Min-Bias Physics:
Jet Evolution & Event Shapes

Rick Field and David Stuart


Ten plots from our study of min-bias physics
(10 pages: Acrobat PDF file or zipped PS file)


We examine charged particles in the region PT > 0.5 GeV and |eta| < 1 and use a simple charged particle jet definition (with R = 0.7) that works well even when jets consist of only a few charged particles (jet algorithm). We compare the data with the QCD "hard" 2-to-2 parton scattering predicitions of Isajet, Herwig, and Pythia (with PT(hard) > 3 GeV). A "hard scattering" event consists of two outgoing large transverse momentum partons which fragment into "jets".
The underlying event in a "hard" 2-to-2 parton scattering consists of the remnants of the beam and the target hadron plus initial state parton radiation. Pythia includes multiple parton interactions which increases the activity of the underlying event.


Plot 1: Average number of charged particles in the leading (charged) jet versus the transverse momentum of the leading (charged) jet. (1 page: Acrobat PDF file or zipped PS file)
Plot shows the average number of charged particles (PT > 0.5 GeV, |eta| < 1) within the leading jet (R = 0.7) as a function of the PT of the leading jet (charged). The errors on the (uncorrected) data include both statistical and correlated systematic uncertainties. The QCD "hard scattering" theory curves are corrected for the track finding efffiency and have an error (statistical plus systematic) of around 5%.


Plot 2: Average size of the leading charged particle jet versus the transverse momentum of the leading (charged) jet. (1 page: Acrobat PDF file or zipped PS file)
Plot shows the average radius in eta-phi space containing 80% of the charged particles (and 80% of the charged PT) as a function of the PT of the leading (charged) jet . The errors on the (uncorrected) data include both statistical and correlated systematic uncertainties. The QCD "hard scattering" theory curves are corrected for the track finding efffiency and have an error (statistical plus systematic) of around 5%.


Plot 3: Average number of charged particles (PT > 0.5 GeV, |eta| < 1, including jet#1) versus the transverse momentum of the leading (charged) jet. (1 page: Acrobat PDF file or zipped PS file)
Plot shows the average number of charged particles (PT > 0.5 GeV, |eta| < 1, including jet#1) as a function of the PT of the leading jet (charged). The errors on the (uncorrected) data include both statistical and correlated systematic uncertainties.


Plot 4: Average number of "toward", "transverse", and "away" charged particles versus the transverse momentum of the leading (charged) jet. (1 page: Acrobat PDF file or zipped PS file)
Plot shows the average number of "toward", "transverse", and "away" charged particles (PT > 0.5 GeV, |eta| < 1, including jet#1) as a function of the PT of the leading jet (charged). The errors on the (uncorrected) data include both statistical and correlated systematic uncertainties.
Event Shape for PT(charged jet#1) = 20 GeV (PT > 0.5 GeV, |eta| < 1):


Plot 5: Average PTsum of "toward", "transverse", and "away" charged particles versus the transverse momentum of the leading (charged) jet. (1 page: Acrobat PDF file or zipped PS file)
Plot shows the average PTsum of "toward", "transverse", and "away" charged particles (PT > 0.5 GeV, |eta| < 1, including jet#1) as a function of the PT of the leading jet (charged). The errors on the (uncorrected) data include both statistical and correlated systematic uncertainties.
Event Shape for PT(charged jet#1) = 20 GeV (PT > 0.5 GeV, |eta| < 1):


Plot 6: Average number of "toward", "transverse", and "away" charged particles versus the transverse momentum of the leading (charged) jet. (1 page: Acrobat PDF file or zipped PS file)
Plot shows the average number of "toward", "transverse", and "away" charged particles (PT > 0.5 GeV, |eta| < 1, including jet#1) as a function of the PT of the leading jet (charged). The errors on the (uncorrected) data include both statistical and correlated systematic uncertainties. The QCD "hard scattering" theory curves (Herwig 5.9, Isajet 7.32, Pythia 6.115) are corrected for the track finding efficiency and have an error (statistical plus systematic) of around 5%.


Plot 7: Average number of "transverse" charged particles versus the transverse momentum of the leading (charged) jet. (1 page: Acrobat PDF file or zipped PS file)
Plot shows the average number of "transverse" charged particles (PT > 0.5 GeV, |eta| < 1) as a function of the PT of the leading jet (charged). The errors on the (uncorrected) data include both statistical and correlated systematic uncertainties. The QCD "hard scattering" theory curves (Herwig 5.9, Isajet 7.32, Pythia 6.115) are corrected for the track finding efficiency and have an error (statistical plus systematic) of around 5%.


Plot 8: Average PTsum of "transverse" charged particles versus the transverse momentum of the leading (charged) jet. (1 page: Acrobat PDF file or zipped PS file)
Plot shows the average PTsum of "transverse" charged particles (PT > 0.5 GeV, |eta| < 1) as a function of the PT of the leading jet (charged). The errors on the (uncorrected) data include both statistical and correlated systematic uncertainties. The QCD "hard scattering" theory curves (Herwig 5.9, Isajet 7.32, Pythia 6.115) are corrected for the track finding efficiency and have an error (statistical plus systematic) of around 5%.



Plot 9: Average number of "transverse" charged particles versus the transverse momentum of the leading (charged) jet. (1 page: Acrobat PDF file or zipped PS file)
Plot shows the average number of "transverse" charged particles (PT > 0.5 GeV, |eta| < 1) as a function of the PT of the leading jet (charged). The errors on the (uncorrected) data include both statistical and correlated systematic uncertainties. The QCD "hard scattering" theory curves (Pythia 6.115, Pythia 6.125, Pythia with no multiple parton scattering) are corrected for the track finding efficiency and have an error (statistical plus systematic) of around 5%.


Plot 10: Average PTsum of "transverse" charged particles versus the transverse momentum of the leading (charged) jet. (1 page: Acrobat PDF file or zipped PS file)
Plot shows the average PTsum of "transverse" charged particles (PT > 0.5 GeV, |eta| < 1) as a function of the PT of the leading jet (charged). The errors on the (uncorrected) data include both statistical and correlated systematic uncertainties. The QCD "hard scattering" theory curves (Pythia 6.115, Pythia 6.125, Pythia with no multiple parton scattering) are corrected for the track finding efficiency and have an error (statistical plus systematic) of around 5%.


Send comments, suggestions, etc. to rfield@phys.ufl.edu
Rick Field
Last modified: November 2, 1999