what is the higgs boson why do some call it the ”god particle”?
TRANSCRIPT
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What is the Higgs BosonWhy do some call it the ”God Particle”?
Andrei Gritsan
Johns Hopkins University
30 July 2014
Johns Hopkins University
JHU QuarkNet meeting
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What is the Higgs Boson
• From the Big Bang to present
• What is the Higgs boson?
• What is mass and energy?
• Why is it important to us? Is it the God particle?
• How did we find the the Higgs particle?
• Puzzles of the Universe: beyond the Higgs boson
• Optional topics:
– Science of the Nuclear Energy
– Space-Time
– Higgs boson in motion pictures
Andrei Gritsan, JHU II July 30, 2014
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The Nobel Prize in Physics 2013
Andrei Gritsan, JHU III July 30, 2014
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The Higgs Particle
• The Nobel prize for the Higgs mechanism
– theoretical idea ∼50 years ago
• This idea became the reality with the Higgs particle
– experimental discovery <2 years ago
Andrei Gritsan, JHU IV July 30, 2014
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Why do some call it the ”God Particle”?
Andrei Gritsan, JHU V July 30, 2014
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Lets Start from ”Nothing”: Vacuum
• As far as we can tell vacuum (empty space)
is not exactly empty
• like a bank account balance:
when you take all your money out
there is a minimum balance left
• Invisible ”force” present
– dark energy
– Higgs field
Andrei Gritsan, JHU VI July 30, 2014
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And also Look at the Beginning: The Big Bang
• Early moments of the Universe (astronomical observations):
– current expansion points to a singular origin
– nucleosynthesis in 20 minutes
– 13.8 billion years ago
• Recreate early Universe in a lab
– re-create now extinct particles at accelerators
– re-create conditions and understand laws
Andrei Gritsan, JHU VII July 30, 2014
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The Big Bang
Andrei Gritsan, JHU VIII July 30, 2014
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What is the Higgs Boson ?
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What is a Boson?
• Named after Satyendra Nath Bose
– foundation of Bose - Einstein statistics
– describing particles of integer spin S = 0, 1h̄, 2h̄, .. (”force”)
Andrei Gritsan, JHU X July 30, 2014
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What is a Fermion?
• Named after Enrico Fermi
– foundation of Fermi - Dirac statistics
– describing particles of half-integer spin S = 12h̄, 3
2h̄, .. (”matter”)
– one of the fathers of the atomic bomb (Italy → USA in 1938)
Andrei Gritsan, JHU XI July 30, 2014
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How many Bosons did we know in 2012?
• We knew 12 bosons: photon, Z0, W+, W−, 8 gluons
• Photons (γ) are massless vector (spin=h̄=1) bosons
• Z0 and W± are heavy → weak force
• Gauge bosons in unified electro-weak theory
after spontaneous symmetry breaking
|γ〉 = cos θW |B0〉+ sin θW |W
0〉 light (massless)
|Z0〉 = sin θW |B0〉+ cos θW |W
0〉 heavy
θW - Weak mixing (Weinberg) angle
Andrei Gritsan, JHU XII July 30, 2014
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Path from Light to Heavy
• Early moments of the Universe
– massless particles: B0 and W 0, W+, W−,..
– all forces unify
-1.5 -1 -0.5 0 0.5 1 1.5
-0.2
0
0.2
0.4
0.6
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1
• As Universe cools down
– symmetry spontaneously breaks
– weak interactions become weak (Z0, W± mass)
– Higgs field – possible mechanism
Andrei Gritsan, JHU XIII July 30, 2014
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The Englert-Brout-Higgs Mechanism
• Symmetry spontaneously breaks near minimum (vacuum) energy
of Higgs field (φ1, φ2, φ3, φ4)
V =1
4λ
[
φ21 + φ2
2 + φ23 + φ2
4
]2+
1
2µ2
[
φ21 + φ2
2 + φ23 + φ2
4
]
1φ
-1 -0.5 0 0.5 12φ
-1-0.50
0.51
-0.2
-0.1
0
0.1
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0.3
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0
0.2
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0.6
0.8
1 T > Tc
T = Tc
T < Tc
• Higgs particle described by one component of the Higgs field
h = φ1 − v
• The other Higgs field components φ2, φ3, φ4 couple to Weak bosons
Z0, W−, W+ and generate mass, longitudinal polarization (not γ)
Andrei Gritsan, JHU XIV July 30, 2014
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Idea - the Higgs Field
• Empty space filled with invisible ”force” – the Higgs field
Andrei Gritsan, JHU XV July 30, 2014
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Idea - the Higgs Field
• The Higgs field clusters around the particle – gives mass
Andrei Gritsan, JHU XVI July 30, 2014
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Idea - the Higgs Field
• Pass energy into the Higgs field (no particle)
Andrei Gritsan, JHU XVII July 30, 2014
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Idea - the Higgs Field
• The Higgs particle cluster created from the Higgs field
Andrei Gritsan, JHU XVIII July 30, 2014
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What is Higgs?
• There are several phenomena:
– Peter Higgs
– Higgs mechanism
– Higgs field
– Higgs particle (boson)
• People sometimes confuse these phenomena
– especially the last two
• We have hard evidence for two:
– 1964 article by Peter Higgs in Physics Review Letters
– 2012 discovery of a new Boson by CMS and ATLAS
Andrei Gritsan, JHU XIX July 30, 2014
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More on the History of the Higgs Mechanism
• In fact, there are several names of the Higgs mechanism:
– Brout-Englert-Higgs mechanism
– Higgs-Brout-Englert-Guralnik-Hagen-Kibble mechanism
– Anderson-Higgs mechanism
– Higgs mechanism is just simpler
– all for authors of independent papers on the topic
• Partly due to ironic history with the paper by Higgs:
– rejected from European Physics Letters
“of no obvious relevance to physics”
– added a reference to predicting a new particle
Andrei Gritsan, JHU XX July 30, 2014
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More on the History of the Higgs Mechanism
1950: Ginzburg- Landau model of superconductivity
1959-60: Nambu- Goldstone bosons in spontaneous symmetry breaking
1962: P. Anderson - nonrelativistic example
1964: R. Brout & F. Englert; P. Higgs; G. Guralnik & C. R. Hagen & T. Kibble
1967: Incorporated into Standard Model by S. Weinberg and A. Salam
-1.5 -1 -0.5 0 0.5 1 1.5
-0.2
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0.2
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1T > T
c
T = Tc
T < Tc
Andrei Gritsan, JHU XXI July 30, 2014
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What is Mass?
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What is Mass?
• We are all familiar with either inertial mass or gravitational mass
~F = m~a or ~F = m~gthey are equivalent in General Relativity
• Mass and Energy are equivalent
E = mc2 in Special Relativity
• Mass is important even without Gravity (e.g. in vacuum)
• The Higgs Mechanism provides mass to elementary particles
• Is our MASS due to the Higgs Mechanism ???
Andrei Gritsan, JHU XXIII July 30, 2014
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What gives us mass? Molecules? Atoms?
Andrei Gritsan, JHU XXIV July 30, 2014
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What makes mass?
• What gives us mass?
Molecules Atoms Nucleus
Andrei Gritsan, JHU XXV July 30, 2014
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“Periodic Table” of Baryons: Proton, Neutron,...
• Three quarks make up a Baryon:
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All Elementary Particles get Mass from Higgs Field
• Fermions S =h̄2 (matter)
leptons
quarks
(anti-matter)
• Bosons S = h̄ (force carries):
← massless
(weak force bosons mass)
EM strong
Andrei Gritsan, JHU XXVII July 30, 2014
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Mass of Matter
• Most of our mass is protons and neutrons
– most mass is energy of quark-gluon soup: mpc2 = E
Mass from quark-glue soup energy:
mpc2 = 938 MeV ≃ 1.7× 10−27 kg
Mass from the Higgs field:
muc2 ∼ 3 MeV, mdc
2 ∼ 5 MeV
but Higgs field is very important
Andrei Gritsan, JHU XXVIII July 30, 2014
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But Higgs Mechanism is Very Important
• Makes Weak Interactions weak: mass of Z,W−,W+
similarly first step in sun fusion
p + p→ d + e+ + νe
• Recall: mass is very important without gravity (energy)
• Higgs Mechanism makes certain hierarchy of masses
essential for our existence
Andrei Gritsan, JHU XXIX July 30, 2014
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Hypothetical Scenario: Different Quark Mass
• Again, normally proton is stable and neutron decays:
m(n) > m(p) + m(e) + m(νe)
• Why is m(n) > m(p)
– m(p) = 938 MeV, m(n) – m(p) = 1.3 MeV
– tiny difference makes a big difference!
– naively expect m(p) > m(n) if u and d were the same
– but m(d) > m(u)
• New scenario:
– what if m(d) ≤ m(u)
Andrei Gritsan, JHU XXX July 30, 2014
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Higgs Field in our Life
• Remove the Higgs field:
– catastrophic decay of a proton
– no H2O (water), no life
• Origin of Sun light
starts from Weak fusion
p+ p→ d(pn) + e+ + νe
slow burning due to heavy W+
Remove the Higgs field – Sun burns out quickly
Andrei Gritsan, JHU XXXI July 30, 2014
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Stability of the Vacuum
• Higgs self-coupling λ < 0 at higher scale
– may tunnel thru ”potential barrier” ⇒ unstable Universe
– tunneling time > Universe lifetime ⇒ metastable Universe
– for mH ∼ 126 GeV/c2 and SM Higgs field ⇒ metastable
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arXiv:1205.6497
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The Higgs Boson
Andrei Gritsan, JHU XXXIII July 30, 2014
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Create Higgs Boson from the Higgs Field
• Idea: if the Higgs field exists, like soap:
– blow into the soap, create a bubble (Higgs boson)
Andrei Gritsan, JHU XXXIV July 30, 2014
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How Do We Know This ?
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We Smash Matter
• Supply Energy into tiny spot: produce new matter / energy E = mc2
Andrei Gritsan, JHU XXXVI July 30, 2014
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The Large Hadron Collider
Andrei Gritsan, JHU XXXVII July 30, 2014
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The Large Hadron Collider
one of the coldest places (1.9 K, 96t He)
one of the hottest places (1016 ◦C)
vacuum emptier than outer space (10−10 Torr)
the fastest racetrack (vp = 0.999999991c)
the largest electronic instrument (27 km)
Andrei Gritsan, JHU XXXVIII July 30, 2014
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The Large Hadron Collider
• Enormous amount of data from LHC
> 2000 trillion proton-proton collisions in 2011-2012
> 20 billion events recorded, ∼0.6 Mbyte each (Petabytes)
> 200 million Z0 bosons
> 200 thousand Higgs bosons produced – assuming we see it
• LHC Computing Grid
world’s largest computing grid
over 170 computing centers in 36 countries
∼ 25 Petabytes / year (25× 1015 bytes)
(> 5 million DVDs, comparable to Facebook storage)
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Production of New Particles at LHC
• Particles are produced and decay: X = Z0, H iggs, RS Graviton, ...
(Z0)
(H)
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The CMS Detector
• Complex detector
to sort collision debris out
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The CMS Detector
Total weight 12500 t
Diameter 15 m
Length 22 m
Magnetic field 4 T
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The Silicon Pixel Detector
1440 digital pixel ”cameras”
65 million channels, ∼100× 150µm
Alignment: hardware and software
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The Silicon Strip Detector
15 148 digital strip (2D) ”cameras”
10 million channels
area the size of a tennis court
Alignment analysis: software
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Electromagnetic Calorimeter
76 200 crystals lead tungstate
heavier than stainless steel
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Hadronic Calorimeter and Muon System
>1 million WWII brass shells ⇒ HCAL absorber
HCAL scintillator ⇒ light signal
1400 Muon chambers in iron ”return yoke,” 2 million wires
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How the Detector Works
• Tracking: electrons e± (EM Calorimeter), muons µ± (Muon System)
• Photons γ (EM Calorimeter)
• Quark q & gluon g jets → flow of partciles thru Hadronic Calorimer
• Neutrinos ν ⇒ missing energy
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Computer Reconstruction of a ”Bubble”
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Global Effort at the Large Hadron Collider
• 1991: first World Wide Web (http://www...) server at CERN
• 20 years later: LHC Computing Grid
– distributed across 36 countries
– 200,000 computer cores
– 150 Petabytes of disk space
Petabyte = Million Gigabytes
1 Gigabyte ≃ 1 CD
• Flow of data from one experiment alone (CMS):
> 300 trillion proton-proton collisions in 2011
> 3 billion ”events” recorded on disk in 2011
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Production and Decay of a Higgs Boson
gg → H → γγ, ZZ(∗), W+W−, bb̄, τ+τ−,..
[GeV] HM80 100 200 300 400 1000
H+
X)
[pb
]
→(p
p
σ
-210
-110
1
10
210= 8 TeVs
LH
C H
IGG
S X
S W
G 2
01
2
H (NNLO+NNLL QCD + NLO EW)
→pp
qqH (NNLO QCD + NLO EW)
→pp
WH (NNLO QCD + NLO EW)
→pp
ZH (NNLO QCD +NLO EW)
→pp
ttH (NLO QCD)
→pp
[GeV]HM
100 200 300 1000
BR
[pb]
× σ
-410
-310
-210
-110
1
10
LH
C H
IGG
S X
S W
G 2
012
= 8TeVs
µl = e, τν,µν,eν = ν
q = udscb
bbν± l→WH
bb-l+ l→ZH b ttb→ttH
-τ+τ →VBF H
-τ+τ
γγ
qqν± l→WW
ν-lν+ l→WW
qq-l+ l→ZZ
νν-l+ l→ZZ
-l+l-l+ l→ZZ
gg→H
qq→qqH
V→V H
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Data Analysis
Andrei Gritsan, JHU LI July 30, 2014
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Data Analysis
Andrei Gritsan, JHU LII July 30, 2014
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H → ZZ → 4ℓ
Andrei Gritsan, JHU LIII July 30, 2014
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H → ZZ → 4ℓ
Andrei Gritsan, JHU LIV July 30, 2014
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July 2012: Observation of a New Boson
• Observation of a New Boson on CMS: 5σ excess
X → Z(∗)Z(∗) X → γγ
• Probability of background
∼ 0.2× 10−6
Higgs boson mass (GeV)116 118 120 122 124 126 128 130
Loca
l p-v
alue
-1210
-1110
-1010
-910
-810
-710
-610
-510
-410
-310
-210
-110
1σ1σ2
σ3
σ4
σ5
σ6
σ7
Combined obs.
Exp. for SM H
γγ →H
ZZ→H
WW→H
CMS Preliminaryγγ ZZ + WW + →H
-1 = 7 TeV, L = 5.1 fbs-1 = 8 TeV, L = 5.3 fbs
Andrei Gritsan, JHU LV July 30, 2014
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July 2012: Observation of a New Boson
• Observation of a New Boson on ATLAS: 5σ excess
X → Z(∗)Z(∗) X → γγ
[GeV]4lm100 150 200 250
Even
ts/5
GeV
0
5
10
15
20
25
30
35
-1Ldt = 4.8 fb∫ = 7 TeV: s-1Ldt = 5.8 fb∫ = 8 TeV: s
4l→(*)ZZ→H
Data(*)Background ZZ
tBackground Z+jets, t=125 GeV)
HSignal (m
=150 GeV)H
Signal (m=190 GeV)
HSignal (mSyst.Unc.
Preliminary ATLAS
100 110 120 130 140 150 160
Eve
nts
/ GeV
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
Data 2011 and 2012 = 126.5 GeV)
HSig + Bkg inclusive fit (m
4th order polynomial
Selected diphoton sample
-1 Ldt = 4.8 fb∫ = 7 TeV, s
-1 Ldt = 5.9 fb∫ = 8 TeV, s
ATLAS Preliminary
[GeV]γγm
100 110 120 130 140 150 160
Dat
a - B
kg
-100
0
100
• Probability of background
∼ 0.2× 10−6
[GeV]Hm
110 115 120 125 130 135 140 145 150
0Lo
cal p
-710
-410
-110
210
510
810
Exp. Comb.
Obs. Comb.γγ →Exp. H
γγ →Obs. H
llll→ ZZ* →Exp. H
llll→ ZZ* →Obs. H
νlν l→ WW* →Exp. H
νlν l→ WW* →Obs. H
bb→Exp. H
bb→Obs. H
ττ →Exp. H
ττ →Obs. H
ATLAS Preliminary 2011 + 2012 Data = 7 TeVs, -1 L dt ~ 4.6-4.8 fb∫ = 8 TeVs, -1 L dt ~ 5.8-5.9 fb∫
σ0 σ1 σ2
σ3
σ4
σ5
Andrei Gritsan, JHU LVI July 30, 2014
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Is it the Higgs Boson?
• We found the new boson, but is the Higgs boson?
– all indications: it is consistent
– its spin is 0
– its symmetry (mirror image) is +
• New state of matter-energy never seen before (like vacuum 0+)
Andrei Gritsan, JHU LVII July 30, 2014
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Could have we seen this earlier?
• Superconducting Super Collider (in Texas) cancelled in 1993
3 times longer, 3 times stronger than LHC
almost 1/3 tunnel done, $2 billion spent
Andrei Gritsan, JHU LVIII July 30, 2014
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Puzzles of the Universe
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The Particle World: the Smallest to the Largest
• On the smallest and largest scale:
what are we made of and why
(Galaxy cluster 1E 0657-66: X-ray, Optical, Grav. Lensing)
Andrei Gritsan, JHU LX July 30, 2014
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Nobel Prize Prize in Physics
• Accelerating expansion of the Universe
requires some kind of ”dark energy” through empty space
Andrei Gritsan, JHU LXI July 30, 2014
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Start from the Beginning: The Big Bang
• Early moments of the Universe (astronomical observations):
– current expansion points to a singular origin
– nucleosynthesis in 20 minutes
– 13.8 billion years ago
• Recreate early Universe in a lab
– re-create now extinct particles at accelerators
– re-create conditions and understand laws
Andrei Gritsan, JHU LXII July 30, 2014
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The Big Bang
Andrei Gritsan, JHU LXIII July 30, 2014
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Expanding Universe
• Observe stars as trains moving AWAY from us
Andrei Gritsan, JHU LXIV July 30, 2014
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Will Universe Expand Forever?
• Several scenarios
– Big Bang followed by a ”Big Crunch” or not ?
Andrei Gritsan, JHU LXV July 30, 2014
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Expansion of the Universe
• Future depends on density of matter and energy in the Universe
Andrei Gritsan, JHU LXVI July 30, 2014
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Example: WMAP Explorer Mission
Wilkinson Microwave Anisotropy Probe
launched by NASA in 2001
Headed by Prof. C.Bennett, JHU
Andrei Gritsan, JHU LXVII July 30, 2014
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Example: Hubble Space Telescope
launched by NASA in 1990
operated by Space Telescope Science Institute
replace by James Webb Space Telescope in 2018
Andrei Gritsan, JHU LXVIII July 30, 2014
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Gravity Should Slow Expansion
Andrei Gritsan, JHU LXIX July 30, 2014
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Expansion is Accelerating
• Accelerating Universe: requires some kind of Dark Energy
– Nobel Prize in Physics 2011
Andrei Gritsan, JHU LXX July 30, 2014
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Puzzles of the Universe
Andrei Gritsan, JHU LXXI July 30, 2014
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Puzzles of the Universe
• Dark energy (∼70%)
– do not know what it is; explain accelerated expansion
• Dark matter (∼25%)
– does not emit light, but seen with gravity
• Ordinary matter (∼5%)
– the only thing we knew until recently: from Hydrogen to Uranium
• Ordinary antimatter (∼0%)
– equal amount of matter and antimatter in the Big Bang
• Origin of mass
– everything created equal and massless in the Big Bang
Andrei Gritsan, JHU LXXII July 30, 2014
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Dark Matter
• Dark matter (25%) – ”dark” does not emit light, unknown
– left over from Big Bang, may create in accelerators...
(Galaxy cluster 1E 0657-66: X-ray, Optical, Grav. Lensing)
Andrei Gritsan, JHU LXXIII July 30, 2014
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Ordinary Matter in Big Bang
• Quark-gluon soup fraction of a second after Big Bang
– within minutes protons and neutrons formed
– billions of years to create all known elements
proton/neutron atom moleculeAndrei Gritsan, JHU LXXIV July 30, 2014
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Periodic Table of Matter
Andrei Gritsan, JHU LXXV July 30, 2014
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Formation of All Elements
• Success of Big Bang theory – predict formation of elements
– light elements (H, He) in early moments
– heavy elements (C – U) in fusion within stars
• Nuclear energy – in the gluon soup binding the quarks
natural resources in the Solar system
Andrei Gritsan, JHU LXXVI July 30, 2014
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The Big Bang
Andrei Gritsan, JHU LXXVII July 30, 2014
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Puzzles of the Universe
Andrei Gritsan, JHU LXXVIII July 30, 2014
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Puzzles of the Universe
• Dark energy (∼70%)
– do not know what it is; explain accelerated expansion
• Dark matter (∼25%)
– does not emit light, but seen with gravity
• Ordinary matter (∼5%)
– the only thing we knew until recently: from Hydrogen to Uranium
• Ordinary antimatter (∼0%)
– equal amount of matter and antimatter in the Big Bang
• Origin of mass
– everything created equal and massless in the Big Bang
Andrei Gritsan, JHU LXXIX July 30, 2014
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Anti-Matter: Mirror Object of Matter
• matter
leptons
quarks
anti-matter
• Produced equal in Big Bang
energy → matter + antimatter
anti-matter should behave differently than matter
Andrei Gritsan, JHU LXXX July 30, 2014
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Nobel Prize in Physics 2008
• 12 Prize – Mechanism leading to matter-antimatter asymmetry
– still not sufficient on cosmological scale
• 12 Prize – related to the next topic
Andrei Gritsan, JHU LXXXI July 30, 2014
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Origin of Mass
• Created equal and massless in the Big Bang
– light and glue carried by massless ”bosons”
• As Universe cooled
– sister ”bosons” to light got mass (spontaneous symmetry breaking)
Andrei Gritsan, JHU LXXXII July 30, 2014
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Need something else to explain these puzzles
• One idea: (super)symmetry
Q|fermion〉=|boson〉
Q|boson〉=|fermion〉
• Solve:
(1) natural light
H iggs
(2) dark matter
lightest χ̃01
(3) large matter/antimatter
• May be just around the corner in mass...Andrei Gritsan, JHU LXXXIII July 30, 2014
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LHC – The Big Bang Machine
• LHC program:
– test of the Higgs field
– may connect to dark energy
– may explain antimatter puzzle
– may produce dark matter
– re-create quark-gluon plasma
– extra dimensions of space ?
– prepare for unexpected ...
Andrei Gritsan, JHU LXXXIV July 30, 2014
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Reaching Highest Energy
• mc2 = E
Andrei Gritsan, JHU LXXXV July 30, 2014