Search for Direct CP Violation in 3-body Cabibbo Suppressed D0 Decays

Kalanand Mishra,G. Mancinelli, B. T. Meadows, M. D. Sokoloff

University of Cincinnati

• Motivation • Strategy • Summary and outlook

Charm AWG08/17/2006

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CP Violation in D0 Decay

Look for particle anti-particle rate differences

)()(

)()(00

00

fDfD

fDfDACP →Γ+→Γ

→Γ−→Γ=

Where f is: +-0 [π, …] and K+K-0 [K*K, π0 , …]. Decays to these final states are Cabibbo-suppressed, enhancing the possibility that interference with non-SM amplitudes could produce direct CP violation.

CPV expected to be small in the charm sectorSM predictions O(0.1%)

CPV > 1% will be a strong evidence for non-SM processes

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Why 3-body CS modes ?• The best hope for SM predicted CP violation in

Charm decays is in CS modes. The prediction for CF decays are too small.

• 3-body decays permit the measurement of phase differences which are required to create direct CP violation in the interference between SM and non-SM processes.

• These are relatively high statistics modes (45000 D0/D0barπππ0 & 6800 D0/D0barKKπ0 events).

• Since we can normalize measurements relative to the whole phase space (Dalitz plot), the dependence on πs tagging efficiency is negligible.

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Strategy

• need interference between diagrams with different strong (i) and weak phases (i) :

• Perform separate Dalitz plot analyses of D0π-π+π0 (K-K+π0) and D0barπ+π-π0 (K+K-π0).

• Models have already been established in both cases that provide good description of data.

( ) ( )∑ −−−=−ji

jijijiff AAAA,

22 sinsin2|||| δδφφ

0|||| 22 ≠− ff AA direct CPV

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What is Known ?

• CLEO measure ACP in D0π-π+π0 mode

ACP = 0.01 + 0.05

• No ACP measurements available for D0K-K+π0

• Other analysis are under way to measure CP asymmetry in D0K-K+, π-π+ modes

+0.07

-0.05

• ACP(K+K-) = 0.014 ± 0.010

• ACP(π+π-) = 0.013 ± 0.012

• ACP(π0π0) = 0.00 ± 0.05

• ACP(K+K-π+π-) = -0.08 ± 0.07

PDG 2006

Measure the difference between the integral of the coherent sum of all amplitudes across the DP for D0 and D0bar, divided by the area of the DP.

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Dalitz Plot Fit Results: π-π+π0

BAD 1174

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Dalitz Plot Fit Results: K-K+π0

BAD 1502

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What we have looked at ?• Our sensitivity to observe CP asymmetry is higher in the D0π-π+π0 decay because of the higher statistics in this mode.• However, I have started with D0K-K+π0 mode since recently I have been working on this Dalitz plot analysis.• Start by looking at the distribution of moments of the cosine of the helicity angle in data for both D0 and D0bar events.• Then perform separate Dalitz plot fit for CP conjugate events.

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Moments of cosH [K+π0]

D0

__ D0

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Moments of cosH [K-π0]

D0

__ D0

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Moments of cosH [K-K+]

D0

__ D0

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Separate DP Fits

f0(980) 0.65 ± 0.14 0.48 ± 0.13 0.9 103.2 ± 13.4 83.0 ± 18.1 0.9f2’(1525) 1.12 ± 0.21 0.85 ± 0.20 0.9 -38.8 ± 8.5 -45.0 ± 10.6 0.5(1020) 0.74 ± 0.02 0.73 ± 0.02 0.3 -17.7 ± 10.3 -21.0 ± 12.6 0.2

K*-(892) 0.64 ± 0.02 0.65 ± 0.02 0.3 -30.5 ± 3.5 -40.6 ± 3.3 2.1K*+(1410) 0.64 ± 0.60 1.09 ± 0.57 0.5 120.6 ± 36.7 115.5 ± 20.5 0.1K*-(1410) 2.91 ± 0.45 2.94 ± 0.53 0.0 184.1 ± 9.8 159.6 ± 8.4 1.9K+π0 SW 4.50 ± 1.39 3.08 ± 1.11 0.8 63.1 ± 8.9 100.4 ± 11.4 2.6K-π0 SW 4.92 ± 0.68 4.12 ± 0.86 0.7 154.0 ± 14.8 114.7 ± 16.2 1.8

Amplitude Phase

D0 D0bar D0 D0bar# SD # SD

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Separate DP Fits

K*-(892) 0.63 ± 0.02 0.66 ± 0.02 1.1 -30.8 ± 3.3 -41.1 ± 3.2 2.2K*+(1410) 0.30 ± 0.31 1.04 ± 0.30 1.7 87.6 ± 70.5 100.7 ± 16.0 0.3K*-(1410) 2.80 ± 0.27 2.72 ± 0.28 0.2 182.8 ± 6.9 168.8 ± 6.1 1.5K+π0 SW 4.85 ± 0.74 3.65 ± 0.58 1.3 66.9 ± 7.2 86.3 ± 10.3 1.6K-π0 SW 4.78 ± 0.63 3.59 ± 0.57 1.4 160.0 ± 8.6 123.6 ± 10.5 2.7

Amplitude Phase

D0 D0bar D0 D0bar# SD # SD

Parameters for CP eigen states are fixed to the ones obtained from the combined fit.

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Summary

• After performing D0π-π+π0, K-K+π0 Dalitz plot analysis, we have started looking into CP asymmetries in the conjugate decays.

• We will keep documenting (BAD 1531) as we move along.

• We aim for a preliminary result for DPF 2006.