Dear Marcel, all

[ Explicit post to Rob and Gerhard as they may (should?) know what the topo does to semileptonic decays ]

Just as a bit of background to those not following this saga too closely: this paper measures DeltaAcp between D->pipi and D->KK using semileptonic B decays. It gets a result that  inconsistent with the world average obtained from D*-tagged D decays. The plan is to show this in Moriond and at the same time show an update of the D* analysis (to be approved next week).

I have been thinking a lot about how to get a fake DeltaA_cp in this mode and may have come up with something that is probably small but not accounted in the systematics. It's all related to them using the topological trigger. They have a 3-body final state much and use the 3-body topo, which is fine and the the 2-body topo. That's where I have a worry.

In the analysis note (p.78) they report the raw asymmetries for events triggered by 2 and 3 body topos and all seems fine. Still, there could be an effect. They do not say which of the 3 tracks are being used in the 2 body topo. If it's the h+h- it's all fine. If it's mostly muh combinations then I'd like to know if the efficiency of the topo is the same for mu^+h^+ and mu^+h^- (and cc). I could well imagine that they are not identical due to the remaining field in the velo giving a better separation of opposite charge vertices, or decay kinematics (but then wouldn't know how). There could also be a time and charge-dependent tracking efficiency in the Hlt that does not cancel with magnet flips. A misalignment of a T station for instance could make it more difficult for positive than negative to have a good chi2. We had something like that in early 2012 (not included in that analysis).

Now say after trigger we have more mu+h- and mu-h- than the 2 others, then we could cause an asymmetry due to the tracking efficiency of the remaining track not used in the Hlt. The asymmetry between K+ and K- for instance is well known. That's where I'm puzzled, because if I present things like that it looks dangerous. If I start from reconstructed decays and then think about the trigger get to the conclusion there's no effect.

Any thoughts?

Other comments to the paper:

Line 10: why the comma after two-body ?
Line 15: is report the right word here?
Line 19: no ref for Babar?
Line 30 (and abstract): Why write B->DmunuX and say X is what's not reconstructed. The nu is not reconstructed. I'd write B->DmuX and thus would make sure I never have X=0. It would anyway be nubar. Also, why "B"? Are Lambda_b->D0munuppi not included or negligible? In line 47 you for the first time say it has to be a meson. And what about Bs?
Eq: 2: The order of terms is not the same as in the text.
Line 41: a detection asymmetry
Line 99: imply -> produce
Line 100: $pp$
Line 183: m(D*-D) -> m(D*)-m(D)
Line 224-227 I am a bit lost with effective lifetime and true decay time distribution. What do you mean? Why do you give a systematic error in the result below if that's not a measurement?

Cheers,

Patrick




On 02/21/2013 06:31 PM, Marcel Merk wrote:
Dear bfys friends,

Due to the absence of too many people, the bfys meeting tomorrow (Friday 22 Feb) will be cancelled.
Please send me your comments on the paper below before Monday and I will collect and upload them.

best regards,
- Marcel

On 18 February 2013 14:20, Marcel Merk <marcel.merk@nikhef.nl> wrote:
Dear Friends,

We have been assigned to review the following interesting paper:
Search for direct CP violation in D0->K-K+, pi^-pi^+ using semileptonic B decays.
For details, please see below.

If there is a volunteer to collect the comments for this paper, please contact me.
The bfys meeting to discuss it will be Friday 22 Feb, at 9h30 in N328.

best regards,
- Marcel

---------- Forwarded message ----------
From: Ulrik Egede <U.Egede@imperial.ac.uk>
Date: 12 February 2013 23:12
Subject: First circulation of publication draft for PAPER-2013-003, Search for direct $CP$ violation in $D^0 \to K^- K^+$, $\pi^- \pi^+$ using semileptonic $B$ decays
To: LHCb General mailing list <lhcb-general@cern.ch>


Dear Colleagues,

A paper is available for your comments:

Title           :
Search for direct $CP$ violation in $D^0 \to K^- K^+$, $\pi^- \pi^+$
using semileptonic $B$ decays

Journal         : PLB
Contact authors : Jeroen van Tilburg, Thomas Ruf
Reviewers       : Tim Gershon (chair),
                  Sheldon Stone, Tom Blake
EB reviewer     : Jaap Panman
Analysis note   : ANA-2012-012
Deadline        : 26-Feb-2013
e-group         : lhcb-paper-2013-003-reviewers
Link            : http://cds.cern.ch/record/1514660
Extra authors   :
Twiki           : https://twiki.cern.ch/twiki/bin/view/LHCbPhysics/D2hhFromB

The following institutes are requested to make institutional comments:
LAPP, Annecy-Le-Vieux, France
Tsinghua University, China
Faculty of Physics and Applied Computer Science, Cracow, Poland
Birmingham, United Kingdom
EPFL, Lausanne, Switzerland
NIKHEF, Netherlands


Please send any comments via the CDS system. It is the responsibility
of the contact authors to provide replies on all comments
made. Subsequent modification to the publication are made in
consultation with the referees and during the EB reading. Following
this, there will be a final meeting of the editorial board with
contact authors and reviewers present where final decisions are
made. As the last step a short presentation is given to the
collaboration and the paper is sent for publication.

You can find all paper and conference report drafts open for comments
via the EB web-page, by clicking on Current Drafts.

http://lhcb.web.cern.ch/lhcb/lhcb_page/collaboration/organization/editorial_board/default.html

Regards,
      Ulrik Egede
--
=====================================================================
Latest news from Editorial Board:
 - Update front page of PAPERs and CONFs to include license. See
   template.
 - Use new reference for trigger. See template
 - Instructions for submitting to PLB and JHEP updated in FAQ,
   http://cern.ch/go/Xz7d
 - Acknowledgements and detector section updated in template. Make
   sure to update your template.
 - When the arXiv and journal bibliographic data disagree (e.g author
   initials or titles), the journal information should always be used.
 - Remember to check out new template from SVN each time you start
   editing a new document.
=====================================================================

Prof. Ulrik Egede,          Tel    : +44 20 759 47688
Department of Physics,      Fax    : +44 20 782 38830
Blackett Laboratory,        E-mail : U.Egede@imperial.ac.uk
Imperial College London,
London SW7 2AZ, UK.




_______________________________________________
Bfys-physics mailing list
Bfys-physics@nikhef.nl
https://mailman.nikhef.nl/mailman/listinfo/bfys-physics



-- 
========================================================================
 Patrick Koppenburg                                   Nikhef, Amsterdam
 http://www.koppenburg.org/address.html