Analysis Tools
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Description and Usage
This page contains a glossary of cuts used in the d2n analysis for both the LHRS and BigBite detectors. By utilizing these cuts, one may reproduce our analysis of the data. The processed data files---ROOT files--- are located on the d2n machine (at JLab) in the following locations:
- LHRS data: /data1/flay/ROOTfiles/20110404/SkimROOTfiles/Skim1/
- LHRS file names: e06014_det_L_skim1_run.root (e06014_det_L_skim1_run_i.root),
where run = run number. The file name in parentheses is that for which a run has multiple files (for i=1,...,n).
LHRS
The list of cuts below are presented in the form in which they are used in ROOT macros when carrying out calculations. These variable names are compatible with the Hall A Analyzer.
The acceptance cuts on the target variables have not been included below as they are currently being studied.
Electron Cuts
| Cut | Description |
|---|---|
| (DL.edtpl==0)&&((DL.evtypebits&(1<<3))==(1<<3)) | Taken as a whole, this is the good electron trigger (T3) cut. The first component of the cut removes the dead-time pulse trigger. The latter requires that a good trigger from the LHRS was generated (that is, a coincidence between the S1 and S2m scintillating planes). The efficiency of the T3 trigger is discussed here. NOTE: Be careful concerning the use of the parentheses! |
| L.tr.n==1 | The one-track event cut. We choose only those particles for which the VDCs have assigned one good track to. The efficiency of this cut is discussed here. |
| L.vdc.i.nclust==1 | The VDC one-cluster reconstruction cut. This is to be applied for i VDC planes, where i = u1, u2, v1 and v2 (lowercase letters are to be used in the code). This ensures that one cluster has fired in each of the VDC planes when a track for a particle is reconstructed by the VDC software. See the previously mentioned technical note for the VDCs for more information. |
| L.cer.asum_c>400 | The gas Cherenkov ADC cut. The gas Cherenkov was calibrated so that the one photoelectron peak is centered at 200 ADC channels. PID cut efficiency studies show that the optimal cut position is at 400 ADC channels (2 photoelectrons). This is due to the fact that pions will primarily show up in the one photoelectron peak, while good electrons will yield roughly 6--7 photoelectrons in the gas Cherenkov ADC spectum. |
| abs(L.cer.t[i]-mean)<lim | The gas Cherenkov TDC cut. This cut is to accompany the above ADC cut. Note that this is a sum over i PMTs from 0 to 9. 'mean' is the mean TDC peak position, while 'lim' is the cut window (in TDC channels). It is best to determine each of the i PMT mean peak positions for each run. |
| (prl_E_P>0.54)&&(L.prl1.e>200) | The pion rejector E/p and first pion rejector layer cut. This cut removes pions from our sample. The first cut is on the pion rejector's E/p distribution, while the second requires that the energy deposited by the particle in the first pion rejector layer is greater than 200 MeV. Pions typically deposit less than 200 MeV in this pion rejector layer, so this cut is further reinforcement of the E/p cut. The cut efficiency study relating to the pion rejector may be found in the previously mentioned technical note for PID studies. |
| L.tr.beta>-0.15 | The beta distribution cut. The particle's speed is determined from its corresponding TDC distribution in the S1 and S2m scintillating planes. This distribution is typically centered on 1 for good particles (e.g. not cosmics). In this way, we ensure the removal of cosmic particles, which typically have a beta distribution centered on -1, indicating that they travel backwards through our detectors. The choice of -0.15 is due to the way the software handles multihit events in the various PMTs of the scintillators. It turns out that these events that show up as a large spike at -0.15 in the beta distribution are in fact good events. (Technical note forthcoming.) |
| (ExTgtCor_L.p>0)&&(ExTgtCor_L.p<10) | Reasonable reconstructed momentum cut. There are instances when the software will fail to reconstruct a track for a particle, in which case the momentum of the particle is set to a very large, unrealistic value. Such events are not desirable and are removed. The units of this variable is GeV, so we require the modest range of 0 to 10 GeV in momentum for a reconstructed track. We use this variable for the momentum, since it incorporates corrections to the reconstructed momentum and out-of-plane angle that are due to a finite x-position of the reaction point at the target. See the THaExtTarCor.C source code of the Hall A Analyzer for further details. |
| skim_beam_trip==0 | The beam-trip removal cut. Ideally during data taking, the beam current remains very steady. Sometimes problems may arise where the beam will trip, causing the current to drop to very low values. The data during such trips where the current is changing is not desirable. We have encoded into our ROOT files a variable which removes these bad segments of data. Setting this variable to 0 removes beam trips. Setting it to 1 removes good data, leaving only the tripped data. |
BigBite
4.734 GeV Electron Cuts
Data Quality Cuts
| Cut | Description |
|---|---|
| BB.tr.n > 0 | This cut requires that the MWDC hardware is able to reconstruct a track from a given event. For a given event, there could be more than one track, so all non-zero tracks are considered and only those that satisfy all other cuts are kept. |
| skim.p[]>0 && skim.p[]<10 | A cut is applied to the momentum in order to select a reasonable momentum range. |
Acceptance Cuts
| Cut | Description |
|---|---|
| TMath::Abs(BB.tr.vz[])<0.17 | This is a cut on reconstructed vertex position. This cut is used to select scattered electrons that are incident on the 40cm <math>^3</math>He target. |
| (BB.optics.vzflag[]==1)&&(BB.tr.tg_th[]<0.2) | Two geometrical cuts were used to select electrons from the target that passed through the BigBite magnet. The first cut was developed by Xin Quian during E06-010. It is based on the position where the projected front and back tracks intersect the bend plane which bisects the magnet. If the particle falls on an undesirable location in the bend plane, it is assumed that the particle passed through an undesirable magnet location. This cut is refereed to as the vz-flag cut. The second geometrical cut is a cut on the vertical slope of the front track, (see geometry 2 cut Superelastics section for more info, *note BB.tr.tg_th[] definition was changed to -1*BB.tr.tg_th[] after this talk) was applied to further remove faulty optics reconstruction. |
Particle ID Cuts
| Cut | Description |
|---|---|
| (DBB.evtypebits&(1<<2))==(1<<2) | This cut is used to select T2 events, which is the main electron trigger for the d2n experiment. The T2 trigger is a geometrical over lap between 4 of the the BigBite Cerenkov mirrors and a cluster of Shower+Preshower blocks. See trigger set-up and trigger note for more information. |
| BB.optics.charge[]==(1,-1) | The charge type of each particle can be specified by a charge cut of, +1 for particles bending down in BigBite magnet or -1 for particles bending up in BigBite magnet. When The BigBite magnet is set to negative polarity, this corresponds to charge=1 for positive charge and charge=-1 for negative charge. When the magnet is in positive polarity setting, charge=1 corresponds to negative charge (bend down in magnet) and charge =-1 for positive charge (bend up in magnet). Because the charge selection cut uses the bend direction of the track on the first wire chamber, the higher momentum particles are discarded. This is because at high momentum the particles will not be bent by the magnet. |
