An article from the economist.
A PARTICULAR sheep has haunted stem-cell researchers for years. In 1996 Ian Wilmut, of the Roslyn Institute, in Edinburgh, removed the nucleus of an ovine egg cell and replaced it with that of an adult cell. The resulting hybrid was grown into a tiny embryo known as a blastocyst, implanted into the womb of a surrogate mother, and went on to become Dolly, the world’s most famous ewe.
This trick—cloning an adult mammal by nuclear transplantation—has never, as far as anyone knows, been repeated on humans. Apart from the technical difficulties, the ethical objections have dissuaded most serious researchers from even trying. But those researchers would like to get to the blastocyst stage, because that would allow them to make what are known as pluripotent stem cells, which are cells that can go on to turn into a wide variety of other cell types. In the immediate future, such cells might be used (because they are genetically identical to known individuals) to screen drugs for gene-specific side effects. In the longer term they might yield transplantable organs with the same genotype as the recipient, thus eliminating the problem of rejection.
This week Scott Noggle of the New York Stem Cell Foundation, a charitable research institute, and his colleagues report a step towards that goal. In a paper in Nature they describe a way of creating pluripotent human stem cells (albeit imperfectly, since the cells in question end up with two sets of chromosomes) by nuclear transplantation. Intriguingly, they seem, at the same time, to have dealt with one of the ethical objections to this sort of work. This is: how do you get your hands on enough human eggs to do it in the first place?
Doing well by doing good
In America, fertile women sometimes sell eggs to sterile members of their sex for reproductive purposes. Such sales are not frowned on if no coercion is involved. Bioethicists have, however, been reluctant to sanction egg sales for research. Indeed, California and Massachusetts, two important centres of stem-cell science, forbid the practice. Dieter Egli, one of Dr Noggle’s co-authors, once tried to get round this restriction by asking women in Massachusetts to donate eggs to a project he was undertaking in that state. He and his colleagues advertised extensively and received many calls. But when the inquirers learned what was involved, most of them shied away. The main deterrent, it turned out, was the lack of payment.
In 2006 the International Society for Stem Cell Research (ISSCR) suggested a possible solution. Scientists might pay for eggs, they opined, so long as a suitable committee monitored the exchange. The money, the ISSCR suggested, should not be enough to provide “undue inducement” for women to sell their eggs.
In the study they have just published, Dr Noggle and Dr Egli tested this idea out. They worked in New York state, which has, since 2009, allowed the use of public funds to buy eggs for research. And, to be sure there was no undue inducement, they approached only women who had already decided (in order to help another woman’s fertility) to sell an egg. They offered these women the same price, $8,000, to sell their eggs for research instead.
It worked. And, armed with 270 eggs, the researchers got down to business. They swapped some of the eggs’ nuclei with those of adult male skin cells—basically, the same procedure Sir Ian used to create Dolly. Using a pulse of calcium ions as a stimulant, they persuaded the cells to start dividing. However, the process of division stopped abruptly when between six and ten daughter cells had been created.
That, Dr Noggle and Dr Egli reasoned, might be caused by problems linked either to the adult cell nucleus, or to the process by which the egg’s nucleus was extracted. To test this, they took some of the remaining eggs and did a different experiment. Instead of enucleating them, they kept them intact and inserted the adult cell’s nucleus alongside the original one. In this case, development proceeded apace, resulting in a blastocyst. Dr Noggle and Dr Egli were then able to create pluripotent stem cells from their tiny embryo—but these had chromosomes both from the egg and the skin cell, making them useless for therapy.
Despite that wrinkle, this piece of research marks a turning point. The next step is to try to create stem cells without the leftover chromosomes from the egg. If that can be done, the new method may take over from the existing lash-up by which pluripotent stem cells with the genomes of particular individuals are made using transcription factors. A transcription factor is a molecule that regulates gene activity, and a particular combination of four of them has been found to turn ordinary body cells into something that looks remarkably like a pluripotent stem cell. “Remarkably like”, however, is not the same as “identical”. The route Dr Noggle and Dr Egli are taking may deal with that distinction.
Which is not to say that there will be no further controversy—at least, in the United States. The laws in California and Massachusetts, for example, have not been changed, so in those states eggs will continue to be in short supply. Moreover, America’s National Institutes of Health will not pay for research on stem cells, such as these, that are derived from embryos created for research. Other countries may not be so squeamish. China, for one, is particularly interested in stem-cell research. No doubt its scientists are reading Dr Noggle’s paper with interest.
Showing posts with label Science. Show all posts
Showing posts with label Science. Show all posts
Wednesday, February 1, 2012
Hype Over Hope
An article from the economist on hype over hope.
THE unrelenting pace of scientific accomplishment often outstrips the progress of moral thought, leaving people struggling to make sense, initially at least, of whether heart transplants are ethical or test-tube babies desirable. Over the past three decades scientists have begun to investigate a branch of medicine that offers astonishing promise—the ability to repair the human body and even grow new organs—but which destroys early-stage embryos to do so. In “The Stem Cell Hope” Alice Park, a science writer at Time magazine, chronicles the scientific, political, ethical and personal struggles of those involved in the work.
Embryonic stem cells are pluripotent: they have the ability to change into any one of the 200-odd types of cell that compose the human body; but they can do so only at a very early stage. Once the bundle has reached more than about 150 cells, they start to specialise. Research into repairing severed spinal cords or growing new hearts has thus needed a supply of stem cells that come from entities that, given a more favourable environment, could instead grow into a baby.
Immediately after the announcement of the birth of Dolly the sheep—the clone of an adult ewe whose mammary cells Ian Wilmut had tricked into behaving like a developing embryo—American scientists were hauled before the nation’s politicians who were uneasy at the implication that people might also be cloned. Concern at the speed of scientific progress had previously stalled publicly funded research into contentious topics, for example, into in vitro fertilisation. But it did not stop the work from taking place: instead the IVF industry blossomed in the private sector, funded by couples desperate for a baby and investors who had spotted a lucrative new market.
That is also what happened with human stem cells. After a protracted struggle over whether to ban research outright—which pitted Nancy Reagan, whose husband suffered from Alzheimer’s disease, against a father who asked George Bush’s advisers, “Which one of my children would you kill?”—Mr Bush blocked the use of government money to fund research on any new human embryonic stem-cell cultures. But research did not halt completely: Geron, a biopharmaceuticals company based in Menlo Park, California, had started “to mop up this orphaned innovation”, as Ms Park puts it, by recruiting researchers whose work brought them into conflict with the funding restrictions.
Meanwhile, in South Korea a maverick scientist claimed not only to have cloned human embryos but also to have created patient-specific cultures that could, in theory, be used to patch up brain damage or grow a kidney. Alas, he was wrong. But a Japanese scientist did manage to persuade adult skin cells to act like stem cells. If it proves possible to scale up his techniques, that would remove the source of the controversy over stem-cell research.
Three months after he took office, Barack Obama lifted restrictions on federal funding for research on new stem-cell cultures, saying that he thought sound science and moral values were consistent with one another. But progress has been slow: the first human trials in America, involving two people with spinal-cord injuries who have been injected with stem cells developed by Geron, are only just under way. The sick children who first inspired scientists to conduct research into stem cells in order to develop treatments that might help them are now young adults. As Ms Park notes, the fight over stem-cell research is not over, and those who might benefit from stem-cell medicine remain in need.
THE unrelenting pace of scientific accomplishment often outstrips the progress of moral thought, leaving people struggling to make sense, initially at least, of whether heart transplants are ethical or test-tube babies desirable. Over the past three decades scientists have begun to investigate a branch of medicine that offers astonishing promise—the ability to repair the human body and even grow new organs—but which destroys early-stage embryos to do so. In “The Stem Cell Hope” Alice Park, a science writer at Time magazine, chronicles the scientific, political, ethical and personal struggles of those involved in the work.
Embryonic stem cells are pluripotent: they have the ability to change into any one of the 200-odd types of cell that compose the human body; but they can do so only at a very early stage. Once the bundle has reached more than about 150 cells, they start to specialise. Research into repairing severed spinal cords or growing new hearts has thus needed a supply of stem cells that come from entities that, given a more favourable environment, could instead grow into a baby.
Immediately after the announcement of the birth of Dolly the sheep—the clone of an adult ewe whose mammary cells Ian Wilmut had tricked into behaving like a developing embryo—American scientists were hauled before the nation’s politicians who were uneasy at the implication that people might also be cloned. Concern at the speed of scientific progress had previously stalled publicly funded research into contentious topics, for example, into in vitro fertilisation. But it did not stop the work from taking place: instead the IVF industry blossomed in the private sector, funded by couples desperate for a baby and investors who had spotted a lucrative new market.
That is also what happened with human stem cells. After a protracted struggle over whether to ban research outright—which pitted Nancy Reagan, whose husband suffered from Alzheimer’s disease, against a father who asked George Bush’s advisers, “Which one of my children would you kill?”—Mr Bush blocked the use of government money to fund research on any new human embryonic stem-cell cultures. But research did not halt completely: Geron, a biopharmaceuticals company based in Menlo Park, California, had started “to mop up this orphaned innovation”, as Ms Park puts it, by recruiting researchers whose work brought them into conflict with the funding restrictions.
Meanwhile, in South Korea a maverick scientist claimed not only to have cloned human embryos but also to have created patient-specific cultures that could, in theory, be used to patch up brain damage or grow a kidney. Alas, he was wrong. But a Japanese scientist did manage to persuade adult skin cells to act like stem cells. If it proves possible to scale up his techniques, that would remove the source of the controversy over stem-cell research.
Three months after he took office, Barack Obama lifted restrictions on federal funding for research on new stem-cell cultures, saying that he thought sound science and moral values were consistent with one another. But progress has been slow: the first human trials in America, involving two people with spinal-cord injuries who have been injected with stem cells developed by Geron, are only just under way. The sick children who first inspired scientists to conduct research into stem cells in order to develop treatments that might help them are now young adults. As Ms Park notes, the fight over stem-cell research is not over, and those who might benefit from stem-cell medicine remain in need.
Stem Cell Research
An article from the economist which I am to be very interesting.
FOURTEEN years ago James Thomson of the University of Wisconsin isolated stem cells from human embryos. It was an exciting moment. The ability of such cells to morph into any other sort of cell suggested that worn-out or damaged tissues might be repaired, and diseases thus treated—a technique that has come to be known as regenerative medicine. Since then progress has been erratic and (because of the cells’ origins) controversial. But, as two new papers prove, progress there has indeed been.
This week’s Lancet published results from a clinical trial that used embryonic stem cells in people. It follows much disappointment. In November, for example, a company in California cancelled what had been the first trial of human embryonic stem cells, in those with spinal injuries. Steven Schwartz of the University of California, Los Angeles, however, claims some success in treating a different problem: blindness. His research, sponsored by Advanced Cell Technology, a company based in Massachusetts, involved two patients. One has age-related macular degeneration, the main cause of blindness in rich countries. The other suffers from Stargardt’s macular dystrophy, its main cause in children. Dr Schwartz and his team coaxed embryonic stem cells to become retinal pigment epithelium—tissue which supports the rod and cone cells that actually respond to light—then injected 50,000 of them into one eye of each patient, with the hope that they would bolster the natural supply of these cells.
The result was a qualified success. First and foremost, neither patient had an adverse reaction to the transplant—always a risk when foreign tissue is put into someone’s body. Second, though neither had vision restored to any huge degree, each was able, four months after the transplant, to distinguish more letters of the alphabet than they could beforehand.
Whether Dr Schwartz’s technique will prove truly useful remains to be seen. Experimental treatments fail far more often than they succeed. But the second paper, published in Nature by Lawrence Goldstein of the University of California, San Diego, and his colleagues, shows how stem cells can be of use even if they do not lead directly to treatment.
Since 2006 researchers have been able to reprogram adult cells into an embryonic state, using proteins called transcription factors. Though these reprogrammed cells, known as induced pluripotent stem (iPS) cells, might one day be used for treatment, their immediate value is that they are also an excellent way to understand illness. Using them, it is possible to make pure cultures of types of cells that have gone wrong in a body. Crucially, the cultured cells are genetically identical to the diseased ones in the patient.
Dr Goldstein is therefore using iPS cells to try to understand Alzheimer’s disease. The brains of those with advanced Alzheimer’s are characterised by deposits, known as plaques, of a protein-fragment called beta-amyloid, and by tangles of a second protein, called tau. But how these plaques and tangles are related remains unclear. To learn more, Dr Goldstein took tissue from six people: two with familial Alzheimer’s, a rare form caused by a known genetic mutation; two with sporadic Alzheimer’s, whose direct cause is unknown; and two unaffected individuals who acted as controls. He reprogrammed the cells collected into iPS cells, then nudged them to become nerve cells.
In three of the four Alzheimer’s patients these lab-made nerve cells did, indeed, show higher levels of beta-amyloid and tau—and also of another characteristic of the disease, an enzyme called active GSK3-beta. Since he now had the cells in culture, Dr Goldstein could investigate the relationship between the three.
To do so he treated the cultured cells with drugs. He found that a drug which attacked beta-amyloid directly did not lead to lower levels of tau or active GSK3-beta; but a drug which attacked one of beta-amyloid’s precursor molecules did have that effect. That is useful information, for it suggests where a pharmacological assault on the disease might best be directed.
In the short term, at least, iPS-based studies of this sort are likely to yield more scientific value than clinical experiments of the type conducted by Dr Schwartz, even though they are not treatments in themselves. That will, though, require many more pluripotent cells. And at least one firm is selling a way to make billions of iPS cells for just that purpose. Its founder, appropriately, is Dr Thomson.
FOURTEEN years ago James Thomson of the University of Wisconsin isolated stem cells from human embryos. It was an exciting moment. The ability of such cells to morph into any other sort of cell suggested that worn-out or damaged tissues might be repaired, and diseases thus treated—a technique that has come to be known as regenerative medicine. Since then progress has been erratic and (because of the cells’ origins) controversial. But, as two new papers prove, progress there has indeed been.
This week’s Lancet published results from a clinical trial that used embryonic stem cells in people. It follows much disappointment. In November, for example, a company in California cancelled what had been the first trial of human embryonic stem cells, in those with spinal injuries. Steven Schwartz of the University of California, Los Angeles, however, claims some success in treating a different problem: blindness. His research, sponsored by Advanced Cell Technology, a company based in Massachusetts, involved two patients. One has age-related macular degeneration, the main cause of blindness in rich countries. The other suffers from Stargardt’s macular dystrophy, its main cause in children. Dr Schwartz and his team coaxed embryonic stem cells to become retinal pigment epithelium—tissue which supports the rod and cone cells that actually respond to light—then injected 50,000 of them into one eye of each patient, with the hope that they would bolster the natural supply of these cells.
The result was a qualified success. First and foremost, neither patient had an adverse reaction to the transplant—always a risk when foreign tissue is put into someone’s body. Second, though neither had vision restored to any huge degree, each was able, four months after the transplant, to distinguish more letters of the alphabet than they could beforehand.
Whether Dr Schwartz’s technique will prove truly useful remains to be seen. Experimental treatments fail far more often than they succeed. But the second paper, published in Nature by Lawrence Goldstein of the University of California, San Diego, and his colleagues, shows how stem cells can be of use even if they do not lead directly to treatment.
Since 2006 researchers have been able to reprogram adult cells into an embryonic state, using proteins called transcription factors. Though these reprogrammed cells, known as induced pluripotent stem (iPS) cells, might one day be used for treatment, their immediate value is that they are also an excellent way to understand illness. Using them, it is possible to make pure cultures of types of cells that have gone wrong in a body. Crucially, the cultured cells are genetically identical to the diseased ones in the patient.
Dr Goldstein is therefore using iPS cells to try to understand Alzheimer’s disease. The brains of those with advanced Alzheimer’s are characterised by deposits, known as plaques, of a protein-fragment called beta-amyloid, and by tangles of a second protein, called tau. But how these plaques and tangles are related remains unclear. To learn more, Dr Goldstein took tissue from six people: two with familial Alzheimer’s, a rare form caused by a known genetic mutation; two with sporadic Alzheimer’s, whose direct cause is unknown; and two unaffected individuals who acted as controls. He reprogrammed the cells collected into iPS cells, then nudged them to become nerve cells.
In three of the four Alzheimer’s patients these lab-made nerve cells did, indeed, show higher levels of beta-amyloid and tau—and also of another characteristic of the disease, an enzyme called active GSK3-beta. Since he now had the cells in culture, Dr Goldstein could investigate the relationship between the three.
To do so he treated the cultured cells with drugs. He found that a drug which attacked beta-amyloid directly did not lead to lower levels of tau or active GSK3-beta; but a drug which attacked one of beta-amyloid’s precursor molecules did have that effect. That is useful information, for it suggests where a pharmacological assault on the disease might best be directed.
In the short term, at least, iPS-based studies of this sort are likely to yield more scientific value than clinical experiments of the type conducted by Dr Schwartz, even though they are not treatments in themselves. That will, though, require many more pluripotent cells. And at least one firm is selling a way to make billions of iPS cells for just that purpose. Its founder, appropriately, is Dr Thomson.
Tuesday, December 13, 2011
Higgs Boson!
Just a bit of stuff I have been reading for leisure to todate. Opps, nothing related to finance!
WHEN it emerged that two experiments at CERN, the world's leading particle-physics laboratory on the outskirts of Geneva, are sending their most senior scientists to present the latest lowdown from the search for the Higgs particle on December 13th, speculations swirled. Will they at last confirm the existence of the boson, famously implicated in endowing other elementary particles with mass, which has eluded physicists for over 40 years? Might they say for sure that it does not exist, consigning the Standard Model, a framework which has governed particle physics for nearly as long on the assumption that it does, to the dustbin of dislodged theories—and sending their theoretically inclined colleagues back to the drawing board?
In the event, Fabiola Gianotti and Guido Tonelli, who lead ATLAS and CMS collaborations respectively, tried to sound a cautionary note. But the excitement during and after their presentations was palpable. For the two experiments have provided the most tantalising, though inconclusive, evidence to date for the existence of the sought-after particle, which Peter Higgs, a British physicist, plucked from mathematical formulae he had been working on in 1964 while trying to spruce up the Standard Model.
The model postulates the existence of 17 particles. Of these, 12 are fermions, like quarks (which coalesce into neutrons and protons in atomic nuclei), electrons (which whiz around these nuclei) and neutrinos (the ubiquitous, diaphanous beasts which have themselves been grabbing headlines of late by seemingly travelling faster than light). These make up ordinary matter. (All have corresponding anti-fermions which, logically, constitute antimatter.)
A further four particles, known as bosons, transmit three fundamental forces of nature. Familiar photons, particles of light, convey the electromagnetic force which holds electrons in orbit around atoms. Gluing quarks into protons and neutrons are appositely named gluons. Finally, W and Z bosons carry the weak nuclear force responsible for certain types of radioactive decay, as well as the hydrogen fusion which fuels stars. (How the fourth force, gravity, fits into all this remains arguably the greatest unsolved puzzle in physics.)
Physicists need the Higgs to make sense of the properties of these other 16 subatomic species. Without it, or something like it, they have no way to explain how fermions and some bosons get their mass. That, though, is not its main virtue. As far as the Standard Model is concerned, one could simply assume that mass is a fundamental property of particles with no need for further explanation. The rub is that a Higgs-less Standard Model predicts that all bosons should have no mass. Photons and gluons abide by this rule. The W and Z, by contrast, flout it, weighing almost as much as 100 protons.
Dr Higgs figured out (as did five other physicists around the same time) that this could be explained by postulating the existence of a field, later dubbed the Higgs field, which pervades all space. To understand how it works consider a ferromagnet which is heated up and then chilled. Each atom inside it acts as a minature magnet. At high temperatures, they wiggle around willy-nilly, not preferring any one direction to any other. The system is, in a sense, symmetrical: the milling atoms look the same whatever the observer’s vantage point. On reaching a particular temperature, though, they suddenly pick a preferred direction, creating a uniform magnetic field. They no longer look the same to different observers.
Something similar is believed to have happened with the Higgs field. At the scorching temparatures instants after the Big Bang it was in disarray and all elementary particles were oblivious to it. They were, in other words, massless. Moreover, photons, Ws and Zs all looked the same. There was no distinction between electromagnetism and the weak interaction. Instead, the three bosons conveyed the same “electroweak” force.
As the universe cooled, however, the pleasing uniformity suddenly collapsed: the Higgs field picked a direction. The W and Z feel the resulting field but the photon does not, just as some metals feel the pull of a ferromagnet and others don’t. Physicists say that on reaching a critical temperature, the symmetry between electromagnetic and weak force was spontaneously broken. The upshot may not look at all symmetrical, but it nonetheless reflects a deeper symmetry which just happens to be hidden from view in the low-temperature world. The Higgs boson emerges from the mathematical wizardry used to flesh out this symmetry-breaking mechanism.
Playing hard to get
Rolf-Dieter Heuer, the head of CERN, once quipped that physicists know everything about the Higgs apart from whether it exists. There are several reasons why the particle has proved so elusive. For a start, as Dr Heuer knows full well, his assertion is not strictly speaking true: theory is irritatingly noncommital about the particle’s mass. That means that searching for it involves looking across a wide range of possible masses. Past experiments at CERN's old accelerator, the Large Electron-Positron Collider (LEP), ruled out masses below 114 gigaelectron-volts (GeV), the esoteric unit particle physicists like to use. Anything higher, though, has been fair game.
Both ATLAS and CMS draw their subatomic cannon fodder from the LEP’s snazzier successor, the Large Hadron Collider (LHC), CERN’s (and the world’s) biggest particle accelerator. The LHC, housed in a 27km circular tunnel beneath the Franco-Swiss border, collides protons whizzing around it in opposite directions at a smidgen below the speed of light. The colliding protons’ kinetic energy is converted into other particles (since, as Einstein showed, energy and mass are one and the same). More precisely, each proton-proton collision involves a handful of quarks and gluons. It is only two of these that actually collide. The remaining lot cannot exist by themselves and decay to produce obfuscating detritus.
Moreover, the Higgs, should it emerge from such a collision, is unstable and immediately decays into less fleeting bits. ATLAS and CMS are honed to detect particular patterns of the less chimerical particles that the Higgs is believed to morph into. Unfortunately, the same patterns are not specific to the Higgs; other subatomic processes produce an abundance of identical telltales. So the experiments are not after a signature signal but a excess of such signals—a fraction of a percent or less—over what would be expected were the Higgs not real. Each having analysed some 380 trillion collisions recorded since the LHC got cracking in earnest in 2010, both have now seen just such an excess, around 125GeV.
At between one chance in 2,000 to one in 20 of being a fluke—depending on what statistical method is used—the findings fall short of the exacting one-in-3.5m target particle physicists have set themselves to claim discovery with confidence. But the fact that independent measurements of different possible decay patterns (especially extremely rare ones involving the production of two photons) from two separate experiments point to a mass of the putative Higgs within a few GeV of each other has led some physicists to claim that discovery is afoot.
Other see this as premature. Earlier this year both CMS and ATLAS presented alluring bumps around 130-140GeV but these evaporated on closer inspection. However, at the time they also observed smaller spikes around 125GeV which now appear to have grown into something statistically sturdier.
Importantly, ATLAS and CMS have also ruled out pretty much the entire range below 115GeV and between 130-600GeV, beyond which the LHC currently lacks the oomph to whip up anything of interest. This means that they can now focus their efforts on probing the interesting 15GeV-wide band. Dr Tonelli and Aleandro Nisati, who helps co-ordinate ATLAS’s research efforts, are wary of committing to a date by which a definitive answer to the Higgs question will be known. If all goes well, though, it could be as early as a few months from now.
Should the latest findings be confirmed, the next step will be to ascertain that the bump in question really is the sort of Higgs its eponymous conjurer envisaged. That will mean making precise measurements not just of its mass, but also of other properties like its assorted charges. If this ends in success, the Standard Model will finally be complete, and Dr Higgs will no doubt have earned his Nobel Prize, together with two other of the six physicists who came up with the same idea. (The Nobel committee’s rules prevent the prize being split more than three ways.)
A Higgs with a mass of 125GeV is also, in the words of John Ellis, a former head of theory at CERN, “just dandy” for a theory called supersymmetry which many see as the most viable successor to the Standard Model. It postulates the existence of heavier partners to all the known particles, and by doing so neatly explains many aspects of the physical reality the Standard Model has no purchase on. If a Higgs exists and weighs around 125GeV, then, the LHC ought, in principle, to be powerful enough to create the lighest supersymmetric particles.
WHEN it emerged that two experiments at CERN, the world's leading particle-physics laboratory on the outskirts of Geneva, are sending their most senior scientists to present the latest lowdown from the search for the Higgs particle on December 13th, speculations swirled. Will they at last confirm the existence of the boson, famously implicated in endowing other elementary particles with mass, which has eluded physicists for over 40 years? Might they say for sure that it does not exist, consigning the Standard Model, a framework which has governed particle physics for nearly as long on the assumption that it does, to the dustbin of dislodged theories—and sending their theoretically inclined colleagues back to the drawing board?
In the event, Fabiola Gianotti and Guido Tonelli, who lead ATLAS and CMS collaborations respectively, tried to sound a cautionary note. But the excitement during and after their presentations was palpable. For the two experiments have provided the most tantalising, though inconclusive, evidence to date for the existence of the sought-after particle, which Peter Higgs, a British physicist, plucked from mathematical formulae he had been working on in 1964 while trying to spruce up the Standard Model.
The model postulates the existence of 17 particles. Of these, 12 are fermions, like quarks (which coalesce into neutrons and protons in atomic nuclei), electrons (which whiz around these nuclei) and neutrinos (the ubiquitous, diaphanous beasts which have themselves been grabbing headlines of late by seemingly travelling faster than light). These make up ordinary matter. (All have corresponding anti-fermions which, logically, constitute antimatter.)
A further four particles, known as bosons, transmit three fundamental forces of nature. Familiar photons, particles of light, convey the electromagnetic force which holds electrons in orbit around atoms. Gluing quarks into protons and neutrons are appositely named gluons. Finally, W and Z bosons carry the weak nuclear force responsible for certain types of radioactive decay, as well as the hydrogen fusion which fuels stars. (How the fourth force, gravity, fits into all this remains arguably the greatest unsolved puzzle in physics.)
Physicists need the Higgs to make sense of the properties of these other 16 subatomic species. Without it, or something like it, they have no way to explain how fermions and some bosons get their mass. That, though, is not its main virtue. As far as the Standard Model is concerned, one could simply assume that mass is a fundamental property of particles with no need for further explanation. The rub is that a Higgs-less Standard Model predicts that all bosons should have no mass. Photons and gluons abide by this rule. The W and Z, by contrast, flout it, weighing almost as much as 100 protons.
Dr Higgs figured out (as did five other physicists around the same time) that this could be explained by postulating the existence of a field, later dubbed the Higgs field, which pervades all space. To understand how it works consider a ferromagnet which is heated up and then chilled. Each atom inside it acts as a minature magnet. At high temperatures, they wiggle around willy-nilly, not preferring any one direction to any other. The system is, in a sense, symmetrical: the milling atoms look the same whatever the observer’s vantage point. On reaching a particular temperature, though, they suddenly pick a preferred direction, creating a uniform magnetic field. They no longer look the same to different observers.
Something similar is believed to have happened with the Higgs field. At the scorching temparatures instants after the Big Bang it was in disarray and all elementary particles were oblivious to it. They were, in other words, massless. Moreover, photons, Ws and Zs all looked the same. There was no distinction between electromagnetism and the weak interaction. Instead, the three bosons conveyed the same “electroweak” force.
As the universe cooled, however, the pleasing uniformity suddenly collapsed: the Higgs field picked a direction. The W and Z feel the resulting field but the photon does not, just as some metals feel the pull of a ferromagnet and others don’t. Physicists say that on reaching a critical temperature, the symmetry between electromagnetic and weak force was spontaneously broken. The upshot may not look at all symmetrical, but it nonetheless reflects a deeper symmetry which just happens to be hidden from view in the low-temperature world. The Higgs boson emerges from the mathematical wizardry used to flesh out this symmetry-breaking mechanism.
Playing hard to get
Rolf-Dieter Heuer, the head of CERN, once quipped that physicists know everything about the Higgs apart from whether it exists. There are several reasons why the particle has proved so elusive. For a start, as Dr Heuer knows full well, his assertion is not strictly speaking true: theory is irritatingly noncommital about the particle’s mass. That means that searching for it involves looking across a wide range of possible masses. Past experiments at CERN's old accelerator, the Large Electron-Positron Collider (LEP), ruled out masses below 114 gigaelectron-volts (GeV), the esoteric unit particle physicists like to use. Anything higher, though, has been fair game.
Both ATLAS and CMS draw their subatomic cannon fodder from the LEP’s snazzier successor, the Large Hadron Collider (LHC), CERN’s (and the world’s) biggest particle accelerator. The LHC, housed in a 27km circular tunnel beneath the Franco-Swiss border, collides protons whizzing around it in opposite directions at a smidgen below the speed of light. The colliding protons’ kinetic energy is converted into other particles (since, as Einstein showed, energy and mass are one and the same). More precisely, each proton-proton collision involves a handful of quarks and gluons. It is only two of these that actually collide. The remaining lot cannot exist by themselves and decay to produce obfuscating detritus.
Moreover, the Higgs, should it emerge from such a collision, is unstable and immediately decays into less fleeting bits. ATLAS and CMS are honed to detect particular patterns of the less chimerical particles that the Higgs is believed to morph into. Unfortunately, the same patterns are not specific to the Higgs; other subatomic processes produce an abundance of identical telltales. So the experiments are not after a signature signal but a excess of such signals—a fraction of a percent or less—over what would be expected were the Higgs not real. Each having analysed some 380 trillion collisions recorded since the LHC got cracking in earnest in 2010, both have now seen just such an excess, around 125GeV.
At between one chance in 2,000 to one in 20 of being a fluke—depending on what statistical method is used—the findings fall short of the exacting one-in-3.5m target particle physicists have set themselves to claim discovery with confidence. But the fact that independent measurements of different possible decay patterns (especially extremely rare ones involving the production of two photons) from two separate experiments point to a mass of the putative Higgs within a few GeV of each other has led some physicists to claim that discovery is afoot.
Other see this as premature. Earlier this year both CMS and ATLAS presented alluring bumps around 130-140GeV but these evaporated on closer inspection. However, at the time they also observed smaller spikes around 125GeV which now appear to have grown into something statistically sturdier.
Importantly, ATLAS and CMS have also ruled out pretty much the entire range below 115GeV and between 130-600GeV, beyond which the LHC currently lacks the oomph to whip up anything of interest. This means that they can now focus their efforts on probing the interesting 15GeV-wide band. Dr Tonelli and Aleandro Nisati, who helps co-ordinate ATLAS’s research efforts, are wary of committing to a date by which a definitive answer to the Higgs question will be known. If all goes well, though, it could be as early as a few months from now.
Should the latest findings be confirmed, the next step will be to ascertain that the bump in question really is the sort of Higgs its eponymous conjurer envisaged. That will mean making precise measurements not just of its mass, but also of other properties like its assorted charges. If this ends in success, the Standard Model will finally be complete, and Dr Higgs will no doubt have earned his Nobel Prize, together with two other of the six physicists who came up with the same idea. (The Nobel committee’s rules prevent the prize being split more than three ways.)
A Higgs with a mass of 125GeV is also, in the words of John Ellis, a former head of theory at CERN, “just dandy” for a theory called supersymmetry which many see as the most viable successor to the Standard Model. It postulates the existence of heavier partners to all the known particles, and by doing so neatly explains many aspects of the physical reality the Standard Model has no purchase on. If a Higgs exists and weighs around 125GeV, then, the LHC ought, in principle, to be powerful enough to create the lighest supersymmetric particles.
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