Dear colleagues,

I prepared my comments for the Conference draft 2011-017
with a dead line for comments of 6 April.
Please, add, remove or question comments as you wishi,
before I send them on Tuesday.

Best regards,
  Tjeerd
=========================================================
Comments on Bc+ to B+ production cross section ratios

Dear authors of this draft,
I like your short and comprehensive paper on Bc+ to J/Psi pi+
decay. I have first a few general questions.
After that follows a number of possible improvements for the text
to illustrate problems I encountered during reading.

=========================================================
1. I am not convinced we measure the production cross section ratio
of Bc+ and B+.

2. I cannot find an argument why the decays to J/Psi pi+ for Bc+
and to J/Psi K+ for B+ should be compared.
Is it just a matter of yields or are the branching ratios expected
to be very similar or are the efficiencies very similar?

3. Is there any prediction of the Bc+ decay branching ratio?
Without this we do NOT have an 'indirect measurement of the Bc+
production cross-section'.

4. Are there arguments why the integrated (over range in pT and eta) 
total efficiency for the Bc+ decay channel is almost two times larger 
than for that of B+?
The measured numbers 43+/-13 and 3476+/-62 and the efficiency
corrected numbers 756+/-286 and 35029+/-984 could be
summarized in a table, including the integrated luminosity
32.5+/-3.3 pb-1.

5. The question also arises why the statistical errors of the
efficiency corrected numbers do not increase proportional.
This suggests that the samples in the Monte Carlo are too small,
even for the modest statistics of this measurement.
The ratio could be 20 % more precise!

=========================================================
page 1:
Title: 
Why not, 'Measurement of the relative yields of
Bc+ to J/Psi pi+ and B+ to J/Psi K+ at sqrt(s)=7 TeV
in LHCb'?

   It is not clear that 'relative' means 
   'in comparing similar decay channels', or what it means at all.
   In line 9 they are called 'indirect measurements'.
   It is also only one 'ratio' and not 'ratios' in the title.

Abstract: 
The sentence 'The analysis ... Collider' can be removed, 
when 'in 2010' is added to the first sentence after 'detector'. 

   As no precise yields are presented, it not necessary to
   give '32.5 pb-1' in the abstract. 
   The correct value and the months are also given in line 24.

'The ratio of these Bc+ and B+ yields, including the opposite
charges, is measured as, Rc+=...'
  
   Rc+ is clearly NOT the production ratio of Bc+ and B+.
   As also indicated in footnote 2, the yields
   of the J/Psi pi+ and J/Psi pi- decays from Bc+ and Bc-
   decays are added.

Footnote 2:
'Charge conjugation symmetry is used in this analysis.
Theredore, the yield for the opposite charges are added.'

   Make a sentence. 'Symmetry' is missing. 
   'Implied' is not clear.
   Mention the consequences.

line 4:
Remove 'then'.

line 14:
'The Bc+ production is measured relatively to the B+ production
in the decay mode B+->J/Psi K+, when the branching ratio of
Bc+->J/Psi pi+ becomes known,'

   It is only when Bc+->J/Psi pi+ branching is known that you have
   a measurement of the production ratio of Bc+ and B+.

lines 25-34:
'The analysis uses events selected by single muon and dimuon
triggers at different levels. At the hardware trigger level (L0)
one muon candidate or two muon candidates are required
with limited values of pT1mu.
At the software trigger level three possible scenarios (lines) in the
high level trigger (HLT1) are defined. 
The first line ... 2.5 GeV/c2.
At the highest level of the software trigger
(HLT2) events are selected that contain ...'

   The sentence in 25-27 is difficult to read. 
   The value of 1.4 GeV/c is superseded by 1.8 GeV/c, 
   and 0.56 GeV/c and 0.48 GeV/c are supperseded by 0.9 GeV/c.
   Use 'trigger levels' consistently while explaining the different 
   triggers.
   Explain the meaning of 'lines'.

line 37 to line 3 on page 2:
'... opposite sign muons that must have pT larger than 0.9 GeV/c,
... track fits (chi2/ndf<4). The muon identification is chosen
such that the muon hypothesis is at least 10^3 more probable than that
of a pion.'

   Combine 'tracks' and 'identified as muons' into 'muons'.
   Use for the momentum 'GeV/c' or 'MeV/c' consistently in the paper.
   For the mass use 'GeV/c2' or 'MeV/c2', including the figures.
   DeltaLLmupi is not used further; this is not needed to be introduced.
   It is not clear what is meant by the 'combined likelihood LLmupi'.
   Also the singular in 'difference' and the plural in 'logarithms'
   and 'likelihoods' are not understood.
   
page 2:
Fig.1:
What is the red peak resonance at 5320 MeV/c2? And why does it
not show up in the data points?

   Explain the curves.

line 5, 9-10:
Remove 'and only candidates ... are kept.' 
Add in line 5 'reconstructed from the triggering muons' after
'J/Psi candidates'.

   In line 5 we start with the J/Psi requirements first and in
   line 7 we continue with B requirements. It is strange to go
   back to J/Psi again in line 9.

line 20:
'... is obtained by allowing also J/Psi particles of which the
decay muons were not selected in the trigger. This is show in Fig.2. 

   'removing the trigger requirement' is not clear.
   A discussion why you do not use this number in the ratio
   may be needed.

Page 3:
line 10, 11:
'... related to the selection requirement on the proper lifetime
of the B meson (t(B)>0.3 ps).
'The Bc+ average lifetime is only known with ...'

   Use t instead of tau.
   Definition of tau is average lifetime or also mean life.
   Spelling correction: 'known'.

line 13-14:
'The variation of the number of selected events is found to be
equal to \pm 6~\%, which is taken as the contribution to the 
systematic uncertainty of the efficiency due to the limited
knowledge of the Bc+ average lifetime.'

   A variation of 6 % would mean \pm 3 %.
   An 'observed' efficiency of (20\pm 6) %, for instance, 
   would mean a contribution of \pm 30 % to the systematic
   uncertainty.

Page 4:
Table 1:
Change 'Quantity' in 'Source', 
'Systematic error (%)' in 'Contribution (%)',
'Total' in 'Total systematic uncertainty'.

Eq. (4):
Rc+^model = sigma^model(Bc+)/sigma^Pythia(B+) = 1.4 %.

   '^model-dependent' is too long for a superscript.
   This shows that the branching ratios are not included.
   I cannot believe that the statistical error is that
   large (0.4 %) at the level of generator events that do
   not need to include efficiencies.

line 6:
Move the sentence 'Integrated total efficiencies ... Ref.[11].'
to page 3 line 5.

   It is strange that detector efficiencies are discussed 
   when generators are discussed in Results and Conclusions.

line 11:
Remove '32.5+/-3.3 pb-1'.

   This precise value is not important for the ratio.

line 13:
Change 'life-time' in 'average lifetime' or 'mean life'.
Add 'and decay branching ratios'.

   I am surprised that more statistics seems only important
   for the mass and the lifetime and not for the topics discussed
   in this paper: the production cross section and the branching
   ratio.