Embed Size (px)
Citation preview
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
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
The Nobel Prize in Physics 2013
Andrei Gritsan, JHU III July 30, 2014
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
Why do some call it the ”God Particle”?
Andrei Gritsan, JHU V July 30, 2014
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
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
The Big Bang
Andrei Gritsan, JHU VIII July 30, 2014
What is the Higgs Boson ?
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
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
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
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
0.8
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
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
0.2
0.3
-1.5 -1 -0.5 0 0.5 1 1.5
-0.2
0
0.2
0.4
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
Idea - the Higgs Field
• Empty space filled with invisible ”force” – the Higgs field
Andrei Gritsan, JHU XV July 30, 2014
Idea - the Higgs Field
• The Higgs field clusters around the particle – gives mass
Andrei Gritsan, JHU XVI July 30, 2014
Idea - the Higgs Field
• Pass energy into the Higgs field (no particle)
Andrei Gritsan, JHU XVII July 30, 2014
Idea - the Higgs Field
• The Higgs particle cluster created from the Higgs field
Andrei Gritsan, JHU XVIII July 30, 2014
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
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
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
0
0.2
0.4
0.6
0.8
1T > T
c
T = Tc
T < Tc
Andrei Gritsan, JHU XXI July 30, 2014
What is Mass?
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
What gives us mass? Molecules? Atoms?
Andrei Gritsan, JHU XXIV July 30, 2014
What makes mass?
• What gives us mass?
Molecules Atoms Nucleus
Andrei Gritsan, JHU XXV July 30, 2014
“Periodic Table” of Baryons: Proton, Neutron,...
• Three quarks make up a Baryon:
Andrei Gritsan, JHU XXVI July 30, 2014
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
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
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
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
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
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
-1.5 -1 -0.5 0 0.5 1 1.5
-0.2
0
0.2
0.4
0.6
0.8
1
arXiv:1205.6497
Andrei Gritsan, JHU XXXII July 30, 2014
The Higgs Boson
Andrei Gritsan, JHU XXXIII July 30, 2014
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
How Do We Know This ?
We Smash Matter
• Supply Energy into tiny spot: produce new matter / energy E = mc2
Andrei Gritsan, JHU XXXVI July 30, 2014
The Large Hadron Collider
Andrei Gritsan, JHU XXXVII July 30, 2014
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
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)
Andrei Gritsan, JHU XXXIX July 30, 2014
Production of New Particles at LHC
• Particles are produced and decay: X = Z0, H iggs, RS Graviton, ...
(Z0)
(H)
Andrei Gritsan, JHU XL July 30, 2014
The CMS Detector
• Complex detector
to sort collision debris out
Andrei Gritsan, JHU XLI July 30, 2014
The CMS Detector
Total weight 12500 t
Diameter 15 m
Length 22 m
Magnetic field 4 T
Andrei Gritsan, JHU XLII July 30, 2014
The Silicon Pixel Detector
1440 digital pixel ”cameras”
65 million channels, ∼100× 150µm
Alignment: hardware and software
Andrei Gritsan, JHU XLIII July 30, 2014
The Silicon Strip Detector
15 148 digital strip (2D) ”cameras”
10 million channels
area the size of a tennis court
Alignment analysis: software
Andrei Gritsan, JHU XLIV July 30, 2014
Electromagnetic Calorimeter
76 200 crystals lead tungstate
heavier than stainless steel
Andrei Gritsan, JHU XLV July 30, 2014
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
Andrei Gritsan, JHU XLVI July 30, 2014
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
Andrei Gritsan, JHU XLVII July 30, 2014
Computer Reconstruction of a ”Bubble”
Andrei Gritsan, JHU XLVIII July 30, 2014
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
Andrei Gritsan, JHU XLIX July 30, 2014
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
Andrei Gritsan, JHU L July 30, 2014
Data Analysis
Andrei Gritsan, JHU LI July 30, 2014
Data Analysis
Andrei Gritsan, JHU LII July 30, 2014
H → ZZ → 4ℓ
Andrei Gritsan, JHU LIII July 30, 2014
H → ZZ → 4ℓ
Andrei Gritsan, JHU LIV July 30, 2014
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
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
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
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
Puzzles of the Universe
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
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
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
The Big Bang
Andrei Gritsan, JHU LXIII July 30, 2014
Expanding Universe
• Observe stars as trains moving AWAY from us
Andrei Gritsan, JHU LXIV July 30, 2014
Will Universe Expand Forever?
• Several scenarios
– Big Bang followed by a ”Big Crunch” or not ?
Andrei Gritsan, JHU LXV July 30, 2014
Expansion of the Universe
• Future depends on density of matter and energy in the Universe
Andrei Gritsan, JHU LXVI July 30, 2014
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
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
Gravity Should Slow Expansion
Andrei Gritsan, JHU LXIX July 30, 2014
Expansion is Accelerating
• Accelerating Universe: requires some kind of Dark Energy
– Nobel Prize in Physics 2011
Andrei Gritsan, JHU LXX July 30, 2014
Puzzles of the Universe
Andrei Gritsan, JHU LXXI July 30, 2014
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
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
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
Periodic Table of Matter
Andrei Gritsan, JHU LXXV July 30, 2014
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
The Big Bang
Andrei Gritsan, JHU LXXVII July 30, 2014
Puzzles of the Universe
Andrei Gritsan, JHU LXXVIII July 30, 2014
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
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
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
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
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
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
Reaching Highest Energy
• mc2 = E
Andrei Gritsan, JHU LXXXV July 30, 2014
