Showing posts with label cdf. Show all posts
Showing posts with label cdf. Show all posts
Higgs at the Tevatron
This is the week of the Higgs. Indeed, wednesday, at CERN, ATLAS and CMS announced the results of the elaboration of the data collected in the first part of 2012... and a lot of journalists write about the probable discover of the Higgs boson. Indeed the two collaborations are disegned in order to discover the boson related to the mechanism that provides the mass to the other particles. Waiting for the conference, today CDF and DZero, the two collaborations of Tevatron, publicize in two conferences the first elaboration of the complete set of data about Higgs research. Their result was summarize by the following plot:
In the image there is the combination of the final results from the two collaborations. The two experiments combined detecte an excess in signals around 125 GeV with a 2.5 sigma. It is not the discover of the Higgs boson, but it could be a good clue for the existence of the boson. So I don't know if ATLAS and CMS will confirm or update this result in their next conferences, but in every case I must remmber to the readers that with a mass of 125 GeV we have need of physics beyond Standard Model, because the only SM is not sufficient to explain our universe. In order to explain better, I reprint here some considerations that I just published for the previous Higgs day:
Higgs' research: CDF and D0 confirm ATLAS and CMS results
Do you remember the conference of ATLAS and CMS about their Higgs' preliminary results? Well. Today during Moriond 2012 conference, the two Tevatron's collaboration, CDF and D0, presented their results about Higgs research:
(the plot shows the upper limit on the Higgs boson production rate)
In synthesis they confirm LHC's results (Tevatron's Higgs range: 115 GeV - 135 GeV, with $sigma = 2.2$).
More details on: Fermi Lab's press release, Tommaso Dorigo, the source of the image.
Special thanks to Peppe Liberti.
(the plot shows the upper limit on the Higgs boson production rate)
More details on: Fermi Lab's press release, Tommaso Dorigo, the source of the image.
Special thanks to Peppe Liberti.
Refining the mass of W
In our standard model of elementary particles we have four fundamental interactions: gravity, electromagnetism, strong nuclear force and weak interaction. In particular the last force is responsible for the radioactive decay and for the hydrogen fusion in stars. The bosons of the interaction (the particle exchanged between two fermions) are $W^\pm$ and $Z$ bosons. An example of weak interaction is $\pi^+$ decay:
The weak bosons are predicted in 1968 by Glashow, Weinberg and Salam(1) and discovered at CERN in 1983 in a series of experiments conducted by Carlo Rubbia and Simon van der Meer(2). Now, from one of the last analysis from Tevatron, we have the last measure of W bosons. Indeed CDF's researchers propose the following preliminary value for $W$:
\[M_W = (80.387 \pm 0.019) GeV\]
and combining it with previous measures, the new preliminary world average is
I must remember that $(80.390 \pm 0.016) GeV$ will became the new $W$ mass only after the publication of the CDF's preprint (pdf) in a peer review journal and after the publication of the further calculation on the Particle Data Group. Indeed Wired (and en.wiki, following Wired), following Tommaso Dorigo, who simply described the experimental process that carries to the measure and to the new proposal, has just setted the new mass, forgetting the reviewing scientific process. So, until then, the average mass is $(80.399 \pm 0.023) GeV$(3).
A circle around Higgs boson
After the post about D0 abstracts, I return to write about Higgs boson after the last Fermilab's press release about the mass limit of Higgs boson. Combinig data from D0 and CDF, Tevatron's limits are 114-137 GeV/c2. The results was presented last week in Grenoble at the EPS High-Energy Physics conference, that it will finish on the 27th July.
During the same conference also LHC's experiments presented their first results, analyzed in about one month! And the conclusion seems un-huppy for Tevatron: the Fermilab's particle accelerator has only one chance to find Higgs boson before LHC. Why? We can simply see the following plots presented by ATLAS and CMS (via Résonaances, Tommaso Dorigo):
The two european experiments presented only a little region around 115 GeV/c2, the Tevatron's region, to 140 GeV/c2. The data from this region are probably analized and published before the end of the year, so we must wait only some months to know if Tevatron could found Higgs or not(1).
Tomasso examined in details some CMS preprint in which they are studied a lot of Higgs production channels, and also Philip Gibbs write a great summary about LHC presentations, who realize a great conclusion plot:
During the same conference also LHC's experiments presented their first results, analyzed in about one month! And the conclusion seems un-huppy for Tevatron: the Fermilab's particle accelerator has only one chance to find Higgs boson before LHC. Why? We can simply see the following plots presented by ATLAS and CMS (via Résonaances, Tommaso Dorigo):
Tomasso examined in details some CMS preprint in which they are studied a lot of Higgs production channels, and also Philip Gibbs write a great summary about LHC presentations, who realize a great conclusion plot:
Observation of a new neutral baryon
In the origin (late 1960s) the particle zoo(1) is the colloquially word used to describe the extensive list of known elementary particles. Indeed, before Standard Model becames the more accepted theory in particle physics, physicists discovered a lot of particles in their accelerators, but we know today that they are simply a combination of a little numbers of particles classified in three fundamental families: leptons, quarks (that they constitute fermions, particles with half-integer spin) and bosons (particles with integer spin).
We can classify also particles in a lot of sub-families, like baryons, the heavy particles constituted by three quarks: for example proton and neutron are barions, with the following composition: uud and udd respectively, where u is the up quark and d the down quark.
We know six types of quarks: up (u) and down (d), that explain protons and neutrons, charm (c), strange (s), top (t) and bottom (b) that explain a lot of other heavy particles. Standard Model predicts a series of combination of this quarks that they are summirized in a picture like this:
In the up there is with angular momentum $J =1/2$ and down with angular momentum $J=3/2$. Today we examine $J=1/2$ group, in particular to the last discover by CDF, one collaboration at Tevatron in Fermilab. Indeed, not all particles predicted by SM are found, and the hunt to them is open. On the 20th July, Pat Lukens announced the first observation of $\Xi_b^0$, a baryon with the structure usb:
In orther to detect the new baryon, researchers at Tevatron must reconstruct the following decay chain:
We can classify also particles in a lot of sub-families, like baryons, the heavy particles constituted by three quarks: for example proton and neutron are barions, with the following composition: uud and udd respectively, where u is the up quark and d the down quark.
We know six types of quarks: up (u) and down (d), that explain protons and neutrons, charm (c), strange (s), top (t) and bottom (b) that explain a lot of other heavy particles. Standard Model predicts a series of combination of this quarks that they are summirized in a picture like this:
In the up there is with angular momentum $J =1/2$ and down with angular momentum $J=3/2$. Today we examine $J=1/2$ group, in particular to the last discover by CDF, one collaboration at Tevatron in Fermilab. Indeed, not all particles predicted by SM are found, and the hunt to them is open. On the 20th July, Pat Lukens announced the first observation of $\Xi_b^0$, a baryon with the structure usb:
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