p 0 error budget. Completed items (review) Updated and new items (not reported yet) Items to be completed. Completed items. Target (thickness and density) ……...………. 0.1% Target material (impurity) …………...………. -0.4% Photon beam flux ……………………..……… 1.1%
I.Larin pi0 systematic error
This selection efficiency was estimated by:
a) number of elastic p0s rejected by this selection;
syst. error is defined by how well this value can be extracted from the data
b) comparing lifetime fit results for all and “best in time” beam candidates (for double check)
Both methods give efficiency of this selection 99.3% for all runs used in this analysis together (100,130 and 110 nA)
Used Hycal z-uncertainty value is 1.5cm.
Difference in Hycal acceptance was obtained for “standard”
and shifted Hycal z in simulations.
Probe value of 5 mm for Hycal VS beam alignment stability was taken.
Efficiency reduction due to 5mm shift is about -1.4%
dN/dq distortion by 5mm shift affects lifetime fit result -4.7%
For estimated beam pos. uncertainty of 0.2mm
both factors affect lifetime fit negligible
Probe value of 0.5 mrad for Hycal VS beam slope stability was taken.
Efficiency reduction due to 0.5mrad beam slope (with beam and Hycal intersection point fixed in simulations) is -0.1%
dN/dq distortion by 0.5mrad slope affects lifetime fit result -2.5%
For estimated beam slope. uncertainty of 0.12mrad
both factors affect lifetime fit -0.14%
Beam divergence variations from superharp analysis were used to estimate this error budget item
Lifetime fit result show 0.3% variation for different beam divergence used in convolution with Hycal angular resolution
Efficiency variations for different beam divergences look negligible in simulations
Uncertainty value includes lifetime fit variations with 0…+1ns tdiff cut variation and effects of possible timing misalignment for separate T-counters
within 0.5ns window
Used cut value
For used incoherent model fint value was calculated = 0.88rad.
Fit results for fint parameter kept free and for fint parameter fixed to predicted value were compared for pass1 and pass2a and their difference was used as a measure of this uncertainty.
Snake scan with beam centered on W2086:
100pA run; 30pA run; MC “run”
Other stability checks (which don’t go to error budget):
VS raw data (8.02eV) …….......... 0.4%
bit-9 gives 0.5% less value for pass-1
and 0.3% less value for pass-2a……………. -0.4%
varying number of bins …. 0.9%
(within stat. error)
130nA and 110 nA runs VS all runs .…1.5%
(within stat. error)
number of elastic p0
Current total syst. error 2.5%
Value was estimated as a difference in number of elastic p0s for
separate q bins summed and for mass plot for all qs together.
Also a difference innumber of p0s with background fit variations within their errors was estimated.
More background simulations have to be performed for:
) 2 g non-resonant background
(may hide wider part of the signal and decrease efficiency)
) w -> p0g decay
(may or may not (?) produce artificial structure in p0 elasticity distribution around 1 and “mimic” some extra p0)
) Accidentals by “tagged but missed” and untagged photons
(“dips” in p0 elasticity distribution may hide part of signal)