[b1_ana] Fwd: comments/questions to PR12-13-011

[Karl Slifer]

Hi all,

Below please find a draft response to the readers.  I'd appreciate any/all
feedback.

Thanks to Oscar and Dustin for sending comments already.  I hope I have
incorporated them satisfactorily, but let me know if not.

Dustin : any ETA for the updates to the technote? Ideally we can send them
this short email and then provide your note for the full details.
Most important would be to clarify the overall drift numbers, as I had the
same confusion that Ellie raised.

I'll have time to work on this tomorrow morning and early afternoon, but
have to leave for DC mid afternoon.  I'd love to get a response to Ewa
before then if possible.

thanks much,

-Karl


-----------------------------

The measurement is very sensitive to the systematic effects and good
control of them is the
key point. Therefor I would like to know if there are any estimates of
expected size of effects from:

RESPONSE: We agree with the TAC assessment that systematic errors from
drifts must be mitigated, but
                     that they are manageable with a combination of
hardware upgrades and a dedicated collaboration
                     effort.  We note that the recent g2p experiment
involved a similar situation where a significant
                     commitment was made to install and run this polarized
target, but separate groups were tasked
                     with substantial tasks of beamline, DAQ and detector
upgrades.  We are grateful to the TAC for
                     pointing out several effects which were not explicitly
discussed in our submitted proposal.  We
                     have written a short note discussing each of these and
conclude that the overall systematic
                     uncertainty is still of the same order as estimated in
the proposal.

1. beam - one aspect is the stability in terms of position and divergency
     this can change acceptance and produce false asymmetries

RESPONSE: (The TAC report pointed out that the false asymmetries from beam
position drifts are easily
                    removed by "regression".  Can someone fill in the
details?  I assume that this just means
                    that the parity feedback on position is very good, but
we need some numbers/examples to
                    back this up.  This is dealt with in section 1.1.4 of
the note, but there are few details.)

2 beam polarization - how the unpolarized beam will be obtained what kind
of effects are
     expected from beam polarization (ie. to which level exact averaging of
opposite beam polarity
     is needed and how the phase space of the beam is polarization
dependent)

RESPONSE: JLab E06-010 (Transversity) spin-averaged a highly polarized
(~80%) beam in order to
                     obtain an "unpolarized" beam.   The parity feedback
allowed for knowledge of the residual
                     beam polarization at the 2.2*10^{-5} level, according
to the lumi monitors. Please see attached
                     plot, which shows the beam asymmetry from that
experiment.


3. temperature effects on the efficiency (and stability of the detectors
allignment) - proposed scheme
     of polarization reversals will give data with target polarization
during the day and unpolarized
     at night or vice versa. This can introduce false asymmetry related to
any kind of temperature
     dependence in efficiency or allignment. Was it estimated ? Are there
any studies of this kind of effects
     in previous experiments?

RESPONSE: (This could be addressed by the transversity slides, but I'm not
sure if the pion yield plot
                     addresses this.  The main sensitivity to temperature
will be the BCMs and Dave has plans
                     to isolate them, but I don't have any details of that
yet.)



4. for  the drift of efficiency and its time dependence (page 25) linear
evolution in time is assumed.
     for which effects it is justified? It is clear that for example
changes in packing factor of dilution factor
     can have "step like" characteristics. Are there any ideas to what
level such effects can be controlled
     during the run?

RESPONSE : (Linear and sinusoidal drifts are the only type that I've seen.
 Higher orders could theoretically
                     be present, but if they were I suppose they would
become an issue for all experiments, not just ours.)
                     "Step-like" changes in the packing factor or dilution
factor have only been observed once in 700 hours
                     of running the polarized target. It was immediately
obvious from the change in polarization.  If it
                     occurs during this experiment, it would impact only a
single pol/unpol cycle, which is either a 12 hour or
                     24 hour portion of data.  This data would need to be
either discarded or handled with care.


In the proposal  "consistency checks on measured cross section for each
run" is mentioned.
 What precisely is meant? At what level it can be done for the proposed
measurement? Please give
 more detail, especially on the precision of such test.

RESPONSE : Typically we can monitor the unpolarized yields to the better
than 1% level.  Luminosity monitors
                      installed around the beamline can be monitored to the
?? level (J.P.?)


The other test mentioned in the proposal, where I would like to have some
more comments on is "the
measurements of dilution and packing factor - with carbon target "- what
exactly is planed and which
precision can be obtained? is it included in the beam time estimate?

RESPONSE: The polarized target material is deuterated ammonia (ND_3).
                    We determine the dilution factor by the ratio of
simulated radiated rates on D to total
                    rates. The pf is calculated by interpolating the ND3
measured rates between simulated
                    rates for different packing factors, with the
simulation calibrated
by the measured rates
                    on a carbon target of known thickness.  The systematic
uncertainty of this process
                    is at the 4% level.  It is important to note that the
dilution factor is a scale factor so the
                    uncertainty is an overall scale factor.  We have 6
hours assigned to this task in our overhead table 4.
                    This is a relatively short time since all that is
needed is to measure the unpolarized cross section
                    from a carbon disk, and the rate is usually quite high.


It would be interesting to see comparison of expected statistical errors in
each bin with expected false
asymmetries from time variation of beam and efficiency/acceptance.

RESPONSE: We now have plots graphically showing the full systematic
uncertainty, both from the normalization
                     dependent factors and the possible drifts.  The plots
are shown in the technote.


What are the arguments for proposed binning in x?
the last bean is clear, as much data in this configuration as possible, but
splitting of SHMS data taking
in 3 intervals is not discussed from the optimalization point of view, it
would be good to have it in the
presentation.

RESPONSE : (Hmm.  Not sure how to answer this.  Simple answer is that the
points represent the largest
                     spread in x that allows a reasonable overlap with
HERMES in a reasonable amount of beam-time.
                     Ellie has optimized to avoid large systematics from
F1, and suppression of rates. )



In general, also the authors call the measurement "ratio method"  it is the
cross section difference method
as the two data sets are taken at different time. Advantage of "ratio
method" can be fully used when two
target cels are exposed at the same time and next order is reversed. Such
configuration allows several
additional cross checks, but requires two cell target.

RESPONSE : We have examined a two cell configuration, and while it is
attractive for the reason you point
                      out, it was not clear at the time of the proposal
submission that it significantly reduced the
                      overall systematic uncertainty.  We will continue to
examine this option and are open to using
                      it if we are convinced the systematic improvement is
significant.



test of Close-Kumano sum rule - it is very hard to do such test with
limited coverage in x, may be some
estimates of contribution measured/extrapolated can be done for specific
models. For the models mentioned
on page 17 - can one get some idea what would be the contribution in
measured range?

RESPONSE : Yes, this in an excellent suggestion.  G. Miller and M. Sargian
have provided us their curves.
                     We need to integrate to see the contributions for
x<0.15 and x>0.5.  (Ellie, I think you have these
                     now.  Can you look into this?)
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