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Hi Kerstin, I should add that sigma(pi+p)=sigma(pi-n) and sigma(pi-p)=sigma(pi+n) because of isospin symmetry. However, the cross sections for pi+ and pi- in the detector material will be different if the ratio neutrons/protons is different 1 one which is the case in general. Cheers, Heiko On Tue, 11 Sep 2007, Heiko Lacker wrote: > Hi Kerstin, > > > > What are the cuts on the momentum/energy of charged > > > and neutral particles in the recoil? > > We have a table in the next version of BAD 1212 that lists the selection > > criteria. You can see it on page 6 of this unofficial version: > > http://costard.lbl.gov/~kerstin/vubunf/ana32/BAD1212_v5a.ps > > > > It is the selection proposed in BAD 1111 (but we picked it up from the > > BRecoilUser package, so we should not be affected by the typos in earlier > > version of that BAD). > > > > > The total charge distribution for the enriched sample > > > of neutral B gets very asymmetric in data. Is this a loss > > > of negative slow pions in data due to interactions? > > Is there a reason why we would expect to lose negative slow pions with > > higher probability than positive slow pions? > > The cross section for low energy pions with nucleons is different > for pi- and pi+ due to the different combination of isospin states. > > That is in particular relevant if the energy corresponds to an > excitation of a Delta resonance (pi N -> Delta -> pi N). > > E.g. at T_kin(pi)=195 MeV: sigma(pi+p)>>sigma(pi-p). > For small pion energies: sigma(pi+p)< sigma(pi-p). > > Cheers, > Heiko > > > And if so, would we think that for the charged B, the asymmetry is from > > slow pions that come from fragmentation processes or such (not from D* and > > so they would be in both B charge samples)? > > Spontaneously, I don't have an idea how we could test this easily. > > Shouldn't this be something we should know from the B0->D*lnu analyses? > > > > > the effect is much smaller in the charged B, for which > > > you do not apply the D* l nu veto. > > > - have you tried to change the purity of the Breco selection, > > > to see whether this might cause problems? > > We have changed purity cuts earlier in the analysis, but not recently, > > so we have not tried looking at this in this context. We could try this. > > > > > or enlarge the q2 cut on the recoil? > > Do you mean q2 = the invariant mass of the W? We do not apply any cut on > > q2. So are you suggesting we should try cutting on it? > > > > > - Do you understand the large change in charged multiplicity between > > > enriched and depleted samples? The neutral multiplicity increases > > > for the enriched samples, the charged multiplicity decreases. > > > Does this point to problems with the enriched MC? Jet-set > > > fragmentation? > > Are you looking at the background subtracted spectra or the spectra before > > background subtraction? I am not quite sure, but I think the trend is > > similar whether or not we look before or after background subtraction. > > I guess in the neutrals it could be JetSet fragmentation. Backgrounds from > > the detector should also show up in the depleted sample. > > Not sure how we could test this easily. > > > > > - the enriched Emiss-Pmiss and MM*2 distributions do not > > > show the expected peaks. Emiss-Pmiss= MM2/(Emiss+Pmiss) assumes > > > a linear dependence of the MM2 resolution on Emiss. > > For Emiss-pmiss I think it is fair to look at this after the mm2 cut (as > > we tend to think of the mm2 cut as cut to suppress background and > > Emiss-pmiss to then improve the mX resolution). The enriched sample then > > shows a good peak, the depleted is not so great. > > > > > Have you checked MM2 vs Emiss? > > Not on release 18. But we have studies we performed on release 14, which > > you can find here: > > http://costard.lbl.gov/~kerstin/vubunf/resolution/plots.html > > It does not have mm2 vs Emiss, though, but a bunch of other plots related > > to the neutrino (and also other things, resolution and truth matching > > studies). We could check mm2 vs. Emiss on the current ntuples. > > > > > I do not understand the motivation of the additional > > > cut on the MM^2. > > It's really more the Emiss-pmiss cut which is additional. The mm2 cut > > removes a lot of charm background at low mX (the long positive shoulder in > > the enriched sample). We showed this at the June CM: > > http://www.slac.stanford.edu/BFROOT/www/Organization/CollabMtgs/2007/detJun07/Tues2d/Tues2d.html > > > > Basically, mm2 suppresses charm background, Emiss-pmiss improves mX > > resolution. Kinematically it makes sense when you consider what losing a > > kaon does to these distributions. > > > > > - Have you tried to look at these distribution with fewer bins > > > on Mx? > > I am not sure I understand the question. Do you mean whether we have > > performed data-MC comparisons for a restricted range of mX? We have not > > tried that, since we are using the full range for the unfolding. But maybe > > we could learn from making the comparisons in the low mX only, as we would > > change the S/B significantly. Is that what you are thinking of? > > > > Kerstin > > > > > > > So many questions, no clear answers? > > > > > Ciao, > > > Vera > > > > > > > -----Original Message----- > > > From: [log in to unmask] [mailto:[log in to unmask]] On Behalf Of Kerstin Tackmann > > > Sent: Friday, August 31, 2007 2:26 PM > > > To: vub-recoil > > > Subject: Data-MC Agreement (again) > > > > > > > > > Dear vub-recoilers, > > > > > > as you probably know, we are seeing some problems in the data-MC > > > agreement. The most recent plots are here: > > > http://costard.lbl.gov/~kerstin/vubunf/ana32/dataMC/dataMC_KLcorr.html > > > > > > We obtain these plots as follows: > > > *Remove the cut on the given variable from the analysis. > > > *Perform the fit to the mX spectrum with this selection. > > > *Rebin the data and MC in the variable under study and use > > > the *comp from the previous fit to mX to scale the MC > > > components. > > > > > > The main concern is about the neutrino variables and Qtot. > > > > > > If we could have plots using this technique for the Vub analysis, that > > > would be a very interesting comparison, from which we could hopefully > > > learn and which would help us a lot in the review. I would really > > > appreciate if someone could look into this (as soon as possible) > > > -- please let me know if that would be possible. I'd be happy to give > > > more technical details, just let me know if something isn't quite clear! > > > > > > Thanks so much, > > > Kerstin > > > > > > > > > > > >