1. LHCf: a LHC Detector for Astroparticle Physics LHCf: a LHC Detector for Astroparticle Physics Lorenzo Bonechi on behalf of the LHCf Collaboration * University of Florence and INFN LHCf is the smallest one of the six official LHC experiments. It will be installed on the LHC accelerator ring near the ATLAS experiment region. The aim of this experiment is the study at the LHC accelerator of the neutral-particle production cross sections in the very forward region of proton-proton and nucleus-nucleus interactions. Neutral pions, gammas and neutrons production will be investigated during the initial phase of the LHC running, at low luminosity (below 10 30 cm -2 s -1 ). This study will give important information for understanding the development of atmospheric showers induced by very high energy cosmic rays hitting the Earth atmosphere. Methods which are used to extract information about primary cosmic-ray radiation by means of atmospheric-shower experiments data, depend on the interaction model which is considered in shower simulations. Using the statistics which can be accumulated in a few hours running, LHCf will be able to check the validity of several interaction model’s predictions in proton-proton interaction at an equivalent energy of 10 17 ev in the laboratory frame. Kinematical region accessed by the experiment can be improved during non-zero beam crossing angle runs and by moving the LHCf detectors in the vertical direction. In particular two main problems can be addressed by LHCf results at this energy: the first is the uncertainty of cosmic-ray spectrum composition between 10 15 eV and 10 19 eV; the latter is the interpretation of data around and beyond 10 20 eV on the basis of GZK cutoff. Both these items are crucial for understanding the origin of cosmic rays. Simulation results: neutron energy spectrum as reconstructed on the Arm #1 20×20 mm 2 calorimeter centered on the beam line; 30% energy resolution over all energy range has been taken into account. Predictions of different models are well separated! Scientific objectives of the experiment Details on the LHCf detectors Method and location at LHC * http://greybook.cern.ch/programmes/experiments/LHCF.html Simulation results: gamma energy spectrum as measured with the Arm #1 20×20 mm 2 calorimeter, supposing it is centered on the beam line. 5% energy resolution over all energy range has been taken into account. Results can be improved by moving the detector in the vertical direction (only allowed direction) in such a way to cover a wider kinematical region. LHCf collaboration will install two similar detectors (for redundancy and background rejection) near Interaction Point 1 (IP1 - ATLAS region). The study of neutral pions requires the detector to be able identifying both the two gamma particles coming from pion decay. For this purpose each of the two LHCf detectors (Arm #1 and Arm #2) has two independent calorimeters made of tungsten absorber layers (total depth is 44 X 0 or 1.6 I ), 16 scintillator layers (3mm thick) and 4 tracking planes; it allows the measurement of the shower energy releases and the reconstruction of impact points of incoming particle. Arm #1 and Arm #2, differ in tracking system, made of scintillating fibers for Arm #1 and microstrip silicon sensors for Arm #2, and geometry, optimized to cover the greatest kinematical regions in different working scenarios. The two detectors will be installed 140m far from the interaction point on both sided of ATLAS, inside the TAN neutral particle absorbers where the single beam pipe coming from IP1 splits into two separate pipes. They will be positioned on the beam line and will cover, in normal running, the rapidity range beyond 3.7 ATLAS Underground (IP1) LHCf Arm #2 on IP2 side LHCf Arm #1 on IP8 side TAN slot detail: a 9.6cm (w) x 100cm (l) x 60cm (h) slot, designed to house 10 copper bars as absorber, allows positioning of detectors between the two beam pipes; LHCf will replace first 3 bars (total length = 30cm) Photo of TAN absorber taken before installation in LHC tunnel Arm #2 detector inside TAN slot Preliminary installation of Arm #2 detector and electronic box in TAN (April/May, 2007) Box for silicon tracker read-out electronics Recombination chamber is the Region where the single beam pipe from IP turns in two independent pipes Geometry: “towers” are vertically aligned and detector can be remotely moved up and down to improve accessible kinematical region Transverse sizes of calimeter towers: 20×20 and 40×40 mm 2 Tracking layers made of scintillating fibers at 6, 10, 30, 42 X 0 Geometry: “towers” are diagonally aligned to maximize accessible kinematical region without moving the detector Transverse sizes of towers: 25×25 and 32×32 mm 2 Microstrip silicon tracking layers at 6, 12, 30, 42 X 0 SILICON TRACKER PLANE Front-end electronics: high dynamic range PACE3 chip from CMS pre-shower detector Hamamatsu microstrip sensor from ATLAS SCT barrel: 6×6 cm 2 wafer; 768 microstrips; 80  m implantation pitch; 160  m read-out pitch 8 silicon layers are used (4 X-view and 4-Y-view) for impact point reconstruction G10 green frames contain calorimeter parts while black Delrin boxes contain microstrip silicon layers Arm #1Arm #2 SCINTILLATING FIBRES PLANE 1×1mm 2 square scintillating fibres measuring shower lateral development Orthogonal tracking planes for impact point reconstruction Hamamatsu H7546 multi-anode PMTs (MAPMTs) Fibres from tracking layers exit with 45° angle with respect to the vertical direction and are pulled to MAPMTs on top of detector Bundle of fibres connected to multi-anode photomultiplier Hamamatsu H7546 Arm #1 normal position is with beam centred on small calorimetric tower ARM #1 detector has been completed in July 2006 and preliminary installed and tested at CERN in January 2007 ARM #2 detector has been completed in April 2007 in Florence INFN laboratories TANs are massive absorbers which are used to stop neutral particles coming from IPs in the forward directions, protecting cryomagnets from interaction debries