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Recent Charm Results From CLEO Searches for D 0 -D 0 mixing D 0 -> K 0 s + - D 0 ->K *+ l - Conclusions Alex Smith University of Minnesota
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1) Large |x| 2) |x| >> |y| 3) CP violation of any kind
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D 0 – D 0 Mixing Analyses: Preliminaries Use D 0 ’s from D* decays to tag flavor of D 0 D *+ D0+D0+ Categorize D 0 decays according to flavor of D 0 and of K: “Right sign (RS)”: “Wrong sign (WS)”: Cabibbo-favored (CF) decays x, y, or doubly Cabibbo- suppressed decays (DCSD) Complication: Strong phase s due to final state interactions: x and y are what we really want
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Current Status of D 0 -D 0 Mixing Recent Experiments: CLEO, FOCUS, Belle, BaBar, E791 Recent Predictions: = x= y= non-SM (|x|, |y|, etc.) (1/2|Amplitude| 2 )
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Motivation to Study D 0 ->K s 0 + - Measure x and y rather than x ’2 and y ’ RS and WS occupy the SAME Dalitz plot: First measurement of relative strong phase between D 0 and D 0 to to K 0 s + - final state Only mode with sensitivity to sign of x! Doubly-Cabibbo-suppressed modes Comparable sensitivity to y as CP eigenstate (eg., D 0 ->K + K -) analyses Better scaling of sensitivity to x with int. luminosity than D 0 ->K + - analysis Low backgrounds ~1%! ~Flat efficiency in e + e - collisions
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D 0 ->K s 0 + - : Dalitz Formalism Visualize as pseudo- two-body decay: Amplitude for each resonance given by a relativistic Breit-Wigner, with angular distribution determined by J. For J = 1 we have: Total amplitude is the sum with a complex coefficient: We consider 18 resonant and non-resonant decay modes:
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Contributions to the Dalitz Plot K *- K 0 (1430) - K 2 (1430) - K * (1680) - 00 f 0 (980) f 2 (1270) f 0 (1370) 0 (1700)/ 0 (1450) K *+ K 0 (1430) +
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Dalitz Plot Data Fit Result
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ComponentAmplitudePhase ( 0 )Fit Fraction K * (892) + (770) 0 (792) K * (892) - f 0 (980) f 2 (1270) f 0 (1370) K 0 (1430) - K 2 (1430) - K * (1680) - Non-res. Results of Dalitz Plot Fit
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D 0 ->K s 0 + - Summary First observation (4.5 ) of WS D 0 ->K 0 + - We observe 5 new submodes (10 total) of this decay First measurement of strong phase shift s between D 0 ->K 0 + - and D 0 ->K 0 + - = (-3 +/- 14) 0 Time-dependent analysis can measure sign of x (coming soon!) This is the best mode in which to search for mixing: y is likely to be comparable to or larger than x => must measure strong phase
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D 0 ->K *+ e - Reconstruct K *+ in K s 0 +, K s 0 -> + - mode Advantages of this mode: Only mixing contributes to WS signal Distinct proper time distribution of mixing: t 2 e -t K * mass cut rejects backgrounds Drawbacks of this mode: Low momentum tracks due to e final state Soft e momentum due to forward neutrino favored by V – A coupling Must “pseudo-reconstruct” the undetected neutrino Only sensitive to x
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D 0 ->K *+ e - : Fit to the “Right-sign” Data Distributions from Monte Carlo
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D 0 ->K *+ e - : Fit to the “Wrong-signed” Data Fit distributions from Monte Carlo
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D 0 ->K *+ e - Systematic uncertainties: Signal and background shapes MC Statistics Resolution and background parameters Differences in RS and WS efficiencies Results to be combined with D 0 ->K + l - analysis Comparable sensitivity
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Other CLEO Charm Analyses in Progress:
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Summary First observation (4.5 statistical significance) of DCSD D 0 ->K 0 + - (prelim.) We observe 5 new submodes of this decay First measurement of strong phase shift s between D 0 ->K 0 + - and D 0 ->K 0 + - = (-3 +/- 14) 0 (prelim.) First analysis that can measure sign of x (coming soon!) Best channel in which to search for mixing D 0 ->K 0 + - : D 0 ->K *+ l - :
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CP-even and CP-odd intermediate states provide sensitivity to 1 and 2, thus y Sensitivity to sign of x = M/ through sin term in | M | 2 Interference between Cabibbo-favored and DCSD may enhance sensitivity to x D 0 ->K s 0 + - : Time Evolution of the Dalitz Plot Mass eigenstates are also eigenstates of CP: Time evolution is given by: Evaluating and, collecting terms with similar time-dependence, and squaring the amplitude gives:
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