Measurements of strong phase in D 0 Kπ decay and y CP via quantum- correla>ons at BESIII

Transcription

1 Miami 13 DEC/13 1 Measurements of strong phase in D Kπ decay and y CP via quantum- correla>ons at BESIII Hajime Muramatsu, University of Minnesota (for the BESIII collabora>on - Strong phase in D Kπ decay - y CP measurement

2 Miami 13 DEC/13 Beijing Electron Positron Collider (BEPC- II - A symmetric e + e - collider, opera>ng at Ecm ~. ~4.6 GeV (Charm factory!. - It s in Beijing: Easy access to the downtown area of Beijing with a nearby subway sta>on! Storage ring Linac BESIII detector Coun>ng room: where I take shi\s Where I sleep: Next to a Chinese restaurant

3 Miami 13 DEC/13 3 A powerful general purpose detector. BESIII detector Excellent neutral and charged par8cle detec8on and iden8fica8on with a large coverage. Magnet: 1 T Super conducting MDC: small cell & He gas xy =13 m s p /p de/dx=6% TOF: T = 9 ps Barrel 11 ps Endcap EMCAL: CsI crystal E/E GeV φ,z =.5~.7 cm/ E Data Acquisition: Event rate = 3 khz Throughput ~ 5 MB/s Muon ID: 8~9 layer RPC RΦ =1.4 cm~1.7 cm Trigger: Tracks & Showers Pipelined; Latency = 6.4 s

4 Miami 13 DEC/13 4 J/ψ peak Data samples we have : 1. B J/ψ decays and some scan in the vicinity of the peak. ψ(3686 peak :.5 B ψ(3686 decays and some scan in the vicinity of the peak. - Above DDP Ecm = 4.9 GeV, Ecm = 4.6 Ecm = 4.36 GeV, plus some scan samples as well. The above samples have been producing very rich Physics results such as hadron spectroscopy of Charmonia (e.g., h c /η c and of Charmonium- like states (X/Y/Z. - Today, I report recent results from BESIII based on a sample that was taken near DDj = GeV

5 Miami 13 DEC/13 5 Sample at E cm = GeV - The total integrated luminosity of.9 Q - 1 at this energy point is the largest in the world to date. - In the selected hadronic events (mul8ple reconstructed charged/ neutral hadrons or tracks, they are dominated by; e + e - γ * ψ(377 and e + e - γ * (qq light hadrons in which σ(e + e - ψ(377 hadrons/σ(e + e - NR hadrons ~ 1/. - Once ψ(377 is produced, it predominantly decays into a DDP pair. For instance, we have ~1 M D (or DP decays in this sample. - Rela8vely clean event environment. - When the two D mesons are reconstructed, the sample becomes almost background free.

6 Miami 13 DEC/13 6 Things can be done with the sample taken at or around E cm = GeV - There are many interes8ng possible topics to study in D (weak decays based on our sample, such as; - pure leptonic decays (e.g., extrac8on of V cd and/or its decay constant, f D. - Semi- leptonic decays (e.g., extrac8on of their form factors, and then compare them vs B meson case. - With the largest sample of D mesons taken at the near threshold, one should look for rare/forbidden decays (e.g., FCNC, LNV, LFV. - or even ψ(377 itself such as ψ(377 non- DDP final states. - But today, I report our ahempt to measure some of the parameters of DDP mixing using the unique characteris8cs of our ψ(377 data set taken at E cm = GeV.

7 Hajime Muramatsu Introduc>on Miami 13 DEC/13 DDP mixing is highly suppressed by the GIM mechanism and by the CKM matrix elements within the Standard Model. Observa8on of DDP mixing, first seen by the B factories (HFAG: arxiv and now observed by LHCb: PRL11, 118 (13. Improving the constraints on the charm mixing parameter is important for tes8ng the SM, such as long distance effects. DDP mixing is conven8onally described by two parameters: x = (M 1 - M /(Γ 1 +Γ, y = (Γ 1 - Γ /(Γ 1 +Γ, x' [%] where M 1, and Γ 1, are the masses and widths of the neutral D meson mass eigenstates. (Flavor eigenstates, D /DP, are not the same as mass eigenstates, D 1 /D Or x = x cosδ Kπ + y sinδ Kπ, y = y cosδ Kπ - x sinδ Kπ. δ Kπ is the strong phase difference between the doubly Cabibbo suppressed (DCS decay, DP K - π + and the Cabibbo favored (CF decay, D K - π + or K - π + DP / K - π + D = - r e - iδ. So one can connect (x,y with (x,y via δ Kπ. In this talk, I present preliminary results on δ Kπ and y using the quantum correla8on between the produced D and DP pair in data taken at BESIII. [%] y' σ 3σ 1σ No-mixing 7 LHCb

8 Miami 13 DEC/13 8 The decay rate of a correlated state For physical process producing D DP such as e + e - γ * ψ(377 D DP, the D DP pair are in a quantum- correlated state. The quantum number of ψ(377 is J PC = Thus, the D DP pair in this process has C = -. For a correlated state with C = -, the two D mesons are an8- symmetric in the limit of CP invariance: The two produced neutral mesons must have opposite CP (i.e., see Goldhaber and Rosner, PRD15, 154 (1977. That is; Final states of (CP+, CP+ or (CP-, CP- are forbidden. Final states of (CP+, CP- are maximally enhanced (doubled. Final states of CP± against inclusive states (Single tag or ST are not affected. Final states of (K - π +, CP± are affected due to the interference between CF and DCS (δ Kπ.

9 Miami 13 DEC/13 9 Extrac>ng δ Kπ Neglec8ng higher orders in the mixing parameters (e.g., y, one can arrive at the following rela8on: r cosδ Kπ +y = (1+R WS A CP Kπ, where R WS Γ(DP K - π + /Γ(D K - π + and A CP Kπ [B(D K - π + - B(D 1 K - π + ]/B(D K - π + + B(D 1 K - π + ]. We can extract A CP Kπ by tagging one D (tag side with exclusive CP- eigenstates which then defines the eigenvalue of the other D (A CP± K - π + D 1,. Then, with the knowledge of r, y, and R WS from the 3rd par8es (HFAG13 and PDG, we could derive cosδ Kπ in the end. The rest of the analysis becomes measurements of B(D CP± K - π + while simultaneously reconstruc8ng the D CP on the tag side.

10 Miami 13 DEC/13 1 Measuring B(D CP± K - π + Double- Tag technique: B(D CP± Kπ = [B(D CP CP states B(D CP± Kπ]/B(D CP CP states = (n Kπ,CP /n CP (ε CP /ε Kπ,CP, where n Kπ,CP are yields of Kπ when CP states are simultaneously reconstructed on the tag side n CP are yields of CP states (independent of how the other D decays ε CP and ε Kπ,CP are the corresponding reconstruc8on efficiencies. Yields are extracted from M bc distribu8ons : CP states on Tag side (8 modes: beam where we reconstruct K S π + π -, π /η γγ, ω π + π - π, ρ π + π -. No8ce that most of systema8cs on the tag side get canceled in B(D CP± Kπ. The remaining systema8cs (reconstruc8on/simula8on of Kπ are also canceled in the determina8on of A CP Kπ. M BC E p CP+ K + K, π + π,ks π π, π π, ρ π CP KS π,ks η,k S ω D

11 Miami 13 DEC/13 11 Yields of CP states (n CP (reconstruct only one of the two neutral D CP+ CP+ CP- Events/(1 MeV/c Events/(1 MeV/c Events/(1 MeV/c K + K π π K S π Events/(1 MeV/c Events/(1 MeV/c Events/(1 MeV/c π + π ρ π K S η Events/(1 MeV/c Events/(1 MeV/c K S π π K Preliminary - Signal shape: MC shape, convoluted with a Gaussian (to compensate the difference in resolu>on between data and MC. - Background: ARGUS background func>on. S ω Figure 1: ST M BC distributions of the D CP± decays and fits to data. Data are

12 Miami 13 DEC/13 1 Can also check CP purity - When D and Dj are reconstructed, final states with the same CP should yield zero events. preliminary preliminary preliminary preliminary preliminary preliminary CP+ CP- CP+ CP+ CP- Consistent with zero. Consider as one of the systema>cs.

13 Miami 13 DEC/13 13 Events/( MeV/c Yields of Kπ in double tags (n Kπ,CP (reconstruct CP- final state from one D decay, 1 Events/( MeV/c Events/( MeV/c K π, K + K K π, π π K π, K π S with Kπ from the other D Events/( MeV/c Events/( MeV/c Events/( MeV/c K π, π + π K π, ρ π K π, K S η Events/( MeV/c Events/( MeV/c 1 1 K π, K π π S K π, K ω Preliminary - Signal shape: MC shape, convoluted with a Gaussian (to compensate for the difference in resolu>on between data and MC. - Background: ARGUS background func>on. S igure : DT M BC distributions and the corresponding fits. Data are shown in

14 Miami 13 DEC/13 14 Preliminary fit results Preliminary - These yields allow us to obtain B(D CP± K - π + which then provides A CP Kπ. - A CP Kπ = (1.77±1.31(stat (syst.%.

15 Miami 13 DEC/13 15 Preliminary result on δ Kπ - We have measured A CP Kπ = (1.77±1.31(stat (syst.%. - Using the rela>on, r cosδ Kπ +y = (1+R WS A CP Kπ, and with external inputs from HFAG13 and PDG (R D = 3.47±.6%, y=6.6±.9%, R WS = 3.8±.5%, we obtain cosδ Kπ = 1.3±.1(stat.±.4(syst.±.1(external. - Our result is consistent with and more precise than the recent CLEO result (PRD86, 111 (1: cosδ Kπ = (stat (syst..

16 Determina>on of the mixing parameter, y CP - y CP is defined as; y CP = ( q/p + p/q y cosφ - ( q/p - p/q x sinφ, where p and q are mixing parameters, and φ = arg(q/p is the weak phase difference of the mixing amplitudes. No>ce: for no CPV case, p = q = 1/ and y CP y. Miami 13 DEC/13 - For D decays into any CP- eigenstate, its decay rate can be described as; R(D /Dj CP ± A CP± (1 y CP. - When one D decays into a CP- eigenstate, while the other D decays semi- leptonically, the decay rate can be given by; R(D /Dj CP ±, and Dj /D semi- lep A l A CP±. - Semileptonic decay width does not depend on the CP of its parent D. - Yet, the total width of its parent D depends on CP. - Result: semileptonic BF of D 1, gets modified by a factor of 1±y CP. - Combining the above two, and neglec>ng terms with y (or higher, one can arrive at y CP = 1 4 (R l;cp+r CP R l;cp R CP+ R l;cp R CP+ R l;cp+ R CP 16

17 Miami 13 DEC/13 17 Extrac>ng y CP in our experiment - The expression for y CP can be wrien as; y CP = 1[ B + 4 B B B ] + where B*± is the branching hefrac>on, least square averaged meth over different CP tag modes, α, that is obtained by minimizing - All branching frac>ons are obtained in a similar way, the double- tag method. - When the semileptonic decays are reconstructed, however, we use distribu>ons to obtain their yields, instead of M bc, E miss p miss, which peaks ~ if only missing par>cle is neutrino. - Tag modes: χ = α ( B ± B α ± (σ α ± Type Modes CP + K + K, π + π, K S π π CP KS π, KS ω, K S η l ± Keν, Kµν

18 Miami 13 DEC/13 18 Yields of CP states (n CP (reconstruct only one of the two neutral D CP+ CP- Events/.6 MeV/c Events/1. MeV/c K + K - π + π - K + π S π + π - Events/1. MeV/c Events / 1. MeV/c 4 π 4 K S π Kω S ω K η S η S S Events / 1. MeV/c Preliminary Events/1. MeV/c Figure 3: M BC distributions and fits to data.

19 Miami 13 DEC/13 19 Yields of Keν in double tags (n Keν,CP (reconstruct CP- final states from one D decay, Events / (.5 Events / ( (GeV with Keν from the other D 8 K + K -, Keν π + π -, Keν K K K, Keν π + π, Keν S π + π - K π π S, Keν, Keν Events / (.5 Events / ( (GeV Events / ( (GeV 8 K S π K π S, Keν K, Keν S ω, K 6 S Keν 6 K ω, Keν S η, K S Keν η, Keν (GeV (GeV (GeV Preliminary Events / (.1 vents / ( Signal shape: MC shape, convoluted K, Kµν with an asymmetric Gaussian. π + π, Kµν K vents / ( Background: A 1 st 1 order polynomial. vents / (.5 5 K π π S, Kµν

20 4 Summary Hajime Muramatsu Events / ( π + π, Keν Events / ( K π π S, Keν Miami 13 DEC/13 Yields of Kμν in double tags (n Kμν,CP (GeV (GeV Events / (.5 Events / (.5 Events / (.5 (reconstruct CP- final states from one D decay, K S π, Keν with Kμν from the other D (GeV (GeV Events / ( K S ω, Keν (GeV 1 8 K + K K, KKμν -, Kµν π + π -, + π, Kµν Kμν K S π + π - K, π π S Kμν, Kµν (GeV Events / ( (GeV 15 K S π, πkμν, Kµ ν K S ω, ω, Kμν Kµν K 6 S η, η, Kμν Kµ ν K S Events / ( K S Kππ (GeV Events / (.1 Events / (.5 Events / ( K S η, Keν Preliminary (GeV K S (GeV (GeV - Kππ shapes and sizes are fixed based on control samples of actual data. - The control samples are obtained by the same CP states and Kππ, while ignoring the two photons from π decays to calculate. See the next slide for detail. Figure 4: Fits - to Signal shape: distributions MC shape, inconvoluted data for CP-tagged - Background: Keν and A 1Kµν st order modes. polynomial. with an asymmetric Gaussian. Kππ (dominant.

21 Miami 13 DEC/13 1 Fixing the Kππ shape - Obtain E extra Sum of the all un- used energies deposited in EM calorimeter. - E extra tends to be larger if it is Kππ due to the ignored extra photons from π decay and is small if it is Kμν. - We actually do require E extra <. GeV to select Kμν signal candidates. E extra (GeV all KK,Kµν KK,Kππ KK,Keν others (GeV - The fihed. shape MC shape, (GeV (a (Kππ {U yields miss : Ein extra data } in two E extra dimensional <. GeV = R (Kππ plot (b yields in data distribution in E extra >.5 ofgev, Kππ events in where R = (Kππ yields in MC in E extra <. GeV/(Kππ E extra >.5 yields GeV in MC region in E extra and >.5 ingev. E extra <. GeV region.6 Fix shape K + K -, Kππ - Fit to in E extra.4 >.5 <. GeV where Kμν E extra >.5 peak is suppressed. convoluted with a Gaussian. Fix size

22 Miami 13 DEC/13 - Fied yields for each mode: Preliminary results - A\er correc>ng for efficiencies (branching frac>ons, we arrive at y CP = [- 1.6±1.3(stat.±.6(syst.]%. - The result is sta>s>cally limited. - The systema>c uncertainty mainly comes from fišng procedures.

23 Miami 13 DEC/13 3 Comparison with other measurements BESIII (pre ±1.3 ±.6 % - Our result is consistent with the world average (HFAG13; this preliminary result is not included in the average. - Also consistent with the latest result from CLEO- c (PRD86, 111 (1; y CP = (4.±.±1.%. (not listed in the figure. World average directl (BESIII (pre. not inc

24 Miami 13 DEC/13 4 Summary - Quantum- correlated D Dj in e + e - annihila>ons near threshold: Unique way to measure the Charm mixing parameters. - Most precise measurement of strong phase difference in D Kπ. Will improve the determina>on of mixing parameters, x and y. - Measurement of y CP : Sta>s>cally limited, consistent with the world average. - Will collect larger open- charm data samples in years to come: Expect many interes>ng results.