1. Trijets in Neutral Current Deep Inelastic Scattering
A Proposal for Studies
Using the Data
Liang Li
University of Wisconsin
HERA, ZEUS data(intended 96-00, current 96-97)
100GeV<Q2<10000GeV
e+ energy 27.5GeV
p energy 920Gev
Introduction:
SM QCD Various Methods to Determine αs
DIS Structure Function PDF
Feynman Diagrams (1,2,3 jets)
The ratio of the three-jet to the dijet cross section R3/2 and αs
Jet Algorithms Breit Frame Lab Frame
MC Models NLO
Experimental Context

2. 96-97 Data Offline Cuts: Start from Dijets Cuts
• Detector Acceptance and Efficiency yJB > positron found with E > 10 GeV vertex cut: -50cm < z < 50 cm positron position cut: |X| > 14 cm or |Y| > 14 cm
• Signal Selection
38 GeV < E-Pz < 65 GeV A well found track with p > 5 GeV & DCA < 15 cm yEL < 0.95
Give reasons here:
• Physics and Kinematic Requirement GeV2 < Q2 < GeV Three jets found using KTCLUS algorithm
|| < 2.0
ETLAB > 5 GeV
New requirement added to Dijets
ET,1BRT > 8 GeV, ET,2BRT > 5 GeV , ET,3BRT > 5 GeV

3. First Look at DIS Trijets (DA)
ReconstructedQ2, x, y by
Double Angle method Q2 x
Use LO Ariadne
for all MC
OK agreement
between data and Ariadne y
Area normalized

4. First Look at ZEUS DIS Trijets
Conclusions
First glance at DIS Trijets at ZEUS shows reasonable agreement between data & Ariadne
LO Ariadne MC used from Dijet Analysis without changes -> a good starting point
Plans
Calculate cross sections and compare in detail with other QCD calculations and different MC programs (LO & NLO)
Add data for more statistics
Explore systematic uncertainties
Hadron and Parton Level Comparison?