 |
 |
Hello all, we made some plots concerning the mX resolution in signal MC in the ntuples we used for ICHEP. Below are the links. I recognize this became quite lengthy and hope that is not too deterring... It would be interesting to compare this to what we see with the VtxTreeFitter, I guess. The plots are done separately for the nonres and the mix MC, where for mix we use the mix as it is in the files, meaning that there is no nonres component below 1.264 GeV. So for the mix the first four bins we show here show what happens to the resonances. For all those plots we applied the following cuts: pcms<1, |mm2|<1, mes>5.27, (brecoqual==1||brecoqual==5||brecoqual==7) The latter is the cut on the Breco quality as we have been using it for more than a year and cleans up the mes sideband well (the mes cut does the tiny rest). As truth variable we used mxhadgenwoph, which we use for the unfolding. The difference to mxhadgen is that photons which are B daughers according to MC truth and are likely to come from the electron have been taken out (looking at the angle between the photon and the e). You can find the plots here: http://www.slac.stanford.edu/~kerstin/vubfit/mXreso16_vubmix.eps http://www.slac.stanford.edu/~kerstin/vubfit/mXreso16_vubnre.eps http://www.slac.stanford.edu/~kerstin/vubfit/mXreso16_genbch.eps http://www.slac.stanford.edu/~kerstin/vubfit/mXreso16_genbnu.eps http://www.slac.stanford.edu/~kerstin/vubfit/mXreso16_logy_vubmix.eps http://www.slac.stanford.edu/~kerstin/vubfit/mXreso16_logy_vubnre.eps The latter ones are the same as the first ones up to having a log y-axis rather than a linear one. Each of the files has 12 plots. They differ by the region of mxhadgenwoph that is considered. The upper left plots has mxhadgenwoph<0.31, the upper, second left plots is 0.31<mxhadgenwoph<0.62 and so on. The bottom right plot is the sum of the three other bottom plots. This is the 310 MeV binning we are using for the unfolding. The black histos are mxhad-mxhadgenwoph and the orange dash histos are mxhadfit-mxhadgenwoph on the x-axes. In these plots it looks as if the tails in the distributions do not really get a whole lot better by using the kinematic fit, but the region close to the peak at 0 gets somewhat narrower. We looked at two features in more detail. First there is a long tail to the right in the vubmix for mxhadgenwoph<0.31 (top left plot). We checked the Gvxbtyp of the events in this tail and it turns out all are B->pi l nu decays (which is exactly what they should be since there is no nonres down here in the mix, so this is just a sanity check). Here is one more plot: http://www.slac.stanford.edu/~kerstin/vubfit/mXpitail.eps We use the same cuts as given above and focus on the region mxhadgenwoph<0.31 and (mxhad-mxhadgenwoph)>0.1 for the top plots, (mxhad-mxhadgenwoph)<0.1 for the bottom plots. We plot the following quantity: nchg-chgdaugen:nneu-neudaugen, so the y-axis has the difference in numbers in reco and true charged daughters of the X and the x-axis the difference of reco and true neutral daughters of the X. The top left plot is for charged B (Gvxbtyp<0) (and the tail region), the top right plot is for neutral B (and the tail region), the bottom left plot is for charged B (and not the tail region) and the bottom right plot is for neutral B (and not the tail region). This tells us that for charged B in the tail region, we are most likely to pick up an additional neutral particle (not from the X) or to lose a neutral and pick up an extra charged particle. For B0 it looks like we pick up extra neutral particles. It would be interesting to know where these extra neutrals come from - unrecovered bremsstrahlung, FSR, from the true Breco? Second we had a look at the small peak we see left of the peak at zero in the third plot (0.62>mxhadgenwoph>0.93). It contains 39 events, 36 of which are B->rholnu according to Gvxbtyp. Here are the plots of nchg-chgdaugen:nneu-neudaugen for this peak region: http://www.slac.stanford.edu/~kerstin/vubfit/Peakinrhowindow.eps. The left plot is for charged B, the right plot for neutral B. This tells us that for neutral B in this peak we are most likely to miss 2 neutral daughters (or miss both a charged and a neutral daughter) and for charged B in this peak we are most likely to miss one of the charged daughters. Finally, here are the bias and resolution plots we showed earlier, but these are in this 310 MeV binning, using the plots given above: http://www.slac.stanford.edu/~kerstin/vubfit/mXreso16_nre.eps http://www.slac.stanford.edu/~kerstin/vubfit/mXrms16_nre.eps http://www.slac.stanford.edu/~kerstin/vubfit/mXreso16_mix.eps http://www.slac.stanford.edu/~kerstin/vubfit/mXrms16_mix.eps I had a very brief look at generic MC from the ICHEP ntuples to see if I find the same broad structure as in Roberto's plots. I see this structure, but it seems that these are not B->Xlnu events, at least they have vcb==0 and vub==0. Do you see the same, Roberto? Thanks for your patience with this long mail, Kerstin