Letter of Intent to CERN LHCC LHCC 2003-057/I-012 Rev

4 May 2004 Letter of Intent to CERN LHCC LHCC 2003-057/I-012 rev.

Measurement of Photons and Neutral Pions in the Very Forward Region of LHC

O. Adriani(1), A. Faus(2), M. Haguenauer(3), K. Kasahara(4), K. Masuda(5), Y. Matsubara(5), Y. Muraki(5), T. Sako(5), T. Tamura(6), S. Torii(6), W.C. Turner(7), J. Velasco(2) ( The LHCf collaboration (tentative) ) (1) INFN, Univ. di Firenze, Firenze, Italy (2) IFIC,Centro Mixto CSIC-UVEG, Valencia, Spain (3) Ecole-Polytechnique, Paris, France (4) Shibaura Institute of Technology, Saitama, Japan (5) STE laboratory, Nagoya University, Nagoya, Japan (6) Kanagawa University, Yokohama, Japan (7) LBNL, Berkeley, California, USA

Abstract An energy calibration experiment is proposed for ultra high energy cosmic ray experiments in the energy range between 1017eV and 1020eV. Small calorimeters will be located between the two beam pipes in the “Y vacuum chamber” 140m away from the interaction point of the Large Hadron Collider. Within an exposure time of a few hours at luminosity ≈1029 cm-2s-1, very important results will be obtained that will resolve long standing quests by the highest energy cosmic ray physics experiments.

1. Research Purpose

Knowledge of the energy distribution of particles emitted in the very forward region is absolutely necessary for understanding cosmic ray phenomena. So far only one experiment has obtained data in the energy region exceeding 10 14 eV; the CERN UA7 collaboration at 2x1014 eV. This experiment observed the energy distribution of photons and neutral pions in the rapidity range of y=5-7 [1].

A very interesting result has recently been reported by the AGASA cosmic ray experiment [2] that observed a considerable number of gigantic air showers in the energy region greater than 1020 eV (Fig. 1). It is quite difficult to confine cosmic ray protons with energies greater than 6x1019eV in our own Galaxy. Even if we assume the existence of a magnetic field of 3 x 10 -6 gauss in the halo of the Milky Way Galaxy, protons with energy over 6 x 1019eV escape from the halo which extends to a radius of 23kpc (Fig. 2). Furthermore the arrival directions of the highest energy cosmic rays do not correspond to any known celestial bodies. There is also difficulty attributing the origin of these highest energy cosmic rays to extra-galactic objects like Active Galactic Nuclei (AGN). Extragalactic protons of this extreme energy are not expected to arrive at the Earth due to photo-nuclear interactions with 2.7K photons by the 3-3 resonance interaction process (formation of Δ (1232) baryons). This is called the Greisen-Zatsepin-Kuzumin (GZK) cut-off. It is also difficult for extreme energy extragalactic particles other than protons to reach the Earth. Within the present scheme of physics, it is very hard to conceive of the source or the origin of such high-energy particles by a bottom-up scenario.

Therefore, the existence of the events above the GZK cut-off (super GZK events) must be explained by a top-down scenario invoking new physics such as the decay of cosmic strings,

Z0 burst etc. [3] or by some yet unknown scenario. Within top down scenarios, a hypothesis is involved that Lorentz invariance might be violated [4]. On the basis of this situation it seems that detailed study of super GZK cosmic rays may lead to a break-through in the fields of fundamental particle physics and astrophysics. On the other hand the Fly’s- eye group of Utah has reported observation of a cosmic ray energy spectrum that is consistent with the GZK cut-off [5],[6] (Fig. 3).

At present, we cannot draw a definite conclusion on which result of the Fly’s eye and AGASA groups is correct. In view of this fact, new air shower projects - Auger [7] and TA [8] - are being started and the EUSO project is under consideration [9]. These groups use quite different experimental methods, each of which has advantages and drawbacks. Many of the experimental procedures for deriving the energy spectrum depend strongly on the model of nuclear interactions that is used in Monte Carlo simulations of the air showers. Therefore, in order to calibrate the nuclear interaction models in the Monte Carlo codes we think it is very important to establish the energy spectrum of particles emitted in the very forward region (which is effective for air shower development) at an energy much higher than the UA7 case. Since the laboratory equivalent energy of LHC is 10 17eV, the calibration of Monte Carlo codes at such a high energy will give a firm base to explore the GZK problem. We will demonstrate this in more detail with Monte Carlo simulations later in this proposal.

Furthermore it is very important to establish the particle composition of cosmic rays in the energy range between 1017eV and 2x1019eV. According to the experimental results observed by the Utah Fly’s eye detector, the depth of the shower maximum varies from 600g/cm 2 to 800g/cm2 in the energy range between 1017eV and 2x1019eV. When we compare these experimental results with a Monte Carlo calculation based on the QGS (Quark Gluon plasma Shower) jet model, the composition must be changed from iron dominant to proton dominant in the components with energies. However when we compare those results with the prediction by the DPM jet model, the composition of cosmic rays must not change in the energy range mentioned above (Fig. 4) [10]. Therefore the correct knowledge of the forward region is very important to produce a definite scientific result on the composition of cosmic rays.

Since the predominant energy flow in cosmic ray showers is in the very forward direction it is much more important to have knowledge of particles emitted near θ = 0 than to have knowledge of high transverse momentum jets near θ*= 90 degrees in the center of momentum frame for which ATLAS and CMS have been optimized. Filling this physics gap in the very forward direction is another very important purpose of the proposed experiment. We propose to install a small scintillating fiber imaging calorimeter at a forward location 140m from the colliding beam intersection, for example, in the ATLAS intersection region. The final choice of intersection, however, will be determined after discussion with LHC machine people. We will be able to identify neutral pions by measuring individual photon energy (> 100 GeV), incident position and the two-photon invariant mass distribution that shows a clear peak at the neutral pion mass. Our proposal is described in the following sessions.

2. Experimental Method

We propose to install a small electromagnetic shower detector in the forward direction 140m from the interaction point. At this location, there is a neutral absorber (TAN) containing a single large diameter beam pipe separated into two small beam pipes as shown in Fig. 5. Copper bar absorbers and a luminosity monitor are located in the space between the small beam pipes (Fig. 6). The dimensions of the space between beam pipes are: 96mm in wide, 190mm in height, and 1011mm in length (Fig. 7). The luminosity monitor will be located behind two or three of the 100mm long copper bars so the monitor is located near the shower maximum of high energy neutrons from the colliding beam intersection.

We propose to install a 54 radiation length (r.l.) tungsten shower calorimeter in place of three of the copper bars in front of the luminosity monitor. The width of the space between the two small beam pipes is 96 mm as described above. The maximum size of the calorimeter that we want to install there is 90 mm (width) x 355 mm (height) x 290 mm (length). (Note; since the copper bars are each 100mm in length it is desirable to make the length of the calorimeter equal to an integer number of these Cu bars) The calorimeter will be located between the two beam pipes as indicated Fig. 8. The height of the calorimeter can be adjusted by a remote manipulator.

When the calorimeter is installed it will take the place of three copper bars at the front of the TAN instrumentation slot. The calorimeter would then be followed the luminosity monitor, which occupies the length of one copper bar. Six copper bars would then be installed behind the luminosity monitor to fill up the remainder of the TAN instrumentation slot. The number of nuclear interaction lengths of the calorimeter and the three copper bars which it replaces when inserted are nearly equal (to 2.0 nuclear interaction lengths). Consequently the performance of the luminosity monitor would not be strongly influenced by the interchange of calorimeter and copper bars.

The calorimeter is composed of 3 separate calorimeters with a tower structure, with each calorimeter having dimensions 2cm x 2cm x 28cm, 3cm x 3cm x 28cm and 4cm x 4cm x 28cm respectively (Fig. 9). The calorimeters will be mounted on a special aluminum support frame as shown in Fig. 10. The calorimeter is composed of tungsten plates, each plate having a thickness of 1 r.l.. Total weight of the calorimeter is expected to be 15kg. The total thickness is 54 r.l., including one r.l. projected thickness for the Cu beam tube. This length is sufficient to accurately measure the photon energy up to few TeV. A typical shower curve which will be expected to develop in the calorimeter is given in Fig. 11. Our Monte Carlo calculation shows that the energy of showers can be obtained with an accuracy of +/-2.8% for the photons with energy 1 TeV in case that the center of shower hits inside 1.5mm from the edge of the calorimeter. The results are shown in Fig. 12 (See also Fig. 22).

To identify the position of a single photon or to resolve the positions of multiple photons, x and y detectors are prepared, each of which consists of a 1 mm x 1 mm square scintillating fiber (SciFi). Signals from SciFi are read out by using multi-anode (=64) photomultipliers (MAPMT), Hamamatsu H7546. The quantum efficiency of H7546 photomultipliers is 20%. The SciFi detectors are installed at depths of 8, 10, and 38 r.l.. The total number of fibers will be 512 which will require 8 MAPMTs. Signals from the MAPMTs are sent to a front-end circuit (FEC) (Fig. 13), including analog ASIC (VA32HDR14), FPGA and 16 bits ADC (Fig. 14). The Viking read-out system,VA32HDR14, has been developed to optimize the signals from the MAPMTs and the linearity is guaranteed up to 19 pC which corresponds to about 2000 MIPs. The FEC is necessary to sample and hold the input analog signal for 1.9 μs, while the analog signal is held, the pulse height will be measured by a 16bit ADC. A data taking rate up to - 3kHz is possible with the system described. . The space above the detector is open so the detector can be installed from above by a small remote manipulator similar to the ones used for Roman pots.

Thin plastic scintillator plates (0.3 cm in thickness) will also be installed at every 2-4 r.l. for triggering and for measuring the total deposited energy. The trigger signal will be derived by using these plate scintillators within a 100ns delay time after arrival of shower signal. The signal of the plastic scintillators will be read out by the small photomultipliers, Hamamatsu R1635 (Fig. 10 shows H3164-10 phototubes) which have a quantum efficiency of 25%. The photomultipliers have a dynamic range between 1 to 1000 particles (MIPs) and the pulse height will be measured by using normal CAMAC ADCs. (LeCroy 2249W) The photomultipliers will be set on a plate located 190mm from the bottom of the aluminum frame and high voltage will be supplied by using E1761 sockets for each photomultiplier. In actual operation, after calibration of the energy deposited by a single MIP, the high voltage for the photomultipliers will be reduced from 900V to 500V. Then they can measure up to fifty thousand MIPs in the plastic scintillator. This corresponds to the number of electrons produced at the shower maximum of a 5 TeV photon. (see Fig. 11a, multiply the shower curve for 1TeV by five). The calibration of the gain of the photomultipliers is a very important task for this experiment. We will prepare a laser calibration system for this calibration. A short laser pulse with a typical duration of 10ns will be created and the light will be separately sent to each photomultiplier by the optical fiber, after passing through a shutter- filter system with the attenuation of the light intensity by 1 (0dB), 1/10 (20db) , 1/100 (40db) and 1/1000 (60db) times. Those four different intensities of the light will be read out under normal voltage (900V) where we can see the peak of the energy deposited by a single MIP and under lower voltage (500V) where we can measure the light produced by 50,000 MIPs.

3. The Beam Condition, Exposure Time and Radiation Damage

To avoid the possibility of photons from multiple pp collisions entering the calorimeter during a single bunch crossing it is desirable to operate the LHC at luminosity less than 1x1030/cm2sec. The expected collision rate should be one event per every ~10 microseconds. (one interaction of any kind every 10 microsec ) Since the ADCs for the multi-anode photomultipliers convert every charge entering within 10 microseconds, we prefer to put ≤ 10 approximately equally spaced bunches in the machine with ~2x1010 protons in each beam bunch. Under these conditions we expect the beam spread to be ≥ 60-80 microns (in r.m.s. radius). (Note : we shall develop in 2004-2005 years, a new ASIC which has an analogue gate of 100ns. )

Assuming the beam conditions described above have been achieved, the detector will be installed with the middle calorimeter positioned on the expected center of the photon flux from pp interactions (assuming zero crossing angle). We will then take data to establish where the center of the photon flux appears on the SciFi arrays. If everything goes well this will be finished in ten seconds. Of course it will take longer than this to understand the data and we also wish to repeat this procedure a few times, moving the calorimeter array vertically with the remote manipulator until we are satisfied that the calorimeters are operating properly.

Next we will fix the vertical position of the calorimeter and start the taking data. According to our Monte Carlo calculations, we need only 10 seconds to obtain the two photon invariant mass peak of the neutral pions with luminosity L≈ 10 30 /cm2sec. However under the L≈ 1029 /cm2sec, we need 100 seconds as the data-taking time. Since we would like to measure the energy spectrum of the photons as a function of transverse position by changing the position of the calorimeter, probably 20 minutes net exposure time is necessary. These data taking times are undoubtedly shorter than the time needed for on-line verification of the quality of the data. So probably we need a few hours to be sure we have obtained good quality data.

Finally we would like to discuss the possibility of radiation damage to this detector. Radiation damage characteristics for the silicon detector [11], the optical fiber [12], and the plastic scintillator in the calorimeter [13] have been reported. Typical radiation dose values given are 2x1014 MIPs in the silicon detector and 10kGy for the plastic scintillators. If the radiation doses exceed the above values, the detectors do not show their proper character. The 10kGy corresponds to an energy deposition in the material of 108 erg /g. A minimum ionizing particle will loose 10-6 erg in scintillator with 3mm thickness, which corresponds to the thickness of present calorimeter. Since the density of plastic scintillator is ~ 1g/cm3, up to 1014 MIPs in 3.3cm2 area of the detector, or 3.0x1013 MIPs/cm2 will not cause any remarkable damage. For the luminosity 1030 cm-2 s-1, 105 MIPs will pass through the scintillators per second per cm2. This means that 1010 particles per day will pass through 1cm2 of the detector. The detector would not suffer any remarkable radiation damage for up to 3000 days operation which is orders of magnitude longer than we envision the calorimeter being installed. Furthermore during the early running of LHC, the luminosity will be even less, 5X1028 -1029 /cm2/sec [14]. It is clear that radiation damage is not an issue for our calorimeter.

4. Some Results from Monte Carlo Calculations

4.A The importance of measurement of production cross sections for interpretation of cosmic ray air shower experiments

. We introduce some results that are expected to be obtained from the proposed experiment and indicate how they will be useful for interpretation of cosmic ray shower experiments. These results have been obtained by Monte Carlo calculations. In Fig.15, we represent how important it is to measure the very forward region. The simulation has been done using the dpmjet model 3 which includes pythia and phojet. The Monte Carlo simulation has been done 17 for showers with an inclination angle 60 degrees and for incident energy E 0 = 10 eV. The bottom curve of Fig 15 shows the shower development contributed by pions and kaons emitted in a region of X < 0.1 and the middle curve represents the shower curve produced by photons emitted in a region of X < 0.05. The top curve is the shower curve without neglecting any components of the shower. From this graph you can understand the importance of the contribution of particles with large values of the Feynman variable X for total shower development.

For the next step, we artificially change the Monte Carlo generator in the region of X= 0.01-1.0. Of course the generator has been built to obey energy conservation. As shown in Fig. 16, the type A production cross-section deposits its energy in the deeper region of the atmosphere, while the type B cross-section leads to the early development of showers. If we do not know the production cross-section in the very forward region, we shall misunderstand an incident proton incident for curve A and an incident iron nucleus for curve B. Therefore the establishment of the very forward cross-section is very important. In Fig. 17a, we present the results of simulation with a more realistic cross-section model which could be obtained by actual experiments. In other words, Fig. 17a represents the differential cross- section possibly obtained by the proposed experiment. Fig. 17b is the same but for neutral pions. Fig. 17c shows that our experiment will be able to distinguish clearly production models presented by curve A and curve B in Fig. 16 for neutrons. Fig. 15 indicates another very important factor for us. If we measure giant air-showers at an altitude of 900 g/cm2, we can misidentify the energy of the showers by a factor of 1.75 due to the difference between type A and B production cross sections. This possibility may resolve the debate between the AGASA and Utah Fly’s Eye groups which has been shown in Fig. 3(b).

4.B Detection efficiency

Now we will discuss Monte Carlo simulation results of the detection efficiency of gamma

rays and neutral pions. Fig. 18 represents an Eγ-PTγ plot of photons. The photons which fall in the area under the curve can be detected. From this curve you can understand almost all photons with energy higher than 1 TeV can be detected by this experiment, however if we

shift our calorimeter in the vertical direction in order to detect higher PTγ, the region of high

detection efficiency can be extended to lower energy. The photon PTγ spectrum is shown in

Fig. 19 for various ranges of Eγ. Again for high energy photons with Eγ > 2 TeV, photons emitted in a wide range of the PTγ can be detected. Fig. 20 shows that 78% of photons emitted in the kinematical region with Feynman X = 0.1 and PTγ < 0.5 GeV/c can in principle be detected by the present detector. Similarly for X = 0.2 93% of the photons with PT < 1

GeV/c can be detected. Half of the photons emitted in the region of PTγ< 0. 25 GeV/c with an

energy XF=0.05 can be detected by present calorimeter. The real efficiency of photons must take account of the geometrical factor and this factor is estimated to be about 10%. This value of the geometrical factor of the detector depends strongly on where we position the beam center. The results of Monte Carlo calculations of the geometrical factor of present detector are shown in Fig. 21.

4.C Energy resolution

Next we describe the energy resolution of the present shower counter. In order to avoid background from low energy photons, if we count only the energy deposited beyond 6 r.l. or 8 r.l., the energy resolution of the shower counter will be 6.3% and 13.8 % for 100 GeV photons and 2.8% and 5.6% for 1 TeV photons respectively (Fig. 22). The calibration of the absolute value of the energy can be made by using the neutral pion peak as shown in Fig. 23. Since we are going to install geometrically small calorimeters, the leakage of shower particles from the sides must be taken into account. According to our Monte Carlo calculations, we can neglect leakage when the shower center is more than 1.5 mm inside the sides.

4.D Position resolution and Neutron detection

According to the Monte Carlo calculations, the position resolution will be 160 microns for photons with energy 2 TeV and 170 microns for neutrons with energy 1 TeV. It is interesting that we could identify the neutron energy from the shape of the cascade shower as shown in Fig. 24. We will have a possibility to detect an important quantity, the inelasticity K, by this experiment. We have obtained the position resolution by selecting three highest points of energy deposition and used them to obtain the center of deposited energy.

4.E Removal of two-photons

Finally we will discuss how two photons entering the same shower calorimeter are removed from the data. As shown in Fig 25, we could not avoid the double entrance of photons in a single calorimeter. The possibility that two photons enter a single calorimeter is around 20% of the total number of events. We propose to remove such events from the data analysis. Of course we are also considering installation of one layer of u-chamber in actual experiment. This will help to separate the multi-hit showers in a calorimeter. A large fraction of the two-photon events comes from neutron contamination and we can discriminate against them by the signals in the rear part of the calorimeters. Also multi-track position information from the SciFi counters may be used to identify development of more than one shower in a calorimeter.

4.F A test of the Landau-Pomeranchuk-Migdal effect

Here we would like to point out briefly that we can check the famous Landau- Pomeranchuk-Migdal effect by this experiment. When the photon energy becomes very high, the radiation length must be extended from the usual value. This was pointed out by Landau-Migdal-Pomeranchuk. As shown in Fig. 26, for photons with energy higher than 1 TeV, the effect will be clearly observed by an increase in the shower depth.

4.G An experiment on nucleus-nucleus collisions At the LHC, it is expected to operate with heavy ions and observe nucleus-nucleus collisions. Since nuclei as well as protons are involved in cosmic rays we would like to install our detector during heavy ion operation as well.

5. Preparation up to the Present

1) A SciFi imaging calorimeter with an image intensifier for read-out has been tested using CERN SPS beams. Data demonstrating e/p separation, energy resolution and position resolution have been obtained. The imaging calorimeter has been applied to observe cosmic ray primary electrons above 10GeV in balloon flight experiments [15]. It has also been used to observe atmospheric gamma rays above 5 GeV to calibrate Monte Carlo calculations for the atmospheric neutrino effect observed by the Super- Kamiokande group [16]

2) We have tested the SciFi-MAPMT read-out system up to 512 channels with 1 ADC in 2002 using the CERN SPS electron and proton beams up to 200 GeV [17]. In 2003, we upgraded the system so that a more realistic calorimeter test is possible and exposed the detector to the CERN SPS electron and proton beams up to 150 GeV. A new front-end system (model VA32HDR14) will include 1 ADC for 1 Viking chip so that faster data acquisition (> 3 kHz) is possible.

3) Monte Carlo calculations show that an energy resolution better than 6% and position resolution better than 0.2mm are expected to be attained. This will enable us to construct two-photon invariant mass distribution in which we can see a clear peak of neutral pions, when each photon hits a different tower calorimeter. Using this peak, we can calibrate our system and thus derive reliable photon and π0 energy distributions. In some events, it may be impossible to resolve two individual photons but such a case is estimated to be less than 20% of total events

4) Our UA7 experience tells us that x, y and u directional deployment of SciFi will enables us to resolve individual photons and determine their energy. The energy and position resolution needed to establish the peak of neutral pions in the photon invariant mass distribution can be obtained with this deployment (For single photons, the energy resolution at 100 GeV is ~ 5 %, therefore getting an energy resolution of 15 % for multiple photons is considered to be reasonable).

6.Budget, Schedule, Beam Conditions

The proto-type detector will be completed in Japan by the end of 2004 using a Grant-in-Aid of Ministry of Science and Education of Japan. During this period, we will also test the new read-out system at CERN SPS beams. If the LHCC approves our proposal, the additional budget possibly needed to improve the detector will be approved immediately. The final detector will be shipped to CERN in 2005 for exposure to the test beam either in North or West Areas of CERN in 2006. The European collaborators will prepare an installation system in the beam line and a shutter system possibly needed to avoid unnecessary radiation before the beam tests. The experiment will be ready for data-taking at the beginning of LHC operation in 2007.

We require that the LHC operate with luminosity less than L=10 30 /cm2s ( L= 1029 is preferable). We prefer low luminosity operation and with high beta. If the luminosity is less than 1030/cm2s, there will be no pile up in our detector although the trigger rate is much less than the actual event rate. Also we don’t expect any radiation damage during our experimental period that we expect to last the order of 1 week. If everything goes well a few hours recording data is enough for our purposes, however we require that we can expose three times in the beam region although each exposure time is short. The average event rate with photon energy greater than 100 GeV is expected roughly to be <1 per bunch crossing.

During the experiment many postgraduate course students from Japan will join and cover the shifts in addition to the present researchers.

References

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Fig. 1 Energy spectrum of cosmic rays. The spectrum continues over 1020eV without showing any bending. The maximum proton energy confined by the Milky Way Galaxy is 6x1019eV. Compilation by S. Swordy. Fig. 2 A schematic view of the trajectory for highest energy cosmic rays in our Galaxy. Even the magnetic field does exist at the halo of our Galaxy, cosmic rays with an energy over 6x1019eV will flow out. Fig. 3a The energy spectra of cosmic rays at highest energies. Blue triangles represent AGASA shower counter. Red and black symbols represent Fly’s eye data taken at Utah by the observation of fluorescent light. A clear discrepancy can be seen for energy exceeding 1020eV.

3b The same energy spectra as Fig. 3a but multiplied by E3. In case the absolute value of Akeno data (red circle) is shifted 15% lower in energy, HiResI data (blue square) coincide with AGASA data very well. Crosses correspond to simulation data. One of the main purposes of this experiment is to calibrate the absolute value of the highest energy cosmic ray experiments using the LHC beam. So present experiment may be called as an energy calibration experiment of Auger, TA and EUSO projects. The graph has been cited from a paper by D. De. Marco et al., Proceed. 28th ICRC, Vol. 2 (2003) 655. Fig. 4 The depth of the shower maximum in units of g/cm2 is shown as a function of the shower energy. The simulations predict that for a given energy iron dominated showers have short depth and proton dominated showers have long depth. There are significant variations amongst the simulations that need to be resolved in order to infer the shower composition from the experimental data. Resolving these variations is one of the main purposes of the proposed LHC experiment. Fig. 5 The “Y” beam tube vacuum chamber 140m from the interaction point. The “Y” chamber makes the transition from a single beam tube in the interaction region to two beam tubes in the arcs of the LHC. Fig. 6 Some details of the shielding around the “Y” vacuum chamber showing the slot in the shielding that has been allowed for instrumentation. Fig. 7 A more detailed drawing of the instrumentation region in the TAN. The space between beam pipes is 96mm wide and 1011mm long. Fig. 8 The calorimeter will be located between two beam pipes. Fig. 9 A schematic view of the tower calorimeter. It will be composed of three individual diamond shaped calorimeters in a vertical stack. Fig. 10 The three calorimeters are supported by the aluminum frame and the photomultipliers are mounted inside the aluminum frame in the positions shown in the right side drawing. Fig. 11 a. The shower transition curve for 100 GeV and 1 TeV photons.

11 b. W represents a tungsten plate, Scin corresponds to a 3mm thick scintillator and SciFi means a scintillation fiber detector for determining the center of the showers.

Fig. 12 If photons enter inside 1.5mm from the corner of the shower counter, the energy of photons can be reproduced.

Fig. 13 Schematic diagram of the FEC (front end card) and DAQ. Fig. 14 The read-out system. FPGA : th Field Programmable Gate Array. 19 Fig. 15 The transition curve of proton showers expected by dpmjet 3 model for E 0=5x10 eV. ‘No cut’ means without cutting any kinds of particles, while γ : x < 0.05 means showers created by only particles less than x < 0.05 and , π, K : x<0.1 represents particles created by the pion and kaons with Feynman variable x < 0.1. Fig. 16 On the top two different types of production models of secondary particles are presented as functions of the Feynman variable X in the center of mass. On the bottom the numbers of shower electrons and positrons as functions of shower depth are shown for these two models. Proton energy is 1017 eV in the lab frame. At 900 g/cm2, the number of particles differs about 1.75 times. Fig. 17 The energy spectrum which will be actually obtained by this detector. The number of vertical axis represents the number of events which will be detected in each energy bin per one interaction. It depends on the beam center and the detector will be shifted vertically during the exposure time, however in case when we fix the position of the calorimeter, an energy distribution of the photons will be obtained. To reproduce the original production cross-section, a geomrtrical correction factor will be applied.

Fig. 18 The Eγ -Ptγ diagram. High energy photons with small Ptγ can be recorded by present shower counter. The red curve comes from a geometrical cut for our calorimeter arising from the configuration of the beam pipe and magnet.

Fig. 19 The Ptγ spectrum of photons is presented as a function of Eγ.

Fig. 20 The energy spectrum of photons is shown as a function of P tγ. 78% means that

photons emitted in the phase space with Ptγ < 0.5 GeV/c and Feynman X = 0.1, 78% of showers can be sensed by this detector in principle (without taking account of geometrical factor).

Fig. 21 The geometrical correction factor for various positions of the calorimeter to the beam center,

Fig. 22 Energy resolution of shower calorimeter. At 1TeV, the value turns out to be 2.8%. The top graph shows the number of total particles deposited in the calorimeter deeper than the radiation length 6. The total number of electrons amounts to 50,000 at 1 TeV. Fig. 23 The invariant mass distribution for two photons expected by present experiment. Red line represents when we are taking account of the experimental errors and green curve shows when we have taken account of double hits in one calorimeter. A clear peak of neutral pions is expected by the MC. Fig. 24 The transition curve of the showers expected for photons (black) and neutrons (red). Vertical axis represents the number of particles while the horizontal axis corresponds to the depth of the calorimeters. If we take account of the last layer information, we can separate photons from neutrons. Fig. 25 The numbers of showers having a given energy contamination due to multiple photon hits in a single calorimeter. The fraction of all events with 5% or greater contamination is ~20% and most contamination comes from low energy photons with energy less than 20 GeV. Fig. 26 The effect of Landau-Pomeranchuk-Migdal effect can be seen clearly in This experiment for the photons with energy higher than 1 TeV.