[Frost] Prospects for Double Pions in Deuterized Butanol

[Volker Crede]

Eugene,

I have attached the results from g9a again (same I sent out earlier which 
showed an average of all 4 topologies we use), but now I have superimposed 
results (blue data points) from using only the topology with all particles 
detected (proton and the two pions). The modulation (2nd picture attached) 
is for 0.6 < cos(theta) < 0.7 and for the third data point therein. The 
overall statistics for the blue data points is still very good (binned in 
three independent variables) and agrees very nicely with the average; no 
background subtraction has been applied and also no energy and momentum 
correction has been used, yet.

Once again, these preliminary results are based on only 35 hours of data 
taking (all of the g9a statistics for this configuration). Even if we drop 
the efficiency by a factor of 10 due to the neutron detection efficiency 
(sounds like a conservative estimate) and assume that the neutron cross 
sections are of the order of about 70% of the proton cross sections (based 
on older measurements of the threshold region for gn -> n pi+pi- and some 
extrapolations to higher energies I did with Winston Roberts last week), 
the expected statistics for us should be similar assuming three weeks of 
additional beam time. Of course (like for all other possible reactions), 
the degree of polarization will be somewhat smaller and certainly, we can 
only afford ONE position of the coherent edge. I think 1.1 or 1.3 GeV 
would be the most promising and interesting for double pions in terms of 
statistics and physics.

     Volker


On Sun, 30 May 2010, Eugene Pasyuk wrote:

> Volker,
>
> In case of deuterium target we will have to detect all three particles,
> pi+, pi- and neutron. Neutron detection efficiency in EC is about 50%
> and about 10% in TOF. Also momentum resolution for neutrons obviously is
> not as good as for charged particles.
> We should take 3 perticle topology from g9a as a start pint for
> estimates. An then drop it by a factor of 10 or so.
> If we go with deuterium target it makes sense to bring LAC on-line to
> have better efficiency for neutrons.
>
> -Eugene
>
>
> On 5/26/10 6:12 PM, Volker Crede wrote:
>> Dear Eugene,
>>
>> you suggested this morning the possibility to study double-pion
>> production with a deuterized butanol target. I have attached some
>> pictures from g9a using a lineary-polarized beam with a coherent edge at
>> 1.3 GeV; only one target orientation has been used (L-+,<=) to make
>> these distributions. For this polarization configuration, we have a
>> total of 5 observables (all degrees of polarization are set to 1.0):
>>
>> I = I_0 ( ( 1 + P_z ) +
>> sin [ (2 beta) (I_s + P^s_z) ] + cos [ (2 beta) (I_c + P^c_z) ] )
>>
>> The picture 'I_s_energyIndex13.eps' shows (very, very preliminary) the
>> combination of (I_s + P^s_z), i.e. the combination of the beam asymmetry
>> I_s (that Chuck Hanretty has been extracting from g8b data) and the new
>> beam-target observable P^s_z. The photon energy is [1100, 1150] MeV; the
>> observable is plotted versus phi*, which is the azimuthal angle of the
>> pi+ in the rest frame of the two mesons. The different distributions
>> show the binning in the corresponding cos(theta*) variable (pretty much
>> the same thing that Chuck always shows). It starts out very flat, but
>> polarization effects are clearly visible at larger values for cos(theta*).
>>
>> The other two pictures show the missing proton peak integrated over all
>> bins (only pi+ and pi- detected) as well as the lab_beta modulation for
>> just 0.1 < cos(theta*) < 0.2 and the corresponding fourth data point in
>> there ... a very fine binning.
>>
>> These are distributions for double-polarization and with a pretty fine
>> binning in three of the 5 independent variables. The statistics is very
>> good. No background subtraction has been performed and there is still a
>> lot of background involved (of the order of 50%). The total cross
>> section for two-pion production off the proton is of the order of 40-60
>> microb for this energy range; the cross sections off the neutron are
>> about 60-70% of the proton cross sections ... still pretty big. Most
>> important, the attached distributions are based on just 35 hours of
>> data-taking ... less than two days. The total number of events for PARA
>> is 179,647,134 and for PERP is 163,187,819.
>>
>> If we decide to go with just 1.1 GeV or 0.9 GeV coherent-edge position,
>> the count rates should even be better. This corresponds to the 1500-1700
>> MeV mass region, very interesting to study for example N* decays into
>> Delta pi, which are poorly understood for many states. Delta-pi decays
>> in D-wave seem to be stronger or equal in strength to Delta-pi decays in
>> S-wave ... not expected from naive phasespace arguments. This could be
>> part of a physics motivation.
>>
>> Best wishes
>>
>> Volker
>>
>>
>>
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