Very forward measurement at LHC for U ltra -H igh E nergy C osmic -R ay physics SAKO Takashi for the LHCf collaboration (Solar-Terrestrial Environment Laboratory & Kobayashi-Maskawa Institute, Nagoya University) RIKEN seminar, 21-Jul

Outline Current UHECR observations Forward emission in hadronic interaction LHCf – Experiment overview – Analysis of single photon at √s=7TeV pp collisions – Impact on UHECR (on going work) Future 2

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 3

Observations (10 years ago and now) 4 GZK cutoff prediction at eV Debate in AGASA, HiRes results in 10 years ago Proton at rest 100MeV photon 3K CMB eV proton GZK Cutoff mechanism

Observations (10 years ago and now) 5 Auger, HiRes (final), TA indicate GZK-like 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 6 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 at accelerators are indispensable. 7

8 ① Inelastic cross section ② Forward energy spectrum If large k rapid development If small k deep penetrating If large  rapid development If small  deep penetrating ④ 2ndary interactions ③ Inelasticity k (1-E leading )/E 0 If softer shallow development If harder deep penetrating

What should 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

The LHCf experiment 10

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 A-L.Perrot CERN, Switzerland The LHCf Collaboration 11

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 ) 12 Charged particles (+) Neutral particles Beam pipe Protons Charged particles (-) √s=14TeV ] E lab =10 17 eV

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) 13

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 14

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

Calorimeters viewed from IP Geometrical acceptance of Arm1 and Arm2 16 η ∞ 8.7 θ [μrad] crossing angle Projected edge of beam pipe

Expected Results at 14 TeV Collisions (MC assuming 0.1nb -1 statistics) Detector response not considered

Operation at LHC

Summary of Operations in 2009 and 2010 With Stable Beam at 900 GeV Total of 42 hours for physics About  10 5 showers events in Arm1+Arm2 With Stable Beam at 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+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 2014

run summary (7TeV) Integrated showers at 7TeV # of showers Detector removed High luminosity (L=3~20e29cm 2 s -1 ) (1e11ppb, b*=3.5m,Nb=1~8) 100  rad crossing Arm1  0 stat. Low luminosity (L=2~10e28cm 2 s -1 ) (1~2.5e10ppb,  =2m,N b =1~4) No crossing angle 500K 1000K # of  0 900GeV 4/1 5/27 7/22 4/4 5/30 7/25

Analysis for single photon spectra 21 (Photons are mostly decay products of π 0 and η) arXiv: v2 PLB Received

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 22

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. 23 Longitudinal development Lateral development Silicon X Silicon Y Small calorimeter Large calorimeter

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 24

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) 25 Light collection non-uniformityShower leakage-out Shower leakage-in

Analysis Step.2 Single event selection (multi-hit cut) –Single-hit detection efficiency –Multi-hit identification efficiency (using superimposed single photon-like events) 26 Double hit in a single calorimeter Single hit detection efficiency Small towerLarge tower Double hit detection efficiency Arm1 Arm2

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. 27 photon hadron

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 28 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 Energy scale error not included in plot (maybe correlated) N ine = σ ine ∫Ldt (σ ine = 71.5mb assumed) 29

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

Systematic errors 31 Major sources of systematic error Absolute energy PID Multi-hit detection efficiency Beam position

32 Comparison with Models

33 DPMJET 3.04 QGSJET II-03 SIBYLL 2.1 EPOS 1.99 PYTHIA 8.145

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

Impact on CR physics 35

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? What happens at LHC energy? => On-going 36 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

Future 37

Next step Analysis – π 0 energy spectrum Fundamental in EM component of air shower – P T spectrum for photon and π 0 Extrapolation to the non-observable phase space – Hadron (neutron) analysis Elasticity in the air shower development – Analysis for 900GeV collision data Energy dependence of the interaction Measurements – 14 TeV p-p collisions at LHC after 2014 – Study for p-Pb data taking at LHC (2012)? – Detector upgrade for 14TeV run – Measurements at other accelerators? 38

Measurements at other colliders? -hadron collider is not only LHC- Systematic forward measurements for different types of collision using the LHCf detectors p-p collision at lower energy – No dedicated forward measurement since UA7 at SppS (√s=630GeV) – Lower energy but wide acceptance required (LHC 900GeV is not appropriate) Ion collisions to understand p-p to A-A – In CRs, p-N, N-N, Fe-N are important (N; Nitrogen) – p-Pb collisions at LHC 39

LHCf stands for Long-island Hadron Collider forward?? 40 Potential Advantages – Having ZDC installation slots close to IP possible wide rapidity coverage π 0 ->2γ pair detectable – √s=500GeV p-p collision. Equivalent to UA7, but more data available with LHCf detectors. – Ion collisions; essential for CR physics excellent if light ions are available η = -ln(tan(θ/2)) When θ = (415mm/2)/(9.8m+14.3m) = 8.6 mrad => η = 5.44

41 π 0 energy and photon opening angle Feasibility to test the existing models is under study by MC Detail input of the geometry (crucial to know the rapidity coverage) is necessary

Summary LHCf has successfully finished first measurements at LHC for √s=0.9 and 7 TeV p-p collisions. First analysis result of single photon spectra is published. Impact of LHCf results on CR physics is in investigation. Further measurements at LHC 14TeV p-p collisions is programmed after LHC p-Pb run in study. Measurements at other accelerators in study. 42

Backup 43

Uncertainty in Step.2 Fraction of multi-hit and Δε multi, data-MC Effect of multi-hit ‘cut’ : difference between Arm1 and Arm2 44 Single / (single+multi), Arm1 vs Arm2Effect of Δε multi to single photon spectra

Uncertainty in Step.3 Imperfection in L 90% distribution 45 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

Beam Related Effects Pile-up (7% pileup at collision) Beam-gas BG Beam pipe BG Beam position (next slide) 46 MC w/ pileup vs w/o pileup Crossing vs non-crossing bunches Direct vs beam-pipe photons

Where is zero degree? 47 Effect of 1mm shift in the final spectrum Beam center LHCf vs BPMSW LHCf online hit-map monitor

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 48 Very similar!? π 0 energy at √s = 7TeV Forward concentration of x>0.1 π 0

Last forward experiment at hadron collider – UA7 - No sizable violation of Feynman scaling in forward √s = 630GeV, E lab = 2x10 14 eV 49

π 0 energy flow at 500GeV p-p collisions predicted by PYTHIA mm/20m (2.5mrad acceptance) 200mm/25m (8mrad acceptance) 400mm/20m (20mrad acceptance) Geometrical acceptance and rapidity coverage