MC Event Weights

MC event weights general information

A detailed description of the event weights used in KORALW03 and available in the Common Ntuples has been written by A. Valassi and can be found here

A description of the weights used for the single W final state has been written by A. Valassi and can be found here.

The event weights available in KORALW03 output are stored in the bank KWGT in the EPIO file and in the array MCEWEIGHT in the Common Ntuples. The table below is to help the translation between the two sets of weights

`MCEWEIGHT(1)`	`KWGT(3)/KWGT(2)`	O(alpha²)/O(alpha¹) ISR weight
`MCEWEIGHT(2)`	`KWGT(4)/KWGT(3)`	O(alpha³)/O(alpha²) ISR weight
`MCEWEIGHT(3)`	`KWGT(90)`	Complete NL O(alpha) correction weight (from YFSWW)
`MCEWEIGHT(4)`	`KWGT(101)`	Coulomb correction weight
`MCEWEIGHT(5)`	`KWGT(102)`	Screened Coulomb correction (KC) weight
`MCEWEIGHT(6)`	`KWGT(51)`	Full 4f matrix element squared
`MCEWEIGHT(7)`	`KWGT(50)`	CC03 matrix element squared
`MCEWEIGHT(8)`	`KWGT(52)`	NC02 matrix element squared
`MCEWEIGHT(9)`	`KWGT(62)`	single W t-channel ISR
`MCEWEIGHT(10)`	`KWGT(63)`	single W alpha(t)

MC event weight shortcuts

What follows is a list of recipes to obtain useful sets of weighted events from the ALEPH generated 4f (and CC03) unweighted events by using the weights available in the Common Ntuples (and in the EPIO files). More complete and additional information can be found in Andrea's document. Let me know if you are aware of any other use of weights which can be useful.

How to obtain CC03 events from the 4f samples
- Use the weight MCEWEIGHT(7)/MCEWEIGHT(6)
How to obtain 4f events with full DPA NL O(alpha) correction from the 4f samples
- Additive prescription: use the weight (1+(MCEWEIGHT(3)-1)*MCEWEIGHT(7)/MCEWEIGHT(6))
- Multiplicative prescription: use weight MCEWEIGHT(3)

BE CAREFUL: these weights can be negative !!

How to obtain CC03 events with full DPA NL O(alpha) correction from the 4f samples
- Use the weight MCEWEIGHT(7)/MCEWEIGHT(6)*MCEWEIGHT(3)
How to obtain CC03 events with full DPA NL O(alpha) correction from the CC03 samples
- Use the weight MCEWEIGHT(3)
How to obtain 4f events with unscreened Coulomb correction from the 4f samples
- Use the weight (1+MCEWEIGHT(7)/MCEWEIGHT(6)*(MCEWEIGHT(4)/MCEWEIGHT(5)-1))

MC event weight miscellaneous results and end-user experiences

MC event weight distributions for the LEP 4f working group (by A. Venturi)

References

ALEPH talks

Andrea Valassi's talk in Cetraro about ALEPH WW MC production plans

Non-ALEPH talks

Papers

28/04/02

Andrea Venturi