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

1CERN Joint EP/PP/LPCC seminar, 17-May2011, 503-1-001 Council Chamber

arXiv:1104.5294CERN-PH-EP-2011-061Submitted to PLB

Thanks to…

CERN, especially LHC crewATLAS collaborationMichelangelo and LHCC refereesFinancial support mainly from Japan and Italy

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Plan of the talk

1. Motivation– History and recent progress in the UHECR observation– Hadron interaction models and forward measurements

2. The LHCf Experiment3. Single photon spectra at 7TeV pp collisions4. 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

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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) >1020eV was predicted in 1966

Acceleration limit5

Observations (10 years ago and now)

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Debate in AGASA, HiRes results in 10 years agoNow Auger, HiRes (final), TA indicate cutoffAbsolute values differ between experiments and between

methods

Estimate of Particle Type (Xmax)

Xmax gives information of the primary particle

Results are different between experiments

Interpretation relies on the MC prediction and has model dependence

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0g/cm2

Xmax

Proton and nuclear showers of same total energy

AugerTA

HiRes

Summary of Current CR Observations

Cutoff around 1020 eV 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.

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What to be measured at collidersmultiplicity 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 forward9

2. The LHCf Experiment

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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, JapanH.Menjo Kobayashi-Maskawa Institute, Nagoya University, Japan K.Yoshida Shibaura Institute of Technology, JapanK.Kasahara, Y.Shimizu, T.Suzuki, S.Torii Waseda University, JapanT.Tamura Kanagawa University, JapanM.Haguenauer Ecole Polytechnique, FranceW.C.Turner LBNL, Berkeley, USAO.Adriani, L.Bonechi, M.Bongi, R.D’Alessandro, M.Grandi, P.Papini, S.Ricciarini, G.Castellini INFN, Univ. di Firenze, ItalyK.Noda, A.Tricomi INFN, Univ. di Catania, Italy J.Velasco, A.Faus IFIC, Centro Mixto CSIC-UVEG, SpainD.Macina, A-L.Perrot CERN, Switzerland

The LHCf Collaboration

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Detector Location

96mmTAN -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 )

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Charged particles (+)

Neutral particlesBeam pipe

Protons

Charged particles (-)

ATLAS & LHCf

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LHCf Detectors

Arm#1 Detector20mmx20mm+40mmx40mm4 XY SciFi+MAPMT

Arm#2 Detector25mmx25mm+32mmx32mm4 XY Silicon strip detectors

Imaging sampling shower calorimeters Two independent calorimeters in each detector (Tungsten 44r.l.,

1.6λ, sample with plastic scintillators)

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Calorimeters viewed from IP

Geometrical acceptance of Arm1 and Arm2Crossing angle operation enhances the acceptance

η

∞

8.7

θ[μrad]

0

310

η

∞

8.5

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0 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 16

Front Counter

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Fixed scintillation counter

L=CxRFC ; conversion coefficient calibrated during VdM scans

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)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 107 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

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Event Sample (π0 candidate)Event sample in Arm2

Note :• A Pi0 candidate event• 599GeV gamma-ray

and 419GeV gamma-ray in 25mm and 32mm tower respectively.

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Longitudinal development

Lateral development

Analysis

Step.1 : Energy reconstructionStep.2 : Single-hit selectionStep.3 : PID (EM shower selection)Step.4 : π0 reconstruction and energy scaleStep.5 : Spectra reconstruction

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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 calorimeter event)

22Light collection nonuniformity Shower 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)

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Double hit in a single calorimeter

Single hit detection efficiency

Small tower Large tower

Double hit detection efficiency

Arm1

Arm2

Uncertainty in Step.2Fraction of multi-hit and Δεmulti, data-MC

Effect of multi-hit ‘cut’ : difference between Arm1 and Arm2

24Single / (single+multi), Arm1 vs Arm2Effect of Δεmulti to single photon spectra

Analysis Step.3PID (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.

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Uncertainty in Step.3Imperfection in L90% distribution

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Template fitting A

Template fitting B

(Small tower, single & gamma-like)

Artificial modification in peak position　 (<0.7 r.l.) and width (<20%)

Original methodε/P from two methods

(ε/P)B/ (ε/P)A

Analysis Step.4π0 identification from two tower

events to check absolute energyMass 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

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m 140= R

I.P.1

1(E1)

2(E2)

140mR

Arm2 Measurement

Arm2 MC

M = θ√(E1xE2)

Analysis Step.5Spectra in Arm1, Arm2 common rapidityEnegy scale error not included in plot

(maybe correlated)Nine = σine ∫Ldt (σine = 71.5mb assumed)

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Combined spectra

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Weighted average of Arm1 and Arm2 according to the errors

Spectral deformationSuppression due to multi-hit cut at medium energyOverestimate 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

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TRUEMEASURED TRU

E/M

EASU

RED

True: photon energy spectrum at the entrance of calorimeter

Beam Related Effects

Pile-up (7% pileup at collision)Beam-gas BGBeam pipe BGBeam position (next slide)

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MC w/ pileup vs w/o pileup

Crossing vs non-crossing bunches Direct vs beam-pipe photons

Where is zero degree?

32Effect of 1mm shift in the final spectrum

Beam center LHCf vs BPMSW

LHCf online hit-map monitor

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Comparison with Models

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Comparison with Models

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

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1. None of the models perfectly agree with data.2. QGSJET II, DPMJET3, PYTHIA8: good agreement in 0.5-1.5TeV at η>10.94

but large difference >2TeV.3. SIBYLL2 shows good spectral shape >0.5TeV at η>10.94 but only half

yield4. Less deviation at 8.81<η<8.99 but still big difference >2TeV 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

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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?

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π0 spectrum at Elab = 1019eV

QGSJET II originalArtificial modification

Longitudinal AS development

Ignoring X>0.1 meson

X=E/E0

30g/cm2

Model uncertainty at LHC energy

On going works– Air shower simulations with modified π0 spectra at LHC energy– Try&Error to find artificial π0 spectra to explain LHCf photon

measurements– Analysis of π0 events 38

Very similar!?

π0 energy at √s = 7TeV Forward concentration of x>0.1 π0

5. Next PlanAnalysis

– Energy scale problem to be improved– Correction for multi-hit cut / reconstruction for multi-hit

event– π0 spectrum– Hadron– 900GeV– PT dependence

Experiment– 14TeV pp collisions– pA, AA collisions (only ideas)

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14TeV: Not only highest energy, but energy dependence…

7 TeV10 TeV14 TeV 　 (1017eV@lab.)

SIBYLL

7 TeV10 TeV14 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)

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LHC-COSMIC ?p-Pb relevant to CR physics?CR-Air interaction is not p-p, but A1-A2 (A1:p, He,

…,Fe, A2:N,O)

LHC Nitrogen-Nitrogen collisionsTop: energy flow at 140m from IPLeft : photon energy spectra at 0 degree

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TotalNeutronPhoton

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 predictionsStudy on the effect of LHCf measurements to

the CR air shower is on-goingFurther analysis and preparation for next

observations are on-going42

Backup

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CR Acceleration limit

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Surface Detectors (SD) to sample particles on ground

Telescopes to image the fluorescence light (FD)

Key measurements

E leading baryon

Elasticity / inelasticityForward spectra

(Multiplicity)Cross section

EM shower

E0

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Nagoya University

LHCf Arm2 LHCf Arm1

ATLASALICE LHCb/MoEDAL

CMS/TOTEM

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Neutral particles

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Detectors are installed in TAN attached to the vertical manipulators

Neutral particles (predominantly photons, neutrons) enter in the LHCf calorimeters

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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 paperhttps://lpc-afs.web.cern.ch/lpc-afs/tmp/note1_v4_lines.pdf

Beam sizes sx and sy measured directly by LHCf

Operation 2009-2010　With Stable Beam at √s = 900 GeV Total of 42 hours for physics About 105 showers events in Arm1+Arm2

With Stable Beam at √s = 7 TeVTotal of 150 hours for physics with different setups

Different vertical position to increase the accessible kinematical rangeRuns with or without beam crossing angle

~ 4·108 shower events in Arm1+Arm2~ 106 p0 events in Arm1 and Arm2

StatusCompleted program for 900 GeV and 7 TeV

Removed detectors from tunnel in July 2010Post-calibration beam test in October 2010

Upgrade to more rad-hard detectors to operate at 14TeV in 201451

Beam test at SPS Energy Resolution for electrons with 20mm cal.

Position Resolution (Scifi)

Position Resolution (Silicon)

Detector

p,e-,mu

σ=172μmfor 200GeVelectrons σ=40μm

for 200GeVelectrons

- Electrons 50GeV/c – 200GeV/c- Muons 150GeV/c- Protons 150GeV/c, 350GeV/c

Effect of mass shiftEnergy rescaling NOT applied but included in energy

errorMinv = θ √(E1 x E2)

– (ΔE/E)calib = 3.5%– Δθ/θ = 1%– (ΔE/E)leak-in = 2%=> ΔM/M = 4.2% ; not sufficient for Arm1 (+7.8%)

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145.8MeV(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)

π0 mass shift in study

Reanalysis of SPS calibration data in 2007 and 2010 (post LHC) <200GeV

Reevaluation of systematic errorsReevaluation of EM shower using different MC

codes (EPICS, FLUKA, GEANT4)Cable attenuation recalibration(1-2% improve

expected)Re-check all 1-2% effects…

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Summary of systematic errors

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