E il Tevatron gabbò LHC :D

[lowenz]

1 a 0 per Tevatron

http://physicsworld.com/cws/article/news/38140

An important missing piece of the Standard Model of particle physics has been discovered by researchers at Fermilab in the US, home to the world’s most powerful operational particle collider, the Tevatron. On Wednesday the CDF and D0 experiments independently reported unambiguous evidence that top quarks, the heaviest of the six known quark flavours, can be produced individually rather than in pairs as had been observed until now (arXiv 0903.0885v1 and arXiv 0903.0850v1 both submitted to Phys. Rev. Lett.).

Because singly produced top quarks decay into final states that mimic the signature expected for the standard-model Higgs boson – the biggest missing chunk of the 35–year old theory — the results bode well for the Higgs search currently gathering pace at the Tevatron while CERN’s more powerful Large Hadron Collider (LHC) is being repaired. “We would not be able to claim evidence for a low mass Higgs if we did not first observe single top quark production,” says D0 co-spokesperson Darien Wood.
No fourth generation

The top quark was discovered by CDF and D0 in 1995, completing the “three generation” structure of the standard model in which the up and down quarks that make up ordinary nuclear matter (with electrical charges of +2/3 and -1/3, respectively) have heavier copies: charm and strange; top and bottom. The same mysterious hierarchy exists for leptons, the lightest generation comprising the electron and the electron neutrino.

In the discovery of the top quark and subsequent measurements of its properties, the particle (weighing 180 times more than the proton) was produced in pairs along with its antimatter partner — a process which only involves the strong nuclear force. But the standard model predicts that tops are also produced singly via the electroweak force, for example when a proton–antiproton collision produces an excited W boson that decays into a top and a bottom quark.

While the process is rarer than pair-produced tops and mired in similar-looking background events, the rate at which single tops are produced gives a direct measurement of V_tb — one of the elements in the 3x3 Cabibbo–Kobayashi–Maskawa “mixing” matrix which describes how quarks transform into different flavours via the weak force. Having now measured the cross section for single-top production and shown that V_tb is closer to one than to zero, the Fermilab results strongly disfavour the existence of a fourth generation of quarks.
Healthy competition

Paul de Jong, who works on the LHC’s ATLAS experiment, describes the Fermilab results as a tour de force, requiring sophisticated analysis techniques that potentially will lead to an earlier observation of the Higgs. “At the LHC will we will collect a significantly larger sample of single top quarks,” he adds, “but we can only congratulate D0 and CDF for this fine piece of work.”

Although CDF and D0 first reported evidence for single-top production in 2007, in the past 18 months the experiments have doubled the number of number of proton-antiprotons collisions recorded. The extra data have allowed each collaboration to achieve, based on rather different analysis techniques and with CDF using 40% more events than D0, a statistical significance of over five standard deviations.

The CDF and D0 preprints were posted just hours apart, yet both claim first observation of single top production. “There is a constructive rivalry which improves both experiments,” says CDF member Mark Lancaster of University College London. “We happily combine our results for the Higgs searches.”

New Higgs limits based on the latest Tevatron data are expected to be presented in the coming months, potentially excluding larger regions of the Higgs mass range than the 170 GeV already excluded by Fermilab last year.

[killercode]

An important missing piece of the Standard Model of particle physics has been discovered by researchers at Fermilab in the US, home to the world’s most powerful operational particle collider, the Tevatron

rigiriamo il coltello eh?

comunque ottima scoperta, poco importa chi l'ha fatta (rosica)

[lowenz]

Originariamente inviato da killercode

rigiriamo il coltello eh?

comunque ottima scoperta, poco importa chi l'ha fatta (rosica)

Chi avvisa Gravis?

[cangia]

Originariamente inviato da killercode

rigiriamo il coltello eh?

comunque ottima scoperta, poco importa chi l'ha fatta (rosica)

ehm .. qualcuno mette il riassunto riassuntato in ita ?

[lowenz]

Originariamente inviato da cangia

ehm .. qualcuno mette il riassunto riassuntato in ita ?

Prima si erano solo visti quark "spuntare" in coppia, ora singoli
E sembra che non ci siano errori nelle misurazioni.

[sempreio]

e quindi?

[Lucrezio]

E quindi un punto in più a favore del modello standard!

[gugoXX]

Cosa vorrebbe dire che sarebbero riusciti a "riprodurre singolarmente piuttosto che in coppia" parlando di un quark?
Sono riusciti ad isolare un quark singolo?

[lowenz]

2 a 0

http://www.universetoday.com/2009/03...n-higgs-boson/

Scientists 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, a tighter understanding of the W boson mass will also lead researchers closer to the mass of the elusive Higgs boson particle.

The Higgs boson is a theoretical but as yet unseen particle, also called the "God particle," that is believed to give other particles their mass. The W boson, which is about 85 times heavier than a proton, enables radioactive beta decay and makes the sun shine.

Today's announcement marks the second major discovery in a week for the international DZero collaboration at Fermilab. Earlier this week, the group announced the production of a single top quark at Fermilab's Tevatron collider.

DZero is an international experiment of about 550 physicists from 90 institutions in 18 countries. It is supported by the U.S. Department of Energy, the National Science Foundation and a number of international funding agencies. In the last year, the collaboration has published 46 scientific papers based on measurements made with the DZero particle detector.

The W boson is a carrier of the weak nuclear force and a key element of the Standard Model of elementary particles and forces, which also predicts the Higgs boson. Its exact mass is crucial for calculations 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/c^2. The collaboration presented its result at the annual conference on Electroweak Interactions and Unified Theories known as Rencontres de Moriond on 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 electrons and electron neutrinos. Performing the measurement required calibrating the DZero particle detector 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, of 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.“

[drakend]

Scusate ma LHC che sta facendo? È ancora in manutenzione? Se sì 'sto coso è sempre in manutenzione...

[harbinger]

Se gara deve essere ( ) confido in una grandiosa rimonta del se-funzionasse-tutto-LHC.


Fanboy: tanto a dimostrare che l'Higgs non c'è (?!) ci arriviamo prima in Europa.

[lowenz]

Originariamente inviato da harbinger

Se gara deve essere ( )

Un SANO agonismo non può che fare bene

Almeno usiamo in maniera utile gli istinti umani.