A. Djouadi “The Anatomy of Electro-Weak Symmetry Breaking.

hardE – from 10 keV = 104 eVT – from 2 million Kν – from 2 1018 Hzλ – up to 10-10 m

Having distinguished a new type of study, Wilhelm Roentgen called it X-rays. It is known under this name all over the world, except for Russia.

The most prominent source of X-rays in space is the hot inner regions of accretion disks around neutron stars and black holes. Also in the X-ray range, the solar corona shines, heated to 1–2 million degrees, although there is only about 6 thousand degrees on the surface of the Sun.

But X-rays can be obtained without extreme temperatures. In the emitting tube of a medical X-ray machine, electrons are accelerated by a voltage of several kilovolts and cut into a metal screen, emitting X-rays during braking. The tissues of the body absorb X-rays in different ways, which makes it possible to study the structure of internal organs.

X-ray does not penetrate through the atmosphere; cosmic X-ray sources are observed only from orbit. Hard X-rays are recorded with scintillation sensors. When X-ray quanta are absorbed, a glow appears in them for a short time, which is captured by the PMT. Soft X-rays are focused by oblique metal mirrors, from which the rays are reflected at an angle of less than one degree, like pebbles from the surface of water.

Sources of

X-ray sources near the center of our Galaxy

Fragment of the image of the vicinity of the center of the Galaxy, obtained by the X-ray telescope « Chandra ». A number of bright sources are visible, which, most likely, are accretion disks around compact objects – neutron stars and black holes.

The vicinity of the pulsar in the Crab Nebula

The vicinity of the pulsar in the Crab Nebula is a supernova remnant that exploded in 1054. The nebula itself is a stellar shell scattered in space, and its core has compressed and formed a superdense rotating neutron star about 20 km in diameter.

The rotation of this neutron star is tracked by strictly periodic oscillations of its radiation in the radio range. But the pulsar also emits in the visible and X-ray ranges. In X-rays, the Chandra telescope was able to obtain an image of the accretion disk around the pulsar and small jets perpendicular to its plane (cf. Accretion disk around a supermassive black hole).

Accretion disc in a close binary argumentative essay on drinking age system (artist’s drawing)

Solar prominences in x-ray

The visible surface of the Sun is heated to about 6 thousand degrees, which corresponds to the visible range of radiation. However, the corona surrounding the Sun is heated to a temperature of over a million degrees and therefore glows in the X-ray range of the spectrum.

This picture was taken during the maximum solar activity, which changes with a period of 11 years. The very surface of the Sun in X-rays practically does not emit and therefore looks black. During the solar minimum, the X-ray emission from the Sun is significantly reduced. The image was taken by the Japanese satellite Yohkoh (Sunbeam), also known as Solar-A, which operated from 1991 to 2001.

Receivers

X-ray telescope « Chandra »

One of the four « Great Observatories » of NASA, named after the American astrophysicist of Indian origin Subramanian Chandrasekhar (1910–95), Nobel Prize laureate (1983), a specialist in the theory of the structure and evolution of stars.

The main instrument of the observatory is an oblique-incidence X-ray telescope with a diameter of 1.2 m, containing four nested oblique incidence parabolic mirrors (see diagram), turning into hyperbolic ones. The observatory was launched into orbit in 1999 and operates in the soft X-ray range (100 eV – 10 keV). Among the many discoveries of the Chandra Observatory is the first image of an accretion disk around a pulsar in the Crab Nebula.

Diagram of an X-ray telescope with oblique incidence mirrors

Optical and radio telescopes use the property of a paraboloid to bring a parallel beam of radiation from a distant object to one point in the focal plane. But for this, the radiation must be reflected from the mirror surface of the paraboloid. X-ray quanta are so energetic that they pierce the surface and are absorbed in the substance of the mirror. Therefore, it is impossible to build a traditional X-ray telescope. Except for one possibility.

Soft X-rays can bounce off polished metal if they strike it very gently, at an angle of less than one degree. This makes it possible to use a parabolic mirror for focusing a soft X-ray. Only you have to take not the top of the paraboloid, but the ring belt at a considerable distance from it. An oblique X-ray mirror looks like a piece of pipe tapering slightly towards one end. Such a ring intercepts a very small fraction of the radiation. To increase the efficiency of the telescope, several of these oblique incidence mirrors are concentrically nested within each other. The manufacture of such a system requires the highest precision and is extremely labor intensive.

Since X-ray telescopes can only operate in space, they are all unique instruments.

INTEGRAL Gamma Observatory (INTErnational Gamma-Ray Astrophysics Laboratory)

Photomultiplier tube (PMT)

PMT matrix

Sky views

X-ray sky in the range of 0.1-2.4 keV (ROSAT)

The review was prepared based on the data of the German orbital observatory ROSAT (short for « Röntgensatellit »), which operated from 1990 to 1999 in the range of vacuum ultraviolet radiation and soft X-rays (6 eV – 2.4 keV). An X-ray telescope with oblique incidence mirrors was installed on board the observatory.

Earthly application

X-ray tube

An electronic tube serving as a soft X-ray source. A voltage of 10–100 kV is applied between two electrodes inside a sealed vacuum flask. Under the action of this voltage, electrons are accelerated to an energy of 10–100 keV. At the end of the path, they collide with a polished metal surface and decelerate sharply, releasing a significant part of their energy in the form of radiation in the X-ray and ultraviolet range.

X-ray

The image is obtained due to the unequal permeability of the tissues of the human body to X-rays. In a conventional camera, a lens refracts light reflected by an object and focuses it on the film, where the image is formed.

However, X-rays are very difficult to focus. Therefore, the operation of an X-ray machine is more like a contact print of a picture, when a negative is placed on photographic paper and illuminated for a short time. Only in this case, the human body acts as a negative, a special photographic film sensitive to X-rays acts as a photographic paper, and an X-ray tube is taken instead of a light source.

Next: Ultraviolet

If the section Design and tasks of the LHC described the “anatomy” of the LHC, then here we will talk about its “physiology”. We will talk about specific work plans and discoveries that will be made at the LHC. We will follow the current news in the LHC news feed, and large summaries will appear here.

Different subsections are written at different times, so don’t be surprised, for example, to tell you about plans for 2009 or 2012 in the future.

Large Hadron Collider monitorsChronology of creation and operation of the Large Hadron Collider NEWGeneral work schedule of LHC NEW How to follow the news with LHC Collider duty cycleEarly stages of the LHC’s work Schedule for 2008 The accident on September 19, 2008 and its aftermath Schedule for 2009 Results of work in 2009Session LHC Run 1 NEWSchedule for 2010 Results of work in 2010 Schedule for 2011 Results of work in 2011 Schedule for 2012Technical break LS1Session LHC Run 2 NEW LHC’s work in 2015 NEW LHC work in 2016 NEW LHC’s work in 2017 NEW LHC work in 2018 NEW »

The birth of the Higgs boson at the LHC

Four main channels of Higgs boson production at the LHC (adapted images from Physics of and with Leptons)

There are four main channels for the production of the Higgs boson in the collision of partons from two colliding protons:

Creation in the merger of gluons: gg → H. In an ultrarelativistic proton, gluons (with the required kinematics) prevail over other partons, so this is the dominant production channel. This process turned out to be rather difficult to calculate because the high-order corrections turned out to be not small, but after several years of work they were calculated with good accuracy. Creation of vector bosons WW → H or ZZ → H in a merger. Virtual vector bosons emitted and absorbed by quarks can also be considered as partons, which, however, are extremely small in a proton. Nevertheless, they are very strongly (much stronger than the quarks themselves) associated with the Higgs boson, so the cross section for this process is only several times smaller than the merging of gluons. Associative production with W or Z boson. This process is often called Higgsstrahlung (« Higgs boson bremsstrahlung » – by analogy with bremsstrahlung, photon bremsstrahlung). Associative production with top quarks. This process can be thought of as the production of two top-quark-antiquark pairs, with the quark and antiquark from different pairs then merging, giving rise to the Higgs boson. The cross section of this process is even smaller, but it has its own specific signature (the decay pattern in the detector), which can be used to search for the Higgs boson.

The graph shows the cross sections for the production of the Higgs boson in one channel or another.

Cross section of the Higgs boson production at the LHC in various parton subprocesses (image from the website of the Higgs boson search group in the CMS experiment)

Higgs boson decays

By its nature, the Higgs boson must be associated with all massive fundamental particles, and the greater the mass of the particles, the more strongly it is associated with them. This means that the Higgs boson prefers to decay into the heaviest particle-antiparticle pairs, which are still available according to the law of conservation of energy. In addition, due to the loops of virtual particles, the Higgs boson is also associated with massless particles – photons and gluons.

Probabilities of the Higgs boson decay into various final states (image from the website of the Higgs boson search group in the CMS experiment)

Let us recall the masses of the heaviest known particles: b-quark – 5 GeV, W-boson – 80 GeV, Z-boson – 91 GeV, t-quark – 170 GeV. This means that a Higgs boson with a mass, for example, 120 GeV, will decay predominantly into b – anti-b pairs, a boson with a mass of 250 GeV will decay mainly into WW and ZZ pairs, a heavier boson will decay into WW -, ZZ- and t-anti-t-pairs.

What is curious about this picture is that the breakup into WW-pairs begins long before the threshold. If the W bosons were stable, then the H → WW decay would be possible only if the Higgs boson mass exceeded the threshold value 2MW = 160 GeV. However, due to the fact that W-bosons are unstable, this process is actively going and « far below the threshold », starting with a Higgs boson mass of about 130 GeV. In this case, one of the W-bosons is born virtual and immediately decays.

Additional literature:

The key properties of the Higgs boson are discussed in LB Okun’s book Leptons and Quarks. For detailed information on the production and decays of the Higgs boson in the Standard Model, see A. Djouadi’s review “The Anatomy of Electro-Weak Symmetry Breaking. I: The Higgs boson in the Standard Model « // hep-ph / 0503172. S. Bolognesi, G. Bozzi, A. Di Simone. « Higgs at the LHC » // arXiv: 0804.4401.

Seven and a half orders

Artificial satellites of the Earth

Echoes of earthquakes

Killer asteroid

How the heat spreads

Tatiana Romanovskaya

The world around us is filled with objects of millions of colors and shades. Their diversity will be even wider when you consider that many insects and birds see in the ultraviolet part of the spectrum. This article is devoted to how all these colors and overflows are obtained in living nature – thanks to the laws of optical physics and the ingenious device of living cells and tissues created by biological evolution.

Chemistry and physics of color

The color of an object can be formed by two mechanisms. More widely known and in a sense more familiar to us is chemical. It is related to the ability of certain molecules to selectively absorb, reflect, or emit light at a specific wavelength. This is how, for example, the color of the most common paints for painting is determined. Biological molecules with these properties are called pigments. In plants, these are mainly chlorophylls (they are green), carotenoids (yellow, orange and red) and flavonoids (give different shades of yellow, blue or purple). In animals, these are mainly different variants of melanin, which are yellow, orange, red or brown-black. Pigments of blue color in representatives of this kingdom appear only as extremely rare exceptions. In addition to the « usual » colored substances, some animals and fungi produce fluorescent substances, which do not reflect the light incident on them, but absorb and then emit their own light with a different wavelength. Jellyfish, some marine fish and molluscs have been particularly successful in this.

The second method of color formation is structural. The color formed in this way does not depend on the chemical properties of the molecules, but on the structure of the surfaces on which the light from the source falls. Another name for the structural method of color formation is iridescence, or irisation. An explanation for this phenomenon was proposed in 1803 by the English physicist Thomas Jung, one of whose most important achievements is the proof of the wave nature of light by demonstrating the phenomenon of interference of light waves.

In all cases, iridescence is based on nanostructures in the form of ribs, fibers, plates, organized in regularly spaced rows or lattices (in physics, structures of this type are called photonic crystals). It is important that the linear dimensions of the alternating elements of the lattice and the spaces between them are close to the wavelengths of the light spectrum. Photonic crystals create specific optical effects, such as diffraction and interference (for more details on the mechanisms of formation of structural color, see the article « Structural color », « Chemistry and Life » No. 11, 2010). For the interference effect to occur, it is necessary that the light waves repeatedly reflected from the grating elements are in the same phase. The amplitudes of the waves for which this condition is met are summed up, and the wavelengths of these waves determine the main visually perceived color background.

The general physical mechanism determines both the iridescent color of some natural minerals (mother of pearl and pearls, moonstone, opal), and the structural color of the outer covers of many living organisms. Examples of such coloration are extremely numerous, and the nature of the nanostructures providing this coloration is also very diverse.

The shades and brightness of the structurally determined color can change when the angle at which the viewer is to the object changes: remember how feathers shimmer from gray to green on the wings of starlings or on the neck of a drake. Iridescence, in addition to painting an object in different colors, can also create glitter (like the cherry weevil) or specular (seen in many fish) effects.