Martin zur Nedden, HU Berlin 1 Physics at the LHC, Academic Training DESY Zeuthen June 2007 Physics...

Martin zur Nedden, HU Berlin 1Physics at the LHC, Academic Training DESY Zeuthen June 2007

Physics at the LHC

Academic Training, Part 4:Higgs Search and Beyond Standard Model

Dr. Sven Moch, DESY Zeuthen (Theory)

Dr. Martin zur Nedden, HU Berlin (Experiment)

June 2007 DESY Zeuthen, based on a lecture in WS 06/07 at Humboldt University Berlin


Plan

● LHC: Experimental Overview and

Standard Model Physics (Part 3)– Monday, June 11, 2007, 9.00 - 10.30

● LHC: Higgs Searches and

Physics beyon the Standard Model (Part 4)– Thursday, June 14, 2007, 10.00 – 11.30


Contents

● Discoveries at the energy frontier● Overview: LHC and its experiments● Hadron-Hadron interactions● Jets: fragmentation, signature and algorithms● Standard model channels at LHC● top-physics and heavy flavor reconstruction● Higgs: event topologies and search strategies● SUSY: searches in the MSSM


Higgs Searches

● Yukava-coupling, masses of fermions● experimental evidence:

– production

– decays and search channels

● results from TEVATRON● searches at LHC


Higgs Mechanism in the Standard Model

• Doublet Φ of scalar Higgs fields H(x) exists due to the massive gauge field W,Z and the massless γ

• Complex fields Φ+ , Φ0

4 real components Φ1, …Φ4, produce mass in symmetry breaking due to self-interaction

• Goldstone/Higgs-mechanism: 3 components absorbed in the longitudinal

polarization of the massive 3 Wi-bosons• 1 physical state H remains • coupling to mass with gffH

• No prediction of Higgs mass by SM

00

2

1H

HgHff


Yukava coupling, Mass of Fermions

),,( 0

0L

eRRLe eeeeGL

)(22)(

0

2

1xheeee

Geeeev

GL

xhv LRRLe

LRRLe

)(2

xheev

meemL

vGm e

ee

e

mnew term in Lagrangien needed: excluded due to gauge invariance

eR(T=0, Y=-2)

eL(T=1/2, Y=-1)

h0 (T=1/2, Y=1)

igme/(2MW)igMW

W

W

(Singlet in I,Y)

choose:

Coupling to the higgs field

h0


Consequences from Yukava-Coupling

● electron gets mass● neutrino rest massles● strength of coupling proportional to the mass of the

fermion● mass is not predicted by the theory● masses for quarks:

– same formalism as for leptons

– difference: both quarks within the doublet have mass● new Higgs Doublet Φc


Higgs-Production in Hadron-Hadron Interactions

gluon-gluon interaction (LHC/TEVATRON):big production cross section,decay in 2 gammas

gluon-gluon interaction (LHC/TEVATRON):production cross section very small

quark-antiquark interaction (TEVATRON):big production cross section at 2TeV (TEVATRON)decay: W,Z leptons

quark-quark interaction (LHC):big production cross section at 14TeV (LHC)decay: W,Z 2 γ (or leptons)


Decay Width of Different Higgs Channesl

2

3

2

22

)4

1(24

)(H

fHfFc M

mMmGNffH

)124

1()41(28

)(4

4

2

22

1

2

23

H

W

H

W

H

WHF

M

M

M

M

M

MMGWWH

)124

1()4

1(216

)(4

4

2

22

1

2

2

2

2300

H

Z

H

Z

H

Z

Z

WHF

M

M

M

M

M

M

M

MMGZZH

2

2

2

2

22

3

32

)()(32128

)(H

WW

H

qqq

q

HF

M

MI

M

mIe

MGH

Calculations in the standard model:


Higgs – Decay Channels

(H VV) ~ GF M3H

(H γγ) ~ α2 GF M3H

(H ff) ~ GF m2f MH


Possible Higgs Decays / coupling constants

ffH 0

WWH 0

/0 ggH

WW

f

Hff M

emg

sin2

W

WWWH

eMg

sin

WW

ZZZH

eMg

cossin

22

1

2

2

)2(228 WFWWHF

W

MGgG

M

g


Higgs Search Strategies

bbHZpp *

Good channel for TEVATRON:

M(H) > 135 GeV: H WWM(H) < 135 GeV: H bb

gg-fusion dominant at all Higgs masses, not to separate from BG at M < 135 GeV

qq: Higgs-Strahlung: small contribution, but god to separate from BG


Cross Sections at TEVATRON


Higgs Search at TEVATRON, upper Limit

signal: 2 b-Jet + MET + 2 leptons

if M(H) > 135 GeV


Upper Limit for Higgs production at TEVATRON

if M(H) < 135 GeV


Higgs Decay Channels: Branching Ratios


Higgs Decay in the Standard Modell

fermions

bosons

decay width branching ratio


Higgs Cross Sections at LHC

gluon-gluon fusion

vector boson fusion


Higgs: Signal to background ratio at LHC

for M(Higgs) = 150 GeV:

S/B < 10-10


Higgs to 2 Z and 4 Leptons

CMS TDR

Very clean an good measurabe event signature:4 high pT leptons, 2 invariant masses at MZ


Gluon-Gluon Fusion to 4 Leptonen (Atlas/LHC)

Atlas TDR

invariant masse (ZZ 4 l)

Background, not todistinguish from Higgs-Signal:qq ZZ 4 leptons


Higgs to 2 Gamma

CMS

also very clean signature, but small cross section:2 high pT isolated EMC-clusters


Gluon/Gluon Fusion to 2 Gamma (Atlas/LHC)

ATLAS TDR

Background:Not reducable: pp γγXReducable: pp γJγJ


Vektor-Boson Fusion: Decay to 2 W-Bosons

H WW e

Atlas TDRH WW l l υ υ (l υ qq )

Signature:Jets + 2 high pT leptons + MET

No mass peak (MET from neutrino), calculate the transverse mass

Background:tt, Wt, WWJJ production


Higgs to 2 Tau

H ττ e :

H ττ l l + 4ν (l +J +3ν)

Atlas TDR

2 high pT leptons, big MET

Mass reconstruction possible, even with high MET

Background:Zjj , tt


Higgs Discovery potential of LHC/ATLAS

Dependency on Higgs mass and decay channel


Discovery potential of ATLAS/LHC

Dependency of Higgs-mass and Luminosity


SUper SYmmetry

● “Beyond the Standart Model”● introduction into SUper SYmmetry● Minimal Super Symmetric extension of the

standard Model (MSSM)● super symmetric interactions● SUSY breaking● particle spectra of SUSY (phenomenology)● SUSY searches


Global Fit of Standard Model Parameter


Weinberg Angle and Higgs-Masse


Standard Model Symmetry

• SM describes strong and electroweak interactions, L/R asymmetry• Based on symmetries and gauge invariance• All forces propagated by exchange of gauge fields (local gauge fields)

YLC USUSU )1()2()3( Gauge-Bosons (Spin = 1):

gluons Gaμ SU(3) (8,1,0)

vector bosons Wiμ SU(2) (1,3,0)

abelian boson Bμ U(1) (1,1,0)

Fermions Spin = ½:

quarks [Uiα,Di

α]L (3,2,1/3)quarks [Ui

α]R (3,1,4/3)quarks [Di

α]R (3,1,-2/3)

leptons [Lα]L (1,2,-1)leptons [e]R (1,1,-2)

Higgs (Spin = 0):

H-Doublet [H0,H-] (1,2,-1)

Masses of quarks, leptons and vectorbosons by spontanous symmetry breaking


Motivation for Super Symmetry

Fermion ↔ Boson Symmetry

basic idea: unification of all forces, no difference between fermions (matter) and bosons (forces)

generator of the SUSY algebra: Q|boson> = |fermion> Q|fermion> = |boson>

Difference in spin = ½, doubling of the number of particles

SUSY transformation: δ|b> = ε|f> (anti-) kommutator relations {f,f} =0, [b,b] = 0,

{ε,ε} = 0 : SUSY generators are fermionic

Q has spin = ½ , may change the helicity 2-component spinor super symmetric algebra: connection of particles with different spins


electron

selectron

quark

squark

photon

photino

Unification ofUnification ofbosons withbosons with fermionsfermions

forces withforces with mattermatter

fermiosfermios

bosonsbosons

bosonsbosons

fermionsfermions

Super symmetric Partners


Minimal Super Symmetric Model (MSSM)

Most simple case: N=1 generators 2 super multiplets:

NDoF (bosons) = NDoF(fermions)

1. chiral super multiplet [Φ , Ψ] (spin 0, ½), fermions: 2 scalars,

Weyl-spinor with helicity, L/R

2. vector multiplet [λ , A] (spin ½, 1), bosons: gauge boson,

massless spin ½ fermion

● each fundamental particle has to occur in a super multiplet

● each SM particle has a SUSY-partner, Δs = ½ (minimal number of new particles)

● fermions in the vector multiplet transforms like gauge bosons (same for L/R)

● chiral multiplet contains all fermions, also with different transformation behaviour

● unbroken super symmetry: all masses were the same obviously not the case……

SUSY must be (weakly) broken, big masses of super symmetric partners

● More than 100 new parameters for the theory !?


Extended Higgs Model in MSSM

tand

u

H

H

22'2

222

)174(2

GeVgg

MHH Zdu

2 Higgs Dublets needed, to give all particles mass

Complex fields 8 degrees of freedom 3 absorbed in the longitudinal components of W- and Z-bosons 5 higgs bosons remains, 3 are neutral

h0 : light Higgs, scalar H0 : heavy Higgs, scalar A0 : neutral Higgs, pseudo-scalar, PC-odd H+/H- : charged Higgs, scalar

h0/H0 mixing states of Re(Hu

0) and Re(Hd0),

Mixing angle α

A0 mixing state ofRe(Hu

0) and Re(Hd0),

Mixing angle tanβ

H+/H- mixing state ofHu

+ and Hd-,

Mixing angle tanβ

222AWHmMm 2cos4

2

1 22222222, ZAZAZAhH MmMmMmm

new parameter

For the masses follows:


Higgs Masses in MSSM

● Higgs masses depends on 2 parameters: tan β and mA :

– tan β 1 : mh = 0 , mH2 = MZ

2 + mA2

– tan β ∞: mh = min(MZ, mA), mH = max(MZ,mA)

– Mass terms for A0, H0 and H+/H- could be very big!

– If mA big: mA ~ mH ~ m H+/-

– Mass of h0 is limited: 0 < mh < |cos2β|MZ

mh < mA < mH

mH > MZ, m H+/- > MW

– Radiative corrections important for mh (enlarges the mass)

– mh0 < 150 GeV upper limit for MSSM

– mh0 < 190 GeV limit for SUSY


MSSM Higgs Masses

All Higgs masses are fixed relative to 2 parameters:


Cancelation of Quantum corrections in SUSY Models


Supersymmetric Particles

Chargino :

(partner of W)

Neutralino :

(partner of Z, g)

Smuon :

(partner of muon)


Super Partners

● qL, qR, lL, lR squarks, sleptons (spin = 0)

● Gauge bosons g, W, B (gluino, Wino, Bino) = gauginos

● SM: coupling of W0/B0 to Z0/γ Zino, Photino

● Higgs (scalar) 2 Higgsinos (chiral super multiplet)

● chiral super multiplet: left handed particles only

● gauge interaction the same for squarks/sleptons and quarks/leptons

● unification with gravity: Graviton Gravitino

● neutral fermionic partners Wino/Bino have the same quantum numbers as the super symmetric Higgs partners: mixing to 4 neutralinos χ0

i (i=1..4) :

the lightest neutralino is the LSP (if R-parity is conserved)

● charged Higgsinos: mixing to charginos χ+/-j, (j=1,2)


SUSY Interactions (R-Parity conserved)

R-parity: +1 for “normal particles, -1 for super symmetric partners

Feynman graphs:

replace at any SM-vertex(3 or 4 particle interaction)two legs by the correspondingsuper symmetric partners

The coupling constants remains the same as in SM (strong or electroweak)


MSUGRA - Parameters

● m0 : universal scalar mass at GUT scale

● m½ : universal gaugino mass at GUT scale

● tan β : ratio of Higgs vacuum expectation value

● A0 : universal s-fermion mass mixing parameter

● sgn μ: sing of Higgsino mass parameter ● M(SUSY) < 1 TeV for LSP● important limits from LEP and TEVATRON


MSUGRA Masses


MSUGA Szenarios 1


MSUGRA Szenarios 2


SUSY at Hadron-Colliders

search strategy: Big contribution from standard model QCD-background (Jets) look for high pT leptons and MET

- squarks and gluinos: MET (strong interaction)- neutralinos and charginos: MET and high pT leptons (electro weak interaction)


Squark und Gluino Searches at TEVATRON

production:

decay:

Search for Jets und ETmiss


Result: Upper Limits (exclusions limits)


Search for Neutralinos and Charginos

01

01

021

~~~~~ leepp

01

01

~~ le

No improved SUSY limit foundby TEVATRON up to now


Recostruction of SUSY Particles

Neutralino 2 Sbottom Gluino

CMS MC analysisM = 595 GeV

M = 510 GeV

M = 174 GeV

M = 150 GeV

M = 96 GeV

edge = 78.9 +/- 2.1 GeV M = 499.4 +/- 6.6 GeV M = 585.1 +/- 11.1 GeV


SUSY in R-Parity violating Processes

neutralino (LSP) unstable, no longer a dark matter candidate lepton / and baryon number conservation violated much more possible decay channels ….

L - violation B - violationL - violation


Neutralino in R-Parity violating Decays

production:

decay:

Evidence: 3 charged leptons in FS


Search at Tevatron (Neutralino decay)

production:

decay:

Evidence: 3 charged leptons in FS

Result from D0, TEVATRON:upper limit


Masse of the lightest MSSM-Higgs

Mass of the lightestHiggs as a functionof MA und tan(ß) from 1.6 to 15


Supersymmetric Higgs


Search for the neutral MSSM Higgs

Searches at TEVATON: using multi – jet events


Di-Jet Mass (D0 / Tevatron) MSSM Higgs

Search for overshoot in the invariant mass distribution of the two jets with the highest pT

At least 3 b-flavoured jetare requested per event

BG: multi jet production


Upper Limit for the MSSM-Higgs Mass

based on di-Jet events


Search for the MSSM charged Higgs

Search for MET + J + X:

Direct production in weak IA,compeditiv to t Wb


MSSM – Higgs Search at LHC

All region is coverd…


SUSY Mass Spectra

Martin zur Nedden, HU Berlin 1 Physics at the LHC, Academic Training DESY Zeuthen June 2007 Physics...

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