I made the following plots for each sector for all time-based
tracks (no cuts on anything) for Eg1b run 27499 (5.6 GeV inbending):
The plots are located in Hall-B/secure/eg1/EG2000/Bosted/wiggle
file name quantity
sec5all thdc - th vrsus thdc
sec5allb vertex z vrsus thdc
sec5allc thdc (trl1_theta)
sec5alld th (defined as acos(p_z/p) at vertex
I made the same plots for all tracks but with the requirement
that trigger bits 7 or 8 fired (i.e. no Cherenkov in the trigger)
As before, no PID cuts of any kin were applied to the tracks.
file name quantity
sec5 thdc - th vrsus thdc
sec5b vertex z vrsus thdc
sec5c thdc (trl1_theta)
sec5d th (defined as acos(p_z/p) at vertex
My conclusions:
a) using events with no Cherenkov in the trigger seems to make
no difference that I can see
b) For this run, and all other ones I looked at, sector 5
seems to have a probelm near 20 deg.: thdc is smooth, while
th is not, and average vertex z is clearly shifted. Presumably,
this is something wrong in the mapping of the hit positions
on the wire chamber cards. My guess is that it is region 3
or maybe region 2, otherwise we would see a wiggle in the
thdc distribution. One can also clearly see an offset between
th and thdc in this region, so presumably momentum comes
out wrong as well. So it seems sounds to remove events with
17.5<th<22.5 deg for sector 5, as we all agreed to do.
c) Sector 3 shows wiggles in the rates for th<20 deg. They
are low compared to other sectors. For another run (27323),
the rates are close to zero in this region. So my guess is
that there were some bad readout cards in this region, leading
to large and time-varying inefficinecy. Since v_z and
th-thdc look normal, it is probably not a wire-mapping
problem (as in sector 5), but just bad cards. It could also
be due to gain variations in the EC (since EC is required for
all triggers), but this seems unlikely to give such a sharp
structures
d) at large angles, one can notice a consierable difference
between sector 6 and other sectors (more events). Note the
10% or so jump up in rate near 34 deg. My guess is that this
is due to gain variation in the EC. It is seen both both
the all trigger and trigger 7,8 plots.
Prof. Peter Bosted
email: bosted@jlab.org
phone: (757) 269-5851
address: Jefferson Lab Suite 6, 12000 Jefferson Ave, Newport News VA 23606
On Fri, 7 Mar 2008, Marco Ripani wrote:
> Hi Peter,
> even though the trigger is different, RECSIS is still looking for the
> Cherenkov signal when trying to define a good electron candidate. You
> should remove this requirement from within RECSIS and apply only
> calorimeter cuts in your analysis to be sure that the Cherenkov has
> nothing to do with it. Raffaella could you please remind us what routine
> one has to modify to remove the Cherenkov cuts in PID ? Raffaella is now
> at JLab, perhaps there is a chance to talk with her.
>
> Regards
> Marco
>
> Peter Bosted wrote:
> > Hi all,
> > The *Big* wiggle problem in Eg1b (ie sector 5, 17.5<th<22.5 deg)
> > does not go away when I re-made the plots using events with
> > trigger bits 7 or 8 only (i.e. no Cherenkov in the trigger, only
> > E/P for PID cut). This seems to be something in the DC itself:
> > it shows up clearly as a several cm shift in reconstructed z,
> > and also in trl1_theta vrsus vertex theta.
> > For ruh 27323 (2 gev inbending), there also seems to be a
> > dead region in sector 3 for theta<20 deg. This dead region is
> > still there without the Cherenkov in the trigger or event selection.
> > This doesn't affect the asymmetry analysis, because these
> > events seem to just be gone, rather than shifted the wrong
> > kinematics.
> > For this run, I don't see any other *Big* DC problems:
> > certainly there can be some more suble effects that are hard
> > to see.
> > Yours, Peter
> >
> > Prof. Peter Bosted
> > email: bosted@jlab.org
> > phone: (757) 269-5851
> > address: Jefferson Lab Suite 6, 12000 Jefferson Ave, Newport News VA 23606
> >
> > On Fri, 29 Feb 2008, burkert wrote:
> >
> >
> >> Hi all, we should be careful when discussing the "wiggle problem". There
> >> are potentially a number of sources for "theta wiggles" and they depend
> >> on the specific configuration, e.g. inbending vs outbending electrons.
> >> (If you do see wiggles for non-electron tracks ignore the following, as
> >> such effects are more likely related to DC tracking aspects.)
> >>
> >> A 2 degree wiggle pattern seen for electrons can be the result of
> >> inefficiencies of the Cerenkov counter due to the mirror system. Since
> >> we have 18 mirrors covering about 9 - 45 degrees in geometrical angles,
> >> i.e. 36 degrees in Delta(theta) you do expect something like a 2deg.
> >> oscillation pattern just from the geometry of the mirror system if
> >> inefficient regions, such as fringes have not been eliminated carefully.
> >> This is particularly important for or out-bending electrons. I order to
> >> study the problem in for electrons in detail I suggest to make the
> >> following selections:
> >>
> >> 1) Look at in-bending electrons: Make narrow fiducial cuts that make
> >> absolutely sure that you avoid the fringe regions of the Cerenkov
> >> counter. Make a cut around the sector mid-plane to eliminate events near
> >> the mid-plane where the efficiency is known to be somewhat lower than in
> >> other regions. Then look for wiggles at fixed momentum.
> >>
> >> 2) Look at outbending electrons in eg1a,b: Here it is hard to avoid
> >> seeing wiggles from Cerenkov counter inefficiencies as the Cerenkov has
> >> been designed biased toward high efficiency for in-bending tracks and as
> >> a result has significant inefficiencies due to the mirror arrangement.
> >> This pattern has been studied by Vipuli in her PhD thesis and fiducial
> >> cuts have been developed to correct for it. This should, of course, not
> >> be the case for eg4 as this Cerenkov detector has specifically be
> >> designed for out-bending electrons, i.e. wiggles in eg4 must have a
> >> different origin.
> >>
> >>
> >> A wiggle pattern that is very different from 2 degree , or is seen for
> >> pions, is likely not related to the Cerenkov counter but more to effects
> >> that Sebastian mentioned earlier.
> >>
> >> Volker
> >>
> >>
> >>
> >>
> >> Sebastian Kuhn wrote:
> >>
> >>> Dear all,
> >>>
> >>> sorry for this "spam" mail, but several people have expressed interest
> >>> in our findings about "theta oscillations", which may be relevant also
> >>> for E4 and E1-DVCS.
> >>>
> >>> Shortly, the problem seems to be that with some CLAS experiments (with
> >>> targets upstream of the regular target position?), there is a clear
> >>> pattern in the angular distribution of scattered electrons (other
> >>> particles remain to be checked), in particular if one selects a tight
> >>> momentum region (e.g., 2.0 GeV/c - 2.2 GeV/c). This pattern can
> >>> (sometimes) be seen in theta-reconstructed as well as theta at the
> >>> first DC superlayer and sometimes even for various projections of y or
> >>> theta on the scintillator or EC plane.
> >>>
> >>> This problem was originally encountered during the analysis of EG1a
> >>> (see my message below for relevant links). Some additional plots can
> >>> be found at
> >>> http://www.jlab.org/Hall-B/secure/eg1/jyun/ecyi.gif
> >>> http://www.jlab.org/Hall-B/secure/eg1/alex/waves/oscillations.html
> >>> http://www.jlab.org/Hall-B/secure/eg1/tforest/Wiggle/Wiggle.html (for
> >>> explanation)
> >>>
> >>> The most recent analysis on EG1b data is from Nevzat Guler - see
> >>> http://www.jlab.org/Hall-B/secure/eg1/EG2000/nevzat/ThetaWigglePage_wfid/thetaWiggle.html
> >>>
> >>> Slava Tkachenko has looked at this for BoNuS - see
> >>> http://www.jlab.org/~slava/Check44/Check44_18/ThetaEL/0227/
> >>>
> >>> It is not clear what exactly is happening, but the most likely
> >>> explanation is that tracks are getting shifted out of the "valleys"
> >>> into the "peaks", leading to wrong theta assignment by about 1-2
> >>> degrees. (It is less likely that the valleys are just inefficiencies).
> >>> This may or may not affect inclusive data, but it might be useful to
> >>> ascertain this for each experiment.
> >>>
> >>> - Sebastian
> >>>
> >>>
> >>> Sebastian Kuhn wrote:
> >>>
> >>>> Dear (former) EG1ers (and especially "oldtimers"),
> >>>>
> >>>> I am trying to remember what our final conclusion was regarding the
> >>>> infamous "wiggle/theta oscillation" problem with EG1a - see
> >>>> http://www.jlab.org/ccc/mail_archives/CLAS/eg1_run/msg00274.html to
> >>>> jog your memory. I went through all my accumulated notes but couldn't
> >>>> find any conclusive solution (and my memory is just not as good as it
> >>>> used to be... ;-)
> >>>> It appears possible that we have a similar problem in EG1b, see
> >>>> http://www.jlab.org/Hall-B/secure/eg1/EG2000/sharon/theta_compare/theta_compare_5_6.gif
> >>>> (and BoNuS, for that matter! ->
> >>>> http://www.jlab.org/~slava/Check44/Check44_18/ThetaEL/thetael_raw_0211_44_1_pre_el5gev.jpg
> >>>> ).
> >>>>
> >>>> Any recollections are welcome - Sebastian
> >>>>
> >>
> >
> >
>
> --
>
> Marco Ripani
> Senior Scientist, Istituto Nazionale di Fisica Nucleare - Genova
> Address:
> INFN
> Via Dodecaneso 33
> 16146 GENOVA - ITALY
> tel./fax 39-010-3536458
> cell. 39-328-2191138
> Jlab office room F332
> tel. 1-757-269-7266 fax 1-757-269-6273
> E-Mail: ripani@ge.infn.it
>
>