Run 9 Underlying Event and Hadronization Investigation
Updated on Wed, 2015-05-06 00:53. Originally created by pagebs on 2015-05-05 00:01.
A closer look at the underlying event and hadronization correction to the theoretical cross section ...
After some discussion at a previous jet meeting, I wanted to take a closer look at the size of the underlying event and hadronization correction. Remember that the correction is found by taking the difference of the particle and parton level cross sections. To look in more detail, I have calculated the cross sections using just the SVD unfolding as well as the unfolding and subsequent efficiency correction.
Figure 1: Ratio of the particle-parton cross section difference to the theoretical cross section. The blue points show the ratio for the case where only the SVD unfolding was done (no efficiency correction). The red points show the ratio for the case where the SVD unfolding and the efficiency correction was done.
As can be seen in figure 1, the UEH correction found from the full (unfolding + efficiency) cross section extraction is roughly constant over the invariant mass range. This is not necessarily what one would expect given that the UEH effects should come in at lower pt. To investigate this behavior, I look at the particle and parton levels from the full pythia sample, ie, the sample which is used to calculate the efficiency correction.
The plots below show the individual jet pt, rapidity, and mass before and after dijet cuts were applied. The plots include the two highest pt jets in the event and the cuts are the opening angle condition, the asymmetric pt condition, and the jet eta cuts.
Figure 2: Comparison of the particle (blue) and parton (red) level jet transverse momenta. The left column shows the spectra before any cuts are applied and the right column shows the spectra after the dijet cuts are applied.
Figure 3: Same as figure 2, but for jet rapidity.
Figure 4: Same as figure 2, but for jet mass.
Figure 5: Scatter plot of the jet mass vs jet pt. The left column is before cuts and the right column is after cuts. The top row is for the particle level and the bottom row is for the parton level.
As can be seen, there is a large discrepency between the particle and parton level jet masses. The parton level jet mass spectrum has some odd features which I cannot yet explain. To see if the jet mass is the cause of the particle/parton level dijet mass discrepency, I plotted the dijet mass spectra in which I disregard the individual jet masses.
Figure 6: Comparison of the particle (blue) and parton (red) dijet mass spectra. The left column shows the comparison for the full dijet mass expression and the right column shows the comparison for the dijet mass expression where the jet mass is ignored.
The particle / parton level dijet mass spectra which were calculated using the massless approximation are consistent above ~19 GeV, whereas the spectra calculated using the full expression are offset by a roughly constant factor of ~20-30%.
After some discussion at a previous jet meeting, I wanted to take a closer look at the size of the underlying event and hadronization correction. Remember that the correction is found by taking the difference of the particle and parton level cross sections. To look in more detail, I have calculated the cross sections using just the SVD unfolding as well as the unfolding and subsequent efficiency correction.
Figure 1: Ratio of the particle-parton cross section difference to the theoretical cross section. The blue points show the ratio for the case where only the SVD unfolding was done (no efficiency correction). The red points show the ratio for the case where the SVD unfolding and the efficiency correction was done.
As can be seen in figure 1, the UEH correction found from the full (unfolding + efficiency) cross section extraction is roughly constant over the invariant mass range. This is not necessarily what one would expect given that the UEH effects should come in at lower pt. To investigate this behavior, I look at the particle and parton levels from the full pythia sample, ie, the sample which is used to calculate the efficiency correction.
The plots below show the individual jet pt, rapidity, and mass before and after dijet cuts were applied. The plots include the two highest pt jets in the event and the cuts are the opening angle condition, the asymmetric pt condition, and the jet eta cuts.
Figure 2: Comparison of the particle (blue) and parton (red) level jet transverse momenta. The left column shows the spectra before any cuts are applied and the right column shows the spectra after the dijet cuts are applied.
Figure 3: Same as figure 2, but for jet rapidity.
Figure 4: Same as figure 2, but for jet mass.
Figure 5: Scatter plot of the jet mass vs jet pt. The left column is before cuts and the right column is after cuts. The top row is for the particle level and the bottom row is for the parton level.
As can be seen, there is a large discrepency between the particle and parton level jet masses. The parton level jet mass spectrum has some odd features which I cannot yet explain. To see if the jet mass is the cause of the particle/parton level dijet mass discrepency, I plotted the dijet mass spectra in which I disregard the individual jet masses.
Figure 6: Comparison of the particle (blue) and parton (red) dijet mass spectra. The left column shows the comparison for the full dijet mass expression and the right column shows the comparison for the dijet mass expression where the jet mass is ignored.
The particle / parton level dijet mass spectra which were calculated using the massless approximation are consistent above ~19 GeV, whereas the spectra calculated using the full expression are offset by a roughly constant factor of ~20-30%.
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