UT-ICEPP 97-02 hep-ph/9706382 June 1997 Hadron colliders as the \neutralino factory": Search for a slow decay of the lightest neutralino at the CERN LHC

Prospects are examined for the detection of a slow decay of the lightest neutralino (or any other longlived particles) at the CERN LHC and at Very Large Hadron Collider (VLHC). We rst point out that such hadron colliders will become the \neutralino factory" producing 10{10 neutralinos/yr, if gluinos and/or squarks actually exist below O(1) TeV. The lightest neutralino (~ 01), usually assumed to be stable, will be unstable if lighter superparticles such as the gravitino ( ~ G) or axino (~ a) exist, or R-parity is not conserved. The decay signal would, however, be missed in usual collider experiments, particularly when the decay mostly occurs outside the detector. In order to search for such a slow decay of ~ 01, we propose a dedicated experiment where the collision products are dumped by a thick shield, which is followed by a long decay tunnel. The decay product of ~ 01 can be detected by a detector located at the end of the tunnel. The slow arrival time and the large o angle (to the direction of the interaction point) of the decay product will provide a clear signature of slowly decaying ~ 01's. One can explore the decay length (c ) in a wide range, i.e., 0.2 m to 1 10 km for m~ 1 = 25 GeV and 1 m to 2 km for m~ 1 = 200 GeV at the LHC. This corresponds to the range of the SUSY breaking scale p F = 2 10 to 2 10 GeV in case of the ~ 01 ! ~ G decay predicted in gauge-mediated SUSY breaking models. At VLHC, one can extend the explorable range of m~ 1 up to 1000 GeV, and that of p F up to 1 10 GeV. In case of the ~ 01 ! ~ a decay, the Peccei-Quinn symmetry breaking scale Fa can be explored up to 5 10 GeV. The mass of the decaying particle can be determined by using the correlation between the energy and the arrival time of the decay product. With the setup we propose, one can also search for (i) other decay modes of ~ 01 such as R-parity violating one, (ii) slow decays of any other longlived neutral or charged particles, and (iii) heavy stable charged particles. E-mail: [email protected]. Present address: Hitachi Research Laboratory, Hitachi, Ltd., 7-1-1 Omika-cho, Hitachi-shi, Ibaraki 319-12, Japan. E-mail: [email protected].