B2hh GFact Asymmetry Fitting page

The aims for the asymmetry fitter are the following

• Perform basic checks of current fitting package with toy data for Bd and Bs asymmetries.
• Add proper time pdf to the fitting package
• Add Bs→KK pdf to fit package
• Think about adding the other background pdfs (3 body, Λ's)
• Alter the parameters that are being varied by the minimiser to d, θ and γ
• Move to MC data/ real data (Bd) for first looks. So far 0.3fb-1 data is enough for asymmetry fitter

Most of the following is on my web page http://ppewww.physics.gla.ac.uk/~alison/B2hh.html where all the attached files are there and work. I have now stopped using my web page and will now just post all my results here.

Basic Checks with asymmetry fitter

1. B_d → π π

50 datasets were generated with 6099 events per data set using 0.68 b2pipi (sf1=1 and ssb = 0.68) and 0.32 combinatoric background (MassDistribution) mass distribution. The asymmetry fitter was used to fit for Bd asymmetries only with sf1'=0.68 and obtained the following:
Adir Bd - input was 0.38 and fitted was 0.3953 ± 0.0476 ( A^dir_Bd)
Amix Bd - input was 0.61 and fitted was 0.6503 ± 0.0311 ( A^mix_Bd)
Then re-ran same job with 150 data sets with 2000 events per data set and fitted for the following:
Adir Bd - input was 0.38 and fitted was 0.4338 ± 0.0196 ( A^dir_Bd)
Amix Bd - input was 0.61 and fitted was 0.6619 ± 0.0197 ( A^mix_Bd)
The asymmetry plot is shown here .

2. B_s → K K

50 datasets were generated with 6099 events per data set using 0.68 bs2KK (sf3=1 and ssb = 0.68) and 0.32 combinatoric background ( mass distribution ). The asymmetry fitter was used to fit for Bs asymmetries only with sf3'=0.68 and obtained the following Adir for Bd and Amix for Bs which in numbers are:
Adir Bs - input was 0.1 and fitted was 0.0811 ± 0.0275
Amix Bs - input was 0.25 and fitted was 0.1799 ± 0.0346

3. B_d → π π and B_d → K π

50 data sets were generated with 6099 events per data set using 0.68 bd2pipi and bd2Kpi (sf1=sf2=0.5 and ssb = 0.68) and 0.32 combinatoric background ( mass distribution ).The asymmetry fitter was used to fit for Bd asymmetries only with sf1'=sf2'=0.34 and obtained the following Adir for Bd and Amix for Bd which in numbers are:
Adir Bd - input was 0.38 and fitted was 0.298 ± 0.206
Amix Bd - input was 0.61 and fitted was 0.660 ± 0.062

Now using 150 data sets with 100k events per data set using bd2pipi and bd2Kpi (sf1= 0.845 and sf2=0.155 and ssb = 0.664, see Laurence's thesis, page 183). The asymmetry fitter was used to fit for Bd asymmetries with sf1'=0.561 and sf2'=0.103 and obtained the following:
Adir Bd - input was 0.38 and fitted was 0.4241 ± 0.0017 ( A^dir_Bd) and Laurence got 0.407 ± 0.033
Amix Bd - input was 0.61 and fitted was 0.6818 ± 0.0018 ( A^mix_Bd) and Laurence got 0.655 ± 0.024
The asymmetry plot is shown here . The pull plots show a large bias. The only difference was the large mass window I used (4800 - 5800 MeV) compared with Laurence (5229 - 5329 MeV). Hence I have re-run the same signal fractions in a 5fb-1 job (288 data sets with 100k events per data set) with the much tighter mass window and found the following:

Adir Bd - input was 0.38 and fitted was 0.4245 ± 0.0022 ( A^dir_Bd) and Laurence got 0.407 ± 0.033

Amix Bd - input was 0.61 and fitted was 0.6811 ± 0.0019 ( A^mix_Bd) and Laurence got 0.655 ± 0.024

The asymmetry plot is shown here . However the pull plots are still showing a large bias in the mean of the pull plot (the widths are approximately ok). What's causing the bias in the pull plots? It is not present in the first case when on ly B2pipi and combinatoric background are used....looking in to this now.

4. B_d → π π, B_d → K π and B_s → K K

50 datasets were generated with 6099 events per data set using all 3 channels with sf1=sf2=sf3=0.333 and ssb = 0.68) and 0.32 combinatoric background ( mass distribution ). The asymmetry fitter was used to fit for Bd asymmetries only with sf1'=sf2'=sf3'=0.226 and obtained the following Adir for Bd and Amix for Bd which in numbers are:
Adir Bd - input was 0.38 and fitted was 0.4917 ± 0.0638
Amix Bd - input was 0.61 and fitted was 0.6852 ± 0.0456
Then re-ran the asymmetry fitter for the B_s asymmetries and found;
Adir Bs - input was 0.1 and fitted was 0.0416 ± 0.0606 ( A^dir_Bs)
Amix Bs - input was 0.25 and fitted was 0.1505 ± 0.0598( A^mix_Bs)

-- AlisonBates - 2010-08-06