The Discovery of the Higgs Boson New trends in Higgs Physics at LHC
Marumi Kado Laboratoire de l’Accélérateur Linéaire (LAL) and CERN
Taller de Altas Energias, Benasque 2013 Disclaimer The Higgs boson
“The” refers to the one discovered
It is nevertheless the main question: which Higgs boson is it? Menu “A la Carte…” 1.- Historical context 2.- Brief History of the Discovery 3.- How to read an exclusion or significance plot? 4.- Overview of channels and their results 5.- Couplings analysis 6.- Main quantum numbers 7.- Implications (Vacuum stability, SUSY) 8.- Electroweak precision data 9.- Searches for BSM Higgs (concise review) 10.- Total width through interferometry 11.- Future projects Menu “A la Carte…” 1.- Historical context 2.- Brief History of the Discovery 3.- How to read an exclusion or significance plot? 4.- Overview of channels and their results 5.- Couplings analysis 6.- Main quantum numbers 7.- Implications (Vacuum stability, SUSY) 8.- Electroweak precision data 9.- Searches for BSM Higgs (concise review) 10.- Total width through interferometry 11.- Future projects … in 2013 Entrance of the H0 in the PDG!
Inaugural entrance of the Higgs boson in the PDG particle listing ! H 0 2013 EPS-HEP Prize
The 2013 High Energy and Particle Physics Prize, for an outstanding contribution to High Energy Physics, is awarded to the ATLAS and CMS collaborations, “for the discovery of a Higgs boson, as predicted by the Brout-Englert-Higgs mechanism”, and to Michel Della Negra, Peter Jenni, and Tejinder Virdee, “for their pioneering and outstanding leadership rôles in the making of the ATLAS and CMS experiments”. October 8, 2013… ?
Crowning of half a century of theoretical developments and Higgs Hunt ? Digression on the origin of Mass - Gallilean and Newtonian concept of mass : Inertial mass (F=ma) Gravitational mass (P=mg)
Single concept of mass Conserved intrinsic property of matter where the total mass of a system is the sum of its constituents
- Einstein : Does the mass of a system depend of its energy content? 2 Mass = rest energy of a system or m0=E/c - Atomic level : binding energy ~O(10eV) which is ~10-8 of the mass - Nuclear level : binding energy ~2% of the mass - Nucleus parton level : binding energy ~98% of the mass Most of the (luminous) mass in the universe comes from QCD confinement energy The insight of the Higgs mechanism :
Understanding the origin of mass of gauge bosons and fermions a How Would it Be Without Elementary Particle Masses?
Electron mass (me = 511 keV)
Bohr Radius a = 1/(aEM me) so :
If me = 0 : Then no atomic binding
W boson mass (mW = 81 GeV)
-2 GF ~ (MW)
If no or lower W mass : shorter combustion time at lower temperature
Everything would be completely different! 1964 Five pages that changed the course of the Standard Theory of particles…
2 pages
1 page
2 pages
The BEH mechanism allows: - Massive gauge bosons - Massive fermions - Renormalizability - Unitarity Splendid… but yet the least elegant part of the Standard Model - No gauge principle - Accounts for most free param. 1976 1990
Proceedings of LHC Workshop (Aachen, 1990): √s = 16 TeV, 100 fb-1
14 20 Years, projecting, constructing and Simulating…
Latin American Workshop on HEP 15 4 µ event … Standard EW only or Higgs? 2011
7 TeV Latin American Workshop on HEP 16 ATLAS Electromagnetic Calorimeter From RD3 to the LAr Calorimeter
First prototype 1990
Construction 1998
Installation 2004 The Di-Photon Channel Historical Prospective
1991 Analysis Moriond-1 2013 Analysis -1 16 TeV, 100 fbFirst EAGLE (ATLAS) note 7 - 8 TeV, ~25 fb ATLAS diphoton channel diphoton channel July 4, 2012 … On the NY Times front Page! Menu “A la Carte…” 1.- Historical context 2.- Brief History of the Discovery 3.- How to read an exclusion or significance plot? 4.- Overview of channels and their results 5.- Couplings analysis 6.- Main quantum numbers 7.- Implications (Vacuum stability, SUSY) 8.- Electroweak precision data 9.- Searches for BSM Higgs (concise review) 10.- Total width through interferometry 11.- Future projects The SM Lagrangian after Breaking (See A. Casas)
Massive scalar : The Higgs boson
Massive gauge bosons
Gauge-Higgs interaction
In order to derive the mass eigenstates :
Diagonalize the mass matrix
Where g# g sin"W = cos"W = g2 + g# 2 g2 + g# 2
The Weinberg angle was actually first introduced by Glashow (1960)
! ! Keep this in mind for the next lecture… Consequences of the Brout-Englert-Higgs Mechanism
1.- Two massive charged vector bosons :
Corresponding to the observed charged currents
Thus v = 246 GeV Given the known W mass and g coupling
2.- One massless vector boson :
The photon correponding to the unbroken U(1)EM 3.- One massive neutral vector boson Z :
4.- One massive scalar particle : The Higgs boson
Whose mass is an unknown parameter Which of these consequences are actually predictions ?
1.- The theory was chosen in order to describe the weak interactions mediated by charged currents.
2.- The masslessness of the photon is a consequence of the choice of developing the Higgs field in the neutral and real part of the doublet. 3 & 4.- The appearance of massive Z and Higgs bosons are actually predictions of the model.
One additional very important prediction which was not explicitly stated in Weinberg’s fundamental paper… although it was implicitly clear :
There is a relation between the ratio of the masses and that of the couplings of gauge bosons :
2 MW g 2 = 2 2 = cos #W or MZ g + g"
! " =1
WilczekLEP celebration : The Higgs mechanism is corroborated at 75%
! Menu “A la Carte…” 1.- Historical context 2.- Brief History of the Discovery 3.- How to read an exclusion or significance plot? 4.- Overview of channels and their results 5.- Couplings analysis 6.- Main quantum numbers 7.- Implications (Vacuum stability, SUSY) 8.- Electroweak precision data 9.- Searches for BSM Higgs (concise review) 10.- Total width through interferometry 11.- Future projects How to read Higgs Search Plots… Starting from PRL Cover Plot Statistical Interpretation How to read Higgs Search Plots
Hypothesis testing using the Likelihood Definition: Profile likelihood ratio… Simplified
L(µ,!) = fb"b (M## )+ fs"s (M## )
Relates to Higgs mass hypothesis f ! µ s Global coherent factor
ns = µ! BrL" How to Read Higgs Exclusion Limits Plots ˆ L(µ,"ˆ(µ)) !µ = !(µ,") = qµ = !2ln !µ L(µˆ,"ˆ)
10
9 Background likeliness 8
7 likelihood ratio without profiling )
! 6 ( " 5
4
-2 ln -2 ln 3 q0 2 qμ 1
0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 !# !test ! Signal likeliness Statistical Interpretation How to read Higgs Search Plots
Hypothesis testing using the Profile likelihood ratio…
µˆ Expected Relate to Higgs Signal mass hypothesis
3 ATLAS Preliminary HAaa Best fit Ldt = 4.9 fb-1 2 ±1 m 0 s = 7 TeV 1 Signal strength
0
-1
-2 3 ATLAS Preliminary HAaa Best fit Ldt = 4.9 fb-1 2 ±1 m 0 s = 7 TeV 1 Signal strength -3 2011 Data 0 -1 110 115 120 125 130 135 140 145 150 -2 MH [GeV] -3 2011 Data 110 115 120 125 130 135 140 145 150 MH [GeV] Excess Not a measurement of mass Expected Background Not a measurement of cross section Deficit How to Read Higgs Exclusion Limits Plots ˆ 3 ATLAS Preliminary HAaa L( , ˆ( )) -1 µ " µ Best fit Ldt = 4.9 fb !µ = !(µ,") = 2 ±1 m 0 ˆ ˆ s = 7 TeV L(µ,") 1 Signal strength q = !2ln ! 0 µ µ
-1 Background likeliness
-2
-3 2011 Data 110 115 120 125 130 135 140 145 150 MH [GeV]
CLs+b Probability that a signal-plus- background experiment be more background-like than observed
Expected Excess Background Deficit How to Read Higgs Observation Estimates
3 ATLAS Preliminary HAaa -1 Best fit 0 Ldt = 4.9 fb ˆ 2 ±1 m L(0,"ˆ(0)) s = 7 TeV ! = !(0,") = 1 0 Signal strength L(µˆ,"ˆ) 0 q = !2ln ! -1 0 0
-2 Signal likeliness -3 2011 Data 110 115 120 125 130 135 140 145 150 MH [GeV]
p0 Probability that a background only experiment be more signal like than observed
32 Deficit Excess Expected Signal Local vs. Global Probability Look Elswhere Effect (over)Simplified View
Probability of observing an excess at one specific mass (in absence of signal)…
What is the probability of observing an excess at least as large as observed within a mass range ?
Trial factor ~ Number of possible independent outcomes within a mass range… (dependence on the significance) Local vs. Global Probability Look Elswhere Effect Approximate Formula
3 ATLAS Preliminary HAaa Based on counting the numbers of Best fit Ldt = 4.9 fb-1 up-crossings 2 ±1 m 0 s = 7 TeV 1 Signal strength 0 Then applying the very simple
-1 following formula (Z is the local significance) -2 N Z 2 -3 2011 Data " 2 110 115 120 125 130 135 140 145 150 p = p + N ! e MH [GeV] global local
Trial factor ~ Here the dependence is explicit… Menu “A la Carte…” 1.- Historical context 2.- Brief History of the Discovery 3.- How to read an exclusion or significance plot? 4.- Overview of channels and their results 5.- Couplings analysis 6.- Main quantum numbers 7.- Implications (Vacuum stability, SUSY) 8.- Electroweak precision data 9.- Searches for BSM Higgs (concise review) 10.- Total width through interferometry 11.- Future projects Other Higgs Programs
- LEP limits mH > 114 GeV Absolute limit! - In general reinterpretation of low mass searches
- PreLEP era - Absence of Higgs related effects in Nuclear Physics, neutron stars and neutron scattering
experiments mH>20 MeV - Kaon abd B-Meson decays limits mH>5 GeV
- LHCb
- Standard Model H in bb - Higgs decays to long lived partices - (MSSM) Higgs to ττ
- LHC diffractive Higgs production
- BaBar and Belle search for NMSSM a Center-of-Mass Energy (Nominal) 14 TeV ? Center-of-Mass Energy (close to nominal) 13TeV LHCb ATLAS Center-of-Mass Energy (2012) 8 TeV CMS ALICE Center-of-Mass Energy (2010-2011) 7 TeV 37 Three Years of LHC opera ons at the Energy fron er The LHC - Circumference 27 km - Up to 175 m undergroundEvent taken at random (filled) bunch crossings - Total number of magnets 9 553 - Number of dipoles 1 232 … in LS1 - Operation temperature 1.9 K (Superfluid He)
Parameter 2010 2011 2012 Nominal C.O.M Energy 7 TeV 7 TeV 8 TeV 14 TeV Bunch spacing / k 150 ns / 368 50 ns / 1380 50 ns /1380 25 ns /2808 ε (mm rad) 2.4-4 1.9-2.3 2.5 3.75 β* (m) 3.5 1.5-1 0.6 0.55 L (cm-2s-1) 2x1032 3.3x1033 ~7x1033 1034 The first LHC run
] 2010 -1 35 ATLAS Online Luminosity O(2) Pile-up 2011 2010 pp s = 7 TeV 2012 30 -1 2011 pp s = 7 TeV 23 fb events Event taken at random 2012 pp s = 8 TeV 25 at 8 TeV 150 ns inter-bunch spacing (filled) bunch crossings 20 4th July seminar and ICHEP 15 2011 Delivered Luminosity [fb 5.6 fb-1 10 at 7 TeV 2010 0.05 fb-1 5 2011 at 7 TeV 0 O(10) Pile-up Jan Apr Jul Oct Month in Year events Event taken at random 50 ns inter-bunch spacing (filled) bunch crossings Design value (expected to be reached at L=1034 !) 2012 O(20) Pile-up
events 39 50 ns inter-bunch spacing The Main Production Modes at the LHC - Gluon fusion process : Dominant process known at NNnLO TH uncertainty ~O(10%) ~0.5 M events produced! - Vector Boson Fusion : known at NLO TH uncertainty ~O(5%) Distinctive features with two forward jets and a large rapidity gap ~40 k events produced! - W and Z Associated Production :
known at NNLO TH uncertainty ~O(5%) Very distinctive feature with a Z or W decaying leptonically ~20 k events produced!
- Top Associated Production : ~3 k events produced! known at NLO TH uncertainty ~O(15%) Quite distinctive but also quite crowded
* TH uncertainty mostly from scale variation and PDFs, δσ PDF-αs~8-10% and δσ Scale~ 7-8% Overview of Cross Sections Expected Standard Model and Higgs Productions
proton - (anti)proton cross sections Theory and simulation “Next-to…” revolution : 109 109 - NNLO PDFs sets 108 108 !tot
7 7 - Calculations at unprecedented order in perturbation theory 10 Tevatron LHC 10 - Parton Shower (and Matrix Element matching) improvements 106 106
5 5 10 10 -1 s
!b -2 104 104 cm 3 3
10 10 33 jet !jet(ET > "s/20) 102 102 # = 10
1 1 L nb 10 !W 10 ! !!!" Z 0 0 ! 10 jet 10 !jet(ET > 100 GeV) 10-1 10-1
10-2 10-2
10-3 10-3
!t events / sec for 10-4 10-4 !Higgs(MH=120 GeV) -5 -5 10 200 GeV 10 10-6 10-6
WJS2010 500 GeV 10-7 10-7 0.1 1 10 "s (TeV) Decay Modes - Dominant decay mode b (57%) Very large backgrounds, associated production W,Z H and Boost! - The ττ channel (6.3%) VBF, VH, but also ggF with new mass reconstruction techniques H → WW→ lvlv W(H → bb) VBF(H → ττ) - The channel (0.2%) γγ H → γγ Discovery channel, high mass resolution Z(H → bb) (High stat, and backgrounds) - The ZZ Channel (3%) - Subsequent all leptons decays (low statistics): H → ZZ → llll golden channel - llqq and llvv sensitive mostly at high mass - The WW Channel (22%) - Subsequent lvlv very sensitive channel - lvqq sensitive mostly at high mass - The µµ channel (0.02%) and Zγ (0.2%) Low statistics from the low branching in µµ or both the low branching and subsequent decay in leptons (Zγ) - The cc channel (3%) Very difficult Channels investigated
ATLAS CMS TeVatron Channel categories ggF VBF VH ttH ggF VBF VH ttH VH ggF
γγ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ (inclusive) ✓
ZZ (llll) ✓ ✓ ✓ ✓ ✓
WW (lνlν) ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
ττ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
H (bb) ✓ ✓ ✓ ✓ ✓ ✓
Zγ (inclusive) ✓ ✓ ✓
µµ (inclusive) ✓
Invisible ✓ ✓ ✓ H → γγ Update
Since “Discovery Paper” PLB 716 ATLAS-CONF-2013-012
γγ channel basic facts sheet : Signal (SM Signal purity Main 126 Production 7 & 8 TeV L dt GeV) s/b backgrounds !
~450 2% - 60% γγ,γj and jj Hgg, VBF, VH 4.9 & 20.7 fb-1 H → 4e candidate (m4e ~ 124 GeV) 4l channel basic facts sheet : Signal Purity Main Signal Production 7 & 8 TeV s/b backgrounds ! L dt ggH, VBF & ~16 ~1.5 ZZ, Z+jets, top 4.9 & 20.7 fb-1 VH H → WW(*) ll + 2ν
0,1, 2 jet Channel
ATLAS- CONF-2013-030
WW channel basic facts sheet :
Signal Sig. Purity s/b Main backgrounds Production 7 & 8 TeV ! L dt
~250 ~5%-40% WW, W+jets, top, etc… ggH & VBF 25fb-1 H → ττ
Reoptimised 7+8 TeV analysis ATLAS-CONF-2012-160
H → τhadτhad candidate in VBF channel (mMMC = 131 GeV) ττ channel basic facts sheet : Signal purity Main Signal (SM) Production 7 & 8 TeV L dt s/b backgrounds !
~330 0.3% - 30% ZZ, Z+jets, top VBF, Hgg, VH 4.9 & 13 fb-1 VH production with H → bb Combined and reoptimised 7+8 TeV analysis
VH(bb) channel basic facts sheet : Signal purity Signal (SM) Main backgrounds Production 7 & 8 TeV L dt s/b !
~50 ~1% - 10% Wbb,Zbb, top, etc… VH 4.9 & 21 fb-1 A Textbook Discovery! Birth of a particle (different prospective) 0 ATLAS s = 7 TeV (2011), 0Ldt = 1.2 fb-1 1 -1 1 Local p 10 m 2 m 10-2 -3 3 10 07/11 EPS Prel. m -4 Observed 10 Expected 4 m 10-5 10-6 5 m 10-7 10-8 10-9 6 m 10-10 110 115 120 125 130 135 140 145 150
mH [GeV] 2012 : Year of the p0 A Textbook Discovery! Birth of a particle (different prospective) CERN Council (December 2011) 0 ATLAS s = 7 TeV (2011), 0Ldt = 1.24.9 fb-1 1 -1 1 Local p 10 m 2 m 10-2 -3 3 10 07/11 EPS Prel. m -4 Observed 10 Expected 4 -5 12/11 CERN Prel. m 10 Observed 10-6 Expected 5 m 10-7 10-8 10-9 6 m 10-10 110 115 120 125 130 135 140 145 150
mH [GeV] 2012 : Year of the p0 A Textbook Discovery! Birth of a particle (different prospective) Moriond (March 2012) 0 0 0 ATLASATLAS ss == 77 TeVTeV (2011),(2011), 00LdtLdt == 4.94.81.2 fbfb-1-1 11 -1-1 11 Local p Local p Local p 1010 mm 22 mm 1010-2-2 -3-3 33 1010 07/1107/11 EPSEPS Prel.Prel. mm -4-4 ObservedObserved 1010 ExpectedExpected 44 -5-5 12/11 CERN Prel. mm 1010 Observed 1010-6-6 Expected 55 -7-7 Spring 2012 PRD mm 1010 Observed 1010-8-8 Expected 1010-9-9 66 mm 1010-10-10 110110 115 115 120 120 125 125 130 130 135 135 140 140 145 145 150 150
mmHH [GeV][GeV] 2012 : Year of the p0 A Textbook Discovery! Birth of a particle (different prospective) ICHEP (July 2012) 0 0 -1 ss == 77 TeVTeV (2011),(2011), 00LdtLdt == 4.94.81.24.8 fbfb-1-1 ATLASATLAS -1 s = 8 TeV (2012), 0Ldt = 5.9 fb 11 -1-1 11 Local p Local p 1010 mm 22 mm 1010-2-2 -3-3 33 1010 07/1107/11 EPSEPS Prel.Prel. mm -4-4 ObservedObserved 1010 ExpectedExpected 44 -5-5 12/1112/11 CERNCERN Prel.Prel. mm 1010 ObservedObserved 1010-6-6 ExpectedExpected 55 -7-7 SpringSpring 20122012 PRDPRD mm 1010 ObservedObserved 1010-8-8 ExpectedExpected -9-9 04/12 CERN Prel. 1010 Observed 66 mm Expected 1010-10-10 110110 115 115 120 120 125 125 130 130 135 135 140 140 145 145 150 150
mmHH [GeV][GeV] 2012 : Year of the p0 As a Layman : We have it! A Textbook Discovery! Birth of a particle (different prospective) PLB (August 2012) 0 0 -1 ss == 77 TeVTeV (2011),(2011), 00LdtLdt == 4.94.81.24.8 fbfb-1-1 ATLASATLAS -1 s = 8 TeV (2012), 0Ldt = 5.9 fb 11 -1-1 11 Local p Local p 1010 mm 22 mm 1010-2-2 -3-3 33 1010 07/1107/11 EPSEPS Prel.Prel. mm -4-4 ObservedObserved 1010 ExpectedExpected 44 -5-5 12/1112/11 CERNCERN Prel.Prel. mm 1010 ObservedObserved 1010-6-6 ExpectedExpected 55 -7-7 SpringSpring 20122012 PRDPRD mm 1010 ObservedObserved 1010-8-8 ExpectedExpected -9-9 04/12 CERN Prel. PLB 07/12 1010 Observed Observed 66 mm Expected Expected 1010-10-10 110110 115 115 120 120 125 125 130 130 135 135 140 140 145 145 150 150
mmHH [GeV][GeV] 2012 : Year of the p0 The Discovery!
A Giant Leap For Science!
… in 2012 Backup Slides ATLAS-CONF-2012-166 Searching for SUSY with Tops ATLAS-CONF-2012-167 Seeking to Solve the Hierarchy Problem…
~~ ~~ ~ ¾" ¾"~ (*)¾0¾0 t1t1 production,t1t1 production, t1 A b+r , r tA1A W t r+r Status: December 2012Status: December 2012 350 350 1 1 1 1
-1 -1 ATLAS preliminaryATLAS preliminaryLint = 13 fb s=8 TeV and Lint = 4.7 fb s=7-1 TeV -1 L=7int = 13 fb s=8 TeV Lint = 4.7 fb s TeV [GeV] [GeV] 0 1 0 1 - 2L [1208.4305], 1-2L [1209.2102] mr" = 106 GeV - 0L [1208.1447] ¾ ¾ r r 300 3001 1L ATLAS-CONF-2012-166 - mr" = 150 GeV 1L ATLAS-CONF-2012-166 1L [1208.2590] m m 1 ~ 2L ATLAS-CONF-2012-167 - mr" = mt - 10 GeV - 2L [1209.4186] 1 1 m " = 2 ! m 0 1L ATLAS-CONF-2012-166 1-2L [1209.2102] r ¾r 1 1 250 250 Observed limitsObservedObserved limits limits (-1Observedmtheo ) limits Expected (-1 mlimitstheo ) Expected limits
~ -10) t 1 = m " ¾ r 1 0 ¾ r 1 200 200 " ( m ¾ r 1 +m t > m 0 0) ¾ ¾ r 1
0 " m¾ > m¾ ( = 106 GeV) 0 r r mr" = 2 ! m¾ 1 1 1 r t! t -1 1 ! ! 100 100 L = 13 fb int ~ mr" = mt - 10 GeV 1 1 -1 Lint = 13 fb
50 50 m " < 106 GeV Complemented in the r¾ 1 -1 -1 Lint = 4.7 fb Lint = 13 fb mr" = 106 GeV mr" = 150 GeV 1 1 lower mass range by: -1 -1 Lint = 4.7 fb Lint = 13 fb 0 0 t! ! b(! ± ! W ± !) 150200 200 250 250 300 300 350 350 400 400 450 450 500 500 550 600 650 m~ [GeV] m~ [GeV] t1 t1 Significantly improved sensitivity at high stop masses with expected limits up to 620 GeV 57 Also, strongly enhanced sensitivity for lower mass stop decaying into b + chargino