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Vertex characteristics

J. Bouchet

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outlines• Spiros has some ‘concerns’ about the cut on primary

vertex resolution.• Are we loosing a lot/ good events ?• I run the macro with filling only the vertex

properties(position, resolution, number of vertices/per event, gRefMult)

• I use day122 ProductionMinBias (~30k events, which seems enough to draw some conclusions in term of statistic)

• The cuts we were using in the first production are :– |VZ|<10 cm– σVZ<200μm– No cut on the index of the vertex

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Vertex position in XY (old prod)

All vertices All vertices with |Vz|<10cm

All vertices with σVZ<200μm and |VZ|<10cm

•The right plot represented the cuts we were using•We see that even with the loop over all vertices, we were taking relatively good events by adding the cut on the primary vertex resolution

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Vertex resolution in XY(old prod)

All vertices All vertices with |Vz|<10cm

All vertices with σVZ<200μm and |VZ|<10

•The right plot represented the cuts we were using•We see that even with the loop over all vertices, we were taking relatively good events by adding the cut on the primary vertex resolution

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Vertex position in XY (new)

•We see that with the cut on the vertex Z resolution, we clean up the vertex position in XY•The cut on the first vertex makes also a big cleaning (see next slide)

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All vertices Vertices with l=0 , |Vz|<10 cm

Vertices with l=0,σVZ<200μm and |VZ|<10cm

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Cut on the best vertex for the vertex resolution in XY (new)

•The second plot shows when we apply the best vertex rank cut

•It cleans up the primary vertex resolution in X,Y

•Adding cuts on Vz(position) and resolution Vz cleans to have ResVx~ResVy < 300 microns

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What are we gaining with the best vertex rank cut

We remove vertex withLow refMultiplicities

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Primary vertex resolution with the best vertex rank only

Black : no cutRed : index ==0

Black : no cutRed : index ==0

Black : no cutRed : index ==0

• the cut on the best vertex makes the primary vertex resolution (in X,Y and Z) better

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• if we add the cut on the index l =0, we have 33394 events (red curve)•If then we add the cut on primary vertex resolution Z (200 microns) ,we cut 3k events , which represents 7% of the event

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Primary Z vertex resolution

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Summary/ to check• We see that with our previous cuts (|Vz|<10cm, Vz<200µm),

we were selecting good events (by ‘good’ I mean a relatively tigh X,Y position and small resolution

• It seems that the cut on the first vertex also clean the resolution for the 3 components but that the cut on the resolution Z is needed to clean up more the X,Y primary vertex resolution (see slide 6)

• It would be interesting to see the implication for TCFIT: – We set the total single track resolution as the quadratic sum of the

single DCA + primary vertex resolution– Caveat : we don’t use later any cuts on single track resolution