] David Bruce Cline (December 7, 1933 – June 27, 2015) was an American particle physicist known for his contributions to the discovery of the Higgs boson and the W and Z intermediate bosons. After receiving his Ph.D. from the University of Wisconsin–Madison, he went on to join the university's physics faculty and founded the "Pheno Group". Shorthand for phenomenology, the group consisted of particle physicists designing and running experiments alongside developing theoretical models that went beyond the current standard model of particle physics. He later moved to UCLA where he became a Distinguished Professor of Physics & Astronomy for his contributions to the growth of the UCLA Physics & Astronomy Department.
Rather than working in a U.S. based particle accelerator, the Superconducting Supercollider, Cline chose to work on CERN's Large Hadron Collider. While there, he and others founded the Compact Muon Solenoid (CMS) experiment, which is still active today in investigating the Standard Model and is one of the largest international scientific collaborations in history. Cline was also involved in the development of the ICARUS neutrino detector. When assembled, it would be the largest detector of its time, built with the purpose of detecting neutrinos from the sun and the beams from CERN.
In the later part of his career, Cline shifted his interests towards astroparticle physics. He pioneered the use of liquified noble gases in particle detectors to enhance the detection through the use of a Time Projection Chamber. Not only did this facilitate work in investigating neutrino oscillations, the introduction of noble gases into detectors could be exploited to detect dark matter. Dark matter's elusive nature inspired Cline to organize a biannual international conference for dark matter research, which will go on to have its 14th meeting in March 2020.
Early life and education Cline was born on December 7, 1933, in Rosedale, Kansas. He attended and graduated from Rosedale High School in the same city, and after being discharged from the army, attended Kansas State University, where he received a BS in physics in 1959 and MS in physics in 1961 in physics. He continued his studies and pursued a PhD at the University of Wisconsin - Madison under the guidance of Dr. William Fry. He completed his PhD thesis in 1965, titled "A Study of Some Rare Decay Modes of the Positive Kaon". His PhD work investigated the existence of the then undiscovered electrically charged W boson and electrically neutral Z boson. His observations of decaying kaons dismissed the existence of the neutral weak force carrier, but he would later go on to withdraw this belief when experiments at CERN claimed to require the existence of the Z boson for certain interactions.
Career In 1967, Cline was appointed to the faculty at the University of Wisconsin. Once there, he co-founded the "Pheno Group", which consisted of physicists dedicated to pursuing a broad range of particle physics research in both theory and phenomenology.
The same year, Cline began working at CERN, and with Alfred E. Mann of the University of Pennsylvania and Carlo Rubbia of Harvard, the team produced a document that launched the first experiments to study the weak force using neutrino beams at the new Fermilab accelerator complex. After a period of uncertainty, Cline and collaborators agreed with the claim coming from the CERN laboratory in Geneva that certain neutrino interactions required the existence of weak neutral currents. In 1976, the group proposed upgrading the single-beam proton accelerator at CERN to a dual-beam proton-antiproton collider. The installation of this 270 GeV antiproton-proton collider, along with the implementation of more advanced beam-cooling techniques, prompted the investigation for intermediate vector bosons (IVB). With a theorized mass of 80-90 GeV, it was expected that the high energy of the collider would lead to the first observations of these particles. The experiment at CERN proved successful, and in 1983 IVBs were detected and differentiated the weak force from the electromagnetic force for the first time. The discovery warranted the 1984 Nobel Prize in Physics, awarded to Dr. Carlo Rubbia and Dr. Simon van der Meer for the discovery of the W and Z bosons.
Following his involvement in the discovery of the W and Z boson, Cline moved to the UCLA Physics Department in 1986. Once there, he began actively pursuing efforts to grow the university's particle physics department and incorporate new areas of research. He was focused on hiring faculty with a specialization in accelerator physics, which was a rapidly growing field at the time. Cline became a distinguished professor of physics and astronomy for his contributions to the growth of astroparticle physics and accelerator physics with the support of the UCLA Physics & Astronomy department that gained him global recognition in the field. He proposed investigations into the mass of the νΤ & νe neutrinos using terrestrial solar and supernova neutrino sources, nucleon decay using the ICARUS detector in Italy, and neutrino oscillations. To accomplish his projects, Cline and a small group of US physicists proposed the new design of a supernova neutrino detector large enough to observe extra-galactic supernova bursts.
Cline was part of the experiment that made their discovery in 1983 at CERN which first implemented the scheme they proposed in 1976. Later Cline was also a member of the Fermilab experiment that discovered the top quark and of one of the CERN experiments that discovered the Higgs boson in 2012.
At UCLA he was also one of the pioneers of the use of liquefied noble gases as particle detectors and made innovative contributions to the development of the use of liquid argon and xenon to detect dark matter.
In the early 1990s, the U.S. had plans to build the Superconducting Supercollider. Cline was among many other U.S. scientists who chose to work on a competing European based supercollider, CERN's Large Hadron Collider . He continued working at CERN's LHC and was a cofounder of the Compact Muon Solenoid (CMS) experiment. The goal was to detect and measure the stable particles that remain after colliding protons at nearly the speed of light, in an effort to investigate physics beyond the Standard Model and identify the conditions of the early universe.
The CMS was constructed and is located at one of the four collision points that make up the LHC and is designed to detect muons with high accuracy and be the most powerful solenoid magnet of its time, being capable of producing a magnetic field of 4 tesla. The international collaboration that was CMS would come to be one of the largest of its kind, incorporating over 200 institutes and 50 countries. The collaboration proved to be successful, as the CMS was involved in the first 7 TeV proton-proton collisions, the discovery of the Xib baryon, and the discovery of the Higgs Boson. David Cline is listed as a contributor to these experiments for his contribution to the creation of CMS.
Cline was also involved in a collaboration between over 25 universities across the globe who proposed the construction of a neutrino detector in Fermilab in 2005. The proposed detector would be a 30 Kiloton Off-Axis Detector, with the purpose of studying νμ → νe Oscillations in the NuMI Beamline. The NuMI Off-axis νe Appearance, or NOvA, collaboration brings together over 240 scientists from 51 institutions to study the effects neutrinos may have had on the evolution of the universe
Notable Involvements
Super Proton-Antiproton Synchrotron & Compact Muon Solenoid Although Cline is not credited for the discovery of the W and Z bosons, Cline and Rubbia's proposal of the installation of a proton-antiproton collider has led to advances in particle physics through the investigation of heavy bosons. Cline's role as a co-founder of the CMS experiment has also earned him the status of a contributor to the first 7 & 8 TeV proton-proton collisions, as well as the discovery of the Higgs Boson and Xib baryon.
Investigation of Dimuon Events In the early 70s, Cline investigated the production of dimuons from neutrinos and antineutrinos. These neutrino events require the generation and decay of intermediate particles that did not agree with models that predicted the intermediate particles to be heavy leptons and semi-weak vector bosons.
In February 1975, Cline and others reported on their observation of a new particle produced by high energy neutrino and antineutrino interactions. 14 dimuon events were observed, and due to the characteristics of the event and the absence of any trimuon events, the interaction seemed to require the presence of a new massive particle. The theorized particle, which was expected to have a previously unobserved quantum number, would need to decay weakly in order to have two muons in the final state.
The source of the second muon was argued to be due to the decay of pions and kaons. Cline and others provided evidence against this by observing "(i) the rate of dimuon events, (ii) the opposite signs of their electric charges, (iii) the different densities of the target materials in which they were produced, and (iv) the distributions in muon momentum and transverse momentum."
The neutrino interactions leading to dimuon events required the existence of a new particle that they called the y particle. The group theorized that, if the particle was a hadron, the mass is between 2 and 4 GeV and the lifetime would have to be less than 10−10s. The alternate theory was that the neutrino interaction produced a neutral heavy lepton that decayed into two muons and a neutrino/antineutrino.
Physics potential of a few 100-GeV mu+ mu- collider Cline's most cited single-author paper describes the potential applications of " a few 100-GeV μ+μ− collider". His proposal was inspired by the evidence that the Standard Model and SUSY Model should exhibit a resonance at a mass just under 2Mz. At this energy range, it was very difficult to accurately detect and measure interactions at the LHC. Reaching such high energies was needed to search for the Higgs. The μ+μ− collider would have also had applications in investigating TeV interactions with higher resolution than colliders at the time.
High-Transverse-Momentum Secondaries and Rising Total Cross Sections in Cosmic-Ray Interactions While he was still at UW - Madison, Cline worked with Dr. Francis Halzen and studied hadron collisions from cosmic ray interactions. Their observations showed evidence for high-transverse-momentum secondaries in excess of the predicted exponential cutoff, which matched data from CERN at the time. Experiments at CERN ISR had shown that the cross sections of hadron collisions had been larger than expected. The data supported the quark model of the proton, where small momentum collisions would scatter at the "surface", leading to an exponential cutoff of the transverse-momentum. High momentum collisions, however, lead to interactions with the quarks and produce high-transverse momentum along with a jet of hadrons. Their study concluded that the rise in the total cross section of the interactions of cosmic rays and the detection of hadron jets supports the theory of a composite model of the proton.
Observation of Elastic Neutrino-Proton Scattering