PHENIX
Phenix ( acronym for P ioneering H igh E nergy N uclear I nteractions e X periment) is one of four experiments at Brookhaven National Laboratory after Quark Gluon plasma research. PHENIX concentrates on the measurement of leptonic and electromagnetic observables (in contrast to STAR , which searches for hadronic signals). PHENIX is also designed to investigate the spin structure of the proton .
PHENIX consists of many different detectors. Photons , leptons and also hadrons at medium rapidity are measured with the central spectrometer, while muons in the forward direction are measured by a muon spectrometer, which is located on both sides of the collision point in the beam direction.
550 scientists from 62 institutes in 13 countries are working on the experiment (as of 2005). From Germany, the University of Münster is involved in PHENIX.
The spokesperson for the experiment was Barbara Jacak from 2007 to 2012 .
Individual detectors
Global detectors
Beam-Beam-Counter
The two identical beam-beam counters (BBC) are located on both sides of the collision point in the direction of the beam. The detector consists of quartz Cherenkov detectors and is used to determine the time and place and other parameters of a particle collision.
Zero degree calorimeter
The two identical zero degree calorimeters (ZDC) are also located in the direction of the beam, but at a significantly greater distance (18.25 m) than the BBC. The detector supports the BBC in determining the centrality of collisions.
Multiplicity Vertex Detector
The multiplicity vertex detector (MVD) surrounds the collision region. This highly segmented silicon detector measures the vertex position with high precision and is also used to determine the number of particles.
Central spectrometer
The central spectrometer is arranged concentrically around the beam axis at the collision point. It consists of two arms (east arm and west arm), each of which covers an azimuthal angle of 90 degrees. There is a large magnet in the central spectrometer.
Drift Chamber
The innermost detector of the central spectrometer is the drift chamber (DC). It helps to measure the position of charged particles and their deflection in the magnetic field.
Pad Chamber
A first pad chamber (PC) adjoins the drift chamber in both arms. Further pad chambers are located in both arms in front of the calorimeter (see below), in the western arm there is also such a detector directly behind the RICH (see below). The pad chamber helps to reconstruct the traces of charged particles, and it also serves as a veto detector for such particles in front of the calorimeter.
Ring Imaging Čerenkov Detector
A Ring Imaging Čerenkov Detector (RICH) is located behind the first PC in both arms . This detector can distinguish electrons and charged pions with the help of the light cones of the Čerenkov radiation , which hit mirrors in the detector in a ring. The RICH is filled with gas that reduces the speed of light .
Electromagnetic calorimeter
The electromagnetic calorimeter (EMCal) is the outermost detector in both arms. It consists of a total of eight sectors, two of which are lead glass calorimeters (PbGl), the other six are lead scintillator sandwich calorimeters (PbSc). These calorimeters are used to measure the energy and position of photons and electrons. Thanks to their fine segmentation, they achieve good spatial and energy resolution and enable, for example, neutral pions to be measured up to transverse pulses of approx. 20 GeV / c.
Muon spectrometer
Muon tracker
The muon trackers (MuTR) are located along the beam axis on both sides of the collision point. They open outwards like a funnel. With the help of three drift chambers, muons can be tracked in a radial magnetic field .
Muon ID
A muon identification detector (MuID) is attached to the muon tracker. Hadrons are absorbed with the help of absorber plates, so that the particles detected in the detector are almost exclusively muons (99.9%), which, however, must have a minimum energy of 1.9 GeV, otherwise they would also be suppressed.
Important results
Like the other RHIC experiments, PHENIX was able to demonstrate for the first time a strong suppression (compared to the expectation from proton-proton collisions) of particles with high transverse pulses in gold-gold collisions at the highest energies (200 GeV per nucleon). This suppression is explained by the strong interaction of hard scattered partons with the resulting dense and hot state of matter (quark-gluon-plasma). It could also be shown that in such gold-gold collisions one of two opposing particle jets, which are caused by hard scattering processes, more or less disappears.
Web links
- Official PHENIX Homepage (English)
- PHENIX publications on the preprint server (English)
Coordinates: 40 ° 52 '59 " N , 72 ° 52' 54" W.