analysis of ratio br( k 0 )/br(k )
DESCRIPTION
Analysis of ratio BR( K 0 )/BR(K ). Motivation Selection and cuts Trigger efficiency Signal and Background fit Selection efficiency Result and conclusion. M. Martemianov V. Kulikov. Motivation / I. - PowerPoint PPT PresentationTRANSCRIPT
M. Martemianov, ITEP, October 2003
Analysis of ratio
BR(K 0)/BR(K )
M. Martemianov
V. Kulikov
Motivation
Selection and cuts
Trigger efficiency
Signal and Background fit
Selection efficiency
Result and conclusion
M. Martemianov, ITEP, October 2003
Motivation / I
2A
23)A(K
, 2
A32
0A
31 )A(K
,2
A6
10
A3
1-)A(K
0
000
0
ChPT theory for K decays gives total amplitude as mixture of two isospin (I=0 and I=2) amplitudes :
CPM (chiral pole model) predicts amplitude A(K+ + 0) by formula2)/22m-2
K(m)0(cos sin)A(K 0 ffccFGCPM
PDG values : GF = 1.16610-5 GeV (Fermi constant)
sinc = 0.2196 and cos c = 0.9734 (c - Cabibbo angle)
f+(0) = 0.96 and f = 93 MeV
GeV810764.1)A(K 0 CPM
M. Martemianov, ITEP, October 2003
Motivation / II
RFPK
MallK
KBRtot /28exp)A(K
00
Using PDG constants and the most precise experiment :
GeV810)012.0835.1(exp)A(K 0
Difference between prediction and experiment : 3.8 %
Best experiment,
LEAR (CERN), 1992
ν)μBR(K)0ππBR(K
First step :
measurement of
at precision around (less ?) 1 %
Precision 1.5 %
M. Martemianov, ITEP, October 2003
DST - version N 15 for kpm - stream
Run numbers : 23542-27133 (2387 DST - files)
All runs of 2002 year
Total statistics : 283.5 pb-1
Number of pions candidates : 1.649 106
Number of muons candidates : 4.919 106
Statistical estimation of result
Selected - window :
190 - 220 MeV/c
Selected - window :
220 - 260 MeV/c
- hyphotesis for
secondary particles
Statistical error on the level of 0.1 %
M. Martemianov, ITEP, October 2003
cos.
exp,)
KK()
KKR(
00
KvetoKselKfit.Ktrigger
window
Ktrigger - trigger efficiency, extracted from EXP. data
Kfit - efficiency of signals and background rejection,
based on MC data and performed of EXP data,
Ksel - selection efficiency, from MC and EXP. data
Kvetocos - efficiency of cosmic veto rejection, EXP. data
Tag strategy
M. Martemianov, ITEP, October 2003
0
Splitted tracks
“Wrong” orientation of tracks
At least one secondary kaon vertex with
40 cm < Rxy < 150 cm, |Z| < 210 cm
20 MeV/c < P sec < 320 MeV/c
Rejection of “Splitted” tracks
(events with |PK- P_sec| < 40 MeV/c . AND .
DF < 80 . OR . DF > 1720) , where
DF = | - | - acos (PK P sec)||
Secondary track selection
Kaon candidates from ECLO2
Only events with two kaons and Charge1 x Charge2 < 0
Selection by momenta in the first point in DC 40 < PK < 160
MeV/c
M. Martemianov, ITEP, October 2003
Trigger efficiency / I
,
2
1
K
K+
Drift Chamber
K
K+
Auto - triggering for K+, based on EMC trigger
Trigger effciency = 100 %
Pion trigger (from K+ +0) based on the maximal number of clusters = 3, muon trigger (from K+ +) number of clustres = 1
+ - trigger :
Based on DC track information
Two tracks go to ECL
Rejection tracks fired same ENDCAP
M. Martemianov, ITEP, October 2003
Trigger efficiency / II
Linear fit for both trigger (p0)
- auto - triggering : p0 = 0.3348 0.0008(stat.)
- auto - triggering : p0 = 0.3341 0.0007(stat.)
Trigger difference : 0.0007 0.0008 (trigger error = 0.2 % )
- tag, no auto-triggering : p0 = 0.3356 0.0004(stat.)
- auto - triggering : p0 = 0.3341 0.0008(stat.)
Trigger difference : 0.0014 0.0008 (trigger error = 0.4 % )
M. Martemianov, ITEP, October 2003
0 - selection
Number of clusters > 2
No association to charged track
Ecl > 25 MeV
| t | < 3 ns
Search a minimum :
| (Ecl1 + Ecl2) - M(0) |
50 < M(0) < 210 MeV
space < 30 0, where space -
angle between 0 momenta from ECL
and calculated from DC
| Mfit(0) - M(0) | 0.7 MeV
space
M. Martemianov, ITEP, October 2003
Selection of K decays
All selected events
Events with reconstructed as pions from K 0
Events selected as muons from K
Rejected clusters associated
to the neutral tracks
Minimum | (Ecl1 + Ecl2) -
M(0) | if 0 has common clusters
for both vertex
Procedure needs to get a clear signal for the both peak in windows
Good selection of - decay, small contamination of 0 - events survived
Selection didn’t change the shape of two peak’s shape
MC
M. Martemianov, ITEP, October 2003
Four main modes in geanfi :K K e0K 0K 0 0
Three-body decays
ppexp1
p)(
21
03 xxf
Sum = 15.3 % 0 - selection doesn’t change shape of three - body decays
2 = 1.2
MC data
MC data
MC data + 0 - sel.
M. Martemianov, ITEP, October 2003
Description of - peak
Exp. tails
Step N2 :
Experiment - extracting launch shape of peak for experimental data
Two contributions : and three - body background
Step N1 :
Pure MC - extracting launch shape of peak (3 Gaussians at the same mean value + 2 exponential functions due to effect of multiple scattering)
three-body backg.
- backg.
M. Martemianov, ITEP, October 2003
Description of - peak
Step N1 :
Pure MC - extracting launch shape of peak (4 Gaussians, each 2 Gaussians have the same mean value + 2 exponential functions)
Exp. tails
Step N2 :
Experiment - extracting launch shape of peak for experimental data
One contribution : - background
-backg.
M. Martemianov, ITEP, October 2003
Fit of two peaks
MCthreexfpxfpxfpxF
,)(
3)(
1)(
0)(
Fit gives a full description of all type of kaon decays in DC
f(x)three - extracted from MC
M. Martemianov, ITEP, October 2003
Total statistics
Run Set Signal( -peak)
Signal( -peak)
Bothsignals
23542-24071 201469 600392 80186124072-24626 203407 608802 81220924627-25166 206973 618981 82595425167-25627 208149 620540 82868925628-26065 208810 622589 83139926068-26390 210602 626575 83717726391-26759 207853 618144 82599726761-27133 201755 603302 805057
Total value 1649018 4919325 6568343`
All data diveded on 5 sets
M. Martemianov, ITEP, October 2003
Fit quality
Run Set Correctioncoefficient, %
2( -peak)
2( -peak)
2(both signals)
23542-24071 92.46 0.33 1.30 1.48 1.61
24072-24626 92.69 0.33 1.23 1.50 1.5824627-25166 92.26 0.33 1.32 1.29 1.6125167-25627 92.41 0.33 1.33 1.38 1.5125628-26065 92.55 0.33 1.34 1.48 1.6426068-26390 92.82 0.33 1.24 1.34 1.6026391-26759 92.68 0.33 1.41 1.38 1.6326761-27133 92.53 0.33 1.35 1.46 1.55
`
M. Martemianov, ITEP, October 2003
Correction coefficient on background
Ratio as function of data set
Linear fit gives : 0.3352 0.0003(stat.)
Stat error : 0.09 %
Correction coeff. physical background
Linear fit gives :
Kfit = 0.9255 0.0012(fit.)
Fit error : 0.13 %
M. Martemianov, ITEP, October 2003
Comparison data / MC
Fit can be checked by MC data using the same way :
KMC = 97.10 0.25 %
Kfit = 96.66 0.24 %
Ratio = 0.3174 0.0006
Ratio Kmc = (0.30863 0.00055)MC
Kfit = 0.9255 0.0012
Ratio = 0.3352 0.0003
Ratio Kfit = 0.3102 0.0012
MC : EXP :
On MC fit and real number of ratio coefficient are very close (difference = 0.44 0.35) (contribution to the syst. error)
Total MC correction coefficient : Ksel. = 1.080 0.002
M. Martemianov, ITEP, October 2003
Selection efficiency / I
Ksel = decay vertex window
decay - correction on decay of charged pions vertex - selection of vertex for pions and muons window - correction of signals for all momentum range
decay - can be extracted on MC only using a convenient cut on the track length of secondary particles
vertex, window - estimated on MC and EXP, must be different in MC and EXP. Data due different momentum resolution
M. Martemianov, ITEP, October 2003
Selection efficiency/ II
Distributions on MC and EXP are the same Cut for tracks length on all tracks (> 40 cm) gives
decay = 1.0443 0.0016 (stat.)
Calculation of decay
Main part of this value (1.036) can be calculated from PDG pion decay length, its mass and averaged laboratory momentum (205 MeV/c).
The rest can be attributed to pion decay at larger than 40 cm length with spoiled reconstraction of the pion track due to the presence of pion decay product.
M. Martemianov, ITEP, October 2003
Selection efficiency/ IV
Exp. data
Correction for pions : 96.3 %
Correction for muons : 99.5 %
Correction coefficient for
windows by fit :
1.030 0.002(stat.) (0.2 %)
MC. data Correction for pions : 97.2 %
Correction for muons : 99.2 %
Correction coefficient for
windows by fit : 1.019 0.003
MC real coefficient :
1.020 0.003
Calculation of window
Based on fit parameters
Calculates the percentage muons and pions inside window
Different for MC and EXP data
M. Martemianov, ITEP, October 2003
Selection efficiency/ V
Calculation of vertex
K
K+
+KK+
EMC - cluster
Two EMC clusters only for charged tracks, + - seleclted by momenta
Investigated vertex
vertex = vertex cuts
Investigated vertex
Two EMC clusters only for charged tracks, + - seleclted by momenta, two clusters from gammas
21
M. Martemianov, ITEP, October 2003
Selection efficiency/ VI
Mean value of efficiency (sum by all kaons momenta gives vertex efficiency :
Pions : 86.79 0.18 %, Muons : 86.65 0.08 %
Difference : 0.14 0.20 % (contribution of stat error for vertex efficiency)
Selected muons
Selected pions
Efficiency of vertex efficiency for muons and pions as function of kaons momenta
M. Martemianov, ITEP, October 2003
Selection efficiency/ VI
Calculation of cuts Calculated by MC and corrected by EXP
Includes cuts to reject splitted tracks and cuts on momenta of secondary tracks
MC : cuts = 1.0137 0.0016(stat)
Difference between MC and EXP based only on momenta cuts on high region (main contribution based on muons) and differnece equal to 0.5 %
EXP : cuts = 1.0086 0.0020(stat)
MC distribution of the secondary particles in the laboratory system for muons and pions
from K
from K 0
M. Martemianov, ITEP, October 2003
Summary of selection efficiency
Type Correction coefficient(MC/ EXP)
Syst. error,%
Selection and pions decays 1.0443 0.16
Vertex selection 1.0137 1.0086 0.16 0.26
Kinematical window 1.020 1.0302 0.3 0.2
Total value 1.080 1.085 0.38 0.36
`
M. Martemianov, ITEP, October 2003
Cosmic veto
S = N(vetocos=0) + N(vetocos=1,t3flag=0)+N(t3flag=1)
Kvetocos = 1+64N(t3flag=1) / S
Check cosmic veto for runs 26111-27133
Type of events vetocos = 0 vetocos =1 t3flag = 1 Kvetocos
+, 4.789106 4466 5564 1.00073 0.00010
+0, 0 0.621106 111 5 64 1.00051 0.00020
No difference between rejection of different type of event by cosmic veto on the level 210 4
M. Martemianov, ITEP, October 2003
Corrections and erros
Type Correctioncoefficient
Syst. error,%
Source
Trigger 1.0 0.2 EXP
Background / fit 0.9255 0.46 EXP
Selection and pions decays 1.085 0.36 MC/EXP
Cosmic veto 1.0 0.2 EXP
K decay 0.994 Nucl. Phys.,B115, 55*
Total value MC/EXP 0.9981 0.65
`
*) Taken from previous experiments, we plan to recalculate the coefficient, but now use the same value to compare with pevious experiments.
M. Martemianov, ITEP, October 2003
Comparison with world data
0.00220.00030.3346ν)μBR(K
)ππBR(K (syst.)(stat.)0
2(syst.)(stat.) 10)65.00.09(133.46
M. Martemianov, ITEP, October 2003
Conclusion
ν)μBR(K)ππBR(K 0
was measured
Result has a good agreement with world data
Statistical error is negligible due to the huge sample of kaon decays (more than 6.5 M).
Systematic error ( 0.65 %) dominates. It improves accuracy for the ratio by a factor of 2.7
In principal, result can be updated by further investigation of MC / EXP uncertanties and true calculation of K decay