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 1 LLR seminar, 23-May2011, Ecole Polytechnique arXiv: CERN-PH-EP Submitted to PLB

CR group, STE lab LHCf Super-Kamiokande XMASS Fermi (, CTA) Solar Neutron Observation Radioactive Carbon for ancient solar activity MOA (Microlensing Observations for Astronomy) Press release for free floating planet last week 2

Plan of the talk 1.Motivation – History and recent progress in the UHECR observation – Hadron interaction models and forward measurements 2.The LHCf Experiment 3.Single photon spectra at 7TeV pp collisions 4.Impact on the CR physics – Introduction to on-going works 5.Next plan – Further analysis of 0.9 and 7 TeV collision data – 14TeV pp / pA, AA collisions 6.Summary 3

1. Motivation 4

Frontier in UHECR Observation What limits the maximum observed energy of Cosmic-Rays? Time? Technology? Cost? Physics? GZK cutoff (interaction with CMB photons) >10 20 eV was predicted in 1966 Acceleration limit 5

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

Estimate of Particle Type (X max ) X max gives information of the primary particle Results are different between experiments Interpretation relies on the MC prediction and has model dependence 7 0g/cm 2 Xmax Proton and nuclear showers of same total energy Auger TA HiRes

Summary of Current CR Observations Cutoff around eV seems exist. Absolute energy of cutoff, sensitive to particle type, is still in debate. Particle type is measured using X max, 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. 8

What to be measured at colliders multiplicity and energy flux at LHC 14TeV collisions pseudo-rapidity; η= -ln(tan(θ/2)) MultiplicityEnergy Flux All particles neutral Most of the energy flows into very forward 9

Last forward experiment at hadron collider – UA7 - No sizable violation of Feynman scaling in forward √s = 630GeV, E lab = 2x10 14 eV 10

2. The LHCf Experiment 11

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.Menjo Kobayashi-Maskawa Institute, Nagoya University, Japan K.Yoshida Shibaura Institute of Technology, Japan K.Kasahara, Y.Shimizu, T.Suzuki, S.Torii Waseda University, Japan T.Tamura Kanagawa University, Japan M.Haguenauer Ecole Polytechnique, France W.C.Turner LBNL, 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.Tricomi INFN, Univ. di Catania, Italy J.Velasco, A.Faus IFIC, Centro Mixto CSIC-UVEG, Spain D.Macina, A-L.Perrot CERN, Switzerland The LHCf Collaboration 12

Detector Location 96mm TAN -Neutral Particle Absorber- transition from one common beam pipe to two pipes Slot : 100mm(w) x 607mm(H) x 1000mm(T) ATLAS 140m LHCf Detector(Arm#1) Two independent detectors at either side of IP1 ( Arm#1, Arm#2 ) 13 Charged particles (+) Neutral particles Beam pipe Protons Charged particles (-)

62cm 64cm BABY SIZE DETECTOR! *photo: two years ago. She is now larger than LHCf

LHCf Detectors Arm#1 Detector 20mmx20mm+40mmx40mm 4 XY SciFi+MAPMT Arm#2 Detector 25mmx25mm+32mmx32mm 4 XY Silicon strip detectors Imaging sampling shower calorimeters Two independent calorimeters in each detector (Tungsten 44r.l., 1.6λ, sample with plastic scintillators) 15

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

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

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

Data Set for this analysis Data – Date : 15 May :45-21:23 (Fill Number : 1104) except runs during the luminosity scan. – Luminosity : ( )x10 28 cm -2 s -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 10 7 pp 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 19

Event Sample (π 0 candidate) Event sample in Arm2 Note : A Pi0 candidate event 599GeV gamma-ray and 419GeV gamma- ray in 25mm and 32mm tower respectively. 20 Longitudinal development Lateral development

Analysis Step.1 : Energy reconstruction Step.2 : Single-hit selection Step.3 : PID (EM shower selection) Step.4 : π 0 reconstruction and energy scale Step.5 : Spectra reconstruction 21

Analysis Step.1 Energy reconstruction : E photon = f(Σ(dE i )) (i=2,3,…,13) ( dE i = AQ i 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 calorimeter event) 22 Light collection nonuniformityShower leakage-out Shower leakage-in

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) 23 Double hit in a single calorimeter Single hit detection efficiency Small towerLarge tower Double hit detection efficiency Arm1 Arm2

Uncertainty in Step.2 Fraction of multi-hit and Δε multi, data-MC Effect of multi-hit ‘cut’ : difference between Arm1 and Arm2 24 Single / (single+multi), Arm1 vs Arm2Effect of Δε multi to single photon spectra

Analysis Step.3 PID (EM shower selection) –Select events <L 90% threshold and multiply P/ε ε (photon detection efficiency) and P (photon purity) –By normalizing MC template L 90% to data, ε and P for certain L 90% threshold are determined. 25

Uncertainty in Step.3 Imperfection in L 90% distribution 26 Template fitting A Template fitting B (Small tower, single & gamma-like) Artificial modification in peak position (<0.7 r.l.) and width (<20%) Original method ε/P from two methods (ε/P) B / (ε/P) A

Analysis Step.4 π 0 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 error in energy 27 I.P.1   1 (E 1 )  2 (E 2 ) 140m R Arm2 Measurement Arm2 MC M = θ√(E 1 xE 2 )

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

Combined spectra 29 Weighted average of Arm1 and Arm2 according to the errors

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 30 TRUE MEASURED TRUE/MEASURED True: photon energy spectrum at the entrance of calorimeter

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

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

33 Comparison with Models

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

35 1.None of the models perfectly agree with data. 2.QGSJET II, DPMJET3, PYTHIA8: good agreement in TeV at η>10.94 but large difference >2TeV. 3.SIBYLL2 shows good spectral shape >0.5TeV at η>10.94 but only half yield 4.Less deviation at TeV in DPMJET3 and PYTHIA8 DPMJET 3.04 QGSJET II-03 SIBYLL 2.1 EPOS 1.99 PYTHIA 8.145

4. Impact on the CR physics 36

π 0 spectrum and air shower Artificial modification of meson spectra and its effect to air shower Importance of E/E 0 >0.1 mesons Is this modification reasonable? 37 π 0 spectrum at E lab = eV QGSJET II original Artificial modification Longitudinal AS development Ignoring X>0.1 meson X=E/E 0 30g/cm 2

Model uncertainty at LHC energy On going works – Air shower simulations with modified π 0 spectra at LHC energy – Try&Error to find artificial π 0 spectra to explain LHCf photon measurements – Analysis of π 0 events 38 Very similar!? π 0 energy at √s = 7TeV Forward concentration of x>0.1 π 0

5. Next Plan Analysis – Energy scale problem to be improved – Correction for multi-hit cut / reconstruction for multi-hit event – π 0 spectrum – Hadron – 900GeV – P T dependence Experiment – 14TeV pp collisions – pA, AA collisions (only ideas) 39

14TeV: Not only highest energy, but energy dependence… 7 TeV 10 TeV 14 TeV (10 17 SIBYLL 7 TeV 10 TeV 14 TeV QGSJET2 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 Note: LHCf detector taken into account (biased) 40

LHC-COSMIC ? p-Pb relevant to CR physics? CR-Air interaction is not p-p, but A 1 -A 2 (A1:p, He,…,Fe, A2:N,O) LHC Nitrogen-Nitrogen collisions Top: energy flow at 140m from IP Left : photon energy spectra at 0 degree 41 Total Neutron Photon

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 42

Backup 43

CR Acceleration limit 44

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

Key measurements E leading baryon Elasticity / inelasticity Forward spectra (Multiplicity) Cross section EM shower E0E0 46

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

ATLAS & LHCf 48

Neutral particles 49 Detectors are installed in TAN attached to the vertical manipulators Neutral particles (predominantly photons, neutrons) enter in the LHCf calorimeters

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Front Counter 51 Fixed scintillation counter L=CxR FC ; conversion coefficient calibrated during VdM scans

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 BCNWG paper afs/tmp/note1_v4_lines.pdf Beam sizes  x and  y measured directly by LHCf

Operation With Stable Beam at √s = 900 GeV Total of 42 hours for physics About  10 5 showers events in Arm1+Arm2 With Stable Beam at √s = 7 TeV Total of 150 hours for physics with different setups Different vertical position to increase the accessible kinematical range Runs with or without beam crossing angle  4·10 8 shower events in Arm1+Arm2  10 6  0 events in Arm1 and Arm2 Status Completed program for 900 GeV and 7 TeV Removed detectors from tunnel in July 2010 Post-calibration beam test in October 2010 Upgrade to more rad-hard detectors to operate at 14TeV in

Beam test at SPS Energy Resolution for electrons with 20mm cal. Position Resolution (Scifi) Position Resolution (Silicon) Detector p,e-,mu σ=172 μm for 200GeV electrons σ=40 μm for 200GeV electrons - Electrons 50GeV/c – 200GeV/c - Muons 150GeV/c - Protons 150GeV/c, 350GeV/c

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

π 0 mass shift in study Reanalysis of SPS calibration data in 2007 and 2010 (post LHC) <200GeV Reevaluation of systematic errors Reevaluation of EM shower using different MC codes (EPICS, FLUKA, GEANT4) Cable attenuation recalibration(1-2% improve expected) Re-check all 1-2% effects… 56

Summary of systematic errors 57

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