[Frost] Prospects for Double Pions in Deuterized Butanol

[Michael Dugger]

Hi,

The neutron efficiency is highly dependent on the momentum. The EC gets an 
efficiency for protons of ~50% when the momentum is about 1.8 GeV. For a 
neutron with a momentum of 1 GeV we only get an efficiency of ~25% At 0.6 
GeV momentum the efficiency drops to ~10%.

-Michael

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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