Indication of new physics in B <FONT FACE=Symbol>® F</FONT>Ks decays at the BELLE experiment

Indication of new physics in B ® FK_s decays at the BELLE experiment

Jens Sören Lange

Frankfurt University, on behalf of the BELLE Collaboration

The BELLE experiment at the asymmetric e⁺e^– (3.5 GeV and 8 GeV) accelerator KEK-B at Tsukuba, Japan, has recorded 152 Million B meson pairs in 4 years of data taking. In the standard model, the size of CP violation in the B meson system is characterized by a quantity called sin(2j₁), in which j₁ denotes one of the angles in the unitarity triangle. This quantity was determined precisely to be sin(2j₁)=0.733±0.059±0.028, based upon N=1997 events with the decay B®J/YK_s and N=914 other B®charmonium+Kaon decays [1] [2] [3]. The measurement is consistent with the measurement of the BABAR detector at SLAC [4]. In the standard model, the decay B®FK_s is expected to show identical CP violation. However, a measurement of N=68 events revealed –0.96±0.50+0.09–0.11 (opposite sign from expectation), which is a 3.5s deviation from the expected standard model value [1] [5]. The probability of obtaining the observed result for B®FK_s as a statistical fluctuation of the B®J/YK_s result is less than 0.1%. In the standard model, B®FK_s is dominated by a penguin diagram with a W boson and a top quark in a loop. The top quark itself radiates a gluon which creates an s pair. Two additional decay channels, namely B®h'K_s and B®K⁺K^–K_s are dominated by the same diagram. However, their CP violation seems to be consistent (within still large statistical errors) with the sin(2j₁) value from B®J/YK_s [6] [7]. The difference between the three different decay channels is given by the spin of the F meson J^P=1^– (vector meson), while all Kaons and the h' are J=0^– (pseudoscalar mesons). In an additional analysis, angular distributions have been investigated. In the case of B®VV¹ a helicity analysis can be performed. For this purpose, the B®J/YK^* [8] (pseudoscalar meson K_s replaced by vector meson K^*) and B®FK_s [9] were compared. As pointed out recently by Grossman [10], differences between the two decay channels seem visible, and are difficult to be explained within the standard model.

BELLE will resume data taking in 10/2003, with an improved Silicon Vertex Detector (4 layers, larger angular coverage). An update of the analysis results is envisaged for summer 2004.

References

[1] T. Browder, XXI International Symposium on Lepton and Photon Interactions at High Energies, 08/11-16/2003, Fermilab, Batavia, Illinois, USA, hep-ex/0312024, Int. J. Mod. Phys. A19, 965 (2004).

[2] BELLE Collaboration, Improved Measurement of Mixing-induced CP Violation in the Neutral B Meson System, hep-ex/0208025, Phys. Rev. D66, 071102(R) (2002).

[3] BELLE Collaboration, Observation of Large CP Violation in the Neutral B Meson System, hep-ex/0107061, Phys. Rev. Lett. 87, 091802 (2001).

[4] BABAR Collaboration, Measurement of the CP-violating Asymmetry Amplitude sin2b², hep-ex/0207042, Phys. Rev. Lett. 89, 201802 (2002).

[5] BELLE Collaboration, Study of Time-Dependent CP-Violating Asymmetries in b®s

q Decays, hep-ex/0212062, Phys. Rev. D 67, 031102(R) (2003).

[6] BELLE Collaboration, Measurement of Time-Dependent CP-Violating Asymmetries in Bº®FK_s, K⁺K^–K_s and h'K_s Decays, hep-ex/0308035, Phys. Rev. Lett. 91, 261602 (2003).

[7] BELLE Collaboration, Measurement of CP-Violating Parameters in B®h'K Decays, hep-ex/0207033, Phys. Lett. B546, 196 (2002).

[8] BELLE Collaboration, Measurement of Branching Fractions and Polarization in B®FK^(*) Decays, hep-ex/0307014, Phys. Rev. Lett. 91, 201801 (2003).

[9] BELLE Collaboration, Measurements of Branching Fractions and Decay Amplitudes in B®J/YK^* decays, hep-ex/0205021, Phys. Lett. B538, 11 (2002).

[10] Y. Grossman, XXI International Symposium on Lepton and Photon Interactions at High Energies, 08/11-16/2003, Fermilab, Batavia, Illinois, USA, hep-ph/0310229, Int. J. Mod. Phys. A 19, 907 (2004).

Received on 22 October, 2003

1

V denotes a vector particle (

J^P=1

^–).

2

The BELLE and BABAR collaborations differ in nomenclature. The angle b is identical to f

₁.

Publication Dates

• Publication in this collection
  26 Oct 2004
• Date of issue
  Sept 2004