Wit Busza Interivew - Special Topic of Hadron Colliders
Special Topic of Hadron Colliders Interview, April 2010
We would also like to get a confirmation that our current understanding is correct. So one of the very early measurements we will certainly make is of this flow phenomenon, and see if our understanding of it from RHIC is correct. We can more or less predict now the way the liquid flows. If, by chance, it turns out to be completely different at the LHC, that would send us back to the drawing board to make sure we have not misinterpreted the results at RHIC. If this flow is much bigger than everybody expects, it will be a major surprise.
So these are the kind of measurements we will be doing. We can characterize them as having two components: one is seeing if this system, when it's bigger and hotter, behaves as we'd expect based on what we saw at RHIC. And the other one is making use of the powerful probes to learn more about this medium. On one hand, it would be a confirmation and extension of what is known. On the other, it would be new studies of the properties of this interesting material.
Now is this matter you're creating in the collisions a quark-gluon plasma or is it something else?
I knew you would ask me that. And my answer is that we are now in the realm of semantics. So let me explain. Before RHIC, most people had a preconceived idea that the only thing we will see is the so-called quark-gluon plasma. In their minds, this was a system of essentially non-interacting quarks and gluons. In retrospect, this was naïve.
If we go back to my analogy, it's as if we said let's start from this system in outer space where we saw one electron and proton per cubic meter and then we said, look, if we compress this enough, we'll end up with a very interesting gas called hydrogen and nothing else. So that will be the goal of our new experiment: we will find that hydrogen exists and nothing else. But we know that's crazy. We can produce helium and wood; we can produce a mouse, a PC, you name it.
And that's the same here. People had this naïve idea that if we compress this strongly-interacting material enough, if we compress quarks and gluons to close enough distances, they will essentially not interact and we will get non-interacting quarks and gluons. And that's not what we found, fortunately.
Something much more interesting is happening, which any intelligent human being should have expected, but clearly we were not intelligent enough. In fact, we're only just now beginning to get some idea of the kind of systems that exist when we take strongly interacting matter and compress it. We found a very interesting system, a fluid, and it has extremely (relatively speaking) low viscosity. And it's this system that we would have predicted would be the first thing we'd see, if we had been smart enough.
PHOBOS Detector
Courtesy of Brookhaven National
Laboratory.
Working on the spectrometer detectors of the PHOBOS detector.
The interview series
with Brookhaven National Labs >
So some people call this the quark-gluon plasma, and some call it a strongly interacting quark-gluon plasma. And since this is the first system where we no longer have separate protons and neutrons, etc., and since we got used to the term quark-gluon plasma, people said why not use this term for this system. And so that's what we've done.
I still stick by the statement that what we found is far more interesting than what people originally expected to see. I think we've now entered a field that I call the condensed matter of quantum chromodynamics. That's what it is. That's what our field should be called. Who knows what we might find.
How much running time will heavy-ion collisions be getting at CERN?
We'll get one month a year for the next 20 years. It's a long time. What is interesting is that for the last year the LHC has been colliding protons on protons. And the first interesting results have actually been obtained by the physicists who are interested in heavy ion collisions. This machine, the Large Hadron Collider, was primarily constructed to look at very short distance phenomena—the Higgs particle, supersymmetry, etc. But at the moment they're getting so few events, by their standards, that they can't yet find those rarer phenomena.
For us, these are the perfect conditions to see, for comparison, how these proton-proton collisions look at these high energies. Out of the first five publications from CMS, three, including the first one, were produced by the people preparing for the heavy ion program. Already in this early work we have found surprises.
A paper just recently published describes the so-called "ridge" in proton-proton collisions. This is a feature that is quite similar to what we already saw in the heavy ion collisions at RHIC. So some people think that maybe at these extremely high energies, even in proton-proton, you produce a system that has collective properties.
By a ridge, it sounds like ripples on a drop of water?
Yes, that's a pretty good analogy. Imagine you had a drop of water, with a long structure, a ripple on it. That would be a ridge. That's a pretty analogy.
How much of the PHOBOS collaboration moved to CMS and where did the others go?
Roughly speaking, MIT was about a third of PHOBOS, maybe even half. And all of the MIT group moved to CMS. PHOBOS was a very small collaboration—50 to 60 people. I would say two-thirds have moved to CMS. And the others have spread around. Some stayed at Brookhaven to continue to work on RHIC. Some went to the ATLAS collaboration. And one very gifted young man has gone into biophysics.
Wit Busza
Francis Friedman Professor of Physics
Massachusetts Institute of Technology
Cambridge, MA, USA
and
Spokesperson, the PHOBOS Collaboration
Brookhaven National Laboratory
Upton, NY, USA
BROOKHAVEN NATIONAL LAB'S MOST CURRENT MOST-CITED PAPER IN ESSENTIAL SCIENCE INDICATORS:
- Yao WM, et al., "Review of particle physics," J. Phys. G-Nucl. Particle Phys. 33(1): 1-+ Sp. Iss. SI July 2006 with 2,980 cites.
- Back BB, et al., "The PHOBOS perspective on discoveries at RHIC," Nucl. Phys. A 757 (1-2): 28-101, 8 August 2005 with 577 cites.
Source: Essential Science Indicators from Clarivate.
ADDITIONAL INFORMATION:
-
Menu for the institutional interview series with Brookhaven National Lab from the Special Topic of Hadron Colliders.
KEYWORDS: BROOKHAVEN NATIONAL LAB, NUCLEAR PHYSICS, PARTICLE PHYSICS, RHIC, RELATIVISTIC HEAVY ION COLLIDER, PHOBOS, MARS, MODULAR ARRAY FOR RHIC SPECTRA, MATTER, EXTREME HIGH ENERGY, MATTER DENSITY, CHARGED PARTICLES, FOUR-PI SOLID ANGLE, SLOW PARTICLES, WAVELENGTH, ENERGY DENSITY, CHARGED-PARTICLE PSEUDORAPIDITY DENSITY DISTRIBUTIONS, GOLD, COPPER, LEAD, FLOW, QUANTUM ELECTRODYNAMICS, QUANTUM CHROMODYNAMICS, LHC, J/PSI PARTICLES, UPSILON, QUARK-GLUON PLASMA, CONDENSED MATTER.