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Possible hints of much-sought mystery particle reported

Aug. 17, 2011
Courtesy of Caltech
and World Science staff

New re­sults from the world’s larg­est par­t­i­cle smash­er might hint at the ex­ist­ence of an elu­sive par­t­i­cle phys­i­cists have been seek­ing for years, the Higgs bos­on, some re­search­ers say.

This ent­ity is thought to be re­spon­si­ble for en­dow­ing eve­ry oth­er fun­da­men­tal par­t­i­cle of mat­ter with mass, or weight. This is ac­cord­ing to the con­ven­tion­al think­ing in phys­ics, em­bod­ied in a set of ideas called the Stand­ard Mod­el. The Higgs bos­on is in fact the last par­t­i­cle that is pre­dicted by the Stand­ard Mod­el but not yet de­tected.

The Com­pact Mu­on So­le­noid de­tec­tor, one of two in­stru­ments at the Large Had­ron Col­lider whose un­u­su­al read­ings are lead­ing some to spec­u­late that the elu­sive Higgs par­t­i­cle may have been found. (Cred­it: Bore­ham, S; Brice, M; Gin­ter, P; Mar­cel­loni, C; Col­lab­o­ra­t, CMS)


The particle smash­er re­ported to have gath­ered the in­tri­guing da­ta, called the Large Had­ron Col­lider, blasts beams of subat­omic par­t­i­cles to­geth­er at near-light speed to break them in­to their parts for stu­dy. Many of the re­sult­ing par­t­i­cles dis­in­te­grate al­most in­stant­ly, mak­ing their anal­y­sis hard, but phys­i­cists hope to tease out signs that some of them are Higgs bos­ons.

Al­though some of the sig­nals gen­er­at­ed from the col­lid­er’s de­tec­tors are sta­tis­ti­cal noise, two re­cent ex­pe­ri­ments have found an “ex­cess” of sig­nals con­sist­ent with a char­ac­ter­is­tic ex­pected for the Higgs, re­search­ers say. That char­ac­ter­is­tic is its the­o­rized range of mass, be­lieved to be be­tween 130 and 150 gi­ga­elec­tron volts, the un­its used to weigh subat­omic par­t­i­cles.

The da­ta aren’t yet statis­tic­ally sig­nif­i­cant enough to be called a def­i­nite sig­nal, let alone a dis­cov­ery of a par­t­i­cle, cau­tioned Har­vey New­man, a phys­i­cist at the Cal­i­for­nia In­sti­tute of Tech­nol­o­gy in­volved with the proj­ect. How­ev­er, the da­ta come from two dif­fer­ent types of de­tec­tors con­nect­ed to the col­lider, which lies un­der­ground near Ge­ne­va, Switz­er­land.

The un­usu­al read­ings could be due to some un­known source or could be the first signs of the Higgs, New­man said. "One could spec­u­late that it's an un­usu­al sta­tis­ti­cal fluctua­t­ion," he added, "but I don't think so." The de­vel­op­ments were an­nounced a meet­ing of the Eu­ro­pe­an Phys­i­cal So­ci­e­ty in Gre­no­ble, France, held from July 21 to 27.

The Higgs bos­on con­cept dates to 1964, when a phys­i­cist, Pe­ter Higgs, pro­posed the ex­ist­ence of a “field” that per­me­ates the uni­verse. Just as a mag­net­ic field in­ter­acts with iron fil­ings, this “Higgs field” fills the space be­tween eve­ry fun­da­men­tal par­t­i­cle and in­ter­acts with those par­t­i­cles. These in­ter­ac­tions slow a par­t­i­cle as it moves through the field. A low-mass par­t­i­cle such as the elec­tron, for ex­am­ple, is that way be­cause it does­n't in­ter­act with the Higgs field much. Thus it can zip through the field with ease like a sleek an­cho­vy swim­ming through the ocean. But par­t­i­cles like the so-called top quark, which is part of the nu­cle­us of at­oms, in­ter­act with the Higgs field more strongly, so to them, the field is more like an ocean of mo­las­ses. The top quark is thus heavy and slug­gish, weigh­ing in at more than 300,000 times the mass of an elec­tron. 

In phys­ics, eve­ry field has an as­so­ci­at­ed par­t­i­cle; the electromag­net­ic field, seen by us as light, is as­so­ci­at­ed with the pho­ton, for in­stance. For the Higgs field, the as­so­ci­at­ed par­t­i­cle is the Higgs bos­on. By in­ter­acting with it­self, it's re­spon­si­ble for its own mass.

The Large Had­ron Col­lider is still in the pro­cess of be­ing in­creased in pow­er, so phys­i­cists hope to raise the num­ber of col­li­sions to im­prove the chances of pro­duc­ing Higgs bos­ons. Some spec­u­late that by the end of next year, they may de­ter­mine once and for all wheth­er the Higgs ex­ists.

If it turns out not to, phys­i­cists will have to do some se­ri­ous rethink­ing about the Stand­ard Mod­el. "But even if the Higgs ex­ists, the Stand­ard Mod­el still has fun­da­men­tal prob­lems," New­man said. For ex­am­ple, the the­o­ry is not self-con­sist­ent. "The most nat­u­ral way to solve these prob­lems," he said, is with a the­o­ry called "su­per­sym­me­try," for which some re­search­ers hope the col­lider will al­so turn up sup­port­ing ev­i­dence.

This the­o­ry pre­dicts each known par­t­i­cle has a mas­sive, un­seen com­pan­ion par­t­i­cle called its “su­per­part­ner.” The scheme cre­ates a tidy cor­re­spond­ence be­tween two fam­i­lies of par­t­i­cles, those that make up mat­ter and those that trans­mit forc­es. As a bo­nus, su­per­sym­me­try pre­dicts the ex­ist­ence of par­t­i­cles that could be the dark mat­ter—a stuff as­tro­no­mers say they have de­tected through its gravita­t­ional ef­fects, but that oth­erwise seems in­vis­i­ble.


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New results from the world’s largest particle smasher might hint at the existence of an elusive particle physicists have been seeking for years, the Higgs boson, some researchers say. The tiny entity is thought to be responsible for endowing every other fundamental particle of matter with mass, or weight. This is according to the conventional thinking in physics, embodied in a set of ideas called the Standard Model. The Higgs boson is in fact the last particle that is predicted by the Standard Model but not yet detected. The atom smasher reported to have gathered the intriguing data, called the Large Hadron Collider, blasts beams of subatomic particles together at near-light speed to break them into their component parts for study. Many of the resulting particles disintegrate almost instantly, making their analysis challenging, but physicists hope to tease out signs that some of these particles are Higgs bosons. Although some of the signals generated from the collider’s detectors are statistical noise, two recent experiments have found an “excess” of signals consistent with a characteristic expected for the Higgs, researchers say. That characteristic is its theorized range of mass, believed to be between 130 and 150 gigaelectron volts, the units used to weigh subatomic particles. The data aren’t yet statistically significant enough to be called a definite signal, let alone a discovery of a particle, cautioned Harvey Newman, a physicist at the California Institute of Technology involved with the project. However, the data come from two different types of detectors connected to the collider, which lies underground near Geneva, Switzerland. The unusual readings could just be background events due to some unknown source or the first signs of the Higgs, Newman said. "One could speculate that it's an unusual statistical fluctuation," he added, "but I don't think so." The developments were announced a meeting of the European Physical Society in Grenoble, France, held from July 21 to 27. The Higgs boson concept dates to 1964, when a physicist, Peter Higgs, proposed the existence of a “field” that permeates the universe. Just as a magnetic field interacts with iron filings, this “Higgs field” fills the space between every fundamental particle and interacts with those particles. These interactions slow a particle as it moves through the field. A low-mass particle such as the electron, for example, is that way because it doesn't interact with the Higgs field much. Thus it can zip through the field with ease like a sleek anchovy swimming through the ocean. But particles like the so-called top quark, which is part of the nucleus of atoms, interact with the Higgs field more strongly, so to them, the field is more like an ocean of molasses. The top quark is thus heavy and sluggish, weighing in at more than 300,000 times the mass of an electron. In physics, every field has an associated particle; the electromagnetic field, seen by us as light, is associated with the photon, for instance. For the Higgs field, the associated particle is the Higgs boson. By interacting with itself, it's responsible for its own mass. The Large Hadron Collider is still in the process of being increased in power, so physicists hope to raise the number of collisions to improve the chances of producing Higgs bosons. Some speculate that by the end of next year, they may determine once and for all whether the Higgs exists. If it turns out not to, physicists will have to do some serious rethinking about the Standard Model. "But even if the Higgs exists, the Standard Model still has fundamental problems," Newman says. For example, the theory is not self-consistent. "The most natural way to solve these problems," he says, is with a theory called "supersymmetry," for which some researchers hope the collider will also turn up supporting evidence. This theory predicts each known particle has a massive, unseen companion particle called its “superpartner.” The scheme creates a tidy correspondence between two families of particles, those that make up matter and those that transmit forces. As a bonus, supersymmetry predicts the existence of particles that could be the dark matter—a stuff astronomers say they have detected through its gravitational effects, but that otherwise seems invisible.