P 0 error budget
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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%

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p 0 error budget

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P 0 error budget

p0error budget

  • Completed items (review)

  • Updated and new items (not reported yet)

  • Items to be completed

I.Larin pi0 systematic error


Completed items

Completed items

  • Target (thickness and density)……...………. 0.1%

  • Target material (impurity) …………...………. -0.4%

  • Photon beam flux ……………………..……… 1.1%

  • Trigger efficiency……………………... ………. +0.1%

  • ADC channels status during run time………. negligible

  • Photon beam energy uncertainty……..... 0.3%

  • Photon beam flux distribution within

    E-counters……………………...….…… 0.1%

  • p0branching ratio ……………………..………. negligible


Completed items1

Completed items

  • Energy cut for single g ………………..………. 0.2%

  • Energy cut for p0 ……………………...………. negligible

  • p0 production angle resolution uncertainty …. 0.25%

  • CIparameter uncertainty ……………..………. 1.0%


Updated and new items not reported yet

Updated and new items (not reported yet)

  • MC eff. simulations (statistical) accuracy……. 0.3%

  • Selection of “best in time” beam candidates... 0.3%

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)


Updated and new items not reported yet1

Updated and new items (not reported yet)

  • Hycal z uncertainty……………................ 0.4%

Used Hycal z-uncertainty value is 1.5cm.

Difference in Hycal acceptance was obtained for “standard”

and shifted Hycal z in simulations.


Updated and new items not reported yet2

Updated and new items (not reported yet)

  • Beam position uncertainty ………................ negligible

Probe value of 5 mm for Hycal VS beam alignment stability was taken.

Efficiency reduction due to 5mm shift is about -1.4%

(from simulations)

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


Updated and new items not reported yet3

Updated and new items (not reported yet)

  • Beam direction uncertainty ………............... +0.14%

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%


Updated and new items not reported yet4

Updated and new items (not reported yet)

  • Beam divergence uncertainty ………............ 0.3%

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


Updated and new items not reported yet5

Updated and new items (not reported yet)

  • Timing cut (tdiff)………............ 1.0%

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


Updated and new items not reported yet6

Updated and new items (not reported yet)

  • fint parameter uncertainty ………............ 0.5%

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.


Updated and new items not reported yet7

Updated and new items (not reported yet)

  • Hycal response function………............ 1.0%

Snake scan with beam centered on W2086:

100pA run; 30pA run; MC “run”


Updated and new items not reported yet8

Updated and new items (not reported yet)

Other stability checks (which don’t go to error budget):

  • pass1 (8.06eV) VS pass2a (8.02eV)

    VS raw data (8.02eV) …….......... 0.4%

  • use of bit-9 VS bit-2 in tdif (aligned separately):

    bit-9 gives 0.5% less value for pass-1

    and 0.3% less value for pass-2a……………. -0.4%

  • p0 mass plot (constrained) fit :

    varying number of bins …. 0.9%

    (within stat. error)

  • 100nA runs VS all runs and

    130nA and 110 nA runs VS all runs .…1.5%

    (within stat. error)


Items to be completed

Items to be completed

  • Coherent formfactor dependence on photon beam energy

  • Incoherent shape check with all Hycal

  • Effect of background on extracted

    number of elastic p0


Items to be completed1

Items to be completed

  • Background separation: (currently used value) ….1.0%

    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)


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