LHC Olympics

http://wwwth.cern.ch/lhcOlympics/lhcolympicsII.html

Yeong Gyun Kim

LHC (the Large Hadron Collider) : 2007 ~

a proton + proton collider at 14 TeV c.m energy in the 26.6 km tunnel

1033 cm-2 s-1 ~ 10 fb-1/yr (low luminosity)1034 cm-2 s-1 ~ 100 fb-1/yr (high luminosity)

Modern multi-purpose detector at colliders

ATLAS

CMS(The Compact Muon Solenoid)4 Tesla B-field

(A Toroidal LHC Apparatus)

2 Tesla B-field

Total weight : 12500 tonsOverall diameter : 15 mOverall length : 21 m

Diameter : 25 mOverall length : 46 mOverall weight : 7000 tons

Particle signatures left in the detector components

Photons (0)A photon is detected as energy in the ECAL, with no high-transverse-momentum track, and little energy in the HCAL

Electrons (1)An electron is detected as energy in the ECAL, with a high-transverse-momentum track pointing toward it, and little energy in the HCAL

Muons (2) A muon leaves little energy in the calorimers, has a track, and travels all the way to the muon-detector system outside the calorimeters.

Hadronically-Decaying Taus (3)The most common hadronic decays of the tau are to a neutrino plus------• A charged pion• One charged pion and one or two pi-zeros

“1-prong” tau : A single charged track that leaves energy in HCAL Any hadronic or EM energy is clustered in a very narrow cone surrounding the charged track------• Two pions of one charge and a third of the opposite charge

“3-prong” tau : A very narrow jet, with invariant mass no greater than 2 GeV, and with 3 tracks.

Jets (4)Jets are defined to be groups of particles (tracks and energy bumps in calorimeters) that fit inside a cone in azimuth and pseudo-rapidity space.(cone algorithm) The properties of these jets are expected to correspondclosely to the kinematics of the partons in hard process.

Cone size of a jet

Transverse energy

(dR ~0.7 : a common choice)

(η= ln [cot(θ/2)] : pseudo-rapidity)

ET = pT = E sin θ = E (cosh η)-1

Missing Transverse Energy (6)

Missing Et is defined by summing (as a vector) the transverse energy deposited in all of the calorimeter cells(this combines, ideally, the momenta of all photons, electrons,hadronically-decaying taus, and jets) and adding to this the transverse momenta of any muons, whose energy is measured using the muon detection system.

The magnitude of the resultant vector is the missing ET.

One of the most important signatures of SUSY with R-parity conservation is large “missing transverse energy”.

Heavy flavor tagging (b-tagging)

Particles of a life-time τ ~ 10-12 s, such as B0,+, D0,+ maytravel a distinguishable distance (cτ ~ 100 μm) beforedecaying into charged tracks, and thus result in a displacedsecondary vertex and a nonzero impact parameter

The observation, within a jet, of a displaced vertex, tracks with nonzero impact parameter,and/or a single muon all give evidence thata heavy quark was somewhere in the jet.

The decays also can producemuons which are close to the jet.

Raw Data

Physics Analysis

Collider(LHC)

Event generator:

(1) Feyman diagrams Production process(CompHEP, Pythia, Hewig, MadGraph etc.)

(2) quarks and gluons jets of hadrons, Decay of short-lived particles

(Phythia, Herwig)Detectors(ATLAS, CMS)

Detector Simulation(GEANT4)

Reconstruction Program(leptons, photons, jets,missing Et)

MC raw data

Flow chart for Physics analysis

The LHC Olympics

New Physics (???) event generator+

Pythia 6.234 (hadronization, decays etc.)

PGS (Pretty Good Simulation)

[Detector Simulation + Reconstruction]

Black box“classics”

with 20 fb-1

Black box“uw1”

with 25 fb-1

Black box“harvardbb”

with 5 & 40 fb-1

t tbar sample

diboson sample(WW,WZ,ZZ)

GOAL : Figure out what is in each black box !!

An example of a top-antitop pair prodcution event

1 2 -1.419 2.873 24.94 1.00 0.0 0.0 2 4 -0.804 2.307 130.99 16.14 10.0 1.0 3 4 1.046 4.245 82.75 14.11 2.0 0.0 4 4 1.247 5.996 78.72 13.75 14.0 1.0 5 4 -2.154 3.884 13.85 5.83 3.0 0.0 6 6 0.000 6.245 92.14 0.00 0.0 0.0

The 2nd column : Type of object

[0=photon, 1=electron, 2=muon, 3=hadronically-decaying tau, 4=jet, 6=missing transverse energy]

The next three columns : pseudorapidity, the azimuthal angle, tranverse mom.

The next column : the invariant mass for a jet, its charge for not a jet. The next column : some additional information about the object

The final column : 1 for a “heavy quark” jet

2 b-jets, 2 jets, an isolated muon and missing ET

t tbar

b W+

μ+ ν

bbar W-

q q’

2 b-jets, 2 jets, an isolated muon and missing ET

A Quick Look at diboson sample and black box datawith OS-dilepton invariant mass distribution

KAIST LHCO team : W.Cho, YGK, C.Park and S.Shin

Di-lepton invariant mass (GeV)

Diboson (ZZ,WZ,WW) sample

UW1 black box data

Di-electron invariant mass (GeV)

Di-muon invariant mass (GeV)

A LHC SUGRA Point with χ2 -> χ1 l+ l- decay

Harvard black box data

Black box“classics”

with 20 fb-1

Black box“uw1”

with 25 fb-1

Black box“harvardbb”

with 5 & 40 fb-1

Princeton TeamJohns Hopkins Team Harvard Team

Harvard Team

Washington TeamCornell Team

Revealing of the Washington Black Box (M. Strassler)

Next LHC Olympics

August(?) 2006 at CERN (?)

Backup

Neutralino mass matrix

In the basis

0 0 01 2( , , , )B W H H

1

2

0 cos sin sin sin

0 cos cos sin cos

cos sin cos cos 0

sin sin sin cos 0

Z W Z W

Z W Z W

Z W Z W

Z W Z W

M M M

M M M

M M

M M

θ θ θ θ

θ θ μ θ θ μ

1 2,M M : Bino, Wino mass parameters

μ : Higgsino mass parameter

tan

0 0 0 01 2 3 1 4 2i i i i iN B N W N H N H

: ratio of vev of the two neutral Higgs

Lightest Neutralino = LSP in many cases (WIMP !! )