The possibility of a high-mass Higgs boson may have just evaporated with new data released today by the Fermi National Accelerator Laboratory in Batavia, Illinois. The result could mean a tougher, more protracted search for a welterweight version of the Higgs, the much-sought-after subatomic particle whose discovery would be a major triumph for particle physics and bring fame to the team who finds it first.
At the heart of the new result is a more precise measurement of the W boson. This is a well known particle, a mediator of the weak force, whose mass is theoretically linked to the Higgs.
The improved measurement will undoubtedly narrow the range of allowable values for the Higgs mass, and may well close off a narrow window on the upper end of that range where direct searches have not yet penetrated.
Prior to last summer, the Higgs was known to reside somewhere in an energy range between 114 Gev and 185 Gev (assuming it exists at all). This is near the limit of where Fermilab's Tevatron can reliably search, but over time researchers have steadily amassed data that could reveal or rule out the Higgs at various energies.
In August, researchers announced they had excluded a value near 170 GeV, the energy where it would be statistically easiest to separate the Higgs signal from background noise. Since then, the possibility that the Higgs might be seen first by the Tevatron, rather than by its successor, the Large Hadron Collider in Europe, has added incentive and drama to the search.
The improved W boson measurement released today was performed by DZero, one of the Tevatrons's two key detectors. The new value, which researchers kept hidden even from themselves until last week, to avoid bias, is 80.401 +/- .044 GeV. This is remarkably close to the current world average of 80.398 GeV.
The chief impact of the measurement is not its value but how much it will reduce the overall uncertainty in the W boson mass. According to Heidi Schellman of Northwestern University, that error could shrink by as much as 10% once it is combined with other measurements. This, in turn, could drop the upper limit on the Higgs mass by 5 GeV or more, making the remaining space between 170 and 180 GeV uncomfortably tight, even for a tiny particle like the Higgs.
"If someone is trying to sell you a 175 GeV Higgs, I wouldn't buy it," Schellman told me.
The news comes just ahead of a widely anticipated announcement on Friday from DZero and its counterpart, CDF, that a wider swath of values around 170 GeV have now been excluded. In other words, a heavy Higgs could be gone by the weekend.
If so, attention will shift to a region below 160 GeV where it is somewhat harder for both the Tevatron and the LHC to see the Higgs. Tevatron seems to be at an advantage, however, because it is working steadily and gradually building up data, while the LHC is on the sidelines following a liquid helium spill last fall.
Earlier this week, researchers at Fermilab also announced they've spotted collisions that produce single top quarks. Such collisions are easily concealed by background noise. Their discovery reinforces predictions that Fermilab should be able to spot a Higgs boson as light as 120 GeV by late 2010.
The Higgs boson is the last undiscovered particle in the so-called Standard Model of particle physics. A first discovery of the Higgs at Fermilab would be electrifying for a facility that is perceived as having long passed its heyday and a shot in the arm for US experimental physicists who have felt that the momentum in their field has shifted to Europe. Researchers agree that even if the Higgs is spotted first at Fermilab, the LHC will still be needed to confirm the find and to explore the new physics that lies beyond, as researchers move into a high-energy domain where the Tevatron cannot follow.
Illustration: The green shading in the graphs above shows the masses that seem to be ruled out for the Higgs boson. Today's new W boson result lowers the upper limit to an estimated 180 GeV or less. Friday's result is expected to significantly grow the excluded range around 170 GeV, which could seal off the right-hand window of possible values completely. (Courtesy of Dmitri Denisov, DZero)
The possibility of a high-mass Higgs boson may have just evaporated with new data released today by the Fermi National Accelerator Laboratory in Batavia, Illinois. The result could mean a tougher, more protracted search for a welterweight version of the Higgs, the much-sought-after subatomic particle whose discovery would be a major triumph for particle physics and bring fame to the team who finds it first.
At the heart of the new result is a more precise measurement of the W boson. This is a well known particle, a mediator of the weak force, whose mass is theoretically linked to the Higgs.
The improved measurement will undoubtedly narrow the range of allowable values for the Higgs mass, and may well close off a narrow window on the upper end of that range where direct searches have not yet penetrated.
Prior to last summer, the Higgs was known to reside somewhere in an energy range between 114 Gev and 185 Gev (assuming it exists at all). This is near the limit of where Fermilab's Tevatron can reliably search, but over time researchers have steadily amassed data that could reveal or rule out the Higgs at various energies.
In August, researchers announced they had excluded a value near 170 GeV, the energy where it would be statistically easiest to separate the Higgs signal from background noise. Since then, the possibility that the Higgs might be seen first by the Tevatron, rather than by its successor, the Large Hadron Collider in Europe, has added incentive and drama to the search.
The improved W boson measurement released today was performed by DZero, one of the Tevatrons's two key detectors. The new value, which researchers kept hidden even from themselves until last week, to avoid bias, is 80.401 +/- .044 GeV. This is remarkably close to the current world average of 80.398 GeV.
The chief impact of the measurement is not its value but how much it will reduce the overall uncertainty in the W boson mass. According to Heidi Schellman of Northwestern University, that error could shrink by as much as 10% once it is combined with other measurements. This, in turn, could drop the upper limit on the Higgs mass by 5 GeV or more, making the remaining space between 170 and 180 GeV uncomfortably tight, even for a tiny particle like the Higgs.
"If someone is trying to sell you a 175 GeV Higgs, I wouldn't buy it," Schellman told me.
The news comes just ahead of a widely anticipated announcement on Friday from DZero and its counterpart, CDF, that a wider swath of values around 170 GeV have now been excluded. In other words, a heavy Higgs could be gone by the weekend.
If so, attention will shift to a region below 160 GeV where it is somewhat harder for both the Tevatron and the LHC to see the Higgs. Tevatron seems to be at an advantage, however, because it is working steadily and gradually building up data, while the LHC is on the sidelines following a liquid helium spill last fall.
Earlier this week, researchers at Fermilab also announced they've spotted collisions that produce single top quarks. Such collisions are easily concealed by background noise. Their discovery reinforces predictions that Fermilab should be able to spot a Higgs boson as light as 120 GeV by late 2010.
The Higgs boson is the last undiscovered particle in the so-called Standard Model of particle physics. A first discovery of the Higgs at Fermilab would be electrifying for a facility that is perceived as having long passed its heyday and a shot in the arm for US experimental physicists who have felt that the momentum in their field has shifted to Europe. Researchers agree that even if the Higgs is spotted first at Fermilab, the LHC will still be needed to confirm the find and to explore the new physics that lies beyond, as researchers move into a high-energy domain where the Tevatron cannot follow.
Illustration: The green shading in the graphs above shows the masses that seem to be ruled out for the Higgs boson. Today's new W boson result lowers the upper limit to an estimated 180 GeV or less. Friday's result is expected to significantly grow the excluded range around 170 GeV, which could seal off the right-hand window of possible values completely. (Courtesy of Dmitri Denisov, DZero)
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