Day2: Physics at TESLA - Deutschlands größtes … · · 2003-08-08Day2: Physics at TESLA ......

Klaus Desch, Physics at e+e- Colliders, DESY Summer Student Lecture 08/2002 Page 61

Day2: Physics at TESLADay2: Physics at TESLA

• Origin of Electroweak Symmetry Breaking as one

great Motivation for a Linear Collider

• The TESLA project

• Higgs Precision Physics at TESLA

• Leaving the Standard Model Behind…

• Precision tests

• Summary


ElectroElectro--Weak Symmetry BreakingWeak Symmetry Breaking

Quantum Field Theory with massive Quanta fails at high Energies:

Cross section:σ∼ sViolates unitarity at

(if forces remain weak)

TeVs 2.1~

“if nothing happens, something must happen…”

The SM solution:(rescue of the beautiful gauge principle) Introduction of a new scalar field with non-zero field strength In the vacuum: the Higgs Field.


The Higgs MechanismThe Higgs Mechanism

21 2

2222

vgMwhereMq

=−

Paradigm:All (elementary) particles are massless (per se)

gauge principle worksrenormalizable theory (finite cross sections)

permanent interaction with the Higgs field acts as if particles hada mass (effective mass)

2q1gv 2

2

24

2

2q1gv

2q1


Where is the Where is the HiggsHiggs Boson?Boson?

Theory:Upper bound: perturbativity (λ<1)Lower bound: vacuum stabilityModels: minimal SUSY: m<135 GeV

GUT’s : m<180 GeV

Experiment:Precision measurements (LEP,SLC,Tevatron) are sensitive tovirtual corrections:

m<200 GeV (95% CL)

The Higgs Boson is probably “light”!


Higgs Search at TevatronHiggs Search at Tevatron

Maybe…


Higgs Search at the LHCHiggs Search at the LHC

Production processes:

For m=120 GeV: σ ~ 25 pb 2.5 million Higgs/yearLHC = Higgs factory ?



Gigantic backgrounds!

look for rare but wellmeasureable final states

!hopelessisbbHgg →→


Higgs Search at the LHC (m<150 GeV)Higgs Search at the LHC (m<150 GeV)

Loop induced decay:

Backgrounds:γγ production 2pb/GeV need σ(m)/m ~ 1%γ + jet, jet-jet production (reducibel) need 10 γ/πsuppression -3 0


Up to m<600 GeV:Standalone discoverywith 30Above: ZZ llνν andWW lνqq needed

Higgs Search at the LHC: m> 150 GeVHiggs Search at the LHC: m> 150 GeV

ATLAS clear 4-lepton signature,almost background free

1−fb



Discovery potential:

Single channels: Combined channel + expts:

With 10 fb : 5σ discovery in the whole mass range!


Higgs at the LHC after discovery: Measurements?Higgs at the LHC after discovery: Measurements?

In the SM, all properties of the Higgs boson are predicted, onceits mass is known crucial test of EW symmetry breaking

Absolute measurements are difficult at hadron machines, due touncertainties in production cross sections (QCD,structure functions)and background modelling

Some first measurements can be done:

•Mass: 0.1 – 0.4%•Total Width: 10-20%, model dependent•Production rates: 10-20%•Ratios of couplings: W/Z, W/t, W/τ: 10-20%

To really establish the Higgs mechanism, higher precision and less model depence is needed: Linear Collider!


•Superconducting e e linear collider

•Phase 1: 500 GeV •Phase 2: 800++ GeV•Luminosity: 3-5x10 cm s•300 – 500 fb / year•Polarized beams•Running options: γγ, eγ, e e ,Giga-Z•Integrated X-Ray Free Electron Laser

The TESLA ProjectThe TESLA Project

+ -

-1

34 -12

- -


BeamstrahlungBeamstrahlung


BeamstrahlungBeamstrahlung


A Detector for TESLAA Detector for TESLA

Detector optimized forprecision physics

Design driven by Higgsphysics in many cases:

-Vertex detector (b/c separation)-Momentum resolution( )-Energy flow: jet reconstruction

Broad R&D programCurrently starting

0Z + −→


CalorimetryCalorimetry


CalorimetryCalorimetry


MaskMask


Physics Program at TESLAPhysics Program at TESLA

Highlights:

• Origin of Elctroweak symmetry breaking: precision Higgs physics

• Breakdown of the Standard Model

• Supersymmetry

• Extra Space Dimensions

• New Gauge Bosons

• Flavour physics: top quark

• (SM?) Precision measurements


After the discovery of a Higgs boson, the key task is to establish the Higgs mechanism in all elements as responsiblefor EW symmetry breaking

Electron-Positron Linear Colliders (NLC,JLC,TESLA) withenergies up to 1 TeV and high (300-500 fb /year) are

1. Technologically within reach2. The ideal tool for precision Higgs physics

Precision Measurements should comprise:• Mass• Total Width• Quantum numbers J (Spin 0 ?)• Higgs-Fermion couplings (~ mass ?)• Higgs-Gauge-Boson couplings (W/Z masses)• Higgs self coupling (spontaneous symmetry breaking)

Measurements should be precise enough to distinguish betweendifferent models (e.g. SM/MSSM, extra dimensional effects, …)

Precision Higgs Physics at a Linear ColliderPrecision Higgs Physics at a Linear Collider

-1

PC


The Higgs Boson Profile at TESLAThe Higgs Boson Profile at TESLA

decay-mode independent Higgs tag:

• select di-lepton eventsconsistent with Z ll

• calculate recoil mass

∆σ ~ 3%model independentmeasurement!

∆m ~ 50 MeVMass measurement:



Key issue: momentum resolution:

“Lep”-like resolution Goal with TESLA TPC+Si



large cross section atlarge

model independent handleon total width, when combinedwith BR(H WW):

s

)WWH(BRWW

tot →Γ

=Γ

%tot 5≅∆Γ

WW-fusion process:



Higgs field responsible for particle masses Couplings must be proportional to the particle masses

Decisive Test: precision analysis of the Higgs branching ratios:

Decay Precision

for 500 fb , m=120 GeV-1


Separation ofand


bbH →ccH → Needs high resolution vertex dector:

First layer at 1.5 cm from interaction point!



b- and c-tagging efficiencies:



Higgs Quantum Numbers: Is it really a Higgs?

Spin from threshold scan:

10 fb /point-1

CP quantum numbers from:

-Angular distribution of H and Z

-Transverse polarisation correlations in H ττ



Top quark Yukawa coupling:

-need highest energy-heaviest quark surprises?-small cross section-complicated final state

achievable precision:



Global fit of Higgs couplings (HFITTER):

Measurements precise enough to obatain sensitivity beyond cms energy!



Higgs self-coupling (‘the holy grail’):

Close connection to the shape of the Higgs potentialessential test of the mechanism of spontaneous symmetry breaking

Tiny cross sectionComplicated multi-jet final state

detector design: energy flow

Need highest luminosityPrecision for 1 ab :

%20≅∆λ

λ

-1

LEP TESLA


divergent W W W W amplitude

new strong interaction at

spontaneously broken chiral symmetry

Goldstone bosons (“Pions”) = W states (“technicolor”)

no calculable theory until today in agreement with precision data

Experimental consequences: deviations in triple and quartic gauge

couplings:

No Higgs Boson?No Higgs Boson?

L L L L

L


Triple Gauge CouplingsTriple Gauge Couplings

TGC’s are a universalprecision test fornew physics

Sensitivity to new physicsscale Λ:

At 500 GeV, 500 fb -1


Quartic Gauge CouplingsQuartic Gauge Couplings

Sensitivity to new physicsscale Λ:

- complicated final state- need to separate WW 4q and ZZ 4qenergy flow!

complete threshold regionof new strong interactioncovered


Physics beyond the Standard ModelPhysics beyond the Standard Model

SM cannot be the ultimate theory!

Why???

• Hierarchy problem

• Gravity

• Many free parameters

• Cold dark matter

• Baryon asymmetry

• Connection between quarks and leptons? Q(proton) = Q(positron)

• Connection between the families: ‘flavour physics’


The Hierarchy problemThe Hierarchy problem

In Nature, there are two largely different mass scales:

1. The electroweak scale: v = 246 GeV

2. The Planck scale:

The particle masses (especially the Higgs mass) recieve largescale dependent corrections, e.g.

19PlanckM =10 GeV

2 2Mδ Λ∼ Λ is the scale up to whichThe SM should be valid

⇒ If it is hard to believe that the correctionGets compensated by a bare mass which is alsoTo yield a physical Higgs massSomething should “protect” the Higgs mass!

2 2PlanckM Mδ ∼

2Planck(M )o

2(v )o


SupersymmetrySupersymmetry

is one of the most attractiveextensions to the SM!

Simple Idea:

Symmetry betweenBosons and Fermions

each SM particle has aSUSY partner with sameQuantum numbers andSpin differing by ½.

But where are the SUSYPartners? Must be heavy

SUSY must be broken!

Why is it so attractive, then?


Why is SUSY so attractive?Why is SUSY so attractive?

1. It solves the Hierarchy problem:

The divergency in the Higgs mass corrections if cancelled exactlyFor unbroken SUSY.

If it is not broken too heavily (i.e. if the SUSY partners are at<~ 1 TeV), there is no fine tuning necessary.



2. It shows a path to Grand unification:

This is achieved for

Experiment:

2 SUSYWsin θ = 0.2335(17)

2 exp.Wsin θ = 0.2315(2)

Minimal SUSY prediction:



3. Cold Dark Matter:

The lightest SUSY partner particle might well be stable andAn excellent candidate for the observed cold dark matter

4. Link to Gravity:

SUSY offers the theoretical link to incorporate gravity. Most stringmodels are supersymmetric.

5. Light Higgs Boson:

SUSY predicts a light (< 135 GeV) Higgs boson as favoured byElectro-weak precision data from LEP and Tevatron.


The Supersymmetric particle spectrumThe Supersymmetric particle spectrum


SUSY precision measurements at TESLASUSY precision measurements at TESLA

Typical production in collisions: pair production, e.g.: + -e e

Detector signature:2 Muons + miss.Energy

Muon energies:‘box spectrum’Endpoints contain informationabout masses of Smuon and Neutralino

Reachable precision o(100 MeV)



Alternative: mass from threshold scan

0 0 0 0

2 2 1 1e e χ χ χ χ+ − → →

Reachable precision < 100 MeV

Disentangle different states, in caseThere are many SUSY particles



Beam Polarisation allows SUSY parameter determination.Example: Neutralino-sector depends on 4 parameters:

2 1tan , , ,M Mβ µ

1M can be obtained from polarisation dependence of cross sectionand FB-Asymmetry


But maybe more demanding signatures…But maybe more demanding signatures…

In some SUSY scenarios(‘GMSB’) the Neutralinois not stable:

‘non-pointing’ photonsignaturedemanding for calorimetry!

01 Gχ γ→


Extrpolation to very high scalesExtrpolation to very high scales

• SUSY parameters ‘run’ with energy (like SM coupling constants)

• Running described by Renormaisation Group Equations (RGE’s)

• Precise measurement of SUSY parameters at ‘low’ (i.e. TESLA)allows to extrapolate to very high (e.g. GUT) scales and test thehigh energy behaviour of SUSY

Test of Grand Unification becomes possible

Information about the mechanism which breaks SUSY can be

obtained

“mSUGRA” “GMSB”


Extra Space Dimensions?Extra Space Dimensions?

• Completely alternative approach to solve the hierarchy problem:‘There is no hierarchy problem’

• Suppose, the SM fields live in ‘normal’ 3+1D space• Gravity lives in 4 + δ Dimensions• δ extra Dimensions are curled to a small volume (radius R):



For r < R, gravity follows Newtons law in 4+δ dimensions:

1( ) SGV rrδ +

=

w( h) itS N SN

G G GV r GR r r Rδ δ= = =

For r > R, gravity follows effectively Newton’s law in 4 dimensions,since the ‘distance’ in the extra dimensions does not rise anymore:

If e.g. R ~ o(100 µm) and δ=2 one obtains ! (1TeV)SM o=

The Planck-Mass only effectively appears

so high at large distances. The true scale of gravity is

2 /Planck NM c G=

2 / /S S NM c G cR Gδ= =

Gravity might become visible in TeV-scale colliders as TESLA!!



Effects from real graviton emission:

measures the numberof extra dimensions!



Effects from virtual graviton exchange:

can prove Spin-2 exchange!


New Gauge BosonsNew Gauge Bosons

If there is a GUT, the GUT gauge group (e.g. SU(5)) might be brokenin steps e.g. new U(1) at the TeV scale new Z’ boson.TESLA has reach up >10 TeV through interference of Z’ with Z and γ.


New Gauge BosonsNew Gauge Bosons

If LHC observes at Z’, TESLA can measure itscouplings and pin down the model


Top Quark precision physicsTop Quark precision physics

∆m(top) ~ 100 MeV

∆Γ(top)/Γ(top) ~ 5%

Threshold scan of e e tt+ − →

study top production anddecay angular distributions


Return to the Z0: GigaReturn to the Z0: Giga--ZZ

Operate TELSA at the Z-Pole and WW-threshold1 Billion Z0’s in a few months (100xLEP)

• (factor 10 better than LEP) •

2sin 0.000013Wθ∆ =6 MeVWM∆ =


SummarySummary

• TESLA physics is fascinating

• Higgs Mechanism can be established in all essential details

• Precision SUSY measurements reconstruct fundamental theory

• Precision is the key sensitivity far beyond collider energy

• World-wide consenus that a Linear Collider should be the next major step in HEP

• This will be YOUR machine!

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Day2: Physics at TESLA - Deutschlands größtes … · · 2003-08-08Day2: Physics at TESLA ......

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