We present new results on hadronic B and D decays from the BABAR experiment.
The first part of this document presents searches for new channels which may be
used for CP measurements. The second part is dedicated to hadronic decays with
tests of QCD factorization predictions and other models for B structure and
decay mechanisms. A new result on the reference branching ratio Ds+ -->phi pi+
is also reported.Comment: 4 pages, 1 eps figure, contributed to the proceedings of 40th
  Rencontres de Moriond QCD 200

/Annecy, LAPP

Couderc, F.

English

arXiv

We present new results on hadronic B and D decays from the BABAR experiment. The first part of this document presents searches for new channels which may be used for CP measurements. The second part is dedicated to hadronic decays with tests of QCD factorization predictions and other models for B structure and decay mechanisms. A new result on the reference branching ratio D{sub s}{sup +} {yields} {phi}{pi}{sup +} is also reported

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Work supported in part by Department of Energy contract DE-AC02-76SF00515SLAC-PUB-11271BABAR-PROC-05-019hep-ex/0506031HADRONIC B AND D STUDIES AT BABARF. COUDERCrepresenting the BABAR CollaborationLaboratoire d’Annecy-Le-Vieux de Physique des Particules9 Chemin de BellevueBP 110 F-74941 Annecy-le-Vieux CEDEX - FranceWe present new results on hadronic B and D decays from the BABAR experiment. The first partof this document presents searches for new channels which may be used for CP measurements.The second part is dedicated to hadronic decays with tests of QCD factorization predictionsand other models for B structure and decay mechanisms. A new result on the referencebranching ratio D+s → φπ+ is also reported.1 CP related analysisIn this section, we present new CP violation related analysis of channels which could be used,in the future, to measure some of the CKM matrix parameters like γ ≡ arg[−VudV∗ubVcdV∗cb]or acombination of γ and β ≡ arg[−VcdV∗cbVtdV∗tb]. To do this, one needs to measure CP asymmetrieswhich are defined, for the B → f decay, as :ACP =B(B → f) − B(B → f)B(B → f) + B(B → f)1.1 Measurement of the branching fraction and decay rate asymmetry of B− → Dπ+π−π0K−The decays B → D(∗)0K(∗) can be used to measure the angle γ taking advantage of the in-terference between b → ucs and b → cus decay amplitudes. Different approaches have beendeveloped, and among which, γ measurements involving D decays to multi-body, using a Dalitzplot analysis technique as described in reference 1. In this analysis, we study the decay modeB− → DK− with the D-decay : D → π+π−π0 which is Cabibbo suppressed. This yields amuch smaller event sample compared to Cabibbo allowed decay but its interfering D0 and D0amplitudes have similar magnitudes. Due to these interferences, the production rate might beSLAC, Stanford Univesity, Stanford, CA  94309Presented at 40th Rencontres De Moriond On QCD And High Energy Hadronic Interactions, March 12-19, 2005, La Thuile, Italydifferent from the product Bprod ≡ B(B− → D0K−) × B(D0 → π+π−π0) = (4.1 ± 1.6) × 10−6(ref. 2). From a sample of 229 million of BB pairs, we found 133± 23 signal events which corre-spond to a branching ratio of B(B− → Dπ+π−π0K−) = (5.5±1.0±0.7)×10−6. We determine theraw asymmetry and do not find any significant deviation from zero : ArawCP = 0.02± 0.16± 0.03.The γ extraction needs a full Dalitz analysis of the D-decay.1.2 Search for B → D+s Xlight with Xlight ≡ π0, a−0 , a−1The value of sin(2β + γ) can be extracted from the measurement of the time dependent CPasymmetry in B → D−X+light decays with, for instance, X+light ≡ π+, a+0 , a+2 . In this casethe asymmetry is given by : ACP (∆t) = r × sin(2β + γ) × sin(∆md∆t) where r = B(B0 →D+X−light)/B(B0 → D−X+light). The decay B0 → D+X−light is doubly Cabibbo suppressed anddifficult to measure directly. Using SU(3) flavor symmetry, it is possible to infer the value ofB(B0 → D+X−light) from the value of B(B → D+s Xlight), the latter being less suppressed.If X+light ≡ π+, then r is expected to be very small (r ≈ 0.02) which implies a small asymmetry.In this case r might be deduced from the rate B(B+ → D+s π0). We measure this branchingratio from a sample of 124 millions of BB pair, we do not see any significant signal and quotean upper limit of : B(B+ → D+s π0) < 2.8 × 10−5 in agreement with a previous measurementby CLEO (< 2.4 × 10−4 from ref. 2) and with the value of 0.9 × 10−5 expected from the rateof B(B0 → D+s π−) measured by Belle and BABAR experiments. If X+light ≡ a+0 (a+2 ), r mightbe quite large. This is due to the coupling constant of the W to the a0 scalar meson (a2meson of spin 2) which is small and decreases the production rate of the Cabibbo allowed decayB0 → D−a+0 (a+2 ). The factorization hypothesis predicts a similar rate for Cabibbo allowed andCabibbo suppressed decays 3 which results in r ≈ 1. These decays are not yet in the reachof experiment (branching ratios around 10−6), nevertheless, the theoretical predictions can betested with the measurement of the branching ratio of the decay B0 → D+s a−0 (a−2 ) expectedat larger values : B(B0 → D+s a−0 (a−2 ) ≈ 7.5(1.5) × 10−5 (ref. 3,4). From a sample of 230million of BB pairs, we measure these two branching ratios. The a−0 (a−2 ) is reconstructed ina−0,2 → η(→ γγ)π+ which has a branching ratio of the order of 100 % (only 15 % for the a−2which lowers the experimental sensitivity). We do not find any significant signal and quote theupper limits : B(B0 → D+s a−0(2)) < 4.0 (25) ×10−5 which shows a discrepancy of at least a factortwo with the theoretical predictions.1.3 Charmless decaysThe decay B+ → K∗+(→ K+π0)π0 and its CP asymmetry is particularly interesting in light ofthe recent measurement of direct CP violation in the decay B0 → K+π− 5. From a sample of 232million of BB pairs we find 88.5 ± 25.7 signal events which correspond to the branching ratio :B(B+ → K∗+π0) = (6.9 ± 2.0 ± 1.3) × 10−6 and do not find any hint of direct CP violation :ACP = 0.04 ± 0.29 ± 0.05 (reference6).Other types of charmless decays such as : B → η(′)π, ρ, ω, K are studied as well. These decaysprocess via b → u CKM-suppressed trees and/or b → s penguins. They provide a good test ofQCD factorization, may have large CP asymmetry and may provide sensitivity to the CKM angleγ. From a sample of 232 million of BB pairs, we measure the four branching ratios, and theirasymmetries, and give two upper limits. Details on this analysis can be found in reference 7, nosignificant CP asymmetry is observed and measured branching ratios are in good agreement withtheoretical predictions. We make the first observation of the decays B+ → η′π+ and B+ → ηρ+and measure the corresponding decay rates : B(B+ → η′π+) = (4.0 ± 0.8 ± 0.4) × 10−6 andB(B+ → ηρ+) = (8.4 ± 1.9 ± 1.1) × 10−6.2 Non CP related analysis2.1 Measurement of the B0 → D∗−D∗+s and D+s → φπ+ branching ratiosWe present measurements of the branching ratio B(B0 → D∗−D∗+s ) which may lead to a precisedetermination of the reference B(D+s → φπ+). They have been performed on a sample of 123million of BB pairs. The B0 → D∗−D∗+s → (D0π−)(D+s γ) decay is reconstructed using twodifferent methods. The first one combines the fully reconstructed D∗− with the photon fromthe D∗+s → D+s γ decay, without explicit reconstruction of the D+s . To extract the numberof partially reconstructed events, we compute the ”missing mass” mmiss recoiling against theD∗−γ system assuming that a B0 → D∗−D∗+s → (D0π−)(D+s γ) decay took place. For signalevents, mmiss peaks at the Ds mass. We find, with this method, the following branching ratio :B1 ≡ B(B0 → D∗−D∗+s ) = (1.88 ± 0.09 ± 0.17) % which is in agreement with the factorizationmodel : B(B0 → D∗−D∗+s )theo = (2.4±0.7) %. The second one is a full reconstruction techniqueof the decay chain B0 → D∗−D∗+s where the Ds candidate is reconstructed in the mode :D+s → φπ+ → (K+K−)π+. We measure with this method, the branching ratio B2 ≡ B(B0 →D∗−D∗+s ) × B(D+s → φπ+) = (8.81 ± 0.86stat) × 10−4.From the ratio B2/B1, where many systematics cancel out, we get a precise measurement of :B(D+s → φπ+) = (4.81 ± 0.52 ± 0.38) %.which represents an improvement on the error by about a factor of two over previous measure-ments 2. Details on this work can be found in the reference 8.2.2 Search for the rare decays B+ → D(∗)+K0This decay is expected to occur via a pure annihilation diagram. Such processes provide interest-ing insights into the internal dynamics of B mesons. This kind of diagram cannot be calculatedin QCD factorization since both the quarks play a role. These amplitudes are expected to besuppressed, with respect to the amplitudes of spectator quark trees, by a factor fB/mB ≈ 0.04and have never been observed. Some studies 9 indicate , though, that processes with a spectatorquark can contribute to annihilation-mediated decays by rescattering. The branching ratio isexpected to be either at the level of the current sensitivity (10−5) if large rescattering occurs, orthree orders of magnitude below if not 9. We reconstruct the two decay modes B+ → D∗+K0Sand B+ → D+K0Swithin a sample of 226 million of BB pairs. We do not see any significantexcess of signal and therefore we set the upper limits at 90 % CL : B(B+ → D+K0S) < 0.5×10−5and B(B+ → D∗+K0S) < 0.9 × 10−5.2.3 Search for B → J/ψD DecaysThe spectra of the momentum of inclusive J/ψ mesons in the Υ (4S) rest frame observed byCLEO and by BABAR, compared with calculations using non-relativistic QCD (NRQCD), showan excess at low momentum, corresponding to a branching fraction of approximately 6 × 10−4.Many hypothesis have been proposed to explain this result but no experimental evidence hasbeen found to support them. The presence of bucc components (intrinsic charm) in the B-meson wave function has also been suggested to enhance the branching ratio of decays suchas B → J/ψD(π) to the order of 10−4 while pertubative QCD predicts a branching ratio forB → J/ψD of 10−8-10−9. We test the decay channels B → J/ψD within a sample of 124 millionof BB pairs. We do not find any evidence of signal and obtain upper limits of 1.3 × 10−5 forB0 → J/ψD0 and 1.2×10−4 for B+ → J/ψD+ at 90 % CL. Therefore, we conclude that intrinsiccharm is not supported as the explanation of low momentum J/ψ excess in B decays. Moredetails on this analysis can be found in reference 10.2.4 Production and decay of the Ξ0c at BABARWe present a study of the Ξ0c (csd) charmed baryon using a luminosity of 116.1 fb−1 throughtwo decay modes : Ξ0c → Ω−K+ and Ξ0c → Ξ−π+. First, we measure the ratio of thesetwo decay rates to be 0.294 ± 0.018 ± 0.016 which is compatible with the prediction, in aspectator quark model calculation, of 0.32. Then, we measure the p∗ distribution of the Ξ0cbaryons, in the Υ (4S) frame, in order to study the production mechanisms in both cc andBB events. Results are shown on Figure 2.4. The double-peak structure seen in the p∗ spec-trum is due to two production mechanisms: the peak at lower p∗ is due to Ξ0c productionin B meson decays and the peak at higher p∗ is due to Ξ0c production from the cc contin-uum. From these spectra we compute the cross-section of the production of Ξ0c in continuum :σ(e+e− → cc→ Ξ0cX)×B(Ξ0c → Ξ−π+) = (388± 39± 41) fb and the rate of Ξ0c production inB decay : B(B → Ξ0cX) × B(Ξ0c → Ξ−π+) = (2.11 ± 0.19 ± 0.25) × 10−4.0 1 2 3 4 501000020000300004000050000On-resonanceOff-resonancep* (GeV/c)Figure 1: The p∗ spectrum of Ξ0c . Black dots represent on-peak data. Empty dots are off-resonance data(e+e− → uu/dd/ss/cc only) scaled to account for the difference in integrated luminosity and cross-section withon-peak data.The high rate of Ξ0c production at low p∗ in B decays (below 1.2 GeV/c) is particularlyintriguing, it implies that the invariant mass of the recoiling antibaryon system is typicallyabove 2.0 GeV/c2. This can be explained naturally by a substantial rate of charmed baryon pairproduction through the b→ ccs weak decay process which was observed indirectly in a previousBABAR analysis. Further details on this Ξ0c production analysis can be found in reference11.References1. A. Giri, Y. Grossman, A. Soffer and J. Zupan, Phys. Rev. D 68, 054018 (2003).2. S. Eidelman et al. [Particle Data Group], Phys. Lett. B 592, 1 (2004).3. M. Diehl, G. Hiller, hep-ph/01051944. C.S. Kim, J.P. Lee, and M. Bauer, Z. Phys. C 29, 637 (1985).5. B. Aubert et al. [BABAR collaboration], Phys. Rev. Lett. 93, 131801 (2004); Y. Chao etal. [Belle collaboration], Phys. Rev. Lett. 93, 191802 (2004).6. B. Aubert et al. [BABAR collaboration], hep-ex/0504009.7. B. Aubert et al. [BABAR collaboration], hep-ex/0408058, hep-ex/0503035.8. B. Aubert et al. [BABAR collaboration], hep-ex/0502041 and references therein.9. M. Blok, M. Gronau and J.L. Rosner, Phys. Rev. Lett. 78, 3999 (1997).10. B. Aubert et al. [BABAR collaboration], hep-ex/0503021 and references therein.11. B. Aubert et al [BABAR collaboration], hep-ex/0504014 and references therin.

Hadronic B and D studies at BABAR

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