[Frost] Prospects for Double Pions in Deuterized Butanol

Tue Jun 1 18:41:26 EDT 2010

Hi all,

The threshold energy for rho and omega mesons is  E_gamma ~1.1 GeV.  The
cross section at threshold is very small.  Why not run at 1.5 GeV?  That
way you will have access to double pions from rho meson decay as well.

Just a thought.
Phil

> 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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-- 
   Philip L. Cole
   Associate Professor
   Idaho State University
   Department of Physics
   Pocatello, Idaho 83209
   (208) 282-5799  office
            -4649  fax
    cole at athena.physics.isu.edu
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