B-meson decays. Our understanding of these de-
cays has improved considerably with the development and application of Heavy Quark Effective Theory (HQET) [3,4] and Soft Collinear Effective Theory (SCET) [5], which have given factorization a more solid foundation. The recent observation [6,7] of the colorsuppressed B°--+D°r° decay completed the measurement of the D r final states and made possible the determination of the strong phase difference 5i. A value of cos (it inconsistent with unity would signal the presence of final-state interactions in the B - + D r process [8,9], and thus motivated us to make efforts to improve the precision of measurements of the branching fractions for the colorfavored decays B - - + D ° r - and -B°--+ D+ Tc-. In this analysis, neutral D mesons are reconstructed in the modes: K - r +, K - r + T r ° and K - ~ r + r - ~ r +. Charged D mesons are reconstructed via K-Tr+Tr +. In each case, D meson candidates are required to have a mass within 3a (standard deviations) of the PDG D mass [10] before kinematic fitting. Mass resolutions for the various D modes range from 6 to 12 MeV. B meson candidates are reconstructed using D and additional r tracks For each candiate, the beam-constrained mass M B =- ~ / E ~ e a m - p 2 , and the energy difference A E = E B -- Ebeam are calculated. 1 Final selection of B candidates (one per event, selected as the candidate with smallest AE) before fitting requires M B > 5.24 G e V / c 2 and A E E (--50, 50) MeV, and cuts on event 1Ebeam denotes the beam energy, and EB and PB the candidate momentum and energy, respectively.
0920-5632/03/$ - see front matter © 2003 Published by Elsevier Science B.V. doi:l 0.1016/S0920-5632(02)01962-X
T.K. Pedlar~Nuclear Physics B (Proc. Suppl.) 115 (2003) 98-102
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of the partial rates for the three B~D~r decays. The calculation of cos(f1 in the D r system as well as the overall systematic error for B(B--+D°Tr -) takes full account of correlations of various systematic error contributions by means of a detailed Monte Carlo method. 2 We consider correlations between the two color-favored decay modes B--~D%r- and B-°--~D+lr-, those among the measurements of B(B--+D°7r -) via different D o decay modes, and those due to ]oo and f+_. Details are found in Ref. [11]. We thus obtain the following final results for the color-favored branching fractions:
B(B--~D°~-) -- (49.7+1.2±2.9±2.2) Figure 1. Fitted distributions of the quantity MB -- x/E~eam - p~ for the indicated decays.
shape variables which are very effective in reducing the background from e+e ---~qq events. To obtain event yields for B ~ D r - for each D meson decay mode, the MB distribution of candidates surviving the above slection cuts are subject to a maximum likelihood fit. The fit function is a Ganssian distribution plus an empirically determined background shape. Fitted MB distributions are shown in Fig. 1. A small, non-negligible background from the decay B--~DK- contributes to the yields obtained by the fits described above. The D K contamination fraction is determined from Monte Carlo, and yields obtained from the fit are corrected by this fraction before being used to calculate branching ratios for B~D~r. Using efficiencies determined from Monte Carlo, we obtain the branching fractions, assuming that charged and neutral B mesons are produced in equal fractions f+_ and f00 at the T(4S). The three B--+Dr decay branching fractions form a complete set of branching fractions with which we may calculate cos 5x, the cosine of the strong phase angle difference between the two isospin amplitudes I = 1/2 and I = 3/2 that contribute to the decay process. The expression for cos(ix is given, e.g., in Ref. [8], and is a function
x 10-4(1)
B(-~-+D+~r-) -- (26.8±1.2±2.4±1.2) x 10-4.(2) In eac~hmeasured quantity, the first error is statistical and the second is systematic. The third error is a separate systematic error which corresponds to the experimental uncertainty on foo and f+_. [12] Our results for B(-B°-+D+~r -) and for B(B---+D°Tr-) each reflect improvementwith respect to the present PDG average values [I0]. Our result for B(B-°-+D+r-) may be directly compared with Ref. [3]. Their prediction of 32.7 x I0 -a is marginally consistent with our result. Our final results for cos(f/ and (fl utilize the branching ratios above as well as the world average of 13(-B°-~D°1r°) = 2.92 + 0.45 x 10-4 [6,7]. We thus obtain: COS (~I
n ~ ' : l +0"024+0"036+0"038 -~- v'~'vv--O.023--0.035--0.030,
16.5 ° < (fl < 38.1° (90% CL).
and
(3) (4)
In summary, we have measured the branching ratios for the color-favored B~D~r decays, and used these measurements to determine the value of the strong phase difference (ii: Our result for cos (fi strongly suggests final-state interactions in B ~ DIr decays. 2 T h e overall s y s t e m a t i c error for o u r m e a s u r e m e n t of BC'B°--~D+~r- ) is o b t a i n e d by s t a n d a r d error p r o p a g a t i o n of t h e individual c o n t r i b u t i o n s .
100
TK. Pedlar~NuclearPhysics B (Proc. Suppl.) 115 (2003) 98-102
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Figure 2. M and A E projections for B --+ K°Tr+~r- (left) and B -+ K*+(892)zr - (middle), which include the two K*+(892) submodes, K%r+ (light) and K+Tr° (dark). The dashed and solid lines show the fit predictions for background and the sum of signal and background, respectively. M(K°Tr +) projection for B --~ K°r+Tr - . Shown in the rightmost figure is the M distribution for K°Tr+ data (points) and expected background (shaded).
3. The Decays B--~KTrTr and B--~K*~" The second result we present is the observation of two rare charmless B decays. [13] Recently, first observations of several two-body charmless hadronic decays of B mesons, including the four B -~ KTr transitions, have been reported. These two-pseudoscalar decays have received considerable attention due to their expected role in improving our understanding of the weak interaction and in the extraction of the complex quark couplings described by the CKM matrix [14]. The pseudoscalar-vector analogs of these decays, B ~ K*Tr and Kp, present additional opportunities for observing direct C P violation [13] and physics beyond the Standard Model. We have investigated B decays to the threepseudoscalar final states, K ° h%r - , K+ h-Tr °, and K ° h % r ° (h + denotes a charged pion or kaon). We have performed one fit to our data for each topology, allowing for six signal and background components, pion and kaon hypotheses for h + for each of the following: signal, continuum background, and background from b -~ c decays. The probability for an event to be consistent with
a given component is the product of the probability distribution function (PDF) values for each of the input variables (neglecting correlations). The likelihood for each event is the sum of probabilities over the six components, with relative weights determined by maximizing the total likelihood of the sample. The parameters of the PDFs are measured from high-statistics Monte Carlo samples and independent data samples. The impact of correlations among the input variables is reduced by determining the PDFs as a function of the event location in the Dalitz plot. We use Monte Carlo simulation to estimate the systematic error associated with neglecting any remaining correlations. Detection efficiencies and crossfeed among the signal modes are also obtained from these Monte Carlo studies. The statistical significance of the raw yield reported by the fit is determined by repeating the fit with the yield fixed to be zero. We calculate fit yield upper limits at the 90% confidence level by integrating the likelihood function. We observe a signal for B --¢ K~r+Tr - with a statistical significance of 8.1a. No other contribution to the three signal topologies shows ev-
T.K. Pedlar/NuclearPhysics B (Proc. Suppl.) 115 (2003) 98-102 idence of a significant signal. We also perform Dalitz plot fits for the three topologies with up to nine resonant and non-resonant components. The only two-body channel in which we observe a statistically significant signal is B -~ K*+(892)Tr with a yield of .19 4-6 for K*+(892) -~ K°zr + . . .a+ . 3.9 and av . ~1+2.2 for K*+(892) --+ K+zr ° and a com--l. 9 bined significance of 4.6a. The size of the signal is insensitive to the choice of other resonances included in the fit. In the K°h+~r - , we find N(K*+(892)~r-)/N(K%r+~r - ) to be n~ ' ~gn+0.o8 "--0.07" Our result for the branching ratio is:
13(B -+ K*+(S92)~r - ) = \0 6 +6 + 4) x 10 -6. --5
(5)
Most theoretical predictions [13] for this branching fraction lie in the range 2-14x10 -6. Figure 2 shows the event distributions in M and A E for modes where we claim an observation. The background in these plots has been suppressed with cuts on the ratios of signal and background likelihoods, computed without M and A E respectively. Overlaid are the fit projections for the signal and background components, scaled by the efficiency of the likelihood ratio requirements (40-50% for K%r+Tr - and 70-80% for K*+(892)zr-). Figure 2 shows the M(K°Tr +) distribution for events in the K°h+lr - fit satisfying a likelihood ratio requirement. Overlaid is the expected distrubtion for background. In summary, we have made first observations of both the three-body decay B -~ K%r+Tr - , as well as a significant two-body submode, B -+ K*+(892)Tr - . The measured branching fraction for B --~ K*+(892)7~ - is larger than but consistent with most theoretical predictions.
4. N e w Results in D Mixing In the final analysis presented in this talk, we report on new results in D mixing measurements via the decay D ° ~ K s l r + T r - . In searching for the mixing, it is important to understand possible final state interactions [15]. As such, an interesting final state which allows for the study of both Cabbibo favored and Cabbibo suppressed (or mixing) and their relative phase, is the final state D°--+KsTr+~r - . Both favored and suppressed channels may be observed via Dalitz anal-
101
ysis of this final state. The 9.1 f b - 1 data sample taken with the CLEO II.V configuration allows sufficient statistics to observe substructure in the Cabbibosuppressed decays contributing to this final state - a key limitation of previous analyses. [16] The event selection depends heavily on the CLEO II.V silicon vertex detector [17], which dramatically improves the resolution on the common KsTr+U vertex, and thus the selection of D mesons. 5299 candidates are obtained through the above methods, and are then subjected to a Dalitz analysis. The distribution is parameterized according to the method described in Ref. [18]. Nineteen resonant subcomponents and a fixed phase, non-resonant contribution are considered. The phases and widths of the resonant contributions are determined as described in Ref. [19]. An initial unbinned maximum likelihood fit shows only ten resonant contributions axe found to be signficant. The final results are obtained from a fit with only the ten "significant" resonant components, as well as the non-resonant contribution. Figure 3 shows the three projections of this fit. There is a significant "wrong sign" D°-+K*+~ - amplitude. Mistags are insigificant, having a rate of just 0.3 ± 0.5%. When the likelihood of the fit is compared to a fit in which the wrong sign D°-+K*+Tr - amplitude is fixed to zero, the statistical significance of this amplitude is shown to be 4.9 standard deviations. In order to check for CP-violation, the data sample was split into D o and ~-o tags. No statistically significant difference between the two analyses was observed. In summary, we obtain the wrong sign ratio R w s -- B(D° ~K*+Tr-)/13(D° ~K*-Tr+ ):
R w s = (0.6 ± 0.3 ± 0.2)%.
(6)
Further, the relative phase between wrong sign and right sign decays is found to be
A C w s - n s = ( - 3 ± 11 ± 8) °.
(7)
This wrong sign rate may arise from either Doubly Cabbibo suppressed decays or from mixing. Future work on this decay mode will include an
T.K. Pedlar~Nuclear Physics B (Proc. SuppL) 115 (2003) 98-102
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a)
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200
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2
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Figure 3. Projections of the results of the fit described in the text to the KsTr+Tr- Dalitz distribution. The curve shows the results of the fit and the data are represented by the black points.
investigation of time dependence of the Dalitz plot as described in Ref. [19]. Such an analysis will be necessary in order to discern the difference between Doubly Cabbibo suppressed and mixing contributions to the wrong-sign rate. In addition, time dependent analysis will be sensitive to the mixing parameters x and y at the few percent level, (i.e. as good or better than experiments using the KTr or CP eigenstate final states) as well as Sign(x), which no other method can resolve. REFERENCES 1. Y. Kubota et al., Nucl. Instrum. Meth. Phys. Res., Sect. A 320, 66 (1992). 2. T. Hill, Nucl. Instrum. Meth. Phys. Res., Sect. A 418, 32 (1998). 3. M. Beneke etal., Nucl. Phys. B591, 313
(2000). 4. M. Neubert and B. Stech in Heavy Flavors, edited by A.J. Buras and M. Lindner (World Scientific, Singapore, 2nd edition 1998). 5. C.W. Bauer, D. Pirjol, and I.W. Stewart, Phys. Rev. Lett. 87, 201806 (2001). 6. CLEO Collab., T. E. Coan et al., Phys. Rev. Lett. 88, 062001 (2002). 7. Belle Collab., K. Abe etal., Phys. Rev. Lett. 88, 052002 (2002). 8. J.L. Rosner, Phys. Rev. D 60, 074029 (1999).
9. M. Neubert and A. Petrov, Phys. Lett. B 519 (2001) 50. 10. Particle Data Group, D.E. Groom etal., Eur. Phys. J. C15, 1 (2000). 11. CLEO Collab., S. Ahmed etal., hep-
ex/0206030, accepted for publication in Phys. Rev. D., and references therein. 12. CLEO Collab., J.P. Alexander etal., Phys. Rev. Lett. 86, 2737 (2001) 13. CLEO Collab., E. Eckhart
etal., hepex/0206024, accepted for publication in Phys. Rev. Lett., and references therein.
14. M. Kobayashi and K. Maskawa, Prog. Theor. Phys. 49, 652 (1973). 15. E. Golowich and A. Petrov, Phys. Lett. B 427 (1998) 172. 16. Mark III Collab., J. Adler etal., Phys. Lett. B 196 (1987) 107, E687 Collab., P. L. Frabetti etal., Phys. Lett. B 286 (1992) 195, and Phys. Lett. B 331 (1994) 217, E691 Collab., J. C. Anjos etal., Phys. Rev. D 48, 56 (1993), ARGUS Collab., H. Albrecht etal., Phys. Lett. B 308 (1993) 435. 17. T. Hill etal., Nucl. Instr. Meth. A418 (1998) 32. 18. CLEO Collab., S. Kopp etal., Phys. Rev. D 63, 092001 (2001). 19. D. Asner, UCRL-JC-147296-DR.
PROCEEDINGS SUPPLEMENTS ELSEVIER
Nuclear Physics B (Proc. Suppl.) 115 (2003) 98-102
www.elsevier.com/locate/npe
Recent Results in B and D Decays from CLEO Todd K. Pedlar a, for the CLEO Collaboration a Department of Physics The Ohio State University Columbus, OH 43210 We present three new results in the physics of B and D decays obtained by the CLEO Collaboration. These axe new measurements of B--.-~DTr branching ratios and subsequent evaluation of the strong phase in these decays, a first measurement of the decay B--~K%-, and an update on D meson mixing results.
1. Introduction On June 26, 2001, the CLEO experiment took its last data at the T(4S). Since its advent, CLEO has written or re-written most of the initial chapters in the story of heavy meson spectroscopy. While the lead has been handed off to the B-factories, CLEO continues to produce significant results in the field. In this paper we present the results of three recent analyses by CLEO in the realm of B and D decays. All of the data used in the analyses presented in this talk were obtained using CLEO II a n d / o r II.V detector configurations, which have been described in detail elsewhere [1,2]. The data were taken in symmetric e+e - collisions at energies near v ~ = 10 GeV, provided by the Cornell Electron-positron Storage Ring (CESR). The hadronic B results utilize the full CLEO data set of 9.7 million B B pairs, while the D mixing result is based on the 9 fb -1 sample of e+e - collisions observed by the CLEO II.V detector. 2. T h e D e c a y s B--~DT~ and M e a s u r e m e n t o f the Strong Phase 6i In this section we present the results of measurements of the branching fractions for B - - + D ° r - and -JB°-+D+r- and the extraction of the strong phase difference 51 between the I = 1/2 and I = 3/2 isospin amplitudes in the D r system. These decays are an excellent testing ground for the theoretical description of hadronic B-meson decays. Our understanding of these de-
cays has improved considerably with the development and application of Heavy Quark Effective Theory (HQET) [3,4] and Soft Collinear Effective Theory (SCET) [5], which have given factorization a more solid foundation. The recent observation [6,7] of the colorsuppressed B°--+D°r° decay completed the measurement of the D r final states and made possible the determination of the strong phase difference 5i. A value of cos (it inconsistent with unity would signal the presence of final-state interactions in the B - + D r process [8,9], and thus motivated us to make efforts to improve the precision of measurements of the branching fractions for the colorfavored decays B - - + D ° r - and -B°--+ D+ Tc-. In this analysis, neutral D mesons are reconstructed in the modes: K - r +, K - r + T r ° and K - ~ r + r - ~ r +. Charged D mesons are reconstructed via K-Tr+Tr +. In each case, D meson candidates are required to have a mass within 3a (standard deviations) of the PDG D mass [10] before kinematic fitting. Mass resolutions for the various D modes range from 6 to 12 MeV. B meson candidates are reconstructed using D and additional r tracks For each candiate, the beam-constrained mass M B =- ~ / E ~ e a m - p 2 , and the energy difference A E = E B -- Ebeam are calculated. 1 Final selection of B candidates (one per event, selected as the candidate with smallest AE) before fitting requires M B > 5.24 G e V / c 2 and A E E (--50, 50) MeV, and cuts on event 1Ebeam denotes the beam energy, and EB and PB the candidate momentum and energy, respectively.
0920-5632/03/$ - see front matter © 2003 Published by Elsevier Science B.V. doi:l 0.1016/S0920-5632(02)01962-X
T.K. Pedlar~Nuclear Physics B (Proc. Suppl.) 115 (2003) 98-102
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of the partial rates for the three B~D~r decays. The calculation of cos(f1 in the D r system as well as the overall systematic error for B(B--+D°Tr -) takes full account of correlations of various systematic error contributions by means of a detailed Monte Carlo method. 2 We consider correlations between the two color-favored decay modes B--~D%r- and B-°--~D+lr-, those among the measurements of B(B--+D°7r -) via different D o decay modes, and those due to ]oo and f+_. Details are found in Ref. [11]. We thus obtain the following final results for the color-favored branching fractions:
B(B--~D°~-) -- (49.7+1.2±2.9±2.2) Figure 1. Fitted distributions of the quantity MB -- x/E~eam - p~ for the indicated decays.
shape variables which are very effective in reducing the background from e+e ---~qq events. To obtain event yields for B ~ D r - for each D meson decay mode, the MB distribution of candidates surviving the above slection cuts are subject to a maximum likelihood fit. The fit function is a Ganssian distribution plus an empirically determined background shape. Fitted MB distributions are shown in Fig. 1. A small, non-negligible background from the decay B--~DK- contributes to the yields obtained by the fits described above. The D K contamination fraction is determined from Monte Carlo, and yields obtained from the fit are corrected by this fraction before being used to calculate branching ratios for B~D~r. Using efficiencies determined from Monte Carlo, we obtain the branching fractions, assuming that charged and neutral B mesons are produced in equal fractions f+_ and f00 at the T(4S). The three B--+Dr decay branching fractions form a complete set of branching fractions with which we may calculate cos 5x, the cosine of the strong phase angle difference between the two isospin amplitudes I = 1/2 and I = 3/2 that contribute to the decay process. The expression for cos(ix is given, e.g., in Ref. [8], and is a function
x 10-4(1)
B(-~-+D+~r-) -- (26.8±1.2±2.4±1.2) x 10-4.(2) In eac~hmeasured quantity, the first error is statistical and the second is systematic. The third error is a separate systematic error which corresponds to the experimental uncertainty on foo and f+_. [12] Our results for B(-B°-+D+~r -) and for B(B---+D°Tr-) each reflect improvementwith respect to the present PDG average values [I0]. Our result for B(B-°-+D+r-) may be directly compared with Ref. [3]. Their prediction of 32.7 x I0 -a is marginally consistent with our result. Our final results for cos(f/ and (fl utilize the branching ratios above as well as the world average of 13(-B°-~D°1r°) = 2.92 + 0.45 x 10-4 [6,7]. We thus obtain: COS (~I
n ~ ' : l +0"024+0"036+0"038 -~- v'~'vv--O.023--0.035--0.030,
16.5 ° < (fl < 38.1° (90% CL).
and
(3) (4)
In summary, we have measured the branching ratios for the color-favored B~D~r decays, and used these measurements to determine the value of the strong phase difference (ii: Our result for cos (fi strongly suggests final-state interactions in B ~ DIr decays. 2 T h e overall s y s t e m a t i c error for o u r m e a s u r e m e n t of BC'B°--~D+~r- ) is o b t a i n e d by s t a n d a r d error p r o p a g a t i o n of t h e individual c o n t r i b u t i o n s .
100
TK. Pedlar~NuclearPhysics B (Proc. Suppl.) 115 (2003) 98-102
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3. The Decays B--~KTrTr and B--~K*~" The second result we present is the observation of two rare charmless B decays. [13] Recently, first observations of several two-body charmless hadronic decays of B mesons, including the four B -~ KTr transitions, have been reported. These two-pseudoscalar decays have received considerable attention due to their expected role in improving our understanding of the weak interaction and in the extraction of the complex quark couplings described by the CKM matrix [14]. The pseudoscalar-vector analogs of these decays, B ~ K*Tr and Kp, present additional opportunities for observing direct C P violation [13] and physics beyond the Standard Model. We have investigated B decays to the threepseudoscalar final states, K ° h%r - , K+ h-Tr °, and K ° h % r ° (h + denotes a charged pion or kaon). We have performed one fit to our data for each topology, allowing for six signal and background components, pion and kaon hypotheses for h + for each of the following: signal, continuum background, and background from b -~ c decays. The probability for an event to be consistent with
a given component is the product of the probability distribution function (PDF) values for each of the input variables (neglecting correlations). The likelihood for each event is the sum of probabilities over the six components, with relative weights determined by maximizing the total likelihood of the sample. The parameters of the PDFs are measured from high-statistics Monte Carlo samples and independent data samples. The impact of correlations among the input variables is reduced by determining the PDFs as a function of the event location in the Dalitz plot. We use Monte Carlo simulation to estimate the systematic error associated with neglecting any remaining correlations. Detection efficiencies and crossfeed among the signal modes are also obtained from these Monte Carlo studies. The statistical significance of the raw yield reported by the fit is determined by repeating the fit with the yield fixed to be zero. We calculate fit yield upper limits at the 90% confidence level by integrating the likelihood function. We observe a signal for B --¢ K~r+Tr - with a statistical significance of 8.1a. No other contribution to the three signal topologies shows ev-
T.K. Pedlar/NuclearPhysics B (Proc. Suppl.) 115 (2003) 98-102 idence of a significant signal. We also perform Dalitz plot fits for the three topologies with up to nine resonant and non-resonant components. The only two-body channel in which we observe a statistically significant signal is B -~ K*+(892)Tr with a yield of .19 4-6 for K*+(892) -~ K°zr + . . .a+ . 3.9 and av . ~1+2.2 for K*+(892) --+ K+zr ° and a com--l. 9 bined significance of 4.6a. The size of the signal is insensitive to the choice of other resonances included in the fit. In the K°h+~r - , we find N(K*+(892)~r-)/N(K%r+~r - ) to be n~ ' ~gn+0.o8 "--0.07" Our result for the branching ratio is:
13(B -+ K*+(S92)~r - ) = \0 6 +6 + 4) x 10 -6. --5
(5)
Most theoretical predictions [13] for this branching fraction lie in the range 2-14x10 -6. Figure 2 shows the event distributions in M and A E for modes where we claim an observation. The background in these plots has been suppressed with cuts on the ratios of signal and background likelihoods, computed without M and A E respectively. Overlaid are the fit projections for the signal and background components, scaled by the efficiency of the likelihood ratio requirements (40-50% for K%r+Tr - and 70-80% for K*+(892)zr-). Figure 2 shows the M(K°Tr +) distribution for events in the K°h+lr - fit satisfying a likelihood ratio requirement. Overlaid is the expected distrubtion for background. In summary, we have made first observations of both the three-body decay B -~ K%r+Tr - , as well as a significant two-body submode, B -+ K*+(892)Tr - . The measured branching fraction for B --~ K*+(892)7~ - is larger than but consistent with most theoretical predictions.
4. N e w Results in D Mixing In the final analysis presented in this talk, we report on new results in D mixing measurements via the decay D ° ~ K s l r + T r - . In searching for the mixing, it is important to understand possible final state interactions [15]. As such, an interesting final state which allows for the study of both Cabbibo favored and Cabbibo suppressed (or mixing) and their relative phase, is the final state D°--+KsTr+~r - . Both favored and suppressed channels may be observed via Dalitz anal-
101
ysis of this final state. The 9.1 f b - 1 data sample taken with the CLEO II.V configuration allows sufficient statistics to observe substructure in the Cabbibosuppressed decays contributing to this final state - a key limitation of previous analyses. [16] The event selection depends heavily on the CLEO II.V silicon vertex detector [17], which dramatically improves the resolution on the common KsTr+U vertex, and thus the selection of D mesons. 5299 candidates are obtained through the above methods, and are then subjected to a Dalitz analysis. The distribution is parameterized according to the method described in Ref. [18]. Nineteen resonant subcomponents and a fixed phase, non-resonant contribution are considered. The phases and widths of the resonant contributions are determined as described in Ref. [19]. An initial unbinned maximum likelihood fit shows only ten resonant contributions axe found to be signficant. The final results are obtained from a fit with only the ten "significant" resonant components, as well as the non-resonant contribution. Figure 3 shows the three projections of this fit. There is a significant "wrong sign" D°-+K*+~ - amplitude. Mistags are insigificant, having a rate of just 0.3 ± 0.5%. When the likelihood of the fit is compared to a fit in which the wrong sign D°-+K*+Tr - amplitude is fixed to zero, the statistical significance of this amplitude is shown to be 4.9 standard deviations. In order to check for CP-violation, the data sample was split into D o and ~-o tags. No statistically significant difference between the two analyses was observed. In summary, we obtain the wrong sign ratio R w s -- B(D° ~K*+Tr-)/13(D° ~K*-Tr+ ):
R w s = (0.6 ± 0.3 ± 0.2)%.
(6)
Further, the relative phase between wrong sign and right sign decays is found to be
A C w s - n s = ( - 3 ± 11 ± 8) °.
(7)
This wrong sign rate may arise from either Doubly Cabbibo suppressed decays or from mixing. Future work on this decay mode will include an
T.K. Pedlar~Nuclear Physics B (Proc. SuppL) 115 (2003) 98-102
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a)
:'~ 150 ;>
c) ~.loo
200
50
50
2 M(K°s 7r')2 (GeV2/¢4)
0
0
1 2 3 M(~+Tt')2 (GeV2/c4)
1
2
3
M(K~s It+)2 (GeV2/c4)
Figure 3. Projections of the results of the fit described in the text to the KsTr+Tr- Dalitz distribution. The curve shows the results of the fit and the data are represented by the black points.
investigation of time dependence of the Dalitz plot as described in Ref. [19]. Such an analysis will be necessary in order to discern the difference between Doubly Cabbibo suppressed and mixing contributions to the wrong-sign rate. In addition, time dependent analysis will be sensitive to the mixing parameters x and y at the few percent level, (i.e. as good or better than experiments using the KTr or CP eigenstate final states) as well as Sign(x), which no other method can resolve. REFERENCES 1. Y. Kubota et al., Nucl. Instrum. Meth. Phys. Res., Sect. A 320, 66 (1992). 2. T. Hill, Nucl. Instrum. Meth. Phys. Res., Sect. A 418, 32 (1998). 3. M. Beneke etal., Nucl. Phys. B591, 313
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