Rare, radiative and electroweak penguin decays of heavy flavour hadrons at LHCb Carla Marin Benito on behalf of the LHCb collaboration Rencontres de Moriond Electroweak La Thuile, Italy, 17-23 March 2019
Rare decays of b hadrons Flavour-changing neutral-currents (FCNC) forbidden at tree-level in SM: ✁ ✁ γ γ u, c, t W − u, c, t W − s s b b u, c, t H − Sensitive to new particles at higher scales than direct searches. Model-independent description: Operator Product Expansion. � � � C SM + C NP H eff ∝ · O i i i i ◮ Wilson Coefficients ( C i ) are extracted from global fits to the data. ◮ Any deviation from SM calculations would point to New Physics effects. Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 1 / 15
Experimental status Several deviations in differential branching ratios (BR) and angular observables in b → s ℓ + ℓ − : JHEP 06 (2014) 133 LCSR Lattice Data LCSR Lattice Data LCSR Lattice Data 20 ] ] ] 2 2 2 − − − /GeV 5 → µ µ /GeV 5 → µ µ /GeV → µ µ + + + 0 0 + + *+ + B K B K B K LHCb LHCb 15 LHCb 4 4 4 4 4 c c c × 3 × 3 × 10 -8 -8 -8 [10 [10 [10 2 2 2 2 2 5 q q q 1 1 /d /d /d B B B 0 0 0 d d d 0 5 10 15 20 0 5 10 15 20 0 5 10 15 20 2 2 2 q 2 [GeV / c 4 ] q 2 [GeV / c 4 ] q 2 [GeV / c 4 ] JHEP 09 (2015) 179 , JHEP 06 (2015) 115 , PhysRevD.93.074501 , JHEP 02 (2016) 104 BR theory predictions affected by large uncertainties Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 2 / 15
A sign of New Physics? Global fits point to additional contributions to C 9 or C 9 and C 10 From Eur.Phys.J.C(2017)77:377 See also Phys. J. C (2015) 75: 382, Nucl Phys B 909 (2016) 737-777, JHEP 06 (2016) 092, Phys. Rev. D 96, 093006 (2017), JHEP 1801 (2018) 093, etc. And talks this afternoon and tomorrow! Several NP model proposed to accommodate the data: Leptoquarks [eg. Phys.Rev.D94,115005] , Z’ [eg. Phys.Rev.D93,074003] , etc. → Crucial to improve these measurements and add new modes! → Clean tests provided by Lepton Flavour Universality measurements, see talk by T. Humair with new results! Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 3 / 15
Latest results from LHCb Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 4 / 15
Search for the very rare decay B + → µ + µ − µ + ν µ arXiv:1812.06004 Highly-suppressed decay with BR ∝ | V ub | 2 ◮ Run 1 + 2016 data (4 . 7 fb − 1 ) ) 160 2 c Total Fit Candidates / (50 MeV/ LHCb 140 Data 2011-16 ◮ M min / c 2 Combinatorial µ + µ − < 980 MeV 120 Misidentified Partially reconstructed 100 ◮ Exploit corrected mass variable: Prediction from 80 PAN (2018) 81:347 � µµµ + p T ′ 2 + p T ′ M 2 M corr = 60 40 ◮ Veto charmonium resonances 20 0 ◮ Normalize to B + → J /ψ K + 4000 5000 6000 7000 2 M [MeV/ c ] corr Only one theoretical estimate (vector-meson dominance): B ( B + → µ + µ − µ + ν µ ) ∼ 1 . 3 × 10 − 7 [PAN (2018) 81:347] No signal observed, best world limit set B ( B + → µ + µ − µ + ν µ ) < 1 . 6 × 10 − 8 at 95% CL. Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 5 / 15
Angular analysis of Λ 0 b → Λ µ + µ − JHEP 09 (2018) 146 It is a b → s ℓ + ℓ − transition complementary to B 0 → K ∗ 0 µ + µ − Richer angular distribution due to baryon spin and polarisation Analysis performed with data recorded during 2011 – 2016 (5 fb − 1 ) Focus on low recoil region, 15 < q 2 < 20 GeV 2 / c 4 Analysis exploits method of moments [JHEP 11 (2017) 138] : 34 d 5 Γ 3 � d Ω = K i f i (Ω) 32 π 2 i ◮ f i angular functions ◮ K i coefficients [Phys. Lett. B724 (2013) 27] Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 6 / 15
Angular analysis of Λ 0 b → Λ µ + µ − JHEP 09 (2018) 146 Full set of angular observables measured for the first time: All parameters compatible with SM predictions K 11 ,..., 34 compatible with no initial Λ 0 b polarization Value 0.4 LHCb 0.2 0 − 0.2 − SM prediction 0.4 0 5 10 K i Asymmetries measured from combination of observables FB = 3 A ℓ 2 K 3 = − 0 . 39 ± 0 . 04 ± 0 . 01 FB = K 4 + 1 A h 2 K 5 = − 0 . 30 ± 0 . 05 ± 0 . 02 A h ℓ FB = 3 4 K 6 = +0 . 25 ± 0 . 04 ± 0 . 01 Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 7 / 15
Search for Λ 0 b → Λγ LHCb-PAPER-2019-010 Λ 0 b → Λγ is a FCNC b → s γ transition: H eff ∝ V ∗ ts V tb ( C 7 O 7 + C ′ 7 O ′ 7 ) BR in SM: 10 − 7 − 10 − 5 , large uncertainties from form factors b → Λγ ) < 1 . 9 × 10 − 3 at 90% CL. Best limit so far by CDF: B ( Λ 0 → large room for improvement Λ 0 b → Λγ offers access to the photon polarization [J.Phys.G24 (1998) 979] Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 8 / 15
Search for Λ 0 b → Λγ LHCb-PAPER-2019-010 Search performed using 2016 data (1 . 7 fb − 1 ) Very challenging mode: p ◮ long Λ lifetime π − Λ ◮ no direction from γ cluster PV Λ 0 b → cannot reconstruct Λ 0 b γ decay vertex! Dedicated online and offline reconstruction: ◮ Λ 0 b momentum as direct sum of Λ and γ momenta ◮ large combinatorial background expected → large signal to background separation is crucial Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 9 / 15
Search for Λ 0 b → Λγ LHCb-PAPER-2019-010 High performance BDT using XGBoost algorithm Output requirement optimised using Punzi figure of merit: ǫ S FoM = σ/ 2 + √ N B , σ = 5 Working point: 99 . 8% background rejection with 1 / 3 signal efficiency Exploit neutral PID tools to reject background from π 0 [LHCb-PUB-2015-016] Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 10 / 15
Search for Λ 0 b → Λγ LHCb-PAPER-2019-010 Use well-know B 0 → K ∗ 0 γ as normalization mode: N ( Λ 0 f B 0 × B ( Λ 0 f Λ 0 B ( K ∗ 0 → K + π − ) × ǫ ( Λ 0 B ( Λ → p π − ) b → Λγ ) b → Λγ ) b → Λγ ) N ( B 0 → K ∗ 0 γ ) = b B ( B 0 → K ∗ 0 γ ) × ǫ ( B 0 → K ∗ 0 γ ) f Λ 0 f B 0 from recent LHCb measurement at 13 TeV [arXiv:1902.06794] b Input branching fractions from PDG Efficiencies from simulation and calibration samples Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 11 / 15
Search for Λ 0 b → Λγ LHCb-PAPER-2019-010 From simultaneous unbinned maximum likelihood fit: Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 12 / 15
Search for Λ 0 b → Λγ LHCb-PAPER-2019-010 From simultaneous unbinned maximum likelihood fit: Signal excess with 5 . 6 σ significance → first observation of Λ 0 b → Λγ Branching fraction measurement within range of SM predictions B ( Λ 0 b → Λγ ) = (7 . 1 ± 1 . 5 ± 0 . 6 ± 0 . 7) × 10 − 6 Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 12 / 15
Search for Λ 0 b → Λγ LHCb-PAPER-2019-010 Analysis statistically limited. Main systematics: Source Uncertainty (%) Data/simulation agreement 7 . 7 Λ 0 b fit model 3 . 0 B 0 → K ∗ 0 γ backgrounds 2 . 7 Size of simulated samples 1 . 7 Efficiency ratio 0 . 7 Sum in quadrature 8 . 9 f Λ 0 b / f B 0 8 . 7 Input branching fractions 3 . 0 Sum in quadrature 9 . 2 from external measurements. Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 13 / 15
Summary Rare FCNC b -hadron decays provide high sensitivity to NP effects Experimental status Tensions wrt SM in both differential BR and angular observables Updates and new analyses ongoing to confirm them Lepton Flavour Universality observables provide complementary tests (see talk by T. Humair tomorrow) Latest results from LHCb Best world limit on B + → µ + µ − µ + ν µ Full angular analysis of Λ 0 b → Λ µ + µ − : compatible with SM First observation of Λ 0 b → Λγ : first step towards photon polarisation measurement Many more results with Run 2 data are underway Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 14 / 15
Summary Rare FCNC b -hadron decays provide high sensitivity to NP effects Experimental status Tensions wrt SM in both differential BR and angular observables Updates and new analyses ongoing to confirm them Lepton Flavour Universality observables provide complementary tests (see talk by T. Humair tomorrow) Latest results from LHCb Best world limit on B + → µ + µ − µ + ν µ Full angular analysis of Λ 0 b → Λ µ + µ − : compatible with SM First observation of Λ 0 b → Λγ : first step towards photon polarisation measurement Many more results with Run 2 data are underway Stay tuned! Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 14 / 15
Thanks for the attention! Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 15 / 15
BACK-UP Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 16 / 15
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