At Long Last, Physicists Calculate the Proton's Mass

By Adrian Cho ScienceNOW Daily News 21 November 2008 It's one thing to know a fact, but it's another to explain it, as a curious advance in particle physics shows. Ever since the proton was discovered 89 years ago, physicists have been able to measure the mass of the particle--which, along with another called the neutron, makes up the atomic nucleus. But even with the best computers, theorists had not been able to start with a description of the proton's constituent parts and calculate its mass from scratch. Now, a team of theorists has reached that goal, marking the arrival of precision calculations of the ultracomplex "strong force" that binds nuclear matter. "It's a really big deal," says John Negele, a theorist at the Massachusetts Institute of Technology in Cambridge. "It's the first time that we've really had this kind of confidence that everything is being done right." Like a troubled teenager, the proton is a mess inside and just about impossible to figure out. In the 1970s, experimenters discovered that the proton and the neutron, known collectively as nucleons, consist of more-fundamental particles called quarks and gluons, which are the basic elements of a theory called quantum chromodynamics (QCD). In the simplest terms, a proton contains two "up" type quarks and one "down" type quark, with gluons zipping among them to bind them with the strong nuclear force. (The neutron contains two downs and an up.) In reality, a nucleon is much more complicated. Thanks to the uncertainties of quantum mechanics, myriad gluons and quark-antiquark pairs flit in and out of existence within a nucleon. All of these "virtual" particles interact in a frenzy of pushing and pulling that's nearly impossible to analyze quantitatively. "Everything interacts with everything," says Laurent Lellouch, a theorist with the French National Center for Scientific Research at the Center for Theoretical Physics in Marseille and one of 12 physicists from France, Germany, and Hungary who performed the new calculations. Ninety-five percent of the mass of a nucleon originates from these virtual particles. To simplify matters, the team took a tack pioneered in the late 1970s called lattice QCD. Within their computer programs, the researchers modeled space not as continuous but as a three-dimensional array of points. They also modeled time as passing in discrete ticks, as opposed to flowing smoothly. This turns space and time into a lattice of points. The researchers then confined the quarks to the points in the lattice and the gluons to the links between the points. The lattice sets a shortest distance and time for the interactions, greatly simplifying the problem. Still, the computation involves millions of variables and requires supercomputers. Only since about 2000 have researchers attempted to include not just all of the gluons but the fleeting quark-antiquark pairs as well. The latest work, reported today in Science, incorporates a variety of conceptual improvements to obtain estimates of the mass of the nucleon and nine other particles made of up, down, and slightly heavier "strange" quarks accurate to within a couple of percent. This isn't the first computational tour de force for particle physicists. Five years ago, others made equally precise calculations of more esoteric quantities--somewhat easier to calculate--such as those that govern the decay of a particle called a D+ meson, which contains a down antiquark and a heavy "charm" quark, notes Christine Davies, a theorist at the University of Glasgow in the U.K. Still, she says, the calculation of the well-known masses highlights the ability of lattice QCD to make accurate predictions for the strong force. "This is all good news for lattice QCD," Davies says, "because there are lots of things that we want to calculate that experimenters haven't already measured." For example, Negele says, physicists still don't know distribution of the virtual particles inside the proton or the origin of its spin. --------------------------------------------------------------------------------

Chandrayaan-1 Probe Lands On Moon

India’s first unmanned moon mission touched down on the moon on Friday, according to Indian Space Research Organization officials.

The Moon Impactor probe detached itself from the Chandrayaan-1 (moon vehicle) about 100 km from the moon's surface and crash-landed on the south pole of the moon at 10:01 a.m. EST, making India the fourth nation to have a presence on the Moon.

Miniature Indian flags painted on four sides of the MIP signaled the country's symbolic entry into moon to coincide with the birth anniversary of the country's first Prime Minister Jawaharlal Nehru, observed as Children's Day.

"It will signify the entry of India on Moon," an ISRO official said.

The MIP consists of a C-band Radar Altimeter for continuous measurement of altitude of the probe, a video imaging system for acquiring images of the surface of moon from the descending probe and a mass spectrometer for measuring the constituents of extremely thin lunar atmosphere during its 20-minute descent to the lunar surface.

During its 20-minute descent to the moon's surface, MIP took pictures and transmitted them back to the ground. The first pictures are expected to be made public on Saturday.

This Week in Physics History: Nov. 3 - 9

Nov. 7, 1492 - A meteorite crashes to Earth around noon in a wheat field near Ensisheim, Alsace. The Ensisheim Meteorite is the oldest meteorite with a known date of impact.

Nov. 8, 1854 - Johannes Rydberg, discovery of the Rydberg State of an atom, is born.

Nov. 7, 1867 - Maria Sklodowska is born, remembered to posterity as Marie Curie, pioneer in the study of radioactivity. To date, she is the only person to have earned Nobel prizes in two different fields - physics & chemistry.

Nov. 7, 1878 - Lise Meitner is born. Meitner did ground-breaking work on the discovery of nuclear fission, but was controversially not included in the 1944 Nobel award for the discovery.

Nov. 5, 1879 - Scottish physicist James Clerk Maxwell dies. Maxwell is best known for unifying electricity and magnetism through Maxwell's Laws into electromagnetic theory.

Nov. 7, 1888 - Indian physicist Sir Chandrasekhara Venkata Raman is born. Raman received the 1930 Nobel Prize in Physics for work in molecular scattering of light, specifically the discovery of the Raman effect which bears his name.

Nov. 9, 1921 - Albert Einstein is awarded the Nobel Prize in Physics, primarily for his work in explaining the photoelectric effect.

Nov. 9, 1934 - Carl Sagan, American astronomer and author, is born. Sagan became best known as a populizer of science through television specials, and both fiction and non-fiction writing. He was the author of the science fiction novel Contact, which was later made into a film starring Jodie Foster.

Nov. 6, 1944 - The Hanford Atomic Facility first produces plutonium.

Nov. 5, 1948 - American physicist William Daniel Phillips is born. Phillips won the 1997 Nobel Prize in Physics for his work in laser cooling, which uses lasers to slow the motion of gaseous molecules.

Chandrayaan-1 Camera Tested

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The Terrain Mapping camera (TMC) on board Chandrayaan-1 spacecraft was successfully operated on October 29, 2008 through a series of commands issued from the Spacecraft Control Centre of ISRO Telemetry, Tracking and Command Network (ISTRAC) at Bangalore. Analysis of the first imagery received by the Indian Deep Space Network (IDSN) at Byalalu and later processed by Indian Space Science Data Centre (ISSDC) confirms excellent performance of the camera.The first imagery (image 1) taken at 8:00 am IST from a height of 9,000 km shows the Northern coast of Australia while the other (image 2) taken at 12:30 pm from a height of 70,000 km shows Australia’s Southern Coast.

TMC is one of the eleven scientific instruments (payloads) of Chandrayaan-1. The camera can take black and white pictures of an object by recording the visible light reflected from it. The instrument has a resolution of about 5 metres.

Besides TMC, the other four Indian payloads of Chandrayaan-1 are the Hyper spectral Imager (HySI), Lunar Laser Ranging Instrument (LLRI), High Energy X-ray Spectrometer (HEX) and the Moon Impact Probe (MIP). The other six payloads of Chandrayaan-1 are from abroad.

It may be recalled that the 1380 kg Chandrayaan-1 was successfully launched into an initial elliptical orbit around the Earth by PSLV-C11 on October 22, 2008. This was followed by four orbit raising manoeuvres, which together raised Chandrayaan-1’s orbit to a much higher altitude. The spacecraft is now circling the Earth in an orbit whose apogee (farthest point to Earth) lies at 267,000 km (Two lakh sixty seven thousand km) and perigee (nearest point to Earth) at 465 km. In this orbit, Chandrayaan-1 takes about six days to go round the Earth once. The spacecraft performance is being continuously monitored and is normal.