Contact Persons: Valeria Tano, Joey Huston, Anwar Bhatti , Eve Kovacs
Date Blessed: January 21, 2000
The analysis is described in internal CDF note
5214
See also the discussion in the Les Houches proceedings,
hep-ph/0005114.
In order to determine more accurately the energy contribution in a jet cone
due to the underlying event, we study the energy distributions in cones of radius 0.7,
both in jet events and in minimum bias events. This analysis probes the overlap region
between perturbative and non-perturbative physics.
We compare the results from CDF data
from Run 1b, where the average instantaneous luminosity was about 9 x
1030 cm-2 s-1, with results from Herwig passed through the CDF detector
simulation program QFL.
In jet events, the Jet_20, Jet_50, Jet_70 and Jet_100 trigger data sets are used with EtLeadJet>40, 75, 100, 130 GeV respectively, with the lead jet required to be in the central rapidity region (|eta|<0.7). We generate events with Herwig with ptmin=20,40,60,80 GeV and require EtLeadJet>40, 75, 100, 130 GeV respectively. For each jet event, we examine the transverse energy in two cones of radius 0.7 at +/- 90 degrees in phi and at same eta with respect to the leading jet. The cones are classified according to their relative energies (max/min). In data jet events, one and only one class 10 or 11 or 12 vertex is required in order to reduce any backgrounds from minimum bias pileup. (In general, the higher the vertex quality, the larger the number of tracks composing that vertex).
Plot 1 The transverse energy inside the maximum and minimum cones at 90 degrees in phi and at the same eta as the leading jet, as a function of the leading jet Et. The jet events from the 4 different jet samples are compared to the CDF run 1b data and to the Herwig+QFL simulation. The tower threshold used is 50 MeV.
Plot 2 The level found in a random cone of radius 0.7 in the central region (|eta|<.7) in minimum bias data is compared to the energy levels found in the maximum and minimum cones, in jet events as a function of leading jet Et. One and only one class 12 vertex has been required in the minimum bias data. This requirement selects active minimum bias events. If class 10 or 11 vertices are allowed, the energy in the cone decreases by about 200 MeV.
Plot 3 The transverse energy in the minimum cone is subtracted from the transverse energy in the maximum cone in jet events in both data and Herwig+QFL. For these comparisons, the underlying event contribution should presumably be removed. The difference is plotted as a function of the Et of the leading jet.
Plot 4 The transverse energy inside the maximum and minimum cones at 90 degrees in phi and at the same eta as the leading jet, as a function of the leading jet Et. The jet events from the 4 different jet samples are compared to the CDF run 1b data and to the Herwig+QFL simulation. The tower threshold used is 100 MeV.
Plot 5 The frequency distribution of the transverse energy in the maximum cone, both in Herwig+QFL and in jet data. The number of entries in Herwig is rescaled for a better comparison with data. The tower threshold used is 50 MeV.
Plot 6 The frequency distribution of the transverse energy in the minimum cone both in Herwig+QFL and in jet data. The number of entries in Herwig is rescaled for a better comparison with data. The tower threshold used is 50 MeV.
Plot 7 The frequency distribution of the transverse energy difference between the maximum and the minimum cone, both in Herwig+QFL and in jet data. The number of entries in Herwig is rescaled for a better comparison with data. The tower threshold used is 50 MeV.
Plot 8 Swiss cheese plot. The transverse energy in the two/three most energetic jets in the central region (|eta|<1) is subtracted from the transverse energy in the entire central region (|eta|<1.0). This difference is plotted as a function of the leading jet Et. When the two leading jets are subtracted the transverse energy increases by about 12 GeV in the jet range from 20-200 GeV, while the distribution with three jets subtracted stays flatter ( with an increment of about 4 GeV). The tower threshold used is 50 MeV.
Plot 9 The transverse energy level in the whole central calorimeter region (|eta|<1) in minimum bias events is shown on the Swiss Cheese plot. The offset between the level found when three jets are subtracted in jet events and the minimum bias level varies by about 6-8 GeV over the leading jet Et range. The tower threshold used is 50 MeV. One and only one class 12 vertex is required in the minimum bias events.