437 Calorimetry for the NLC Detector James E. Brau, Anatoli A. Arodzero, and David M. Strom Physics Department, University of Oregon, Eugene, OR 97403, USA representing the NLC Detector Group ABSTRACT The physics goals of discovery and measurement at the NLC depend on excellent calorimetry. Of the options, we find a high granularity silicon-tungsten sampling electromagnetic calorimeter combined with a relatively well segmented hadron calorimeter to surpass the requirements. This technique pro- vides enormous strength in understanding the details of jet en- ergy deposition, and therefore, can provide excellent jet energy resolution. We present some ideas of how such a device could be configured and what performance might be expected. I. INTRODUCTION Most physics goals of the NLC depend on the performance of the NLC calorimetry. The intermediate mass Higgs search and studies require optimal jet resolutions for and Higgs reconstruction[2] , hermiticity for tagging the mode[2], and good electromagnetic energy resolution for measurement of the branching fraction[3]. Suppression of backgrounds to the requires good W and Z mass resolution to reject the ZZ and WW production. A 4% unconstrained reso- lution for Ws and Zs, improving to 2% with the Z h constraint, would be the goal. Top studies will demand precision energy measurements which have implications on calorimetry calibra- tion and resolution. The SUSY searches demand the best pos- sible hermeticity. Elimination of two-photon processes within a bunch train requires timing resolution as near the inter-bunch spacing ( 1.4 nsec) as possible. At higher energies, the study of strongly interacting gauge bosons through and requires two-jet mass resolution sufficient to distinguish from [1]. The NLC Detector design employs a 4 Tesla solenoidal field, driven by the requirement to protect the vertex detector from the enormous number of pairs produced in the beam-beam interaction[4]. Optimal electromagnetic energy resolution de- mands that the solenoid be outside the EM calorimeter, and the coil radius should be minimized to contain costs. For this study, a 50 centimeter radius EM calorimeter has been chosen, although larger radii may be required for acceptable separation of electromagnetic showers from charged tracks. The requirement of optimal EM resolution clashes with opti- mal jet resolution. Compensated calorimeters, which yield the best jet resolutions, call for compromised EM resolution to pro- vide uniformity between the EM and hadronic sections. The calorimeter-dominated jet measurement technique also relies on a limited disruption of the jet by a modest magnetic field. Our plan for a 4 Tesla field and an EM calorimeter optimized for EM calorimetry runs counter to this approach. We are there- fore adopting the strategy of a combined tracker with calorime- ter energy measurements. Jets will be measured by using the excellent measurements of the inner tracker for charged tracks, with electromagnetic showers measured in the EM calorime- ter, and neutral hadrons detected and measured in the EM or hadronic calorimeter. It is important to note that the NLC inner tracker not only provides much better energy measurements of the charged tracks than the calorimeter could, but does so with nearly 100 percent efficiency, an important requirement for re- liable jet energy measurements. The EM calorimeter must be able to provide the best possible separation of EM showers from the charged particles, meaning it must be dense with a small Moliere radius and highly segmented. The concept of study then is an inner electromagnetic calorimeter, separated in the barrel from the hadronic calorime- ter by the solenoidal magnetic coil. The hadronic calorimeter is assumed to be a modest sampling calorimeter but with very good granularity, such as lead/scintillator or steel/scintillator. The bulk of the jet energy is measured in the tracker and the EM calorimeter, and the hadron calorimeter must be very effi- cient in measuring neutral hadrons. Table I presents the major design goals for the calorimeter. The main focus of this paper is the electromagnetic calorime- ter. The most stringent energy resolution issue for the EM calorimeter is the suppression of the background to Higgs , primarily from . The issues for Higgs are different for an NLC Detector and an LHC Detec- tor. In the latter case this decay mode must provide the dis- covery, while at the NLC discovery will come easily with the prominent decay modes, and one is measuring the branching ratio of an established state, a qualitatively different task. Fig- ure 1 presents the expected dependence of the fractional error in on the EM calorimeter energy resolution[3]. The calorimeters studied and presented in this figure are (I) , (II) , (III) , and (IV) [3]. Some improve- ment on these numbers might result from constrained fits to the events. An integrated luminosity of 150 fb (three years of design luminosity) is assumed. Clearly there is an advantage to the best possible EM energy resolution. However, this ad- vantage must be evaluated in the context of the trade-offs with losses to other physics goals. The approach taken here is to op- timize the overall EM calorimeter performance, which includes resolution, but also other properties such as granularity needed for optimal jet resolution. A number of options for the EM calorimeter have been con- sidered. As described above we are searching for a technique which will give good energy resolution, with fast (few nanosec- ond) response, operating in a 4 Tesla magnetic field, with as compact a shower development as practical. The options con- sidered include crystals, silicon-tungsten sampling, lead (or