Hot answers tagged

32

A large portion of the 'big science under developement' is directed towards astrophysics and cosmology. The Square Kilometre Array (SKA) and the European Extremely Large Telescope (E-ELT) are the two flagship facilities for ground-based astronomy in the future. Both are planned to be operational in the twenties of this century. SKA - artist impression ...


23

I'm really excited about the results of Fermilab and J-PARC on the measurement of $(g-2)_\mu$, that is, the anomalous magnetic moment of the muon. The current value of $g-2$ is \begin{align} a_\mu^\mathrm{exp}&=0.001\;165\;920\;91(63)\\ a_\mu^\mathrm{SM}&=0.001\;165\;917\;64(52) \end{align} where $\mathrm{SM}$ is the full Standard Model prediction, ...


20

The Gaia Spacecraft is another hugely anticipated physics experiment. First conceived of in the early 90's it has been operational since 2013. The aim of this ambitious experiment is to create a 3D map of the location and velocity of up to 1% of all objects in the Milky Way. This should enable us to refine our models on galactic dynamics and allow us to ...


19

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 ...


18

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 ...


16

There are plans for a linear collider of electron positron, to study the new physics that is appearing at the LHC, two are in design. The International Linear Collider (ILC) is a proposed linear particle accelerator.1 It is planned to have a collision energy of 500 GeV initially, with the possibility for a later upgrade to 1000 GeV (1 TeV). The host ...


9

European Extremely Large Telescope The European Extremely Large Telescope (E-ELT) is an astronomical observatory and the world's largest optical/near-infrared extremely large telescope now under construction. Part of the European Southern Observatory (ESO), it is located on top of Cerro Armazones in the Atacama Desert of northern Chile. The design ...


9

James Webb Space Telescope The James Webb Space Telescope (JWST), previously known as Next Generation Space Telescope (NGST), is a flagship-class space observatory under construction and scheduled to launch in October 2018. The JWST will offer unprecedented resolution and sensitivity from long-wavelength (orange-red) visible light, through near-infrared ...


7

Facility for Antiproton and Ion Research The Facility for Antiproton and Ion Research (FAIR) is an international accelerator facility under construction which will use antiprotons and ions to perform research in the fields of: nuclear, hadron and particle physics, atomic and anti-matter physics, high density plasma physics, and applications in condensed ...


7

Edit: I am leaving this in because some effort has been made to present how decisions are made on complicated channels.The simple answer by @atlas-insider clarifies the general point that the OP is asking. From the sample ATLAS paper given in the comments Search for supersymmetry at $\sqrt{s}=13\ \rm TeV$ in final states with jets and two same-sign ...


6

European x-ray free electron laser The European X-Ray Free-Electron Laser (European XFEL) is an X-ray research laser facility currently under construction and as of 2015 is scheduled to start user operation in 2017. The international project with 11 participating countries (Denmark, France, Germany, Hungary, Italy, Poland, Russia, Slovakia, Spain, Sweden ...


4

Disclaimer: I've never done the particular class of measurements you ask about, but I have done other low raw-rate, precision measurements (neutrino mixing and weak form-factors). The focus of experimental work for low count rates is multi-pronged: Maximize the quantity of data. For counting experiments the raw fractional statistical uncertainty goes by ...


3

The oldest work on this preceeds quantum mechanics by more than 100 years. it was done by Malus in 1809 about experiments with polarized light. See http://www.mat.univie.ac.at/~neum/papers/physpapers.html#CQlightslides


2

Yes the human body has a gravitational field, and yes it's large enough to be measured experimentally (see the Cavendish experiment).


2

It's not as fundamental as the other mentioned projects, but I am excited about ITER. If everything goes according to schedule, ITER should be the first fusion reactor that produce more energy than it consumes in 2030.


2

Under the suggestion of L. Levrel, I'll expand upon my comment. We can look at the constants included within an equation to get an idea of whether it was theoretically derived, or an empirical result. If we have fundamental constants, such as $\hbar, \epsilon_0, e, c,$ etc, then it was probably theoretically derived. An empirical law would have an arbitrary ...


2

Courtesy of its spin the electron has a magnetic dipole moment. That means if we place it in a magnetic field the two states aligned with and against the magnetic field have different energies. The magnitude of the energy difference depends on the strength of the field and the size of the magnetic dipole moment, which in turn depends on the spin. So by ...


2

A helium nucleus is not two protons, it is two protons and two neutrons. Instead you can compare two deuterium nuclei (one proton and one neutron) with one helium nucleus, so you have the same number of nucleons of the same types. And the answer is (as far as I am aware): no, there is no experimental evidence for the magnitude gravitational forces produced ...


2

The article says "Consequently, there can only ever be an experimental lower bound on the mass of a supposedly massless particle; in the case of the photon, this confirmed lower bound is of the order of $3×10^{−27} eV = 10^{−62} kg$." It is saying that the rest mass of the photon, if it exists, is less than $10^{−62} kg$ which is different to the frequency ...


2

I am not sure that this is the best method but it is the only one I can think of. Find a location of minium ($0$) visibility (which is easy to detect) [1]. Looking at the center of the intensity distribution, move one the mirrors to until you reach the next location of minium ($0$) visibility. When moving the mirrors count the number $n$ of minium is ...


1

There is a nice review of the subject here. At high volume fractions of the corn starch the viscosity is approximately described by the equation: $$ \eta = \left( 1 - \frac{\varphi}{\varphi_m} \right)^{-B\varphi_m} $$ where $\varphi_m$ and $B$ are experimentally fitted parameters. This known as the Krieger–Dougherty equation. $\varphi_m$ tells you at ...


1

Okay, so I am taking this question to mean what is the lowest-energy photon that can be individually detected. This is certainly an interesting technological question. I can't give an authoritative answer, but the lowest energy detectors I am familiar with is at the CMB microwave background energy of ~ $3Kk_B$, which corresponds to a wavelength of about 5 ...


1

A compression shock at subsonic flight speed only occurs when a supersonic pocket of air collapses downstream. Neither of your options is correct, and in that shock the speed drops from mildly supersonic (typically Mach 1.25) to the inverse of that Mach number (that would then be typically Mach 0.8). Acceleration into the supersonic regime is smooth and ...


1

Well the first step would be to plot $f(x)/x$. From this you should be able to identify two regions of linearity to which you can apply linear regression to find the $\alpha$ and $\beta$ constants: Without knowing the relevant physics or seeing the data, it's difficult to say what the best approach for handling the 'intermediate' region would be. If the ...


1

What method should I use to find the best fit curve that satisfies the model constraints (quadratic at low x, linear at large x, anything goes for intermediate x) and fits the data as best as possible? It depends on what your goal exactly is, whether you want to find $\alpha,\beta$ as accurately as possible or whether you want "good fit" in the sense ...


1

Water freezes from the outside in, as the outside is exposed to the coldest temperature. Therefore any impurities as pushed inwards as the water crystallises. These impurities are then compacted in the centre of the ice, making it cloudy as seen in your photo.


1

Judging by your Q1, I think you are asking about error bars for data points in graphs, especially in relation to plotting a line or curve of best fit. Error bars are not often calculated statistically for this purpose. To do so, a sample of N measurements must be made for each chosen value of the independent variable x and a mean and SD calculated. The ...


1

It does't really make much sense to talk about a tree-level truncation (it helps for calculations, but that's it) or to take the first Feynman diagram as a true representation of reality. By the way, in your $e^- e^- \to e^- e^-$ example, the whole notion of spatial separation is ill-defined since this is a t-channel process. If going from virtual to real ...


1

I've talken your diagram and attempted to draw on the grid lines for $Q = 2e$, $Q=3e$, etc: The problem is that the vertical spacing between the points is much smaller than $e$. If you were picking up ambient charge that charge would still have to increase in steps of $e$ and it isn't doing so. I would guess that your experimental errors are larger than ...



Only top voted, non community-wiki answers of a minimum length are eligible