1. Status and Physics Programme of LHCf experiment Sergio Ricciarini for the LHCf collaboration Istituto Nazionale di Fisica Nucleare (INFN) Structure of Florence, Italy Workshop on “Diffractive and electromagnetic processes at LHC” ECT Trento - 5 January 2010

2. S. Ricciarini 2010-01-05 Summary 1. Physics motivations 2. LHCf experimental setup 3. LHCf physics performances 4. Preliminary results for 2009 operation 5. Future programme

3. 1. Physics motivations

4. S. Ricciarini 2010-01-05 The LHCf Collaboration USA LBNL Berkeley: W.C. Turner FRANCE Ecole Polytechnique Paris: M. Haguenauer SPAIN IFIC Valencia: A.Faus, J.Velasco ITALY Firenze University and INFN: O.Adriani, L.Bonechi, M.Bongi, G.Castellini, R.D’Alessandro, H. Menjo, P.Papini, S.Ricciarini, A.Viciani Catania University and INFN: A.Tricomi JAPAN STE Laboratory Nagoya University: K. Fukui, Y.Itow, T.Mase, K.Masuda, Y.Matsubara, H.Matsumoto, T.Sako, K.Taki Konan University Kobe: Y.Muraki University of Tokyo: Y.Shimizu Kanagawa University Yokohama: T.Tamura Waseda University: K.Kasahara, M.Mizuishi, S.Torii Shibaura Institute of Technology Saitama: K.Yoshida CERN: D. Macina, A.L. Perrot

5. S. Ricciarini 2010-01-05 LHCf: LHC “forward” experiment The smallest of the six LHC experiments. LHCf is fully dedicated to High Energy Cosmic Rays (HECR) Physics. Experimental observation of HECR (E > 10 14 eV) achieved only through Extensive Air Showers (EAS). LHCf will provide useful data to calibrate the hadronic interaction models used in Monte Carlo simulations of EAS. LHCf: Calibration of hadronic Monte Carlo used in HECR Physics with data collected at LHC

6. S. Ricciarini 2010-01-05 Hadronic Monte Carlo codes need tuning with beam-test data. In this forward region the highest energy measurements of π 0 production cross section were obtained by UA7 at SppS: E lab = 10 14 eV. For LHCf: √s = 14 TeV → E lab = 10 17 eV EAS: Extensive Air Showers Determination of E and M of HECR primary depends on comparison between Monte Carlo and experimental description of EAS. The dominant contribution to the energy flux is in the very forward region (  ≈ 0) and mainly depends on the first hadronic interaction.

7. S. Ricciarini 2010-01-05 Cosmic ray spectra at GZK cutoff GZK cutoff (1020 eV) would limit energy to 10 20 eV for protons, due to Cosmic Microwave Background p γ(2.7K) → Δ → N π Different results between different experiments. Agasa points toward super-GZK events (and therefore exotic physics). Based on data presented at the 30 th ICRC Merida (Mexico). Figure prepared by Y. Tokanatsu

8. S. Ricciarini 2010-01-05 Importance of Monte Carlo tuning Same data after arbitrarily scaling energy: AGASAx 0.9 HiResx 1.2 Yakutskx 0.75 Augerx 1.2 AGASA energy systematics 18% of which 10% from hadron interaction model (QGSJET, SYBILL) Berezinsky 2007

9. S. Ricciarini 2010-01-05 HECR composition The depth of the shower maximum X max in the atmosphere depends on energy and type of primary particle. Different hadronic interaction models give different answers about the composition of HECR. Unger, ECRS 2008

10. 2. LHCf experimental setup

11. S. Ricciarini 2010-01-05 LHCf experimental setup Two independent electromagnetic calorimeters equipped with different position sensitive layers, on both sides of IP1. Measure energy and impact point of γ from π 0 decays and neutrons from pp interaction with “very-forward” kinematics: pseudorapidity η > 8.4 or, equivalently, angle from beam axis θ < 450 μrad. 140 m n π0π0 γ γ ”Arm 1”: W absorber + scintillator layers. Scintillating fibers. ”Arm 2”: W absorber + scintillator layers. Silicon microstrips. ATLAS interaction point (IP1) 8 cm6 cm

12. S. Ricciarini 2010-01-05 LHCf experimental setup Each “arm” is installed in the “Total Absorber for Neutral particles” (TAN) 140 m away from IP 1. Here the beam pipe splits in 2 separate tubes. No background from charged particles, swept away by magnets (dipole D1). Charged particles Neutral particles IP 1 Protons - Beam 2 Protons - Beam 1 Arm 1 TAN Arm 1 (or 2) 9.6 cm

13. S. Ricciarini 2010-01-05 beam axis 4 cm 2 cm “Arm 1” detector 2 towers stacked vertically with 5 mm gap. Calorimeter: 17 W layers (7 mm or 14 mm thick); 16 scintillator layers (3 mm thick). Total thickness 22 cm: 44 X 0 1.7 λ I Tracking: 4 X-Y double layers of scintillating fiber (SciFi, 1mm cross-section) at 6, 10, 30, 42 X 0.

14. S. Ricciarini 2010-01-05 “Arm 2” detector Tracking: 4 X-Y double layers of Si microstrips (read-out pitch 160 μm) positioned at 6, 12, 30, 42 X 0. beam axis 3.2 cm 2.5 cm 2 towers stacked on their edges and offset from one another. Same structure of calorimetric layers as Arm 1.

15. S. Ricciarini 2010-01-05 Arm 2 assembly W layer scintillator and light guide Si microstrip sensor fiberglass pitch adapter front-end hybrid Si X Si Y (on opposite side)

16. S. Ricciarini 2010-01-05 Arm 2 assembly Si microstrip sensor scintillator layer (2 towers)

17. S. Ricciarini 2010-01-05 Assembled LHCf 9 cm 29 cm Arm 1 Arm 2

18. 3. LHCf physics performances

19. S. Ricciarini 2010-01-05 Arm 2: maximization of the acceptance in R (distance from beam center) Transverse projection in the TAN slot Dimensions in mm Arm 1: maximization of the acceptance for vertical beam crossing angle (it can be moved down by 2 cm) Both detectors are kept at +12 cm (“garage”) when beam is not stable, to minimize radiation damage of scintillators

20. S. Ricciarini 2010-01-05 140 0 Detectable kinematics for γ (Arm 1) detectable kinematics limited by the projection of dipole D1 vacuum pipe on the detector impact plane (first W layer) kinematics depend on beam vertical crossing angle at IP1 expected background (beam-gas/pipe) < 1%

21. S. Ricciarini 2010-01-05 Detector acceptance vs. γ impact point 0 rad beam crossing angle of the γ impact point of the incoming γ Effective geometrical acceptance depends on impact point on detector. Detectors can be moved up/down by few cm to efficiently cover the whole kinematic range allowed by D1 projection. Arm 1 Arm 2 Fraction of showers fully contained in the fiducial acceptance volume (2 mm cut on lateral tower edge) for 0μrad beam vertical crossing angle. It does not depend on energy.

22. S. Ricciarini 2010-01-05 Position resolution for EM shower σ X = 40 μmσ Y = 64 μm X position (mm) Y position (mm) number of events Position of shower centre on Arm 2 first Si module for 200 GeV electrons Similar results for Arm 1 first module (SciFi): σ ≈ 170 μm (with a design requirement < 200 μm) Measured at SPS beam test by using auxiliary tracking system (ADAMO) with few μm resolution

23. S. Ricciarini 2010-01-05 Position resolution for EM shower Measured position resolution improves with energy With impact point: - transverse momentum; - correction for lateral shower leakage (ρ Mol (W) = 9 mm). NOTE: correction is independent from energy. Measured energy before and after correction (SPS beam test data) Arm 2 (Si) fiducial volume MIP equivalent particles

24. S. Ricciarini 2010-01-05 Energy resolution for EM shower Measured at SPS beam test with electrons. Energy defined as sum of signals over all the scintillator layers, after applying fiducial volume cut and leakage correction. Excellent agreement between simulation and beam-test data for two different PMT gain settings. Resolution improves with energy. Linearity of read-out for all scintillator layers and different PMT gains was characterized with laser light up to 2x10 5 MIP equivalent particles.

25. S. Ricciarini 2010-01-05 Expected energy resolution for γ Simulation for Arm 1 inner (smaller) tower. Simulation validated with beam test as previously shown. 5 % only physics physics + PMT (L.G.) physics + PMT (H.G.) By using different PMT gains (to avoid saturation of read- out stages), resolution is better than 5% region of interest

26. S. Ricciarini 2010-01-05 Expected gamma energy spectrum on Arm 1 inner tower at beam centre particles/bin (arbitrary units) Model discrimination with γ Quantitative discrimination with the help of a properly defined χ 2 discriminating variable based on the spectrum shape. - Simulation of 10 6 LHC interactions (i.e. 1 minute exposure at 10 29 cm -2 s -1 luminosity) with 5% energy resolution (conservative). - Discrimination between various models is feasible.

27. S. Ricciarini 2010-01-05 Model discrimination with neutrons Expected neutron energy spectrum on Arm 1 inner tower at beam center Original n spectrum Given the limited depth (1.7 λ I ) only n interacting in the first half of the calorimeter can be efficiently characterized After introducing energy resolution particles/bin (arbitrary units) contamination from K 0

28. S. Ricciarini 2010-01-05 Model discrimination with π 0 Detector segmentation in two towers specifically designed for π 0 → γγ identification. Arm 1 in “normal” position Arm 1 moved down by 1 cm 10mm Lower Detectable kinematics can be improved by moving down the towers. gap between towers

29. S. Ricciarini 2010-01-05 Model discrimination with π 0 Simulated reconstructed spectrum after 20 min at 10 29 cm -2 s -1 is in good agreement with original spectrum (using DPMJETIII). Main systematic error comes from energy resolution (here assumed 5% conservatively).

30. S. Ricciarini 2010-01-05 Reconstructed π 0 mass Peak: 134 ± 5 MeV From simulation, expected mass resolution is better than 4%. Performance verified at SPS beam test (350 GeV proton beam on C target) with worse conditions than LHC: - low γ energy (20 to 50 GeV); - direct protons in the towers; - multiple hits in the same tower. π 0 mass [MeV] ≈ 250 π 0 events Powerful tool: - absolute energy calibration; - reject background from randomly correlated γ pairs. sigma: 8 MeV resolution: 6%

31. 4. Preliminary results for 2009 operation

32. S. Ricciarini 2010-01-05 LHCf 2009 operation From End of October 2009 LHC restarted operation. LHCf collected > 6000 shower events at 450+450 GeV in stable beam conditions with typically 4x4 or 5x5 bunch configuration. –effective running time ~ 1 day, peak luminosity at IP1 < 10 27 cm -2 s -1. To minimize radiation damage, LHCf is allowed to move to running position on beam axis from “garage” (+12 cm) only with stable beam. No stable beam at 1.2+1.2 TeV which means no data for LHCf at this energy for this year.

33. S. Ricciarini 2010-01-05 Arm 1 γ event in inner tower lateral profile SciFi X lateral profile SciFi Y longitudinal profile (inner tower) (outer tower)

34. S. Ricciarini 2010-01-05 Arm 2 γ event in inner tower longitudinal profile (inner tower) lateral profile Si microstrip X lateral profile Si microstrip Y

35. S. Ricciarini 2010-01-05 Arm 2 neutron event in inner tower longitudinal profile (inner tower)

36. S. Ricciarini 2010-01-05 γ/neutron discrimination Discrimination achieved with longitudinal profile. Here L(90%) and L(20%) expressed in X 0. L(90%) < 20 X 0 for most γ. photons neutrons Cut with 99% hadron rejection power (verified at beam test with protons)

37. S. Ricciarini 2010-01-05 Arm 1 preliminary γ plots Collision data are identified by coincidence with signal of “bunch crossing” at IP1. “Single bunch” data are background from beam- gas or beam-pipe interactions. Dipole D1 shadow affects only particles coming from IP1 dN/(dE*BC)

38. S. Ricciarini 2010-01-05 Arm 2 preliminary γ plots dN/(dE*BC) Different profiles of two data samples point out their different origin (IP1 collision or beam background).

39. 5. Future programme

40. S. Ricciarini 2010-01-05 LHCf future running scenario After LHC restarts in February 2010, LHCf will take data for 1.2+1.2 TeV and 3.5+3.5 TeV collisions. LHCf will be removed when luminosity becomes too high (>10 31 cm -2 s -1, with integrated luminosity 2 pb -1 ). LHCf will be reinstalled when beam energy reaches 5+5 TeV (end 2010). A second removal and a subsequent third installation are foreseen for 7+7 TeV collisions. Why remove LHCf? Its scintillator and SciFi layers are designed to run during beam commissioning (low luminosity).

41. S. Ricciarini 2010-01-05 Study of scintillator radiation damage scintillators and SciFi used in LHCf at 1 kGy light output is reduced by 20%

42. S. Ricciarini 2010-01-05 Luminosity and radiation damage Initial LHC schedule implied a fast, low-luminosity energy ramp up to 7+7 TeV, but now long high-luminosity runs at lower energies are scheduled. 1 kGy total absorbed dose is reached, with detectors in running position, with an integrated luminosity of 2 pb -1 for 3.5+3.5 TeV collisions. At 10 30 cm -2 s -1 this means ~ 1 month effective running time (but: with such luminosity, few hours are already sufficient to collect enough statistics). Garage position is used when beam not stable (dose is reduced by 10 3 ). Light output and transparency is continuously calibrated by sending laser pulses from ATLAS underground counting room (USA15) to the scintillator layers.

43. S. Ricciarini 2010-01-05 Improve LHCf radiation hardness A new detector concept is being prepared for the second LHCf installation. Plastic scintillator will be replaced by GSO (rad-hard). The order and number of silicon X-Y double layers will be changed to improve the energy measurement with the Si system and use it as cross-check for scintillator measurement. The new detector will be precisely calibrated with a dedicated beam test before installation.

44. S. Ricciarini 2010-01-05 (whole calorimeter) γ energy measurement with Si layers Showers from γ mostly develop in the first half of the detector, where currently there are 2 Si double layers (at 6 and 12 X 0 ).

45. S. Ricciarini 2010-01-05 Conclusions LHCf is an interesting link between High Energy Cosmic Rays and accelerator physics. LHCf is working very fine and already got its first data at LHC. With more statistics and increase of beam energy, as foreseen for the first months of 2010, it will be possible to publish the first spectra and begin discriminating among different Monte Carlo models.