IV. Kern/Teilchenphysik und Kosmologie IV. Kern/Teilchenphysik und Kosmologie

IV. Kern/Teilchenphysik und Kosmologie IV. Kern/Teilchenphysik und Kosmologie

18. Offene Fragen der Teilchenphysik 18. Offene Fragen der Teilchenphysik

  Physik jenseits des Standardmodells Physik jenseits des Standardmodells

Teilchen Massen

Teilchen Massen ?

Vereinheitlichung der Kräfte ?

Materie-Antimaterie Asymmetrie ?

Dunkle Materie ? Dunkle Materie ?

Offene Fragen: Teilchenphysik Kosmologie

Offene Fragen: Teilchenphysik Kosmologie

Time after Big Bang

Teilchen Massen

P. Higgs P. Higgs

LEP:

m(Higgs) ≈ 115 GeV ?

CMS

Higgs Signal am LHC

Offene Frage:

Offene Frage: Ursprung der Teilchenmassen Ursprung der Teilchenmassen

Covered by LEP

Covered by LEP

Fundamental Open Question in Standard Model: Higgs sector

Problems:

Elw scale ≈ 10

²

GeV Hierarchy Planck scale ≈ 10

¹⁹

GeV problem

1

Radiative corrections: m

_Higgs

≈

Λ (Higgs is scalar !!)

Naturalness problem/fine tuning

2

If m_Higgs ≈ 130 – 180 GeV:

SM works up to GUT scale

Peter Higgs

ELW data

Direct searches

Scale up to which SM is valid

Elw precision measurements: m_Higgs < 207 GeV (95%CL) Direct searches: m_Higgs > 114.4 GeV (95% CL)

1.7σ excess at m_Higgs ≈ 115 GeV

LEP

Peter Higgs

Possible Solutions to Fundamental Open Questions

Higgs

Salam Glashow Weinberg

For all proposed solutions: new particles should appear at TeV scale or below

Extra Dimensions

New dimensions introduced m_Gravity ≈ m_elw  Hierarchy problem

solved

New particles at ≈ TeV scale

Supersymmetry

New particles at ≈ TeV scale, light Higgs Unification of forces

Naturalness solved (Higgs mass stabilized) No new interactions

Technicolor

New (strong) interactions produce EWSB No elementary scalar  naturalness solved

New particles at TeV scale However:

no real predictive theory Problems with fermion masses, FCNC, EW data

Rubbia van der

Meer

Veltman ‘t Hooft Gross

Wilczek Politzer

Cronin Fitch

Reines

Perl

Friedman

Kendall

Taylor Lederman

Schwartz Steinberger

Richter Ting

Gell-Mann Alvarez Feynman

Schwinger Hofstadter

Yang Lee

NP since

1957Except P. Higgs

Supersymmetry Supersymmetry

Possible Answer to some of the Fundamental open Questions in Possible Answer to some of the Fundamental open Questions in

Particle Physics Particle Physics

Super- particle

fermion boson

Super- symmetry

Motivation:

Connection to string theory Include gravity

Finite radiative corrections to m_Higgs Consistent with electroweak data Gauge coupling unification at GUT scale

scale (GeV) scale (GeV)

(coupling strength) -1

No unification

Unification

Example : Electron Spin 1/2

Selectron Spin 0

Searches for SUSY Particles at LHC:

Searches for SUSY Particles at LHC:

(pp collisions at

(pp collisions at E E

_{cm cm}

= 14 TeV = 14 TeV) )

n leptons + n jets + missing E_T

Mass reach for gluino and squark

~ 2-3 TeV

Typical event signature in CMS Detector at LHC:

10⁵ events

@10³³/year

Fundamental Scales

Generally assumed

: consistent Quantum Theory of Gravity must be a String Theory  requires additional dimensions

String Theory has some inherent scale: String Scale M_S

Additional dimensions must be compactified:

Radius of curvature: l_PL = 1/M_PL ~ 10^-33 cm too small for experimental observation

However:

R could be much lager  fundamental scale of Gravity (M_S) close to elw scale (M_W)

Only ONE scale in Particle Physics: Electroweak Scale

Can test Geometry of Universe and Quantum Gravity in the Lab Gravity

Newton Constant G_N = 6.707 10^-39 GeV^-2

Weak Scale Fermi Constant G_F = 1.166 10^-5 GeV^-2

SUSY Mass Scale

Order of TeV Planck Scale

M_Pl = G_N^-1/2 ~ 10¹⁹ GeV

Gravitational interactions play no role

Electroweak scale is derived quantity Not yet Fundamental scale proven

Extra Dimensions (ED)

 String Theory: ED of space-time required, size of ED ≈ l l

_Pl

≈ 10

^-32

cm

δ = 1: excluded by validity of Newton’s law at astronomical scale

δ

= 2: not likely, cosmological arguments: cooling of SN1987a: M

_D

> 31 TeV

Idea:

Idea: extra dimensions could be much larger ( extra dimensions could be much larger ( TeV TeV scale) scale)



 Large variety of models exist: depend on which particles are allowed to propagate in the ‘‘bulk bulk’’ of the δ -ED

ADD models:

(Arkani-Hamed, Dimopoulos, Dvali):

only gravity propagates in ED hierarchy problem taken care of by a large volume of ED space

M

_Pl²

= V

_δ

M

_D^2+δ

Volume of compactified

dimensions Gravity scale: fundamental scale

Derived quantity

ADD: only gravity can propagate in ED

Graviton

Our world:

3+1 dimensions

Gavition

≡

tower of Kaluza-Klein (KK) states

with mass spectrum M

_l

= l ^/R

^{(l = 0,1,2..)}

Separation between states:

O

^{(1/R) ~}

O

^{(10-4) eV}

Each couples to SM fields with strengths

1/M_Pl

KK like continuum spectrum Sum over all KK states  Interaction has strengths 1/M

_D

= O ^(TeV)

 may detect graviton effects at colliders

KK : in ED is quantification of energy (like wire vibration)

if looked at from 4-dimensions  tower of objects with different mass Collider signatures:

 Sub-Planckian: energy scale below M_D

 Trans-Planckian: energy scale above M_D

Sub-Planckian ^: ED effects observable at colliders (ADD)

Graviton escapes from our 3-dimensional world in extra dimensions

Exchange of virtual Gravitons in pp or p- antiproton collisions

resulting in 2 photons

Slight modification of SM rates Apparent energy non-conservation

in our 3-dimensional world

Recoil Kaluza-Klein Graviton

Our universe

Sub-Planckian (ADD): Experimental Searches

2 Parameters

:

_δ

(or n) .. Number of Extra Dimensions, M

_D

…. Fundamental scale

LEP ^{: }

Precision measurements: contribution to graviton loops suppressed

(M

_z

/M

_D

)

^δ+2

, for

δ

= 2: factor 10

^-4

 Direct searches: e

⁺

e

^-

 γ *  γ G :

Single photon + missing energy Lower limits: M_D ≈ 1 TeV (δ = 2), M_D ≈ 0.6 TeV (δ = 6)

LHC ^{: }

Virtual Graviton exchange: pp  l⁺l^- and pp  γ γ Deviation from SM predictions



Direct Graviton production: Graviton production: pp pp  q G : jet + missing E q G : jet + missing E_TT pp pp  γγ G : G : γγ + missing E + missing E_TT

95% CL reach on Gravity scale for

95% CL reach on Gravity scale for δδ = 3 = 3

Trans-Planckian (ADD): Energy scale above M

_D

Since fundamental Planck scale is at TeV  E

_CM

> Planck scale, possible particle scattering would show features of quantum gravity, because fundamental Planck

scale is where quantum gravity effects become strong

Behaviour of scattering when energy scale increases

particle scattering

E

_CM

string

scattering strings highly excited → string ball

black hole

BH: characterized by its mass, charge and angular momentum Production:

(R_s =Schwarzschild radius)

R_S parton

parton

M

²

= s ^

σ ~ πR_S² ~ 1 TeV ⁻² ~ 10⁻³⁸ m² ~ 100 pb

Impact parameter < R

_s

Decay: 30 - 50 SM particles

(each few hundred GeV)

of few TeV BH

First Studies of Black Hole Production at LHC by ATLAS and CMS

Simulated black hole event in the ATLAS detector

Challenges at LHC

Theory

Extra Dimensions ?

??

Experiments

LHC: E_CM

= 14 TeV, L = 10

³⁴

cm

^-2

s

^-1

High interaction rate: 40 MHz collision rate must be reduced to ~ 100 Hz