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          Institute: MPI für Physik     Collection: MPI für Physik     Display Documents

ID: 543482.0, MPI für Physik / MPI für Physik
A New Experiment for the HERA Collider - Expression of Interest
Authors:Abramowicz, H.; Abt, I.; Adamczyk, L.; Arneodo, M.; Bracinik, J.; Brock, I.; Bruell, A.; Caldwell, A.; Chekanov, S.; Chwastowski, J.; Ciborowski, J.; Dabrowski, W.; Devenish, R.; Eisenberg, Y.; Ermolov, P.; Eskreys, A.; Fiegiel, J.; Gladilin, L. K.; Grabowska-Bold, I.; Grindhammer, G.; Gustafson, G.; haas, T.; Hafidi, K.; Hasell, D.; Holt, R. J.; Ingelman, G.; Jackson, H. E.; Jönsson, L.; Jung, H.; Karshon, U.; Kiesling, C.; Kinney, E.; Kisielewska, D.; Kotanski, A.; Kokwalski, H.; Levy, A.; Liu, X.; Lönnblad, L.; Lukina, O.; Magill, S.; Makins, N.; Merkin, M.; Mildner, R.; Naroska, B.; Peng, J.; Potterveld, D.; Proskuryakov, A.; Przybycien, M.; Reimer, P. E.; Repond, J.; Schlenstedt, S.; Schmidke, W.; Schneekloth, U.; Shekelian, V.; Sjöstrand, T.; Slominski, W.; Stanco, L.; Stroili, R.; Whitmore, J.; Yoshida, R.; Zawiejski, L.; Zotov, N.
Audience:Not Specified
Intended Educational Use:No
Abstract / Description:Quantum Chromodynamics is now widely acknowledged to be the correct theory for the strong hadronic interactions. Knowing the correct Lagrangian for the theory does not however imply that we know everything we want to know about the strong interactions. Experimental observations such as the confinement of color or the energy dependence of scattering cross sections cannot today be predicted from the QCD Lagrangian. These are striking results which should be calculable from first principles if we are to claim to understand our universe.

We describe with this document a program dedicated to the study of the strong hadronic interactions with a unique probe - the HERA accelerator. The immediate aim is to push our understanding of these interactions to a new level. A possible outcome is a completely new way of thinking about the fundamental constituents and their interactions.

One might ask,"How is it possible that experiments on nucleon structure in the energy range of HERA will advance our understanding of elementary particles and forces when the Standard Model already predicts everything?" In this document, we describe the particulars of measurements which have not yet been performed, or which have not been performed with enough accuracy. To place these in context, we recall a few historical events reflecting times when experiments were done in regions where "everything is understood."

1. In the early twentieth century, the force electromagnetism) and components involved in atoms were basically known after the discovery of the electron and the Rutherford experiment. And yet knowing the force and the constituents was not the entire story: important input from experiments on atoms were essential to finally understanding Quantum Mechanics. Today, even if QCD, quarks, and gluons were all true as we now understand them, there could be much more when the full story is completed.

2. In the 1960's, verified predictions made it clear that SU(3) and the quark model explained hadronic spectra as then understood. At the same time, even some originators of these ideas doubted whether quarks had any physical reality. The first deep inelastic experiments, which many thought would be unproductive, unexpectedly demonstrated the physical reality of the quarks and provided a crucial step to realizing QCD as the theory of the strong force and one backbone of the Standard Model. Since then, experiments have continued to verify the nature of QCD for high momentum transfers, where theory predicts much more than experiments can measure. At the same time, experiment leads theory in delineating hadronic structure and the behavior of strong interactions at energies corresponding to the bound states found in the everyday world.

HERA is particularly well suited to study radiation patterns in strong interactions, and all the measurements described in this document have as basic goal the understanding of these radiation patterns. The structure function measurements will probe the evolution of the parton densities as longitudinal and transverse distance scales are varied, while the forward jet measurements will allow detailed and direct tests of our understanding of radiation over a large and fixed rapidity interval. Measurements of exclusive processes will allow for a much more detailed mapping of the distribution of strongly interacting matter in hadrons, while measurements of particle production and correlations will yield sensitive tests of perturbative and non-perturbative QCD calculations. These measurements will be performed in much wider kinematical regions than possible with ZEUS and H1, thus providing greatly enhanced sensitivity to the underlying physics. Heavier targets than the proton will allow the study of nuclear matter in a more uniform medium, and may in many ways be simpler to understand theoretically. HERA with heavy nuclei (e.g., Mercury) will allow to study a novel state of matter - the saturated gluon state or Color Glass Condensate. Revealing experimentally the CGC would be pivotal in understanding the high energy limit of QCD and the origin of quark and gluon distributions.

We first review the physics topics which we consider to be the highlights of the proposed program. The increased sensitivity to the correct understanding of radiation in strong interactions is made clear in these sections. We then describe some first ideas on what the optimized detector for this physics would look like. We note that the physics described in the following sections cannot be carried out with HERA-II. This second phase of HERA running is focused on high Q² physics, which requires high luminosities. These are achieved by placing combined dipole/quadrupole magnets very near the H1 and ZEUS interaction points, thus limiting access to the small-x, low Q² physics which would be a central element in the proposed program. Also, many of the topics one would like to study require a different type of detector than the current H1 and ZEUS detectors.

We close with a brief discussion of a possible time scale for the construction of a new detector and what we would consider to be a viable running plan.
Classification (PACS, MeSH, etc.):HERA-3
Document Type:Other
Communicated by:N.N.
Affiliations:MPI für Physik
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