Distributions

1
Distributions

• Veronica Sorin
• Universidad de Buenos Aires
• DØ RunI Meeting,
• August 18, 2000

2
Outline

• Introduction
• Motivation
• Definition
• Goals
• MC and Data samples
• Systematic Errors
• Comparison with JETRAD predictions
• Plans

3
Event Shapes

• Extensively studied at ee- and ep
• experiments
• test QCD
• sensitive to resummations and non-perturbative
  effects
• measurement of as

Non-perturbative effects Power-corrections, of
the order of 1/Q . Related with hadronization
effects. Resummations at small values of the
shape variable (two-jet limit) fixed-order
perturbative calculations are not
reliable. Thats because of the presence of large
logarithms due to the emission of soft and
collinear gluons.
4
Thrust
direction which maximizes T

• The sum is over all particles/towers/jets/subjets
  in the event

T Pencil-likeness of the event
5
T in Hadron Colliders Busy environment
underlying event, pile-up, multiple
interactions
particles jets

• calculate T using only the 2 leading jets ( T2 )

Transverse Thrust
3D 2D
replacing jet momenta by transverse momenta

6

• Measurement of distributions
• Data vs Herwig
• Comparison with LO (JETRAD) and NLO QCD (program
  recently available) predictions.

Well analyze the need of resummations on the LO
and NLO theoretical calculations in the
limit due to the presence of large logarithms
7
MC Samples

• HERWIG Generator
• - parton ??? ? 0.9
• - partonET?30,50,75,110,150 (GeV)
• Detector Simulation (Showerlib)
• Overlayed with zerobias and minimum bias events
• min_bias crossing with inelastic interaction
  (underlying event), low lum
• zero_bias just a crossing (Noise, pileup, extra
  pp ), various lum.

Jet Reconstruction
K T algorithm infrared safe at all orders
D 1
8
DATA Samples

• Run Ib , Triggers Jet_30, Jet_50, Jet_85,
  Jet_Max
• Cuts
• - jet quality cuts
• 0.05 lt EM fraction lt 0.95
• CH fraction lt 0.4
• missing ET lt 0.7
• ET (jet 1)
• - vertex_z ? 50 cm
• - Remove bad runs

• h1,2 lt 1, h3 lt 3
• 4 HT3 bins
• (HT3 scalar sum of the transverse
• momentum of the three leading jets)

9
Triggers Turn On
10
Corrections and Systematic Errors

• Energy Scale
• Misvertexing
• ? bias
• Resolutions

We can estimate the global effect by means of a
study of luminosity dependence.
Integrated luminosity for each subsample from the
PDB. We analyzed cross section ratios of ET1
(leading jet), ET2, ET3 and HT3, requiring the
trigger to be fully efficient. Any luminosity
dependence will affect either the shape or the
normalization , or both.
11
Comparison with JETRAD
JETRAD LO prediction for
Lower limit
NLO prediction
It will improve the prediction at low values of
12
Plans

• We have studied almost all the systematics
• Energy Scale 10-15
• Misvertexing, Vertex Resolution
  small corrections
• Good agreement between Data and Herwig.
• Comparison with Jetrad shows that the variable
  is sensitive to resummations and higher order
  effects
• To Do
• quantitative studies of systematics
• comparison with NNLO QCD prediction
• Goal
• approval for winter or spring
  conferences,
• publication for the summer.

13
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