kalanand mishra april 27, 2006 1 branching ratio measurements of decays d 0 π - π + π 0, d 0 k...
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Kalanand Mishra April 27, 2006 1
Branching Ratio Measurements of DecaysBranching Ratio Measurements of Decays
DD00ππ--ππ++ππ00, , DD00KK--KK++ππ00 Relative toRelative to DD00KK--ππ++ππ00
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
D0π-π+π0 ____________
D0K-π+π0D0K-K+π0 ____________
D0K-π+π0
= (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.
Kalanand Mishra April 27, 2006 2
Track SelectionTrack 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/c2 < M < 150 MeV/c2
• We search for decays of type D*+D0s
+
D0-+0, D0K-K+0, D0K-+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 SampleData 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 m0 at h-h+ vertex 1.70 < m( h-h+0 ) < 2.0 GeV/c2
PCM ( D0 ) > 2.77 GeV/c
DD00hh--hh++00 Reconstruction Reconstruction D* Reconstruction D*+ candidate is made by fitting the D0 and
s+ to a vertex constrained in x and y to the
measured beam-spot for the run. |mD* - m D0 - 145.5| < 0.6 MeV/c2
Chose a single best candidate with smallest vtx 2 for the whole decay chain.
Summary of Event SelectionSummary of Event Selection
Kalanand Mishra April 27, 2006 3
Background Sources: Monte Carlo StudyBackground Sources: Monte Carlo Study
GeV/c2GeV/c2
GeV/c2 GeV/c2
--++00
KK--KK++00
Zoomed inZoomed in
Zoomed inZoomed in
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
Reflection StudyReflection Study
Monte Carlo: Shape
data: number
Monte Carlo: Shape
data: number
K-K+π0
Kalanand Mishra April 27, 2006 5
signal yield from datasignal yield from data
--++00 KK--KK++00KK--++00
• Signal fit with sum of 3 Gaussians
• Linear background
• K- +0 reflection peak in the sidebands of -+0 and K-K+0
Kalanand Mishra April 27, 2006 6
PID-corrected Reconstruction Efficiency on DPPID-corrected Reconstruction Efficiency on DP m2(K-π0) m2(π+π0) m2(K-π+)
m2(π-π0) m2(π+π0) m2(π-π+)
--++00
m2(K-π0) m2(K+π0) m2(K-K+)
KK--KK++00
KK--++00
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 3rd 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.
Sproduced = S . < w >
• 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 BRsCalculation of ratio of BRs
Kalanand Mishra April 27, 2006 8
Compares well !
Comparison of background in Data and Monte Carlo sidebandsComparison of background in Data and Monte Carlo sidebands
2D pull pull Sideband
1.93 < mπ-π+π0
< 1.99 GeV/c2
Sideband
1.75 < mK-K+π0
< 1.80 GeV/c22D pullpull
--++00
KK--KK++00
Kalanand Mishra April 27, 2006 9
Comparison of background in signal region and in sideband of MCComparison of background in signal region and in sideband of MC
2D pull pullSideband
1.93 < mπ-π+π0
< 1.99 GeV/c2
Compares well !
2D pullpull
Sideband
1.75 < mK-K+π0
< 1.80 GeV/c2
--++00
KK--KK++00
Kalanand Mishra April 27, 2006 10
Efficiency-corrected Dalitz plotEfficiency-corrected Dalitz plot
m2(K-π0) m2(π+π0) m2(K-π+)~ 0.5 % bkg
m2(π-π0) m2(π+π0)m2(π-π+)~ 2 % bkg
m2(K-π0) m2(K+π0)m2(K-K+)~ 5 % bkg
--++00
KK--++00
KK--KK++00
Kalanand Mishra April 27, 2006 11
data generic ccbarCLEO model
Why we believe we are correcting the Dalitz plots Correctly ?Why we believe we are correcting the Dalitz plots Correctly ?
m2(K-π+)m2(K-π0) m2(K-π0)
m2(K-π+)m2(π+π0)m2(π+π0)
KK--ππ++00
KK--ππ++00
Kalanand Mishra April 27, 2006 12
Why we believe we are correcting the Dalitz plots Correctly ?Why we believe we are correcting the Dalitz plots Correctly ?
m2(π+π0)m2(K-π0) m2(K-π+)
2D pull pull
Comparison of Kππ0 data DP ( bkg 0.5%) with CLEO-model generated MC DP ( bkg 0.9%)
Kalanand Mishra April 27, 2006 13
Consistency Checks
• Separate analysis in different D0 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 SystematicsStudy of Systematics
Kalanand Mishra April 27, 2006 14
Consistency Check : Results for Disjoint SamplesConsistency Check : Results for Disjoint Samples
SP6 SP6 Generic Generic ccbar ccbar
DataData
We repeated exactly the same analysis procedure to obtain ratio of BRs for D0 and D0bar events separately and in five different lab momentum bins. All results are consistent within errors.
Full data sample: 0.12470.0004Generated : 0.1249
Full data sample: 0.01510.0002Generated : 0.0150
Result for MC treated as Data Result for disjoint Data samples
Kalanand Mishra April 27, 2006 15
Consistency Check : <w> and Yield for Disjoint Data SamplesConsistency Check : <w> and Yield for Disjoint Data Samples
KK--++00 --++00 KK--KK++00
< w >< w >
YieldYield
Kalanand Mishra April 27, 2006 16
Systematic Studies : Monte Carlo StatisticsSystematic Studies : Monte Carlo Statistics
D0 decay mode Average Weight MC Stat. Error
Kπ0 10.7471 0.0182πππ0 9.4308 0.0198
Kπ0 12.6101 0.0530
Effect of Background PDF model on Signal Yield: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+π0 signal yield, up to 0.8 % in case of π-π+π0 and up to 1.5 % in case of K-K+π0 .
Kalanand Mishra April 27, 2006 17
Systematic Studies : Systematic Studies : m Variationm Variation
m cut = m cut = 0.4 MeV0.4 MeV
m cut = m cut = 0.6 MeV0.6 MeV
m cut = m cut = 0.8 MeV0.8 MeV
B(πππ0 )/ B(Kπ0)
0.1065
0.0006
0.1064
0.0006
0.1061
0.0006
B(KKπ0 )/ B(Kπ0)
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+π0) / B(K-π+π0) and 0.84 % in B(K-K+π0) / B(K-π+π0) due to m cut.
We repeat the analysis with different m cuts. Any variation in the results is a systematic error.
Kalanand Mishra April 27, 2006 18
Systematic Studies : Background SubtractionSystematic Studies : Background Subtraction
KK--++00 Truth-Truth-matchedmatched
Non Non truth-truth-matchedmatched
Truth-Truth-matchedmatched
Truth-Truth-matchedmatched
Non Non truth-truth-matchedmatched
Non Non truth-truth-matchedmatched
--++00
KK--KK++00
Comparison of mass plots of truth-matched and non truth-matched events
Kalanand Mishra April 27, 2006 19
Systematic Studies : Background SubtractionSystematic Studies : Background Subtraction
KK--++00
--++00
KK--KK++00
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+π0 )/B(K-π+π0)And 0.9 % forB(K-K+π0) /B(K-π+π0).
2D pull
2D pull
2D pull
pull
pull
pull
Kalanand Mishra April 27, 2006 20
Systematic Studies : PID Systematics Systematic Studies : PID Systematics ( ( datadata ) )
Kalanand Mishra April 27, 2006 21
Systematic Studies : PID Systematics Systematic Studies : PID Systematics ( ( MCMC ) )
Kalanand Mishra April 27, 2006 22
Systematic Studies : PID Systematics Systematic Studies : PID Systematics ( ( datadata / / MCMC ) )
With this new PID correction factor, we find a systematic error in the average weight of 0.31 % for K-π+π0, 0.58 % for π-π+π0 and 0.84 % for K-K+π0 modes. We conservatively assign a PID systematics of 0.8% to B(π-π+π0)/B(K-π+π0) and 1.0% to B(K-K+π0)/B(K-π+π0).
Kalanand Mishra April 27, 2006 23
Systematic Studies : Tracking EfficiencySystematic Studies : Tracking EfficiencyThere 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.
Kalanand Mishra April 27, 2006 24
BAD 1469 ‘almost’ ready for AWG review. Hopefully, I will upload it by early next week. Get review done and write conference note for ICHEP. Prepare a journal draft for publication in PRD.
D0 decay mode Our Current Results(%)
B(πππ0 )/B(Kπ0) 10.64 0.06 0.15
B(Kπ0 )/B(Kπ0) 2.38 0.03 0.06
PDG Results(%)
8.40 3.11
0.95 0.26
The present results are preliminary.
Results and StatusResults and Status
Kalanand Mishra April 27, 2006 25
Backup SlidesBackup Slides
Kalanand Mishra April 27, 2006 26
Results for Disjoint Samples -1Results for Disjoint Samples -1
Kalanand Mishra April 27, 2006 27
Results for Disjoint Samples -2Results for Disjoint Samples -2