From: FUNC: vxdesy NAME: CALDWELL To: NAME: zeus+all RFC-822-Headers: X-VMS-To: IN%"zeus+all@desy.de" MIME-version: 1.0 Content-type: TEXT/PLAIN; CHARSET=US-ASCII Content-transfer-encoding: 7BIT Dear ZEUS member, You will find below the statement from the DESY PR department on the high-x,Q2 data. The text was generated in agreement between H1, ZEUS and the directorate. This can be used as a guide for discussions. I remind you that no numbers should be given out until after the time of the seminars tomorrow. A note on the tables circulated this morning. They are only to be used for ZEUS internal discussions. They should NOT be shown to non ZEUS people. Only the data in the Q2 table will appear explicitely in the papers. Regards, Allen Hamburg, February 18, 1997 DESY Information for some Science Journalists and Editors __________________________________________________________________ EMBARGO until Wednesday, February 19, 1997, 11:00 a.m. (Local Hamburg Time) SPERRFRIST: Mittwoch, 19. Februar 1997, 11.00 Uhr __________________________________________________________________ More events than expected from the Standard Model - Deep inelastic electron-proton scattering measurements at the DESY accelerator HERA in a previously unexplored kinematic region - The two HERA experiments, H1 and ZEUS, observe an excess of events above expectations at high-x ( or M = sqrt(xs) ), y, and Q-squared. For Q-squared > 15,000 GeV-squared, the joint distribution has a probability of less than one per-cent to come from Standard Model NC DIS processes. Within this model, the predictions are known with confidence. Similar probabilities occur for masses M larger than 175 GeV. The events at high Q-squared and large M are particularly interesting because they occur in a previously unexplored region for deep inelastic scattering. Increased luminosities from the forthcoming data taking period, March-October, 1997, will clarify whether the observed effect is a statistical fluctuation or a signal of new physics. HERA Hadron-Electron Ring Accelerator facility DIS deep inelastic scattering NC neutral current (exchange of a Z-boson or a photon) x Bjorken scaling variable (fraction of the proton momentum carried by the scattered parton) s center-of-mass energy of the electron-proton collision Q-squared squared momentum transfer of the collision y Q-squared / M-squared M center-of-mass energy of the electron-parton system GeV Gigaelectronvolt Both international teams, H1 and ZEUS, independently analysed their data sample of high-energy deep inelastic scattering accumulated since 1994 at HERA. During these three years HERA ran with 27,5 GeV positrons colliding head-on with 820 GeV protons. The observed events have the typical signature of DIS reactions: the positron is scattered off a parton inside the proton through a large angle; the struck parton generates a high-energy hadron jet. Both groups compared their measurements with Monte Carlo calculations based on the Standard Model of NC DIS. Both HERA collaborations, H1 and ZEUS, have presented their results in a DESY Seminar on Wednesday, February 19, 1997. Both papers will be submitted to ,Zeitschrift fuer Physik" on Monday, February 24, 1997. The preprints can then be found on the World Wide Web. The title of the H1 paper is ,Observation of Events at very High Q-squared in ep Collisions at HERA". DESY Preprint No 97-024. http://www-h1.desy.de/h1/www/publications/org_publ.html The title of the ZEUS paper is: ,Comparison of ZEUS Data with Standard Model Predictions for e+p -> e+X Scattering at High x and Q-squared". DESY Preprint No 97-025. http://www-zeus.desy.de/zeus_papers/zeus_papers.html The H1 group has about 400 members from the following 12 countries: Belgium, Czech Republic, France, Germany, Italy, Poland, Russia, Slovak Republic, Sweden, Switzerland, United Kingdom, United States of America. The ZEUS group has about 430 members from the following 12 countries: Canada, Germany, Israel, Italy, Japan, Korea, Netherlands, Poland, Russia, Spain, United Kingdom, United States of America. Both detectors were planned, financed, constructed and are operated by these joint international collaborations. The Deutsches Elektronen-Synchrotron DESY is the German research center for basic research in particle physics and investigations with synchrotron radiation. It is a publicly funded national research center based in Hamburg, with a branch institute in Zeuthen near Berlin. The annual budget amounts to 275 million German marks. The Federal Government (Federal Ministry for Education, Science, Research and Technology ( bmbf )) bears 90 per-cent of the budget and the City of Hamburg or the federal state of Brandenburg the remaining 10 per-cent. DESY is a member of the Hermann von Helmholtz Association of German Research Centers (HGF). 3000 scientists from 280 universities and research institutes from 35 countries all over the world are participating in the research at DESY, 1300 of them in particle physics, 1700 in experiments with synchrotron radiation. The Hadron-Electron Ring Accelerator facility HERA is the only facility in the world in which electrons or positrons and protons collide. At HERA physicists are able to observe electron/positron proton collisions at center-of-mass energies which are an order of magnitude above energies previously available. In this type of collision structures inside the proton can be studied down to one part in a thousand of the size of the proton itself. Inside HERA the two particle beams circulate in opposite directions in separate storage rings and are brought to head-on collision at two interaction points. These are equipped with the detectors H1 and ZEUS, which have both been taking data since the beginning of the HERA research program in 1992. As well as these collision experiments HERA accomodates two beam-target experiments: HERMES, in operation since 1995, uses the polarized electron beam to investigate the origin of nucleon spin; HERA-B, scheduled to start in 1998, will use the proton beam for the study of CP violation in the B-meson system. The underground storage ring facility HERA has a circumference of 6,336 meters. It was constructed from 1984 to the end of 1990, when the operation began. The first particle collisions were observed in October 1991; the research program started in June 1992. Since then the integrated HERA luminosity continuously increased from 0,05 inverse picobarn (1992), to 1 inv.pb (1993), to 6,2 inv.pb (1994), to 12,3 inv.pb (1995), to 17,2 inv.pb (1996). For the 1997 HERA run an integrated luminosity of 25 inverse picobarn is expected. HERA was constructed in an international collaboration: about fifteen per-cent of the total costs of about 1110 million German marks came from foreign countries. Institutions in Canada, China, Czechoslovakia, France, Israel, Italy, Netherlands, Poland, United Kingdom, and USA contributed through components and delegation of physicists, engineers, and technicians to Hamburg during the construction of HERA.