Events of August 4, 2013
As our car turned off the highway and past the entrance sign that read "BNL: Brookhaven National Laboratory", everything seemed much as it had two weeks before. The same sign, the same summer sun, the same straight road stretching ahead of us past the security checkpoint.
Except that this time, there were several cars ahead of us at the checkpoint.
"They're probably here for Summer Sundays, like us." My father said, "This one must be popular."
"One of the women we talked to last time said the tour of the RHIC always draws the most people. I mean, how many times in your life do you get to see the inside of an atom-smasher?" I said.
My father agreed with the point as we once again followed the signs for visitors down the streets of the laboratory campus to Berkner Hall. The lobby, too, looked very similar to how it had been at the previous event--crowded with visitors (some of whom were eagerly watching a demonstration with a Van De Graaff generator), and well-staffed with blue-shirted employees handing out information sheets. Once again, films about Brookhaven Lab's work were being shown in loops on screens mounted on the walls. I noticed that the special video about the Relativistic Heavy Ion Collider that we would be going to see today playing on one screen had scenes of scientists being interviewed at what I recognized as a hotel down the street from the dorm where I'd lived when interning in DC the year before. After stopping by the front desk to say hello to Nora Detweiler, we found a quiet corner to call the Media and Communications specialist who had volunteered to meet with us, Justin Eure.
Justin said he was already at the RHIC and that we should head over to join him. As we headed out the door at Berkner Hall, we passed a young boy with his mother who was also headed for a tour.
"What do you think it's going to be like?" I heard her ask.
"They're probably gonna smash a table made of atoms!" The boy declared, causing me to chuckle. While EVERY table is made of atoms, the RHIC collides the nuclei of individual atoms of gold, not anything so large as a whole table.
Heading down the familiar streets of the Lab campus, we drove by the facility we'd visited on our last trip, the National Synchrotron Light Source II.
"That's where we went last time. Wow, it's big." My dad commented.
"The RHIC is even bigger, though!" I said. Although I'd never visited the RHIC (pronounced "Rick") before, I knew it was true--at my High School, we'd had posters showing satellite photographs of Long Island taken from space where it was visible as a small white ring. The RHIC and the NSLS II are both particle accelerators--facilities that use magnets to accelerate a beam of atoms or subatomic particles to nearly the speed of light (that's what "relativistic" means). At the NSLS II, the beam will be used to create radiation at various wavelengths that can be used in experiments--for all its complexity, the particle beam is just a means to an end.
But at the RHIC, what matters is the particles, or, more precisely, what happens when the particles from one of the accelerator's two rings collide with particles from the other. At the moment of collision, the particles may break apart into their even smaller components that can then merge into strange new forms of matter. The RHIC has two rings (called the yellow and blue rings) that accelerate particles going in opposite directions around the 3,834 meters (2.4 miles) of the accelerator tunnel. The distance around the ring is about the same as the distance around the Indy 500 racetrack, but the particles travel far faster than racecars do--they make 80,000 circuits of the ring per second!
As big as the RHIC is, it doesn't do all the work of creating collisions on its own--the journey of the gold particles collided starts in other accelerators elsewhere on the Brookhaven Lab campus. The negatively-charged electrons are removed from a gold atom, giving it a positive charge and turning it into an ion (an atom with a positive or negative electric charge, as opposed to a normal atom, which is neutral because its positive and negative charges cancel each other out.) The other accelerators boost up the speed of the ion beam before it is funneled into the yellow and blue rings or the main RHIC tunnel, where powerful magnets accelerate it even more, until the particles are moving at 99.9 percent of the speed of light. Gold atoms are used because gold is a "heavy" element containing many protons and neutrons, densely packed together. (Ions of the heavy element gold are accelerated to nearly the speed of light until they collide--thus, relativistic heavy ion collider.)
So, we knew the RHIC was very large, and that it was set somewhat apart from the main laboratory campus, but neither of us had ever seen it before. Heading to the RHIC, the buildings became fewer and the trees became thicker, until at one point we were driving down a road with nothing but forest visible on either side. We caught glimpses of deer and pheasants between the trees.
"This must be what all of Long Island used to look like, before the English and Dutch came." My father commented. I agreed--it was hard to believe there were cutting-edge laboratories behind those trees, even if we had seen them the week before!
As we came out of the woods, the view opened up, although there were still many trees and a lot of brush. Very large metal buildings, looking something like small factories, were at the end of offshoots of the road, with only the weather-beaten green signs out front revealing their significance: "RHIC--Relativistic Heavy Ion Collider", "STAR Detector", "PHENIX Detector".
We got out at the RHIC headquarters building, where a crowd was gathered to listen to physicists and engineers explain what they would be seeing. I recognized Lawrence Hoff, the engineer who'd given our NSLS II tour, as one of the speakers. He discussed the RHIC's construction throughout the 1990s and how it had opened for business in 2000. "People ask me how it feels to be an engineer working in a lab full of physicists. I tell them, watch The Big Bang Theory and you'll get a good idea!" He quipped, earning a laugh from the audience.
When the gold ions enter the RHIC, they're composed of only protons and neutrons. When a collision occurs, the fundamental particles inside of those protons and neutrons are exposed--gluons and quarks. These particles briefly create a strange form of matter called quark-gluon plasma nicknamed "the perfect liquid". Quark-gluon plasma is 4 trillion degrees Kelvin--hundreds of thousands of times hotter than the interior of the sun-- and is believed to be similar to the first material in the Universe just a few microseconds after the Big Bang! Of course, quark-gluon plasma didn't last very long then, and it doesn't last very long now--it very quickly changes into other particles that expand outwards, after about 10-to-the-minus-24 seconds. (That's a decimal point, 23 zeroes, and then 1.) The RHIC's detectors measure the path and properties of the particles produced in these collisions. (That's a lot of "P"s!)
After hearing the introductory talk, we headed over to the PHENIX detector to meet with Jason and physicist Achim Franz. Dr. Franz explained that both PHENIX and STAR study the RHIC's particle collisions, but they monitor different products of those collisions. PHENIX is built to detect electrons, muons and photons produced by collisions, while STAR detects kaons, pions, and protons. The detector hardware was immense--40 feet of complicated machinery that towered over the heads of all of the visitors.
Surprisingly, a very important part of the particle detection at PHENIX is simple-sounding system of gas and wires--when the particles hit atoms of the gas, they ionize them, giving off a signal that the wires detect and send along to the rest of the system. It is important to know the exact path and direction of the particles produced by collisions. Electromagnets help determine a particle's speed (slower-moving particles will bend more than fast ones) and charge (negative particles will curve one way, positive the other). All of this data--location, direction, speed, charge--helps determine the nature and type of the particles produced in collisions.
Muons, PHENIX's specialty, are tricky little particles known for their ability to travel through a lot of material before finally stopping. They aren't quite as ghostly as the neutrinos from the sun that pass straight through the Earth without a second thought, but the muons created by RHIC collisions travel can through large slabs of steel around the beam to finally leave their marks on detectors meters away. To avoid false alarms by muons from the sun, physicists looking for neutrinos have to set up their experiments deep underground in mineshafts.
The data gathered is compared to computer models of collisions created according to current understanding of physics to test the validity of these models. One of the early surprises in comparing the observations and models was that as quark-gluon plasma disappears, it acts more like a liquid than a gas.
While the RHIC is no longer the most powerful particle collider in the world, it does have a special claim to fame--flexibility. While most RHIC collisions use gold ions, ions of other elements like copper, uranium, and carbon, can also be substituted in, as well as protons unattached to a nucleus. (Better understanding of protons, Dr. Franz added, has the potential to help improve MRI scanning.) This lets scientists at the RHIC not only study gold-gold collisions, but collisions between particles of any of these types, or combinations thereof--what do you get when you mix gold and carbon? Or copper and protons? At the RHIC, they can find out!
Dr. Franz took us to the PHENIX control room, where a bevy of computer screens were set up to monitor data from collisions and the status of the various pieces of hardware used in the experiment. There's a lot of data to record--the equivalent of a full CD every second, and one and a half million gigabytes of data were produced over the course of last year's operations. The RHIC wasn't running at the time, though--their last collision had been in June. It may sound surprising, but the RHIC typically stops collisions no later than July 1st and restarts in the fall because Brookhaven Lab is connected to the main Long Island power grid, which is most heavily used during the summer because everyone is using their air conditioning. However, this downtime is still important--the RHIC is a very complicated machine and requires several months of examination and maintenance anyway.
Detecting quark-gluon plasma and measuring its super-high temperature for the first time was definitely the most exciting part of Dr. Franz's time working at the RHIC, he told us. He had previously worked at CERN on a smaller collider where the scientists had created what they had believed to be quark-gluon plasma, but the proof hadn't been as clear.
After PHENIX, it was time to head to STAR, the RHIC's other operational detector--two others, PHOBOS and BRAHMS, were still marked on the maps visible on the walls in the building, but had finished their work years before. Our guide at STAR was Paul Sorensen, who had worked on RHIC for twelve years--he'd joined the team as a graduate student just months after the accelerator was first turned on. STAR creates "pictures" of all of the particles that come out of a collision that resemble a human iris. (The PHENIX tracks look more like a butterfly or two wedges connected at their thin ends, because the detectors are set up differently.)
Tens or hundreds of thousands of collisions occur every second when the beam is on, and PHENIX can detect 5 or 6 thousand collisions per second. STAR doesn't detect as many collisions, but it can gather more data on the ones it does detect. These different capabilities let the two detectors complement each other, and the teams check each others' work--creating an atmosphere Sorensen described as serious but friendly competition similar to a chess game. Even if it can be embarrassing to have the other team find your group has made a mistake, it's better for our understanding of physics in the long run.
Dr. Sorensen said the most exciting part of his time at the RHIC had been his early days on the project, when the team was just beginning to realize that they had indeed detected quark-gluon plasma. If this was really what they thought it was, they'd made a huge step towards understanding the very beginning of the Universe, how it got to where it is today, what underlying properties all matter in it possesses, and maybe even what might happen to it in the future. And this was how they would find out. He'd spent all of his time analyzing the data, working 80 hours a week, feeling disappointed when he had to stop to use the bathroom or eat. "We're scientists, we have to get to the truth. Nature will tell us what's right, and we are basically subservient to nature. What nature says, goes."
As much as the atmosphere in the field of particle physics was one of competition, it was also one of collaboration. The RHIC and the European Large Hadron Collider (LHC) are the only operational particle colliders of their kind in the world, and scientists travel from all over to be part of the research there. Many people working at the RHIC, like Dr. Franz, had previously worked at CERN, and many people from Brookhaven were in Geneva working on the LHC. Institutions from 15 countries were participating in the operation of PHENIX and 12 of STAR. Dr. Sorensen had made friends from many countries who he looked forward to seeing at international conferences--at his first conference in Germany, his team had presented those hard-won findings about the quark-gluon plasma and then celebrated with drinks at a Brazilian bar with their international colleagues. At the next conference, they'd gone to Brazil, and found themselves celebrating with the exact same people--in a German bar!
In addition to Germany and Brazil, Dr. Sorensen's RHIC work had also taken him to South Africa and China. "That's one of the great things about these international collaborations--it draws people from all over the world who are interested in studying physics, it brings together people from all different backgrounds, and you get to learn about people from different cultures, you really get to learn a lot about the world and its different people. Some good things, some bad things, but we all work towards the same goal, which is not really true in the larger world all of the time." He said.
After the detectors, we finally got to see the RHIC tunnel itself, where the beam rings are contained in the large segmented pinkish-beige tube that filled the center of the tunnel. The segments were straight, but arranged at small angles to produce a curve. The tunnel didn't look very much different from the NSLS tunnel, except that the larger size of the RHIC ring meant that the area we were in seemed to hardly be curved at all. We knew the tunnel was a circle, but it was so large that the part we were in seemed nearly straight. The tunnel runs underground with small monitoring stations and access ports around its circumference sticking out of the long grass. Being underground means the area above and inside the ring can grow wild, like the forest we'd driven through on the way there--imagine, deer grazing a few meters above ions speeding around at near-lightspeed!
Accelerator physicist Guillaume Robert-Demolaize, another CERN alum, showed us around the tunnel. He explained that most of the electricity used at the RHIC is for cooling, just because the equipment gets so hot. While I'd been impressed by the tricks done with liquid nitrogen at the NSLS II demonstration, the RHIC uses even-colder liquid helium--50 tons of it per run, or, as Dr. Robert-Demolaize explained, enough to fill all the balloons in 400 years of Macy's parades!
Because of that cooling, even though people weren't supposed to be in the tunnel when the beam was running, if someone was inside and touched the outside of the tube, it would feel room-temperature. I did touch the tube, and take a picture of myself there in the tunnel, just so I could remind myself I'd been there. Of course I was really there, but it still felt somehow unreal--the tunnel and the beam tube and the detectors I'd seen all looked like the photos on science sites I'd seen of scientists or reporters who'd taken trips to the LHC or to Fermilab and their now-decommissioned Tevatron. But this was only an hour's drive from my home, under the familiar pine barrens.
As we headed back above ground and to the parking lot, I sprinted up a little hill to pose for another photo with the sign outside the main RHIC building. From the level of the road, you could see that building and its parking lot, and the STAR and PHENIX buildings further down the road, with big tanks to hold liquid helium nearby. Overhead, the sky was mostly clear, but some storm clouds were blowing in from the sea. I couldn't see the underground beam tunnel that connected the buildings, but I knew it was there.
I thought of something I'd read about another particle accelerator, a speech in defense of funding that a scientist had given before Congress during Fermilab's early construction in 1969.
"Is there anything connected in the hopes of this accelerator that in any way involves the security of the country?" The questioning senator had asked.
"It only has to do with the respect with which we regard one another, the dignity of men, our love of culture. It has to do with those things ... Are we good painters, good sculptors, great poets? I mean all the things that we really venerate and honor in our country and are patriotic about." Physicist Robert Wilson had replied, "In that sense, this new knowledge has all to do with honor and country, but it has nothing to do directly with defending our country except to help make it worth defending."