Studies of hadronic B decays at LHCb Neus Lopez March for the LHCb collaboration 1
Outline Motivation Recent results on branching fractions measurements ‣ B + → D +s Φ : annihilation diagram, sensitive to new physics ‣ Double charm decays, B → DD’ : measure γ , Φ s, Δ Γ s ‣ B 0s → D * ∓ π ± : weak exchange decay, help understand rescattering e fg ects in other modes ‣ B 0 → D *- π + π - π + : can be used as normalization channel for B 0 → D *- 𝝊 + ν 𝝊 ‣ B 0s → D 0 K - π + and B 0 → D 0 K + π - decays : measure γ 2
Outline Motivation Recent results on branching fractions measurements ★ Open charm decays of b hadrons o fg er a means by which both the electroweak and QCD sectors of the ‣ Standard Model (SM) may be tested B + → D +s Φ : annihilation diagram, sensitive to new physics ★ Measuring their Branching Fractions can help us to ‣ understand these processes better. In particular one can Double charm decays, B → DD’ : measure γ , Φ s, Δ Γ study if for certain suppressed modes long-distance ‣ processes are dominant B 0s → D * ∓ π ± : weak exchange decay, help understand rescattering e fg ects in other modes ★ Beyond measurements of CPV and the phases derived from the CKM matrix and rescattering e fg ects, ‣ B 0 → D *- π + π - π + and B 0 → D *- π + K - π + : can be used as rare B → DX decays may be used to search for new normalization channel for B 0 → D *- 𝝊 + ν 𝝊 physics in decays mediated via annihilation or exchange processes. ‣ B 0s → D 0 K - π + and B 0 → D 0 K + π - decays : measure γ 3
General strategy p + p + • Requirements on vertex separation, pointing quantities to ensure D candidates originate from B decay B D’ • Cross feeds are suppressed using PID information and kinematics D • Multivariate selections combining topological information to suppress light-quark background ‣ The branching fraction ratios are calculated normalized to decay modes with the same final states ( systematics largely canceled) Yields extracted B(B 0s → D +s D - ) N Bs → D+sD- f d from the invariant ϵ rel = mass distributions f s B(B 0 → D +s D - ) N B → D+sD- b fragmentation fraction Accounts for geometric ratio from: acceptance, detection and LHCb measurement trigger efficiencies arXiv:1301.5286 4
General strategy p + p + • Requirements on vertex separation, pointing quantities to ensure D candidates originate from B decay B D’ • Cross feeds are suppressed using PID information and kinematics D • Multivariate selections combining topological information to suppress light-quark background ★ All the analysis use the 2011 data set corresponding to 1fb -1 ‣ The branching fraction ratios are calculated normalized to decay modes with the same final states ( systematics largely canceled) Yields extracted B(B 0s → D +s D - ) N Bs → D+sD- f d from the invariant ϵ rel = mass distributions f s B(B 0 → D +s D - ) N B → D+sD- b fragmentation fraction Accounts for geometric ratio from: acceptance, detection and LHCb measurement trigger efficiencies arXiv:1301.5286 5
Search for the decay B + → D +s Φ LHCb-PAPER-2012-025 arXiv:1210.1089 ‣ Occurs only via annihilation of the B meson constituent quarks in SM • highly suppressed in the SM: BF predictions (neglecting rescattering) are (1-7) x 10 -7 Never seen before! BaBar measurement BF <1.9 x10 -6 (90%CL) ‣ Can be generated by rescattering from a process whose amplitude is of the color suppressed tree form ‣ Contributions from new Physics could enhance the BF or produce large CP asymmetries: charged Higgs can mediate the annihilation diagram ‣ Interest in annihilation type decays with |V ub | • tension between |V ub | and sin2 β in unitary fit • Measured BF of the decay B + → 𝝊 ν 6
Dominant amplitudes: color-favored tree ( T ) , color-suppressed tree ( C ) and penguin ( P ). These three amplitudes are approximately independent of the light “spectator” quark. Amplitudes considerably suppressed in comparison with them, all of which require participation of the spectator quark, are exchange (E), annihilation (A), and penguin annihilation (PA). E fg ects of the amplitudes E, A, and PA can also be generated by rescattering from processes whose amplitudes are color-favored tree (T), color-suppressed tree (C), or penguin (P) M.Gronau, D. London, J.L. Rosner. ArXiv:1211.5785v2 (2012) 7
Dominant amplitudes: color-favored tree ( T ) , color-suppressed tree ( C ) and penguin ( P ). These three amplitudes are approximately independent of the light “spectator” quark. Amplitudes considerably suppressed in comparison with them, all of which require participation of the spectator quark, are exchange (E), annihilation (A), and penguin annihilation (PA). E fg ects of the amplitudes E, A, and PA can also be generated by rescattering from processes whose amplitudes are color-favored tree (T), color-suppressed tree (C), or penguin (P)] M.Gronau, D. London, J.L. Rosner. ArXiv:1211.5785v2 (2012) 8
Search for the decay B + → D +s Φ 12 12 ) ) 2 2 c c B → D φ A LHCb B Candidates/(40 MeV/ Candidates/(40 MeV/ s B + → D +s (K + K + π + ) Φ (K + K - ) 10 10 B → D * φ +4.5 s - 0 + B → D K K* 6.7 s s - 0 + B → D * K K* 8 8 s s -2.6 • Normalized to: Combinatorics 6 6 B + → D +s (K + K + π + ) D 0 (K + K - ) 4 4 2 2 0 0 • Fit performed in 4 regions: 5200 5400 5600 5200 5400 5600 2 2 D KK Mass [MeV/ c ] D KK Mass [MeV/ c ] s s 12 12 ) ) 2 2 | m kk -m Φ | (MeV/c 2 ) c c C D Candidates/(40 MeV/ Candidates/(40 MeV/ 10 10 8 8 <20 (20,40) |cos θ k | 6 6 4 4 >0.4 A B 2 2 0 0 <0.4 C D 5200 5400 5600 5200 5400 5600 D KK Mass [MeV/ c 2 ] D KK Mass [MeV/ c 2 ] s s First observation + 1.25 B (B + → D +s Φ ) = 1.87 ± 0.19 ± 0.32(norm) x 10 -6 with 3.6 σ - 0.73 significance! Consistent with SM predictions given A cp (B + → D +s Φ ) = -0.01 ±0.41±0.03 the large uncertainties on both the theoretical and experimental values 9
B + → D +(s) K *0 and B + → D +(s) K *0 decays K *0 K *0 σ σ Candidates/4 Candidates/4 16 • Same Feynman diagrams: 25 a) b) LHCb 14 20 12 D + 10 15 8 Blue: 6 10 interpolation 4 5 2 0 0 5200 5300 5400 5200 5300 5400 Grey: μ ± σ 2 2 DK Mass (MeV/c ) DK Mass (MeV/c ) π π background σ σ 30 50 Candidates/4 Candidates/4 intervals c) d) 25 40 • Partially reconstructed 20 30 D +s background expected to be much 15 20 larger due to the large K *0 mass 10 window. Used sidebands to 10 5 extract expected yield 0 0 5200 5300 5400 5200 5300 5400 2 2 D K π Mass (MeV/c ) D K π Mass (MeV/c ) s s No signal hypothesis excluded at 89% CL +0.6 B (B + → D + K *0 ) = 0.8 x 10 -6 -0.5 Best limits set to-date! 10
Studies of B (s) → D D ’ decays LHCb-PAPER-2012-050 arXiv:1302.5854 ‣ Double charm decays of B meson can be interested for a variety of reasons • B d → DD and B d → D s D can be used to measure γ • sin2 β from B 0d → D + D - • sin2 β s and Δ Γ s / Γ s from B s → D s D s ‣ In addition, the study of B → DD’ can also provide better theoretical understanding of the processes that contribute to the B meson decay - (c) (a) W (b) s - c D b D s - s - b c W q ' D g s 0 c g - B c W b B (s) D B c q' D D q q q q q c • many of these decays are mediated by the W-exchange, penguin (short range) and also rescattering (long range) • important to know BF of these decays that might substantially alter branching fraction estimates based on the CKM matrix elements in processes that can be generated by rescattering through this modes 11
Studies of B (s) → D D ’ decays LHCb-PAPER-2012-050 arXiv:1302.5854 ‣ Double charm decays of B meson can be interested for a variety of reasons • B d → DD and B d → D s D can be used to measure γ • sin2 β from B 0d → D + D - • sin2 β s and Δ Γ s / Γ s from B s → D s D s ‣ In addition, the study of B → DD’ can also provide better theoretical understanding of the processes that contribute to the B meson decay - (c) (a) W (b) s - c D b D s - s - b c W q ' D g s 0 c g - B c W b B (s) D B c q' D D q q q q q c • many of these decays are mediated by the W-exchange, penguin (short range) and also rescattering (long range) • important to know BF of these decays that might substantially alter branching fraction estimates based on the CKM matrix elements in processes that can be generated by rescattering through this modes 12
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