Precision measurement of W boson mass portends stricter limits for Higgs particle

Mar 11, 2009
The Standard Model describes the interactions of the fundamental particle of the world around us. Experimental observations agree with the predictions of the Standard Model with high precision. The W boson, the carrier of the electroweak force, is a key element in these predictions. Its mass is a fundamental parameter relevant for many predictions, including the energy emitted by our sun to the mass of the elusive Standard Model Higgs boson, which provides elementary particles with mass. Credit: Fermilab

(PhysOrg.com) -- Scientists of the DZero collaboration at the Department of Energy's Fermi National Accelerator Laboratory have achieved the world's most precise measurement of the mass of the W boson by a single experiment. Combined with other measurements, the reduced uncertainty of the W boson mass will lead to stricter bounds on the mass of the elusive Higgs boson.

The W boson is a carrier of the weak nuclear force and a key element of the of elementary and forces. The particle, which is about 85 times heavier than a proton, enables and makes the sun shine. The Standard Model also predicts the existence of the , the origin of for all .

Precision measurements of the W mass provide a window on the Higgs boson and perhaps other not-yet-observed particles. The exact value of the W mass is crucial for calculations that allow scientists to estimate the likely mass of the Higgs boson by studying its subtle quantum effects on the W boson and the top quark, an elementary particle that was discovered at Fermilab in 1995.

Scientists working on the DZero experiment now have measured the mass of the W boson with a precision of 0.05 percent. The exact mass of the particle measured by DZero is 80.401 ± 0.044 GeV/c2. The collaboration presented its result at the annual conference on and Unified Theories known as Rencontres de Moriond last Sunday.

"This beautiful measurement illustrates the power of the Tevatron as a precision instrument and means that the stress test we have ordered for the Standard Model becomes more stressful and more revealing," said Fermilab theorist Chris Quigg.
The DZero team determined the W mass by measuring the decay of W bosons to and electron .

Performing the measurement required calibrating the DZero with an accuracy around three hundredths of one percent, an arduous task that required several years of effort from a team of scientists including students.

Since its discovery at the European laboratory CERN in 1983, many experiments at Fermilab and CERN have measured the mass of the W boson with steadily increasing precision. Now DZero achieved the best precision by the painstaking analysis of a large data sample delivered by the Tevatron particle collider at Fermilab. The consistency of the DZero result with previous results speaks to the validity of the different calibration and analysis techniques used.

"This is one of the most challenging precision measurements at the Tevatron," said DZero co-spokesperson Dmitri Denisov, Fermilab "It took many years of efforts from our collaboration to build the 5,500-ton detector, collect and reconstruct the data and then perform the complex analysis to improve our knowledge of this fundamental parameter of the Standard Model."

The W mass measurement is another major result obtained by the DZero experiment this month. Less than a week ago, the DZero collaboration submitted a paper on the discovery of single top quark production at the Tevatron collider. In the last year, the collaboration has published 46 scientific papers based on measurements made with the DZero particle detector.

Provided by Fermilab

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User comments : 15

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THEY
3.8 / 5 (6) Mar 11, 2009
When they keep proving Tevatron as such a powerful detector, why are they going to shut it down next year? Even if the LHC has no more glitches, we need BOTH detectors. Competition is good for science!

KEEP TEVATRON ALIVE!
Szkeptik
2.7 / 5 (3) Mar 11, 2009
Ah, the Standard Model. One of those things that make me proud to be a human.

I can't wait for that LHC restart!
LeeSawyer
4 / 5 (2) Mar 11, 2009
Actually, with the delays to the LHC, it is looking like the Tevatron will run for sure in 2010, and maybe (depending on funding) in 2011.
ryuuguu
3.5 / 5 (2) Mar 11, 2009
The exact mass of the particle measured by DZero is 80.401 ± 0.044 GeV/c2


I wish they had mentioned the previous best estimate s we could see how much improvement there was.
Scalziand
2 / 5 (1) Mar 11, 2009
80,413 /- 48 MeV/c2 is one of the older estimates found here:
http://www.allame...de/17469
It's a small improvement in uncertainty.
Alexa
1 / 5 (7) Mar 12, 2009
..why are they going to shut it down next year..
US government knows about risk of strangletet formation connected with powerful colliders, so it stopped it wisely by the same way, like Superconducting Super Collider (SSC) project in 1992. It's strategic decision.
Alexa
1 / 5 (6) Mar 12, 2009
..Standard Model. One of those things that make me proud to be a human..
This is very naive and uniformed stance. SM doesn't enable mainstream physics to predict mass of elementary particles in better way, then fifty years old Heims theory enables already, the predictions of Higgs boson mass the more - it's apparent, scientists only guessing its properties by blind scanning whole energy spectrum from 80 to 200 TeV.

The true ingenious model is Heim's theory, which can handle these predictions in many orders of precision with using of only five constants and without using of ad hoced particles, like Higgs boson. No results from LHC could improve these calculations or to decrease the number of constants needed, the discovery of Higgs boson the less - they can just a bring a huge explosion, which can destroy our civilization - that's all.

Adding of new constants into regression can never replace the clever ab initio model - it just can prolong safe life of some scientists and companies from our taxes.
Ethelred
4.7 / 5 (3) Mar 12, 2009
If they existed the would have been produced by cosmic rays. That has been pointed out to you before Alexa.

Ethelred
Alexa
1.7 / 5 (6) Mar 12, 2009
Cosmic rays are always forming sparse, individual particles - they never come in dense counteracting jets. Every scientist, who knows, what the strangelet really is (i.e. a dense cluster of many particles similar to tiny neutron or quark star) can never say, such strangelet can be produced by cosmic rays.

Not saying, the product of cosmic ray collisions always have a large speed toward Earth, while product of collider collisions can have a zero momentum toward Earth - so they have a lotta time to interact with it.

These connections are so obvious, that the every notion of cosmic rays in connection of LHC risk should be considered a naive propaganda, supposed to fool the rest of layman society. Those who spreading such "objections" are simply liars.
Alexa
1.5 / 5 (4) Mar 12, 2009
Currently our civilization has a more important problem, then to feed a crowds of incompetent scientists. If some collider experiments must be done, they should be carried out at safe distance from Earth in cosmic space.

If our society isn't sufficiently rich to do such experiments, it simply means, it has a different priorities by now and it should invest for example into research of could fusion. Why the hell latest Arata tabletop experiments weren't replicated even after one year? The cost and practical significance of such experiments are incomparable to LHC experiments. Every year we are depleting the nonrecoverable supplies of fossil fuels, destroying life environment and risking global wars - just because we aren't able to concentrate our research to fundamental problems. The main purpose of Higgs boson research is to mask intellectual crisis of contemporary physics.

http://nextbigfut...eat.html

It's apparent, high energy physicists transformed into alchemists, looking for Philosopher's stone instead of solving practical problems - thus being separated from the rest of society. They ignoring fundamental finding, just because they don't play well with their silly theories, full of ad-hoced constants.

http://arxivblog.com/?p=664
LeeSawyer
5 / 5 (3) Mar 12, 2009
This is very naive and uniformed stance. SM doesn't enable mainstream physics to predict mass of elementary particles in better way, then fifty years old Heims theory enables already, blah blah blah


Sheesh, you are the naive one. There is no Heim's "theory" just some pseudoscience that does not even predict the mass of the particle discussed here, the W boson. The Standard Model has very good predictions of the Higgs mass, and the improved W and top masses narrow the range of allowed masses significantly. You know nothing about high energy physics, go back to talking to your cats and making tinfoil hats.
Alexa
1 / 5 (4) Mar 12, 2009
At first, string theory cannot predict mass of W bosons, it cannot predict mass of any particles - and it's not considered a pseudoscience - so your stance is biased in terms of pseudoskepticims ("double standards in the application of criticism")

http://en.wikiped...isbelief

At second, 8-dimensional extension of Heim theory made by Dröscher supports quarks and vector bosons and even provides some estimation of rest mass.

At third, W boson was never observed directly and while basic Heim theory predicts mass / lifetime of real, existing particles only, it doesn't need to consider ad-hoced artifacts in doing it with extremely high precision.

http://superstrun...heim.gif

Science should always follow an Occam's razor principle - and if some theory doesn't require ad-hoced artifacts for explanation of observation, it should be considered first.

Or science becomes a God based religion.
Alexa
1 / 5 (4) Mar 12, 2009
Standard Model has very good predictions of the Higgs mass
Unfortunatelly, exactly the opposite is true. Standard Model is heavily confused concerning the Higgs Mass prediction. 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). As the search continued, this range was restricted to 170 GeV. The confirmation of single top-quark discovery reinforces predictions that Fermilab should be able to spot a Higgs boson as light as 120 GeV by late 2010 from obvious reasons: Higgs boson becomes undistinguishable from top-quark/antiquark pair.

http://www.newsci...ght.html
Modernmystic
1 / 5 (1) Mar 13, 2009
..why are they going to shut it down next year..
US government knows about risk of strangletet formation connected with powerful colliders, so it stopped it wisely by the same way, like Superconducting Super Collider (SSC) project in 1992. It's strategic decision.


Um, aren't stranglets a postulation of the STANDARD MODEL you reject?

Have your cake, eat it, or kindly shut the hell up...one of the three....
Alizee
Mar 13, 2009
This comment has been removed by a moderator.
Velanarris
not rated yet Mar 18, 2009
Alexa/Alizee:

I've pointed out to you (or "you both"), on several occasions how by simple probability over the course of the planet's lifetime that if stranglette creation and subsequent interaction was possible through the sort of collisions taking place in the LHC and Tevatron that it would have already happened.

The comment that completely blows my mind is this:
US government knows about risk of strangletet formation connected with powerful colliders, so it stopped it wisely by the same way, like Superconducting Super Collider (SSC) project in 1992.


What part of the preceding statement makes any sense?

If the US Government was aware of the risk of stranglette creation we would not have been involved in the construction of the LHC, nor would we have funded it or sat idlly by while it was built.

Also, how exactly would it be a strategic decision? By the mathematics, if a stable stranglette was created and interacted with our resident matter it would take mere minutes to completely "strange goo" the planet, I don't know what other crazy conspiracies you think the government is up to but unless they have a way to leave Earth without leaving behind so much as an atom thick trail of exhaust within seconds there is no "strategy" to be seen.

There's a few points that the Aether theorists completely discount, and this is because of the ignorance inherent in the framework on which it's based.

Atoms are not dense. Realistically you could be bombarded by strangelettes for a millenia without actually encountering or interacting with one.

Stable Strangelettes are virtually impossible within AWT due to reflexive surface tension aspect of the theory.

Stranglettes are theorized by application of the standard model, which we know to be wrong in some way, shape, or form. Any physicist will tell you it's a "sick" theory. There are too many pieces that are either missing or unaccounted for, and it's ridiculously un-elegant in application as it discounts many necessary aspects of observed physics, for example, Mass, or particle-field mass interaction.