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
> > >
> > >
> > >
> > 
>