Relativistic Heavy Ion Collider

Coordinates: 40°53′2″N 72°52′33″W

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Relativistic Heavy Ion Collider (RHIC)

The Relativistic Heavy Ion Collider at Brookhaven National Laboratory.
General properties
Accelerator type	synchrotron
Beam type	polarized p to U ion
Target type	collider
Beam properties
Maximum energy	255 GeV per beam (p), 100 GeV/nucleon per beam (Au ions)
Maximum luminosity	2.45×1032/(cm2⋅s) (p+p),  1.55×1028/(cm2⋅s) (Au+Au)
Physical properties
Circumference	3834 m
Location	Upton, New York
Coordinates	40°53′2″N 72°52′33″W
Institution	Brookhaven National Laboratory
Dates of operation	2000 - present

The Relativistic Heavy Ion Collider (RHIC /ˈrɪk/) is the first and one of only two operating heavy-ion colliders, and the only spin-polarized proton collider ever built. Located at Brookhaven National Laboratory (BNL) in Upton, New York, and used by an international team of researchers, it is the only operating particle collider in the US.^[1][2][3] By using RHIC to collide ions traveling at relativistic speeds, physicists study the primordial form of matter that existed in the universe shortly after the Big Bang.^[4][5] By colliding spin-polarized protons, the spin structure of the proton is explored.

RHIC is as of 2019 the second-highest-energy heavy-ion collider in the world, with nucleon energies for collisions reaching 100 GeV for gold ions and 250 GeV for protons.^[6] As of November 7, 2010, the Large Hadron Collider (LHC) has collided heavy ions of lead at higher energies than RHIC.^[7] The LHC operating time for ions (lead–lead and lead–proton collisions) is limited to about one month per year.

In 2010, RHIC physicists published results of temperature measurements from earlier experiments which concluded that temperatures in excess of 345 MeV (4 terakelvin or 7 trillion degrees Fahrenheit) had been achieved in gold ion collisions, and that these collision temperatures resulted in the breakdown of "normal matter" and the creation of a liquid-like quark–gluon plasma.^[8]

In January 2020, the US Department of Energy Office of Science selected the eRHIC design for the future Electron–Ion collider (EIC), building on the existing RHIC facility at BNL.

The accelerator

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RHIC is an intersecting storage ring particle accelerator. Two independent rings (arbitrarily denoted as "Blue" and "Yellow") circulate heavy ions and/or polarized protons in opposite directions and allow a virtually free choice of colliding positively charged particles (the eRHIC upgrade will allow collisions between positively and negatively charged particles). The RHIC double storage ring is hexagonally shaped and has a circumference of  3834 m, with curved edges in which stored particles are deflected and focused by 1,740 superconducting magnets using niobium-titanium conductors. The dipole magnets operate at  3.45 T.^[9] The six interaction points (between the particles circulating in the two rings) are in the middle of the six relatively straight sections, where the two rings cross, allowing the particles to collide. The interaction points are enumerated by clock positions, with the injection near 6 o'clock. Two large experiments, STAR and sPHENIX, are located at 6 and 8 o'clock respectively. The sPHENIX experiment is the newest experiment to be built at RHIC, replacing PHENIX at the 8 o'clock position.^[10]

A particle passes through several stages of boosters before it reaches the RHIC storage ring. The first stage for ions is the electron beam ion source (EBIS), while for protons, the  200 MeV linear accelerator (Linac) is used. As an example, gold nuclei leaving the EBIS have a kinetic energy of  2 MeV per nucleon and have an electric charge Q = +32 (32 of 79 electrons stripped from the gold atom). The particles are then accelerated by the Booster synchrotron to 100 MeV per nucleon, which injects the projectile now with Q = +77 into the Alternating Gradient Synchrotron (AGS), before they finally reach 8.86 GeV per nucleon and are injected in a Q = +79 state (no electrons left) into the RHIC storage ring over the AGS-to-RHIC Transfer Line (AtR).

To date the types of particle combinations explored at RHIC are p + p, p + Al, p + Au, d + Au, h + Au, Cu + Cu, Cu + Au, Zr + Zr, Ru + Ru, Au + Au and U + U. The projectiles typically travel at a speed of 99.995% of the speed of light. For Au + Au collisions, the center-of-mass energy is typically 200 GeV per nucleon-pair, and was as low as 7.7 GeV per nucleon-pair. An average luminosity of 2×10²⁶ cm⁻²⋅s⁻¹ was targeted during the planning. The current average Au + Au luminosity of the collider has reached 87×10²⁶ cm⁻²⋅s⁻¹, 44 times the design value.^[11] The heavy ion luminosity is substantially increased through stochastic cooling.^[12]

One unique characteristic of RHIC is its capability to collide polarized protons. RHIC holds the record of highest energy polarized proton beams. Polarized protons are injected into RHIC and preserve this state throughout the energy ramp. This is a difficult task that is accomplished with the aid of corkscrew magnetics called 'Siberian snakes' (in RHIC a chain 4 helical dipole magnets). The corkscrew induces the magnetic field to spiral along the direction of the beam ^[13] Run-9 achieved center-of-mass energy of 500 GeV on 12 February 2009.^[14] In Run-13 the average p + p luminosity of the collider reached 160×10³⁰ cm⁻²⋅s⁻¹, with a time and intensity averaged polarization of 52%.^[11]

AC dipoles have been used in non-linear machine diagnostics for the first time in RHIC.^[15]

• Accelerator components
• 
  The 25 MW Helium refrigeration system that cools the superconducting magnets down to the operating temperature of 4.5 K^[16]
 
• 
  An arc dipole magnet. Electrical bus slots (top and bottom) and beam tube (middle) at the top section of the vacuum shell^[17]
 
• 
  Curvature of beam tube seen through the ends of an arc dipole magnet
 
• 
  Two main accelerator rings inside the RHIC tunnel
 
• 
  STAR detector
 
• 
  A Forward Silicon Vertex Detector (FVTX) sensor of PHENIX detector on a microscope^[18]

The experiments

[edit]

A view of gold ions collisions as captured by the STAR detector.

There are two detectors currently operating at RHIC: STAR (6 o'clock, and near the AGS-to-RHIC Transfer Line) and sPHENIX (8 o'clock), the successor to PHENIX. PHOBOS (10 o'clock) completed its operation in 2005, and BRAHMS (2 o'clock) in 2006.

Among the two larger detectors, STAR is aimed at the detection of hadrons with its system of time projection chambers covering a large solid angle and in a conventionally generated solenoidal magnetic field, while PHENIX is further specialized in detecting rare and electromagnetic particles, using a partial coverage detector system in a superconductively generated axial magnetic field. The smaller detectors have larger pseudorapidity coverage, PHOBOS has the largest pseudorapidity coverage of all detectors, and tailored for bulk particle multiplicity measurement, while BRAHMS is designed for momentum spectroscopy, in order to study the so-called "small-x" and saturation physics. There is an additional experiment, PP2PP (now part of STAR), investigating spin dependence in p + p scattering.^[19]

The spokespersons for each of the experiments are:

• STAR: Frank Geurts (Rice University) and Lijuan Ruan (Brookhaven National Laboratory)
• PHENIX: Yasuyuki Akiba (Riken)
• sPHENIX: Gunter Roland (MIT) and David Morrison (Brookhaven National Laboratory)

For the experimental objective of creating and studying the quark–gluon plasma, RHIC has the unique ability to provide baseline measurements for itself. This consists of both the lower energy and also lower mass number projectile combinations that do not result in the density of 200 GeV Au + Au collisions, like the p + p and d + Au collisions of the earlier runs, and also Cu + Cu collisions in Run-5.

Using this approach, important results of the measurement of the hot QCD matter created at RHIC are:^[20]

• Collective anisotropy, or elliptic flow. The major part of the particles with lower momenta is emitted following an angular distribution ��/��∝1+2�2(�T)cos⁡2� (p_T is the transverse momentum, � angle with the reaction plane). This is a direct result of the elliptic shape of the nucleus overlap region during the collision and hydrodynamical property of the matter created.
• Jet quenching. In the heavy ion collision event, scattering with a high transverse p_T can serve as a probe for the hot QCD matter, as it loses its energy while traveling through the medium. Experimentally, the quantity R_AA (A is the mass number) being the quotient of observed jet yield in A + A collisions and N_bin × yield in p + p collisions shows a strong damping with increasing A, which is an indication of the new properties of the hot QCD matter created.
• Color glass condensate saturation. The Balitsky–Fadin–Kuraev–Lipatov (BFKL) dynamics^[21] which are the result of a resummation of large logarithmic terms ln(1/x) for deep inelastic scattering with small Bjorken-x, saturate at a unitarity limit ��2∝⟨�part⟩/2, with N_part/2 being the number of participant nucleons in a collision (as opposed to the number of binary collisions). The observed charged multiplicity follows the expected dependency of �ch/�∝1/��(��2), supporting the predictions of the color glass condensate model. For a detailed discussion, see e.g. Dmitri Kharzeev et al.;^[22] for an overview of color glass condensates, see e.g. Iancu & Venugopalan.^[23]
• Particle ratios. The particle ratios predicted by statistical models allow the calculation of parameters such as the temperature at chemical freeze-out T_ch and hadron chemical potential ��. The experimental value T_ch varies a bit with the model used, with most authors giving a value of 160 MeV < T_ch < 180 MeV, which is very close to the expected QCD phase transition value of approximately 170 MeV obtained by lattice QCD calculations (see e.g. Karsch^[24]).

While in the first years, theorists were eager to claim that RHIC has discovered the quark–gluon plasma (e.g. Gyulassy & McLarren^[25]), the experimental groups were more careful not to jump to conclusions, citing various variables still in need of further measurement.^[26] The present results shows that the matter created is a fluid with a viscosity near the quantum limit, but is unlike a weakly interacting plasma (a widespread yet not quantitatively unfounded belief on how quark–gluon plasma looks).

A recent overview of the physics result is provided by the RHIC Experimental Evaluations 2004 Archived 2017-02-02 at the Wayback Machine, a community-wide effort of RHIC experiments to evaluate the current data in the context of implication for formation of a new state of matter.^{[27][28][29][30]} These results are from the first three years of data collection at RHIC.

New results were published in Physical Review Letters on February 16, 2010, stating the discovery of the first hints of symmetry transformations, and that the observations may suggest that bubbles formed in the aftermath of the collisions created in the RHIC may break parity symmetry, which normally characterizes interactions between quarks and gluons.^[31][32]

The RHIC physicists announced new temperature measurements for these experiments of up to 4 trillion kelvins, the highest temperature ever achieved in a laboratory.^[33] It is described as a recreation of the conditions that existed during the birth of the Universe.^[34]

In late 2012, the Nuclear Science Advisory Committee (NSAC) was asked to advise the Department of Energy's Office of Science and the National Science Foundation how to implement the nuclear science long range plan written in 2007, if future nuclear science budgets continue to provide no growth over the next four years. In a narrowly decided vote, the NSAC committee showed a slight preference, based on non-science related considerations,^[35] for shutting down RHIC rather than canceling the construction of the Facility for Rare Isotope Beams (FRIB).^[36]

By October 2015, the budget situation had improved, and RHIC continued operations into the next decade.^[37]

RHIC began operation in 2000 and until November 2010 was the highest-energy heavy-ion collider in the world. The Large Hadron Collider (LHC) of CERN, while used mainly for colliding protons, operates with heavy ions for about one month per year. The LHC has operated with 25 times higher energies per nucleon. As of 2018, RHIC and the LHC are the only operating hadron colliders in the world.

Due to the longer operating time per year, a greater number of colliding ion species and collision energies can be studied at RHIC. In addition and unlike the LHC, RHIC is also able to accelerate spin polarized protons, which would leave RHIC as the world's highest energy accelerator for studying spin-polarized proton structure.

A major upgrade is the Electron–Ion Collider (EIC), the addition of a 18 GeV high intensity electron beam facility, allowing electron–ion collisions. At least one new detector will have to be built to study the collisions. A review was published by Abhay Deshpande et al. in 2005.^[38] A more recent description is at:^[39]

On January 9, 2020, It was announced by Paul Dabbar, undersecretary of the US Department of Energy Office of Science, that the BNL eRHIC design has been selected for the future electron–ion collider (EIC) in the United States. In addition to the site selection, it was announced that the BNL EIC had acquired CD-0 (mission need) from the Department of Energy.^[40]

Wikinews has related news:

• Possible black hole created in US

Before RHIC started operation, critics postulated that the extremely high energy could produce catastrophic scenarios,^[41] such as creating a black hole, a transition into a different quantum mechanical vacuum (see false vacuum), or the creation of strange matter that is more stable than ordinary matter. These hypotheses are complex, but many predict that the Earth would be destroyed in a time frame from seconds to millennia, depending on the theory considered. However, the fact that objects of the Solar System (e.g., the Moon) have been bombarded with cosmic particles of significantly higher energies than that of RHIC and other man-made colliders for billions of years, without any harm to the Solar System, were among the most striking arguments that these hypotheses were unfounded.^[42]

Wikinews has related news:

• Fireball generated in U.S. laboratory resembles black hole

The other main controversial issue was a demand by critics ^{[citation needed]} for physicists to reasonably exclude the probability for such a catastrophic scenario. Physicists are unable to demonstrate experimental and astrophysical constraints of zero probability of catastrophic events, nor that tomorrow Earth will be struck with a "doomsday" cosmic ray (they can only calculate an upper limit for the likelihood). The result would be the same destructive scenarios described above, although obviously not caused by humans. According to this argument of upper limits, RHIC would still modify the chance for the Earth's survival by an infinitesimal amount.

Concerns were raised in connection with the RHIC particle accelerator, both in the media^[43][44] and in the popular science media.^[45] The risk of a doomsday scenario was indicated by Martin Rees, with respect to the RHIC, as being at least a 1 in 50,000,000 chance.^[46] With regards to the production of strangelets, Frank Close, professor of physics at the University of Oxford, indicates that "the chance of this happening is like you winning the major prize on the lottery 3 weeks in succession; the problem is that people believe it is possible to win the lottery 3 weeks in succession."^[44] After detailed studies, scientists reached such conclusions as "beyond reasonable doubt, heavy-ion experiments at RHIC will not endanger our planet"^[47] and that there is "powerful empirical evidence against the possibility of dangerous strangelet production".^[42]

The debate started in 1999 with an exchange of letters in Scientific American between Walter L. Wagner and F. Wilczek,^[48] in response to a previous article by M. Mukerjee.^[49] The media attention unfolded with an article in UK Sunday Times of July 18, 1999, by J. Leake,^[50] closely followed by articles in the U.S. media.^[51] The controversy mostly ended with the report of a committee convened by the director of Brookhaven National Laboratory, J. H. Marburger, ostensibly ruling out the catastrophic scenarios depicted.^[42] However, the report left open the possibility that relativistic cosmic ray impact products might behave differently while transiting earth compared to "at rest" RHIC products; and the possibility that the qualitative difference between high-E proton collisions with earth or the moon might be different than gold on gold collisions at the RHIC. Wagner tried subsequently to stop full-energy collision at RHIC by filing Federal lawsuits in San Francisco and New York, but without success.^[52] The New York suit was dismissed on the technicality that the San Francisco suit was the preferred forum. The San Francisco suit was dismissed, but with leave to refile if additional information was developed and presented to the court.^[53]

On March 17, 2005, the BBC published an article implying that researcher Horaţiu Năstase believes black holes have been created at RHIC.^[54] However, the original papers of H. Năstase^[55] and the New Scientist article^[56] cited by the BBC state that the correspondence of the hot dense QCD matter created in RHIC to a black hole is only in the sense of a correspondence of QCD scattering in Minkowski space and scattering in the AdS₅ × X₅ space in AdS/CFT; in other words, it is similar mathematically. Therefore, RHIC collisions might be described by mathematics relevant to theories of quantum gravity within AdS/CFT, but the described physical phenomena are not the same.

The RHIC project was sponsored by the United States Department of Energy, Office of Science, Office of Nuclear physics. It had a line-item budget of 616.6 million U.S. dollars.^[1]

For fiscal year 2006 the operational budget was reduced by 16.1 million U.S. dollars from the previous year, to 115.5 million U.S. dollars. Though operation under the fiscal year 2006 federal budget cut^[57][58] was uncertain, a key portion of the operational cost (13 million U.S. dollars) was contributed privately by a group close to Renaissance Technologies of East Setauket, New York.^[59][60]

• The novel Cosm (ISBN 0-380-79052-1) by the American author Gregory Benford takes place at RHIC. The science fiction setting describes the main character Alicia Butterworth, a physicist at the BRAHMS experiment, and a new universe being created in RHIC by accident, while running with uranium ions.^[61]
• The zombie apocalypse novel The Rising by the American author Brian Keene referenced the media concerns of activating the RHIC raised by the article in The Sunday Times of July 18, 1999, by J. Leake.^[50] As revealed very early in the story, side effects of the collider experiments of the RHIC (located at "Havenbrook National Laboratories") were the cause of the zombie uprising in the novel and its sequel City of the Dead.
• In the Rayloria's Memory novel series by the American author Othello Gooden Jr, beginning with Raylorian Dawn (ISBN 1466328681), it is noted that each Lunar City and their space station is powered by a RHIC.

Start-up of 22nd Run at the Relativistic Heavy Ion Collider (RHIC)

Physicists will try out innovative accelerator techniques and deliver high-energy polarized protons for explorations of protons' inner structure using new detector components at STAR

December 13, 2021

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Run 22 at the Relativistic Heavy Ion Collider (RHIC) will feature collisions of polarized protons, new data collected by upgraded components of the STAR detector, and tests of innovative accelerator techniques.

UPTON, NY—Particle smashups have begun for Run 22 at the Relativistic Heavy Ion Collider (RHIC). RHIC, a 2.4-mile-circumference particle collider at the U.S. Department of Energy’s Brookhaven National Laboratory, operates as a DOE Office of Science user facility, serving up data from particle collisions to nuclear physicists all around the world. On the menu this run: collisions between beams of polarized protons interspersed with tests of innovative accelerator techniques. During the run, RHIC’s recently upgraded STAR detector will track particles emerging from collisions at a wider range of angles than ever before.

The new data will add to earlier RHIC datasets exploring the fundamental building blocks of visible matter. In addition, the physics findings, accelerator tests, and detector technologies will play important roles in the Electron-Ion Collider (EIC)—DOE’s next planned nuclear physics facility, which will reuse key components of RHIC.

Discovering the universal properties of protons and how they emerge from the interactions of quarks and gluons, the building blocks within protons, is a central goal of both facilities. RHIC’s proton-proton collisions could reveal unprecedented details and a preview of how certain characteristics depend on the dynamic motions of the quarks and gluons.

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Brookhaven Lab physicist Elke Aschenauer, who led the STAR upgrade project, notes how the new detector components will enable measurements at RHIC that advance our understanding of nucleon structure and help to lay the foundations for future measurements at the Electron-Ion Collider.

“Our goal this run is basically doing EIC physics with proton-proton collisions,” said Brookhaven Lab physicist Elke-Caroline Aschenauer, a member of the STAR collaboration who is also involved in planning the experiments and scientific program at the EIC. “It’s important to do both [measurements at RHIC and the EIC] because you have to verify that what you measure in electron-proton collisions at the EIC and in proton-proton events at RHIC is universal—meaning it doesn’t depend on which probe you use to measure it,” she explained.

The measurements rely on RHIC’s ability to align the “spins” of protons in an upward pointing direction. This alignment, or polarization—a capability unique among colliders like RHIC—gives scientists a directional frame of reference for tracking how particles generated in the collisions move.

“We are using polarization as a vehicle to study proton structure, and particularly the 3D structure, including how the internal particles (quarks and gluons) are moving inside the proton,” Aschenauer said.

Delivering proton beams

The physicists in Brookhaven Lab’s Collider-Accelerator Department (C-AD), who steer the beams around RHIC, are determined to give STAR what it needs.

“For Run 22 we are going to focus on being as efficient as possible and racking up the collisions at the highest possible polarization,” said C-AD physicist Vincent Schoefer, this year’s run coordinator.

When we spoke with Schoefer, he was busy “waking up” equipment that hasn't been used since Run 17—the last time polarized protons were collided at RHIC. This equipment includes “helical dipole” magnets that help preserve the polarization of the protons as they make millions of turns around RHIC’s twin accelerator rings. This year’s run will take place at the highest collision energy: 500 billion electron volts (GeV) per colliding proton pair.

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C-AD physicist Haixin Huang with some of the accelerator components that keep RHIC's proton beams aligned as they make their way around the 2.4-mile-circumference tunnel (right).

The C-AD team was also preparing “polarimeters” to measure just how aligned those proton spins are.

“It doesn't matter how highly polarized your beam is if you can't measure that. So, the polarimetry is really crucial,” Schoefer said.

Accelerator physicists in C-AD and experimental physicists involved in making measurements that rely on polarized beams collaborated on the design of RHICs polarimeters.

“This work is an example of the type of collaboration between groups that has been going on since the start of RHIC,” said C-AD physicist Haixin Huang.

Pumping up polarization

Keeping proton beams tightly packed helps preserve polarization. It also maximizes the likelihood that you get collisions when the beams cross. But keeping protons close together is a challenge.

“They're all positively charged particles, so they want to repel one another,” Schoefer explained. “The more tightly you pack them, the more they resist that packing.”

The repulsion is particularly strong in the early stages of acceleration—before protons have been ramped up to full collision energy. So, this run, the C-AD team will try a technique that’s worked when RHIC accelerates larger particles but has never been used with protons before.

“We are going to split each proton bunch into two when they’re still at low energy in the Booster, and accelerate those as two separate bunches,” Schoefer said. “That splitting will alleviate some of the stress during low energy, and then we can merge the bunches back together to put very dense bunches into RHIC.”

This merging maneuver is challenging, Schoefer said, because it takes “a really long time—where a really long time is one second! For the protons, that’s 300,000 turns around the Alternating Gradient Synchrotron (AGS).” (The AGS is the link in the accelerator chain after the Booster that feeds particle beams into RHIC.) “During those 300,000 turns, we have to handle the protons very gently, so we don’t ruin the nice beams we have prepared.”

The CA-D team will also calculate very careful trajectories for the particles’ paths through the collider. This step should help counteract the tendency of the accelerator’s magnetic fields (which physicists use to steer and focus the beams) to rotate the spins of protons away from ideal alignment.

“We're going to try different trajectories and see if we can learn something about what is making this misalignment happen,” Schoefer said.

The combination of techniques is now delivering highly polarized proton beams to collide inside STAR.

STAR upgrades

When they analyze results from these collisions, STAR physicists will be looking for differences in the numbers of certain particles emerging to the left and right of the polarized protons’ upward pointing direction.

For example, they want to test whether there’s a repulsive interaction between particles with like “color” charges that’s opposite to the attractive interaction observed between unlike color-charged particles. (Color charge is the type of charge through which quarks interact.) The opposite force should produce the opposite directional preference for certain particle decay products.

STAR first saw hints of this effect in data collected in 2011, published in 2016. A preliminary analysis of additional data collected in Run 17 indicates a small effect but with large uncertainties. Run 22 will help STAR reduce those uncertainties with larger data sets.

In addition, the recently installed STAR upgrades will give physicists the ability to track particles at previously inaccessible angles toward the front and rear of the detector.

“This is the region where we expect the left-right directional preference to be larger,” Aschenauer said.

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A side view of the STAR detector with an inset showing particle tracks (left) and particle detector "hits" (right) from a collision. The top part of the inset shows the coverage with the new iTPC sectors compared to the old sectors (bottom). Notice how the new sectors record more hits per track, especially close to the beamline, as well as tracks at more forward and rearward angles (more to the left and right in the inset view).

The upgrades include an inner Time Projection Chamber (iTPC), installed in 2019, which placed many more sensors in the inner sectors of the cylindrical STAR detector, close to the colliding particles. Then, earlier this year, the STAR team installed “forward” particle-tracking components outside one end of the detector.

To picture how these upgrades increase STAR’s particle tracking range, think of STAR as a barrel lying on its side with colliding particles entering at each end. Ever since RHIC’s first collisions in 2000, STAR has tracked particles emerging perpendicular to the colliding particles’ path all around the barrel. The classic end-on views of STAR particle tracks showcase this 360-degree detection capability. But looking from the side, the original STAR detector could only track particles emerging at angles up to 45 degrees off vertical in either the forward or rearward direction.

The upgrades “open wider the cone where the particles can go and be detected,” said Zhenyu Ye, a STAR collaborator from the University of Illinois, Chicago. Ye led the design and construction of the new silicon-based particle-tracking components installed at the forward end of STAR, working with scientists from National Cheng Kung University in Tainan and Shandong University in Qingdao.

These components give scientists the ability to detect particles emerging almost in line with the colliding beams, including jets of particles that reveal information about the colliding quarks’ energy, direction, and spin.

“This information is essential for mapping the 3D arrangement of the proton’s inner building blocks,” said Chi Yang from Shandong University. Yang worked with colleagues from the University of Science and Technology of China and Brookhaven Lab to build additional subdetector systems for the forward tracking detector.

“These upgrades cover exactly the angles where jets would go in the EIC,” said Brookhaven Lab physicist Prashanth Shanmuganathan. So, in addition to increasing the data set for exploring the color charge interactions, “Run 22 will help us learn about the detector technology and the behavior of nucleon structure so we can apply that knowledge to the EIC.”

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Left: One plane of three silicon tracker detector modules installed around the beampipe at one end of the STAR detector. The shiny mirrorlike wedges, arrayed in alternating "inner" and "outer" positions, form a ring around the beampipe, with each sector connected to readout electronics. Right: Zhenyu Ye inspects the silicon tracker after insertion into the STAR Time Projection Chamber (TPC), where it will operate closer to the point where particles collide. Violet tubes encase signal readout cables while clear tubes carry a cooling fluid to the detector.

Cooling protons

Interspersed with delivering proton-proton collisions for STAR’s Run 22 measurements, the C-AD team will also spend the equivalent of two weeks’ time testing a technique for keeping high-energy protons tightly packed.

You’ll recall that keeping particles packed is important for maximizing collision rates and maintaining polarization. But particle spreading, or heating up, is a problem for all accelerated ion beams—from protons to uranium nuclei (the heaviest ions that have been collided at RHIC).

“There’s no natural shrinking of these ion beams; they never get denser by accident,” Schoefer said.

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This view of STAR shows the endcap calorimeter electronics (blue with black cables) and four new planes of small-strip Thin Gap Chambers (copper colored with white at edges).

So RHIC accelerator physicists have developed a variety of successful techniques to keep ion beams “cool.” Some of these cooling methods involve delivering “kicks” to push particles closer together, while others literally use cool beams of other particles (electrons) to extract heat from circulating ions.

Realizing that different cooling techniques work best for different types of particles at different energies, physicists are exploring several strategies for possible use at the EIC. In Run 22 they’ll test something called “coherent electron cooling” (CeC) on high energy polarized protons.

Instead of just being cool in temperature, as described above, the negatively charged electrons in CeC play a more active role: They clump around each positively charged proton to create a “mold” of the proton beam.

“It's a little bit like getting braces when the orthodontist takes a mold of your teeth,” Schoefer said. “We take a mold of the proton beam and then we adjust the electron beam slightly to attract the protons closer to a central position. As the electrons move, their electrical attraction drags the protons with them.”

In 36-hour stints, the C-AD physicists will test and try to fine-tune the technique.

Measuring ion polarization

In addition, every two weeks during Run 22, the C-AD team will stop proton acceleration for 12- to 16-hour stretches of accelerator R&D experiments. For one of these projects, they’ll ramp up beams of Helium-3 ions to work on methods for measuring the polarization of particles other than protons.

“In RHIC, the only polarized species we’ve ever had is polarized protons. But EIC will do experiments with polarized ions such as Helium-3. That’s an entirely different beast,” Schoefer said.

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Felix Archampong, Robert Soja, William Struble, and Rahul Sharma of the STAR technical support group completed the mechanical design, construction, and installation of the small-strip Thin Gap Chambers—shown here in position for collecting data—with support from the STAR electronic support group.

The C-AD team worked in collaboration with members of the “Cold-QCD” group in the Physics Department to design ways to measure the polarization of these more complicated ions.

To measure polarization, physicists spray a gas through the beam to act as a target, and measure how the particles in the beam scatter.

“For a proton, that’s already a challenge, but at least the proton stays a proton. When Helium-3 scatters off a target, it may break up into two protons and a neutron, or a proton and a deuteron. To accurately measure the polarization, we have to identify when breakup occurs,” said William Schmidke, a scientist in the physics department who’s been developing polarimetry detectors to make the measurements.

During Run 22, physicists will test the components’ ability to accurately characterize scattering products using unpolarized beams of Helium-3.

“We can do these tests, without measuring polarization, to develop the methods so we’ll be able to measure polarization when we eventually have polarized beams at the EIC,” said Brookhaven physicist Oleg Eyser, another member of the Cold-QCD team.

“Many people made important contributions to the detector and accelerator components needed for Run 22 at RHIC. We are looking forward to the exciting opportunities for physics discoveries and for advancing the technologies and physics analysis methods we will need for the EIC,” said Haiyan Gao, Brookhaven’s Associate Laboratory Director for Nuclear and Particle Physics.

Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit science.energy.gov.

Acelerador relativista de iones pesados

Coordenadas: 40°53′2″N 72°52′33″O (mapa)

 

El Acelerador Relativista de Iones Pesados o RHIC por sus siglas en inglés (Relativistic Heavy Ion Collider BTS) es un colisionador de iones pesados, localizado y operado por el Brookhaven National Laboratory (BNL) en Upton, Nueva York.¹​ Al usar el RHIC para colisionar iones viajando a velocidades relativistas, los físicos estudian la forma primordial de materia que existió en el Universo poco tiempo después del Big Bang,²​ y también la estructura de los protones.

Actualmente, el RHIC es el segundo colisionador de iones pesados más potente del mundo, después de que el Gran colisionador de hadrones (LHC) comenzó su operación en 2010 chocando iones pesados de plomo a mayor energía. Es también importante considerar su capacidad de colisionar protones con polarización de spin.

 Véase también

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• The ISABELLE Project
• Large Hadron Collider