Recent results from the B-Factories on radiative decays such as b {yields} s(d){gamma}, b {yields} s{ell}{ell} and leptonic decay B{sup 0} {yields} {tau}{sup +}{tau}{sup -} are reviewed

Cuhadar-Donszelmann, T.

U., /British Columbia

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Work supported in part by US Department of Energy contract DE-AC02-76SF00515Radiative Penguin decays at the B FactoriesTülay Çuhadar-Dönszelmann (on behalf of the Babar Collaboration)Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1CANADAAbstract. Recent results from the B-Factories on radiative decays such as b→ s(d)γ , b→ s andleptonic decay B0 → τ+τ− are reviewed.Keywords: Rare decays, Leptonic decaysPACS: 12.15.Hh, 13.20.-v, 13.20.He, 13.30.Ce, 13.35.DxINTRODUCTIONThe flavor changing neutral current (FCNC) rare B decays such as b→ s(d)γ and b→ splay a crucial role in testing the Standard Model (SM) as well as probing physics beyondthe SM. Such processes proceed via one loop (penguin or box) diagrams. The effec-tive hamiltonian for b → s transition is given by He f f =−4GF√2V∗tsVtb ∑iCi(μ)Oi(μ) [1],where GF and Vts,tb are the Fermi constant and the Cabibbo-Kobayashi-Maskawa(CKM) matrix elements, respectively. The FCNC operators, Oi, can be considered asthe vertices of the effective theory and the Wilson coefficients, Ci, play the role of cou-pling constants. Contributions in the loops of these decays from the Higgs boson orsupersymmetric particles can lead to an enhancement in their rates which range between10−4 to 10−6 in the SM. A comparison between the measurement and the SM predic-tion provides a stringent constraint on such new particles. At lowest order b → s(d)γ isdescribed by the coefficient C7 (photon penguin operator) and is computed up to next-to-leading order (NLO). The decay b→ s is defined by a Z-penguin and a W -box diagramin addition to the radiative penguin. Its amplitude depends on the coefficients C7,C9 andC10 (vector and axial vector operators) which are computed next-to-next-to-leading or-der (NNLO).The Babar and Belle detectors are located at the PEP-II and KEKB asymmetric energye+e− colliders, respectively. BB pairs are produced coherently from the ϒ(4S) decays.Up to now, approximately 400 fb−1 and 600 fb−1 of data have been recorded by theBabar and Belle experiments, respectively.b→ sγThe signature of a b → sγ decay is an energetic photon of E∗γ = (2− 2.7) GeV. Dueto the confinement of the b-quark inside the B meson, the energy spectrum is smearedinstead of producing a monochromatic energy of E ≈ mb/2. A fit to E∗γ , or to the firstand second moments of the photon energy spectrum, can be used to extract informationon the Heavy Quark Expansion (HQE) parameters, mb (b-quark mass) and μ2π (b-quarkContributed to CIPANP 2006: 9th Conference on the Intersections of Particle and Nuclear Physics,05/30/2006--6/3/2006, Westin Rio Mar Beach, Puerto RicoSLAC-PUB-12384kinetic energy inside the B meson). The Eγ spectrum is also input to semileptonic Bdecay analyses to extract |Vcb| and |Vub|. The inclusive decay B → Xsγ is studied withtwo methods. In the fully inclusive method, the photon energy spectrum is measuredwithout reconstructing the Xs system. In the semi exclusive method, the Xs system isreconstructed from a kaon (K or Ks) and up to four pions (one or two π0 allowed). Thereconstructed Xs system is then combined with a photon to form a B meson.Babar and Belle have measured the branching fraction and the moments from thephoton energy spectra using 82 fb−1 and 140 fb−1, respectively [2, 3]. The branchingfraction results are summarized in Fig.1(left) which also includes the earlier measure-ment by CLEO at 9.1 fb−1 [4]. The world average of B(b→ sγ) = (3.55±0.26)×10−4is published by the Heavy Flavor Averaging Group (HFAG) [5]. It is in good agreementwith the SM prediction of B(b → sγ) = (3.61+0.37−0.49)× 10−4 [6]. A fit to all availableb → sγ and B → Xcν data results in the HQE parameters of mb = 4.590±0.039 GeVand μ2π = 0.401± 0.040 GeV2 (in the kinetic scheme) [7]. As shown in Fig.1(right),the moments obtained from the Eγ spectra are consistent among the different mea-surements as well as with the theory predictions that rely on data from B → Xcνmoments. The b → sγ decay mode has also been measured in many exclusive finalBaBarfully inclusive ’05BaBarsum-of-exclusive ’05CLEOmixed technique ’01Bellefully inclusive ’04Bellesum-of-exclusive ’012 2.5 3 3.5 4 4.5 5024681012)-4) (10γs X→B(B SM Theory1.8 1.9 2 2.1 2.2 2.31st Moment (GeV)2.22.32.4Minimum Photon Energy (GeV)1.8 1.9 2 2.1 2.2 2.3)22nd Moment (GeV00.020.04CLEO inclusiveBelle inclusive untaggedBaBar inclusive taggedBaBar sum-of-exclusiveTheory Central valueTheory rangeFIGURE 1. (left) Results on branching fraction of b → sγ . (right) First and second moments fromphoton spectra of b→ sγ .states. For example, the most recent Babar result on B → Kηγ confirms the earlierBelle measurement. Both charged and neutral decays are observed at better than 5σsignificance. The combined average limits are B(B+ → K+ηγ) = (9.3± 1.1)× 10−6,and B(B0 → K0ηγ) = (10.3+2.3−2.1)× 10−6 [5]. Babar has also reported an upper limitB(B+(0)→ K+(0)η ′γ) < 4.2(6.6)×10−6 at the 90% C.L. [8].b→ dγThe decay b → dγ has similar sensitivity to the new physics (NP) as b → sγ , but itsbranching fraction is suppressed by the ratio of |Vtd/Vts|2. The exclusive decay B →(ρ,ω)γ were first observed by Belle using 386×106 BB. Assuming isospin symmetry, asimultaneous fit to three decay modes (B → (ρ+,ρ0,ω)γ) results in B(B→ (ρ,ω)γ) =(1.32+0.34−0.31(stat)+0.10−0.09(sys))×10−6 [9]. Based on 211×106 BB events, Babar observedno evidence for these processes and placed combined upper limits of B(B→ (ρ,ω)γ)<1.2× 10−6 at the 90% C.L. [10]. The SM predictions for these branching fractionsare in the range of (0.8− 1.8)× 10−6 [11]. The UTfit collaboration has performeda fit to the b → dγ data to extract the |Vtd/Vts| ratio. The fit results in the value of|Vtd/Vts|= 0.16±0.02 [12]. The most recent value of |Vtd/Vts|= 0.208+0.008−0.007 is reportedby CDF Collaboration [13] from the Δms/Δmd measurement.b→ sIn addition to the decay rate of b→ s, other observables such as the forward-backwardasymmetry (AFB) can be used to identify the sign of the Wilson coefficient C7 and themagnitudes of C9 and C10. The CP asymmetry, ACP, and the ratio of the muon to electronrate, RK(∗) = B(B→ K(∗)μμ)/B(B → K(∗)ee), are sensitive to NP.-1-0.500.510 2 4 6 8 10 12 14 16 18 20        GeV2/c2A FB (bkg-sub)q20 0.5 1 1.5 2 2.5×-l+Kl-l+l*KBaBarBelleAli et al.Zhong et al.Branching Fraction10-6FIGURE 2. (left) Comparison of the B → K (∗) branching fraction measurements and the two SMpredictions. (right) AFB in B→ K∗ measured by Belle Collaboration. The solid line is for negative A 7,dashed line is for positive A7, dot-dashed is for positive A10 and dotted is for positive A7 and A10.Semi exclusive decay b → s is reconstructed from two leptons ( = e,μ), a kaonand up to four pions (one or two π0 allowed). Babar and Belle have measured thebranching fraction summing up 10 and 18 hadronic states [14, 15], respectively. Inorder to avoid the resonance regions, the branching fraction has been reported in two q2(dilepton mass squared) regions: q2 = [1−6] GeV2 and q2 > 14 GeV2. For q2 = [1−6]GeV2, branching fraction measured by Babar [Belle] B(B → s) = (1.8± 0.9)[1.5±0.6]×10−6 is consistent with the SM prediction of (1.6±0.2)×10−6 [16]. For q2 > 16GeV2, the branching fraction results from Babar and Belle are (5.6± 2.0)× 10−6 and(4.1± 1.1)× 10−6, respectively. These result agree well with the SM expectation of(4.4±0.7)×10−6 [16].The exclusive decay B → K(∗) has been studied extensively by Babar [17] andBelle [18] using 208 fb−1 and 253 fb−1 of data. The measured branching fractionsare summarized on Fig.2(left). The CP asymmetries, AKCP = (−0.07±0.22) and AK∗CP =(0.03± 0.23) measured by Babar are very small, consistent with the SM expectation.For the ratio, Babar has reported RK = (1.06±0.49) and RK∗ = (0.91±0.45). For theseratios, Belle obtains RK = (1.38±0.41) and RK∗ = (0.98±0.32). The results of RK andRK∗ agree well with the SM expectation of unity [19] and 0.75 [20], respectively.The AFB(q2) measurement from Belle [21] is shown in Fig.2(right). The plot showsNP scenarios as well as the SM one. The Belle results exclude the NP scenarios wherethe sign of C9C10 is flipped with respect to the SM. The models with C7 and −C7 agreewell with data, hence no conclusion can be made on the sign of C7. Babar has measuredAFB in two regions. At large q2, the C9C10 is found to be consistent with the SM. Atlow q2, a lower limit AFB > 0.19 at 95% C.L. has been set. The fraction of longitudinalpolarization, FL, in the K∗ mode has the same importance as AFB in measuring the signof C7. Babar has measured FL, however data does not favor either of the C7 sign.LEPTONIC DECAYS B0 → τ+τ−The recent result from Babar on B0 → τ+τ− is also presented. This decay proceedsvia W -box and penguin diagrams. Due to the large τ mass, the branching fraction isless suppressed with respect to electron and muon modes (e : μ : τ = 10−7 : 10−3 : 1).However, the multiple neutrinos in the final states make it harder to measure. The SMprediction is B(B0 → τ+τ−) = 1.2×10−7˙[ fB/200 MeV ]2˙[|Vtd|/0.007]2 where fB is theB meson decay constant [1]. Using 210 fb−1, no evidence was found for this decay. Atthe 90% C.L., the upper limit of B0 → τ+τ− < 4.1×10−3 has been obtained [22].CONCLUSIONSuch rare decays, pioneered by CLEO, are brought to a more mature state by theB-Factories. The results shown here are based on one-fourth to one-half of the totalintegrated luminosity. Both theoretical and experimental updates will further constraintphysics beyond the SM.REFERENCES1. P. Harrison and H. Quinn, Tech. Rep. SLAC-R-504, SLAC (1998).2. BABAR Collaboration, B. Aubert et al., hep-ex/0507071; Phys. Rev. D 72, 052004 (2005).3. Belle Collaboration, P. Koppenburg et al., Phys. Rev. Lett. 93, 061803 (2004); K. Abe et al.,Phys. Lett. B 511, 151 (2001).4. CLEO Collaboration, S. Chen et al., Phys. Rev. Lett. 87, 251807 (2001).5. E. Barberio et al., hep-ex/0603003; online update at http://www.slac.stanford.edu/xorg/hfag .6. T. Hurth et al., Nucl. Phys. B 704, 56 (2005).7. O. Buchmüller and H. U. Flächer, Phys. Rev. D 73, 073008 (2006).8. BABAR Collaboration, B. Aubert et al., hep-ex/0603054, submitted to Phys. Rev. Lett.9. Belle Collaboration, D. Mohapatra et al., Phys. Rev. Lett. 96, 221601 (2006).10. BABAR Collaboration, B. Aubert et al., Phys. Rev. Lett. 94, 011801 (2005).11. A. Ali et al., Phys. Lett. B 595, 323 (2004); S. W. Bosch and G. Buchalla Nucl. Phys. B 621, 459(2002).12. UTfit Collaboration, M. Bona et al., http://utfit.roma1.infn.it/btovg/ckm-btovg.html.13. Talk by Guillelmo Gomez-Ceballos, “Update on CDF Bs Mixing”, Flavor Physics and CP Violationconference, CANADA, 2006 .14. BABAR Collaboration, B. Aubert et al., Phys. Rev. Lett. 93, 081802 (2004).15. Belle Collaboration, M. Iwasaki et al., Phys. Rev. D 72, 092005 (2005).16. P. Gambino, U. Haisch and M. Misiak, Phys. Rev. Lett. 94, 061803 (2005).17. BABAR Collaboration, B. Aubert et al., Phys. Rev. D 73, 092001 (2006).18. Belle Collaboration, K. Abe et al., hep-ex/0410006 .19. G. Hiller and F. Krüger Phys. Rev. D 69, 074020 (2004).20. A. Ali et al.Phys. Rev. D 66, 034002 (2002).21. Belle Collaboration, A. Ishikawa et al., Phys. Rev. Lett. 96, 251801 (2006).22. BABAR Collaboration, B. Aubert et al., Phys. Rev. Lett. 96, 241802 (2006).

Radiative Penguin Decays at the B Factories

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Radiative Penguin Decays at the B Factories

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