Transcript First LHCf measurement of photon spectra at pseudorapidity
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
LLR seminar, 23-May2011, Ecole Polytechnique
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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
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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 1966 eV was predicted in Acceleration limit 5
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 6
Estimate of Particle Type (X
max
)
0g/cm 2 Xmax Auger HiRes TA
Proton and nuclear showers of same total energy
X max gives information of the primary particle Results are different between experiments Interpretation relies on the MC prediction and has model dependence 7
Summary of Current CR Observations
Cutoff around 10 20 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.
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What to be measured at colliders
multiplicity and energy flux at LHC 14TeV collisions pseudo-rapidity; η= -ln(tan(θ/2))
Multiplicity Energy 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
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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.Menjo
K.Yoshida
Kobayashi-Maskawa Institute, Nagoya University, Japan Shibaura Institute of Technology, Japan
K.Kasahara, Y.Shimizu, T.Suzuki, S.Torii
Waseda University, Japan
T.Tamura
M.Haguenauer
Kanagawa University, Japan 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
J.Velasco, A.Faus
D.Macina, A-L.Perrot
INFN, Univ. di Catania, Italy IFIC, Centro Mixto CSIC-UVEG, Spain CERN, Switzerland
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Detector Location
LHCf Detector(Arm#1) ATLAS
Two independent detectors at either side of IP1 ( Arm#1, Arm#2 ) 140m Protons
96mm
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
BABY SIZE DETECTOR!
64cm 62cm
*photo: two years ago. She is now larger than LHCf
LHCf Detectors
Imaging sampling shower calorimeters Two independent calorimeters in each detector (Tungsten 44r.l., 1.6λ, sample with plastic scintillators) Arm#1 Detector 20mmx20mm+40mmx40mm 4 XY SciFi+MAPMT Arm#2 Detector 25mmx25mm+32mmx32mm 4 XY Silicon strip detectors
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θ [ μrad] 310 8.7
Calorimeters viewed from IP
η
0 crossing angle 100urad crossing angle
8.5
η 0 ∞ ∞ Projected edge of beam pipe Geometrical acceptance of Arm1 and Arm2 Crossing angle operation enhances the acceptance 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
3. Single photon spectra at LHC 7TeV pp collisions
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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)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
Longitudinal development Lateral development
• • Note : A Pi0 candidate event 599GeV gamma-ray and 419GeV gamma ray in 25mm and 32mm tower respectively.
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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 ( dE i = AQ i = f(Σ(dE i )) (i=2,3,…,13) 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)
Light collection nonuniformity Shower leakage-out Shower leakage-in
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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 Single hit detection efficiency Double hit detection efficiency
Arm2 23
Uncertainty in Step.2
Fraction of multi-hit and Δε multi, data-MC Effect of multi-hit ‘cut’ : difference between Arm1 and Arm2
Effect of Δε multi to single photon spectra Single / (single+multi), Arm1 vs Arm2
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Analysis Step.3
PID (EM shower selection) – Select events 25 Imperfection in L 90% distribution Template fitting A Original method ε/P from two methods (Small tower, single & gamma-like) Template fitting B Artificial modification in peak position (<0.7 r.l.) and width (<20%) (ε/P) B / (ε/P) A 26 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 R 1 (E 1 ) 2 (E 2 ) = R 140 m 140m I.P.1 M = θ√(E 1 xE 2 ) Arm2 Measurement Arm2 MC 27 Spectra in Arm1, Arm2 common rapidity Enegy scale error not included in plot (maybe correlated) N ine = σ ine ∫Ldt , σ ine = 71.5mb (σ ine = 71.5mb assumed) assumed 28 Weighted average of Arm1 and Arm2 according to the errors 29 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: photon energy spectrum at the entrance of calorimeter 30 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 31 LHCf online hit-map monitor Beam center LHCf vs BPMSW Effect of 1mm shift in the final spectrum 32 33 DPMJET 3.04 QGSJET II-03 SIBYLL 2.1 EPOS 1.99 PYTHIA 8.145 34 DPMJET 3.04 QGSJET II-03 SIBYLL 2.1 EPOS 1.99 PYTHIA 8.145 1. 2. 3. 4. 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 at η>10.94 but only half yield Less deviation at 8.81<η<8.99 but still big difference >2TeV in DPMJET3 and PYTHIA8 35 36 0 QGSJET II original Artificial modification X=E/E 0 Ignoring X>0.1 meson π 0 spectrum at E lab = 10 19 eV Longitudinal AS development Artificial modification of meson spectra and its effect to air shower Importance of E/E 0 >0.1 mesons Is this modification reasonable? 30g/cm 2 37 Very similar!? π 0 energy at √s = 7TeV Forward concentration of x>0.1 π 0 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 Analysis – Energy scale problem to be improved – Correction for multi-hit cut / reconstruction for multi-hit event – π 0 spectrum – – 900GeV – P T dependence Experiment – Hadron 14TeV pp collisions – pA, AA collisions (only ideas) 39 SIBYLL QGSJET2 7 TeV 10 TeV 14 TeV (10 17 eV@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 40 p-Pb relevant to CR physics? CR-Air interaction is not p-p, but A 1 -A 2 He,…,Fe, A2:N,O) (A1:p, Total Neutron Photon LHC Nitrogen-Nitrogen collisions Top: energy flow at 140m from IP Left : photon energy spectra at 0 degree 41 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 43 44 Surface Detectors (SD) to sample particles on ground Telescopes to image the fluorescence light (FD) 45 E 0 EM shower Cross section E leading baryon Elasticity / inelasticity Forward spectra (Multiplicity) 46 CMS/TOTEM Nagoya University ALICE ATLAS LHCf Arm2 LHCf Arm1 LHCb/MoEDAL 47 48 Detectors are installed in TAN attached to the vertical manipulators Neutral particles (predominantly photons, neutrons) enter in the LHCf calorimeters 49 50 Fixed scintillation counter L=CxR FC ; conversion coefficient calibrated during VdM scans 51 • Luminosity for the analysis is calculated from Front Counter rates: L = CF ´ R FC • The conversion factor CF is estimated from luminosity measured during Van der Meer scan L VDM s x = n b and s y f rev 2 I 1 I 2 ps x s y measured VDM scan BCNWG paper https://lpc-afs.web.cern.ch/lpc afs/tmp/note1_v4_lines.pdf 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 p 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 2014 53 Detector Energy Resolution for electrons with 20mm cal. Position Resolution (Scifi) σ=172 μm for 200GeV electrons - Electrons 50GeV/c – 200GeV/c - Muons 150GeV/c - Protons 150GeV/c, 350GeV/c Position Resolution (Silicon) σ=40 μm for 200GeV electrons Energy rescaling NOT error applied but included in energy 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%) 135MeV ± 3.5% Gaussian probability ± 7.8% flat probability 145.8MeV (Arm1 observed) Quadratic sum of two errors is given as energy error (to allow both 135MeV and observed mass peak) 55 0 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 57 58Uncertainty in Step.3
Analysis Step.4
Analysis Step.5
Combined spectra
Spectral deformation
Beam Related Effects
Where is zero degree?
Comparison with Models
Comparison with Models
4. Impact on the CR physics
π
spectrum and air shower
Model uncertainty at LHC energy
5. Next Plan
14TeV: Not only highest energy,
but energy dependence…
LHC-COSMIC ?
6. Summary
Backup
CR Acceleration limit
Key measurements
ATLAS & LHCf
Front Counter
Luminosity Estimation
Operation 2009-2010
Beam test at SPS
Effect of mass shift
π
mass shift in study
Summary of systematic errors