atlas status and results michael kobel dresden university of technology on behalf of the atlas...

ATLASStatus and Results

Michael Kobel

Dresden University of Technologyon behalf of the ATLAS Collaboration

Fakultät Mathematik und Naturwissenschaften, Fachrichtung Physik

8th VIENNA CENTRAL EUROPEAN SEMINAR 25.November 2011

Michael Kobel

The big picture

LHC LEPParticle-accelerator

s:

History of physicsback to the Big Bang

Recreate processes between elementary particles having happened about 10-12 s after the Big Bang

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Michael Kobel

Why?Vienna, 25.11.2011 3 of 47

Standard Model: simple, elegant and amazingly successful fundamental fermions

come in certain representationsw.r.t. the 3 Symmetry Groups

define their charge eigenvaluesand sensitivity to interactions

3 types of charges generate3 Symmetry Groups:• SU(3)C Ä SU(2)L Ä U(1)Y

local Gauge Invariance requires presence of interactions in Lfully predicting all their properties

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2

1300

173000

590

4200

0,5

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0,0000000010,000000009

0,00000005

1E-121E-111E-101E-091E-081E-07

0,0000010,00001

0,00010,001

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1001000

10000100000

1000000

0 1 2 3 4

family number

ma

ss

(M

eV

/c²)

Up Type

Down Type

Lepton +/-

Neutrino

Michael Kobel

can emerge only after spontaneous symmetry breaking• was this caused by a Higgs field ~ 10-11 sec after Big Bang ?

Neutrino : Top = Sand Corn : Ocean Liner ~ 10-13

• How can a mass mechnism create such a huge range ?

Is the top quark special?

?

3x105 2x1013

The masses of the building blocks

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Michael Kobel

Particle masses not only of theoretical importance!

Size and binding energy of matter (us!) depend on me

• Binding energy (Atoms, Molecules) increases with me

• Size of bound states (Atoms, Molecules) falls with me

Stability of nucleons i.e. p-n mass differencedepends on delicate balance between• Strong force• Electromagnetic Force• Mass differences md - mu , md – me

The universe would have evolved differently with different masses

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actual cosmology

lower d-mass lower e-mass

lower W-mass( www.tricklabor.com/en/portfolio/what-if-particle-masses )

Michael Kobel

Most prominent goals of the LHC

Further scrutinize the Standard Model• Are there indeed only 3 families? Why?• Is the top quark just a normal quark?

Find symmetry breaking mechanism at the Origin of Mass• LHC is exactly at the right energy ~ TeV (10-12 sec)!• Something MUST happen!

SM Higgs mechanism will either be detected or excluded If excluded, another mechanism should be found

Are there additional symmetries?• Supersymmetry between Fermions and Bosons?• Extra Gauge symmetries (Z´, W´, …)

Any other expected or unexpected New Physics?• Even exotic…

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Michael KobelVienna, 25.11.2011 8 of 47

LHC: Cross-sections and Luminosity

Story of success:• 2010:

L ~ 1031cm−2s−1 òLdt ~ 0.04 fb−1

• 2011: L = 1-3 x 1033cm−2s−1 òLdt = 5 fb−1

• 2012: L = 3-5 x 1033cm−2s−1 ? òLdt = 10 fb−1 ?

• ³ 2015: L ³ 1034cm−2s−1 ? òLdt ³ 100 fb−1 per year ?

For L = 1033cm−2s−1

Michael Kobel

LHC: performance 2011

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°ATLASCMS

° ° LHC-b

° ALICE

Michael Kobel

ATLAS:

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Michael Kobel

ATLAS Performance: pT , Et

miss, … understood over many orders of magnitide

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Michael Kobel

Strategy to reach physics goals

2010 • Understand an calibrate detector• „Rediscover“ Standard Model (SM)

2011 • Precise understanding of SM at high energies

Influence of parton density function in p Distribution of extra jets in SM processes Background to searches

• New Physics Discover, if lucky Else, restrict allowed regions

2012• Closing in on the mass mechanism

(Higgs?)• … and maybe more

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Michael Kobel

Parton density functions (pdf) (ignoring renormalization and factorization scales)

ij

ijji dxdxppxfxf 212121 ),(ˆ)()(

Inner Structure of Protons

Interaction of Partons

Constituent of Proton =Parton Valence Quark uv, dv

Gluon g Sea Quarks

PROTON MAINLY CONSISTS OF 2u + 1d VALENCE QUARKS AND *MANY* GLUONS

Parton Density Functions

Hard Parton-Parton Cross Sections

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Michael Kobel

STANDARD MODEL MEASUREMENTS

1. W/Z + Jets2. Di-Boson Production (WW,ZW,ZZ)

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W and Z cross-sectionshttp://arxiv.org/abs/1109.5141 (27.9.11)

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Agree impressively well w/ predictions No distinction between pdfs possible

• Lumi uncertainty: 3.4%• Other Syst uncertainties: ~ 1% • Stat uncertainties 2010: 0.2%(W)-0.6%(Z)

W and Z Bosons• Large x-sections*BR of 1-10 nb (~ 1-10 /s)• can be reconstructed with extremely high purity in both e and µ final state

n Zµµ

W charge asymmetryATLAS-CONF-2011-129 (22.8.11)

Only valence quarks and gluons: q+g W+X g+g W+X

W+

W-

Charge asymmetry

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01111

31

1212

WWWW##

##

Sensitive test for parton density function (pdf) models h-dependent mix between contributing processes (plus sea quarks):

• dependence on parton distributions visible as function on hℓ

• Very forward hℓ : sign inversion due to weak parity violation (ℓL- preferred)

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ℓ

W+Jets ATLAS-CONF-2011-060 (12.4.11)

W µn (en similar)

Selection:• Exactly one charged lepton• Mt = Ö[2pt

lepptn(1-cosDf)] > 30 GeV

Background:• QCD from Et template fits to data

• Other background from simulation

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Berends-Giele scaling:• Berends, Giele, Kuijf, Kleiss,

Stirling, PLB 224, 237 (1989)• Adding one more jet reduces

x-section by constant factor, i.e.(s ³N jets) / (s ³N-1 jets) =const

• Has NLO corrections and depends on jet definition

MC models:• ALPGEN and SHERPA:

LO ME for multipartonic states• MCFM:

NLO pQCD up to Njets = 2LO for Njets = 3

• Blackhat-SHERPANLO pQCD up to Njets = 3LO for Njets = 4

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Z+Jets: No structures in Jet-Jet Massesarxiv.org/abs/1111.2690 (11.11.11)

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Low pt(Z) most |pt|in JetsDfjj ~ pneededfor balance

Well reproducedby simulations

Z

W+b and Z+b cross-sectionshttp://arxiv.org/abs/1109.1403, http://arxiv.org/abs/1109.1470

~ 1/100 of alljets expectedto be b-jets

Crucial for• b-pdfs• Background

to searches Template fits to

• Mvertex, MWb

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Z+b: Fraction of b-jets / all jets:• agree well

with simulations W+b

• Somewhatlarger thanexpected

Di-Boson Productions (ZZ:WZ:WW ~ 1:2:4)

Candidate event for ZZ ee µµ

Aims:• SM test, limits on anomalous triple gauge couplings (TGC)• Understand ZZ and WW background for Higgs searches

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arXiv:1110.5016v1(ZZ), CERN-PH-EP-2011-184 (WZ), ATLAS-CONF-2011-110 (WW)

Di-Boson Production: ZZarXiv:1110.5016v1(ZZ) (23.10.11)

1 fb-1 of 2011 data:• selection in eeee,eeµµ,µµµµ• nearly background-free

Non- SM contributions:• Neutral TGC

f4g,Z : CP-violating

f5g,Z : CP-conserving

• Would introduce excess at high MZZ and pt

Z

• Unitarity reinstalled by

Limits improve over LEP and TeVatron• BSM physics predict typ. O(10-2 – 10-3)• SM loop contribution O(10-4 )

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i

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SM:

Michael Kobel

Charged triple gauge couplings WWg WWZ

W

W

gW

W

Z

general WWg and WWZinteraction: 14 parameters

electric quadrupole moment

magnetic dipole moment

1

2 WW m

e

2

WW m

eQ

applying C and P invariance& low-energy constraints: 3 parameters left

relation with static W properties:

SM values

ΖW2Ζ

1Ζ

Ζ1

1),(θtang

with:SU(2)custodialbyrelated

01,g1,

Deformation

Average W radius

WeW

W mR

2

1

WeW

W Qm

D

45

245

1

relation with W substructure:

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Di-Boson Production: WW and WZATLAS-CONF-2011-110, CERN-PH-EP-2011-184 (WZ) (23.11.11)

1 fb-1 of 2011 data:• All lept.channels• Good agreement

with SM prediction

Total cross-sections:• WW (SM: 46±3 pb)

• WZ (SM: 17±1 pb)

Anomal.TGC limits • esp. good for lZ• Approaching

TeVatron sensitivity

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WW WZ

Michael Kobel

TOP PHYSICS

1. Cross-sections2. Mass3. FCNC

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From: R. di Sipio, LC11, Sept. 11

tt and single t cross-sectionsATLAS-CONF-2011-108 (20.7.11), ATLAS-CONF-2011-101 (20.7.11.)ATLAS-CONF-2011-100 (20.7.11), ATLAS-CONF-2011-035 (20.3.11.)

Single-top t-channel• Sensitive to FCNC (qt) and Vtb

• Cut-based selection (consist. w/ NN-selection) ATLAS: stq = 90±9+31

-20(exp) +28-19(gen) pb

Theory: stq = 65±3 pb

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tt cross-section combination of• Single lepton, ℓ+jets (35 pb-1, likelihood)• Di-lepton (700 pb-1, cut-based)

• Measurement as precise as theory: ATLAS: stt = 176+16

-13 pb

Theory: stt = 165+11-16 pb

top massATLAS-CONF-2011-120 (20.8.11)

Measured in ℓ+jets channel • ≥ 4 jets with ≥ 1 b-tag• jjb combination w/ highest pT defines mt

reco

• In-situ Jet Scaling Factor JSF from mWreco

2d (mtreco,JSF) template analysis resulting in

• JSF(e)=0.996±0.012, JSF(µ)=0.987±0.008• mt

reco =175.9±0.9±2.7 GeV

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t Zq flavor changing neutral currentATLAS-CONF-2011-154 (11.11.11)

ATLAS prelim. : t qZ < 11x10-3 at 95% CL (best to date)

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SM: only top decays: t qW, FCNC loops in SM ~ 10-12 - 14

• BSM physics: FCNC up to O(10-4 ) possible• Best 95% CL limits so far:

t qg HERA: < 6 x 10-3

t qg TeVatron: < 0.2 x 10-3 (u), < 4 x 10-3 (c)

t qZ TeVatron: < 32 x 10-3

ATLAS search for t qZ (q=c+u) with 0.7 fb-1 in 2011:• Final state Zq Wb -> ℓℓq ℓnb • main background: Dibosons ZW, ZZ

ETmiss mℓℓ Njets

Michael Kobel

SM HIGGS SEARCHES

1. ZZ2. WW

3. gg

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Michael Kobel

Discover Higgs field by Higgs Boson production• Higgs Boson ~ excitation of Higgs field

(Rather like a vortex ~ excitation of air) • Need to move massive

particles with high E through mediumto create excitations

Higgs decays predicted• In SM just depend

on unknown MH

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SM Higgs Boson production and decay

Copyright: DLR, Köln

H ZZATLAS-CONF-2011-148 (22.10.11) and -150 (11.11.11), 2.05 fb-1

ZZ: most sensitive channel above mH > 200 GeV• llnn subchannel (most sensitive above 275 GeV)

Discriminant: transverse mass

exclusion range310 GeV<mH<470GeV

• llqq subchannel Discriminant: lljj mass

Cross-section limitssignificantly contribute in limit combination

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HZZ 4 leptonsarxiv.org/abs/1109.5945 (27.9.11)

„Golden channel“ (virtually no background, other than SM ZZ) Most sensitive of all channels for 200 GeV<mH<275 GeV

2nd most sensitive (after WW) for 130 GeV<mH<200 GeV

(Near)exclusion at 95% CLfrom 191-200GeV and 214-224GeV

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H WWATLAS-CONF-2011-134, 24.8.2011

Most sensitive SM Higgs decay channel in range [120;200] GeV Most promising final state: ℓ+nℓ-n, ℓ =(e,µ) Essential preselection cuts:

• > 40(ℓℓ) / 25(eµ)GeV with Df = Ð(ETmiss, ℓ or jet)

• Njets = 0 or 1

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Kinematic separation

Spin correlation: • Leptons from Higgs tend to be close in F:

Further cuts• b-Jet veto, Z tt veto (1-jet)• pT

ℓℓ(0-jet), pTtot(1-jet) > 30 GeV

• 10-15GeV< mℓℓ <50-65GeV (dep. on ℓℓ,mH)

• DFℓℓ < 1.3-1.8 (dep. on mH)

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HHμ+

ν

W-

W+

e-

ν

W-

W+

0-jet

1-jet

DFℓℓ

WW-Results from ATLAS (and LHC) ATLAS-CONF-2011-157, CMS PAS HIG-11-023, 18.11.11

Final cut (mH-dep.)• 0.6-0.75mH< MT <mH

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ATLAS Significance ATLAS Limit

LHC Limit (WW)

H ggarxiv.org/abs/1108.5895 (30.8.11, 1.08 fb-1)

Most sensitive channel for mH < 120 GeV

2nd most sensitive for 120 < mH < 130 GeV

Selection:• 2 high-quality Photons• pT

(1) > 40 GeV, pT(2)> 25 GeV

Current exclusion sensitivity: 4-5 x SM cross-section

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LHC CombinationATLAS-CONF-2011-157, CMS PAS HIG-11-023, 18.11.11

Expected sensitivity per channel

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LHC CombinationATLAS-CONF-2011-157, CMS PAS HIG-11-023, 18.11.11

Observed exclusion per channel (comb. excl.: 141 GeV < mH < 476 GeV)

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LHC CombinationATLAS-CONF-2011-157, CMS PAS HIG-11-023, 18.11.11

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Most significant excess, including „look-elsewhere“ effect: only 1.6s !• Low mass region:

ZZ

WW

Michael Kobel

OTHER SEARCHES

1. SUSY2. Exotics

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Michael Kobel

Phenomenology of Supersymmetry

Super-Symmetrie between Fermions and BosonsO|Boson> = |Fermion> und O|Fermion> = |Boson> • For each Fermion there is a bosonic partner• For each Boson there is a fermionic partner

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Michael Kobel

Masses “run” with known Q2-dependence

Simplifying assumption of ConstraintMSSM: Unification at LGUT

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Example: Jets + Etmiss (1.04 fb-1)

arXiv:1109.6572 (30.09.11)

5 signal channels depending on• Jet multiplicity• meff = ET

miss + S|pT,jet(i)|

huge exclusion gain since 2010

ATLAS exclusion in CMSSM

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2010 2011

SUSY exclusion overviewSeptember 2011

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Exotic example: ADD extra dimensionATLAS-CONF-2011-096, 18.7.11

Signature:• Monojets +ET

miss

N.Arkani-Hamed, S.Dimopoulos and G.Dvali (ADD):• Macroscopic n extra dimensions would solve EW-Planck hierarchy problem:

M2Planck = MD

2+n Rn

with MD~TeV fundamental Planck scale, R ~ nm(n=3) ~10fm(n=6)

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exotic exclusion overviewSeptember 2011

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Michael Kobel

Summary

Brilliant performance of LHC ATLAS detector very well understood Standard Model

• W/Z + ≥ 5 jets: precision measurements• Di-Boson: observation and improvements of TGC limits

Top-Quark• Precision cross-section and mass• Improving BSM limits, e.g. FCNC

SM Higgs• Low-mass window narrowed to 114 < mH < 141 GeV

• Weaker WW and ZZ exclusion, but only 1.6 including „look-elsewhere“ 114 < mH < 120 GeV: most sensitive gg and WW

120 < mH < 130 GeV: most sensitive WW and gg

130 < mH < 141 GeV: most sensitive WW and ZZ4l

SUSY and Exotics• Considerably improved exclusions in parameter spaces

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Michael Kobel 48 of 47

BACKUP

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Michael Kobel

The „look-elsewhere“ effect

ATL-PHYS-PUB-2011-11, CMS NOTE-2011/005

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