First 5 observation of CP violation in the decays of B0. B s at LHCb. Maria Zangoli Per la collaborazione LHCb

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1 First 5 observation of CP violation in the decays of 0 B s at LHCb Maria Zangoli Per la collaborazione LHCb XCIX Congresso Nazionale SIF Trieste 25 settembre 2013 Maria Zangoli First 5 observation of CP violation in the decays of B0 s at LHCb

2 Outline The H b h + h - decay family Importance of charmless two-body B decays The LHCb detector Measurement of the direct CP asymmetries of B 0 K + π - and B0 s K - π + decays Performed with 1/fb collected during s = 7 TeV Analysis main steps Results and conclusions s at LHCb 2/13

3 The H b h + h - decay family The family of charmless charged two-body B decays comprises a rich set of modes B 0 π + π - B 0 K + π - B0 s K + K - B0 s π + K - b pk - B 0 K + K - b pπ - B0 s π + π - Interesting observables are direct and time-dependent CP asymmetries and the branching ratios Direct CP asymmetries A CP = Γ B f Γ B f Γ B f + Γ B f Time-dependent CP asymmetries A( t) = Γ ( t) Γ B f B f ( t) ( t) + Γ B f ( t) Γ B f s at LHCb 3/13

4 Importance of charmless two-body B decays Charmless two-body B decays provide valuable information for: improving knowledge of CKM matrix UT angles and the B0 s mixing phase validating theoretical tools to deal with QCD contributions QCD factorization, pqcd, SCET, constraining New Physics CP-violation observables and branching fractions can differ from Standard Model predictions As penguin topologies are NP? generally sizeable, effects from New Physics in loops may be sizeable as well Theoretical interpretation is however not straightforward, because of unknown hadronic parameters in the amplitudes s at LHCb 4/13

5 Muon chambers RICH system Velo Trigger + µ ID π, K, p ID Precise vertexing 300 mrad Interaction point Dipole magnet 4 Tm Maria Zangoli Tracking stations momentum Preshower/SPD, ECAL, HCAL, Trigger γ/e Energy and ID 5/13

6 B0s Kπ π+ from B0s K- from B0s p-p interaction point Secondary vertex Maria Zangoli 6/13

7 Measurement of the direct CP asymmetries of B 0 K + π - and B0 s K - π + decays Event selection: Two sets of requirements, separately optimized for measuring A CP (B 0 K + π - 0 ) and A CP (B s K - π + ) Looser requirements for B 0 K + π - 0, tighter for B s K - π + Fits to the invariant mass spectra, to determine raw asymmetries Corrections to the raw asymmetries s at LHCb 7/13

8 Invariant mass fit and raw CP asymmetries The raw CP asymmetries are measured from unbinned maximum likelihood fits to the Kπ invariant mass spectra Two different selections have been optimized in order to achieve the best sensitivities on the two CP asymmetries B 0 K + π B 0 K π + Raw A CP (B 0 Kπ) = ± s at LHCb 8/13

9 Invariant mass fit and raw CP asymmetries The raw CP asymmetries are measured from unbinned maximum likelihood fits to the Kπ invariant mass spectra Two different selections have been optimized in order to achieve the best sensitivities on the two CP asymmetries B 0 s K- π + B0 s K + π B0 s K π + 0 Raw A CP (B s Kπ) = 0.28 ± 0.04 s at LHCb 9/13

10 Corrections to the raw CP asymmetries Production asymmetry A P (B 0 0 ), A P (B s ): Determined directly from the studied decays by means of the fit to the data of their full time-dependent decay rate k is a factor that depends on selection and time evolution of neutral B meson A(t) for B 0 K + π - A(t) for B s0 K - π + A P (B 0 ) = (0.1 ± 1.0) % k d = ± A P (B0 s ) = (4 ± 8) % k s = ± s at LHCb 10/13

11 Corrections to the raw CP asymmetries The detection asymmetry A D (Kπ) between K + π - /K - π + pairs has been studied using large samples of D* D 0 (Kπ) π s and D* D 0 (KK) π s decays Combining their raw asymmetries it is possible to determine A D (Kπ) A D (Kπ) for B 0 = (-1.15 ± 0.23) % A D (Kπ) for B0 s = (-1.22 ± 0.21) % transported to LHCb decay time acceptance s at LHCb 11/13

12 Results Using the full 1/fb of integrated luminosity collected during s = 7 TeV we measured A CP (B 0 Kπ) is the most precise measurement of this quantity to date, with a 10.5 significance A CP (B0 s πk) is the first observation of CP violation in the B0 s meson decays with a significance of 6.5 Phys. Rev. Lett. 110, (2013) s at LHCb 12/13

13 Conclusions These results allow a stringent test of the validity of the Standard Model, assuming U-spin [Phys. Lett. B621 (2005) 126] Using additional results for B(B 0 K + π - ) and B(B0 s K - π + ) JHEP 10 (2012) 037 and the world averages for d and s arxiv: we obtain From the measurement of A CP Input values of the BF and lifetimes No evidence for a deviation from zero of is observed within the present experimental precision s at LHCb 13/13