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
1061777
0,0000000010,000000009
0,00000005
1E-121E-111E-101E-091E-081E-07
0,0000010,00001
0,00010,001
0,010,1
110
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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30
21 )( ˆ
,
s
ViV
i
ff
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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