The Particle at the End of the Universe
How the hunt for the Higgs Boson leads us to the edge of a new world
Sean M. Carroll, Penguin Group, 2012About the author
Sean Carroll is a theoretical physicist at the California Institute of Technology. He received his Ph.D. from Harvard in 1993, and worked at MIT, the Institute for Theoretical Physics at UC Santa Barbara, and the University of Chicago before moving to Caltech. His research involves theoretical physics and astrophysics, focusing on issues in cosmology, field theory, and gravitation. He is the author of Spacetime and Geometry, a graduate-level textbook on general relativity; has produced a set of introductory lectures for The Teaching Company entitled Dark Matter and Dark Energy: The Dark Side of the Universe; and blogs regularly at Cosmic Variance. His lives in Los Angeles with his wife, writer Jennifer Ouellette.
p1 2008 The first protons in the Large Hadron Collider (LHC).
p3 July 4, 2012 International Conference on High Energy Physics was held in Melbourne, but program was beamed from CERN in Geneva. Hundreds of particle physicists gathered at CERN. Rolf Heuer, director of CERN introduced program by Joe Incandela and Fabiola Gianotti
p4 This momentous occasion was for the reporting of the experimental results from the LHC. The nature of the data was the appearance of more events than expected with a certain particle energy, the signature of a new particle. "The data are so precise and clear that even scientists who had worked on the experiments for years are taken aback. "Welsh physicist Lyn Evans, who more than anyone else was responsible for guiding the LHC through its rocky path to completion, declared himself 'gobsmacked' at the exquisite agreement between the two experiments."
p5 It's all about the Higgs boson. "[Peter]Higgs himself was in the room for the seminars, eighty-three years old and visibly moved:'I never thought I'd see this happen in my lifetime'."
p5 "The Higgs is important not for what it is but for what it does. The Higgs particle arises from a field pervading space, known as the 'Higgs field'. Everything in the known universe, as it travels through space, moves through the Higgs field; it's always there, lunching invisibly in the background. And it matters.: Without the Higgs, electrons and quarks would be massless, just like photons, the particles of light. They would move at the speed of light themselves, and it would be impossible to form atoms and molecules, much less life as we know it. The Higgs field isn't an active player in the dynamics of ordinary matter, but its presence in the background is crucial. Without it, the world would be an entirely different place."
1. The Point
p7 "The last truly surprising experimental result to emerge from a particle accelerator was in the 1970s .."
p8 Discusses how the last 30+ years of accelerator work have overwhelmingly supported the standard model.
p11 Section on the Higgs boson. Notes that dark matter and dark energy don't fit in the standard model. Discusses matter particles (fermions) and force-carrying particles (bosons)
p12 Includes the standard lines about the role of the Higgs "to give mass to other particles" and "to break symmetries", but goes on to reflect on the fact that the Higgs is essential to the standard model.
p13 After being asked on a radio interview, gives a neat reflection on innate curiosity as a universal trait of the young.
p13-14 "But physics É has pushed the boundaries of understanding so far that we need to build gain accelerators and telescopes just to gather new data that won't fit into our current theories."
p14 Discusses the general relativity correction to GPS satellites.
p15 Discussion of the LHC. $9 billion, began operation in 2009, pointing to 4 July, 2012 as the discovery of a new particle.
p16 Last paragraph a post mortem on the Tevatron, 1983 to September 2011. Made discovery of the top quark.
p17 The LEP, Large Electron Positron accelerator 1989-2000 in same tunnel as the current LHC.
p18 Personnel: Lyn Evans, Giannetti and Incandela
2. Next to Godliness
p19-20 Leon Lederman and "The God Particle", referring to the Higgs. Lederman won Nobel Prize in 88 for neutrino flavors, continued to quark discoveries, director of Fermilab. A good story about Lederman. Physicists hate the term "God particle" but journalists love it.
p21 Quotes Hawking from A Brief History of Time.
p21-22 Discusses influential physicists who were religious, citing Newton and Lemaitre.
p22 "Today, however, most working physicists are much less likely to believe in God than are members of the general public." Goes on to discuss this, but without any cited evidence. Where's the data? Lennox certainly disagrees, and I certainly disagree.
p22 Discusses Einstein's words about God and uses them to build a position that physicists use God as a metaphor for the universe or as a public relations ploy.
p24 Discusses Steven Weinberg before congress
p25 Neat quote from Lederman and Teresi in the preface to the revised edition of "The God Particle" "The title ended up offending two groups: 1) those who believe in God, and 2) those who do not. We were warmly received by those in the middle."
p25 Discusses his own metaphor in his title. Notes that the Higgs doesn't help with gravity, dark matter or dark energy.
p26 Higgs as the final part of the Standard Model of particle physics. After discussing the Standard Model "And it all fits together beautifully, passing a bewildering array of experimental tests, as long as there is the Higgs boson. Without the Higgs, or something even more bizarre to take its place, the Standard Model wouldn't get off the ground."
p27 Addresses how we knew we needed it with a magician story. After that, about the Higgs: "For a long time we hadn't seen it directly, but we saw its effects. Or even better, we saw features of the world that made perfect sense if it's there, and make no sense without it. Without the Higgs boson, particles such as the electron would have zero mass and move at the speed of light; but indeed they do have mass and move more slowly. Without the Higgs boson, many elementary particles would appear identical with one another, but instead they are manifestly different, with a variety of masses and lifetimes. With the Higgs, all these features of particle physics make perfect sense."
p28 Fermions and bosons, a good verbal description. "Particles come in two types: the particles that make up matter, known as "fermions", and the particles that carry forces, known as "bosons". The difference between the two is that fermions take up space, while bosons can pile on top of one another. You can't just take a pile of identical fermions and put them all in the same place; the laws of quantum mechanics won't allow it. That's why collections of fermions make up solid objects like tables and planets: the fermions can't be squeezed on top of one another."
p28 Atoms made out of three types of fermions - up, down, electron. Smaller the mass of the particle, the more space it takes up, so the electrons give matter its solidity. Bosons don't take up space.
p29 four fundamental forces, discusses particle exchange
p30 Nuclear forces: In 1973 Gross, Politzer and Wilczek showed asymptotic freedom - quark interaction strengthens with increasing separation, decreases close. Nobel 2004.
p31 W & Z
p32 Some details of weak force - change identity of particles they interact with - include this idea in hph - hints at symmetries.
p32 Higgs fundamentally different. Discusses Higgs field.
p33 Competition for best explanation of quantum mechanics in five words or less. Winner: Aatish Bhatia "Don't look:waves. Look: particles".
p34 Refers to Einstein's E=mc2 and comments "So lower masses mean less energy mean longer wavelengths mean larger sizes; higher masses mean more energy mean shorter wavelengths mean smaller sizes."
p34 Excellent introduction to Higgs properties in section entitled "Stuck away from zero".
"The Higgs is different. It's a field, just like the others, and it can be zero or some other value. But it doesn't want to be zero; it wants to sit at some constant number everywhere in the universe. The Higgs field has less energy when it's nonzero than when it's zero."
"As a result, empty space is full of the Higgs field. Not a complicated set of vibrations that would represent a collection of individual Higgs bosons; just a constant field, sitting quietly in the background. It's that ever-present field at every point in the universe that makes the weak interactions what they are and gives masses to elementary fermions. The Higgs boson - the particle discovered at the LHC - is a vibration in that field around its average value."
"Because the Higgs particle is a boson, it gives rise to a force of nature. Two massive particles can pass by each other and interact by exchanging Higgs bosons, just like two charged particles can interact by exchanging photons. But this Higgs force is not what gives particles mass, and it's generally not what all the fuss is about. What gives particles mass is this Higgs field sitting quietly in the background, providing a medium through which other particles move, affecting their properties along the way."
p35-36 Executive summary about the Higgs field and symmetries
p37 "Without the Higgs, the intricate variety of the Standard Model would collapse to a featureless collection of pretty much identical particles, and all of the fermions would be essentially massless. There would be no atoms, no chemistry, no life as we know it. The Higgs boson, in a very real sense, is what brings the universe to life. If there were one particle that deserved such a lofty title, there's no question it would be the Higgs."
3.Atoms and Particles
p41 Discussion of electron discovery in 1897 to the detection of the tau neutrino in 2000, ref App 2.
p44 In 1920s Dirac proposed the positron, discovered in 1932. Carl Anderson discovered it in cosmic rays. Good story of Anderson. Summarize this page in Hph. Maybe a sketch of the cloud chamber photograph on pg 46.
p46 1930 Pauli discovered neutrino, Fermi named it.
p48 Muon discovery in 1936 by Carl Anderson and Seth Neddermeyer, Rabi's comment "Who ordered that?!" 1962 Leon Lederman, Schwartz, Steinberger showed that there were two different kinds of neutrinos.
p49 Tau discovered in 1970s, tau neutrino not directly detected until 2000.
p50 Only 3 types of neutrinos needed to explain all known particles.
p50 With the multiplicity of particles, Lamb quote about levying a penalty for discovering any more new particles.
p50 Gell-Mann and Zweig proposed quarks, each quark being a triplet referred to by RGB color.
p51 Quark confinement in colorless combinations.
p52 Quarks in pairs would be identical if it weren't for the meddlesome Higgs field.
p53 Higgs a scalar boson, zero spin.
p53 "The Higgs boson is a vibration in the Higgs field, and the Higgs field is what gives mass to all of the massive elementary particles. So the Higgs boson interacts with all of the massive particles in our zoo - the quarks, the charged leptons, and the W and Z bosons. (Neutrino masses aren't completely understood as yet, so let's pretend that they don't interact with the Higgs, although the jury is still out.) And the more massive a particle is, the more strongly it couples to the Higgs. Really it's the other way around: The more strongly a particle couples to the Higgs, the more mass it picks up by moving through the ambient Higgs field that pervades empty space."
4.The Accelerator Story
p55 Bevatron of Berkeley, CA 1950s and 60s
p56 Bevatron contributed to two Nobel prizes:
p59 Energy chart with Higgs included. Energy up to LHC energy.
p60 LHC Higgs boson at 125 GeV
p61 CERN council established 1954 with 12 countries.
p62 In 1983 Carlo Rubbia upgraded the SPS to a proton-antiproton collider to discover the W and Z, Nobel Prize 1984. The current SPS is at 450 GeV, hands off to the LHC.
p63 In 1989 the Large Electron Positron (LEP) accelerator. It was shut down in 2000 to use its tunnel for the LHC.
5. The Largest Machine Ever Built
p75 Sep 10,2008 LHC came to life. Nine days later it exploded. Describes physical dimensions: 330ft underground, 17 mile circumference. Discusses the superconducting magnets.
p80 Data about LEP and planning for LHC
p81 Tribute to Lyn Evans
p82 Roman era villa found underground. Above it an underground river which was frozen with big shafts filled with liquid nitrogen for excavation. In 97 a boost with the commitment of $2billion from US.
p83 >1000 US physicists working at LHC
p84 400 MHz switching field, boosting at one point of the ring. The rest of the 17 miles is to keep the protons on path. 500 trillion protons circulate in 2 beams, one CW and one CCW. All protons from one canister of hydrogen.
p85 Discussion of a "fill", thousands of bunches per beam, 100 billion protons per bunch, inch long, 23 ft apart in thin needle 1/25 in across (about size of lead in pencil) further concentrated to 1/1000 inch.
p86 99.999996c, compared to rest energy of just under 1GeV for proton, first run was 3500GeV, in 2012 8TeV, goal 14 TeV, compare to 2TeV for Tevatron. 1TeV kinetic energy of a mosquito.
p88 The energy of the beam is enough to melt a ton of copper, so dumping the beam has to be done carefully. It goes to a graphite dump block surrounded by 1000 tons of steel and concrete. Heats 10 ton dump block to 1400F.
p88 The path consists of eight arcs of length 1.5 miles, with 1/3 mile straight sections between. Description of physical form.
p89 Data on the superconducting magnets, use of ping-pong ball like ball with radio transmitter to test beam path.
p90 Again comments on Lyn Evans who worked from 69-2010, describes first beam.
p91 Some numbers about LHC
6. Wisdom Through Smashing
p94 Discusses his "dig" at Morrison geological formation, Shell, Wyoming
p95 Bottom quark 10-12 s, Higgs 10-10 of that.
p96 Determine mass, charge and strong interaction
p97 A jet is a signature of a quark or a gluon.
p97 Carl Anderson discovered the positron 1930 with a device 5ft long and weighing 2 tons. Discusses comparison with ATLAS and CMS detectors, keys in the Higgs search. Five other experiments named.
p98 One month a year, LHC collides lead ions.
p99 Some construction details. Includes 78,000 lead tungstate crystals made in Russia. Atlas torus.
p101 Comments on valence quarks and virtual particles - gluons and quark-antiquark pairs, discusses fact that proton mass far exceeds the sum of the masses of the quarks in these terms.
p101 1400 bunches, 20 million times/sec, 100 billion protons, ~20 interactions - billions of protons, spray of about 100 hadrons.
p103 New idea to me, gluons experience strong interaction and produce jets similar to quarks.
p104 Wu's 3 jet events which established that gluons are real.
p104-106 Short pieces on different parts of the Standard Model.
p107-110 Atlas and CMS detectors.
p108 Details about inner detectors
p111 Role of the "trigger" in an LHC experiment, to let through significant events
p113-113 Sharing the experimental date to tiers 0,1 and 2 laboratories.
p113 World Wide Web beginning based on 1989 proposal
7. Particles in the Waves
p115-118 Discussion of fields
p120 Pierre Simon Laplace - late 1700s gravitational field
p121 1820 Oersted
p122 the Hertz story
p123 Gravity waves and Einstein
p124 10 element "metric" tensor. Hulse and Taylor Nobel Prize for gravity wave experiments.
p125 "Everything is made of fields, but when we look at them closely we see particles."
p126 Cites DAvid Deutsch, The Fabric of Reality. Overview of blackbody radiation.
p126 "High mass implies short wavelength, which means that a particle takes up less space." I have not exploited that in HyperPhysics and need to. He goes on to discuss the implications for atoms.
p127 Einstein and the photoelectric effect. The worked "photon" coined by Gilbert Lewis in the 1920's and popularized by Compton.
p128 Photo analogy for electron spin.
p131 Boson fields and fermion fields - fermion states and the Pauli exclusion principle. "particles are discrete vibrations in sermonic fields" "Inside a nucleus, huddled in close comradeship with a few protons, a neutron can last forever."
8. Through a Broken Mirror
p137 Higgs field "fills space, breaks symmetries and gives mass and individuality to the other particles of the Standard Model"
p138 "the universe is made of fields. But most of these fields are turned off - set to zero - in empty space. .. The Higgs is different, even in empty space, it's not zero. The field takes on a steady value absolutely everywhere, and the Higgs boson particle is a vibration around that value."
p140 Higgs field lowest energy state 246GeV. We get this from experiment, determines the strength of the weak interactions.
p143 Discussing mass and says gluon has zero mass - depicts tiny mass of neutrino as not understood.
p144 Higgs field "other particles are interacting with it constantly - and its those persistent, inevitable interactions with the background that create the mass of the particle." Mass = value of Higgs field x interaction strength. Why is interaction strength different? Nobody knows.
p145 The majority of the mass is protons and neutrons, whose mass comes from the strong interaction.
p145 "The size of atoms, in other words, is determined by a fundamental parameter of nature, the mass of the electron."
p151 Tries to picture gauge invariance. Hermann Weyl. Also called "local" symmetries in contrast to a global symmetry. Introduces idea of a "connection", gauge symmetry implies that there is a connection field.
p152 "Symmetries lead to connection fields and bends and twists in the connection fields lead to forces of nature. Boson fields are connection fields that relate the symmetry transformations, called "gauge bosons". Weak interaction is felt by the Higgs boson.
p153 Gravitons - symmetry 4d space-time, strong symmetry - color, E&M two fields, W&Z-underlying symmetry masked by Higgs.
p154 Yang and Mills proposed a connection field between a proton and neutron in 1954. The gravity and E&M symmetries involved massless exchange particles to give them long range, and symmetries were associated with massless bosons.
p154-156 Very interesting story about the interaction between Yang and Mills with Pauli and Heisenberg when Yang gave a paper on this at Princeton. This gave birth to the idea of bosons with mass. Need to reread and think about this. Applies to both strong and weak nuclear forces. In the strong force, massless bosons (gluons) are hidden inside proton and neutron. In the weak interaction, the Higgs breaks the symmetry, giving mass to the W & Z.
p156-157 Gives some example scenarios to illustrate broken symmetry, then states that the Higgs field breaks the symmetry of the weak interaction so W & Z have mass - a spontaneous symmetry break.
p158 List of sets of particles related by Higgs symmetry breaking. Would be identical without Higgs.
p160 Symmetry breaking gives 1 Higgs, not 4. The other 3 are "eaten" by the W+/- and Z.
p161 Uses his "upside-down pendulum" analogy to approach symmetry at high temperatures near Big Bang. In the early universe symmetry is restored and W&Z are massless. "The moment at which the Higgs went from being zero on average to some nonzero value is known as the "electroweak phase transition". About 1 trillionth of a second after the Big Bang.
p162 Weinberg and Salam in the 1960's predicted the Z, for which there wasn't any experimental evidence. Found evidence for interaction carried by it in 1973. The actual particle discovery was 10 years later at CERN
9. Bringing Down the House
p163 Two experiments CMS and Atlas were in pursuit of the Higgs. Each group represented over 3000 physicists. The December 2011 seminar produced evidence of a resonance at about 125 GeV.
p164 More about Gianotti
p165 Description of the process of the Higgs search.
p166-167 Apply conservation laws, use Feynman diagrams, convert Feynman diagrams to numerical values.
p168 Wilczek proposed gluon fusion, which turned out to be the most important single way that Higgs was produced at LHC.
p169 Ways to get Higgs: gluon fusion, W+W- fusion, 2Z's, Quark-antiquark, W or Z producion with Higgs.
p170 Higgs lifetime < 10-21. Decays to top and bottom, W&Z, tau lepton.
p171 Pie chart of modes of Higgs decay for 125 GeV Higgs. More than 99% of the time, decays to something else are actually measured because you can't measure them directly.
p172-174 Expected production from Higgs in collision
p174 Discussion of 1975 work by Ellis et al, book Higgs Hunters Guide.
p175-176 Good probability discussion in terms of expected deviation in units of sigma. +/- sigma 68% of time, +/- 2 sigma 95% of time, +/- 3 sigma 99.7% of time, so the general practice was to regard 3 sigma as "evidence for" and 5 sigma as "discovery of".
p177 graphic to illustrate the above probability discussion.
p179 Nobel Dreams by Gary Taubes about Carlo Rubbia and the W&Z bosons.
p180 The December 2011 conference reported a 125 GeV peak at Atlas at 3.6 sigma, at CMS at 2.68 sigma.
p183 More discussion of the July 2012 conference. Gianotti reported for Atlas, result 126.5GeV, compared to 125.3 GeV for CMS
ATLAS 126.5 GeV
CMS 125.3 GeV
p185 Another quote from Peter Higgs
p186 Millions of interactions, a couple of hundred through the trigger. For a year's data, about 1000 results at each energy. Discussion of curves on color insert.
p187 A couple of puzzles emerged:
10. Spreading the Word
p193 Comment on communication web at CERN which led to the WWW.
11. Nobel Dreams
p212 Aim is to recount history of Higgs mechanism
p212 Pauli's point, underlying symmetry always comes associated with massless boson particles. Symmetries imply stringent restrictions on the properties that particles can have. I.e., E&M symmetry implies strict charge conservation.
p213 A repeat, but I've got to nail this down in hph, so I'm recording summary statements.
p213 "..strong and weak interactions are also Yang-Mills-type forces, with the massless particles hidden from us for different reasons: In the strong force the gluons are massless but confined inside hadrons, while in the weak force the W and Z bosons become massive because of spontaneous symmetry breaking."
p215 Spontaneous symmetry breaking.
p215 About superconductivity "Because photons obtain a mass in the Landau-Ginzberg and BCS theories, there is a certain minimum energy required to make them. Electrons that don't have enough energy can't make any photons, and therefore can't lose energy: The Cooper pairs flow through the material with zero resistance."
p216 Tribute to Nambu, who, besides his 2008 Nobel Prize, was "one of the first to understand spontaneous symmetry breaking in particle physics", the first to propose quark "color", to suggest the existence of gluons, and to point to the possibility of "strings".
p217 Nambu and Jona-Lasinio showed that spontaneous symmetry breaking could occur even in empty space in the presence of a nonzero field, "a clear precursor to the Higgs field" "this theory also showed how a fermion field could start out massless but gain mass through the process of symmetry breaking."
p217 Nambu's theory also predicted a new massless boson along with this symmetry breaking, and nobody wanted any more particles! But Jeffrey Goldstone confirmed and expanded this idea that the spontaneous breakdown of a global symmetry would produce a new kind of massless boson. Called "Nambu-Goldstone bosons", they were reinforced by Abdus Salam and Steven Weinberg to the status of "Goldstone's theorem". This introduced the idea of scalar fields (spin zero) that broke symmetries by taking on a non-zero value in empty space.
p219 Anderson's role, (Nobel 1977) in suggesting, contrary to Nambu-Goldstone and Yang-Mills, the vacuum theory should come up with a massive boson.
p220-221 Gilbert's role, (Nobel 1980 in biology) . Abraham Klein and Benjamin Lee weigh in with idea that Goldstone could be avoided non-relativistically, Anderson worried about energy of empty space which would appear to be large, now a small value associated with dark energy.
p222 Shared credit for inventing the "Higgs mechanism"
p223 More on Higgs. Published short paper in 1964 in Physics Letters UK, then had second paper rejected and published it in Phys Rev Letters in US, in the process adding comment about the prediction of a massive scalar boson, ultimately resulting in it being named after him.
p224 More discussion of the fact that before the symmetry breaking there would be 4 scalar bosons and 3 massless gauge bosons. Three of these become the W+/- and Z and then the massive scalar Higgs.
p226 Story of Guralnik, Hagen and Kibble
p228 Weak interaction discussion. Fermi in neutron decay 1934 found evidence of particle, named neutrino by Pauli.
p229 Renormalization and handling infinities, Nobel for Feynmann, Schwinger and Tomonaga
p230 Diagram of neutron decay
p232 Electroweak unification. Schwinger, graduate student Sheldon Glashow, had to deal with conservation of parity for E&M and non-conservation of parity for the weak interaction. The predicted the presence of the neutral Z particle. Salam and Ward were pursuing a similar path.
p234 Weinberg's contribution: predicted the masses of the W & Z.
p236 Weinberg and Salam work not noticed much until Gerard t' Hooft showed consistency of electroweak theory. t' Hooft and Veltman Nobel 1999.
p237 Observation of Z effects 1973, GSW Nobel 1979, WZ not actually discovered until 1983.
p237 Story of how particle got named Higgs.
p239 Good summary list of persons instrumental in developing ideas of symmetry breaking
12. Beyond This Horizon
p243 Tribute to Vera Rubin and the story of dark matter. Zwicky and Oort had earlier evidence.
p247 The WIMP story. Assume 100GeV agrees well with the amount of dark matter. Postulate that interaction of WIMPs and ordinary matter would be from exchange of Higgs boson.
p248 The Higgs portal
p253 A kind of "fine tuning" section that muses about why Higgs and vacuum energy are so small (hierarchy problem). Mentions "Planck scale" 1018 GeV "where quantum gravity becomes important and space-time itself ceases to have any definite meaning".
p254 Vacuum energy - dark energy - cosmological constant. Nobel 2011 for Saul Perlmutter, Adam Riess and Brian Schmidt.
p255 When calculated, 10120 times what is observed.
p256 Higgs not connected directly to dark energy
p257 Supersymmetry could connect fermions to bosons
p260 Supersymmetry would give 5 Higgs, one +, one -, 3 neutral. If you had virtual fermions, it could help solve the hierarchy problem - one of the main motivations for pursuing it. neutralino is also a candidate for dark matter.
p261 String theory - traceable to Nambu, Nielsen and Susskind
p265 Branes and the multiverse, M-brane theory
13. Making It Worth Defending
p270 Robert Wilson quote about Fermilab, Weinberg quote
p276 Other proposed accelerators
p278 Particles with sails visualization of Higgs
p280 "We are part of the universe that has developed a remarkable ability: We can hold an image of the world in our minds. We are matter contemplating itself. How is that possible? Particle physics doesn't give us the answer, but it's a basic ingredient in the larger story in which the answer arises."
p281 Primary role of data.
p285 2013 Conference - new boson looks more like the Higgs
p286 Zero spin, even parity.
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