[Olympus] remaining program

Thu Dec 20 12:05:03 EST 2012

Dear Stan and all,

just a quick comment about the 3.6 fb^-1 of integrated luminosity. The TDR was not quite exact at same places. Michael explained to me that we need twice 500h which corresponds to 3.6 fb^-1 in total. So we are not a factor 2 off, but just on track.

I would support Richard's idea of keeping running like it is, because changing too many parameters at a time or having many too small chunks of different datasets might not buy us anything in the end.

Cheers,

Alexander

On Dec 20, 2012, at 4:31 PM, Belostotski, Stanislav wrote:

Dear Richard, Michael and all,
As  indicated in the OLYMPUS TDR, in order to reach something better
than 1 % statistical precision  there must be collected 3.6 1/fb
integrated luminosity for EACH  beam species, which I am afraid not yet
our case. Also, a  data quality cut must  unavoidably be applied, so
we'll lose a (hopefully small) fraction of the data sample in addition.
 We can try to reduce the systematics as much as possible but  can
never jump over the statistical precision. So I would also vote for data
collecting to the end of the run.
Yet ,   I am still   worrying  about a systematics  related to the  beam
energy variation which may affect  the measured asymmetry. A naive MC
estimation shows:
 beam instability of 1 MeV  may result in 0.28% false asymmetry at
scatt. angles >40 deg.
Anyway, we should correct for the beam energy variation which is being
monitored.
To experimentally investigate that, it would take few hours  provided
that beam energy rearrangement, say to 2010 MeV, does  not take much
time.However if it takes  much longer I withdraw this suggestion.The
latter question must be addressed to Frank.
With best regards StanB

On 20.12.2012 14:52, Richard G Milner wrote:
Dear Michael,
I must say that I have significant reservations about using the remaining
beamtime in the way you propose. They are as follows:

- I think it is well understood now that running with negative field
introduces
large, new systematics (Moller background, very different time to distance
relation etc.) beyond any which cancel in the super-ratio. This was a clever
idea but too naive.  Most of our data have been taken with positive field.  We
have to understand the acceptance to of order 1 % as is done in many cross
section experiments.  Axel's recent work is promising that we can approach
this.
Also, we have taken some data already with negative field.

- Our proposal design was 3.6 inv fb. I think it is best if we take somewhat
more than that with positive field as this will allow us to put tighter cuts,
e.g. phi cut, than we had envisaged.

- Changing many things about the running in the holiday period where we (and
DESY) have a minimal crew available to deal with problems is risky.

So my vote is to continue the stable running of the experiment to acquire the
maximum amount of integrated luminosity with positive field in the remaining
time.

with best regards,
Richard

Quoting Michael Kohl <kohlm at jlab.org<mailto:kohlm at jlab.org>>:

Dear all,

we have collected 3.2 fb^-1 so far, almost close to the design
luminosity.

For the 12-day addendum we should make a plan for a set of additional
measurements that could be helpful for the analysis.

Here is my proposal for low-luminosity running:
-run all four configs (e+-,B+-) without shielding but with the intensity
reduced to optimze the noise, each for a day.
E.g. reduce lumi by x10, expect ~3Hz elastics = 250k elastic events per
day -> 20 mA current / 0.2 sccm flow;
vary the magnetic field (100%, 75%, 50%, 25%) every six hours.
Open up the trigger by reducing the prescale on the 3-of-4 trigger type
to max out the DAQ (<30-40% deadtime).

This would cost us four days of running.
A data set with minimized noise can help us train and optimize the
reconstruction software, rather than using "noisy" high-luminosity data.

A dataset with minimized moise in all four configs will show how the
cancelations in the ratio occur and will help us validate the MC. Varying
the magnetic field in addition will serve the same purpose. The statistics
will be good enough for the validation at forward angles, where also the
systematic effects on the single-polarity ratio were the largest.
In the end we will need to be able to trust the MC for B+ at low epsilon.

At low luminosity, a trigger which is more more open also allows to verify
TOF and trigger efficiencies, and to break any inefficiencies further down
as a function of channels, coordinates etc.

We should start producing that set of measurements beginning on Saturday,
so that it could be finished by Wednesday. If it takes longer we still
have a few days left. Any final remaining days would be used to further
improve the statistics.
Frank Brinker also would like to do another Touchek energy measurement,
probably on Dec 31 / Jan 1.

If you have further ideas or wishes, please bring them up.

Best regards
  Michael

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