Hi all,
finally I have some doubts about the use of Vub depleted sample with
reconstructed Ks to get the right Kl background subtraction.
In our data sample we expect to have ~70 signal events for Mx<1.6 Gev.
Since the ratio S/B is 1/2 at the moment, we will have 140 background
events.
From Guglielmo's studies we know that the 50% of background events are
due to Kl => we will have ~70 background event with missed Kl's.
Since for physical reasons the number of Ks's has to be ~the same and
since the efficiency on Ks reconstruction (BR(Ks->pi+pi-)*eff(pi+pi-) is aroud
30% we will end up with ~22 Ks events from the depleted sample.
This implies that the relative statistical error on this component
will be ~20% => the background subtraction related to Kl will have an
error of ~14 events and this is already similar to the statistical error.
The conclusion is that we can't use Ks.
Then my proposal is the following:
- use the depleted sample for all the remaining background component. We
have a lot of events with K+ from the depleted sample and the comparison
looks fine.
- use MC for Kl with the following correction:
* resolution correction looking at the difference in the depleted sample
for a subsample with similar multiplicities
* use control sample to evaluate the difference in the calorimeter
deposits for Kl. This is actually the only check we have to do and we
don't need too much statistics. Suppose for instance to find a
difference of 10-20 MeV in the calorimeter deposit. This should be a
small systematic and we could use the MC shape. phi gamma control
sample could be very nice for us.
We should discuss about this further.
Daniele
