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New results on charm mixing and CP violation

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1 New results on charm mixing and CP violation
5/10/2019 New results on charm mixing and CP violation Stefano Bianco Laboratori Nazionali di Frascati Questa e’ la versione che include j.link, j.wiss and doris’ talks CPConf2000, Ferrara, September CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

2 Basic Mixing Phenomenology FOCUS Detector Part I: Charm Mixing and yCP
5/10/2019 Outline Basic Mixing Phenomenology FOCUS Detector Part I: Charm Mixing and yCP Part II: Search for CP violation Part III: Measurement of D*+ p+ (K+p-) Conclusions and Outlook J.Wiss, Fermilab Seminar Apr 2000 FOCUS Coll. (J.M. Link et al.) Phys.Lett.B485:62-70,2000 FOCUS Coll. (J.M. Link et al.) hep-ex/ Preliminary J.M. Link, DPF2000 Columbus (USA) CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

3 Formalism of P0-P0 mixing
_ Formalism of P0-P0 mixing The time evolution of flavour eigenstates is given by the Schrödinger equation mixing can be described by the ratio r Processes which allow mixing appear in H12 and H21. If are not mass eigenstates. Mass eigenstates are (assuming CP conservation) , |x|>0 mixing is caused by genuine transitions(Df=2) x splits masses |y|> mixing is caused by the short-lived component disappearing rapidly, leaving behind the long-lived component, made of and y splits lifetimes and mixing amplitude is Mass and width differences are parametrized by CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

4 K0, D0, B0 _ Where’s The Difference ?
SHORT DISTANCE KK,pp p0,h LONG DISTANCE Also: recent OPE-based limits I.Bigi, N.G.Uraltsev hep-ph/ q SD/LD x=Dm/G y=DG/(2G) c SD~LD 0.48 100% s SD<<LD ? THIS MEASUREMENT t SD>>LD 0.75 >22 CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

5 Theoretical “guidance”
5/10/2019 From compilation of H.N.Nelson hep-ex/ Triangles are SM x Squares are SM y Circles are NSM x “D0D0 mixing is a window on New Physics” _ . CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

6 TECHNIQUES FOR STUDYING D0D0 MIXING (I)
_ TECHNIQUES FOR STUDYING D0D0 MIXING (I) Measure yCP, the y parameter for CP eigenstates Measure r 2 These Results Also E791, BELLE HADRONIC DECAYS SEMILEPTONIC DECAYS (1 +2)/2 E791, CLEO, ALEPH E791 CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

7 TECHNIQUES FOR STUDYING D0D0 MIXING (II)
_ TECHNIQUES FOR STUDYING D0D0 MIXING (II) Measure r via HADRONIC DECAYS Cabibbo-Favoured Decay mixing Strong phase d between CFD and DCSD mixes x and y D* tags D0 flavour Double Cabibbo-Suppressed Decay CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

8 TECHNIQUES FOR STUDYING D0D0 MIXING (III)
_ 5/10/2019 TECHNIQUES FOR STUDYING D0D0 MIXING (III) Measure r via SEMILEPTONIC DECAYS Cabibbo-Favoured Decay mixing D* tags D0 flavour Controlla se sono giusti I segni dei leptoni CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

9 TECHNIQUES FOR STUDYING D0D0 MIXING (Concl.)
_ TECHNIQUES FOR STUDYING D0D0 MIXING (Concl.) Direct measurement of yCP requires good lifetime resolution Measuring rws in hadronic decays requires to disuntangle rDCS from r; and the knowledge of d Measuring rws in semileptonic decays provides the r parameter, but it is experimentally more difficult CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

10 Spectrometer at FNAL Wide Band Photon Beam
5/10/2019 Spectrometer at FNAL Wide Band Photon Beam Vertexing Cerenkov Over 1 million reconstructed! PWC Successor to E687. Designed to study charm particles produced by ~200 GeV photons using a fixed target spectrometer with updated Vertexing, Cerenkov, EM Calorimeters, and Muon id capabilities. Member groups from USA, Italy, Brazil, Mexico, Korea. CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

11 The FOCUS Collaboration
Univ. of California-Davis, CBPF-Rio de Janeiro, CINVESTAV-Mexico City, Univ. Colorado-Boulder, FERMILAB, Laboratori Nazionali di Frascati, Univ. of Illinois-Urbana-Champaign, Indiana Univ.-Bloomington, Korea Univ.-Seoul, INFN and Univ.-Milano, Univ. of North Carolina-Asheville, INFN and Univ.-Pavia, Univ. of Puerto Rico-Mayaguez, Univ. of South Carolina-Columbia, Univ. of Tennessee-Knoxville, Vanderbilt Univ.-Nashville, Univ. of Wisconsin-Madison, Yonsei Univ.-Seoul CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

12 Detector Performance related to lifetime study
5/10/2019 Detector Performance related to lifetime study Segmented target: 62% of charm decay in air. small absorption correction. Extremely good proper time resolution: ()/(D0) = 8 % (30fs) No resolution convolution systematics/error inflation  Binned likelihood method. Vertex algorithm is driven by D candidates: The Fit variable ( reduced proper time ) acceptance is flat. Excellent ( and flexible) Cerenkov identification: Minimized systematics on particle ID misidentification. Detachment cut Decays/200 m BeO tarsil primary vtx secondary vtx Z (cm) CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

13 Selection of D K, KK 5/10/2019 Common base cuts: detachment (l /s > 5), Kaon ID (Wp-WK > 4) Tagged sample: Or inclusive sample: More Cerenkov cuts : pion ID (W*-W > -2), Kaon ID 2 ( WP-WK > -2 ) Primary vertex in target (PIT) Important: Get a sample with a flat efficiency over t’ K Base is l/ >7 & kaon>1 D K: selected D  KK: selected CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

14 DKK signal for several cleanups
5/10/2019 Y=10331 S/N=2.7 l / > 5 Wp-WK>1 l / > 5 Wp-WK>4 Y=16532 S/N=2.3 Kp reflection l / > 9 Wp-WK>1 l / > 9 Wp-WK>4 Y=11528 S/N=4.3 Y=7151 S/N=5.7 CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

15 Fit technique: non-parametric background
5/10/2019 Binned likelihood: 20  200 fs Acceptance/absorption f(t’) correction by MC ~ nearly 1 mi: signal in each t’ bin bi: background from sidebands Fit t (Kp), B (Kp) (but see next page) K KK f(t’) vrs t’ (fs) option: w or w/o B-tie term. N1 N2 Ns B DK CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

16 Results on Charm Mixing and CPV - S.B.
Fitting technique 5/10/2019 The KK sample has some K reflection at its side; B2 = Kp + nominal  one more player in fitting. Subtract K reflection by a mass fit. The reflection mass shape from MC. The subtraction level by the mass fit. Time evolution of the reflection from t (Kp) Background under KK signal  B1 + (B2 - K reflection) Simultaneous time evolution fit of both K and KK histos. 4 variables in the time fit: t (Kp), yCP, B (Kp), B (KK) DKK Region B1 Region B2 Kp reflection CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

17 Fitted time evolutions
5/10/2019 K back+signal background l/ > 5 Wp-WK>4 K KK KK Background subtracted and f(t’) corrected time evolution of Kp and KK events in the final fit. CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

18 Ycp: Results and Systematics
5/10/2019 CL 3 K ID  3 l/  B-tie or not  15/20 bin = 36 fit variants shown. B- tie 15 bin 20 bin YCP yCP = 3.421.390.74 % Sample standard deviation of fit variants is 0.63. K (K) = 409.21.3?? fs Sample standard deviation of fit variants 0.3. Absolute lifetime systematics not ready until we analyze K3, etc. CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

19 Additional systematic checks
5/10/2019 Could curvature in reflection line- shapes cause the sideband background to fail? Let’s reduce the sideband size by half and see... Results are nearly identical to standard fits 15 bins 20 bins How important is the f(t’) correction? Set f(t’)=1 and rerun all the fits. CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

20 Consistency of D* and full sample
5/10/2019 15 bins 20 bins B- tie Further suppress non-charm and non-Do reflection by looking at D*-only sample. Inclusive +D* tag l/ > 5 Wp-WK>4 D* tag only CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

21 Comparisons to CLEO, E791 and BELLE
5/10/2019 The comparison to CLEO is valid only if one assumes a small strong phase difference . About the same sensitivity to the CLEO CP constrained fit, but the opposite sign! FOCUS FOCUS CLEOII.V E791 FOCUS yCP = 3.42  1.39  0.74 % Recent Measurements E791: yCP = 0.8  2.9  1 % CLEO: -5.8 % < y’ < 1% ( 95% CL) BELLE prelim.: yCP = E791 BELLE 95% CL CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

22 Search for CP asymmetry in charm decay
5/10/2019 CP asymmetries may show via the interference of two distinct amplitudes with phases d1 and d2 which contain both a weak (CKM) and a strong (FSI) contribution. The weak contribution in the phases changes sign under CP, while the strong one does not. The most accessible decays which contain two weak phases are the SCSD (tree and penguin diagrams). The CP asymmetry will then be Buccella et al predict state specific asymmetries in the range of  0.14 % The Do asymmetry is complicated by a direct as well mixed contribution but expectation are that the D° might be smaller than D+ CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

23 Search for CP asymmetry in charm decay (DKK)
5/10/2019 Search for CP asymmetry in charm decay (DKK) K MC CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

24 Search for CP asymmetry in charm decay (DKK)
5/10/2019 Search for CP asymmetry in charm decay (DKK) Cabibbo suppressed mode. D+ D– DS+ DS D+  KK+p+ D  KK+p Cabibbo favored mode. D+  K p +p+ D  K+p p CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

25 Results on Charm Mixing and CPV - S.B.
CP asymmetry results 5/10/2019 No evidence for CP violation. Our limits on Need to use tagged Do sample which cuts our sample by 80%. 2~3 times better limit than the previous published measurements. …also, New Unpublished CLEO limits on KK, pp (CIPANP, Quebec City 2000) CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

26 Measurement of D*+ p+ (K+p-)
5/10/2019 Measurement of D*+ p+ (K+p-) Event Selection Very loose Cerenkov based particle id cuts on K and p. The D0 candidate is used as a seed to find the production vertex. The production vertex has at least 2 tracks in addition to the D0. The production vertex is required to be within 1s of target material. Production and decay vertices are required to be well formed (CL>1%). D0 daughter tracks inconsistent with coming from the production vertex. The vertex separation L/sL>5. Cut Kp pairs with high momentum asymmetry and low D0 momentum. CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

27 Measurement of D*+ p+ (K+p-)
5/10/2019 First You Have to Tag the D0 Flavor The decay D+*gD0p+ is used to identify the D0 flavor. So we study the D*-D0 mass difference. D0 K+K- K-p+p0 D*-D0 (CF-like Tags) p+p- CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

28 Measurement of D*+ p+ (K+p-)
5/10/2019 The Worst BG is CF Kp Double Mis-id So we use a tight Cerenkov based mis-id cut in a 4s window about the D0 with Kp reconstructed as pK. m - Standard cuts. - Double mis-id cut. The double mis-id Dm is indistinguishable from the correctly identified signal. CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

29 Measurement of D*+ p+ (K+p-)
5/10/2019 A New Method Divide the data into 1 MeV wide bins in Dm, and fit the D0 in each bin. Fit the KK and pp reflections with Monte Carlo events. D*-D mass difference Kp mass Fit BG to a polynomial. Fit D0 to a gaussian. . DCS-like tags 146<Dm<147 MeV . . A total of 80 fits! CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

30 Measurement of D*+ p+ (K+p-)
5/10/2019 Fit the Dm Distributions Fitted D0 yields are plotted in the appropriate Dm bins. Background is fit to: DCS signal is fit directly to the CF histogram signal region. CLEO: (0.332 0.064 0.040)% rWS= (0.482  0.093)% Preliminary! Stat err only CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

31 Conclusions 5/10/2019 Measurement of yCP, asymmetry between the KK(CP=1) and K(CP=mixed) lifetimes New limits on CPV asymmetries Preliminary Measurement of D*+ p+ (K+p-) Assuming No Mixing rDCS = ( )% (stat only) FOCUS CLEOII.V E791 95% CL BELLE yCP = 3.42  1.39  0.74 % (K) =  1.34 ?? fs CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

32 Results on Charm Mixing and CPV - S.B.
Outlook 5/10/2019 FOCUS yCP result becomes more compatible to CLEO r’ measurement if a very large strong phase d is allowed Fairly intense theory production to explain the CLEO and FOCUS mixing results Expect new FOCUS results on r’ soon Expect new CLEO and FOCUS results on r from semilep analysis soon The FOCUS 2.2s evidence for charm mixing should be verified soon by B-factories FOCUS CLEOII.V E791 95% CL BELLE I.I.Bigi, ICHEP2K Osaka Plenary talk hep-ph/ A.Golutvin, ICHEP2k Osaka Plenary talk A.Petrov, hep-ph/ Yosef Nir, hep-ph/ D.Atwood et al., hep-ph/ J. P. Silva, hep-ph/ J. L. Rosner, hep-ph/ J.L. Rosner, hep-ph/ S.Bergmann et al., Phys.Lett.B486: ,2000 I.I. Bigi, hep-ph/ Citations to date CPConf 2000, Ferrara Results on Charm Mixing and CPV - S.B.

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