Hi Elton,
I hope this answers everyone's questions about the time resolution and
any factors of two. I have told you the formula I have been using
incorrectly. The short note I've attached should clear this up.
-Blake
Elton Smith wrote:
Pine.LNX.4.58.0802130755590.5640@elton01.jlab.org">
Hi Blake,
Thanks for looking into this. But I think the equation for z should not
have the 1/2 for this new definition because of the energy terms:
DeltaT ={t_north*E_north - t_south*E_south}/Sum{E_north+E_south}
At least for the case where E_north - E_south, then
DeltaT = 1/2 (t_north - t_south)
z = veff * (Tleft - Tright)/2 = veff * DeltaT
Or am I still missing a factor?
Thanks, Elton.
Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Suite # 16
Newport News, VA 23606
elton@jlab.org
(757) 269-7625
(757) 269-6331 fax
On Tue, 12 Feb 2008, Blake Leverington wrote:
Hi Elton,
I started rerunning the timing resolution code this morning so hopefully
it should be done tonight. I removed the 1/2 from the previous DeltaT so
that DeltaT now is DeltaT ={t_north*E_north -
t_south*E_south}/Sum{E_north+E_south}, without the factor of 1/2. I'll
see how this affects the resolution but I suspect it will double it as z
was previously assumed to be z = 0.5 *veff *DeltaT so that the z
resolution should be double, from 0.7cm to 1.4cm at 1 GeV. I'll even
redo the mean time resolution tomorrow as I've thought of new things to do.
-Blake
Elton Smith wrote:
HI Blake,
There is still another factor of two. If you simply remove the 1/2 in
the note for E_N=E_S, then DeltaT = 1/2 delta_T and one also needs to
remove the 1/2 in the equation for z.
Now, removing the 1/2 in the note is fine as long as that is what you
actually did to obtain the sigma. And this should be checked. Otherwise,
the measured width is either higher or lower relative the actual value of
delta_T which is what we believe we are measuring. So can you check what
was actually calculated to obtain the width?
Thanks, Elton.
Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Suite # 16
Newport News, VA 23606
elton@jlab.org
(757) 269-7625
(757) 269-6331 fax
On Tue, 12 Feb 2008, Blake Leverington wrote:
Hi Elton,
I was just reviewing my notes, and it seems that if you assume that z =
veff * delta_T / 2 then there should NOT be the factor of 0.5 in
DeltaT. DeltaT should equal delta_T for E_N = E_S. I should remove that
factor of 1/2 in the note.
-Blake
Elton Smith wrote:
Hi Blake,
Yesterday we were going over the correspondence between the expected z
position resolution and the time resolution. We have the following
relation:
z = veff * (Tleft - Tright)/2
delta_z = veff * delta_T/2
for delta_T = Tleft - Tright
We have been assuming that the quoted delta_T (75 ps/sqrt(E) + 30) is
given by the definition above. But the reference for the resolution is
GlueX-doc-804 which you wrote. Refering to eqs 14, you use the following
expression:
DeltaT = 0.5*Sum{t_north*E_north - t_south*E_south}/Sum{E_north+E_south}
At first, it looks like the definition for DeltaT = 0.5*delta_T, removing
the 1/2 from the equation for z. However, on closer inspection, there are
more questions. Taking the simple case where E_north=E_south (center of
calorimeter), then
DeltaT (E_north=E_south) = 0.25 * (t_north - t_south), so it looks like
there is even an additional factor of 2.
Can you help me sort this out?
Thanks, Elton.
Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Suite # 16
Newport News, VA 23606
elton@jlab.org
(757) 269-7625
(757) 269-6331 fax
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