PoS(EPS-HEP2015)543. Measurements of CP violation in B mixing through B J/ψ X decays at LHCb. Greig A. Cowan

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1 Meaurement of CP violation in B mixing through B J/ψ X decay at Univerity of Edinburgh g.cowan@ed.ac.uk B meon provide an ideal laboratory for meaurement of CP violation and earche for CP violation beyond the Standard Model. Recent meaurement of the mixing phae of the B and B meon, φ and inβ, uing decay to J/ψX final tate are preented. In view of future improved meaurement, a good undertanding of pollution from ub-leading penguin topologie in thee decay i needed. Thoe can be probed uing uppreed decay like B J/ψK S and B J/ψK. Recent reult uing thee decay mode are preented. PoS(EPS-HEP15)543 The European Phyical Society Conference on High Energy Phyic 9 July 15 Vienna, Autria On behalf of the collaboration. Speaker. c Copyright owned by the author() under the term of the Creative Common Attribution-NonCommercial-NoDerivative 4. International Licene (CC BY-NC-ND 4.).

2 CP violation in B J/ψ X decay B b W + c c J/ψ h + h B b u, c, t W + c c J/ψ h + h Figure 1: Feynman diagram howing B meon mixing (left) and example b cc tranition via a treelevel (middle) and penguin proce (right). 1. CP violation in B mixing and decay In both the B and B meon ytem a CP violating phae φ d, arie through the interference of B () meon decaying via b cc tranition to CP eigentate and thoe decaying after ocillation 1. Figure 1 how example of thee mixing and decay procee for the B ytem. In the Standard Model (SM), ignoring ub-leading penguin procee, φ i equal to β, where β arg[ (V t Vtb )/(V cvcb )] with V i j being element of the quark-mixing matrix [1, ]. Similarly, in the B ytem the φ d i equal to β, where β arg[ (V cd Vcb )/(V tdvtb )]. Global fit to experimental data give precie determination: φ =.365 ±.1rad and inβ = [3]. Thee phae could be modified if non-sm particle contribute to the B meon ocillation [4, 5] and, therefore, are the ubject of many experimental meaurement. Typically the meaurement require the tudy of the CP aymmetry a a function of the B meon decay time, t. The aymmetry i defined a, A CP (t) Γ B f Γ B f Γ B f + Γ B f = S f in( mt) C f co( mt) coh( Γt/) + A Γ inh( Γt/), (1.1) where Γ B f i the rate of the B f decay, C f 1 λ f, S 1+ λ f f Im(λ f ) and A 1+ λ f Γ Re(λ f ). Here, 1+ λ f m i the ocillation frequency of the B meon ytem, Γ i the width difference between the light and heavy eigentate of the B ytem. The parameter λ f q p A f decribe CP violation in the interference between mixing and decay, with the CP violating phae defined by φ arg(λ f ). Thee proceeding will firt review the experimental meaurement of the CP violating phae, focuing on recent analye of B J/ψ X decay (J/ψ µ + µ ) from the collaboration that have been obtained uing 3. fb 1 of pp colliion data recorded at a centre-of-ma energie of = 7 and 8TeV at the Large Hadron Collider. A will become clear, the increaing preciion of thee meaurement now make it eential to tet the aumption that b cc penguin procee are mall and therefore have little contribution to the CP violating phae. A uch, the econd half of the proceeding will focu on the latet experimental development in thi area. 1 A f PoS(EPS-HEP15)543. inβ from B J/ψ K S The time-dependent analyi of the CP aymmetry in B J/ψ K S decay allow a meaurement of inβ. The latet reult [6] from the collaboration ued 4156 flavour-tagged candidate (Figure (a)) to meaure the parameter S J/ψ K = ±.35 ±. and C S J/ψ K = S 1 Charge-conjugation i implicit unle tated otherwie.

3 CP violation in B J/ψ X decay Candidate / (1 MeV/c ) (a) m (MeV/c ) Signal yield aymmetry t (p) Figure : (a) Ditribution of the J/ψ K S invariant ma for B J/ψ K S candidate with the ignal (bluedotted line) and background (red-dotted) component of the maximum likelihood fit hown. (b) The ignal aymmetry a a function of B decay time..38 ±.3 ±.5, where S J/ψ K S inβ and the firt uncertainty i of tatitical origin and the econd i ytematic. The correlation between the parameter i ρ(s,c) =.483. Figure (b) how the ignal aymmetry a a function of the decay time, where the inuoidal ocillation i clearly viible. The dominant ytematic uncertainty come from knowledge of the tagging aymmetry of the background event. The reult i conitent with the exiting world average and of imilar preciion to exiting meaurement, a hown in Figure 3(a). 3. φ from B J/ψ K + K and B J/ψ π + π In the B ytem the meaurement of φ can be performed via a time-dependent analyi of B J/ψ φ (φ K + K ) and B J/ψ π + π decay. In thee cae the final tate are admixture of both CP-odd and CP-even component uch that the decay angle information mut alo be ued to dientangle the CP tate. Thi give rie to a rich tructure and allow the imultaneou determination of many B mixing parameter from the B J/ψ φ decay, uch a φ, m,γ, Γ, λ f. The collaboration ha meaured thee parameter uing 96 B J/ψ φ decay [8] with an effective tagging efficiency of 3.%, leading to φ =.58 ±.49 ±.6 rad and λ =.964 ±.19 ±.7. Only a % contribution from the K + K S-wave i found in a 6MeV/c window around the φ(1) meon. The main ytematic uncertaintie on the meaurement of φ come from the decription of the angular efficiency of the detector and event election requirement. In the cae of B J/ψ π + π a four-dimenional amplitude analyi i performed to undertand tructure in the full π + π pectrum, finding it to be > 97.7% 95% CL [9] with the main ytematic uncertainty coming from the π + π reonance model. The meaured value of the CP parameter from thi analyi are [1] φ =.7 ±.68 ±.8 rad and λ =.894 ±.5 ±.1. Auming CP violation in decay i the ame in both the K + K and π + π mode i it poible to combining the meaurement [8] giving the mot precie determination of the parameter φ =.1 ±.39 rad and λ =.957 ±.17, where tatitical and ytematic uncertaintie have been combined in quadrature. Figure 3(b) how the current tatu of all mea- (b) PoS(EPS-HEP15)543 3

4 CP violation in B J/ψ X decay (a) (b) Figure 3: Summary of meaurement and the global fit reult for (a) inβ and (b) φ and Γ [7]. urement of φ and Γ and the global fit, which i conitent with the SM prediction [3, 11, 1], indicating that any contribution from beyond-the-sm phyic i a mall. 4. Controlling penguin pollution The contribution to φ d, from penguin decay topologie are uppreed by ε = V u /(1 V u ).5 relative to the tree decay and, a dicued in Section 1, aumed to be negligible. Given the preciion with which φ d, are now known and the projected enitivity in the near-future it i it i eential that uch penguin pollution" i contrained before trying to ue thee CP violating phae in earche for new phyic. Since the hift in φ d, from uch contribution are difficult to calculate due to the non-perturbative nature of QCDit i crucial to make experimental meaurement of the ize of the penguin contribution. Variou approache exit to deal with thi problem [13, 14, 15, 16, 17, 18]. One technique i to meaure the CP violating phae for different polariation of the final tate, any oberved difference then being interpreted a due to the pollution. Thi approach ha been applied to the analyi of B J/ψ φ decay [8] and no evidence of a polariation-dependent CP violating phae i oberved. The econd i to tudy decay where the penguin-to-tree ratio i not uppreed, a i dicued in more detail below. PoS(EPS-HEP15) B J/ψK (89) and B J/ψρ A uitable channel where the penguin amplitude i not uppreed relative to the tree i B J/ψK (89) [13, 15, 16]. The amplitude for thi mode and B J/ψφ are given by, [ A(B (J/ψ K ) f ) = λa f 1 a f e iθ f e iγ], A(B (J/ψ φ) f ) = (1 λ /)A f [ 1 + εa f e iθ f e iγ], (4.1) where f repreent the polariation of the final tate, γ i an angle of the CKM triangle and A ( ) f i a CP-conerving hadronic matrix element. The parameter a ( ) f and θ ( ) f are the magnitude and phae of the penguin amplitude, repectively. The firt tage toward contraining the ize of the penguin phae i to perform an angular analyi of the B J/ψK decay product. Thi allow 4

5 CP violation in B J/ψ X decay Candidate / (11.1 MeV/c ) Data Total PDF B ignal m [MeV/c J/ψ K ] π + B ignal Combinatorial bkg b Λ J/ψ pπ Figure 4: Ditribution of J/ψK invariant ma for all B J/ψK candidate. a a = θ = ( ) 39 % C.L. 68 % C.L. 9 % C.L. C (B J/ψρ ) S (B J/ψρ ) A CP (B J/ψK ) H (B J/ψρ ) H (B J/ψK ) θ [deg] Figure 5: Limit on the penguin parameter a and θ obtained from interecting contour derived from CP aymmetrie and branching fraction meaurement in B J/ψK and B J/ψρ. Superimpoed are the confidence-level contour from a χ fit to the data. the branching fraction of the decay to be meaured along with the polariation fraction of the final tate. By eparating the ample into B and B ubet, the CP aymmetrie for each polariation can alo be meaured after accounting for production and detection aymmetrie [19, ]. The collaboration ha recently publihed [1] the reult of thi analyi uing a ample of 18 B J/ψK ignal event a een in Figure 7. The branching fraction i meaured to be B(B J/ψ K ) = (4.13 ±.16 ±.5 ±.4 ( f / f d )) 1 5 and the CP aymmetrie are all conitent with zero at a preciion of 1%, dominated by the tatitical uncertainty. The econd tage then relate thee experimental obervable to the penguin parameter in both B J/ψK and B J/ψφ. A χ fit i performed to meaure value for the penguin parameter uing the aumption of SU(3) flavour ymmetry (a f = a f and θ f = θ f ), a light-cone um rule calculation [] of A f /A f and γ = ( ) [3]. Thee are ubequently tranlated into value for the penguin phae hift that are hown to be conitent with zero, albeit with large uncertaintie of.5 rad. The dominate ytematic uncertainty from the theoretical calculation of A f /A f can be removed and the overall tatitical uncertainty reduced by including complementary information on the CP violating phae meaured by the collaboration in each polariation tate of the B J/ψρ (ρ π + π ) channel [3]. Figure 5 how the contraint from each meaurement for one polariation tate. The central value of the parameter are meaured uing a χ fit, the reult of which i hown by the black contour in Figure 5. Again, the penguin phae hift are found to be conitent with zero, but now determined to a preciion of.15 rad through the additional information from the B J/ψρ channel. Thi hould be compared with the current experimental preciion on φ d, that are at.3 rad. PoS(EPS-HEP15) B J/ψK S The golden mode for controlling the penguin phae hift to φ d i B J/ψK S. Thi i re- 5

6 CP violation in B J/ψ X decay ) Event / ( MeV/c Downtream K S (a) Candidate / (.15 p ) Downtream K S (b) Pull (MeV/c ) m J/ψ KS Pull t (p) Figure 6: Ditribution of (a) J/ψK S invariant ma and (b) decay time of B J/ψK S candidate. In (a) the ditribution before (red) and after (black) the machine learning election i applied are hown. lated to B J/ψK S via the U-pin ymmetry of trong interaction [13] but i CKM uppreed making it more difficult to oberve the decay. The collaboration ha recently [4] ued machine learning technique to uppre background from combinatoric and mi-recontructed B J/ψ K decay to oberve B J/ψK S. Figure 6 how the ditribution of invariant ma and B decay time for a ubet of B J/ψK S candidate. In total 9 ignal event are found with an effective tagging efficiency of 4%. Thee are ued to meaure the decay time dependent CP violation obervable A Γ,C,S defined in Equation (1.1). All are found to be conitent with zero. The large tatitical uncertainty on thee meaurement i inufficient to contrain the ize of the penguin hift to φ d but thi proof-of-principle meaurement indicate what i poible with future dataet collected by. 4.3 B ψ(s)k + π The collaboration ha recently oberved [5] the B ψ(s)k + π decay, meauring the ratio of branching ratio B(B ψ(s)k + π )/B(B ψ(s)k + π ) = 5.38±.36 (tat)±. (yt) ±.31 ( f / f d )%. Figure 7 how the ditribution of ψ(s)k + π and K + π invariant mae from the ample. Uing a four-dimenional amplitude analyi the fraction of decay proceeding via an intermediate K (89) meon i meaured to be.645 ±.49 (tat) ±.49 (yt) and it longitudinal polariation fraction, f =.54 ±.56 (tat) ±.9 (yt). No exotic Z + ψ(s)π + component [6] wa oberved with the current data ample but thi mode could prove ueful in the future to help undertand the nature of the exotic charmonium tate. In addition, uing the ame technique a dicued in Section 4.1, thi mode could help to contrain the ize of penguin pollution to the CP violating phae in B ψ(s)φ decay. PoS(EPS-HEP15) Summary Thee proceeding have preented the latet meaurement of CP violation in B meon mixing uing B J/ψ X decay collected by the experiment during pp colliion run at the LHC 6

7 CP violation in B J/ψ X decay Candidate/ (6 MeV/c ) Pull (a) + m(ψ(s) K π ) [MeV/c ] ) Candidate / (.4 GeV/c Pull (b) m(k π ) [GeV/c ] Figure -4-7: Ditribution of (a) ψ()k + π and (b) K + π invariant mae of B -6 ψ()k + π candidate. In (b) the contribution from the K (89) (red-dahed), NR (green-dotted) and background (grey-daheddotted) component are viible. at = 7 and 8TeV. Thee repreent the mot precie determination of the CP violating phae φ uing B J/ψ φ and B J/ψ π + π decay along with a very competitive meaurement of the correponding phae in the B ytem uing B J/ψ K S decay. With thi improved preciion it i now eential that contribution to thee decay procee from uppreed, but hard-to-calculate, penguin diagram are under control. By making ue of B meon decay where the penguin decay procee are not uppreed relative to the tree-level contribution (uch a B J/ψ K, B J/ψ ρ and B J/ψ K S ) the collaboration ha been able to contrain the ize of the ocalled penguin pollution, finding it to be mall. The collaboration look forward to collecting even more data during Run- of the LHC and beyond, where making further preciion meaurement of CP violating parameter will be eential a we earch for ign of beyond-the-sm phyic. Acknowledgement The author would like to thank Alex Lenz for commenting on the text. Reference [1] M. Kobayahi and T. Makawa, Prog. Theor. Phy. 49 (1973) 65. [] N. Cabibbo, Phy. Rev. Lett. 1 (1963) 531. [3] J. Charle et al., Phy. Rev. D 91 (15) 7, 737 [arxiv: [hep-ph]]. [4] A. J. Bura, PoS EPS-HEP9 (9) 4 [arxiv:91.13 [hep-ph]]. [5] C. W. Chiang, A. Datta, M. Duraiamy, D. London, M. Nagahima and A. Szynkman, JHEP 14 (1) 31 [arxiv:91.99 [hep-ph]]. [6] R. Aaij et al. [ Collaboration], Phy. Rev. Lett. 115 (15) 3, 3161 [arxiv: [hep-ex]]. [7] Y. Amhi et al. [Heavy Flavor Averaging Group (HFAG) Collaboration], arxiv: [hep-ex] and online update at [8] R. Aaij et al. [ Collaboration], Phy. Rev. Lett. 114 (15) 4, 4181 [arxiv: [hep-ex]]. PoS(EPS-HEP15)543 7

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