CERN:   A simulation of a particle collision inside the Large Hadron Collider. When two protons collide inside the machine, they create an energetic explosion that gives rise to new and exotic particles — including, perhaps, the Higgs boson.

 

 

Dear All, we’re posting these graphics and articles because the Higgs boson was so much in the news this past week and we like to keep our bloggers well informed.  We follow our own curiosity and whatever we’re reading up on, each day, we share.  Now, we’re trying to understand the basic concepts of what’s going on in Cern.  Enjoy and send comments, as usual,  to joycehays@targethealth.com.  This kind of science is for sure, rich material for a discussion of science, philosophy, religion and the arts.  We’re not yet quite sure why anyone (except media and PR) would nickname the Higgs boson, The God Particle.  Maybe it’s a reference to Einstein’s the mind of God.  Just have to keep reading

 

A simulated event, featuring the appearance of the Higgs boson

 

Higg’s Boson, named after Peter Higgs, a physicist at the University of Edinburgh and one of the people who theorized its existence, is the last fundamental piece of the Standard Model that has yet to have been observed. It plays a crucial role in generating a sort of cosmic molasses filling the universe that creates mass in other particles.

The Higgs boson is a hypothetical massive elementary particle that is predicted to exist by the Standard Model (SM) of particle physics. The Higgs boson is an integral part of the theoretical Higgs mechanism. If shown to exist, it would help explain why other particles can have mass. It is the only elementary particle predicted by the Standard Model that has not yet been observed in particle physics experiments. Theories that do not need the Higgs boson also exist and would be considered if the existence of the Higgs boson were ruled out. They are described as Higgsless models.

If shown to exist, the Higgs mechanism would explain why the W and Z bosons, which mediate weak interactions, are massive whereas the related photon, which mediates electromagnetism, is massless. The Higgs boson is expected to be in a class of particles known as scalar bosons. (Bosons are particles with integer spin, and scalar bosons have spin 0.)

Experiments attempting to find the particle are currently being performed using the Large Hadron Collider (LHC) at CERN, and were performed at Fermilab‘s Tevatron until its closure in late 2011. Some theories suggest that any mechanism capable of generating the masses of elementary particles must become visible at energies above 1.4 TeV; therefore, the LHC (colliding two 3.5 TeV beams) is expected to be able to provide experimental evidence of the existence or non-existence of the Higgs boson.

On 12 December 2011, the ATLAS collaboration at the LHC found that a Higgs mass in the range from 145 to 206 GeV/c2 was excluded at the 95% confidence level.  On 13 December 2011, experimental results were announced from the ATLAS and CMS experiments, indicating that if the Higgs boson exists, its mass is limited to the range 116–130 GeV (ATLAS) or 115–127 GeV (CMS), with other masses excluded at 95% confidence level. Observed excesses of events at around 124 GeV (CMS) and 125-6 GeV (ATLAS) are consistent with the presence of a Higgs boson signal, but also consistent with fluctuations in the background. The global statistical significances of the excesses are 1.9 sigma (CMS) and 2.6 sigma (ATLAS) after correction for the look elsewhere effect. As of 13 December 2011, a combined result is not available.

The particle is sometimes called the God particle, a title deplored by some scientists as a media hyperbole that misleads readers.

 

Origin of the theory

 

Five of the six 2010 APS J.J. Sakurai Prize winners. From left to right: Kibble, Guralnik, Hagen, Englert, and Brout.

 

 

The sixth of the 2010 APS J.J. Sakurai Prize winners: Peter Higgs

 

 

The Higgs mechanism is a process by which vector bosons can get a mass. It was proposed in 1964 independently and almost simultaneously by three groups of physicists: François Englert and Robert Brout; by Peter Higgs (inspired by ideas of Philip Anderson and by Gerald Guralnik, C. R. Hagen, and Tom Kibble.

The three papers written on this discovery were each recognized as milestone papers during Physical Review Letters‘s 50th anniversary celebration.  While each of these famous papers took similar approaches, the contributions and differences between the 1964 PRL symmetry breaking papers are noteworthy. These six physicists were also awarded the 2010 J. J. Sakurai Prize for Theoretical Particle Physics for this work.

The 1964 PRL papers by Higgs and by Guralnik, Hagen, and Kibble (GHK) both displayed equations for the field that would eventually become known as the Higgs boson. In the paper by Higgs the boson is massive, and in a closing sentence Higgs writes that “an essential feature” of the theory “is the prediction of incomplete multiplets of scalar and vector bosons”. In the model described in the GHK paper the boson is massless and decoupled from the massive states. In recent reviews of the topic, Guralnik states that in the GHK model the boson is massless only in a lowest-order approximation, but it is not subject to any constraint and it acquires mass at higher orders. Additionally, he states that the GHK paper was the only one to show that there are no massless Nambu-Goldstone bosons in the model and to give a complete analysis of the general Higgs mechanism. Following the publication of the 1964 PRL papers, the properties of the model were further discussed by Guralnik in 1965 and by Higgs in 1966.

Steven Weinberg and Abdus Salam were the first to apply the Higgs mechanism to the electroweak symmetry breaking. The Higgs mechanism not only explains how the electroweak vector bosons get a mass, but predicts the ratio between the W boson and Z boson masses as well as their couplings with each other and with the Standard Model quarks and leptons. Many of these predictions have been verified by precise measurements performed at the LEP and the SLC colliders, thus confirming that the Higgs mechanism takes place in nature.

The Higgs boson’s existence is not a strictly necessary consequence of the Higgs mechanism: the Higgs boson exists in some but not all theories which use the Higgs mechanism. For example, the Higgs boson exists in the Standard Model and the Minimal Supersymmetric Standard Model yet is not expected to exist in Higgsless models, such as Technicolor. A goal of the LHC and Tevatron experiments is to distinguish among these models and determine if the Higgs boson exists or not.

 

Theoretical overview

 

 

Summary of interactions between particles described by the Standard Model.

 

 

A one-loop Feynman diagram of the first-order correction to the Higgs mass. The Higgs boson couples strongly to the top quark so it might decay into top–anti-top quark pairs if it were heavy enough.

The Higgs boson particle is a quantum of the theoretical Higgs field. In empty space, the Higgs field has an amplitude different from zero; i.e. a non-zero vacuum expectation value. The existence of this non-zero vacuum expectation plays a fundamental role; it gives mass to every elementary particle that couples to the Higgs field, including the Higgs boson itself. The acquisition of a non-zero vacuum expectation value spontaneously breaks electroweak gauge symmetry. This is the Higgs mechanism, which is the simplest process capable of giving mass to the gauge bosons while remaining compatible with gauge theories. This field is analogous to a pool of molasses that “sticks” to the otherwise massless fundamental particles that travel through the field, converting them into particles with mass that form (for example) the components of atoms.

In the Standard Model, the Higgs field consists of two neutral and two charged component fields. Both of the charged components and one of the neutral fields are Goldstone bosons, which act as the longitudinal third-polarization components of the massive W+, W, and Z bosons. The quantum of the remaining neutral component corresponds to the massive Higgs boson. Since the Higgs field is a scalar field, the Higgs boson has no spin, hence no intrinsic angular momentum. The Higgs boson is also its own antiparticle and is CP-even.

The Standard Model does not predict the mass of the Higgs boson. If that mass is between 115 and 180 GeV/c2, then the Standard Model can be valid at energy scales all the way up to the Planck scale (1016 TeV). Many theorists expect new physics beyond the Standard Model to emerge at the TeV-scale, based on unsatisfactory properties of the Standard Model. The highest possible mass scale allowed for the Higgs boson (or some other electroweak symmetry breaking mechanism) is 1.4 TeV; beyond this point, the Standard Model becomes inconsistent without such a mechanism, because unitarity is violated in certain scattering processes. There are over a hundred theoretical Higgs-mass predictions.

Extensions to the Standard Model including supersymmetry (SUSY) predict the existence of families of Higgs bosons, rather than the one Higgs particle of the Standard Model. Among the SUSY models, in the Minimal Supersymmetric Standard Model (MSSM) the Higgs mechanism yields the smallest number of Higgs bosons; there are two Higgs doublets, leading to the existence of a quintet of scalar particles: two CP-even neutral Higgs bosons h0 and H0, a CP-odd neutral Higgs boson A0, and two charged Higgs particles H±. Many supersymmetric models predict that the lightest Higgs boson will have a mass only slightly above the current experimental limits, at around 120 GeV/c2 or less.

 

Experimental search

 

 

Status as of March 2011, to the indicated confidence intervals

 

 

A Feynman diagram of one way the Higgs boson may be produced at the LHC. Here, two gluons convert to two top/anti-top pairs, which then combine to make a neutral Higgs.

 

 

A Feynman diagram of another way the Higgs boson may be produced at the LHC. Here, two quarks each emit a W or Z boson, which combine to make a neutral Higgs.

As of November 2011, the Higgs boson has yet to be confirmed experimentally,despite large efforts invested in accelerator experiments at CERN and Fermilab.

Prior to the year 2000, the data gathered at the LEP collider at CERN allowed an experimental lower bound to be set for the mass of the Standard Model Higgs boson of 114.4 GeV/c2 at the 95% confidence level. The same experiment has produced a small number of events that could be interpreted as resulting from Higgs bosons with a mass just above this cut off — around 115 GeV—but the number of events was insufficient to draw definite conclusions. The LEP was shut down in 2000 due to construction of its successor, the LHC, which is expected to be able to confirm or reject the existence of the Higgs boson. Full operational mode was delayed until mid-November 2009, because of a serious fault discovered with a number of magnets during the calibration and startup phase.

At the Fermilab Tevatron, there were ongoing experiments searching for the Higgs boson. As of July 2010, combined data from CDF and experiments at the Tevatron were sufficient to exclude the Higgs boson in the range 158 GeV/c2 – 175 GeV/c2 at the 95% confidence level.Preliminary results as of July 2011 have since extended the excluded region to the range 156 GeV/c2 – 177 GeV/c2 at the 90% confidence level. Data collection and analysis in search of Higgs are intensifying since 30 March 2010 when the LHC began operating at 3.5 TeV.Preliminary results from the ATLAS and CMS experiments at the LHC as of July 2011 exclude a Standard Model Higgs boson in the mass range 155 GeV/c2 – 190 GeV/c2 and 149 GeV/c2 – 206 GeV/c2, respectively, at the 95% confidence level. All of the above confidence intervals were derived using the CLs method.

It may be possible to estimate the mass of the Higgs boson indirectly. In the Standard Model, the Higgs boson has a number of indirect effects; most notably, Higgs loops result in tiny corrections to masses of W and Z bosons. Precision measurements of electroweak parameters, such as the Fermi constant and masses of W/Z bosons, can be used to constrain the mass of the Higgs. As of 2006, measurements of electroweak observables allowed the exclusion of a Standard Model Higgs boson having a mass greater than 285 GeV/c2 at 95% CL, and estimated its mass to be 129+74
−49 GeV/c2 (the central value corresponding to approximately 138 proton masses). As of August 2009, the Standard Model Higgs boson is excluded by electroweak measurements above 186 GeV at the 95% confidence level. These indirect constraints make the assumption that the Standard Model is correct. It may still be possible to discover a Higgs boson above 186 GeV if it is accompanied by other particles between the Standard Model and GUT scales.

In a 2009 preprint,  it was suggested that the Higgs boson might not only interact with the above-mentioned particles of the Standard model of particle physics, but also with the mysterious weakly interacting massive particles (or WIMPS) that may form dark matter, and which play an important role in recent astrophysics.

Various reports of potential evidence for the existence of the Higgs boson have appeared in recent years but to date none has provided convincing evidence. In April 2011, there were suggestions in the media that evidence for the Higgs boson might have been discovered at the LHC in Geneva, Switzerland but these had been debunked by mid May. In regard to these rumors Jon Butterworth, a member of the High Energy Physics group on the Atlas experiment, stated they were not a hoax, but were based on unofficial, unreviewed results. The LHC detected possible signs of the particle, which were reported in July 2011, the ATLAS Note concluding: “In the low mass range (c 120−140 GeV) an excess of events with a significance of approximately 2.8 sigma above the background expectation is observed” and the BBC reporting that “interesting particle events at a mass of between 140 and 145 GeV” were found. These findings were repeated shortly thereafter by researchers at the Tevatron with a spokesman stating that: “There are some intriguing things going on around a mass of 140GeV.”

On 22 August it was reported that the anomalous results had become insignificant on the inclusion of more data from ATLAS and CMS and that the non-existence of the particle had been confirmed by LHC collisions to 95% certainty between 145–466 GeV (except for a few small islands around 250 GeV). A combined analysis of ATLAS and CMS data, published in November 2011, further narrowed the window for the allowed values of the Higgs boson mass to 114-141 GeV. On 12 December 2011, the ATLAS collaboration found that a Higgs mass in the range from 145 to 206 GeV was excluded at the 95% confidence level.

On 13 December 2011, experimental results were announced from the ATLAS and CMS experiments, indicating that if the Higgs boson exists, its mass is limited to the range 116–130 GeV (ATLAS) or 115–127 GeV (CMS), with other masses excluded at 95% confidence level. Observed excesses of events at around 124 GeV (CMS) and 125-6 GeV (ATLAS) are consistent with the presence of a Higgs boson signal, but also consistent with fluctuations in the background. The global statistical significances of the excesses are 1.9 sigma (CMS) and 2.6 sigma (ATLAS) after correction for the look elsewhere effect.  As of 13 December 2011, a combined result is not yet available. The statistical significance of the observations is not large enough to draw conclusions, but the fact that the two independent experiments show excesses at around the same mass has led to considerable excitement in the particle physics community. It is expected that the LHC will provide sufficient data to either exclude or confirm the existence of the Standard Model Higgs boson by the end of 2012.

 

Alternatives for electroweak symmetry breaking

 

Higgsless model

In the years since the Higgs boson was proposed, several alternatives to the Higgs mechanism have been proposed. All of these proposed mechanisms use strongly interacting dynamics to produce a vacuum expectation value that breaks electroweak symmetry. A partial list of these alternative mechanisms are:

 

The God particle”

 

The Higgs boson is often referred to as “the God particle” by the media,after the title of Leon Lederman‘s book, The God Particle: If the Universe Is the Answer, What Is the Question?  Lederman initially wanted to call Higgs boson “the goddamn particle” because “nobody could find the thing.”; but his editor would not let him.  While use of this term may have contributed to increased media interest in particle physics and the Large Hadron Collider, many scientists dislike it, since it overstates the particle’s importance, not least since its discovery would still leave unanswered questions about the unification of QCD, the electroweak interaction and gravity, and the ultimate origin of the universe.  A renaming competition conducted by the science correspondent for the British Guardian newspaper chose the name “the champagne bottle boson” as the best from among their submissions: “The bottom of a champagne bottle is in the shape of the Higgs potential and is often used as an illustration in physics lectures. So it’s not an embarrassingly grandiose name, it is memorable, and [it] has some physics connection too.”

 

 

LHC – Large Hadron Collider

ATLAS experiment  —   A Toroidal LHC ApparatuS

 

ALICE  —   (A Large Ion Collider Experiment) is one of the six detector experiments at the Large Hadron Collider at CERN. The other five are: ATLAS, CMS, TOTEM, LHCb, and LHCf. ALICE is optimized to study heavy ion collisions. Pb-Pb nuclei collisions will be studied at a centre of mass energy of 2.76 TeV per nucleon. The resulting temperature and energy density are expected to be large enough to generate a quark-gluon plasma, a state of matter wherein quarks and gluons are deconfined.

 

 

About the Higgs Field and the Higgs Boson

 

György Ligeti: Lux Aeterna

 

Understanding Our Universe through the Higgs

 

Higgs Boson Particle (The God Particle)

 

GYORGY LIGETI – ATMOSPHERES – Should have been called Ode to the God Particle

 

Michio Kaku on the ‘God Particle’

 

‘The God Particle’: The Higgs Boson

 

Understanding the Universe Through the God Particle

 

CERN scientists break the speed of light

 

Sounds of the God Particle

 

Mass is Energy Moving Faster then Light

 

What’s new @CERN ? Higgs boson, standard model, SUSY and neutrinos

 

Ligeti – Poeme Symphonique for 100 Metronomes (Minimalist Sound Poem)

 

 

Data Hints at Elusive Particle, but the Wait Continues

 

Agence France-Presse – Getty Images: An illustration of photons, provided by the Compact Muon Solenoid team of researchers.

 

 

Physicists will have to keep holding their breath a while longer

 

The New York Times, December 14, 2011, by Dennis Overbye  —  Two teams of scientists sifting debris from high-energy proton collisions in the Large Hadron Collider at CERN, the European Organization for Nuclear Research outside Geneva, said Tuesday that they had recorded tantalizing hints — but only hints — of a long-sought subatomic particle known as the Higgs boson, whose existence is a key to explaining why there is mass in the universe. By next summer, they said, they will have enough data to say finally whether the elusive particle really exists.

If it does, its mass must lie within the range of 115 billion to 127 billion electron volts, according to the new measurements.

The putative particle would weigh in at about 126 billion electron volts, about 126 times heavier than a proton and 250,000 times heavier than an electron, reported one army of 3,000 physicists, known as Atlas, for the name of their particle detector.

Meanwhile, the other team, known as C.M.S. — for its detector, the Compact Muon Solenoid — found what its spokesman, Guido Tonelli, termed “a modest excess” in its data corresponding to masses around 124 billion electron volts. The physicists from the different teams are already discussing whether these differences are significant.

Showing off one striking bump in the data, Fabiola Gianotti, a spokeswoman for the Atlas team, said, “If we are just being lucky, it will take a lot of data to kill it.”

Over the last 20 years suspicious bumps that might have been the Higgs have come and gone — most recently last summer — and the same thing could happen again. Physicists said the chance that these results were a fluke because of random fluctuations in the background of normal physics was about 1 percent, which is too high to claim a discovery, but is enough to inspire excitement.

The fact that two rival teams using two different mammoth particle detectors had recorded similar results was considered good news.

“So CERN is not claiming a discovery, but I am quite optimistic,” said Steven Weinberg of the University of Texas at Austin, whose 1979 Nobel Prize rests partly on the Higgs.

Greg Landsberg of Brown University, a leader of the C.M.S. group, said that how to characterize the new results depended “on whether you see the glass half empty or half full.” He added, “I believe that these are exciting results, but it is just too early to say whether what we see is a glimpse of Higgs or another statistical fluctuation.”

Trying unsuccessfully to hold back an ear-to-ear grin, Kyle Cranmer, a New York University physicist and member of the Atlas team, admitted he was excited. “A bump is the most exciting thing a particle physicist can see on a plot,” he said.

Physicists around the world, fueled by coffee, dreams and Internet rumors of a breakthrough, gathered in lounges and auditoriums early Tuesday morning to watch a lengthy Webcast of the results at CERN.

“Physicists at 8 a.m.,” exclaimed Neal Weiner, a theorist who organized a gathering at New York University. “That’s really impressive!”

The results were posted on the Web sites of Atlas and C.M.S.

As seen on the Webcast, the auditorium at CERN was filled to standing room only. In New York, at the conclusion of the talks, the N.Y.U. physicists burst into applause. And around the world, physicists also seemed cautiously excited.

Lawrence M. Krauss, a cosmologist at Arizona State University, put it this way: “If the Higgs is discovered, it will represent perhaps one of the greatest triumphs of the human intellect in recent memory, vindicating 50 years of the building of one of the greatest theoretical edifices in all of science, and requiring the building of the most complicated machine that has ever been built.”

The Higgs boson is the cornerstone and the last missing part of the so-called Standard Model, a suite of equations that has held sway as the law of the cosmos for the last 35 years and describes all of particle physics. Physicists have been eager to finish the edifice, rule the Higgs either in or out and then use that information to form deeper theories that could explain, for example, why the universe is made of matter and not antimatter, or what constitutes the dark matter and dark energy that rule the larger universe.

The particle is named for the University of Edinburgh physicist Peter Higgs, who was one of six physicists — the others are Tom Kibble, the late Robert Brout, Francois Englert, Gerry Guralnik and Dick Hagen — who suggested that a sort of cosmic molasses pervading space is what gives particles their heft. Particles trying to wade through it gather mass the way a bill moving though Congress gains riders and amendments, becoming more and more ponderous. It was Dr. Higgs who pointed out that this cosmic molasses, normally invisible and, of course, odorless, would have its own quantum particle, and so the branding rights went to him.

In 1967 Dr. Weinberg made the Higgs boson a centerpiece of an effort to unify two of the four forces of nature, electromagnetism and the nuclear “weak” force, and explain why the carriers of electromagnetism — photons — are massless but the carriers of the weak force — the W and Z bosons — are about 100 times as massive as protons.

Unfortunately, the model does not say how heavy the Higgs boson itself — the quantum personification of this field — should be. And so physicists have had to search for it the old-fashioned train-wreck way, by smashing subatomic particles together to see what materializes.

The Large Hadron Collider accelerates protons to energies of 3.5 trillion electron volts around an 18-mile underground racetrack and then crashes them together.

If these crashes have indeed put the Higgs on the horizon of discovery, the news comes in the nick of time. Over the course of the last few years, searches at the CERN collider and the now-defunct Tevatron at the Fermi National Accelerator Laboratory in Batavia, Ill., have come to the verge of ruling the Higgs out.

Perhaps it won’t come to that. Reached in Austin, Dr. Weinberg, who shared the Nobel for coming up with the theory of electroweak unification with Sheldon Glashow, of Boston University, and Abdus Salam, of Pakistan, said: “It’s always a little weird when something that comes out of the mathematics in theoretical work turns out to exist in the real world. You asked me earlier if it’s exciting. Sure is.”

That excitement continues, as Rolf Heuer, CERN’s director general, told the physicists Tuesday. “Keep in mind,” he concluded, “that we are running next year.”