[Frost] Prospects for Double Pions in Deuterized Butanol

[Igor Strakovsky]

Phil,

In this case, we will miss W = 1.68 GeV case which is more important vs
your rho and omega physics

Igor

On Tue, 1 Jun 2010 16:41:26 -0600 (MDT), "Philip L. Cole" <cole at jlab.org> 
wrote:

> 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