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The two{jet invariant mass spectrum as measured in the UA2 experiment is used to search for additional heavy vector bosons decaying to two{jets. The mass of an additional W boson that couples to fermions with a V + A form is constrained to be greater than 261 GeV to the 90% condence level. A limit on the production cross section of additional W and Z bosons is given as a function of the boson mass. A limit on the production of excited quarks is also given as a function of the excited quark mass.

The SwissFEL Injector Test Facility operated at the Paul Scherrer Institute between 2010 and 2014, serving as a pilot plant and testbed for the development and realization of SwissFEL, the X-ray Free-Electron Laser facility under construction at the same institute. The test facility consisted of a laser-driven rf electron gun followed by an S-band booster linac, a magnetic bunch compression chicane and a diagnostic section including a transverse deflecting rf cavity. It delivered electron bunches of up to 200 pC charge and up to 250 MeV beam energy at a repetition rate of 10 Hz. The measurements performed at the test facility not only demonstrated the beam parameters required to drive the first stage of an FEL facility, but also led to significant advances in instrumentation technologies, beam characterization methods and the generation, transport and compression of ultra-low-emittance beams. We give a comprehensive overview of the commissioning experience of the principal subsystems and the beam physics measurements performed during the operation of the test facility, including the results of the test of an in-vacuum undulator prototype generating radiation in the vacuum ultraviolet and optical range.

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The NA52 experiment searches for long-lived massive strange quark matter particles, so-called strangelets, produced in Pb-Pb collisions at a beam momentum of p lab 158 A GeV͞c. Upper limits for the production of strangelets at zero degree production angle covering a mass to charge ratio up to 120 GeV͞c 2 and lifetimes t lab * 1.2 ms are given. The data presented here were taken during the 1994 lead beam running period at CERN. [S0031-9007(96) PACS numbers: 25.75. Dw, 12.38.Mh, 24.85.+p The production of strange quark matter (SQM), socalled strangelets, has long been advertised as an ultimate signature for quark-gluon plasma (QGP) formation in ultrarelativistic heavy ion collisions. Strangelets could be formed from the QGP via a strangeness distillation process [1][2][3][4]. Their production is due to a cooling process of the plasma which results in a strong enhancement of the s quarks in the quark phase. The cooling mechanism of the plasma is started by the evaporation of pions, K 1 and K 0 , which carry entropy and antistrangeness away from the system. The strong s-quark enhancement in the baryon rich environment of the plasma favors the formation of strangelets. In contrast to nuclear matter, strangelets consist of approximately the same number of u, d, and s quarks. On the basis of the Pauli exclusion principle such multiquark states become stable owing to the introduction of strangeness as an additional degree of freedom. Depending on the relative s-quark content, strangelets can exist in neutral or charged form. By virtue of the large s-quark content, the charge to mass ratio of strangelets is expected to be small ͑Z͞A , 0.1͒, which is used as a prominent experimental signature. Bag model calculations indicate that for sufficiently large masses ͑A . 10 GeV͞c 2 ͒ strangelets could be stable with respect to strong and weak nucleon emission and therefore detectable in mass spectrometer experiments [5][6][7][8]. Strangelet formation has also been considered in coalescence models [9]. Strange quark matter could even occur as a decay product of metastable exotic multihypernuclear objects (MEMO's) [10]. The discovery of strangelets would have profound implications beyond the confirmation of the QGP formation: it would establish the existence of strange quark matter (SQM) [11][12][13] [20]. A recent review is given in Ref. [21]. During the 1994 Pb period at CERN, the NA52 Collaboration took data to search for positively and negatively charged strangelets resulting from lead-on-lead collisions at an incident beam momentum of 158A GeV͞c. Preliminary results have been already presented [22]. Now the full statistics have been analyzed and the final results are reported here.The experimental setup (Fig. 1) makes use of the existing H6 beam line at the CERN-SPS to identify the secondary particles produced in the lead target. It is a single particle, double-bend focusing spectrometer transmitting charged particles within a momentum bite of 2.8% for rigidities p͞jZj selectable between 5 and 200 GeV͞c with full particle...

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