Searches for BSM Physics in Rare B-decays at CMS

Transcription

1 Searches for SM Physics in Rare -decays at CMS Martino Margoni Universita` di Padova and INFN Motivation μμ K(*)μμ on behalf of the CMS Collaboration Constraints on New Physics 1

2 Motivation 2

3 Rare decays: New Physics probes Search for deviations from Standard Model (SM) predictions due to virtual contributions of new heavy particles in loop processes Compare experimental results with very precise SM expectations (uncertainty usually dominated by QCD) The most interesting processes are those that are strongly suppressed in the SM: Leptonic -decays, FCNC (K(*)μ+μ-) [but also LFV, CPV in 0 mixing, c & τ] New Physics (NP) could modify expectations by orders of magnitude [e.g. A. uras, arxiv: ] Rare decays can probe high scales potentially sensitive to NP beyond the direct reach of LHC: 3

4 Rare decays: New Physics probes Weak decay of hadron M into fnal state F described via an Effective Hamiltonian expressed by means of Operator Product Expansion: GF i A (M F )= F H eff M = V CKM C i (μ) F Q i (μ) M i 2 C i (μ): Q i (μ): Wilson Coeffcients (perturbative short distance couplings) Hadronic Matrix Elements (non -perturbative long distance effects) NP could modify Wilson Coeffcients C i (μ) and/or add new operators Q i (μ) Complementary information from different rare decays: μμ: K(*)μμ: Vector/axial interactions Scalar/Pseudoscalar interactions 4

5 μ μ Measurement of the 0s μ+μ- branching fraction and Search for 0 μ+μ- with the CMS Experiment [L = 5 fb-1 ( S=7 TeV)+20 fb-1 ( S=8 TeV)] Phys. Rev. Lett. 111, (2013) 5

6 μ μ FCNC process forbidden at tree level Helicity suppressed~(mμ/m)2 Cabibbo suppressed Vts(td) 2 R~10-9: Probe the SM! SM: suppression of d over s ~( Vtd / Vts )2: R(s R(d μ+μ- )=(3.2 ± 0.2) 10-9 [uras et al., Eur. Phys. J C72, 2172] μ+μ- )=(0.11 ± 0.01) 10-9 Uncertainties from fs (lattice),vtbvts,mt,τs 6

7 μ μ Golden mode to search for New Physics with scalar/pseudo-scalar interactions NP scenarios in the extended Higgs sector: May enhance or suppress the R wrt SM Show different tan β dependence: MSSM: R ~ tan6 β/m4a 2 Higgs Doublet Models: R ~ tan4 β [e.g. M. Ciuchini, Run2 Physics R(d μ μ ) vs R(s μ μ ): CMS Workshop, Venice April 2014] Test of Minimal Flavor Violation: general structure of SM FCNC is preserved, flavor violation depends only on CKM 7

8 μ μ Signal: Two isolated muons from a secondary vertex M(μ+μ-)~M(0s(d)) Momentum aligned with flight direction KG: Combinatorial from uncorrelated semileptonic decays Physical: Peaking hh' (h=misidentifed K, π) (R~10-7/10-5) Non Peaking hμν, hμμ, Λb pμν 8

9 μ μ Strategy: Use of dedicated dimuon trigger path: Hardware Trigger: PT(μ)>3 GeV (few khz) High Level Trigger 2011 (2012): Central region ( η <1.8): PT(μ)>4 (3) GeV, PT(μμ)>3.9 (4.9) GeV, 4.8<M(μμ)<6 GeV Forward region (1.8< η <2.2): PT(μ)>4 GeV, PT(μμ)>7, Prob(VTX)>0.5% DT-based muon identifcation: Exploits kinematic quantities, silicon-tracker ft information and combined silicon/muon track ft information Misidentifcation studied on MC/data control samples (K0 π π, Λ ε(π pπ, D* μ)<0.13%, ε(k D0π) μ)<0.22%, ε(p μ)<0.15% 9

10 Strategy: μ μ Events selected by means of a MVA exploiting kinematic, vertexing and isolation variables Δ R= (Δ η) +(Δ ϕ) 2 I= 2 P T () P T ()+ Δ R<0.7, P T >0.9GeV PT 10

11 Strategy: μ μ Events selected by means of a MVA exploiting kinematic, vertexing and isolation variables Measure event yields from an unbinned ft to M(μμ) R obtained relative to the normalization channel + K+J/ψ to avoid systematics from cross section & luminosity, and reduce effciency uncertainty: 0 s ( μ + μ Y S,Y N ϵs, ϵ N fu =0.256±0.020 fs Y S ϵn f U + )= ( K ϵ S YN fs Signal and Normalization Yields + J /ψ K ( + + μ+μ ) 5 )=(6.0±0.2)10 Signal and Normalization Effciencies Ratio between + and 0s fragmentation functions [LHCb, JHEP 04 (2013) 001] Data/MC agreement checked on s J/ψ φ control sample 11

12 Strategy: μ μ Combinatorial KG from Side ands extrapolation Semileptonic & Peaking KG estimated normalizing to + K+J/ψ N (Y X )= ϵ( X ) f Y + N ( K + J / ψ) ϵ ( ) f U (Y X ) ( + K + + Peaking Non-Peaking KG KG Peaking KG checked with independent analysis of J / ψ) hh' 12

13 Results: R(s R(0 μ μ : Results μ μ )=( (stat) -0.4 (syst) 10-9 ) (4.3 σ signifcance) μ+μ-)<1.1 x 95% CL Systematics from muon misidentifcation, R of rare KG decays (Λb pμν) and normalization of peaking KG 13

14 Comparison with other experiments ATLAS from 4.9 fb-1 using a DT analysis: R(s μ+μ-)<1.5 95% CL LHCb from 3 fb-1 using a DT analysis: R(s R(0 [ATLAS-CONF ] [LHCb: PRL 111, ] +1.1 μ+μ-)= (4.0 σ signifcance) μ+μ-)<7.4 x 95% CL 14 14

15 Comparison with other experiments History of a long search 0 μ+μ- : Let's wait for next LHC Runs 15

16 μ μ : Combination CMS-PAS-PH Preliminary CMS+LHCb combination Taking into account correlation from fs/fu R(s R(0 LHCb-CONF [LHCb, JHEP 04 (2013) 001] μ+μ-)=(2.9±0.7) 10-9 (>5 σ signifcance) +1.6 μ+μ-)=( ) (<3 σ signifcance) s μ+μ- 0 μ+μ- 16

17 What Next on 300 fb-1 μ μ? [CMS PAS FTR ] 3000 fb-1 Detector Upgrade Year now Expected number of events assuming SM Rs High Luminosity-LHC: Inner tracker with improved granularity & muon detector with extended coverage 17

18 0 K μ μ *0 Angular analysis and branching fraction measurement of the decay 0 K*0μ+μ- [L = 5.2 fb-1 ( S=7 TeV)] Phys. Lett. 727, (2013)

19 K μ μ * FCNC process forbidden at tree level, R~10-6: Probe the SM! Amplitudes expressed using OPE in terms of: Sensitive to the effects of NP in photon, vector and axial-vector couplings which can enter at the same order as SM contributions Complementary information to μ+μ- Hadronic Form Factors (accuracy ~20%) [A. arucha et al. arxiv ] Wilson coeffcients Ceff7, Ceff9, Ceff10 [A. Ali et al.,prd , Z. Phys. C ] Clean theoretical predictions expecially at low q2=m2(μ+μ-) Experimentally clean signature 19

20 K μ μ * Kinematics of the decay V μ+μ - (V=K*, φ, ρ) determined by three angles: θl, θk, ϕ Event Yields reconstructed in bins of Differential Amplitude: q2=m2(μ+μ-) Observables Include: Differential ranching Ratio d/dq2 AF (forward-backward muon asymmetry) FL (fraction of longitudinally polarized K*) 20

21 K μ μ * Kinematics of the decay V μ+μ - (V=K*, φ, ρ) determined by three angles: θl, θk, ϕ Event Yields reconstructed in bins of Differential Amplitude: q2=m2(μ+μ-) FS: Fraction of spinless Kπ (S-wave) combination AS: Interference amplitude between S-wave and P-wave decays FS=0.01±0.01, AS=-0.10±0.01 ftted on the 0 K*J/ψ control sample21

22 Strategy: K μ μ * Measure event yield YS, AF and FL from an unbinned simultaneous ft to M(Kπμμ), cos(θk) and cos(θl) in bins of q2 PDF (M, cos θ K, cos θl )=Y S S ( M ) S (cos θ K,cos θl ) ϵ(cos θ K, cos θl ) Signal +Y c C (M ) C (cosθ K ) C (cosθ l ) Combinatorial +Y p P (M ) P (cos θ K ) P (cosθ l ) Peaking KG from 0 Event Yields Y S,Y c,y p S (cos θ K,cos θ l ), ϵ(cos θ K,cos θl ) Signal 2D angular shape and effciency Mass PDFs S (M ), C (M ), P (M ) C (cos θ K (l) ), P (cosθ K (l ) ) Angular KG PDFs d/dq2 obtained relative to the normalization channel d ( K μ 2 dq Y S,Y N ϵs, ϵ N + μ K*J/ψ(ψ') ) = Y S ϵn 0 ( K ϵ YN S 0 J /ψ K 0 μ + μ K*J/ψ: ) Signal and Normalization Yields Signal and Normalization Effciencies 22

23 Strategy: K μ μ * Measure event yield YS, AF and FL from an unbinned simultaneous ft to M(Kπμμ), cos(θk) and cos(θl) in bins of q2 flavor tagging from Kπ charge KG PDFs: Combinatorial from MC Peaking parameterized on MC K*J/ψ(ψ') 23

24 K μ μ : Results * Results consistent with SM Theoretical and experimental errors comparable Systematics from Peaking KG mass shape, cos(θl,k) KG shape and S-wave contribution 24

25 Comparison with other experiments LHCb measures the position of the zero-crossing point theoretically clean [JHEP ]: q02=4.9 ±0.9 GeV2 In agreement with the SM [e.g. M. eneke et al., Eur. Phys. J C47, 625] 25

26 Comparison with other experiments What Next from CMS? Results of 8 TeV data analysis expected soon: d/dq2, FL, AF, AF zero crossing-point Use of new angular variables with small Form-Factor dependence 26

27 Constraints on NP 27

28 Constraints from SM4: SM with a 4 th generation MFV: Flavor Violation governed only by μ μ [K.A. Petridis, Moriond QCD 2014, D.M. Straub, arxiv: ] CMS+LHCb Preliminary Combination CKM matrix R(d)/R(s) extremely sensitive probe of NP Result in agreement with SM [0.4 σ for s and 1.7 σ for d] The focus now is on R(d) and on the ratio R(s)/R(d) LHCb (after upgrade): measure 35% with 50 fb-1 28

29 LHCb K μ μ : Hint of NP? * Variables free from Form Factor contributions [JHEP 05, 137] 3.7 σ discrepancy in P'5 in 1 fb-1 4.3<q2<8.68 GeV2 [PRL 111, ] Possible interpretation as a NP contribution to Wilson coeffcient C9 Low q2 K*μ+μ- bins alone 3.9σ discrepancy wrt SM Combined analysis from K*μμ, Xsγ, Xsμμ, K*γ, s μμ [S. Descotes-Genon et al., PRD 88, ] Diffcult to explain with SUSY Consistent with a Z' with m~7 TeV 29

30 LHCb K μ μ : Hint of NP? * Variables free from Form Factor contributions [JHEP 05, 137] 3.7 σ discrepancy in P'5 in 1 fb-1 4.3<q2<8.68 GeV2 [PRL 111, ] Possible interpretation as a NP contribution to Wilson coeffcient C9 Resulting C9NP would imply an inclusive R( of ~ 25% in 1<q2<6 GeV2 and q2>14.4 GeV2 Xs l+l- ) suppression Recent aar R( XSl+l-) result in the high-q2 region shows a ~ 2 σ excess wrt SM prediction in both the XSμ+μ- and XSe+e- channels LHCb effect not confrmed by aar [PRL 112, ] 30

31 Conclusions 31

32 Conclusions Rare decays are an excellent laboratory for the search for physics beyond the SM In the last few years several new measurements from LHC & -Factories experiments released with impressive experimental precision Almost all the results are in agreement with expectations but some tension is present in some sectors (i.e. K*μμ, τν, D(*)τν,...) Strong constraints on NP models from flavor measurements Rich program of measurements is expected from LHC/elle II experiments in the coming years Chances to discover/understand NP in flavor sector in the near Future? 32

33 ackup 33

34 K μ μ : Results * Perturbative region q02=1<q2<6 GeV2: 34

35 K μ μ : Hint of NP? * Study additional variables free from FF contributions [JHEP 05, 137 (2013)] 3.7 σ discrepancy in P'5 in 1 fb-1 [PRL 111, (2013)] 4.3<q2<8.68 GeV2 Possible interpretation as a NP contribution to Wilson coeff. C9 Analysis of the full 3 fb-1 statistics in progress P'5 tension correlated with other minor tensions (too small Rs) Diffcult to explain with SUSY Consistent with a Z' with m~7 TeV Measure other Kμμ decays 35

36 K μ μ [LHCb-Paper ] K* μ+μ- tension motivates studies of AI, AF New Old Update of previous AI measurement (4.4 σ discrepancy integrated on q2) is now in agreement with SM Improvements in effciency ratio ε(kμμ)/ε(j/ψk) (J/ψK0)/(J/ψK+) correction applied vs K momentum AF in agreement with SM 36

37 K μ μ [LHCb-Paper ] K* μ+μ- tension motivates studies of differential Rs All the results are consistent with SM at <2.2 σ ut all of them are lower than the predictions... 37

38 What Next on K (*) Measurements of related b μ μ & friends? dμμ channels are welcome to reveal information on Minimal Flavor Violation nature of New Physics LHCb: R(+ π+μ+μ- )=(2.4±0.6±0.2)10-8 in agreement with MFV [JHEP 12, 125 (2012)] R(+ π+μ+μ- )/R(+ K+μ+μ- ) would provide a comparison of Vtd / Vts from penguin processes and box processes (Δms/Δmd) Improve theoretically very clean measurements of semi-inclusive Xs/dll, (Xs/dγ) 38

39 aar Xs l l q02 [PRL 112, ] Perturbative region q02=1<q2<6 GeV2: R=(1.60 aar ±0.18)10-6 In agreement with SM (1.59±0.11)10-6 q2 region above ψ(2s) : R=(0.57 aar ±0.0)10-6 ~2 σ above SM (0.24±0.07)10-6 LHCb effect not confrmed by XS=K K* aar 39