# Tag Info

72

The energy of a bullet is around 735 joules (see bullet details here). This is about the same energy that I have when I'm running at about 4.6 m/s. Would you rather be hit by me or the bullet? The bullet kills you because it concentrates all the energy onto a small impact area while my impact area is rather larger (and sadly getting even larger as ...

68

7 TeV is not that much kinetic energy, that has been covered by your question and previous answers. However, in the context of a proton, with a rest mass of $1.672×10^{−27}~\mathrm {kg}$ (very, very little mass), when a single proton has 7 TeV then it is travelling at a specific speed: $$E= mc^2$$ \begin{align}E& = E_0 + \text{KE}\\ \text{KE}&=E- ...

52

After they told me about their impressive "LHC Olympics" in which physicists (often hardcore theorists) were reverse engineering a particle physics model from the raw (but fake) LHC data, I proposed the same idea in a circle of physicists at Harvard, including Nima Arkani-Hamed, sometime in 2005 and we have worked on that LHC ideas in some detail. We were ...

32

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 ...

32

Whenever you accelerate a charged particle it emits EM radiation known as Bremsstrahlung, and obviously charged particles moving in a circle are accelerating (towards the centre). This means that any circular collider emits a continual stream of Bremsstrahlung radiation. To counteract the energy lost to Bremsstrahlung you have to put energy in, and that ...

32

Let me first mention that the LHC is in a way a text book experiment: you have a very good control over the experimental conditions and you can repeat your experiment as often as you like. You have, in way, full control over the signal. Results are reproducible in that you just redo the experiment. LIGO is "just" a detector: In particular, you have ...

28

This is actually a really good question. (And I'm not one of these people who insists that there's no such thing as a dumb question; I just think we shouldn't be embarrassed to ask dumb questions. Anyway, this isn't a dumb question.) As you may know, collisions between two protons (like those the LHC usually does) can produce many different types of ...

28

Your reasoning demonstrates precisely why formal logic alone is insufficient to study nature. In particular, it lacks the ingredient of inductive inference that is a cornerstone of empirical science. A cosmic ray striking the Earth is not some random act of the gods that can have any imaginable consequence whatsoever. It is a cosmic ray striking the Earth. ...

25

Most of the reproduction of results in particle physics comes from two sources: Competing experiments running nearly simultaneously. In this case both ATLAS and CMS got comparable results. Now, they are both using the beam from the LHC, so how do we know the beam is properly understood? Because while they were commissioning those machines they reproduced ...

20

Hadronic jets deposit a significant fraction of their energy in the electromagnetic calorimeter, for example because they can contain neutral pions that decay as $\pi^0\to\gamma\gamma$, bottom/charm mesons with semi-leptonic decays... Therefore the jet reconstruction algorithm uses energy deposits from both electromagnetic and hadronic calorimeters, so that ...

19

Those of us who've worked at JLAB (and those who worked at SLAC) know that energetic electrons create a lot of hadronic junk when incident on significant amounts of matter. Think about Deep Inelastic Scattering. Once you have an electron with energy in the few GeV range or higher there is a significant chance of creating pions or other light mesons in the ...

18

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 ...

17

First, no evidence for other dimensions has been found. However, there are ways for particle colliders to detect other dimensions. One of the main ones is to see if any energy "disappears" under certain circumstances...then it could've gone into another dimension. Another way is to look for particles that can only exist if there are other dimensions. ...

16

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, ...

16

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 ...

15

First of all, the uncertainty principle and observer effects are completely irrelevant. The tracking devices in modern detectors are large enough to be firmly in the realm of classical physics. Any uncertainty in the detector's wavefunction is negligible compared to the size and energy of the device itself, and the effect of detected particles on the tracker ...

14

Elastic collisions do happen at the LHC. The TOTEM experiment measures the differential cross section (rate as a function of angle) for proton-proton elastic scattering at the LHC. Here is their latest result. They don't publish an estimate of the elastic cross section, but according to their data it must be at least 25 mb (millibarns) (my first version of ...

13

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

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 ...

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

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 ...

12

The energy lost by a particle doing one turn in a circular machine is $$U_0\propto E^4R^{−1}m^{-4}$$ where $E$ is the beam energy, $R$ is the bending radius, $m$ is the mass of the particle that you want to accelerate. It comes out that for the mass of heavy particles such as muons, protons and heavy ions, the field strength of the bending magnets is ...

11

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 ...

11

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 $J/\... 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 ... 11 Nobody ever tried with LHC, but here is Anatoli Bugorski: http://en.wikipedia.org/wiki/Anatoli_Bugorski Given the damage he received with a beam of 70 GeV protons (intensity ~10^13) you can probably imagine the damage you would receive from 6500 GeV protons (intensity ~10^32). For more info about the "danger" of the LHC beams, I suggest you read about the ... 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 ... 10 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 ... 10 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 ...

10

Apart from the reason mentioned in previous answers (Bremsstrahlung) there is one more thing why proton collider is used: it can scan wide range of collision energies. Because protons are compound particles, their collisions are in fact collisions of the quarks or gluons. These constituents have random energies and thus each collision typically has a ...

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