Transcript _ A Search for D0D0 mixing in Semileptonic decays, A search for CP Violation in D+  K+K-p+ decays and a Measurement of the Branching.

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A Search for D0D0 mixing in
Semileptonic decays, A search for CP
Violation in D+  K+K-p+ decays
and a Measurement of
the Branching ratio
Milind V. Purohit
Univ. of South Carolina
(for the BaBar collaboration)
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
USA [38/301]
The BaBar Collaboration
China [1/5]
Canada [4/19]
Inst. of High Energy Physics, Beijing
U of British Columbia
McGill U
U de Montréal
U of Victoria
Germany [4/28]
Ruhr U Bochum
TU Dresden
Phys. Inst., Heidelberg
U Rostock
France
[5/60]
(78 institutions,
609 Collaborators)
Norway [1/3]
Italy [13/105]
U of Bergen
INFN Bari
INFN Ferrara
INFN Frascati
INFN Genova
INFN Milano
INFN Napoli
INFN Padova
INFN Pavia
INFN Perugia
INFN Pisa
INFN Roma
INFN Torino
INFN Trieste
Russia [1/11]
Budker Inst., Novosibirsk
Netherlands [1/5]
NIKHEF
LAPP, Annecy
Ecole Polytechnique
LAL Orsay
LPNHE des Universités Paris 6/7
CEA, DAPNIA, CE-Saclay
United Kingdom [10/72]
U of Birmingham
U of Bristol
Brunel University
U of Edinburgh
U of Liverpool
Imperial College
Queen Mary & Westfield College
Royal Holloway, University of
London
U of Manchester
Rutherford Appleton Laboratory
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
Caltech, Pasadena
UC, Irvine
UC, Los Angeles
UC, San Diego
UC, Riverside
UC, Santa Barbara
UC, Santa Cruz
U of Cincinnati
U of Colorado
Colorado State
Florida A&M
Harvard
U of Iowa
Iowa State U
LBNL
LLNL
U of Louisville
U of Maryland
U of Massachusets
MIT
U of Mississippi
Mount Holyoke College
U of Notre Dame
Ohio State
U of Oregon
U of Pennsylvania
Prairie View A&M
Princeton
SLAC
Univ. of South Carolina
Stanford U
SUNY, Albany
U of Tennessee
U of Texas at Dallas
U of Texas, Austin
Vanderbilt
U of Wisconsin
Yale U
The BaBar Detector
~250 fb-1 of data collected so far.
•Silicon Vertex Tracker
z hit resolution 15mm
•Drift CHamber
(pT)/pT = 0.14%  pT + 0.45%
•Detector of Internally
Reflected Cherenkov light
K-p separation 4.2 @ 3.0GeV
•ElectroMagnetic Calorimeter
E/E = 2.3%E-1/4  1.4%
•RPC based Instrumented
magnetic field Flux Return
18/19 layers of RPC in 60/65
cm of iron
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
Searching for New Physics in
Charm CP violation with BaBar data




CP violation in charm is expected to first manifest itself in Singly
Cabibbo-suppressed (SCS) decays.
Within the Standard Model, one expects CP violation asymmetries
in SCS Decays ~10-3, while New Physics can give CP violation
asymmetries ~10-2.
[G. Burdman & I. Shipsey, Ann. Rev. Nucl. Part. Sci., 2003, hepph/0310076. See also S. Bianco, F. L. Fabbri, D. Benson & I. Bigi,
hep-ex/0309021.]
Current experimental limits are ~ (2 – 5) x 10-2 leaving a
considerable window for new physics discovery.
The analysis reported here is based on ~43,000 D+  KKp decays
from ~80 fb-1. [BaBar has ~250 fb-1 of data.]
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
Standard Model interfering amplitudes:
A ~Vcs*¢ Vus
A ~ Vcs*¢ Vus, Vcd*¢ Vud, Vcb*¢ Vub
•In the Wolfenstein parameterization, the CKM matrix (below) clearly gives only a
small CP violating asymmetry.
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
Data Sample and Analysis
• Our final sample contains ~43,000 D+  KKp
decays from ~80 fb-1.
• We measure the asymmetry
where
• We also measure the asymmetry in the f & K*
regions.
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
KKp Yields
21632 ± 228 D+ events
20940 ± 226 D- events
23066 ± 217 Ds+ events
22928 ± 214 Ds- events
•Likelihood ratio cut uses p* and beam-spot constrained c2
•Kaons have kaon ID, pions must not have kaon ID
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
ACP in f, K* Regions of KKp Dalitz Plot
1. The f region:
5452 ± 87 D+ events
5327 ± 86 D- events
• f mass is required to lie within 10 MeV/c2 of nominal f mass
• |cos(qH)| is required to be ≥ 0.2 ; qH is helicity angle in f rest frame
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
2. The K* region:
5247 ± 96 D+ events
5113 ± 96 D- events
• K* mass is required to lie within 50 MeV/c2 of nominal K* mass
• |cos(qH)| is required to be ≥ 0.3 ; qH is helicity angle in K* rest frame
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
Systematic Errors on ACP
• Systematic errors on ACP estimated as:
– Largest difference using other normalizations (0.8%)
– Largest uncorrected asym. in control samples (1.1%)
– From table (in units of 10-2):
Source
MC simulation
Background estimate
Event Selection
Total
KKp
0.06
0.63
0.51
0.81
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
fp
0.06
0.32
0.56
0.65
K*0K
0.06
0.49
0.54
0.73
ACP Results
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
The Branching Ratio
G(D+  K-K+p+) / G(D+  K-p+p+)
• Using measured yields and efficiencies in bins of
the Dalitz plots, the total branching ratio is
determined: 0.107 ± 0.001 ± 0.002
• Sources of systematic errors:
Source
Error (10-2)
PID, tracking
0.21
Background estimate
0.05
Event Selection
0.02
Total
0.22
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
The Branching Ratio Compared
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
Searching for New Physics in
mixing with BaBar data

For decays of neutral Ds Rmix
–
–

The standard model predicts a low rate (~10-7) of DD Mixing for the
box diagram which goes up to ~10-3 when long distance effects are
included; nevertheless we would like to observe mixing as a first step.
New physics effects can easily produce > 10-7 rates of mixing, and are
the only way we can get CP violation in mixing.
[G. Burdman & I. Shipsey, Ann. Rev. Nucl. Part. Sci., 2003, hepph/0310076. See also S. Bianco, F. L. Fabbri, D. Benson & I. Bigi,
hep-ex/0309021.]
The analysis reported here is based on ~50,000 semi-electronic
decays of neutral D mesons from ~87 fb-1
with mixing rate sensitivity down to ~10-3.
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
mixing rate = |amplitude|2
Charm Mixing, continued
mixing rate = |amplitude|2
current
experimental
sensitivity
SM Mixing Predictions
y=DG/2G
x=DM/G
New Physics Mixing Predictions
x=DM/G
• Possible enhancements
due to new particles and
interactions in new
physics models:
•gluinos, squarks
•fourth generation
quarks
•lepto-quarks, etc.
• No CP-violating effects
expected in SM -- CP
violation in mixing would
be unambiguous signal of
new physics
(A. Petrov, hep/ph 0311371)
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
cc continuum event topology
e, m
Right-sign unmixed decays
D*+
D*-
D0 p+tag
K-e+
K

D0 p-tag
K+e-
pslow
beamspot
D0
Wrong-sign mixed decays
D*+
D*-
interaction point
D0 p+tag
D0
K+e-
D0 p-tag
D0
other charmed hadron
(will hadronically reconstruct in
next iteration of analysis)
K-e+
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
The Analysis Strategy
• We use neutral D mesons from D*+ decays: D*+  D0p+
• Flavor at birth is tagged by pion from D* decay
• Flavor at decay is tagged by electron: D0  (K-/K*-) e+e
Clearly, an e+ signifies a RS (Right Sign, or unmixed) D0
while an e- would signify a WS (Wrong Sign or mixed) D0
• The mixing rate is given by

t

 

GWS (t )  exp  t

 D 0 


 
  D0
exponential
envelope




2
Quadratic time
dependence
 x2 + y 2


4

mixing rate
• where x  DM / G,
yDG/2G
• No DCS decay background exists
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China




Semileptonic Mixing Analysis Technique
• A neural network event selector is used.
• Another neural network is used for p*(D0) reconstruction.
(p* is the c.m. momentum)
• An unbinned extended maximum likelihood fit
using DM & transverse lifetime is then done, where
DM  m(p D0) – m(D0)
• First, a fit to high-statistics RS sample gets
– signal DM shape and
– unmixed D0 lifetime
for use in WS pdf and to get N(unmixed), the
normalization for Rmix.
• Subsequent fit to WS sample for N(mix)
• Rmix ≈ N(mix) / N(unmixed)
• Data sample: 80 fb-1 on resonance, 7.1 fb-1 off-resonance
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
RS Unmixed Fit to 87 fb-1 of Data
• Unbinned extended maximum likelihood fit to
transverse lifetime and DM = M(D*)-M(D0)
with 15 floated parameters
DM signal region
D0 sgnl
D0 bkgd
zero life
D+
lifetime tails
D0 sgnl
D+
D0 bkgd
zero life
Results of fit:
• Unmixed D0 yield: 49620 ± 324 evts (stat)
• DM and lifetime pdfs
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
DM sideband
WS Mixed D0 Fit to 87 fb-1 of Data
• Mixed signal pdf parameters taken
from high-statistics unmixed data fit
– Ni and zero lifetime triple Gaussian
parameters floated (11 parameters)
DM projection
D0 signal
Peaking D+
Random D+
Random D0
Zero Life
• Distribution of N(mix)
from fits to an ensemble
of 170 WS generic MC
datasets with zero
embedded mixed signal
events
•Unblinded N(mix):
114 ± 61 evts
(~5% probability of getting
a larger result for Rmix=0)
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
WS Mixed D0 Fit to 87 fb-1 of Data
Full lifetime projection
D0 signal
random D+
pkng D+
random D0
Lifetime projection showing mixed signal
zero life
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
Final result for semileptonic mixing
• The fit gives a yield of Nmix=114 ± 61 wrong
sign signal events.
• Systematics evaluated as fraction of
statistical error:
Systematic
Mixed Dm PDF
Mixed decay time PDF
Combinatoric Dm PDF
Bkg D0 decay model
Bkg D+ decay model
Total systematic
Total stat. + syst.
Error
0.27
0.06
0.13
0.13
0.10
0.35
1.06
• Normalising to number of right-sign events
gives result on mixing.
R mix 0.0023 0.0012 stat
R mix 0.0042 90% C.L.
0.0004 syst
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
stat stat + syst
90% Confidence limit
on number of mixing
signal.
Comparison to other results
Summary of all BaBar D mixing
measurements:
•Hadronic (Kp) analysis:
Rmix < 1.3 x 10-3
•Lifetime difference for D0 KK
and D0 pp:
yCP = 0.8 ± 0.4 +0.5 -0.4 %
•This (semileptonic) analysis:
Rmix < 4.2 x 10-3 (90% CL)
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
Conclusions
•
•
•
We have demonstrated that
ACP is consistent with zero. The measured values are:
D+  KKp: +0.0136 ± 0.0103 ± 0.0110
D+  fp: +0.0024 ± 0.0152 ± 0.0080
D+  K*K: +0.0088 ± 0.0177 ± 0.0080
We find that the Branching Ratio for D+  KKp is:
0.1070 ± 0.0009 ± 0.0022
We find, using semi-electronic neutral D decays, that
Rmix < 4.2 x 10-3 (90% CL)
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
Acknowledgements
• Thanks to all BaBar collaborators
including, particularly:
• Francisco Yumiceva, South Carolina
graduate student (D+  K+K-p+ decays)
• Kevin Flood, graduate student at the
Univ. of Massachusetts, Amherst
(semileptonic mixing analysis)
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
Backup Slides
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
The Status of CP Violation




CP violation is necessary if the universe
is indeed matter-antimatter asymmetric
but the Big Bang is not
Standard Model CP violation cannot
explain CP violation in the universe
New physics is needed, SM is not
enough
Charm may be a good place to look
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
Raw CP asymmetries
in control samples
• Ds+  K+K-p+ decays: +3.0 x 10-3
• D+  K-p+p+ decays: -2.9 x 10-3
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
Event Sample
• Nearly all Run 1, 2 on/off-resonance
(R10
processing)
–80.0 fb-1 on-resonance
–7.1 fb-1 off-resonance
• Wrong-sign mixed D0 lifetime: 100k events
• SP4 generics mode N events (x106)
b0
154
b+
156
cc
185
uds
293
equiv lumi (fb-1)
294
298
142
140
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
Track Selection
• Kaon candidates
• Pion candidates
– GoodTracksVeryLoose
– KLHVeryTight
• plus KMicroVeryTight (plab > 2.1 GeV/c)
– .45 < qlab < 2.5
• Electron candidates
– GoodTracksVeryLoose
– PidLHElectrons (default)
– .45 < qlab < 2.409
– 0.8 < E/p < 1.05
– g conversion veto
• K/e vertex
– GeoKin vertex prob. > 0.01
– M(KeVtx) < 1.82 GeV/c2
– Lifetime error < 2 D0 lifetimes
– GoodTracksVeryLoose
– .45 < qlab < 2.5
– p* < 0.45 GeV/c
– track fit prob. > 0.001
– beamspot refit prob. > 0.01
– ≥ 2 SVT r-phi (z) hits with at
least 1 hit on inner 3 r-phi
(z) layers
– ≥ 6 total SVT hits
• Multiple D0 candidates
– Veto events with more than
one RS or WS D0 candidate
passing all selection criteria
(~11% of RS signal lost after other cuts)
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
Neural Network Event
Selection
• Events are selected using a neural
network with the following inputs
taken from signal and generic MC:
– p*(K/e vertex)
– p*(p)
– thrust magnitude (w/o K, e)
– Opening angle between p*(K/e) and
thrust (w/o K, e)
– opening angle between p*(K) and p*(e)
• RS/WS signal selection efficiencies are
identical
• RS/WS signal/bkgd NN event selector
output
Lumi-scaled NN output
final cut optimized signal
for best statistical
bkgd
sensitivity
Normalized NN output
final cut optimized
for best statistical
sensitivity
final cut
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
signal
bkgd
Neural Network D0 Reconstruction
•Novel use of two hidden-layer
neural network to map NN input
vector to signal p*(D0)
p*(D0) Neural Network Residuals
• Momentum resolution fit to double
gssn
– phi core sigma/fraction: 82 mrad /
0.81
– theta core sigma/fraction: 80 mrad /
0.94
– total magnitude RMS:
371 MeV/c
– transverse magnitude RMS: 350 MeV/c
GeV/c
rad
GeV/c
rad
•Trained with inputs from signal MC:
–
–
–
–
p*(K/e vertex)
p*(p)
thrust vector (w/o K, e)
Opening angle between p*(K/e) and thrust (w/o
K,e)
– Opening angle between p*(p) and thrust (w/o
K,e)
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
– opening angle between p*(K) and p*(e)
DM, Lifetime PDFs
1-d DM pdfs
DM = M(D*) fit
1-d lifetime pdfs
M(D0)
off-res
data
fit
RS unmixed D0
from
RS fit
shape
from
MC
mis-reco’d D0
fit
random comb.
signal
fit
signal (zoom)
MC/fit
WS mixed D0
shape
from
MC
D+ (RS only)
D+
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
zero lifetime
Testing the Mixed Fit with Generic MC and Embedded Mixed Events
• WS mixed fit tested with full fit on ~540
lumi-scaled generic MC datasets with
different levels of embedded mixed
events
• N(mix) pull plots (right) show no
evidence of bias or improperly scaled
errors in the fit number of N(mix) with
or w/o the presence of mixed events
N(mix) R(mix) fit mean
err stat mean
0
0
0.008 0.089
-0.066
50
0.001
0.05
0.097
0.091
100
0.002
0.012
0.07
0.012
N(mix) R(mix) fit sigma
err stat rms
0
0
0.965
0.079 0.994
50
0.001
0.995
0.093 0.999
100
0.002
0.994
0.052 0.994
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
Goodness-of-Fit to Run 1,2 Data
• Toy MC datasets generated from
RS/WS data fit pdfs and fit with
unmixed/mixed fit models to
determine goodness-of-fit
• Both RS/WS NLL values from
data fits lie well within range
predicted by the fits to toy MC
NLL Distribution for WS Toy Datasets
WS data fit
NLL value
RS data
fit NLL
value
NLL
distribution
for RS toy
datasets
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
Evaluation of Systematics
• Systematic checks fall into two
categories:
– reasonableness or “sanity”
checks
– systematic variations which
encode lack of knowledge/
understanding and biases in
the fit model
• First class demonstrates
robustness of result
• Latter class determines
quantitative estimation of the
systematic error
Reasonableness Checks
• No significant variations in the
mixing rate were found when
making the following changes:
–
–
–
–
–
–
–
TwoTrksVtx → Hadronic beamspot
GeoKin K,e vertex → FastVtx
KLHVeryTight → KMicroVeryTight
E/p <1.05 → 1.10
Lifetime error cut +/- 10%
Separate fitting of initial D0 and D0
Different NN event selector cuts
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
DM
DM
DM
RS Unmixed DM, Lifetime PDF Fit Classes
full DM range
unmixed lifetime
full DM range
RS D+
DM
DM
RS peaking DM
DM

c
D0
DM
RS random DM D0 lifetime
full DM range
RS random DM zero lifetime
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
DM
DM
DM
WS Mixed DM, Lifetime PDF Fit Classes
full DM range
DM

DM
Random comb. DM D0 lifetime
c
WS peaking DM D0 mixed lifetime
DM
full DM range
DM
DM
WS random DM D+ lifetime
full DM range

c
Peaking DM D+ lifetime
Random comb. DM zero lifetime
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
Quantitative Systematic Error
•Floated unmixed fit RS signal DM shape
parameters correlated, so N(mix) systematic error
from this source calculated using RS fit correlation
matrix
•List of systematic errors:
Delta M shape
Unmixed D0 lifetime
Random comb. shape
Lifetime resolution model
Bkgd D0 lifetime model
Bkgd D+ lifetime model
0.00032
0.00008
0.00015
0.00000
0.00016
0.00012
• Total systematic error
sys = 0.00042 = 0.340 stat
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China
Semileptonic Mixing Summary
• Rmix consistent with no mixing
Rmix = 0.0023 ± 0.0012 (stat) ± 0.0004 (sys)
• CP fit was performed and no
CP-violating effects were found
• Rmix < 0.0047 (95% C.L.) from
NLL scan
N(mix)
NLL Scan
• E791: rmix < 0.50% @ 90% CL
• FOCUS: rmix < 0.05% @ 90% CL
rmix < 0.10% @ 90% CL
(using Feldman-Cousins)
Stat error is ~0.1%
FOCUS result is UNPUBLISHED
(Plot courtesy of G. Burdman &
I. Shipsey, hep/ph 0310076)
M. V. Purohit, Univ. of S. Carolina,
ICHEP 2004, Beijing, China