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Evidence for D 0 -D 0 Mixing at Belle

Evidence for D 0 -D 0 Mixing at Belle. KEK Physics Seminar. B. Golob University of Ljubljana Belle Collaboration. Outline Introduction Phenomenology Measurements semileptonic K + p - K S p + p - K + K - / p + p - CPV 4. Prospects 5. Summary.

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Evidence for D 0 -D 0 Mixing at Belle

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  1. Evidence for D0-D0 Mixing at Belle KEK Physics Seminar B. Golob University of Ljubljana Belle Collaboration • Outline • Introduction • Phenomenology • Measurements • semileptonic • K+p- • KSp+p- • K+K-/p+p- • CPV • 4. Prospects • 5. Summary D0 Mixing 1 B. Golob, Belle KEK Seminar, May 2007

  2. Introduction √s = M(U(4S))c2= 10.58 GeV Physics of c-hadrons increased interest at B-factories in recent years B-factory, c-factory s(c c)  1.3 nb (~850·106 XcYc pairs) s(B B)  1.1 nb (~750·106 BB pairs) benchmark: D*0→ D0p+slow ; D0→ K-p+ D0 Mixing 2 B. Golob, Belle KEK Seminar, May 2007

  3. Central Drift Chamber e+3.5 GeV 3(4) layer Si det. e-8 GeV Aerogel Cherenkov (n=1.015-1.030) m and KL Counter (14/15 layers RPC+Fe) EM calorimeter CsI (16X0) 1.5T SC solenoid Introduction 700 fb-1 Ldt 2000 2007 D0→ <st>/t(D0) ~ 1/2 e(K±) ~ 85% e(p±→K±)  10% for p < 3.5 GeV/c t(D0)/3 st/t(D0) D0 Mixing3 B. Golob, Belle KEK Seminar, May 2007

  4. q2 q1 Decay time distribution of experimentally accessible states X0, X0 sensitive to mixing parameters D0 - D0 Phenomenology q2 q1 Mixing phenomena in course of life neutral meson X0 can transform into anti-meson X0 X0 = K0, Bd0, Bs0 and D0 t-dependent Schrödinger eq.: mass eigenstates: decay time evolution: X0 X0 CP eigenstates if q/p=1; propagate in t according to distinct eigenvalues; D0 Mixing 4 B. Golob, Belle KEK Seminar, May 2007

  5. Vuj* Vci* Vcj Vui u c W+ D0 D0 d, s, b d, s, b W- c u if mi = mj  due to CKM unitarity: no D0 D0 mixing D0 - D0 Phenomenology Mixing description observation of K0: 1950 (Caletch) mixing in K0: 1956 (Columbia) observation of Bd0: 1983 (CESR) mixing in Bd0: 1987 (Desy) observation of Bs0: 1992 (LEP) mixing in Bs0: 2006 (Fermilab) observation of D0: 1976 (SLAC) mixing in D0: 2007 (KEK, SLAC) (evidence of) 6 years 4 years 14 years 31 years d-like quarks in loop |Vcb*Vub|<< |Vcs*Vus|, |Vcd*Vud| mainly d,s contrib.; md ~ ms mixing small (as opposed to Bd0, where term with mt2 |Vtb* Vtd|2 dominates) D0 Mixing 5 B. Golob, Belle KEK Seminar, May 2007

  6. Vuj* Vci* Vcj Vui u c W+ D0 D0 d, s, b d, s, b W- u c K+ D0 D0 K- D0 - D0 Phenomenology x and y in SM 2nd order perturb.: short distance: |x| ~ O(10-5) G. Burdman, I. Shipsey, Ann.Rev.Nucl.Sci. 53, 431 (2003) DCS SU(3) breaking absorptive part (real interm. states)  y dispersive part (off-shell interm. states)  x long distance: |x|, |y| ~ O(10-2) I.I. Bigi, N. Uraltsev, Nucl. Phys. B592, 92 (2001); A.F. Falk et al., PRD69, 114021 (2004) D0 mixing: rare process in SM; possible contrib. from NP D0 Mixing 6 B. Golob, Belle KEK Seminar, May 2007

  7. D0 - D0 Phenomenology Oscillations ~ Bs0 more difficult to observe oscillations within t visually unobservable deviation from pure exponential D0 Mixing 7 B. Golob, Belle KEK Seminar, May 2007

  8. Measurements Belle measurements - semileptonic decays, D0→ K(*) l n - hadronic decays to non-CP final state D0→ K+p- - hadronicdecays to multi-body final state, D0→ KSp+p- - decays to CP final state, D0→ K+K-/p+p- PRD72, 071101 (2005), 253 fb-1 PRL96, 151801 (2006), 400 fb-1 common: D*+ →D0ps+ charge of ps tags the flavor of initially produced D0; p*(D*) > 2.5 GeV/c eliminates D meson production from b → c arXiv: 0704.1000, 540 fb-1 hep-ex/0703036v2, 540fb-1, acc. to PRL D0 Mixing 8 B. Golob, Belle KEK Seminar, May 2007

  9. right sign (RS) PRD72, 071101 (2005), 253 fb-1 Measurements semileptonic D0 → K(*)-e+n • Semileptonic decays • Wrong charge combinations (WS): • D*+→ D0pslow+D0 → D0 → K(*)+e-n • no “DCS” decays  NWS/NRS = RM (x2+y2)/2 • Reconstruct n: • missing momentum with • kinematic constraints • Signal: • DM = M(Kenpslow) - M(Ken) x,y << 1 NRS = (229.45 ± 0.69) ·103 D0 Mixing9 B. Golob, Belle KEK Seminar, May 2007

  10. PRD72, 071101 (2005), 253 fb-1 Measurements semileptonic • Decay time: • reduce bkg., increase sensitivity; • <t >(bkg., RS) < <t >(mix. signal) • 6 bins in 1 < t < 10 Result: allowed RM = (0.20 ± 0.47 ± 0.14) ·10-3 RM < 1.2 · 10-3 95% C.L. dominating systematics from limited bkg. statistics (embedded pslow) D0 Mixing10 B. Golob, Belle KEK Seminar, May 2007

  11. PRL96, 151801 (2006), 400 fb-1 D*+→ D0pslow+D0 → D0 → K+p- Measurements K+p- 3s Q interval Wrong charge combinations (WS): WS DCS decays  interference t-dependence to separate DCS/mixed 3s M interval • Signal: • M=M(Kp) • Q = M(K p pslow) - M(Kp) - M(p) • 2D M-Q fit: WS NWS = 4024 ± 88 NRS 106 D0 Mixing11 B. Golob, Belle KEK Seminar, May 2007

  12. PRL96, 151801 (2006), 400 fb-1 Measurements K+p- WS t dist. Decay time: resol. function from RS t(D0) = 409.9 ± 0.7 fs tPDG=410.1±1.5 fs x’2, y’, RD free parameters Results: RD = (3.64 ± 0.17 ) ·10-3 x’2 = (0.18 ±0.210.23) · 10-3 y’= (0.6 ±4.03.9) · 10-3 (x’2, y’) =(0,0) C.L. 3.9% 95% C.L. (x’2, y’) contour frequentist, FC ordering D0 Mixing12 B. Golob, Belle KEK Seminar, May 2007

  13. arXiv: 0704.1000, 540 fb-1 < f | D0 > analogous forM= < f | D0(t)> Measurements KSp+p- t-dependent Dalitz analysis different decays identified through Dalitz analysis; CF: D0→ K*-p+ DCS: D0→ K*+p- CP: D0→r0 KS their relative phases determined (unlike D0→ K+p-); t-dependence: m±2: Dalitz variables l1,2=f(x,y); n.b.:K+p-:x’2, y’ < f | D0 > sum of intermediate states D0 Mixing13 B. Golob, Belle KEK Seminar, May 2007

  14. M signal rnd slow p combin. arXiv: 0704.1000, 540 fb-1 Measurements KSp+p- t Fit no CPV: fit M(m-2,m+2,t) to data distribution  x, y Signal M(KSp+p- ) and Q= M(KSp+p-ps)- M(KSp+p-)- M(p); 3 s signal region in M, Q Nsig= (534.4±0.8)x103 P95% Dalitz model 13 BW resonances, non-resonant contr.; D0 Mixing14 B. Golob, Belle KEK Seminar, May 2007

  15. arXiv: 0704.1000, 540 fb-1 Measurements KSp+p- K*X(1400)+ Dalitz projection of fit K*(892)+ r/w K*(892)- test of S-wave pp contr. (f0, s1,2): K-matrix formalism Results (fit fractions, phases) in agreement with (measurement of f3) PRD73, 112009 (2006) D0 Mixing15 B. Golob, Belle KEK Seminar, May 2007

  16. t [fs] arXiv: 0704.1000, 540 fb-1 Measurements KSp+p- Decay-t projection of fit x = (0.80±0.29±0.130.16)% y = (0.33±0.24±0.100.14)% most sensitive meas. of x; comb. bkg. x = 1.8 ± 3.4 ± 0.6% y = -1.4 ± 2.5 ± 0.9 % Cleo, PRD72, 012001 (2005) t = 409.9±0.9 fs tPDG=410.1±1.5 fs D0 Mixing16 B. Golob, Belle KEK Seminar, May 2007

  17. hep-ex/0703036v2, 540fb-1, acc. to PRL Measurements K+K- / p+p- D0→ K+K- / p+p- CP even final state; in the limit of no CPV: CP|D2> = |D2> measure 1/G2 side band S. Bergman et al., PLB486, 418 (2000) AM, f: CPV in mixing and interference Signal M, Q, st selection optimized in MC D0 Mixing17 B. Golob, Belle KEK Seminar, May 2007

  18. K-p+ hep-ex/0703036v2, 540fb-1, acc. to PRL MeasurementsK+K- / p+p- Fit simultaneous binned likelihood fit to K+K-/K-p+/p+p- decay-t, common free yCP (M sideband) R : ideally each si Gaussian resol. term with fraction fi; : described by 3 Gaussians  event-by-event st trec-tgen/st each si→ 3 Gauss MC parameters of R depend slightly on data taking conditions t = 408.7±0.6 fs D0 Mixing 18 B. Golob, Belle KEK Seminar, May 2007

  19. K+K-/p+p- and K-p+ratio hep-ex/0703036v2, 540fb-1, acc. to PRL MeasurementsK+K- / p+p- c2/ndf=1.084 (ndf=289) Result + difference of lifetimes visually observable negligible CPV, yCP=y yCP = (1.31 ± 0.32 ± 0.25) % 3.2 s from zero (4.1 s stat. only) evidence for D0 mixing (regardless of possible CPV) D0 Mixing19 B. Golob, Belle KEK Seminar, May 2007

  20. BaBar, hep-ex/0703020, 384fb-1, acc. to PRL MeasurementsK+p- Reminder • Signal: • M=M(Kp) • DM = M(K p pslow) - M(Kp) Fit NWS = 4030 ± 90 D0 Mixing20 B. Golob, Belle KEK Seminar, May 2007

  21. 1 s 2 s 3 s BaBar, hep-ex/0703020, 384fb-1, acc. to PRL MeasurementsK+p- Result RD = (3.03 ± 0.19) ·10-3 x’2 = (-0.22 ±0.37) · 10-3 y’= (9.7 ± 5.4) · 10-3 3.9 s including sys. error Comparison evidence for (x,y)  (0,0) consistent D0 Mixing21 B. Golob, Belle KEK Seminar, May 2007

  22. Measurements Results KSp+p- : (x,y)=(0,0) has C.L. 2.6% K+K- / p+p-:y=0 has C.L. 6x10-4 D0 Mixing22 B. Golob, Belle KEK Seminar, May 2007

  23. Measurements Combination 1996 FNAL E791 R M = (0.11 +0.30−0.27 +0.00−0.014 )% 2005 CLEO II.V R M = (0.16 ± 0.29 ± 0.29 )% 2004 BaBar R M = (0.23 ± 0.12 ± 0.04 )% 2005 Belle R M = (0.020 ± 0.047 ± 0.014 ) 1999 FNAL E791ΔΓ = (0.04 ± 0.14 ± 0.05 ) ps −1 (yCP = (0.8 ± 3.1)%) 2000 FOCUS y CP = (3.42 ± 1.39 ± 0.74 )% 2002 CLEO II.V y CP = (−1.2 ± 2.5 ± 1.4 )% 2003 BaBar y CP = (0.8 ± 0.4 +0.5−0.4 )% 2002 Belle y CP = (−0.5 ± 1.0 +0.7−0.8 )% 2007 Belle y CP = (1.31 ± 0.32 ± 0.25 )% 2006 Belle x' 2 = (0.018 +0.021−0.023 )% y' = (0.06 +0.40−0.39 )% 2007 BaBar x' 2 = (−0.022 ± 0.030 ± 0.021)% y' = (0.97 ± 0.44 ± 0.31)% 2006 BaBar K + π − π 0 RM = (0.023 +0.018−0.014 ± 0.004)% 2006 BaBar K + π − π+ π− RM = (0.019 +0.016−0.015 ± 0.002)% 2005/2007 CLEO II.V x = (1.9 +3.2−3.3 ± 0.4 ± 0.4)% y = (−1.4 ± 2.4 ± 0.8 ± 0.4)% 2007 Belle x = (0.80 ± 0.29 ± 0.17)% y = (0.33 ± 0.24 ± 0.15)% 2006 CLEO-c RM = (0.17 ± 0.15)% y = (−5.8 ± 6.6)% cos δK π= 1.09 ± 0.66 RM semil. yCP x’2, y’ RM Knp x, y Cleo-c D0 Mixing23 B. Golob, Belle KEK Seminar, May 2007

  24. x= (0.94 ± 0.36)% y= (0.68 ± 0.21)% d=21o ± 19o Measurements average Average fit to individual measurements with x, y, d free assuming Gaussian p.d.f.’s; correlation for K+p-; unofficial! x, y ~ 1%, significantly deviating from 0 D0 Mixing 24 B. Golob, Belle KEK Seminar, May 2007

  25. Measurements CPV CPV in D0 system first two generations involved; Wolfenstein param., CPV in D0very small,  10-3; parameterization: D0→ K+p-,K+K- / p+p- ,KSp+p- t distributions depend also on CPV parameters x, y at upper limit of SM expectation →search for CPV; at current level of sensitivity positive signal clear indication of NP; D0 Mixing 25 B. Golob, Belle KEK Seminar, May 2007

  26. Measurements CPV CPV in D0 → K+p- PRL96, 151801 (2006), 400 fb-1 • CPV allowed fit: • separate D0 and D0 tags • (x’2,y’,RD) → (x’±2, y’±,RD±) CPV allowed AD = (23 ± 47) ·10-3 AM = (670 ± 1200) ·10-3 direct CPV indirect CPV hep-ex/0703036v2, 540fb-1, acc. to PRL AG = (0.01 ± 0.30 ± 0.15) % CPV in D0 → K+K- / p+p- indirect CPV D0 Mixing 26 B. Golob, Belle KEK Seminar, May 2007

  27. 3 s 1 s s(x) ~ ±0.25% s(y) ~ ±0.17% Prospects CPV in D0 → KSp+p- arXiv: 0704.1000, 540 fb-1 preliminary study: s(|q/p| 1 + AM/2) ~ 0.30, s(f) ~ 0.3 rad individual meas. test CPV with sensitivity ~ O(0.3) no evidence so far Prospects near future: 1 ab-1 D0 Mixing27 B. Golob, Belle KEK Seminar, May 2007

  28. Prospects combination of results s(x) ~ s(y) ~ 0.10%mixing s(|q/p|) ~ 0.09, s(f) ~0.05CPV Super-B rough expectations,5 ab-1 possible CPV - New Physics - tested with ~ O(5) better sensitivity; (several extensions of SM predict CPV ~ O(1%)) Y. Grossman et al., hep-ph/0609178 D0 Mixing 28 B. Golob, Belle KEK Seminar, May 2007

  29. Summary • Belle and BaBar presented evidence for D0 mixing x= (0.94 ±0.36)% • y= (0.68 ± 0.21)% • Values of mixing parameters at upper end of SM expectations; new measurements to further constrain x, y (and hope for more accurate predictions?) • Search for CPV = NP search; Super-B factory would allow for sensitive searches in reasonable extensions of SM D0 Mixing 29 B. Golob, Belle KEK Seminar, May 2007

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