Recent results on neutral particles spectra from the LHCf experiment

1. 13th ICATPP Conference on Astroparticle, Particle, Space Physics and Detectors for Physics Applications Villa Olmo - Como, Oct 3rd – 7th, 2011 Recent results on neutral particles spectra from the LHCf experiment Massimo Bongi - INFN (Florence, Italy) LHCf Collaboration

2. High-energy cosmic rays SPS Tevatron • Recent excellent observations (e.g. Auger, HiRes, TA) but the origin and composition of HE CR is still unclear LHC AUGER E [eV]

3. Development of atmospheric showers • The depth of the maximum of the shower Xmax in the atmosphere depends on energy and type of the primary particle • Several Monte Carlo simulations (different hadronic interaction models) are used and they give different answers about composition 1019 eV proton • Experimental tests of hadron interaction models are necessary The dominant contribution to the shower development comes from particles emitted at low angles (forward region). LHC gives us the unique opportunity to study hadronic interactions at 1017eV 7 TeV + 7 TeV → Elab ≈ 1 x 1017 eV 3.5 TeV + 3.5 TeV → Elab ≈ 3 x 1016 eV 450 GeV + 450 GeV → Elab ≈ 4 x 1014 eV LHC forward (LHCf) experiment

4. The LHCf collaboration K.Fukatsu, T.Iso, Y.Itow, K.Kawade, T.Mase, K.Masuda, Y.Matsubara, G.Mitsuka, Y.Muraki, T.Sako, K.Suzuki, K.Taki Solar-Terrestrial Environment Laboratory, Nagoya University, Japan H.MenjoKobayashi-Maskawa Institute, Nagoya University, Japan K.YoshidaShibaura Institute of Technology, Japan K.Kasahara, T.Suzuki, S.ToriiWaseda University, Japan Y.ShimizuJAXA, Japan T.TamuraKanagawa University, Japan M.HaguenauerEcolePolytechnique, France W.C.TurnerLBNL, Berkeley, USA O.Adriani, L.Bonechi, M.Bongi, R.D’Alessandro, M.Grandi, P.Papini, S.Ricciarini, G.CastelliniINFN and Universita’ di Firenze, Italy K.Noda, A.TricomiINFN and Universita’ di Catania, Italy J.Velasco, A.FausIFIC, Centro Mixto CSIC-UVEG, Spain A-L.Perrot CERN, Switzerland

5. CMS LHCf ALICE LHCb ATLAS ATLAS 96mm LHCf experimental set-up Protons Charged particles(+) Neutral particles TAN Beam pipe Charged particles(-) 140m LHCf Detector (Arm1)

6. Arm1 detector Scintillating Fibers + MAPMT: 4 pairs of layers (at 6, 10, 30, 42 X0), tracking measurements (resolution < 200 μm) • Sampling e.m. calorimeters: • each detector has two calorimeter towers • which allow to reconstruct 0 • Front counters: • thin plastic scintillators, 80x80 mm2 • monitor beam condition • estimate luminosity • reject background due to beam - residual gas collisions by coincidence analysis 40mm 20mm Absorber:22 tungsten layers, 44 X0, 1.55  Plastic Scintillator: 16 layers, 3 mm thick, trigger and energy profile measurement

7. Arm2 detector Silicon Microstrip: 4 pairs of layers (at 6, 12, 30, 42 X0), tracking measurements (resolution ~ 40 μm) • Sampling e.m. calorimeters: • each detector has two calorimeter towers • which allow to reconstruct 0 • Front counters: • thin plastic scintillators, 80x80 mm2 • monitor beam condition • estimate luminosity • reject background due to beam - residual gas collisions by coincidence analysis 32mm 25mm Absorber:22 tungsten layers, 44 X0, 1.55  Plastic Scintillator: 16 layers, 3 mm thick, trigger and energy profile measurement

8. ATLAS & LHCf

9. 290mm Arm1 detector Arm2 detector 90mm

10. What LHCf can measure • Energy spectra and transverse momentum • distribution of: • gamma rays (E>100 GeV, dE/E<5%) • neutral hadrons (E>few 100 GeV, dE/E~30%) • π0 (E>600 GeV, dE/E<3%) • in the pseudo-rapidity range η>8.4 Front view of calorimeters, @100μrad crossing angle η Projected edge of beam pipe 8.5 Multiplicity @ 14TeV Energy Flux @ 14TeV ∞ mm Low multiplicity High energy flux (simulated by DPMJET3)

11. Event categories LHCf calorimeters leading baryon (neutron) hadron event multi meson production photon π0 • π0 event photon event

12. Summary of operations in 2009 and 2010 • With stable beams at 450GeV+450GeV • Total of 42 hours for physics (6th–15th Dec. 2009, 2nd-3rd,27thMay 2010) • ~ 105 showers events in Arm1+Arm2 • With stable beams at 3.5TeV+3.5TeV • Total of 150 hours for physics (30th Mar.-19th Jul. 2010) • Different vertical positions to increase the accessible kinematical range • Runs with or without beam crossing angle • ~ 4·108 shower events in Arm1+Arm2 • ~ 1060events in Arm1+Arm2 • Status • Completed program for 450GeV+450GeV and 3.5TeV+3.5TeV • Removed detectors from tunnel in July 2010 (luminosity >1030 cm-2s-1) • Post-calibration beam test in October 2010 • Upgrade to more rad-hard detectors to operate at 7TeV+7TeV in 2014

13. Photon energy spectra analysis EXPERIMENTAL DATA • p-p collisions at √s=7 TeV, no crossing angle (Fill# 1104, 15th May 2010 17:45-21:23) • Luminosity: (6.3÷6.5) x 1028 cm-2s-1 (3 crossing bunches) • Negligible pile-up (~0.2%) • DAQ Live Time: 85.7% (Arm1), 67.0% (Arm2) • Integrated luminosity: 0.68 nb-1 (Arm1), 0.53 nb-1 (Arm2) • MONTE CARLO DATA • 107 inelastic p-p collisions at √s=7 TeV simulated by several MC codes: • DPMJET 3.04, QGSJET II-03, SYBILL 2.1, EPOS 1.99, PYTHIA 8.145 • Propagation of collision products in the beam pipe and detector response simulated by EPICS/COSMOS ANALYSIS PROCEDURE • Energy Reconstruction: total energy deposition in a tower (corrections for light yield, shower leakage, energy calibration, etc.) • Rejection of multi-hit events: transverse energy deposit • Particle identification (PID): longitudinal development of the shower • Selection of two pseudo-rapidity regions: 8.81 < η < 8.99 and η > 10.94 • Combine spectra of Arm1 and Arm2 and compare with MC expectations

14. 1 TeVπ0 candidate event scintillator layers – longitudinal development 25mm tower 32mm tower • Energy reconstruction • PID 600 GeV photon 420 GeV photon silicon layers – transverse energy • π0 mass reconstruction X view • Hit position • Multi-hit identification Y view

15. Energy reconstruction • Energy reconstruction: Ephoton = f( ΣEi) (i = layer index) • (Ei = A x Qi determined at SPS; f() determined by MC and checked at SPS) • Impact position from lateral distribution • Position dependent corrections: • light collection non-uniformity • shower leakage-out (and 2 mm edge cut) • shower leakage-in Shower leakage-in Light collection non-uniformity Shower leakage-out 32mm tower correction 25mm tower 2 mm

16. Multi-hit rejection • Rejection of multi-hit events is mandatoryespecially at high energy (> 2.5 TeV) • Multi-hit events are identified thanks to position sensitive layers in Arm1 (SciFi) and Arm2 (Si-mstrip) Arm2 Small tower Large tower Multi-hit detection efficiency Arm1 Single-hit detection efficiency Arm2

17. Particle identification • L90%: longitudinal position containing 90% of the shower energy • Photon selection based on L90% cut • Energy dependent threshold in order to • keep constant efficiency εPID = 90% • Purity P = Nphot/(Nphot+Nhad) estimated by • comparison with MC • Event number in each bin corrected by P/εPID 500 GeV < EREC < 1 TeV photon hadron • MC photon and hadron events are independently normalized to data • Comparison done in each energy bin • LPM effects are switched on 44 X0 1.55 λ

18. π0 mass reconstruction • Energy scale can be checked by π0 identification • Mass shift observed both in Arm1 (+7.8%) and Arm2 (+3.7%) • Many checks have been done to understand the energy scale difference: the estimated systematic uncertainty on π0 reconstruction is 4.2% • Conservative approach: no correction is applied to the energy scale, but an asymmetric systematic error is assigned 1(E1) m ≈ θ√(E1xE2) R 140 m  2(E2) I.P.1 Arm2 MC Peak : 135.0 ± 0.2 MeV

19. Comparison between the two detectors R1 = 5 mm R2-1 = 35 mm R2-2 = 42 mm • We define two common pseudo-rapidity and azimuthal regions for the • two detectors: 8.81 < η < 8.99, Δφ = 20˚ (large tower) • η > 10.94, Δφ = 360˚ (small tower) • Normalized by the number of inelastic collisions • (assuming σine = 71.5 mb) • General agreement between the two detectors • (deviation in small tower within the error) Δφ Red points: Arm1 detector Blue points: Arm2 detector Filled area: uncorrelated systematic uncertainties

20. Combined photon spectra gray hatch: systematic error error bars: statistical error

21. Comparison with MC magenta hatch: MC statistical error gray hatch: systematic error DPMJET 3.04QGSJET II-03SYBILL 2.1EPOS 1.99PYTHIA 8.145

22. Preliminary π0 spectra • Mass range selection: +/- 10 MeV around the measured peak • Acceptance depends on energy and transverse momentum (lowest energy is limited by maximum angle between photons) • Comparison with MC is on-going • Extend the analysis • to events with two • photons in the same • tower m ≈ θ√(E1xE2) Eπ = E1+E2

23. Summary and outlook • Single photon analysis at 3.5 TeV + 3.5 TeV: • first comparison of various hadronic interaction models with experimental data in a challenging phase space region • very safe estimation of systematics • no model perfectly reproduces LHCf data, especially at high energy • new input data for model developers • implications for HE CR physics under study • Neutral pion analysis at 3.5 TeV + 3.5 TeV is in progress: • compare pion spectra with MC • include events with two gammas hitting the same tower • the same analysis can be extended to η and K0 particles • Other analysis: complete the analysis at 450 GeV + 450 GeV, neutrons, transverse momentum distributions, extend pseudo-rapidity range,… • We are upgrading the detectors to improve their radiation hardness (GSO scintillators): • we will come back on the LHC beam for the 7 TeV + 7 TeV runs • discussion is under way to come back for possible p-Pb runs in 2013

24. Backup

25. Open Issues on UHECR spectrum AGASA Systematics Total ±18% Hadr Model ~10% (Takeda et al., 2003) M Nagano New Journal of Physics 11 (2009) 065012 Depth of the max of the shower Xmax in the atmosphere AUGER HiRes

26. Front counters • Thin scintillators with 8x8cm2 acceptance, which have been installed in front of each main detector. Schematic view of Front counter • To monitor beam condition. • For background rejection of beam-residual gas collisions by coincidence analysis

27. Detector vertical position and acceptance Remotely changed by a manipulator( with accuracy of 50 mm) Data taking mode with different position to cover PT gap Viewed from IP G Distance from neutral center Beam pipe aperture N Neutral flux center L All g from IP 7TeV collisions L Collisions with a crossing angle lower the neutral flux center thus enlarging Ptacceptance N

28. Expected results @ 14 TeV collisions • Energy spectra and transverse momentum distribution of: • photons (E > 100 GeV): E/E < 5% • neutral pions (E > 500 GeV): E/E < 3% • neutrons (E > few 100 GeV): E/E ~ 30% • in the pseudo-rapidity range  > 8.4  n 0

29. LHCf energy resolution 2.5 x 2.5 cm2 tower 2.0 x 2.0 cm2 tower Energy resolution < 5% at high energy, even for the smallest tower

30. Arm1 position resolution 200 GeV electrons σX=172µm Number of event σX[mm] x-pos[mm] E[GeV] σY=159µm σY[mm] Number of event y-pos[mm] E[GeV]

31. Arm2 position resolution 200 GeV electrons σX=40µm σX[µm] x-pos[mm] E[GeV] σY=64µm σY[µm] y-pos[mm] Alignmenthasbeentakeninto account E[GeV]

32. Estimation of pile-up • When the circulated bunch is 1x1, the probability of N collisions per crossing is: • The ratio of the pile-up event is: • The maximum luminosity per bunch during runs used for the analysis is 2.3x1028cm-2s-1 • So the probability of pile-up is estimated to be 7.2%, with σ=71.5mb and frev = 11.2 kHz • Taking into account our calorimeter acceptance for an inelastic collision (~0.03) only 0.2% of events have multi-hit due to pile-up

33. Luminosity estimation • Luminosity for the analysis is calculated from Front Counter rates: • The conversion factor CF is estimated from luminosity measured during Van der Meer scan VDM scan Beam sizes sx and sy measured directly by LHCf

34. p0 mass vsp0 energy Arm2 data No strong energy dependence of reconstructed mass

35. 2g invariant mass spectrum @ 7 TeV Arm2 detector, all runs with zero crossing angle True ηmass: 547.9 MeV MC reconstructed ηmass peak: 548.5 ± 1.0 MeV Data reconstructed η mass peak: 562.2 ± 1.8 MeV (2.6% shift)

36. Effect of mass shift • Energy rescaling NOT applied but included in energy error • Minv = θ √(E1 x E2) • (ΔE/E)calib = 3.5% • Δθ/θ = 1% • (ΔE/E)leak-in = 2% => ΔM/M = 4.2% ; not sufficient for Arm1 (+7.8%) ±3.5% Gaussian probability ±7.8% flat probability Quadratic sum of two errors is given as energy error (to allow both 135MeV and observed mass peak) 135MeV 145.8MeV (Arm1 observed)

37. Systematic uncertainties • Energy reconstruction (detector response, from beam test at SPS): 3.5% • Multi-hit rejection (estimated by comparing true MC and reconstructed MC spectra after MH cut): from 1% for E < 1.5 TeV to 20% at E = 3 TeV • PID (by comparing 2 different approaches): 5% for E < 1.7 TeV, 20% for E > 1.7 TeV • Beam center position (by comparing position measured by LHCf and by Beam Position Monitors): 5÷20 % varying with energy and pseudo-rapidity • Luminosity (Front Counter measurement during Van der Meer scans): 6.1%, it causes an energy independent shift of spectra, not included in photon spectra • Energy shift (π0 mass shift, asymmetric): 7.8% Arm1, 3.7% Arm2 • Total energy scale systematic: -9.8% / +1.8% for Arm1 • -6.6% / +2.2% for Arm2 • Systematic uncertainty on spectra is estimated from the difference • between normal spectra and energy scaled spectra

38. Background • Pile-up of collisions in one beam crossing • Low Luminosity fill, L=2.3x1028cm-2s-1 7.2% pile-up at collisions, 0.2% at the detectors. • Collisions between secondary's and beam pipes • Very low energy particles reach the detector (few % at 100GeV) • Collisions between beams and residual gas • Estimated from data with non-crossing bunches. ~0.1% Beam-Gas backgrounds Secondary-beam pipe backgrounds

39. Energy spectra at 900 GeV gamma-ray like hadron like Arm1 PRELIMINARY PRELIMINARY Arm2 Only statistical errors are shown Acceptance is different for the two arms. Spectra are normalized by # of -ray and hadron like events.

40. Radiation damage studies • Dose evaluation on the basis of LHC reports on radiation environment at IP1 • ~ 100 Gy/day @ 1030cm-2s-1 luminosity are expected • ~ 10 kGyduring few months operation lead to ~ 50% light output decrease • continuous laser calibration to monitor scintillators and correct for the decrease of light output • test of Scintillating fibers and scintillators 30 kGy