The second blow to symmetry preservation arrived in 1964, when Val Fitch and Jim Cronin discovered a violation of CP-symmetry in the decays of neutral K mesons (which are quark-antiquark combinations involving a strange quark) into pi mesons. This is equivalent to finding a preferred time direction in the microscopic world. The movie of a K meson decay process would have an observable change in if it were running backwards instead of forward. Recent studies of processes involving B mesons (quark-antiquark combinations involving a bottom quark) have shown similar CP-symmetry violations.
The CP violations that have been observed in these systems are, however, too weak to explain matter dominance. While hinting at a preference for matter over antimatter, they are not strong enough to have produced the part per billion dominance of matter over antimatter in the early universe. The nature of the forces that produced that matter dominance remains as one of the major unsolved mysteries of physics.
* * * *
Fortunately, we now have a way of re-creating the conditions of the early universe in the laboratory, using the Relativistic Heavy Ion Collider (RHIC) facility at Brookhaven National Laboratory. The STAR detector is one of the two major detectors at RHIC. Since its inception in the early 1990s I have been a member of the STAR Collaboration, the group that built and operates the detector. STAR is a large time-projection chamber detector placed inside a 0.5 tesla magnetic solenoid located at the six o'clock position in the RHIC collider ring.
The RHIC facility brings gold (and lighter) nuclei into collision at energies of up to 200 GeV per nucleon, producing a relativistic fireball that replicates conditions in the early universe at about one microsecond after the Big Bang. The temperatures reached in RHIC collisions are several trillion degrees Celsius, about 250,000 times hotter than the central temperature of our Sun. At such temperatures, a strongly-interacting phase of nuclear matter, a quark-gluon plasma, is expected. Further, the highly charged nuclei passing each other in RHIC collisions with a slight offset can produce extremely intense magnetic fields that can reach strengths of up to about 1015 tesla. These conditions make it possible to look for possible symmetry breaking in strong interactions operating in collisions in this new and unprecedented environment.
A new analysis of STAR data may provide a needed clue into the mysteries of fundamental symmetries and their breaking in the early universe. There are experimental and theoretical reasons for expecting that any “global” or overall breaking of P-symmetry in strong interactions should be extremely small, less than one part on 1010, at all energies. However, several theorists have suggested that in small regions of space-time in dense systems at high temperatures, the fields produced by gluons can create “local” violations of the P, PC, and T symmetries. The theory suggests that in these localized regions, particles of the same electric charge should be preferentially emitted in the direction of the local magnetic field and either parallel or anti-parallel to it, thereby producing a symmetry violation.
STAR has studied collisions between gold nuclei and between copper nuclei at collision energies of 200 GeV per nucleon. At this collision energy, the two nuclei are heading toward each other at 99.9957% of the speed of light or only 4.32 parts in 100,000 below light speed. Not all such collisions are head-on, but one can distinguish the offset or “centrality” of the colliding systems by counting the number of neutrons that were non-participants and went straight ahead after the collision. In this way, the collisions can be broken up into eight centrality groups ranging from head-on collisions to near misses. In offset collisions there is a tendency for there to be more particles produced in the “reaction plane,” which includes the beam and the collision offset, than in the direction perpendicular to it. Since thousands of particles are produced in a typical RHIC collision, finding the preferred emission plane gives a good estimate of the reaction plane of each collision, and each particle can be characterized in terms of the angle perpendicular to the beam that it makes with the reaction plane.
Because collision events have randomly oriented reaction planes and magnetic field directions, most of the potentially observable effects of a hypothetical local parity violation are averaged out. However, the STAR Collaboration has looked for an event-by-event signal in the form of two-particle correlations between the particle emission angles with respect to the reaction plane of particles of the same sign of electric charge. To eliminate issues of how accurately the reaction plane was determined, they have moved to three-particle correlations that replace the reaction plane angle with the emission angle of all the other particles observed in the collision.
The results show an unambiguous correlation in the emission of pairs of particles of the same electric charge. There is no similar correlation between pairs of particles with opposite electric charge. The collisions studied prefer to emit same-charge particles in the same direction, which is a strong indication of a local violation of P-symmetry or parity. The effect is present in both gold-gold and copper-copper collisions but stronger in the latter, and it is strongest when the collision offset is about half a nuclear diameter. Theoretical collision calculations that do not include any expectation of local parity violations predict only weak correlations having the opposite sign from those observed, and predict no difference in the correlations of same-charge and opposite charge particle pairs. Thus, there is good evidence that local parity violations occur in RHIC collisions.
As mentioned above, the theory that stimulated the STAR investigation of parity violations also suggested that there should be local violations of CP symmetry created by the high-temperature gluon fields in the environment of RHIC collisions and in the conditions of the early universe. Can this be the missing key to understanding the dominance of matter over antimatter in our universe?
Perhaps. The sign of the possible local CP violations at STAR appears to be in the wrong direction and cannot, if taken at face value, explain the matter-dominance of the universe. However, there are many questions raised by the initial observation that remain to be answered, and these should provide new insights into how such local symmetry violations occur, and into their implications for the universe as a whole. It is expected that the STAR results will checked by other experiments, will be extended to lower energies at RHIC and to higher energies at the LHC, and will trigger more theoretical activity on the issues of local symmetry breaking.
We may be on the verge of answering one of the major questions about the nature of our universe: why is there more matter than antimatter? Watch this column for further results.
Copyright © 2010 John G. Cramer
* * * *
AV Columns Online: Electronic reprints of over 150 “The Alternate View” columns by John G. Cramer, previously published in Analog, are available online at: www.npl. washington.edu/av.
* * * *
STAR Parity-Violation Results: R. I. Abelev, et al, “Observation of charge-dependent azimuthal correlations and possible strong parity violations in heavy ion collisions,” arXiv preprint 0909.1717v1 [nucl-ex]. (See also www.bnl.gov/rhic/)
Theory of Local Symmetry breaking:
D. E. Kharzeev “Parity violation in hot QCD: why it can happen, and how to look for it,” Physics Letters B633, 260-264 (2006), arXiv preprint 0406125 [hep-ph].
D. E. Kharzeev, L. D. McLerran, and H. J. Warringa, “The effects of topological charge change in heavy ion collisions: ‘Event by event P and CP violation',” Nucl.Phys. A803, 227-253 (2008), arXiv preprint 0711.0950 [hep-ph].
[Back to Table of Contents]
* * *
Novella: BUG TRAP
by Stephen L. Burns
There are standard protocols for job-hunting, but things don't always work that way. . . .
Reflections from neon and LEDon lights washed across the rain-soaked night streets like smears of wet paint. They looked like they might be scribing out encrypted messages in obscure calligraphies, useful information there for the deciphering. Maybe even directions out of my present difficulties.
I knew this part of the city pretty well, most of the secret places and hidden sanctuaries. But so did those who were on my ass and after my head. The NYPD had exerted varying degrees of control over this patch of turf since the days of horse-drawn paddy wagons, and their badge-bearing minions knew it the way a hunter knows the patch of woods just outside his back door. The Chrome Lords lacked the law's sweeping history, but easily matched the cops in street-nav, numbers of troops, and weapons. Two sides, polar opposites, closing in with the same objective: to find and crush what was trapped between them.
That would be me: Giorgio Lennon Phale. Posto handle: Glyph. Age: twenty-seven. Employment record: spotty. Legal history: problematic. Prospects: not to be envied.
Does the anvil cooperate with the hammer?
That was a question worth a wordup in any number of places, but I didn't have time to put it out. My career as a posto would have to stay on hold until the time—if I lived to see it—that I wasn't caught between the hammer of the Chrome Lords and the anvil of the police.
As a posto I'm an enthusiastic malcontent who mixes street art, graffiti, sloganeering, muckraking, ad-jacking, and the politics of outrage as a vocation. In other words, a dedicated semi-pro troublemaker. I'd made myself a whole pile of it this time. My mentor, old Slippery Jone, Mistress of the Subversive Koan, always said that if they're not trying to find you to buy you off or work you over, then you're not trying hard enough. Pride points for success, except that I'd managed to piss off both sides of an issue badly enough that both wanted me bagged and slabbed.
If this was success, then receding back into relative obscurity was beginning to have a nice ring to it.
I was crouched low, peering around the corner of a building and down a cross street, wishing I had Deacon Recon out and scouting for me. A spotter of his caliber might have helped make surviving the night undamaged something more than a vaguely theoretical possibility. But the cops had twanged and tanked my phone, so calls for help—other than pointless screaming—were not an option.
I'd crammed myself into a lovely bit of shadow. Being brownish of skin and inclined toward nightside sartorial style helped me blend in instead of standing out like an albino dressed in sequins, and being not particularly tall or wide meant I made a smaller target.
Around the corner, half a block ahead, two street beasts styled up in enough studded leather to wrap a cab stood picket, gleaming chromed clubs in hard, tattooed fists. The idle palm-slap of metal against flesh was intimidating in its suggestion of ready violence, but actually kind of helpful in the way it broadcast their location.
I dug into one particular pocket of the vest under my soggy coat. A familiar, sweetly illegal shape filled my hand: my dummystick. I pulled it out and found the controls I wanted by touch alone. Once it was set, I pointed it around the corner and fingered the trigger.
An invisible beam of sonic and electromagnetic waves leapt out to tickle and override the spielbox in front of a used clothing store. Instead of calling out to past and potential customers passing by, the dummied spielbox blared out a purposefully snotty cry of, "Hey! Copsucker!"
The shaven heads of the streetbeasts rotated like turrets, tracking the jibe. I swung the dummystick toward another storefront, prodding that one's spielbox to blare, "Over here, copsucker!" Shrill, mocking laughter followed that taunt.
A diversion is a terrible thing to waste. I was already on the move, the sound of my sneakers splashing through the puddles masked by the dummied store. I was halfway across the street and thinking I was going to make it when an NYPD street spook suddenly materialized from a dark doorway. The cop's form seemed to shimmer into existence as his—no, check that—her bulletproof nanocamo changed into uniform blue. It was when her hood went transparent, revealing an unsmiling woman with black skin and spiked yellow hair, that I nailed down her gender, and recognized her as the same cop who'd already popped up twice before on the edge of my search for safety.
Her regulation stunwand was pointed in my direction. That wand is related to my dummystick the same way a Glock is related to a Nerf pistol; mine could tickle, hers could deliver a knockout punch that would leave me pants-peed and drooling.
I jinked left and low, aware of a third element entering the equation: a delivery truck rumbling up the street toward me, and maybe offering a ticket out of my situational roach motel.
The copette let out a cry of "Halt!" in a voice cranked up to ear-bleed level by her comm unit. The official rule was warn first, shoot second, and what a jackpot, this finestette was actually following it.
Halting was the least appetizing option in a gutter-sludge assortment. The order to halt caught the attention of the Chrome Lords. Shaved heads turned. Dull eyes fixed on me, brightening at the sight of prey. They started toward me, the steel cleats of their boots clacking on the wet asphalt.
They didn't seem aware of the cop, probably because their small, drug-addled reptile brains were unable to process more than one input at a time. But I saw the cop take notice of them, forcing her to split her attention.
The truck was almost on top of me then, a long blast of its horn proclaiming the driver's warning that there would be no slowing or swerving for anything, least of all some scraggle-ass human speed bump. Not with cargojacking a very popular career path in the big bad city.
I stepped back like an experienced taxiodor, the blunt steel bumper of the truck bulling through the space I'd occupied just a second before. Then, calling on my inner ninja monkey, planted my feet and leapt, grabbing hold of the side of the truck body.
Although not going that fast, it was still trucking along at a sufficient clip to make it all I could do to hang on. But desperation can be an almost magical magnetic force, and I kept my ride.
The truck left the cop behind and swept past the two Chrome Lords. I loosened one hand long enough to give them a proper one-fingered wave good-bye.
My feeling of triumph proved to have the lifespan of a single crystal flake in a hot crack pipe. The truck's horn let out an angry blat. I looked forward, meeting the driver's gaze in the rear-view mirror.
The driver showed me a dough-faced, stubble-jowled scowl, making a motion that was easily enough translated: Get the fuck offa my truck!
I beamed him my most winning smile, loosening a hand to hold up five fingers, the biggest number I could manage. Five miles. Five minutes. Five blocks. Five fill in the blanks, that's all I ask.
For just a moment it seemed like my winning ways and obvious charm had won out. The man did smile.
The bad news was his smile was a prelude to reaching for the big red gitback button on the truck's dash.
I'd spent enough teenage time boardhiking to know what the gitback was for and what it would do. The driver held his hand poised over it, grin widening crazily.
Please don't, I begged, shaking my head.
The hand inched closer, and when it was just the thickness of a buck soyburger—sans bun—over the button, I knew I was going to have to jump.
I made the sad puppy eyes. Couldn't you at least slow down a bit? I tried to beam the message to the driver, a simple, heartfelt plea for a watered-down act of kindness.
The biodiesel engine snorted and roared as the driver laughed and floored it.
Options gone, I pushed off, turning around and bracing for impact, eyes sweeping across the blurry asphalt like I might be able to locate a chunk that happened to be soft as a mattress. As I jumped, the driver, out of sheer dickness, whacked the gitback. Crackling snakes of static electricity discharged all across the outside of the truck, a few questing heads managing to bite me in the ass.
I hit hard, but better than I could have ever hoped, worn sneakers skidding across the wet and oily blacktop like skis on fresh-packed powder, the sort of slick bit you'd only ever see in an old Jackie Chan chopp'emup.
I laughed out loud as
I slid to a stop, feeling like a total action hero, the couple of burnt spots on my butt hardly counting in the cosmic order of how badly such a dismount could have gone. I'd gained almost three blocks thanks to the hitch, leaving the two stomp-booted Chrome Lords way behind. The yellow-haired cop in the spook suit was probably still somewhere back behind them, blocked from pursuit by five hundred pounds of slow, mean meat.
My happy dance got knee-capped when three more members of the gang boiled out of an alley half a block away. As the truck sound lessened I realized I was hearing sirens coming from what sounded like every direction.
I took a deep breath and took off.
* * * *
Sometimes life is like an arcade game where you get just one token, and if you lose, you die.
That would make a great wordup, but I was beginning to think my days of stepping on power toes as a posto had reached toe tag city. There were Chrome Lords everywhere, and where they weren't, the gaps were plugged with cops. That yellow-haired spook-suited finestette seemed to be everywhere, blocking every move I made.
If the gang got me I'd be stomped so badly I'd fit in a pizza box with room left over for extra toppings. If the cops got me I'd be looking at a probable resisting-arrest beating, a likely holding cell rendezvous with the sort of cell troll who would regard his tender new roomie as a tasty bedtime snack, and a guaranteed verdict of being guilty of something. The longer I eluded my pursuers the more I was torquing them off, and at this point surrender was some flavor of suicide.
My bag of tricks and options was empty. My utterly unplanned pinball through the back streets had brought me to the edge of a Bug Trap zone, and that trap was beginning to look like my only available escape route.
Analog SFF, July-August 2010 Page 17