# Presentation: 802345

## Search for a New State of Matter 

- Wire Chamber

- Silicon Detector

**Search for a New State of Matter **

- A state of matter not seen since the first few microseconds after the Big Bang is the object of study of P-25 physicists working at RHIC, the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory. In the very early stages of the Big Bang when the universe was too hot for protons and neutrons to form, it is generally believed that it consisted almost entirely of a soup of truly elementary particles: quarks, and gluons that mediate the force between the quarks. As this quark-gluon plasma (QGP) expanded and cooled, the quarks and gluons condensed to form the protons and neutrons that are part of ordinary matter today.

- The RHIC complex accelerates gold ions to nearly the speed of light and  then collides them at six locations around the accelerator ring. When two of the gold ions undergo a head on collision, for a fleeting instant the temperatures produced are hotter than the sun's center and thought to be sufficient to form a QGP or "Little Big Bang". The PHENIX detector is located at one of these collision points, where it records the particles produced during these "Little Big Bangs". Our staff designed and constructed three of the PHENIX detector systems: the Multiplicity and Vertex Detector (MVD), and the two Muon Spectrometers. We are presently using these detectors to look for potential signatures of the QGP, such as suppression of the production of the J/ particle, which is a bound state of a charm and an anti-charm quark.

- Cartoon of the time evolution of a gold-gold collision. The two highly energetic ions approach and collide, forming a hot and dense medium. If the temperature and density are large enough, the protons and neutrons may “dissolve” into a plasma consisting of free quarks and gluons.  The plasma then expands and cools, with the quarks and gluons recombining into the particles of ordinary matter, which are eventually detected by the experiments.  The final frame shows the tracks that have been reconstructed in one such event in a RHIC detector.

- The MVD is one of the smallest detectors in PHENIX, and uses Silicon pad
- detectors, seen on the left side of the image. On the right side is very
- densely packed readout electronics; the package measures about half the
- size of a credit card. The MVD has 30000 readout channels.

- The PHENIX muon spectrometers contain forty-eight cathode strip chambers (50000 readout channels), which are used to measure the angles and velocities of particles produced in gold-gold collisions.  One of the intermediate sized chambers is shown here.  The muon chambers are of 3 different types and range from 1.5 meters to 3.2 meters in height, some of the largest such chambers ever built.

**Detection of J/******** production**: Using pairs of detected muons one can construct the mass of the parent particle. Shown upper right is a simulated mass spectrum showing various reconstructed particles, including the J/, on top of continuum backgrounds. On the left is a measured mass spectrum, zoomed in on the J/ peak, obtained from our recent deuteron-gold ion collision data.  The deuteron-gold collisions, where no excessive suppression of J/ particles is expected, are used as a control experiment for the gold-gold collision experiments.  We have now established a baseline for J/ production at RHIC and are currently taking data to measure the J/ yield in gold-gold collisions.
- .

- Time evolution of the big bang.  We are attempting to recreate the “Quark Soup” which is hypothesized to have existed for the first 10 microseconds after the initial bang.

- The PHENIX detector hall is shown when the detector was in the early stages of assembly.  The muon chambers now reside inside the conical shaped magnets which are shown in the left foreground and the right background.  The multiplicity vertex detector now resides at the collision point, indicated in the picture.  The inset on the right is a picture of a reconstructed gold-gold collision, with all the tracks reconstructed tracks in the central (purple) detectors shown, as well as just the two tracks from a candidate J/ event in the muon arm region (right side of the picture).

**Au**

**Au**

**5 cm**

- In nuclear collisions (left) , charm (c) and anticharm (c_) quarks are
- sometimes formed. In ordinary nuclear environments, these often pair up to form psi particles. In a QGP however (center), the abundance of other free quarks screens them from each other. Instead, the charm quarks pair up with the more common up or down quarks to form so-called D mesons (bottom right).