[G12] similar study of eloss in g11
Craig Bookwalter
craigb at jlab.org
Wed Sep 14 13:10:21 EDT 2011
I agree that GSIM should be able to tell us how much the neutron peak
ought to move due to tracks losing energy passing through materials in
CLAS. However as my neutron peak from my accepted MC is at 941 MeV w/out
eloss (and 929 MeV w/ eloss), as shown here...
http://clasweb.jlab.org/rungroups/g12/wiki/index.php/Image:C3pi_gsim_neutron_fit_noeloss.png
http://clasweb.jlab.org/rungroups/g12/wiki/index.php/Image:C3pi_gsim_neutron_fit_eloss.png
...I'm thinking that GSIM in the default g12 configuration does not
remove energy from tracks travelling through the target volume and the
start counter. We discussed this long ago and I vaguely remember us as a
group understanding this fact and being OK with it. I believe there is
an FFREAD card that you pass in to GSIM to enable eloss in the target;
however I can't look it up because the link is broken on the Hall-B
webpage (email to clas_offline pending).
I also hear the argument about the eloss correction being larger than
expected for pions, but I wonder what effects our acceptance plays on
the average energy lost by a pion in the target and start counter. We
accept much fewer wide-angle tracks than other CLAS experiments, meaning
our tracks on average travel through more target volume before emerging
into CLAS proper. I've got no idea quantitatively what that translates
to, but it may account for a perceived greater-than-normal correction.
I'm currently generating some plots to look at the correction as a
function of a few different variables, including theta, which should
shed a little more light in this direction.
My feeling is that when all is said and done, I'll end up implementing a
run-by-run beam energy correction.
--cb
On 09/14/2011 12:19 PM, Lei Guo wrote:
> I agree with you. MC data should also be able to tell us how much the
> neutron peak will be moved due to eloss. It seems to me that the shift
> in the data -- excluding the effect of the electron beam energy --- IS
> too big.
>
> Lei
> On Sep 15, 2011, at 3:03 AM, mpaolone at jlab.org wrote:
>
>> I thought that gsim removes energy from the tracks depending on what
>> materials they pass through, then you must run eloss in your analysis to
>> recover what gsim removed. I also think that gsim removes energy
>> from the
>> tracks by default, and you have to turn off a switch somewhere to get
>> rid
>> of that functionality if you want to. I am not a gsim expert, and if
>> anyone else has a different understanding, please correct me.
>>
>> -Michael
>>
>>
>>> I don't recall a conclusive answer as to whether or not GSIM data
>>> requires eloss to be applied (see attached).
>>>
>>>
>>> On 09/13/2011 02:41 PM, Lei Guo wrote:
>>>> HI, Craig,
>>>>
>>>> Nathan Baltzell did a very comprehensive study of eloss for g11. What
>>>> I recall is that he uncovered quite a few mistakes here and there,
>>>> mostly on the gsim side, by comparing the delta_P (momentum change)
>>>> as a function of various variables (vertex positions, theta, momentum,
>>>> etc) using both real data and simulation. I think you already have the
>>>> all the info now. It might be worthwhile now to make sure that we did
>>>> eloss correctly, by checking the delta_p's as a function of z, theta,
>>>> p, and it should be similar to what gsim has, if we are doing eloss
>>>> correctly.
>>>>
>>>> Personally, I still think the low mass might come from the shifted
>>>> electron beam energy.
>>>>
>>>> Lei
>>>>
>>>>
>>>>
>>>> On Sep 14, 2011, at 6:45 AM, Craig Bookwalter wrote:
>>>>
>>>>> Hi folks,
>>>>> I've posted a few more things to the wiki in relation to our
>>>>> discussion Friday about the issues I'm having with energy loss and
>>>>> the
>>>>> mass of the neutron being too low:
>>>>>
>>>>> http://clasweb.jlab.org/rungroups/g12/wiki/index.php/Charged_3pi_event_selection#Neutron_Mass
>>>>>
>>>>>
>>>>>
>>>>> Specifically, Mike Paolone and I each did our own eloss
>>>>> corrections to
>>>>> a
>>>>> common set of events and I find our corrections to be identical. In
>>>>> addition, I've examined a sample of p pi+ pi- events and when I
>>>>> reconstruct the proton via missing mass off the pi+pi-, I see a
>>>>> similar
>>>>> underestimation of the mass of the proton.
>>>>>
>>>>> Feel free to ponder this til Friday, or respond now via the list
>>>>> if you
>>>>> so desire. Any ideas are welcome.
>>>>>
>>>>> --cb
>>>>>
>>>>>
>>>>> --
>>>>> -------------------------------------------------------------------------
>>>>>
>>>>>
>>>>> Craig Bookwalter FSU Office: (850) 644 3808
>>>>> Department of Physics JLab Office: (757) 269 5465
>>>>> Florida State University craigb at hadron.physics.fsu.edu
>>>>> Tallahasse, FL 32306 craigb at jlab.org
>>>>>
>>>>> "Tower, this is Ghostrider requesting a flyby."
>>>>> -------------------------------------------------------------------------
>>>>>
>>>>>
>>>>>
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>>>> / ___ ___ Lei Guo _______________________
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>>>> \ | Physics Dept., CP 212
>>>> / /
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>>>>
>>>
>>>
>>> --
>>> -------------------------------------------------------------------------
>>>
>>> Craig Bookwalter FSU Office: (850) 644 3808
>>> Department of Physics JLab Office: (757) 269 5465
>>> Florida State University craigb at hadron.physics.fsu.edu
>>> Tallahasse, FL 32306 craigb at jlab.org
>>>
>>> "Tower, this is Ghostrider requesting a flyby."
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>
> **************************************
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> / *
> / ___ ___ Lei Guo _______________________
> L_O_/ ____ Florida International University____/_/
> \ | Physics Dept., CP 212
> / /
> / \ | Miami, FL 33199
> / / /
> / I_/ \ ____ USA _____ /______/__________/ /
> / / L / /
> / / /
> / / / /
> / / /
> /_/__________/______/______/__________/_/
> /_/__________/______/______/__________/_/
> 305-348-0234(o)
>
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>
--
-------------------------------------------------------------------------
Craig Bookwalter FSU Office: (850) 644 3808
Department of Physics JLab Office: (757) 269 5465
Florida State University craigb at hadron.physics.fsu.edu
Tallahasse, FL 32306 craigb at jlab.org
"Tower, this is Ghostrider requesting a flyby."
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