1. Kalanand Mishra June 29, 2006 1 Branching Ratio Measurements of Decays D 0  π - π + π 0, D 0  K - K + π 0 Relative to D 0  K - π + π 0 Giampiero Mancinelli, Brian T. Meadows, Kalanand Mishra, Michael D. Sokoloff University of Cincinnati We measure the ratio of Cabibbo-suppressed to Cabibbo- favored branching fractions D 0  π - π + π 0 ____________ D 0  K - π + π 0 D 0  K - K + π 0 ____________ D 0  K - π + π 0 = ( 10.59  0.06  0.13 )  10 -2 = ( 2.37  0.03  0.04 )  10 -2 These can be compared to the current world average values ( 8.40  3.11 )  10 -2 and ( 0.95  0.26 )  10 -2 respectively.

2. Kalanand Mishra June 29, 2006 2 Track Selection è Kaon & pion tracks  P T > 0.1 GeV/c, DCH hits ≥ 20  Within fiducial volume of tracking system and DIRC acceptance è  0 Reconstruction   Candidates with  Single calorimeter bumps not matched with any track  Energy > 100 MeV   0 Energy > 0.350 GeV  0.115 GeV/c 2 < M  < 0.150 GeV/c 2 èWe search for decays D* +  D 0  s + D 0  -  +  0, D 0  K - K +  0, D 0  K -  +  0  0   èIntegrated Lumi 232 fb -1 èFor Bkgd studies and cut optimization: ccbar Continuum 138 fb -1 èFor detection efficiency: Signal MC - phase space ~ 1.4 million K - K +  0 ~ 4.5 million  -  +  0 ~ 4.5 million K -  +  0 Data Sample è PID : LH Tight for both π and K

3. Kalanand Mishra June 29, 2006 3  h - and h + tracks are fit to a vertex  Mass of  0 candidate is constrained to m  0 at h - h + vertex  1.70 < m( D 0 ) < 2.0 GeV/c 2  P CM ( D 0 ) > 2.77 GeV/c D* Reconstruction  D *+ candidate is made by fitting the D 0 and the  s + to a vertex constrained in x and y to the measured beam-spot for the run.  |m D* - m D 0 - 145.5| < 0.6 MeV/c 2  vertex  2 probability > 0.01  Chose a single best candidate with smallest vtx  2 for the whole decay chain ( multiplicity = 1.03 ).  Charged track combinatoric, mis-constructed  0  Real D 0, fake  s  K  0 reflection in  0 and KK  0 modes D 0  h - h +  0 Reconstruction Background Sources

4. Kalanand Mishra June 29, 2006 4 Background Study: Monte Carlo GeV/c 2 D 0 candidate mass [ GeV/c 2 ] -+0-+0-+0-+0 Zoomed in D 0 candidate mass [ GeV/c 2 ] signal K - π + π 0 reflection Comb.Bkg.

5. Kalanand Mishra June 29, 2006 5 K-K+0K-K+0K-K+0K-K+0 Zoomed in D 0 candidate mass [ GeV/c 2 ] K - π + π 0 reflection Comb.Bkg. signal Background Study: Monte Carlo

6. Kalanand Mishra June 29, 2006 6 K -  +  0 reflection in  -  +  0 (top) and K - K +  0 (bottom) samples. I get the shape of the reflection from Monte Carlo (left) and the number of reflection events from data (right). π-π+π0 π-π+π0 Reflection Study Monte Carlo: Shape data: number Monte Carlo: Shape data: number K-K+π0 K-K+π0

7. Kalanand Mishra June 29, 2006 7 signal yield from data -+0-+0-+0-+0 K-K+0K-K+0K-K+0K-K+0 K-+0K-+0K-+0K-+0 Signal fit with sum of 3 gaussians Linear background K -  +  0 reflection peak in the sidebands of  -  +  0 and K - K +  0

8. Kalanand Mishra June 29, 2006 8 PID-corrected Reconstruction Efficiency m 2 (K - π 0 ) m 2 (π + π 0 ) m 2 (K - π + ) m 2 (π - π 0 ) m 2 (π + π 0 ) m 2 (π - π + ) -+0-+0-+0-+0 m 2 (K - π 0 ) m 2 (K + π 0 ) m 2 (K - K + ) K-K+0K-K+0K-K+0K-K+0 K-+0K-+0K-+0K-+0

9. Kalanand Mishra June 29, 2006 9 Since the reconstruction efficiency is not uniform across phase space, each event is weighted according to its efficiency. weight = 1/ efficiency The average weight of reconstructed signal events in signal region is obtained after doing a background subtraction from sideband. The number of observed signal events was obtained directly from fitting the mass plots. The total number of signal events produced in the experiment is product of average signal weight and number of observed signal events for each mode. S produced = S. The ratio of branching fractions is obtained as the ratio of number of events produced for respective modes in the experiment. Calculation of ratio of BRs

10. Kalanand Mishra June 29, 2006 10 Efficiency-corrected Dalitz plot m 2 (K - π 0 ) m 2 (π + π 0 ) m 2 (K - π + ) ~ 0.5 % bkg m 2 (π - π 0 ) m 2 (π + π 0 ) m 2 (π - π + ) ~ 2 % bkg m 2 (K - π 0 ) m 2 (K + π 0 ) m 2 (K - K + ) ~ 5 % bkg -+0-+0-+0-+0 K-+0K-+0K-+0K-+0 K-K+0K-K+0K-K+0K-K+0

11. Kalanand Mishra June 29, 2006 11 Consistency Checks Separate analysis in different D 0 lab momentum ranges. Separate analysis by charge ( i.e., separately for D* + and D* - events ). Analysis using Monte Carlo as Data. Analysis without doing background subtraction. Systematic Errors error from Monte Carlo statistics cut variation systematics (  m cut ) error from estimation of background events in signal region effect of background pdf modeling on signal yield PID systematics Tracking efficiency systematics Study of Systematics

12. Kalanand Mishra June 29, 2006 12 Consistency Check : Results for Disjoint Samples SP6 Generic SP6 Generic ccbar ccbar Data We repeated exactly the same analysis procedure to obtain ratio of BRs for D 0 and D 0 bar events separately and in five different lab momentum bins. All results are consistent within errors. Full data sample: 0.1247  0.0004 Generated : 0.1249 Full data sample: 0.0151  0.0002 Generated : 0.0150 Result for MC treated as DataResult for disjoint Data samples

13. Kalanand Mishra June 29, 2006 13 èMeasure the ratio of BFs by directly fitting the efficiency corrected histograms of D 0 candidate invariant mass and then taking the ratio of the yields. èThe results obtained from this method agree, within stat. error, with the results of the main analysis Consistency Check : Analysis without bkg subtraction D 0  π - π + π 0 ____________ D 0  K - π + π 0 D 0  K - K + π 0 ____________ D 0  K - π + π 0 = (10.62  0.06 ) % = ( 2.40  0.03 ) %

14. Kalanand Mishra June 29, 2006 14 Systematic Studies : Monte Carlo Statistics D 0 decay modeAverage WeightMC Stat. Error K    π 0 10.74710.0182 πππ0πππ0 9.43080.0198 K    π 0 12.61010.0530 Effect of Background PDF model on Signal Yield: We performed the mass plot fits with different background models ( linear, polynomial, and exponential shapes ) and different starting points for the fit. We observed up to 0.014 % variation in K - π + π 0 signal yield, up to 0.157 % in case of π - π + π 0 and up to 0.125 % in case of K - K + π 0.

15. Kalanand Mishra June 29, 2006 15 Systematic Studies :  m Variation  m cut = 0.4 MeV  m cut = 0.6 MeV  m cut = 0.8 MeV B(π  π  π 0 )/ B(K    π 0 ) 0.1060  0.0006 0.1059  0.0006 0.1056  0.0006 B(K  K  π 0 )/ B(K    π 0 ) 0.0236  0.0004 0.0237  0.0003 0.0238  0.0003 Based on this study, we assign a systematic error of 0.3 % in B(π - π + π 0 ) / B(K - π + π 0 ) and 0.9 % in B(K - K + π 0 ) / B(K - π + π 0 ) due to  m cut. We repeat the analysis with different  m cuts. Any variation in the results is a systematic error.

16. Kalanand Mishra June 29, 2006 16 Systematic Studies : Background Subtraction K-+0K-+0K-+0K-+0 -+0-+0-+0-+0 K-K+0K-K+0K-K+0K-K+0 Comparison of Dalitz plot distribution of truth-matched background in signal region and background from sidebands By repeating the analysis on generic ccbar events and doing the background subtraction of ‘true’ background events in the signal region, we find a systematic error of 0.6 % for B( π - π + π 0 )/B( K - π + π 0 ) And 0.9 % for B( K - K + π 0 ) /B( K - π + π 0 ). 2D pull pull

17. Kalanand Mishra June 29, 2006 17 Systematic Studies : PID Systematics (  data /  MC ) With this new PID correction factor, we find a systematic error in the average weight of 0.31 % for K - π + π 0, 0.58 % for π - π + π 0 and 0.84 % for K - K + π 0 modes. Also, PID group provides syst. from PID table. Combining them all, we assign a PID systematics of 0.77% to B(π - π + π 0 )/B(K - π + π 0 ) and 0.84% to B(K - K + π 0 )/B(K - π + π 0 ).

18. Kalanand Mishra June 29, 2006 18 Systematic Studies : Tracking Efficiency There are two types of issues related to tracking efficiency corrections and systematics: 1.) How well does our Monte Carlo mimic the real data with respect to hits-per-plane efficiency and resolution in DCH and SVT ? 2.) As tracks traverse the detector, they can interact, scattering either elastically or inelastically. The Monte Carlo has cross-sections built into it. How much this cross-section differs from the one in real data ? The correction for the first effect is same for both Kaons and Pions ( as studied by Tracking AWG ) and cancel out in the ratio of BRs. The correction for the second effect is also same for Kaons and Pions, but the uncertainty in this correction is slightly different for the two particles. Based on the studies done by ISR people ( Solodov, et. Al., BAD 855 and BAD831), we conservatively assign a tracking efficiency systematics of 0.6 % for each of the two ratio of BFs.

19. Kalanand Mishra June 29, 2006 19 èD 0  K s 0  0 is a Cabibbo- favored decay and is a background for D 0  -  +  0 reconstruction. èWe remove this contribution from D 0  -  +  0 yield. K 0 s Removal

20. Kalanand Mishra June 29, 2006 20 Systematics B(π  π  π 0 )/B(K    π 0 ) MC Statistics 0.27 %  m selection 0.30 % Bg. subtraction 0.60 % Efficiency binning 0.12 % Bg PDF model 0.16 % P* difference 0.24 % PID 0.77 % Tracking 0.60 % K s 0 removal 0.07 % Total 1.25 % B(K    π 0 )/B(K    π 0 ) 0.47 % 0.90 % 0.24 % 0.13 % 0.02 % 0.84 % 0.60 % 0.00 % 1.73 % Summary of Systematics

21. Kalanand Mishra June 29, 2006 21 D 0 decay modeOur Current Results(%) B(π  π  π 0 )/B(K    π 0 )10.59  0.06  0.13 B(K    π 0 )/B(K    π 0 )2.37  0.03  0.04 PDG Results(%) 8.40  3.11 0.95  0.26 Results and Conclusion The decay rate for each mode  =.  where M = decay matrix element  = 3-body phase space = area of the Dalitz plot

22. Kalanand Mishra June 29, 2006 22 D 0 decay mode3-body decay |M| 2 (π  π  )/ |M| 2 (K  π  ) 0.0668  0.0004  0.0008 |M| 2 (K    )/ |M| 2 (K  π  )0.0453  0.0006  0.0008 |M| 2 (K    )/ |M| 2 (π  π  )0.6781  0.0007  0.0011 2-body decay 0.0338  0.0009 0.1114  0.0023 3.52 89  0.0026 Results and Conclusion For 2-body decays D 0  -  + and D 0  K - K +  = 2-body phase space  decay momentum of either particle in D 0 CM frame Differ by factor 5 !

23. Kalanand Mishra June 29, 2006 23 Backup Slides

24. Kalanand Mishra June 29, 2006 24 Results for Disjoint Samples -1

25. Kalanand Mishra June 29, 2006 25 Results for Disjoint Samples -2