1. ATLAS LHCf Detector 140m away from the interaction point LHCf: calibration of hadron interaction models for high energy cosmic-ray physics at the LHC energy T. Mase for the LHCf collaboration, Nagoya University, STEL The left figure shows a measurement of the energy spectrum of primary cosmic rays [1]. But the absolute energy scale doesn't agree with each experiments. It is partially comes from the hadron interaction model which is used in the air shower simulation. On 2. Physics of the LHCf experiment 3. Experimental Overview 4. Discrimination of the hadron interaction models 5. The Plan LHCf is one of the six LHC experiments that will measure the neutral particles emitted in the forward region of the LHC [2][3]. LHCf will measure the energy and transverse momentum of gamma-rays, neutral pions and neutrons in the forward region (pseudo- rapidity  > 8.4). 14TeV collision corresponds to 10x10 17 eV for laboratory system. The LHCf detectors consist of two calorimeters and are located at both side of the IP. LHCf will take data up to 2pb -1 at 7TeV collisions. The detectors will be removed and upgraded for higher energy measurements. The right figures show the expected energy spectra of gamma- rays at 14TeV collision. The models are DPMJET3, QGSJET and SYBILL. Depending on the hadron interaction model used the energy spectra change significantly. The left figure shows the reconstructed  0 spectra (for DPMJET3), and simulation histograms by each model. The bottom table shows the  2 between the reconstructed spectra and expected spectra by each model. The model was discriminated significantly. The plan of the LHC accelerator and LHCf is 2009 Nov -Beam Commissioning 2009 Dec -0.7TeV and 2.2TeV collision 2010 Feb -7TeV and 10TeV collision, detector upgrade 2011 14TeV collision We can take data for various energy and discriminate the hadron interaction models. LHCf will measure the energy and transverse momentum of neutral particles produced in the forward region of the LHC interaction point. In high energy cosmic ray measurements, the results strongly depends on the hadron interaction model which is used in the air shower simulation. LHCf will take data at = 0.7, 2.2, 7, 10 and 14TeV collisions at LHC and provide crucial calibration points for the hadron interaction models. Abstract  ray energy spectrum  0 energy spectrum [1] Engel, Nuclear Phys. B (Proc. Suppl.) 151 (2006) 437-461 [2] LHCf Technical Design Report, CERN-LHCC-2006-004 [3] O.Adriani, et al., JINST, 3 (2008) S08006 1. Air shower simulation and hadron interaction model When the cosmic ray comes from the Universe, the primary particle hits the atmospheric molecule and creates a lot of secondary particles. The air shower is developed through the hadron interaction and electromagnetic cascade. The air shower experiment measure the secondary particles on the ground. To know the primary particle information(energy or composition etc.), the air shower is reconstructed by the simulation. the other hand, a consistent understanding of the chemical composition and the arrival direction has not been achieve. One of the major sources of this problem is the uncertainty in hadron interactions when the properties of primary cosmic rays are derived from the air shower data. LHCf will take data from this year by various energies up to 7TeV. The LHCf detectors, compact imaging calorimeter, are ready for data taking. The results will provide invaluable inputs to the many air-shower Monte Carlo codes currently used for modeling cosmic ray interactions in the Earth's atmosphere. Summary Reference 22 Prob. DPMJET311.50.83 QGSJET-II224.9<10 -20 SIBYLL49.16x10 -5 Arm#1 Arm#2 model discrimination GZK cut off