# Tag Info

25

First, let me emphasize something that is being covered by a thick layer of misinformation in the media these days: it is totally premature to conclude whether the LHC will see SUSY or not. The major detectors have only collected 45/pb (and evaluated 35/pb) of the data. The "slash pb" should be pronounced as "inverse picobarns". The LHC is designed to ...

19

First of all -- it wouldn't be called "the Large Hadron Collider", right? Looks like one would rather call it something like "Large Electron-Positron Collider". In that case one definitely would need another abbreviation for it. Something like "LEP" instead of "LHC"... Now, guess what was there in the same tunnel before? Edit: since my shenanigan got ...

14

The LHC was envisioned as a "discovery" machine, a multipurpose one. The Higgs gets the press but the expectations is that new physics will become accessible with the higher energy available for center of mass collisions. The Z was discovered in the SPS the proton antiproton previous generation collider. The previous machine in the same tunnel as the LHC, ...

12

First of all, the scheme of the CERN accelerator complex you posted contains not only that single chain which brings the protons to the LHC, but also several other chains which are used for many lower energy experiments conducted in parallel at CERN. But let's focus on the LHC accelerator chain: why do we need several successive accelerators instead of a ...

12

Wikipedia actually has a very nice graphic with this information (which roughly agrees with what I remember hearing from people "in the know"): The point is that there are both lower and upper bounds on the mass of the Higgs boson. The LHC should be able to cover pretty much the entire range that has not yet been searched, so if it doesn't find the Higgs, ...

12

There are two points in answering this question: Design: The design of the collider would have to be different. Electrons/positrons in a cyclotron radiate synchrotron radiation when they are accelerated (which itself is a useful device). To get above a few GeV, researchers use linear accelerators, such as SLAC. The proposed International Linear Collider is ...

11

When you accelerate charged particles, they lose energy by emitting photons (a process called "Bremsstrahlung" or "braking radiation"). This is a nuisance in particle accelerators, because (1) you want to impart as much energy as possible to the particles being accelerated (that's the point!) and this is a loss; and (2) the bremsstrahlung can be in the form ...

11

The idea which is being challenged, though certainly not disproved yet, is that there are new particles, other than the Higgs boson, that the LHC will be able to detect. It was very widely supposed that supersymmetric partners of some known particles would show up, because they could stabilize the mass of the Higgs boson. The simplest framework for this is ...

11

These collisions don't produce significant amount of light in the visible range, so the easy answer is "no". They also take place in a vacuum, inside a beampipe which is itself buried in a detector apparatus that is ten meters plus on a side and packed full of stuff with no room for a human. That said, there are several ways in which a high energy ...

10

Well, there's no reason to believe in supersymmetry, beyond some theoretical niceness to it, so if they see THAT at the LHC, then string theory gets a big boost, as there is no way other than supersymmetry to produce fermions in string theory. The other thing that might be relevant to quantum gravity is that if there are large extra dimensions (as in, large ...

9

The most important problem that supersymmetry solves is the hierarchy problem: why is the weak scale, which determines the rate of beta decay or the masses of the W and Z bosons, so much smaller than the Planck scale, which is related to the strength of the gravitational force? In other words, why is the weak force so strong, compared to gravity? The real ...

8

An even more excellent question than the opposite one! Experimenters' job The first happy group of people for whom the discovery of SUSY at the LHC would be spectacular would be the experimenters. They would experience fireworks of activity, facing the task to find as many superpartners as possible and to measure their properties. All their masses - and ...

8

The difference in scattering cross sections is more evident the lower the energy of collisions. Fig 41.11. At the energies of TeV the probability of new physics observations is the same for both choices of collisions. The reason is that at low energies the fact that the proton has three quarks and the anti proton three anti quarks predominates. Quark ...

8

One often says a hadron collider like the LHC is used for discovering, while an electron collider is rather used for precision measurements. There are a couple of benefits of a high-energy electron collider: All electrons have roughly the same energy. One can vary the center of mass energy $\sqrt{s}$ and map out resonances (think $ee\rightarrow Z$ or ...

8

Have a look at http://arxiv.org/abs/1207.1347 or this New Scientist article for a popular science level review. The branching ratios and couplings are consistent with the Standard Model Higgs, though the cross section for diphoton production is a little high. At the moment there is nothing to suggest that the particle found at the LHC is not the Higgs. The ...

8

What exactly is a boson? A boson is a particle whose spin (= intrinsic angular momentum) is an integer number. For example, the photon (the particle that is responsible for the electromagnetic force) is a boson. Contrast this with a fermion, such as the electron, whose spin is a half integer. In everyday terms, the bosons are the microscopic particles ...

8

This document (NB it's a pdf) contains details of the beam operation. Here's a key graph nabbed from the presentation: At the end of an experimental run the beam is dumped, and it takes about an hour and a half to get the beam back up to full energy and intensity. Once the beam is at full strength the LHC generates data continuously for somewhere between ...

8

There are no meson colliders as there is no advantage to using them. In a hadron collider (mesons are hadrons) the interesting collisions occur between the constituents of the hadrons, i.e. the quarks. The hadrons themselves don't have much of an effect on the interesting physics. Protons are easy to create and long lived. So we can create them and not worry ...

8

There are three flavours of quarks in the fundamental $3$ representation of $SU(3)$, the QCD gauge group. Their antiparticles are in the conjugate representation $\bar3$ or $3^\star$. QCD is confining; the quarks form bound, colorless states, which are singlets in $SU(3)$. Mesons are $q\bar q$. The general tensor $3\times\bar 3$ can be decomposed into ...

7

Each bunch of protons circulating in the LHC at full power will have about 120 billion protons of 14TeV each, i.e. $1.6 \times 10^{24}$ eV which is about 250000 Joules. Compare that with a high powered rifle bullet carrying 1000 Joules or a small grenade that releases 600000 Joules. But how much of that energy will be released in your hand? It is said that ...

7

Well, there is the unbelievable story about a guy who actually put his head in a proton beam, the Russian scientist Anatoli Petrovich Bugorski. This happened at the U-70 synchrotron, near Moscow at the Institute for High Energy Physics. But the thing is, is that he actually didn't feel any pain. He did suffer from epyleptic attacks and damage to his skin ...

7

your question is answered by this graph: It was taken from Tommaso Dorigo's blog. The 115 GeV Higgs is the very left beginning of all the lines in the graph. The full lines are the 2x 3.5 TeV beams; the dotted lines describe the 2x 4 TeV beams that were planned as a small upgrade of the energy for a while but the plans were abolished and 7 TeV was kept. ...

7

Well, it is a microscope if the word is understood in a generalized sense that it allows us to learn about microscopic structure of some stuff. To understand the connection one should first recall how good old optical microscopes work. The principle is really quite simple, you throw some stuff at the object you are interested in and observe what happens. In ...

7

I won't discuss issues of mini black holes, strangelets, and so on. I would like to emphasize though that LHC, like any major industrial facility (LHC is not an industrial facility, but it certainly has industrial scale), has some serious safety risks: dmckee mentioned radiation, but the beam itself is not the only source of risk; the superconducting ...

7

It is hype again. Whether such decays are affected by SUSY depends mostly on the masses of scalar superpartners and they have been known to be high enough from other considerations, so existing viable SUSY models, especially those derived from string theory, were predicting the muon pair branching ratio of B-mesons' decays close to the Standard Model i.e. ...

6

A mis-steered beam at CEBAF simply cut a hole thought the niobium wall of the klystron and flooded half the accelerator with helium (super-conducting klystrons need a liquid helium jacket to work...). We were down for more than a week. That is an electron beam machine, and very high current (up to 400 micro-Amps!), so the details would be rather different ...

6

Different pieces of equipment will produce somewhat different looking data, but typically it consists of voltages defined as a function of time. In some cases (spark chambers, for example) the "voltage" is digital, and in others it is analog. Traditionally, the time series for the data is slower than the times required for the (almost light speed) particles ...

6

A barn is a unit of area, equal to $10^{-28}\text{ m}^2$. The prefix femto- signifies $10^{-15}$, so a femtobarn is equal to $10^{-43}\text{ m}^2$. When high-energy physicists talk about inverse femtobarns, they mean collisions per femtobarn of beam cross-sectional area. The inverse femtobarn is not a measure of information, but rather of the effectiveness ...

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