Minutes and action items from 1st Editorial Board Meeting
June 4, 2008
Participants: B. Adeva, D. Drijard, A. Romero, L. Tauscher, A. Lanaro
Armando:
Brief introduction during which the mandate of the editorial board and a proposal for
the board regulations have been presented.
The mandate of the board is to produce one draft on the pionium lifetime with the
broadest consensus, after clarification of all outstanding scientific issues. The baseline is
the two drafts recently submitted to the Collaboration for revision, hereafter referred to as
draft D and S. At completion, the board will provide the Collaboration Executive Board
with a recommendation for submission of the final article to one scientific magazine.
Proposed organization of activity:
Phase 1: revise data processing, event selection, reconstruction and detector efficiencies
Phase 2: analyze event sample, experimental and simulated spectra; analysis and fitting
procedures; backgrounds; pionium and CC signals
Phase 3: determination of Pbr, lifetime, estimation of systematical errors, final result
Bernardo:
Emphasized the role of MSGC/GEM for improving the reconstruction efficiency in the
transverse plane of the emerging pion pairs, and for recovering the SFD inefficiency for
detecting very close by charge hits. All participants agreed with the principle that the
MSGC response should be used in the data analysis if it helps improving the data quality.
However, the issue is what to do in those cases in which the MSGC detector was not
operating?
- The D draft is based on 100% of the collected statistics, but does not take into account
the MSGC response whenever present, and must reject all events unresolved by the SFD.
- The draft S is not based on 100% of the collected statistics (retains only events with
MSGC response and thus depends on the MSGC efficiency), but recovers most of the
SFD inefficiency.
Action 1: quantify fraction of events with MSGC on and all efficiency factors for
upstream tracking (All, as part of phase 1)
Remarks to the D draft:
-
Need to understand possible momentum dependence of Pbr in both D and S
analyses (S reports of a possible slight increase of Pbr pair momentum in Fig 5 of
S draft). For the propagation of pionium inside target, draft S uses C. Santamarina
MC approach, whereas draft D uses M. Zhabitsky exact solution of transport
-
-
-
-
equations. The momentum dependence is, however, considered similar in both
approaches.
Action 2: verify that momentum evolution in Monte Carlo and analytic
approaches are indeed compatible. Quantify differences between two
approaches to describe pionium propagation inside target medium (Ludwig)
Action 3: draft D should perform a study of the momentum dependence of Pbr
(Daniel, Ludwig).
stability of Pbr as a function of two-dimensional (QL, QT) pionium signal. Draft S
shows stability (Fig 4) although errors are large.
Action 4: the Pbr stability versus the 2D boundary region should be analyzed in
the context of draft D and compared to the one of draft S (Ludwig, Daniel)
The quality of the fit of the QT distributions shown in Fig 2 of draft D is argued.
There appear to be a systematic shift of 6 consecutive bins in one direction and
this cannot be accounted by a random fluctuation.
Action 5: the reliability of the simulation to be able to reproduce the data is a
crucial point of the analysis. Extensive consistency checks are necessary
between simulated and experimental spectra, for both signals and background
(All)
There is a substantial agreement between S and D on the number of detected
atomic pairs from 2001 and 2002 data sets. S detects many more atomic pairs
with respect to D from the 2003 data set.
Action 6: the dependence of both atomic and CC pair signals on the run period,
target type, and beam momentum need to be provided by both S and D drafts,
after a comparison between the two original data sets (All, as part of phase 1)
The point was raised on the high Pbr value reported by draft D from 2001 data
with a 94 um target, compared with values from other data sets.
Several points were raised to motivate a submission of the final article to PRL. Other
members of the EdB agreed provided a general consensus is reached.
Ludwig:
Remarks to the S draft:
The conversion function Pbr versus lifetime depends on target thickness and beam
momentum, and therefore should be properly applied to the different data sets.
Action 7: S draft to provide table with infos from different data sets (Bernardo,
Antonio)
The procedure used by draft S to yield one value of the lifetime from the weighted
average (with luminosities as weights) of several Pbr from different data sets is
disfavored with respect to the procedure used in draft D, which considers probability
density functions for the different data sets and their product function from which one
obtains the most likely lifetime value.
Action 8: the procedure followed in draft D is considered more rigorous and thus
should be retained (All)
The 9% relative difference between D and S pionium lifetime needs to be understood
and reconciled.
Action 9: need further investigation (All)
The multiple scattering error estimated to be ~1.5% of X0 upstream (by draft S) seems
not to contribute to the final systematical error in draft S, whereas it contributes in draft
D. Action 10: need further investigation (All)
The relative difference between the Pbr values obtained from a global fit and a
momentum dependent fit, in draft S (Table 1), amounts to ~ 1%. The claim is that these
values should be “numerically identical”.
Action 11: needs to be checked further (Bernardo, Antonio)
Figure 5 in draft S shows some inconsistencies (scale, fluctuation, error bars)
Action 12: need to specify inconsistencies and provide explanation (Ludwig, Antonio)