New Particle Searches at LHC

김 귀 년 (CHEP, 경북대학교 )

2006. 6. 16-17.

What is the Particle Physics?

• the fundamental particles that make up all of matter• how they interact with each other.

What is the Standard Model ?

Why a hadron collider ?

New Particle Searches at LHC

• Particle Physicists study the fundamental particles that make up all of matter, and how they interact with each other.

What is the Particle Physics?

• Particle physicsParticle physics is the study ofis the study of what everything what everything is made of.is made of.

• Everything around us is made up of these fundamental building blocks of nature.

So, what are these building blocks?

Which particles were considered fundamental building blocks throughout History?

• Particle Physicists study the fundamental particles that make up all of matter, and how they interact with each other.

In the early 1900's it was believed that atoms were fundamental; they were thought to be the smallest part of nature and were not made up of anything smaller. Dalton’s Atomic Theory (1803)

(1) all matter was composed of small indivisible particles termed atoms,

(2) atoms of a given element possess unique characteristics and weight,

(3) three types of atoms exist: simple (elements), compound (simple molecules), and complex (complex molecules)

J. Dalton (1766-1844)

Thomson’s Atomic Model: Electrically charged sphere Radius ~ 10-8 cm Positive electric charge Electrons with negative electric charge embedded in the sphere

J.J. Thomson1897: Discovery of the electron

ATOMS are NOT Fundamental Particle

: Rutherford’s scattering experiments Discovery of the atomic nucleus

Ernest Rutherford (1871-1937)

He discovered alpha and beta rays, set forth the laws of radioactive decay, and identified alpha particles as helium nuclei.

Nuclear radius cm x atomic radius

Mass of the nucleus mass of the atom

Atom consists of a positively charged nucleus surrounded by a cloud of electrons

Atomic Model:

particle

Atom: spherical distribution of electric charges

impactparameter b

– atom scattering Experiment

– atom scattering at low energies is dominated by Coulomb interaction

Is the Nucleus Fundamental ??

First (wrong) ideas about nuclear structure (before 1932)Observations Mass values of light nuclei multiples of proton mass (to few %) (proton nucleus of the hydrogen atom) decay: spontaneous emission of electrons by some radioactive nuclei

Hypothesis: the atomic nucleus is a system of protons and electrons strongly bound togetherNucleus of the atom with atomic number Z and mass number A:a bound system of A protons and (A – Z) electronsTotal electric charge of the nucleus = [A – (A – Z)]e = Z eProblem with this model: the “Nitrogen anomaly”Spin of the Nitrogen nucleus =

Spin: intrinsic angular momentum of a particle (or system of particles)In Quantum Mechanics only integer or half-integer multiples of ħ (h )are possible: integer values for orbital angular momentum both integer and half-integer values for spin

Electron, proton spin = ½ħ (measured)Nitrogen nucleus (A = , Z = ): protons + electrons = spin ½ particlesTOTAL SPIN MUST HAVE HALF-INTEGER VALUE Measured spin =

DISCOVERY OF THE NEUTRON1932, Chadwick

Neutron: a particle with mass proton mass but with zero electric charge Solution to the nuclear structure problem:Nucleus with atomic number Z and mass number A:a bound system of Z protons and (A – Z) neutrons

James Chadwick

Nitrogen anomaly: no problem if neutron spin = ½ħ Nitrogen nucleus (A = , Z = ): protons, neutrons = spin ½ particles total spin has integer value

Chadwick’s experiments: a Po radioactive source ( MeV – particles ) mixed with Beryllium powder emission of electrically neutral radiation capable of traversing several centimetres of Pb:

He + Be C + neutron

2222

2

1

2

1cmvmcmvm nnnNNN

NNnn vmvmvm

222

2

1cmcmvm B

mn=938 1.8 MeV

After Chadwick discovers the neutron, the proton, electron and neutron account for all the atoms of all the elements in the Universe.

This was the “simplest” fundamental particle set ever described. LEPTON (leptos = light) : e-, BARYONS (baryos = heavy): p , n

Nucleus is not a Fundamental particle!!

Are the proton and the neutron Fundamental??

1928, antiparticle was predicted by Dirac from relativistic theory of electrons:

P.A.M. Dirac

C. Anderson (1905-1991)

e+

e-

1932, Discovery of the positron by Anderson studying cosmic rays.

Non-relativistic kinetic energy:

2 2 v

2 2

m pE

m

Relativistic kinetic energy (Einstein): 2 2 4 2 2E m c p c 2 4 2 2E m c p c

“negative” solution is related to the existence of antimatter

Photon conversionse+ ein a bubblechamber

-

I.I Rabi, Nobel 1944

In 1937, Discovery of muon () Neddermeyer, Anderson penetrating cosmic ray tracks with unit charge but mass in b

etween electron and proton muons were proven not to have any nuclear interactions and

to be just heavier versions of electrons m decays to electron and two invisible neutrinos via weak i

nteractions ( decay): - → e- e

first encounter of the generation problem

70 years later we still don’t have a good answer

Particle Electric charge (x 1.6 10-19 C)

Mass (GeV=x 1.86 10-27 kg)

e 0.0005 0.106

p 0.938

n 0 0.940

0 0

Discovery of muon ()

C.F. Powell

Discovery of pion meson () Prediction of pion existence :Yukawa 1935

Nucleons (protons and neutrons) are held together by stronger force than electrostatic repulsion of protons

In 1935 Yukawa predicted existence of a mediator of the strong interactions. Estimated its mass to be around 0.1 GeV.

Discovery of pions :Cecil Powell 1947 (Nature 159 (1947) 186.)

detected in cosmic rays captured in photographic emulsion Unlike muons they do interact with nuclei charged pions eventually decay to muons: - →-

view of the particle world seemed complete for entire two months...

Particle Electric charge (x 1.6 10-19 C)

Mass (GeV=x 1.86 10-27 kg)

e 0.0005 0.106

0 0

p 0.938

n 0 0.940

0.14

} Leptons: no strong interactions

} Hadrons: feel strong interactions

Discovery of kaon meson (K) 1947, Discovery of strange meson (kaon) Rochester, Butler

using a cloud chamber saw something unusual. Two tracks appeared from a single point beneath a lead plate, as if from nowhere.

cosmic ray particles with masses in between pions and protons which were just like pions except for strangely long lifetime (decay to pions or a muon and neutrino)

Mass ~ 0.5 GeV (Nature 160 (1947) 855)

Now understood as the lightest 2nd generation meson

ButlerRochester

K0 →+ - 0 →p+ -

The kaons had lifetimes of around 10-10s, however they were produced in strong reactions predicating particle lifetimes of 10-23 s.

The peculiar properties led to the new quantum number, strangeness.

Periodic tables of particles

Q= -1 Q= 0 Q=+1S=+1 K

K

S= 0

S= -1 K

K

Q= -1 Q= 0 Q=+1S= 0 n pS= -1

S= -2

Q=-1 Q= 0 Q=+1 Q=+2S= 0

S= -1

S= -2

S= -3

Q - Electric ChargeS - Strangeness

Spin 0 Meson Octet

Spin 1/2 Baryon Octet

Spin 3/2 Baryon Decimet

• new particles either pion-like (mesons) or proton-like (baryons)• either type can be strange or non-strange• mesons and baryons (hadrons) feel strong interactions contrary to leptons (e,,)

In 1950’s, Discovery of entire particle Zoo thanks to the rapid progress in particle accelerator technology

Quark model of hadrons Gell-Man, Zweig 1964Q= -1/3 Q= +2/3

S= 0 d uS= -1 s

Mesons are bound states of quark-antiquark

Baryons are bound states of three quarks

Quark model was confirmed experimentally by deep inelastic scattering of electrons on protons and bound neutrons at SLAC Friedman, Kendall, Taylor (1968) (Phys. Rev. Lett. 23 (1969) 930)

Quark (i.e. strong) dynamics understood only later: quantum chromodynamics (QCD) gluons (photon like particles) mediate strong forces

mdmu 0.1 GeV

ms 0.30 GeV

Gell-Mann G. Zweig

proton and neutron are consist of 3 quarks

K0 K+

π+

K0K-

π0 ; η

S=1

S= 0

S= 1

Q=0

Q=1

Q=-1

Meson Octet: quark – antiquark pairs

duπ-

3

du2/)( 0 uudd

dsKusK 0 ;

; 0 dsKusK

1833

n p

Σ+

Ξ0Ξ-

Σ-Σ0 ; Λ

S=0

S=-1

S=-2

Q=0

Q=1

Q=-1

Baryon Octect: three quarks bound together

udduud neutron ; proton

; ; 0 sddsudsuu

; 0 ssdssu

10863;3633

A success of the static quark model

The “decuplet” of spin baryons

Strangeness Mass (MeVc )

N*++ N*+ N*° N*– uuu uud udd ddd

– *+ *° *– suu sud sdd

– *° *– ssu ssd

– – (predicted) sss

–: the bound state of three s – quarks with the lowest mass

with total angular momentum =

Pauli’s exclusion principle requires that the three quarkscannot be identical

Prediction and discovery of the – particle

The first – event (observed in the m liquid hydrogen bubble chamber at BNL

using a GeV/c K– beam from the GeV AGS, 1964)

Chain of events in the picture: K– + p – + K+ + K° (strangeness conserving)

– ° + – (S = weak decay)

° ° + (S = weak decay)

– + p (S = weak decay)

° + (electromagnetic decay) with both – rays converting to an e+e – in liquid hydrogen(very lucky event, because the mean free path for e+e – in liquid hydrogen is ~ m)

– mass measured from this event = 1686 ± 12 MeVc2

V.E. Barnes et al. PRL 12 (1964) 204.

Modern View of Atomic Structure

How many fundamental particles in Universe ?

In 1974, Discovery of Charm Quark

• S. C. C. Ting et al.:

p Be → J (→e+ e-) X at Brookhaven AGS proton synchrotron

Phys. Rev. Lett. 33 (1974) 1404

m =3.1 GeV

• B. Richter et al.: e+ e- → ψ(1s) →e+ e- at SLAC SPEAR e+ e- collider with Mark-I detector

m= 3.105 0.003 GeV

Phys Rev. Lett 33 (1974) 1406

mc~1.5 GeV

In 1975, Discovery of Tau Lepton ()

Experiment at the Stanford Linear Accelerator Center in 1975 by M. Perl et al using the Stanford positron-electron asymmetric ring (SPEAR).

Centre of mass energies of order 4GeV 24 events out of 35,000 of form: (Phys. Rev. Lett. 35, 1489 (1975))

• In 1973, at the electron-positron storage ring SPEAR was installed to search for the reaction mechanism for production of new leptons viz., e- + e+ => X+ + X-.

m~1.8 GeV

In 1977, Discovery of Bottom quark ( Fermilab)

Leon Lederman : Upsilon (Y(1s) →+-)

"Observation of a Dimuon Resonance at 9.5 GeV in 400 GeV Proton-Nucleus Collisions," Physical Review Letters 39, p. 252, (1977).

mb~4.7 GeV

p+ nucleus (target) →Υ(1s)X → +- X

1995, Discovery of Top quark (Fermilab)

Double b-tagged dilepton event @ CDF

• The experiment was carried out at Fermi National Accelerator Laboratory's Tevatron, by the CDF and the D0 collaborations.

• The CDF found 37 top candidate events as against an expected background of 12 events. The D0 collaboration found 17 top candidate events and estimated a background of about 4 events

• CDF reports a mass of 176 GeV (statistical uncertainty of 8 GeV and systematic uncertainty of 10 GeV). D0 reports 199 GeV (statistical uncertainty of 20 GeV and systematic uncertainty of 22 GeV)

CDF D0

The fundamental particles are split up into two families, namely the quarks and the leptons. Both of these families consist of six particles, split into three generations, with the first generation being the lightest, and the third the heaviest.

What are the fundamental building blocks?

Summary of Matter Particles

• Particle Physicists study the fundamental particles that make up all of matter, and how they interact with each other.

What holds it together?

There are four fundamental interactions between fundamental particles, and all forces in the world can be attributed to these four interactions!

What holds it together?

There are four fundamental interactions between fundamental particles, and all forces in the world can be attributed to these four interactions!

What's the difference between a force and an interaction?

The force is the effect on a particle due to the presence of other particles.

The interactions of a particle include all the forces that affect it, but also include decays and annihilations that the particle might go through.

All interactions which affect matter particles are due to an exchange of force carrier particles, a different type of particle altogether.

Electric Forcr

Magnetic force

How do matter particles interact?

Electromagnetic Interaction The electromagnetic interaction acts between all particles that have electric charge. It is attractive for oppositely charged particles, and repulsive for particles of the same charge.

The force carrier particle of the electromagnetic interaction is the photon (). 

So the electromagnetic interaction is what allows atoms to bond and form molecules, allowing the world to stay together and create the matter you interact with all of the time.

Strong Interaction

In addition to electric charge, quarks also contain something called “colour charge”. The force between colour charged particles is very powerful, thus it is called the "strong interaction".

• The strong interaction actually acts between quarks, and it's the residual strong force that causes nucleons to attract.

• The force carrier of strong interaction is the gluons.

The nucleus of an atom consists of a bunch of protons and neutrons crammed together.

We cannot account for the nucleus staying together with just electromagnetic force.

While quarks have color charge, composite particles made out of quarks have no net color charge (they are color neutral).

What is the Color Charge ??• Quarks and gluons are color-charged particles.

• Just as electrically-charged particles interact by exchanging photons in electromagnetic interactions, color-charged particles exchange gluons in strong interactions. •When two quarks are close to one another, they exchange gluons and create a very strong color force field that binds the quarks together. The force field gets stronger as the quarks get further apart.

• Quarks constantly change their color charges as they exchange gluons with other quarks.

gluon

Quark Confinement Color-charged particles cannot be found individually. For this reason, the color-charged quarks are confined in groups (hadrons) with other quarks. These composites are color neutral.

The quarks in a given hadron madly exchange gluons. For this reason, physicists talk about the color-force field which consists of the gluons holding the bunch of quarks together. If one of the quarks in a given hadron is pulled away from its neighbors, the color-force field "stretches" between that quark and its neighbors.

At some point, it is energetically cheaper for the color-force field to "snap" into a new quark-antiquark pair.

In 1979, Discovery of Gluon The TASSO experiment at the PETRA of the Deutsches Elektronen-Synchrotron (DESY) shows three jets of particles produced in an electron-positron collision at s= 27.4 GeV.

Similar three-jet event topologies were announced by JADE, MARK J and PLUTO, the other groups working at PETRA.

Three Jet Events in TASSO CollaborationJADE Collaboration 1980 Phys. Lett.B91 142., MARK J Collaboration 1979 Phys. Rev. Lett.43 830.PLUTO Collaboration 1979 Phys. Lett.B86 418., TASSO Collaboration 1979 Phys. Lett.B86 243.

The Weak InteractionWeak interactions are responsible for the decay of massive quarks and leptons into lighter quarks and leptons.

When a quark or lepton changes type (a muon changing to an electron, for instance) it is said to change flavor. All flavor changes are due to the weak interaction.

The force carrier particles of the weak interactions are the W+, W-, and the Z particles. The W's are electrically charged and the Z is neutral.

The only matter around us that is stable is made up of the smallest quarks and leptons, which cannot decay any further.

Neutron decay

1983, Discovery of mediators of weak interaction (W±, Z0)• The W and Z particles were first observed at CERN by the UA1 and UA2 experiments.

• Both proton and antiproton were accelerated to 270 GeV and brought into collision in two interaction regions at √s = 540 GeV.

• In April/May 1983 came the next run with 118 nb-1 of integrated luminosity for UA1. This gave an additional sample of 54 W → eν events, giving Mw = 80.3 + 0.4-1.3 GeV

• In UA1, four Z → e+e- events with no visible experimental background in 55 nb-1 of data were observed. The first mass determination gave Mz = 95.5 ± 2.5 GeV

C. Rubia and van der Meer

Z decay to e+e- in UA1

e

e

W decay to e in UA1

e

The Gravity Gravity acts between all particles that have mass. Mass will attract other mass with a force that gets weaker as the distance between them gets larger. Gravity is responsible for the large scale structure of the universe. Here's a pretty picture of a galaxy, which, of course, is held together by gravity. Although gravity appears to be a very powerful force, when it comes to things on smaller scales, like tiny particles, can be ignored because of its weakness.

The carrier of the gravitational force is the gravitron. Although it has never been observed in experiment, it is strongly believed to exist.

Standard Model of Particle Physics Physicists have developed a theory known as the Standard Model that explains our current understanding of the nature of matter -- what it's made of and how its components interact.

All the particles in the universe can be grouped into just three "families" of particles: quarks, leptons, and force carrier particles.

Matter Particles

Fundamental Forces and Force Carrier Particles

The Standard ModelA quantum theory that successfully describes how all know fundamental particles interact via the strong, weak and electromagnetic interactions

based on a gauge field theory with a symmetry group

YLc USUSUG )1()2()3(

FermionsFermions SymmetriesSymmetries Bosons, InteractionsBosons, Interactions

Three families,Three families,with with leptons

and and quarks

1) 1) Poincaré GroupPoincaré Group

2) 2) Gauge Symmetries:

U(1)U(1)Y Y

SU(2)SU(2)LL

SU(3)SU(3)cc

: QED, : QED, g’

Z, W : Weak, : Weak, g

(electroweak unification)(electroweak unification)

8 gluons : QCD, : QCD, gs

uL

dL

, uR, dR.

eL

eL

, R, eR,

g

gW

tan

Someone said, “Let there be mass !”.

And there was mass…

And others saw that mass was bad,because it broke the SU(2)L symmetry.

Only known solution: the Higgs Mechanism

c

s

t

b

Important Questions of Particle Physics

1. What is the origin of mass? top quark

anti-top quark

ZW+, W-

. . . .e e- u d s c b

gluons

e e+ u d s c b - - - - - - - -

(Mass proportional to area shown but all sizes still < 10-19 m)

leptons quarks

Gauge bosons (force carriers)

Does the Higgs particle exist proposed by P. Higgs (1964)?

The mass of the Higgs is a free parameter in the Standard Model.

Constraints : 114.4 GeV/c2 (exp.) < mH < ~ 1000 GeV/c2 (theo.)

The Higgs BosonThe Higgs BosonThe Higgs BosonThe Higgs Boson

In the “Standard Model” the origin of mass is addressed using a mechanism named after the British physicist Peter Higgs. This predicts a new particle: the Higgs boson. What is the Higgs boson?

In 1993, the then UK Science Minister, William Waldegrave, issued a challenge to physicists to answer the questions 'What is the Higgs boson, and why do we want to find it?' on one side of a single sheet of paper. This cartoon is based on David Millar’s winning entry.

SM Higgs-boson mass now quite constrained: 114.4 < mH < 193 GeV at 95% C.L.

from beautiful precision measurements and direct searches from the e+e- colliders

“This does not necessarily mean that this is the Higgs mass !”

LHC ??

“Particle physics know everything about this particle, the only thing they don’t know is whet

her it exists.”

• Prediction of W- and Z-bosons

• Higgs mechanism as a cornerstone of the model

2. The question of UnificationIs there a universal force, a common origin of the different interactions?

J.C. Maxwell

• 1864, Unification of electricity and magnetism (J.C. Maxwell)• 1962-1973: Glashow, Salam and Weinberg

• Unification of the electromagnetic and weak Interactions electroweak interaction

• Einstein tried to unify electromagnetism and gravity but failed.

• The Standard Model fails to unify the strong and electroweak forces.

• The Super Symmetry (SUSY) Model can unify the strong and electroweak forces.

Need to find SUSY particles in LHC, LC, ..

Strong

Weak

Electromagnetic

What is Supersymmetry ?

There are two types of particles in nature: fermions and bosons.

Fermions have half units of spin, and tend to shy away from each other, like people who always stay in single rooms at the fermion motel.

Bosons have zero or integer units of spin, and like to be with each other, like people who stay in shared dormitories at the boson inn.

Supersymmetry says that for every fermion in Nature there must be a boson and vice-versa. Supersymmetric particles have not been observed (yet) so they must be heavier - SUSY must be broken by some mechanism

u

e

bd

tc

e

Lep

tons

Qua

rks

The Generations of Matter

s

SPIN ½ FERMIONS

u

e

bdtc

e

Sle

pton

sS

quar

ks The Generations of Smatter

s

SPIN 0 BOSONS

BOSONS

Gravitino0W W Z Photino GluinoFERMIONS

Unifying gravity to the other three forces may possible by String theory.

String theory predicts extra hidden dimensions in space beyond the three dimensional space we sense daily.

G

Planck

brane

x5

SM branevev MGUT MPl

GravitationalForce

E [GeV]

EM/HyperchargeForce

Weak Force

Strong ForceInvers

e S

trength

RGE evolution

1016102 1019

3. What is the origin of the matter-antimatter asymmetry in the universe? What is the origin of the CP-violation?

particlesanti-particles

particles

Accelerators

Where did all antimatter go?Can we produce dark matter?Accelerating Universe! Where does energy come from?

BigBang

Inflation

Create particles & antiparticles that existed ~0.001 ns after Big Bang E = mc2

Summary of open questions in SM

• Why do some particles have a mass, and others do not, and what determines the value of a particles mass? Higgs mechanism ??

Where is the Higgs?

• Are there just three generations of matter, and if so, why?

• Are quarks and leptons fundamental, or are they also composed of something smaller?

• What is the origin of the matter-antimatter asymmetry in the universe? What is the origin of the CP-violation?

• Dark Matter

• Dark Energy

• + others

Where do we stand todaye+e- colliders and many other experiments at hadron colliders have explored the energy range up to ~100 GeV with incredible precision

However, the Standard Model is consistent with all experimental data !!

Light Higgs boson favoured.

The role of present and future colliders1. Discoveries

Higgs,

Supersymmetry,

Other Physics beyond Standard Model

Need high Energy : explore the TeV energy domain

2. Precision measurements and tests of the Standard Model

Mass of gauge bosons (W, Z),

Top mass and other parameters related to top,

Other Physical parameters in Standard Model

3. Flavour Physics

b-quark, t-quark, …. , CP-violation, …

Quest for Energy

Ehc 12

)(2.0)( GeVEfm

Increasing energy you probe Nature at smaller distances and you may cross the threshold of new phenomena

e+e-

e-proton

proton-proton

today1970 1980 1990 2000 2010 2020 2030

LHC

ILC

TEVATRON

HERA

LEP,SLC

PEP-II, KEKB

VEPP, CLEO-c, BEPC

DANE

FNAL, CERN, J-PARC

Energy Frontier Colliders:

Flavor Specific Accelerators:

e+e- (b factory)

e+e- (c factory)

e+e- (s factory)

CLIC

Collider

LHCb

PEP-II, SLAC, Palo Alto, USA

HERA, DESY, Hamburg, Germany

KEKb, KEK, Tsukuba, Japan

Tevatron, Fermilab, Chicago, USA

Currently Operating Colliders

Why a hadron collider ? • e+e- colliders are excellent machines for precision physics!!

e+e- are point-like particles, no substructure →clean events complete annihilation, center-of-mass system, kinematic fixed high energy requires linear design high luminosity harder to obtain beam radiation can cause problems

e+e- →q qe+e- →+-

Hadron colliders: High E with high L fairly easy to obtain.

Spread of parton momenta inside protons means that all energies are explored simultaneously at hadron colliders - good for discovery, less good for precision measurement of chosen state.

Final state is messy, due to beam fragments and pileup

LHC: pp collisions at 7 + 7 TeV

Large Hadron Collider

Proton-Proton Collisions at the LHC

• Revised Time Schedule: Dec. 2006 Ring closed and cold Jan. - Mar. 2007 Machine commissioning

Spring 2007 First collisions , pilot run. L=5x1032 to 2x1033 cm-2 sec-1, 1 fb-1

Start detector commissioning, ~ 105 Z , W , tt events June - Dec. 2007 Complete detector commissioning, Physics run 2009 L=1-2 x1034, 100 fb-1 per year (high luminosity LHC)

2835 x 2835 bunchesseparation: 7.5 m ( 25 ns)

1011 Protons / bunch Bunch crossing rate: 40 MHz Luminosity: L = 1034 cm-2 sec-1

Proton-Proton collisions: ~109 / sec(superposition of 23 pp-interactions per bunch crossing)

~1600 charged particles in the detector

Five experiments: ALICE, ATLAS, CMS, LHC-B, TOTEM

CMS

CP violation with b quarksHeavy ion physics

General purpose detector General purpose detector

Cross Sections and Production Rates at LHC

• Inelastic proton-proton reactions: 109 / sec • bb pairs 5 106 / sec • tt pairs 8 / sec

• W e 150 / sec• Z e e 15 / sec

• Higgs (150 GeV) 0.2 / sec• Gluino, Squarks (1 TeV) 0.03 / sec

Rates for L = 1034 cm-2 sec-1:

Interesting physics processes are rare:

high luminosity, extremely challenging detectors (to suppress the huge backgrounds)

The first LHC data from Summer of 2007• L=1fb-1(10fb-1): 6 months with L=1032(1033)cm-2s-1

• 50% efficiency

Channels (Examples) Events for 1fb-1

(per ATLAS, CMS)

Total statistics from previous Colliders

W 7×106 ~104 LEP, ~106 Tevatron

Z ~ 106 ~106 LEP, ~105 Tevatron

tt WbWb+X ~105 ~104 Tevatron

m=1 TeV 102 -103gg~~

• Understand and calibrate detectors in situ using well-known physics samples

- Z , ee : tracker, ECAL, Muon chambers calibration, alignment, etc

- tt-bl bjj :jet scale from Wjj, b-tag performance, etc

• Measure SM physics at s=14 TeV

Prepare the road to discovery … it will take a lot of time.

mainly via gluon fusion

tt-fusion

W,Z fusion: increasinglyimportant at high masses

associated productionin the low mass region

New Particle Searches at LHC1. Standard Model Higgs Boson

• Production at LHC

Low mass bb dominates,

but high multi-jet backgrounds and low mass resolution

: BR low (10-3 to 10-4) - use small Higgs width and high resolution EM calorimetry

Intermediate mass Decay modes to WW and ZZ

become important

Intermediate to high mass HZZ 4 leptons

Decay of Higgs

2. MSSM Higgs Boson Complex analyses; 5 Higgses: Φ = h0, H0, A0, H;

At tree level, all masses and couplings depend on only two parameters; traditionally taken to be MA and tanb (Born level, mh<MZ)

2 complex Higgs doublets 8 d.o.f. 3 eaten by massive vector bosons W±/Z 5 physical Higgs fields

For tanβ > 1. A, H, H± couples dominantly to the heaviest lepton (τ) and to the heaviest down type quark (b)

Radiative corrections from loop containing top quarks & SUSY particles are substantial searches are affected

MSSM Higgs Discovery modes Large variety of observation modes

if SUSY particles heavy SM-like: h , bb; H 4l MSSM-specific: A/H , ττ, tt ; H hh, A Zh; H τν

if SUSY particles accessible: H/A χ2

0 χ2

0 4l + missing Energy

h produced in cascade decays (e.g. χ20 h χ1

0)

H± decays into lightest chargino χ1± and neutralino χ1

0 or decays to sleptons would dominate when kinematically allowed

Studies performed in two steps: SUSY particles are heavy: no contribution to Higgs production/decay

decays only into SM particles possible SUSY particles contribute in production/decays

New Particle Searches

Based on Extra Dimension Model

1. Large Extra Dimension Model (LED or ADD) Model

2. TeV-1 sized Extra Dimension Model

3. Randall-Sundrum (RS) Model

4. Universal Extra Dimensions (UED) Model

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