What have we learnt so far from the LHC? · 2011. 8. 26. · What have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.21. Models

What have we learnt so far from the LHC?

Georg Weiglein

DESY

Hamburg, 08 / 2011

Introduction: exploring the Terascale

What to expect?

Results up to now

Conclusions

What have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.1

Introduction: exploring the Terascale1 TeV ≈ 1000×mproton ⇔ 2× 10−19 m

meV keV

Cathode raytube Cyclotron

W, Z Higgs

W, Z Higgs

eV MeV GeV TeV

Atomic physics Particle physicsNuclear physics

LEP, SLCTevatron ILC, LHC

top SUSY

Extra Dimensions

Temperature / Energy

Inflation

BaryogenesisBBN

Neutrino

CMB

photonDecoupling Decoupling Decoupling

WIMP

10^−1210^−6110^610^1210^17

now

Lambda Matter Radiation dominated

Time (s)What have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.2

Particle accelerators: viewing the early Universe

Today’s universe is cold and empty: only the stable relics andleftovers of the big bang remainThe unstable particles have decayed away with time, and thesymmetries that shaped the early Universe have been brokenas it has cooled

⇒ Use particle accelerators to pump sufficient energy into apoint in space to re-create the short-lived particles anduncover the forces and symmetries that existed in theearliest Universe

⇒ Accelerators probe not only the structure of matterbut also the structure of space-time, i.e. the fabric of theUniverse itself


The Quantum Universe


What can we learn from exploring thenew territory of TeV-scale physics ?

How do elementary particles obtain the property of mass:what is the mechanism of electroweak symmetrybreaking? Is there a Higgs boson (or more than one)?

Do all the forces of nature arise from a single fundamentalinteraction?

Are there more than three dimensions of space?

Are space and time embedded into a “superspace”?

What is dark matter? Can it be produced in thelaboratory?

Are there new sources of CP-violation?Can they explain the asymmetry between matter andanti-matter in the Universe?

. . .What have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.5

What’s so special about the Higgs ?

The fundamental interactions of elementary particles aredescribed very successfully by quantum field theories thatfollow an underlying symmetry principle:“gauge invariance”

This fundamental symmetry principle requires that all theelementary particles and force carriers should bemassless

However: W , Z, top, bottom, . . . , electron are massive,have widely differing masses

How can elementary particles acquire mass without spoilingthe fundamental symmetries of nature?


The Higgs mechanism

Spontaneous symmetry breaking: the interaction obeys thesymmetry principle, but not the state of lowest energy

New field postulated that fills all of the space: the Higgs field

The state of the lowestenergy of the Higgs field(vacuum state) does not obeythe underlying symmetryprinciple (gauge invariance)

)V(|

Φ+ |0

Φ| ,|

|Φ +|

Φ0||

µ >02

µ<02

v/ 2

⇒ Spontaneous breaking of the gauge symmetryWhat have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.7

The Higgs field and the Higgs boson

Higgs mechanism: fundamental particles obtain their massesfrom interacting with the Higgs field

Higgs boson(s): field quantum of the Higgs field(like the photon is the quantum of the electromagnetic field)

The postulated Higgs boson is a scalar particle (spin 0)

Up to now no fundamental scalar particle has been observedin nature


The Higgs mechanism sounds like a rather bold

assumption to cure a theoretical / aesthetical problem

But: Our current description of the fundamental interactionsbreaks down at the TeV scaleWe know that there has to be new physics that is responsiblefor electroweak symmetry breakingThis new physics must manifest itself at the TeV scale⇒ LHC, future Linear Collider (LC)

Possible alternatives to the Higgs mechanism:

A new fundamental strong interaction (“strong electroweaksymmetry breaking”)

New dimensions of space (electroweak symmetrybreaking happens via boundary conditions for SM gaugebosons and fermions on “branes” in a higher-dimensionalspace)


How to find the Higgs (or more than one) ?

Heavy particle

⇒ need high-energy collider, E = mc2

Unstable:⇒ need to look for decay products

Comprehensive set of precision measurements andaccurate theory predictions will be needed to establish theHiggs mechanism and to determine the Higgs properties

⇒ One of the main goals for physics at the LHC and afuture Linear Collider


Higgs: last missing ingredient of the "Standard Model"

But: the Standard Model cannot be the ultimate theory

The Standard Model does not include gravity

⇒ breaks down at the latest at MPlanck ≈ 1019 GeV

“Hierarchy problem”: MPlanck/Mweak ≈ 1017

How can two so different scales coexist in nature?

Via quantum effects: physics at Mweak is affected byphysics at MPlanck

⇒ Instability of Mweak

⇒Would expect that all physics is driven up to thePlanck scale

Nature has found a way to prevent thisThe Standard Model provides no explanation


Hierarchy problem: how can the Planck scale beso much larger than the weak scale ?

⇒ Expect new physics to stabilise the hierarchy

Supersymmetry:Large corrections cancel out because of symmetryfermions ⇔ bosons

Extra dimensions of space:Fundamental Planck scale is ∼ TeV (large extra dimensions),hierarchy of scales is related to a “warp factor”(“Randall–Sundrum” scenarios)


Supersymmetry (SUSY)

Supersymmetry: fermion ←→ boson symmetry,leads to compensation of large quantum corrections


The Minimal Supersymmetric Standard Model(MSSM)

Superpartners for Standard Model particles:[u, d, c, s, t, b

]

L,R

[e, µ, τ

]

L,R

[νe,µ,τ

]

LSpin 1

2

[u, d, c, s, t, b

]

L,R

[e, µ, τ

]

L,R

[νe,µ,τ

]

LSpin 0

g W±, H±

︸︷︷︸γ, Z,H0

1 , H02

︸︷︷︸Spin 1 / Spin 0

g χ±

1,2 χ01,2,3,4 Spin

1

2

Two Higgs doublets, physical states: h0, H0, A0, H±

General parametrisation of possible SUSY-breaking terms⇒ free parameters, no prediction for SUSY mass scale

Hierarchy problem ⇒ expect observable effects at TeV scaleWhat have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.14

Supersymmetry (SUSY)

SUSY: unique possibility to connect space–time symmetry(Lorentz invariance) with internal symmetries (gaugeinvariance):

Unique extension of the Poincaré group of symmetries ofrelativistic quantum field theories in 3 + 1 dimensions

Local SUSY includes gravity, called “supergravity”

Lightest superpartner (LSP) is stable if “R parity” is conserved⇒ Candidate for cold dark matter in the Universe

Gauge coupling unification, MGUT ∼ 1016 GeV

neutrino masses: see-saw scale ∼ .01–.1MGUTWhat have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.15

How does SUSY breaking work ?

Exact SUSY ⇔ me = me, . . .⇒ SUSY can only be realised as a broken symmetry

MSSM: no particular SUSY breaking mechanism assumed,parameterisation of possible soft SUSY-breaking terms⇒ relations between dimensionless couplings unchanged⇒ cancellation of large quantum corrections preservedMost general case: 105 new parameters

Strong phenomenological constraints on flavour off-diagonaland CP-violating SUSY-breaking terms⇒ Good phenomenological description for universal

SUSY-breaking terms (≈ diagonal in flavour space)What have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.16

Simplest ansatz: the Constrained MSSM (CMSSM)

Assume universality at high energy scale (MGUT, MPl, . . . )renormalisation group running down to weak scalerequire correct value of MZ

⇒ CMSSM characterised by

m20, m1/2, A0, tanβ, sign µ

CMSSM has been the most widely studied SUSY scenarioup to nowCMSSM is in agreement with the experimental constraintsfrom electroweak precision observables (EWPO)+ flavour physics + cold dark matter density + . . .


CMSSM phenomenology

m0, m1/2, A0: GUT scale parameters

⇒ Spectra from renormalisation group running to weak scale

Lightest SUSY particle (LSP)is usually lightest neutralino

Gaugino masses run in sameway as gauge couplings⇒ gluino heavier than

charginos, neutralinos

“Typical” CMSSM scenario(SPS 1a benchmark scen.):

0

100

200

300

400

500

600

700

800

m [GeV]

lR

lLνl

τ1

τ2

χ0

1

χ0

2

χ0

3

χ0

4

χ±

1

χ±

2

uL, dRuR, dL

g

t1

t2

b1

b2

h0

H0, A0 H±


Radiative electroweak symmetry breaking

Universal boundary conditions at GUT scale,renormalisation group running down to weak scale

q~

l~

H

H

g~

W~

B~

large corrections fromtop-quark Yukawacoupling

⇒ m2Hu

driven tonegative values

⇒ ew symmetrybreaking

emerges naturally atscale ∼ 102 GeV for100 GeV <

∼ mt<∼ 200 GeV


SUSY-breaking scenarios

“Hidden sector”: −→ Visible sector:

SUSY breaking MSSM

“Gravity-mediated”: SUGRA“Gauge-mediated”: GMSB

“Anomaly-mediated”: AMSB“Gaugino-mediated”

. . .

SUGRA: mediating interactions are gravitational

GMSB: mediating interactions are ordinary electroweak andQCD gauge interactions

AMSB, Gaugino-mediation: SUSY breaking happens on adifferent brane in a higher-dimensional theory


Do we live in a meta-stable vacuum ?

Suppose we live in a SUSY-breaking meta-stable vacuum,while the global minimum has exact SUSY

Recent developments: meta-stable vacua arise as genericfeature of SUSY QCD with massive flavoursMeta-stable SUSY-breaking vacua are “generic” in localSUSY / string theory, can have cosmologically long life times[K. Intriligator, N. Seiberg, D. Shih ’06], . . .

⇒ Many new ideas — hope for experimental input!What have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.21

Models with extra dimensions of space

Small ExtraDimension4D spa etimeRKaluza-Klein Pi ture

4D BraneBrane-world Pi ture

Large ExtraDimensiongraviton

Hierarchy between MPlanck and Mweak is related to the volumeor the geometrical structure of additional dimensions of space

⇒ observable effects at the TeV scaleWhat have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.22

Why extra dimensions ?

String theories predict that there are actually 10 or 11dimensions of space-timeThe “extra” dimensions may be “compactified”, too small to bedetectable so far

To a tightrope walker, thetightrope is one-dimensional:he can only move forward orbackward

But to an ant, the rope has an extra dimension: the ant cantravel around the rope as well


Phenomenological consequences of extradimensions

The wave function of a free particle must be 2πR periodic

⇒ momentum is quantised⇒ Looks in 4-dim like a series of new, more massive partners

associated with each known particle: “Kaluza–Klein tower”What have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.24

Phenomenological consequences of extradimensions

We may be trapped on a (3 + 1)-dimensional brane in ahigher-dimensional space-time, while gravity can enter theextra dimensions

Extra dimensions could be large, even infinite

⇒ Could explain the apparent weakness of gravity in our4-dimensional world

⇒ At the LHC, gravitons could be emitted into the extradimensions

⇒ “missing energy” signals

If gravity is strong at the TeV scale, particle collisions at theLHC could form “mini black holes”


What to expect?Physics of electroweak symmetry breaking

Standard Model: a single parameter determines the wholeHiggs phenomenology: MH

Branching ratios of the SM Higgs:

⇒ dominant BRs:

MH<∼ 140 GeV:

H → bb

MH>∼ 140 GeV:

H → W+W−, ZZ


Production of a SM-like Higgs at the LHC

SM Higgs production at the LHC:

Dominant production processes:

gluon fusion: gg → H, weak boson fusion (WBF): qq → q′q′H

t

t

tg

g

H

q

q

q′

q′

W+

W−

H


Higgs physics beyond the SM

In the SM the same Higgs doublet is used “twice” to givemasses both to up-type and down-type fermions

⇒ extensions of the Higgs sector having (at least) twodoublets are quite “natural”

⇒Would result in several Higgs states

Many extended Higgs theories have over large part of theirparameter space a lightest Higgs scalar with properties verysimilar to those of the SM Higgs bosonExample: SUSY in the “decoupling limit”

But there is also the possibility that none of the Higgs bosonsis SM-like


Higgs physics in Supersymmetry

“Simplest” extension of the minimal Higgs sector:

Minimal Supersymmetric Standard Model (MSSM)

Two doublets to give masses to up-type and down-typefermions (extra symmetry forbids to use same doublet)

SUSY imposes relations between the parameters

⇒ Two parameters instead of one: tan β ≡ vu

vd, MA (or MH±)

⇒ Upper bound on lightest Higgs mass, Mh (FeynHiggs):[S. Heinemeyer, W. Hollik, G. W. ’99], [G. Degrassi, S. Heinemeyer, W. Hollik,P. Slavich, G. W. ’02]

Mh<∼ 130 GeV

Very rich phenomenologyWhat have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.29

MSSM with complex parameters:a very light SUSY Higgs ?

MSSM with CP-violating phases (CPX scenario):Light Higgs, h1: strongly suppressed h1V V couplingsSecond-lightest Higgs, h2, possibly within LEP reach (withreduced V V h2 coupling), h3 beyond LEP reachLarge BR(h2 → h1h1) ⇒ difficult final state

[LEP Higgs WG ’06]mt = 174.3 GeV

1

10

0 20 40 60 80 100 120 140

1

10

mH1 (GeV/c2)

tanβ

Excludedby LEP

TheoreticallyInaccessibleCPX

(b)

⇒ Light SUSY Higgs not ruled out!What have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.30

How to infer the underlying physics from theexperimental signatures ?

A Higgs or not a Higgs?

Fundamental or composite?

SM, MSSM or beyond?

Is there other new physics; what is it?

How does the observed new physics fit into the globalpicture (ew precision observables, flavour physics, . . . )?

. . .

⇒ Intense effort will be needed to identify the nature ofelectroweak symmetry breaking


What to expect?What is the scale of new physics?

EW precision data: Theory:MZ,MW, sin2 θlept

eff , . . . SM, MSSM, . . .

⇓Test of theory at quantum level: loop corrections

H

⇓Sensitivity to effects from unknown parameters: MH, Mt, . . .

Window to “new physics”What have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.32

Constraints on the SM Higgs from electroweakprecision data

Indirect constraint on MHSM, no direct search limits included in

the fit [LEPEWWG ’11]

0

1

2

3

4

5

6

10030 300

mH [GeV]

∆χ2

Excluded

∆αhad =∆α(5)

0.02750±0.00033

0.02749±0.00010

incl. low Q2 data

Theory uncertaintyJuly 2011 mLimit = 161 GeV

⇒ Preference for a light Higgs, MHSM< 161 GeV, 95% C.L.


Global fit in constrained SUSY model: indirectexperimental and cosmological constraints

SUSY search prospects:

Global χ2 fit in the CMSSM (m1/2, m0, A0 (GUT scale), tanβ,sign(µ) (weak scale))

Fit includes (MasterCode, Markov-chain Monte Carlo sampling):[O. Buchmueller, R. Cavanaugh, A. De Roeck, J. Ellis, H. Flacher, S. Heinemeyer,G. Isidori, K. Olive, P. Paradisi, F. Ronga, G. W. ’08]

Electroweak precision observables: MW, sin2 θeff , ΓZ, . . .

+ Cold dark matter (CDM) density (WMAP, . . . ),ΩCDM h2 = 0.1099± 0.0062

+ (g − 2)µ

+ BPO: BR(b→ sγ), BR(Bs → µ+µ−), BR(B → τν), . . .

+ Kaon decay data: BR(K → µν), . . .What have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.34

The anomalous magnetic moment of the muon:(g − 2)µ ≡ 2aµ

Experimental result for aµ vs. SM prediction (using e+e− datafor hadronic vacuum polarisation):

aexpµ − atheo

µ = (30.2± 8.8)× 10−10 : 3.4σ .

Better agreement between theory and experiment possible inmodels of physics beyond the SM

Example: one-loop contributions of superpartners of fermionsand gauge bosons

µ

γ

µχi

νµ

χi

µ

γ

µµa

χ0j

µb


Prediction for the density of cold dark matter(CDM) in the Universe

Cross sections for annihilation and co-annihilation processes

Cold Dark Matter density (WMAP, . . . ):ΩCDM h2 = 0.1099± 0.0062

⇒ Comparison yields constraints on new physicsWhat have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.36

Rare decay: Bs → µ+µ−

[LHCb Collaboration ’10]

⇒ High sensitivity to effects of new physicsWhat have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.37

Pre–LHC: Fit results for the CMSSMfrom precision data

Comparison: preferred region in the m0–m1/2 plane vs. CMS95% C.L. reach for 0.1, 1 fb−1 at 7 TeV[O. Buchmueller, R. Cavanaugh, A. De Roeck, J. Ellis, H. Flacher, S. Heinemeyer,G. Isidori, K. Olive, P. Paradisi, F. Ronga, G. W. ’10]

0 200 400 600 800 1000 1200 1400 1600 1800 20000

100

200

300

400

500

600

700

800

900

1000

LSPτ

0 200 400 600 800 1000 1200 1400 1600 1800 20000

100

200

300

400

500

600

700

800

900

1000

NO EWSB

1

95% C.L.

68% C.L.

parameter space

full CMSSM

CMS preliminary

μ > 0 = 0, 0 = 10, Aβtan

Hadronic search, 95% C.L. curves

=7 TeVs

L = 1000/pb

L = 100/pbCMS-NOTE-2010-008

~

]2 [GeV/c0M

]2

[G

eV

/c1

/2M

⇒ Best fit point was within the 95% C.L. reach with 1 fb−1


Indirect prediction for the Higgs mass in the SM and the

CMSSM / NUHM1 from precision data

χ2 fit for Mh, without imposing direct search limitSM CMSSM SM NUHM1

0

1

2

3

4

10030 300

mH [GeV]

2

Excluded

Δχ

0

1

2

3

4

10030 300

mH [GeV]

2Excluded

Δχ

MCMSSMh = 108± 6 GeV MNUHM1

h = 121+2−14 GeV

⇒ Accurate indirect prediction; Higgs “just around the corner”?What have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.39

Production of SUSY particles at the LHC

SUSY production cross sections at the LHC with 7 TeV:

10-3

10-2

10-1

1

10

100 200 300 400 500 600 700 800 900

χ2oχ1

+

νeνe*

t1t1*

qq

qq*

gg

qg

χ2og

χ2oqLO

maverage [GeV]

σtot[pb]: pp → SUSY √S = 7 TeV

Prospino2.1

⇒ Highest cross section for gluino and squarks of thefirst two generations

Squark and gluino couplings ∼ αs; cross sections mainlydetermined by mq,g, small residual model dependence


SUSY searches at the LHC

Dominated by production of coloured particles:gluino, squarks (mainly first two generations)

Very large mass reach in the searches forjets + missing energy⇒ gluino, squarks accessible up to 2–3 TeV at LHC (14 TeV)

Coloured particles are usually heavier than the colour-neutralones⇒ long decay chains possible; complicated final states

e.g.: g → qq → qqχ02 → qqτ τ → qqττ χ0

1

Many states produced at once, difficult to disentangleWhat have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.41

Results up to now

The LHC:proton–proton collisions at 7 TeV (now) and 14 TeV ( >

∼ 2014)


The Large Hadron Collider (LHC)

Proton–proton scattering at 7–14 TeV: composite objects ofquarks and gluons, bound together by strong interaction

p

g

g

p

⇒ Has opened up new a energy domaincomplicated scattering processes

109 scattering events/s at LHC design luminosity


The LHC physics programme at 7 TeV startedon March 30, 2010

Candidate for a W+ boson decaying into e+νe:

⇒ First steps: “rediscovery” of the Standard ModelWhat have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.44

Example: di–muon invariant mass distribution

[ATLAS Collaboration ’10]

LHC production of W , Z, top, . . . has been observedWhat have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.45

LHC luminosity: where do we stand?


SM Higgs search: latest results from ATLAS

Combined upper limit normalised to the SM expectation[ATLAS Collaboration ’11]

[GeV]Hm120 140 160 180 200 220 240

SM

σ/σ95

% C

L Li

mit

on

-110

1

10

ObservedExpected

σ 1 ±σ 2 ±

ATLAS Preliminary

-1 Ldt = 1.0-2.3 fb∫ = 7 TeVs

CLs Limits


SM Higgs search: latest results from ATLAS

Combined upper limit normalised to the SM expectation (left)and observed result vs. expectation for a SM Higgs signal(right) [ATLAS Collaboration ’11]

[GeV]Hm200 300 400 500 600

SM

σ/σ95

% C

L Li

mit

on

-110

1

10

ObservedExpected

σ 1 ±σ 2 ±

ATLAS Preliminary

-1 Ldt = 1.0-2.3 fb∫ = 7 TeVs

CLs Limits

[GeV]Hm100 200 300 400 500 600

0p

-710

-610

-510

-410

-310

-210

-110

1

ObservedExpected

σ2

σ3

σ4

σ5

-1 Ldt = 1.0-2.3 fb∫ = 7 TeVs

ATLAS Preliminary


SM Higgs search: latest results from CMS

Combined confidence limit vs. expectation for a SM Higgssignal [CMS Collaboration ’11]


SM Higgs search: Tevatron results, CDF + D0

CDF + D0 combined upper limit normalised to the SMexpectation [CDF and D0 Collaborations ’11]

1

10

100 110 120 130 140 150 160 170 180 190 200

1

10

mH(GeV/c2)

95%

CL

Lim

it/S

M

Tevatron Run II Preliminary, L ≤ 8.6 fb-1

ExpectedObserved±1σ Expected±2σ Expected

LEP Exclusion TevatronExclusion

SM=1

Tevatron Exclusion July 17, 2011


Status of SM Higgs searches

LHC excludes (at least at 90% C.L.) the range of145 GeV <

∼MHSM

<∼ 460 GeV

⇒ Results from direct searches are in agreement withindirect constraints from electroweak precision data

LEP exclusion: MHSM> 114.4 GeV, 95% C.L.

Slight excess in the low-mass region, MHSM≈ 130 GeV,

observed by ATLAS, CMS and in Tevatron combination

Compatible with SUSY prediction

⇒ More data needed to clarify the situationWhat have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.51

Search for the heavy SUSY Higgs bosons H, A:limits in the MA–tan β plane

[ATLAS Collaboration ’11] [CMS Collaboration ’11]

[GeV]Am

100 150 200 250 300 350 400 450

βta

n

0

10

20

30

40

50

60All channels

-1 Ldt = 1.06 fb∫ = 7 TeV, s

>0µ, maxhm

ATLAS Preliminary

Observed CLsExpected CLs

σ 1±σ 2±

LEP observed-1ATLAS 36 pb expected-1ATLAS 36 pb

⇒ High sensitivity for large tan β and relatively low MA


SUSY search results for the CMSSM[ATLAS Collaboration ’11] [CMS Collaboration ’11]

[GeV]0m500 1000 1500 2000 2500

[GeV

]1/

2m

150

200

250

300

350

400

450

500

550

600

(600)g~

(800)g~

(1000)g~

(600)

q~

(1000)

q~

(1400)q ~

>0µ= 0, 0

= 10, AβMSUGRA/CMSSM: tan

=7 TeVs, -1 = 165 pbintL

0 lepton 2011 combined

PreliminaryATLAS0 lepton 2011 combined

1

± χ∼LEP 2

-1<0, 2.1 fbµ=3, β, tanq~, g~D0

-1<0, 2 fbµ=5, β, tanq~,g~CDF

Observed 95% C.L. limit

Median expected limit

Observed 95 % C.L. limitsCL

Median expected limit sCL

Reference point

2010 data PCL 95% C.L. limit

CMS 2010 Razor,Jets/MHT

⇒ High sensitivity from search for jets + missing energyPrevious best-fit point is excludedCMSSM starts to get under pressure


Interpretation of SUSY search resultin "simplified model"

"Simplified model": squarks of first two generations, gluino +massless neutralino (LSP), all other SUSY particles heavy


gluino mass [GeV]0 250 500 750 1000 1250 1500 1750 2000

squa

rk m

ass

[GeV

]

0

250

500

750

1000

1250

1500

1750

2000

= 10 pbSUSYσ

= 1 pbSUSYσ

= 0.1 pbSUSYσ

)1

0χ∼Squark-gluino-neutralino model (massless

=7 TeVs, -1 = 165 pbintL

0 lepton 2011 combined PreliminaryATLAS

q~LEP 2 Tevatron, Run ID0, Run IICDF, Run II

CMSSMMSUGRA /

Observed 95% C.L. limit

Median expected limit Observed 95% C.L. limitsCL

Median expected limitsCL

2010 data PCL 95% C.L. limit


Status of SUSY searches

Search for jets (+ leptons) + missing energy

⇒ Bounds on gluino and squarks of first two generationsof O( TeV)

⇒ The constrained scenario CMSSM starts to get undersome tension: direct search limits vs. (g − 2)µ

Limited sensitivity to 3rd generation squarksHardly any LHC constraints on colour neutral SUSYparticles up to now


Search for the rare decay Bs → µ+µ−


BR(Bs → µ+µ−): combined resultfrom LHCb and CMS

⇒ Compatible with SM prediction (so far)What have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.57

Search for dilepton resonances: ATLAS



Search for dilepton resonances: CMS[CMS Collaboration ’11]

⇒ Limits up to 1.9 TeVWhat have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.59

ConclusionsLHC has started the exploration of the new territory ofTeV-scale physics

No discoveries yet

Heavy SM Higgs is disfavoured, in agreement withconstraints from electroweak precision physicsSlight excess in the low-mass region⇒ Closing in on the SM Higgs

BSM searches: limits on coloured states of new physics,heavy resonances, . . .SUSY: limits on gluino and 1st and 2nd gen. squarks⇒ Tension building up for CMSSM-like scenariosLittle sensitivity so far to other parts of a possible SUSYspectrum (similarly for other kinds of new physics)

Stay tuned — the party has just begun!What have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.60

Documents

What have we learnt so far from the LHC? · 2011. 8. 26. · What have we learnt so far from the LHC?, Georg Weiglein, DESY Summer Student Lecture, Hamburg, 08 / 2011 – p.21. Models