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n2doc

(47,953 posts)
Mon Feb 23, 2015, 12:40 PM Feb 2015

What goes on inside a proton?

by Jon Butterworth

I spent part of last week at a meeting in the Pyrenees, northern Spain, discussing the internal structure of the proton. The meeting was in the small village of Benasque, hosted by Juan Rojo at the Centro de Ciencias de Benasque Pedro Pascual.

The proton (my favourite particle) is the nucleus of a hydrogren atom, is useful for curing some cancers, and is the particle collided by the Large Hadron Collider as it extends the frontiers of our knowledge of the structure of matter. Protons are made of two up-quarks and a down-quark, but there is quite a lot more than that to discover about their internal structure.

Most what we know about proton structure comes from the scattering of electrons off protons. Electrons and quarks are both electrically charged, so they repel or attract each other, depending whether the quark in question is positively or negatively charged (the electron has negative charge). By measuring how often, and with what energy and angle, electrons scatter off protons, we can work out several things. Firstly, we can tell the proton is not fundamental; it has something inside it. Consider this sketch:


This is a rough sketch of what we might see if the proton was fundamental - infinitely small and with no internal strucure. The vertical axis (labelled σ, “sigma”) is proportional to the number of times an electron-proton scattering happens, and the horizontal axis (x) is the fraction of the proton which the electron “saw”. If the proton is fundamental, this is always one, hence the spike at unity.

more

http://www.theguardian.com/science/life-and-physics/2015/feb/21/what-goes-on-inside-a-proton

8 replies = new reply since forum marked as read
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Romeo.lima333

(1,127 posts)
1. you always post cool stuff .... thanks
Mon Feb 23, 2015, 12:59 PM
Feb 2015

what makes up quarks is that where string theory comes in? - Protons are made of two up-quarks and a down-quark,is this true for all protons?

DreamGypsy

(2,252 posts)
3. Yes, all protons consist of 2 up quarks and 1 down quark....
Mon Feb 23, 2015, 01:24 PM
Feb 2015

... but neutrons, the other nucleon particle, consist of 2 down quarks and 1 up quark.

An up quark has a positive electric charge equal to 2/3 the magnitude of the charge of an electron; a down down quark has a negative electric charge equal to 1/3 the magnitude of the charge of an electron. This means the charge of the proton is equal in magnitude and opposite in sign to the electron (2/3 + 2/3 -1/3 = 1) and the neutron is electrically neutral (2/3 -1/3 -1/3 = 0).

There are other more exotic hadrons, that is particles made up of quarks and held together by the strong force.

DreamGypsy

(2,252 posts)
6. Sure. Strange and charm quarks are constituents of mesons...
Mon Feb 23, 2015, 05:58 PM
Feb 2015

...as are top and bottom quarks (which some prefer to name truth and beauty)

First, it is worth noting that for every type of quark there is a corresponding antiquark. An antiproton consists of 2 up antiquarks and 1 down antiquark.

A Meson is composed of one quark and one antiquark:

From Wikipedia:

In particle physics, mesons (/ˈmiːzɒnz/ or /ˈmɛzɒnz/) are hadronic subatomic particles composed of one quark and one antiquark, bound together by the strong interaction. Because mesons are composed of sub-particles, they have a physical size, with a diameter roughly one femtometre,[citation needed] which is about 2⁄3 the size of a proton or neutron. All mesons are unstable, with the longest-lived lasting for only a few hundredths of a microsecond. Charged mesons decay (sometimes through intermediate particles) to form electrons and neutrinos. Uncharged mesons may decay to photons.

Mesons are not produced by radioactive decay, but appear in nature only as short-lived products of very high-energy interactions in matter, between particles made of quarks. In cosmic ray interactions, for example, such particles are ordinary protons and neutrons. Mesons are also frequently produced artificially in high-energy particle accelerators that collide protons, anti-protons, or other particles.

In nature, the importance of lighter mesons is that they are the associated quantum-field particles that transmit the nuclear force, in the same way that photons are the particles that transmit the electromagnetic force. The higher energy (more massive) mesons were created momentarily in the Big Bang but are not thought to play a role in nature today. However, such particles are regularly created in experiments, in order to understand the nature of the heavier types of quark which compose the heavier mesons.


Flavourless mesons consist of a quark and an anti-quark of the same type, for example a charm quark and a charm antiquark. Flavoured quarks consist of a quark and a different type of antiquark, for example a charm quark and an antidown quark is a neutral kaon (meson).

The link provides various tables listing the kinds of mesons determined by the types of quark and antiquark constituents.

Hope this helps.

xocet

(3,871 posts)
8. Note that charmed baryons exist...and...that strange baryons also exist.
Tue Feb 24, 2015, 12:47 PM
Feb 2015

Λc is a charmed baryon and Λ is a strange baryon.

The Lambda Baryon

In 1947 during a study of cosmic ray interactions, a product of a proton collision with a nucleus was found to live for much longer time than expected: 10^(-10) seconds instead of the expected 10^(-23) seconds! This particle was named the lambda particle (Λ0) and the property which caused it to live so long was dubbed "strangeness" and that name stuck to be the name of one of the quarks from which the lambda particle is constructed. The lambda is a baryon which is made up of three quarks: an up, a down and a strange quark.

...

http://hyperphysics.phy-astr.gsu.edu/hbase/particles/lambda.html#c1


Here is more:

charmed baryons:

CHARMED BARYONS
Revised March 2012 by C.G. Wohl (LBNL).

There are 17 known charmed baryons, and four other
candidates not well enough established to be promoted to the
Summary Tables.∗

...

The unpromoted states are a Λc(2765)+, a Ξc(2930), a Ξc(3055), and a Ξc(3123). There is also very weak evidence for a baryon with two c quarks, a Ξcc+ at 3519 MeV. See the Particle Listings.

...

http://pdg.lbl.gov/2014/reviews/rpp2014-rev-charmed-baryons.pdf



strange baryons:

First Indirect Evidence of So-Far Undetected Strange Baryons
"Invisible" particles containing at least one strange quark lower the temperature at which other particles "freeze out" from quark-gluon plasma

August 19, 2014

UPTON, NY—New supercomputing calculations provide the first evidence that particles predicted by the theory of quark-gluon interactions but never before observed are being produced in heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC), a facility that is dedicated to studying nuclear physics. These heavy strange baryons, containing at least one strange quark, still cannot be observed directly, but instead make their presence known by lowering the temperature at which other strange baryons "freeze out" from the quark-gluon plasma (QGP) discovered and created at RHIC, a U.S. Department of Energy (DOE) Office of Science user facility located at DOE's Brookhaven National Laboratory.

RHIC is one of just two places in the world where scientists can create and study a primordial soup of unbound quarks and gluons—akin to what existed in the early universe some 14 billion years ago. The research is helping to unravel how these building blocks of matter became bound into hadrons, particles composed of two or three quarks held together by gluons, the carriers of nature's strongest force.

"Baryons, which are hadrons made of three quarks, make up almost all the matter we see in the universe today," said Brookhaven theoretical physicist Swagato Mukherjee, a co-author on a paper describing the new results in Physical Review Letters. "The theory that tells us how this matter forms—including the protons and neutrons that make up the nuclei of atoms—also predicts the existence of many different baryons, including some that are very heavy and short-lived, containing one or more heavy 'strange' quarks. Now we have indirect evidence from our calculations and comparisons with experimental data at RHIC that these predicted higher mass states of strange baryons do exist," he said.

Added Berndt Mueller, Associate Laboratory Director for Nuclear and Particle Physics at Brookhaven, "This finding is particularly remarkable because strange quarks were one of the early signatures of the formation of the primordial quark-gluon plasma. Now we're using this QGP signature as a tool to discover previously unknown baryons that emerge from the QGP and could not be produced otherwise."

...

http://www.bnl.gov/newsroom/news.php?a=11659
 

stone space

(6,498 posts)
2. I didn't know that folks choose favorites.
Mon Feb 23, 2015, 01:00 PM
Feb 2015
The proton (my favourite particle)


On a related note, I've always wondered if theoretical physicists go around calling each other Bosons, as in, "What a Boson!".

 

JDDavis

(725 posts)
5. I love science!
Mon Feb 23, 2015, 03:14 PM
Feb 2015

But I haven't spent any time studying atoms since high school chemistry and physics.

Thank you for these links and this discussion. You are slowly making me smarter.

Warren DeMontague

(80,708 posts)
7. my distinctly layperson's interpretation, as I understand it, is that the question is sort of
Tue Feb 24, 2015, 08:28 AM
Feb 2015

meaningless in terms of how we understand "things" occupying "space" and "doing stuff" in normal 3D macro reality.

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