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Kalanand Mishra April 27, 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,

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Presentation on theme: "Kalanand Mishra April 27, 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,"— Presentation transcript:

1 Kalanand Mishra April 27, 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 present measurements of the relative branching ratios from a sample of 232 fb -1 data. We find that D 0  π - π + π 0 ____________ D 0  K - π + π 0 D 0  K - K + π 0 ____________ D 0  K - π + π 0 = (1.064  0.006  0.015)  10 -1 = (2.38  0.03  0.06)  10 -2 These can be compared to PDG current world average (8.40  3.11)  10 -2 for the first ratio and (0.95  0.26)  10 -2 for the second.

2 Kalanand Mishra April 27, 2006 2 Track Selection Kaon & pion tracks  GoodTracksLoose, ≥ 20 DCH hits  ≥ 6 total SVT hits, ≥ 2 SVT r-phi (z) hits with at least 1 hit on inner layers  0 Reconstruction  Photon Energy > 100 MeV   0 Energy > 350 MeV  115 MeV/c 2 < M  < 150 MeV/c 2 We search for decays of type D* +  D 0  s + D 0  -  +  0, D 0  K - K +  0, D 0  K -  +  0  0   Integrated Luminosity ~ 232 fb -1 For Bkg studies & cut optimization: ccbar Continuum ~ 138 fb -1 For detection efficiency: signal MC 1.4M K - K +  0, 4.5M  -  +  0, 4.5M K -  +  0 Data Sample PID : LH Tight for both π and K  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( h - h +  0 ) < 2.0 GeV/c 2  P CM ( D 0 ) > 2.77 GeV/c D 0  h - h +  0 Reconstruction D* Reconstruction  D *+ candidate is made by fitting the D 0 and  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  Chose a single best candidate with smallest vtx  2 for the whole decay chain. Summary of Event Selection

3 Kalanand Mishra April 27, 2006 3 Background Sources: Monte Carlo Study GeV/c 2 -+0-+0-+0-+0 K-K+0K-K+0K-K+0K-K+0 Zoomed in

4 Kalanand Mishra April 27, 2006 4 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

5 Kalanand Mishra April 27, 2006 5 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

6 Kalanand Mishra April 27, 2006 6 PID-corrected Reconstruction Efficiency on DP 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

7 Kalanand Mishra April 27, 2006 7 Since the reconstruction efficiency is not uniform across phase space, each event is weighted according to its efficiency ( weight = 1/ efficiency ). As, in some parts of phase space, the bin-by-bin and fitted (with a 3 rd order polynomial) efficiencies differ slightly, we use the bin-by-bin efficiency for analysis and the fitted efficiency for cross check. 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 ratios is obtained as the ratio of number of events produced for respective modes in the experiment. The statistical and systematic errors associated with the measurement are determined. Calculation of ratio of BRs

8 Kalanand Mishra April 27, 2006 8 Compares well ! Comparison of background in Data and Monte Carlo sidebands 2D pull pull Sideband 1.93 < m π - π + π 0 < 1.99 GeV/c 2 Sideband 1.75 < m K - K + π 0 < 1.80 GeV/c 2 2D pull pull -+0-+0-+0-+0 K-K+0K-K+0K-K+0K-K+0

9 Kalanand Mishra April 27, 2006 9 Comparison of background in signal region and in sideband of MC 2D pull pull Sideband 1.93 < m π - π + π 0 < 1.99 GeV/c 2 Compares well ! 2D pull pull Sideband 1.75 < m K - K + π 0 < 1.80 GeV/c 2 -+0-+0-+0-+0 K-K+0K-K+0K-K+0K-K+0

10 Kalanand Mishra April 27, 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 April 27, 2006 11 datageneric ccbar CLEO model Why we believe we are correcting the Dalitz plots Correctly ? m 2 (K - π + ) m 2 (K - π 0 ) m 2 (K - π + ) m 2 (π + π 0 ) K-π+0K-π+0K-π+0K-π+0 K-π+0K-π+0K-π+0K-π+0

12 Kalanand Mishra April 27, 2006 12 Why we believe we are correcting the Dalitz plots Correctly ? m 2 (π + π 0 ) m 2 (K - π 0 ) m 2 (K - π + ) 2D pull pull Comparison of Kππ 0 data DP ( bkg 0.5%) with CLEO-model generated MC DP ( bkg 0.9%)

13 Kalanand Mishra April 27, 2006 13 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. 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

14 Kalanand Mishra April 27, 2006 14 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

15 Kalanand Mishra April 27, 2006 15 Consistency Check : and Yield for Disjoint Data Samples K-+0K-+0K-+0K-+0 -+0-+0-+0-+0 K-K+0K-K+0K-K+0K-K+0 Yield

16 Kalanand Mishra April 27, 2006 16 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 0.4 % variation in K - π + π 0 signal yield, up to 0.8 % in case of π - π + π 0 and up to 1.5 % in case of K - K + π 0.

17 Kalanand Mishra April 27, 2006 17 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 ) 0.1065  0.0006 0.1064  0.0006 0.1061  0.0006 B(K  K  π 0 )/ B(K    π 0 ) 0.0236  0.0004 0.0238  0.0003 0.0238  0.0003 Based on this study, we assign a systematic error of 0.28 % in B(π - π + π 0 ) / B(K - π + π 0 ) and 0.84 % 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.

18 Kalanand Mishra April 27, 2006 18 Systematic Studies : Background Subtraction K-+0K-+0K-+0K-+0 Truth- matched Non truth- matched Truth- matched Non truth- matched -+0-+0-+0-+0 K-K+0K-K+0K-K+0K-K+0 Comparison of mass plots of truth-matched and non truth-matched events

19 Kalanand Mishra April 27, 2006 19 Systematic Studies : Background Subtraction K-+0K-+0K-+0K-+0 -+0-+0-+0-+0 K-K+0K-K+0K-K+0K-K+0 Comparison of DPs of truth-matched and non truth-matched events 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

20 Kalanand Mishra April 27, 2006 20 Systematic Studies : PID Systematics (  data )

21 Kalanand Mishra April 27, 2006 21 Systematic Studies : PID Systematics (  MC )

22 Kalanand Mishra April 27, 2006 22 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. We conservatively assign a PID systematics of 0.8% to B(π - π + π 0 )/B(K - π + π 0 ) and 1.0% to B(K - K + π 0 )/B(K - π + π 0 ).

23 Kalanand Mishra April 27, 2006 23 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 0.7 % for each of the two ratio of BRs.

24 Kalanand Mishra April 27, 2006 24 è BAD 1469 ‘almost’ ready for AWG review. Hopefully, I will upload it by early next week. è Get review done and write conference note for ICHEP. è Prepare a journal draft for publication in PRD. D 0 decay modeOur Current Results(%) B(π  π  π 0 )/B(K    π 0 )10.64  0.06  0.15 B(K    π 0 )/B(K    π 0 )2.38  0.03  0.06 PDG Results(%) 8.40  3.11 0.95  0.26 The present results are preliminary. Results and Status

25 Kalanand Mishra April 27, 2006 25 Backup Slides

26 Kalanand Mishra April 27, 2006 26 Results for Disjoint Samples -1

27 Kalanand Mishra April 27, 2006 27 Results for Disjoint Samples -2

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