Heavy Particles Get Caught Up in a Flow

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First formula from new pointing molecule detector designed to vaunt minute properties of subatomic “soup” that mimics a early universe

UPTON, NY—By teasing out signatures of particles that spoil usually tenths of a millimeter from a core of a trillion-degree fireball that mimics a early universe, chief physicists outstanding atoms during a Relativistic Heavy Ion Collider (RHIC) are divulgence new sum about a elemental particles that make adult a world.

Brookhaven Lab physicist Flemming Videbaek during designation of a Heavy Flavor Tracker during a STAR detector during RHIC, a world-class molecule collider during Brookhaven National Laboratory

Particle collisions during RHIC—a U.S. Department of Energy (DOE) Office of Science User Facility located during DOE’s Brookhaven National Laboratory—regularly reconstruct little specs of quark-gluon plasma (QGP), a reduction of quarks and gluons, a elemental building blocks of manifest matter, that final existed as giveaway particles some 14 billion years ago. The collisions giveaway a quarks and gluons from their capture within typical particles (e.g., protons and neutrons) so chief physicists can investigate their interactions and a force that binds them together in a star today.

The new measurements, described in a paper usually published in Physical Review Letters, are a initial to come from a pointing ascent to RHIC’s STAR detector famous as a “Heavy Flavor Tracker” (HFT). Specifically, a paper gives sum about a initial approach dimensions during RHIC of how a form of complicated molecule containing a “charm” quark gets held adult in a upsurge of a expanding fireball. This measurement—a covenant to a capabilities of a HFT—gives scientists a new window into bargain a interactions of a particles that make adult a subatomic soup.

Berkeley Lab’s Heavy Flavor Tracker group enclosed (from left) Mario Cepeda, Kenneth Wilson, Leo Greiner, Howard Wieman, Thomas Johnson and Giacomo Contin. (Photo by Roy Kaltschmidt)

“By comparing a measurements with fanciful predictions that embody a several parameters that play a purpose in these interactions—things like a freeing fellow (how fast a attract quarks widespread via a plasma) and flexibility (how gummy a QGP is)—we can learn about how these opposite properties describe to one another, and eventually since a QGP behaves a approach it does,” pronounced Brookhaven physicist Flemming Videbaek, a plan manager obliged for a altogether phony of a STAR HFT.

Precision molecule tracking

A close-up perspective of components of a Heavy Flavor Tracker, before to designation during STAR.

Particles containing complicated quarks are deliberate ideal probes for bargain quark-gluon plasma since they might correlate differently with a plasma than light quarks do, charity adult pointed clues about a properties. But a QGP spits out particles containing complicated quarks usually rarely, amid thousands of other particles done of a lighter varieties of quarks. The few complicated particles that do emerge spoil into other particles roughly instantly—mere fractions of a millimeter from a QGP fireball in that they were created. This monument and fast spoil make complicated particles formidable to detect.

STAR’s HFT, a state-of-the-art tracking device now sitting during a core of a house-sized detector, was designed to lane a fugitive though critical complicated particles. Developed by chief physicists during Lawrence Berkeley National Laboratory, a HFT is a initial silicon detector during a collider that uses Monolithic Active Pixel Sensor technology—the same record used in digital cameras. The ultrathin sensors—unlike many of a molecule showing components of STAR—sit really tighten to a executive beampipe in that a collisions take place. While not utterly tighten adequate to detect a complicated attract quark itself, this plcae and a detector’s high fortitude (360 million pixels measuring 20 x 20 microns each) concede it to collect adult signs of a complicated particles’ decay.

For this sold study, STAR physicists were tracking particles called kaons and pions that emerge when charm-quark-containing particles famous as a D-zeros decay. A accordant bid from many groups of a collaboration—including researchers from Brookhaven National Laboratory, Lawrence Berkeley National Laboratory, Kent State University, and a University of Illinois during Chicago—made this research successful in a brief time.

“We use a HFT to demeanour for kaons and pions that are really tighten to one another— within fractions of a millimeter of one another—whose paths from a collision emerge from a singular indicate that’s divided from a collision vertex, though not really far, about 100-500 microns,” Videbaek said. That’s a stretch D0s transport before they decay, he explained. If a kaon and pion have usually a right mass and trajectories rising from such a point, a scientists can interpretation that they originated from a D0 during that spot—and use these measurements to lane a presentation of D0s from all around a QGP.

“The pointing of a dimensions is unprecedented,” pronounced Xin Dong, a physicist during Berkeley Lab who led a postdocs and students conducting a production research on a complicated season results. “It was intensely severe due to division from thousands of other particles constructed in a same complicated ion collisions—a bit like picking a needle out of a haystack.”

Free issuing interactions

The findings—based on an research of tens of thousands of such “needles” in 1.1 billion collisions—were rather surprising.

Think of a figure combined when dual round bullion ions hit off core combining an form overlap—something like a football station on end. STAR physicists found some-more D0s rising from a fat partial of a “football” than from a pointy ends. This settlement of “elliptic flow” was informed from measurements of lighter particles rising from a QGP. But chief physicists didn’t primarily design such complicated particles to get held adult in a flow.

“D0s are combined in a really initial partial of a collision, when a quarks and gluons are free,” Videbaek said. “Physicists didn’t consider these heavy-quark particles would have time to interact, or equilibrate, with a QGP, that exists for usually an infinitesimally tiny fragment of a second.”

Instead, a fact that a complicated quarks vaunt a same elliptic upsurge as lighter particles do is justification that they are in equilibrium, interacting with a giveaway quarks and gluons in a QGP.

“The form of upsurge we celebrated for particles with complicated quarks suggests that their interactions inside a quark-gluon plasma are so clever that a complicated quarks themselves turn partial of a quark-gluon ‘soup,’” pronounced Dong.

Grazyna Odyniec, personality of Berkeley Lab’s Relativistic Nuclear Collisions Program, added, “The find of a elliptic upsurge of a really large attract quark is of elemental significance for a bargain of quark-gluon plasma proviso dynamics. It opens adult a extended operation of fanciful speculations about a inlet of a probable resource (or mechanisms) behind this observation.”

Brookhaven Lab physicist and STAR partnership orator Zhangbu Xu remarkable that a ability to lane a upsurge and freeing of a complicated particles gives chief physicists a new approach to “see” and investigate a interactions of a openly relocating quarks and gluons and other properties of a QGP—somewhat equivalent to a approach scientists from a final century tracked a vibrations of pollen grains in H2O to learn about a properties.

“Einstein valid in 1905 that atoms and molecules exist, and that we could use a supposed Brownian suit of pollen grains to magnitude a properties of a liquid and other elemental production constants,” Xu said. “Now we can use a attract quarks like a pollen grains to magnitude a upsurge and other properties of a QGP.”

Source: BNL


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