The D-Zero Experiment - May 7, 2005 
 
 
 The W and Z bosons are particles that carry the weak force, one of 
 the four fundamental forces found in nature. According to our standard 
 model the W and Z bosons will interact with each other due to their 
 weak charge. In contrast, photons, the carriers of the electromagnetic 
 force, do not carry electromagnetic charge, and do not interact with 
 each other. 
 
 At Fermilab, we can study the strength of the interaction of the W boson 
 with the Z boson by identifying and studying collisions in which 
 both are produced at the same time. By counting the number of occurrences
 and measuring the properties of the WZ events, we can test the strength
 of the interaction between the bosons.
 
 These particles are very massive. The W boson weighs in at 85 times 
 the mass of a proton. The Z boson is even heavier. Shortly after they
 are produced, they disintegrate into lighter types of matter and we 
 detect these "decay products". The Figure shows one of our WZ events. 
 
 Fermilab's proton-antiproton collider, the Tevatron, is the only particle 
 accelerator in the world that has ever produced both a W and a Z boson
 in the same collision. They are very rare collisions, indeed, and 
 nobody has ever claimed to have seen them before this. We scoured 
 approximately 14 trillion collisions produced between April, 2002 and 
 June, 2004 and found three events with both a W and a Z boson in them.  
 We estimate that processes which look like, but aren't WZ production, 
 will provide us three or more such events 3.5% of the time. 
 
 With these three candidates we are able to measure the rate the Tevatron 
 produces WZ events. Also, we set the best constraints on the strength of 
 the interaction between the W and Z bosons involving only this process.

 
 An event display picture can be seen here. 

 
 Figure 1. End-on view of one of three WZ events. The collision occured 
 at the center of the detector. A Z boson decayed to two 
 muons (two of the green tracks).  A W boson candidate decayed 
 to a muon and a neutrino (a green track and purple arrow opposite 
 to it). Other lower energy charged-particles were produced in the 
 collision and are represented as grey tracks.  The straighter the track,
 the more energetic the particle. The red and blue towers in 
 between the dark circles represent energy deposited in our 
 calorimeter by the particles created in the collisions. 

 
 This result was sent to Physics Review Letters on April 11, 2005. If 
 you are interested in reading more about this physics please see 
 our paper.