Analysis of the dynamics of the decay
fp+p-po
Referees report
Mario Antonelli,
Luca Passalacqua
KLOE general meeting 10-10-2002
• Detailed description in the KLOE MEMO 274
Comments
General:
• competitive results + 2000 data
 KLOE note soon  draft
Analysis is in a good shape:
• relevant detector effects taken into account
• several checks DATA-MC
• systematic uncertainties evaluation
• robustness of the fit
Main questions:
• bias on momentum measurement
• ISR not taken into account
Momentum bias
• difference in measured momenta between
negative and positive charged particles
observed in the control samples: m+m- and p+p- events
P(+)-P(-) (MeV)
Profiles + lab frame
NOW:
main systematic for
DMs mesaurements
0.5 MeV
ONLY the AVERAGE
enter in d(DMs)
f
P(+)-P(-) (MeV)
Momentum bias
Referees comment: find source(s) of the effect
 correct measured momenta (use control sample)
verify consistency with po mass
systemaitcs from uncertainties on correction
Closer look to the effect:
• f rest of frame + use gaussian fits to slides
slides + f frame
~ 280 KeV average
50o<q<130o
f
Momentum bias
• the wire droop
dw ~ 200 mm
R-Z view
Not in scale
is not taken into account in the present track
reconstruction algorithm
bias on the momentum ?
X-Y view
droop ~ ds
Sagitta (s)
error on the wire poistion
ds
dpt
dpt=pt2/(0.3BLt2)8 ds
100 mm
300 keV @ p=500MeV
Momentum bias
Charge dependent effect:
X-Y view
+ / – ds for + / - charge
f
dependent effect
effective bias
ds
f
f
X-Y view
dw
Parallel
component
to the sagitta
ds=dw cosf
Momentum bias
q
dependent effect
R-Z view
Only relative
positions are important
q
If wires have same droops dw
no effect at q =90o
ds~0
ds=dw
ds~dw
X-Z view f=0
At small angle
Momentum bias
dw is not a constant
WIRE SAGITTA vs. LAYER #
SAGITTA (micron)
450
SAGW micron
400
SAGAl micron
350
300
250
200
150
100
0
20
40
60
80
100
120
LAYER #
effect at q =90o expected (and observed)
Momentum bias
use a toy model to verify consistency with data
• linear droop vs z
z
dw(0)
• evaluate average of effective ds:
q,f dependencies
and differences in dw(0) vs R
taken into account
curvature effect on effective ds also considered
Not negligible R~1 m
f dependence (ds) on the wire
Results
50o<q<130o
P(+)-P(-) (MeV)
check the model at
low angles (large
effects are
expected)
f
results
Use bhabha
P(+)-P(-) (MeV)
35o>q>155o
A bit asymmetric…
under study
Tilted plates?
f
ISR effects?
Initial state radiation not taken into account in the fit
po E,P evaluated from missing E,P using knowledge of W
Fit stability checked
varying cuts on
variables sensitive
to ISR
Some event with
po kinetic energy out
of boundaries?