What is the Higgs Boson Why 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, 1¯h, 2¯h,.. (”force”)

Andrei Gritsan, JHU X July 30, 2014 What is a Fermion?

• Named after Enrico Fermi – foundation of Fermi - Dirac statistics 1 3 – describing particles of half-integer spin S = 2h,¯ 2h,..¯ (”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=h¯=1) bosons

• Z0 and W ± are heavy → weak force

• Gauge bosons in unified electro-weak theory after spontaneous symmetry breaking

0 0 |γi = cos θW |B i + sin θW |W i light (massless) 0 0 0 |Z i = sin θW |B i + cos θW |W i 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 0.8 0.6 0.4 0.2 0 -0.2 -1.5 -1 -0.5 0 0.5 1 1.5

• 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)

1 2 1 V = λ φ2 + φ2 + φ2 + φ2 + µ2 φ2 + φ2 + φ2 + φ2 4 h 1 2 3 4i 2 h 1 2 3 4i

1 T >Tc 0.3 0.8 0.2 T = T 0.1 0.6 c 0 0.4 -0.1 T

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 T >Tc 0.8 0.6 T = Tc

0.4 T

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~g they are equivalent in General Relativity

• Mass and Energy are equivalent 2 E = mc 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 = h¯ (anti-matter) • Fermions S 2 (matter)

leptons

quarks

• Bosons S =¯h (force carries): EM strong ← massless (weak force bosons mass)

Andrei Gritsan, JHU XXVII July 30, 2014 Mass of Matter

• Most of our mass is protons and neutrons 2 – most mass is energy of quark-gluon soup: mpc = E

Mass from quark-glue soup energy: 2 −27 mpc = 938 MeV ≃ 1.7 × 10 kg

Mass from the Higgs field: 2 2 muc ∼ 3 MeV, mdc ∼ 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 2 – for mH ∼ 126 GeV/c and SM Higgs field ⇒ metastable

1

0.8

0.6

0.4

0.2 0 arXiv:1205.6497 -0.2

-1.5 -1 -0.5 0 0.5 1 1.5

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, Higgs, 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 15148 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 76200 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 −, b¯b, τ +τ −,..

2 10 10 s= 8 TeV τ+τ- s = 8TeV pp→ H (NNLO+NNLL QCD + NLO EW) → ±ν H BR [pb] 1 WW l qq

gg→ ×

10 LHC HIGGS XS WG 2012 LHC HIGGS XS WG 2012

σ + - H+X) [pb] H+X) [pb] VBF H → τ τ qq→qqH → +ν -ν → WW l l

pp→ -1 qqH (NNLO QCD + NLO EW) 10

(pp + - pp ZZ → l l qq σ pp → 1 → WH (NNLO QCD + NLO EW) ZH (NNLO QCD +NLO EW) → + -νν pp -2 ZZ l l → ttH (NLO QCD) 10

- - -1 → + + 10 ZZ l l l l -3 → ±ν γγ V →VH 10 WH l bb l = e, µ ttH → ttbb ν ν ν ν = e, µ, τ ZH → l+l-bb q = udscb -2 10 -4 10 100 200 300 1000 80 100 200 300 400 1000 MH [GeV] MH [GeV]

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

1 1σ -1 • Probability of background 10 2σ 10-2 σ −6 -3 3 ∼ 0.2 × 10 10 -4 10 4σ Local p-value 10-5 -6 10 5σ 10-7 -8 10 Combined obs. -9 6σ 10 Exp. for SM H CMS Preliminary H → γγ → γγ 10-10 H ZZ + WW + H → ZZ s = 7 TeV, L = 5.1 fb-1 -11 -1 10 → s = 8 TeV, L = 5.3 fb H WW 7σ 10-12 116 118 120 122 124 126 128 130 Higgs boson mass (GeV)

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 2400 Data 2200 Selected diphoton sample 35 (*) ATLAS Preliminary Background ZZ 2000 Data 2011 and 2012 (*) Sig + Bkg inclusive fit (m = 126.5 GeV) Background Z+jets, t t → → H H ZZ 4l 1800 30 Events / GeV 4th order polynomial Signal (m H =125 GeV) Signal (m =150 GeV) 1600 -1 H s = 7 TeV, ∫ Ldt = 4.8 fb Signal (m =190 GeV) 1400

Events/5 GeV 25 H Syst.Unc. 1200 s = 8 TeV, ∫ Ldt = 5.9 fb -1 20 ∫ -1 1000 s = 7 TeV: Ldt = 4.8 fb 800 ∫ -1 15 s = 8 TeV: Ldt = 5.8 fb 600 400 10 200 ATLAS Preliminary 1000 110 120 130 140 150 160 5 100 0 0 Data - Bkg -100 100 150 200 250 100 110 120 130 140 150 160 m 4l [GeV] m γγ [GeV] 0 108 ATLAS Preliminary 2011 + 2012 Data • Probability of background ∫ L dt ~ 4.6-4.8 fb-1, s = 7 TeV ∫ L dt ~ 5.8-5.9 fb-1, s = 8 TeV −6 Local p 105 Exp. Comb. Exp. H → ZZ* → llll Exp. H → bb ∼ 0.2 × 10 Obs. Comb. Obs. H → ZZ* → llll Obs. H → bb Exp. H → γγ Exp. H → WW* → lνlν Exp. H → ττ 2 10 Obs. H → γγ Obs. H → WW* → lνlν Obs. H → ττ

0 σ -1 1 σ 10 2 σ 3 σ -4 10 4 σ

5 σ 10-7

110 115 120 125 130 135 140 145 150

mH [GeV]

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 molecule

Andrei 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 anti-matter • matter

leptons

quarks

• 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

1 • 2 Prize – Mechanism leading to matter-antimatter asymmetry – still not sufficient on cosmological scale 1 • 2 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|fermioni=|bosoni Q|bosoni=|fermioni • Solve: (1) natural light Higgs (2) dark matter ˜0 lightest χ1 (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