Collider overview and kinematicsweb.mit.edu/8.712/www/Lecture/lecture1.pdfParticle identification 12...

Bernd Surrow

8.712 - Advanced Topics in Nuclear PhysicsCambridge, MA, September 15, 2010 Bernd Surrow

Collider overview and kinematics

Bernd Surrow8.712 - Advanced Topics in Nuclear PhysicsCambridge, MA, September 15, 2010

QCD studies at colliders

PEP,PETRA,Cornell,LEP,SLD,NLC

SLAC,FNAL,CERN,HERA,eRHIC

FNAL,CERN,Tevatron,RHIC,RHICII,LHC

Short Long

distance

Q: large momentum scale

ee - ep - pp QCD collider studies

e+e- QCD collider programExperimental QCD tests in e+e-

Measurement of αs

Fragmentation functions

Color/spin dynamics

Quark-Gluon jet properties

Event shape variables (Sphericity, thrust, …)

LEP at CERN, Geneva

LEP: Centre-of-mass energy (e+e-) up to 205GeV

Circumference: 27km

e+e- QCD collider program4

LEP at CERN, GenevaLuminosity

10 weeks

e+e- QCD collider program

e+e- collisions: Here OPAL at LEP

e+e- QCD collider program

Experimental QCD tests in ep

Measurement of αs

Extraction of parton distribution

functions

Color/spin dynamics

Event shape variables (Sphericity,

thrust, …)

Diffraction

ep QCD collider program

ep kinematics (1)

Four vectors:

Neutral current exchange (NC):

Charged current exchange (CC):

Measurement of structure functions:

• NC: Scattered electron and/or hadronic final state

• CC: Hadronic final state (neutrino escapes detection)

Determine kinematics!

Kinematic variables

fraction of the proton momentum carried by the charged parton

fraction of the electronenergy carried by the virtual photon(ʺ″inelasticityʺ″)

(mass)2 of γ* p system

center of mass energyof ep system

(momentum transfer)2

virtuality of γ*, Z0, W±

⇒ (ʺ″sizeʺ″ of the probe)-1

Ee = 27.5 GeV Ep = 920 GeV

Equivalent to fixed target of Ee = 50600 GeV:

Collider experiment: Electron-Proton collisions at HERA (DESY, Hamburg, Germany)

Circumference: 6.3km

Collider experiment: Electron-Proton collisions at HERA (DESY, Hamburg, Germany)

Luminosity:

10 weeks

ep collisions: Here ZEUS at HERA

Onion-shell structure of various detector systems around the collision point:

Energy measurementMomentum measurementParticle identification

2. Determination of cross-section and extraction of F2:

Efficiency Luminosity

Number of selected

events Background

bin inx and Q2

1. Determination of kinematics (e.g. electron method):

Structure function measurement: Kinematic coverage and measurement

Electron method: scattered electron

Jacquet-Blondel method: hadronic final state

Reconstruction of event kinematics

Electron method: scattered electron

Jacquet-Blondel method: hadronic final state

Resolution of event kinematics

Reconstruction of F2

Correct for FL to get F2!Requires unfolding!

Lines of constant electron energy (E’e)

Lines of constant electron angle (ϑ’e)

Lines of constant hadron energy (F)

Lines of constant hadron angle (γ)

Event kinematics (10GeV electron on 250GeV proton)

• Low-x-low Q2: Electron and current jet (low energy) predominantly in rear direction

• High-x-low Q2: Electron in rear and current jet (High energy) in forward direction

• High-x-high Q2: Electron predominantly in barrel/forward direction (High energy) and current jet in forward direction (High energy)

barrel

forward rear

Event topology (10GeV electron on 250GeV proton)

Experimental QCD tests in pp

Measurement of αs

Extraction of parton

distributionfunctions

Color/spin dynamics

Event shape variables (Sphericity,

thrust, …)

Diffraction

pp QCD collider program

pp kinematics (1)

Two incoming hadron beams:

Spectrum of longitudinal momenta determined by parton distribution functions

Centre-of-mass of parton-parton system is boosted with respect to two incoming hadrons, i.e. x1 ≠ x2

Therefore: Classify final state using variables that transform simply under longitudinal boosts:

Rapidity: y

Transverse momentum: pT

Azimuthal angle: φ

Four-vector formulation:

pp kinematics (2)

Property of rapidity:Additive under the restricted class of Lorentz transformations corresponding to a boost along the z direction.

Therefore: Rapidity differences (Δy) are boost invariant!

Pseudorapidity: y for m → 0

Transverse energy: Measured quantity in a calorimeter system, rather than pT!

Jet definition: Cone jet finder

Concentration of transverse energy ET in a cone of radius R:

Invariant under longitudinal boost!

In the two-dimensional plane, curves of constant R are circles around the jet axis!

pp kinematics (3)

Partonic centre-of-mass energy:

Bjorken x1 and x2 and rapidity y:

Partonic centre-of-mass angle!

LHC at CERN, Geneva (1)

LHC: Centre-of-mass energy (pp): 14000GeV = 14TeV

Circumference: 27km

LHC: Centre-of-mass energy (pp): 14000GeV = 14TeV

Circumference: 27km

Luminosity

ICHEP2010 status

World’s Highest Energy proton-anti-proton collider - Tevatron (1)

Centre-of-Mass Energy: Ecm=1.96 TeV

Circumference: 6.85km

Tevatron p

p CDF DØ

World’s Highest Energy proton-anti-proton collider - Tevatron (2)

CME: √s = 1.96 TeV (Run I 1.8 TeV)

Peak luminosity is now ~ 1032 cm-2 s-1

Summary29

Collider comparison

Summary30

Collider overview

Particle data group:

http://pdg.lbl.gov/2010/reviews/rpp2010-rev-hep-collider-params.pdf

M. Tigner, Physics Today, January 2001

Collider overview and kinematicsweb.mit.edu/8.712/www/Lecture/lecture1.pdfParticle identification 12...

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