Inclusive photon energy spectra at zero degree of the LHC 7 TeV - PowerPoint PPT Presentation

Inclusive photon energy spectra at zero degree of the LHC 7 TeV proton-proton collisions by the LHCf experiment Gaku Mitsuka (Nagoya University) on behalf of the LHCf Collaboration CERN-PH-EP-2011-061 arXiv:1104.5294 submitted to PLB 32nd International Cosmic Ray Conference Beijing, Aug. 16, 2011

Outline Introduction and Physics motivation Data sets : Exp. data and MC simulations Analysis methods Physics analysis results at √ s=7TeV Conclusions and Future prospects

Introduction Run at 7TeV is able to detect π 0 events since an opening angle is enough small to be covered by the acceptance of the LHCf calorimeter. - energy scale calibration is possible by π 0 mass - photon events are first focused on for simplicity gamma π 0 Gamma-like gamma p p n Hadron-like Other analyses are on going ( π 0 spectra, hadron events and data at 900GeV), would be presented in this winter.

Data sets Experimental data 2010 May 15, 17:45-21:23 (Fill# 1104, except for Lumi-scan data) No crossing angle, pile up is negligibly small ~ 0.2% Luminosity : (6.3-6.5)x10 28 cm -2 s -1 DAQ Live Time : 85.7% (Arm1), 67.0% (Arm2) Integrated luminosity : 0.68 nb -1 (Arm1), 0.53nb -1 (Arm2) Monte Carlo simulations DPMJET 3.04, QGSJET II-03, SYBILL 2.1, EPOS 1.99 and PYTHIA8.145 are used to simulate the proton-proton collisions at √ s=7TeV. Transportation in beam pipe and detector response are correctly treated based on the survey and calibration data. Number of simulated collisions are 10 7 s for each hadronic interaction model.

Single-hit selection • SIngle-hit/Multi-hit separation by the number of showers. Single-gamma • Transverse shower development is fitted by a superimpose of a Lorentzian spectra. • Incident position(X, Y) of neutral particle is used to estimate an amount of shower leakage and to cut events by the fiducial volume. • Deviation of “multi-hit selection” efficiency btw. data and MC is assigned to a systematic uncertainty. Double-gamma Multi-hit selection efficiency 1.2 1.2 Efficiency Efficiency Small tower Large tower 1 1 0.8 0.8 0.6 0.6 Data Data MC(EPOS) MC(EPOS) 0.4 0.4 LHCf-Arm1 s =7TeV LHCf-Arm1 s =7TeV Gamma-ray like Gamma-ray like 0.2 0.2 ° ° > 10.94, = 360 8.81 < < 8.99, = 20 η Δ φ η Δ φ 0 0 500 1000 1500 2000 2500 3000 3500 500 1000 1500 2000 2500 3000 3500 Energy[GeV] Energy[GeV]

Particle Identification Shower developement Gamma-like EM and hadronic showers can be discriminated Number of MIPs 8000 by a difference of longitudinal shower 6000 4000 development in calorimeter. 2000 0 L90%(in units of r.l.) is introduced to parametrize 0 2 4 6 8 10 12 14 16 EM shower Hadronic shower Calorimeter layers Shower developement a longitudinal development. Integral of MIPs 1 90% 0.8 0.6 � L 90% 0.4 E dep 0.2 0 = 90% 0 � 44 r.l. 0 2 4 6 8 10 12 14 16 Calorimeter layers E dep -3 10 × 0 0.25 (/1r.l.) LHCf s =7TeV ∫ -1 Arm1, Data 2010, Ldt=0.68nb 500GeV < E < 1TeV ine rec ° Arm1, QGSJET II-03(Photon) η > 10.94, Δ φ = 360 Events/N 0.2 ~90% efficiency and >80% purity for gamma-like Arm1, QGSJET II-03(Hadron) events. Inefficiency and impurity are corrected to Gamma Hadron 0.15 be compared with theoretical expectations. -like -like 0.1 Imperfect agreement of MC simulations with data is considered as a systematic uncertainty. 0.05 0 0 5 10 15 20 25 30 35 40 45 L90[r.l.]

Event selection Reconstructed energy > 100GeV - Trigger efficiency for EM shower achieves >99% above 100GeV. Fiducial volume - Events hitting in the following regions are selected so that Arm1 and Arm2 have the common rapidity and azimuthal areas. 1. Small tower : η >10.94 、 Δφ =360.0˚ Arm1 2. Large tower : 8.99> η >8.81 、 Δφ =20.0˚ Arm2 Single-hit sample - For simple energy reconstruction and better resolution. Gamma-like sample - Reconstruction of hadron-like events is still under investigation.

Systematic uncertainties Energy scale - Estimated by MC simulations vs. the SPS beam test and a π 0 mass shift. - Dominant error source above 2TeV (2-10% to energy axis). Beam center - May cause a distortion of energy spectra, especially sensitive in large tower. - +/-5% at small tower and over 10% at large tower. Particle ID - Slight disagreement of the L90% distribution between data and MC simulations gives a different PID efficiency, and this could be systematics. - 5% at E<2TeV and 20% at E>2TeV. Single-hit/Multi-hit separation - Difference of separation efficiency between data and MC simulations. - 1% at E<2TeV and grows up to 20% as energy.

Photon spectra Correlated syst. uncertainties are removed in the figures. Deviation btw. Arm1 and Arm2 is recognized in small tower, while it is within syst. uncertainty. Consistent each other in large tower. -3 -3 10 10 /GeV /GeV ine ine -4 LHCf s =7TeV -4 LHCf s =7TeV 10 10 Events/N Events/N Gamma-ray like Gamma-ray like -5 -5 10 10 ° ° > 10.94, = 360 8.81 < < 8.99, = 20 η Δ φ η Δ φ -6 -6 10 10 -7 -7 10 10 ∫ ∫ -1 -1 Arm1, Data 2010, Ldt=0.68nb Arm1, Data 2010, Ldt=0.68nb -8 -8 10 10 Arm1, Systematic uncertainty Arm1, Systematic uncertainty -9 -9 10 10 ∫ ∫ -1 -1 Arm2, Data 2010, Ldt=0.53nb Arm2, Data 2010, Ldt=0.53nb -10 -10 10 10 Arm2, Systematic uncertainty Arm2, Systematic uncertainty 500 1000 1500 2000 2500 3000 3500 500 1000 1500 2000 2500 3000 3500 Energy[GeV] Energy[GeV]

Large tower Small tower Combined analysis -3 -3 10 10 /GeV /GeV ine ine -4 -4 LHCf s =7TeV LHCf s =7TeV 10 10 Events/N Events/N Gamma-ray like Gamma-ray like -5 -5 10 10 ° ° > 10.94, = 360 8.81 < < 8.99, = 20 η Δ φ η Δ φ -6 -6 10 10 -7 -7 10 10 -8 -8 10 10 ∫ ∫ -1 -1 Data 2010, Ldt=0.68+0.53nb Data 2010, Ldt=0.68+0.53nb -9 -9 10 10 Data 2010, Stat. + Syst. error Data 2010, Stat. + Syst. error -10 -10 10 10 MC/Data MC/Data 2.5 2.5 2 2 1.5 1.5 1 1 0.5 0.5 0 0 500 1000 1500 2000 2500 3000 3500 500 1000 1500 2000 2500 3000 3500 Energy[GeV] Energy[GeV]

Small tower Large tower DPMJET 3.04, PYTHIA 8.145 Combined analysis - Good agreement in small tower at 0.5-1.5TeV, but too ample flux above 2TeV. SIBYLL 2.1 - Similar behavior at small tower above 0.5TeV, although almost half flux. QGSJET II-03, EPOS 1.99 - Similar tendency each other in small tower. QGSJET II-03 is softest in large tower. -3 -3 10 10 /GeV /GeV ine ine -4 -4 LHCf s =7TeV LHCf s =7TeV 10 10 Events/N Events/N Gamma-ray like Gamma-ray like -5 -5 10 10 ° ° > 10.94, = 360 8.81 < < 8.99, = 20 η Δ φ η Δ φ -6 -6 10 10 -7 -7 10 10 ∫ ∫ -8 -1 -8 -1 Data 2010, Ldt=0.68+0.53nb Data 2010, Ldt=0.68+0.53nb 10 10 Data 2010, Stat. + Syst. error Data 2010, Stat. + Syst. error DPMJET 3.04 DPMJET 3.04 -9 -9 10 10 QGSJET II-03 QGSJET II-03 SIBYLL 2.1 SIBYLL 2.1 -10 EPOS 1.99 -10 EPOS 1.99 10 10 PYTHIA 8.145 PYTHIA 8.145 MC/Data MC/Data 2.5 2.5 2 2 1.5 1.5 1 1 0.5 0.5 0 0 500 1000 1500 2000 2500 3000 3500 500 1000 1500 2000 2500 3000 3500 Energy[GeV] Energy[GeV] DPMJET 3.04 QGSJET II-03 SIBYLL 2.1 EPOS 1.99 PYTHIA 8.145

Constraints to CR observation Constraint of the LHCf results to CR observations is estimated by proton-air simulations: - Proton-air collisions are generated by DPMJET3 - E Proton is 2.5x10 16 eV, equivalent to the energy in lab frame of p-p collision at √ s=7TeV - DPMJET3 outputs are artificially modified to be parallel to the LHCf spectra (split a high-energy π 0 to two low-energy π 0 s) Results in decrease of ~50 g/cm 2 . p-p at √ s=7TeV(E lab =2.5x10 16 eV) p-Air at E lab =2.5x10 16 eV -3 10 Events(/20) /GeV 140 Proton-Air simulations ine 16 -4 E = 2.5 10 eV LHCf s =7TeV × 10 Events/N proton 120 Gamma-ray like -5 10 ° > 10.94, = 360 η Δ φ 100 DPMJET 3 -6 10 DPMJET 3(Modified) 80 -7 10 60 -8 10 ∫ -1 Data 2010, Ldt=0.5nb 40 -9 10 DPMJET 3 20 DPMJET 3(Modified) -10 10 0 500 1000 1500 2000 2500 3000 3500 400 500 600 700 800 900 1000 2 Energy [GeV] Xmax [g/cm ]

Conclusions The 1st phase data at √ s=7TeV was analyzed in which gamma-like events are focused on. Overall good agreement in spectra btw. two independent detectors and analyses. Combined photon spectra concluded no hadronic interaction perfectly reproduce the LHCf measurement.

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599GeV γ 412GeV γ π 0 崩壊からのガンマ線 Event example(Arm2) Longitudinal development Transverse development

SYST. ERROR(ENERGY SCALE) Syst. Error (Energy scale) = Detector response + π 0 mass 2000 200 E/E [%] Events(/1MeV) Events(/1MeV) Beam (450V) 1800 LHCf-Arm1 s =7TeV 180 LHCf-Arm1 s =7TeV Beam (600V) Data MC Simulation(450V) 1600 160 10 Simulation(600V) Δ 1400 140 1200 120 1000 100 5 800 80 600 60 400 40 200 20 0 0 50 100 150 200 0 0 Energy [GeV] 80 100 120 140 160 180 200 80 100 120 140 160 180 200 Invariant mass[MeV] Invariant mass[MeV] Total : +/-3.5% <M π 0 > = 145.8MeV <M π 0 > = 135.2MeV 145.8/135.2 = 7.8%(Arm1) 140.0/135.0 = 3.7%(Arm2)