Tancredi,
One thing to keep in mind is that your signal-to-background rate is Q^2
and pmiss dependent. The picture that you showed is dominated by lower
Q^2 and pmiss. What I notice is that on the average my extracted
asymmetry is heigher for lower Q^2 (being very close to the 40 cm
value). This needs to be investigated in greater detail.
Vitaliy
Tancredi Botto wrote:
>Hello,
>for the sake of today's 40/60 cm discussion
>
>### rate comparison hydrogen data for unpol system####
>
>_ Assumes: only M=2 flow, events in +- 15 cm (Helastic_tight, no cerenkov)
> Elastic yield = N_events/ charge/ Buffer inlet P
>
>_ the elastic yield for runs with V14 CLOSED (runs 7424 vs 6864) increased
> a factor of 12.9/7.8 = 1.65. The expected value is 1.8 (assuming perfect
> cilindrical geometry, neglecting valved off injection tube)
>
>_ the same elastic yield for runs with V14 OPEN (runs 7556 vs 5471)
> increased by a factor of 11.3/9.7 = 1.2. This should be compared to
> 1.4 (15 x 130 mm inlet tube, at 300 K)
> 1.5 (15 x 130 mm inlet tube, at the same temperature as the cell
> wings)
>
>_ So the rate is ~ 10 % lower than expected when v14 is CLOSED, and ~
> 15-25 % lower when v14 is OPEN. Note I integrate over +- 15 cm
>
>_ all in all, the remaining discrepancy is 15-25 % A scenario with an
> inlet tube at 300 K is favoured, but the overall difference is not big,
> given that if the inlet tube is at room temp, it is at room T for both cells.
> I always assume a 15 mm x 130 mm inlet tube
>
>_ In summary V14 open data : unpol (one run) measure 1.2, ABS measure 1.3
> density increase with a 60 cm cell. For the higher ABS increase one may
> invoke a higher molecular fraction at 60 cm (*relative* to 40)
>
>_ Notes: always > 1000 cnts in the sample and the error assuming a linear
> Pbuffer dependence is 5 % at worst (fit gives (P_inlet)^1.075 dependence)
>
>
>### eep comparison polarized deuterium data####
>
>_ In the first attachment I show the missing mass spectrum for d(ee'p)n
>events. Black is 40 cm, red is 60 cm ABS data. Also shown in the second
>plot is the contamination as measured in in empty target runs. All data
>is normalized to charge.
>
>
>Asymmetries are essentially calculated from data in this Mm distribution,
>selected around the M_neutron peak. Apart from a yield increase in the
>ABS, the data has not significantly changed from 40 to 60 cm cell. Please
>note that the ABS realignement brought a 10 % increase of the yield.
>
>Empty-cell background appears to have not increased for 60 cm cell, and
>ABS data do not look any different for 40 and 60 cm cells. I doubt
>"background" is an explanation of the lower polarization data.
>
>
>________________________________________________________________________________
>Tancredi Botto, phone: +1-617-253-9204 mobile: +1-978-490-4124
>research scientist MIT/Bates, 21 Manning Av Middleton MA, 01949
>^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
>
>
> ------------------------------------------------------------------------
>
>
> ------------------------------------------------------------------------
>
This archive was generated by hypermail 2.1.2 : Mon Feb 24 2014 - 14:07:31 EST