First LHCf measurement of photon spectra at pseudorapidity >8.8 in LHC 7TeV pp collisions

1. arXiv:1104.5294 CERN-PH-EP-2011-061 Submitted to PLB First LHCf measurement of photon spectra at pseudorapidity >8.8 in LHC 7TeV pp collisions Takashi SAKO (Solar-Terrestrial Environment Laboratory, Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University) For the LHCf Collaboration CERN Joint EP/PP/LPCC seminar, 17-May2011, 503-1-001 Council Chamber

2. Thanks to… • CERN, especially LHC crew • ATLAS collaboration • Michelangelo and LHCC referees • Financial support mainly from Japan and Italy

3. Plan of the talk • Motivation • History and recent progress in the UHECR observation • Hadron interaction models and forward measurements • The LHCf Experiment • Single photon spectra at 7TeV pp collisions • Impact on the CR physics • Introduction to on-going works • Next plan • Further analysis of 0.9 and 7 TeV collision data • 14TeV pp/ pA, AA collisions • Summary

4. 1. Motivation

5. Frontier in UHECR Observation • What limits the maximum observed energy of Cosmic-Rays? Time? Technology? Cost? Physics? • GZK cutoff (interaction with CMB photons) >1020eV was predicted in 1966 • Acceleration limit

6. Observations (10 years ago and now) • Debate in AGASA, HiRes results in 10 years ago • Now Auger, HiRes (final), TA indicate cutoff • Absolute values differ between experiments and between methods

7. Estimate of Particle Type (Xmax) 0g/cm2 • Xmax gives information of the primary particle • Results are different between experiments • Interpretation relies on the MC prediction and has model dependence Xmax Auger TA HiRes Proton and nuclear showers of same total energy

8. Summary of Current CR Observations • Cutoff around 1020eV seems exist. • Absolute energy of cutoff, sensitive to particle type, is still in debate. • Particle type is measured using Xmax, but different interpretation between experiments. • (Anisotropy of arrival direction also gives information of particle type; not presented today) Still open question : Is the cutoff due to GZK process of protons or heavy nuclei, or acceleration limit in the source? • Both in the energy determination and Xmax prediction MC simulation is used and they are one of the considerable sources of uncertainty. Experimental tests of hadron interaction models are indispensable.

9. What to be measured at collidersmultiplicity and energyflux at LHC 14TeV collisionspseudo-rapidity; η= -ln(tan(θ/2)) Multiplicity Energy Flux All particles neutral Most of the energy flows into very forward

10. 2. The LHCf Experiment

11. 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.TakiSolar-Terrestrial Environment Laboratory, Nagoya University, Japan H.MenjoKobayashi-Maskawa Institute, Nagoya University, Japan K.YoshidaShibaura Institute of Technology, Japan K.Kasahara, Y.Shimizu, T.Suzuki, S.Torii Waseda University, 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.Castellini INFN, Univ. di Firenze, Italy K.Noda, A.TricomiINFN, Univ. di Catania, Italy J.Velasco, A.FausIFIC, Centro Mixto CSIC-UVEG, Spain D.Macina, A-L.Perrot CERN, Switzerland

12. ATLAS 96mm Detector Location LHCf Detector(Arm#1) 140m Two independent detectors at either side of IP1( Arm#1, Arm#2 ) Protons Charged particles(+) Neutral particles Beam pipe Charged particles(-) TAN -Neutral Particle Absorber- transition from one common beam pipe to two pipes Slot : 100mm(w) x 607mm(H) x 1000mm(T)

13. ATLAS & LHCf

14. Arm#1 Detector 20mmx20mm+40mmx40mm 4 XY SciFi+MAPMT Arm#2 Detector 25mmx25mm+32mmx32mm 4 XY Silicon strip detectors LHCfDetectors • Imaging sampling shower calorimeters • Two independent calorimeters in each detector(Tungsten 44r.l., 1.6λ, sample with plastic scintillators)

15. η η θ [μrad] 8.5 8.7 310 ∞ ∞ 0 Calorimeters viewed from IP 100urad crossing angle 0 crossing angle • Geometrical acceptance of Arm1 and Arm2 • Crossing angle operation enhances the acceptance Projected edge of beam pipe

16. LHCf as EM shower calorimeter • EM shower is well contained longitudinally • Lateral leakage-out is not negligible • Simple correction using incident position • Identification of multi-shower event using position detectors

17. Front Counter • Fixed scintillation counter • L=CxRFC; conversion coefficient calibrated during VdM scans

18. 3. Single photon spectra at LHC 7TeV pp collisions

19. Data Set for this analysis • Data • Date : 15 May 2010 17:45-21:23 (Fill Number : 1104) except runs during the luminosity scan. • Luminosity : (6.3-6.5)x1028cm-2s-1 (not too high for pile-up, not too low for beam-gas BG) • DAQ Live Time : 85.7% for Arm1, 67.0% for Arm2 • Integral Luminosity (livetime corrected): 0.68 nb-1 for Arm1, 0.53nb-1 for Arm2 • Number of triggers : 2,916,496 events for Arm1 3,072,691 events for Arm2 • With Normal Detector Position and Normal Gain • MC • About 107pp inelastic collisions with each hadron interaction model,QGSJET II-03, DPMJET 3.04, SYBILL 2.1, EPOS 1.99 and PYTHIA8.145 Only PYTHIA has tuning parameters. The default parameters were used

20. Event Sample (π0 candidate) Event sample in Arm2 Longitudinal development Note : • A Pi0 candidate event • 599GeV gamma-ray and 419GeV gamma-ray in 25mm and 32mm tower respectively. Lateral development

21. Analysis • Step.1 : Energy reconstruction • Step.2 : Single-hit selection • Step.3 : PID (EM shower selection) • Step.4 : π0 reconstruction and energy scale • Step.5 : Spectra reconstruction

22. Analysis Step.1 • Energy reconstruction: Ephoton= f(Σ(dEi)) (i=2,3,…,13) ( dEi = AQi determined at SPS. f() determined by MC. E : EM equivalent energy) • Impact position from lateral distribution • Position dependent corrections • Light collection non-uniformity • Shower leakage-out • Shower leakage-in (in case of two calorimeterevent) Shower leakage-in Light collection nonuniformity Shower leakage-out

23. Analysis Step.2 • Single event selection • Single-hit detection efficiency • Multi-hit identification efficiency (using superimposed single photon-like events) • Effect of multi-hit ‘cut’ (next slide) Small tower Large tower Arm1 Double hit in a single calorimeter Arm2 Single hit detection efficiency Double hit detection efficiency

24. Uncertainty in Step.2 • Fraction of multi-hit and Δεmulti, data-MC • Effect of multi-hit ‘cut’ : difference between Arm1 and Arm2 Effect of Δεmulti to single photon spectra Single / (single+multi), Arm1 vs Arm2

25. Analysis Step.3 • PID (EM shower selection) • Select events <L90%threshold and multiply P/ε ε(photon detection efficiency) and P (photon purity) • By normalizing MC template L90% to data, ε and P for certain L90% threshold are determined.

26. Uncertainty in Step.3 (Small tower, single & gamma-like) • Imperfection in L90% distribution Original method Template fitting A ε/P from two methods Artificial modification in peak position(<0.7 r.l.) and width (<20%) (ε/P)B/(ε/P)A Template fitting B

27. Analysis Step.4 • π0 identification from two tower events to check absolute energy • Mass shift observed both in Arm1 (+7.8%) and Arm2 (+3.7%) • No energy scaling applied, but assigned the shifts in the systematic errorin energy Arm2 Measurement 1(E1) Arm2 MC R 140m  2(E2) I.P.1 M = θ√(E1xE2)

28. Analysis Step.5 • Spectra in Arm1, Arm2 common rapidity • Enegy scale error not included in plot (maybe correlated) • Nine = σine ∫Ldt (σine = 71.5mb assumed)

29. Combined spectra Weighted averageof Arm1 and Arm2 according to the errors

30. Spectral deformation • Suppression due to multi-hit cut at medium energy • Overestimate due to multi-hit detection inefficiency at high energy (mis-identify multi photons as single) • No correction applied, but same bias included in MC to be compared TRUE/MEASURED TRUE MEASURED True: photon energy spectrum at the entrance of calorimeter

31. Beam Related Effects • Pile-up (7% pileup at collision) • Beam-gas BG • Beam pipe BG • Beam position (next slide) MC w/ pileup vs w/o pileup Crossing vs non-crossing bunches Direct vs beam-pipe photons

32. Where is zero degree? Beam center LHCf vs BPMSW LHCf online hit-map monitor Effect of 1mm shift in the final spectrum

33. Comparison with Models

34. Comparison with Models DPMJET 3.04 QGSJET II-03 SIBYLL 2.1 EPOS 1.99 PYTHIA 8.145

35. DPMJET 3.04 QGSJET II-03 SIBYLL 2.1 EPOS 1.99 PYTHIA 8.145 • None of the models perfectly agree with data. • QGSJET II, DPMJET3, PYTHIA8: good agreement in 0.5-1.5TeV at η>10.94 but large difference >2TeV. • SIBYLL2 shows good spectral shape >0.5TeV atη>10.94 but only half yield • Less deviation at 8.81<η<8.99 but still big difference >2TeV in DPMJET3 and PYTHIA8

36. 4. Impact on the CR physics

37. π0 spectrum and air shower • Artificial modification of meson spectra and its effect to air shower • Importance of E/E0>0.1 mesons • Is this modification reasonable? QGSJET II original Artificial modification X=E/E0 Ignoring X>0.1 meson π0 spectrum at Elab = 1019eV Longitudinal AS development 30g/cm2

38. Model uncertainty at LHC energy • On going works • Air shower simulations with modified π0 spectra at LHC energy • Try&Errorto find artificial π0 spectra to explain LHCf photon measurements • Analysis of π0 events Very similar!? Forward concentration of x>0.1 π0 π0 energy at √s = 7TeV

39. 5. Next Plan • Analysis • Energy scale problem to be improved • Correction for multi-hit cut / reconstruction for multi-hit event • π0spectrum • Hadron • 900GeV • PT dependence • Experiment • 14TeV pp collisions • pA, AA collisions (only ideas)

40. 14TeV: Not only highest energy, but energy dependence… SIBYLL QGSJET2 Note: LHCf detector taken into account (biased) 7 TeV 10 TeV 14 TeV(1017eV@lab.) 7 TeV 10 TeV 14 TeV Secondary gamma-ray spectra in p-p collisions at different collision energies (normalized to the maximum energy) SIBYLL predicts perfect scaling while QGSJET2 predicts softening at higher energy Qualitatively consistent with Xmax prediction

41. LHC-COSMIC ? • p-Pbrelevant to CR physics? • CR-Air interaction is not p-p, but A1-A2 (A1:p, He,…,Fe, A2:N,O) Total Neutron Photon LHC Nitrogen-Nitrogen collisions Top: energy flow at 140m from IP Left : photon energy spectra at 0 degree

42. 6. Summary • LHCf has measured photon spectra at η>8.8 during LHC 7TeV p-p collisions. • Measured spectra are compared with the prediction from various models. • None of the models perfectly agree with data • Large suppression in data at >2TeV w.r.t. to DPM3, QGS-II, PYTHIA predictions • Study on the effect of LHCf measurements to the CR air shower is on-going • Further analysis and preparation for next observations are on-going

43. Backup

44. CR Acceleration limit

45. Surface Detectors (SD) to sample particles on ground Telescopes to image the fluorescence light (FD)

46. Key measurements E0 EM shower E leading baryon Forward spectra (Multiplicity) Cross section Elasticity / inelasticity

47. CMS/TOTEM Nagoya University ALICE ATLAS LHCb/MoEDAL LHCf Arm2 LHCf Arm1

48. Detectors are installed in TAN attached to the vertical manipulators • Neutral particles (predominantly photons, neutrons) enter in the LHCf calorimeters Neutral particles

50. 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 BCNWG paper https://lpc-afs.web.cern.ch/lpc-afs/tmp/note1_v4_lines.pdf