Very forward measurement at LHC for Ultra-High Energy Cosmic-Ray physics

SAKO Takashi for the LHCf collaboration(Solar-Terrestrial Environment Laboratory &

Kobayashi-Maskawa Institute, Nagoya University)

RIKEN seminar, 21-Jul-2011 1

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) >1020eV was predicted in 1966

Acceleration limit 3

Observations (10 years ago and now)

4

GZK cutoff prediction at 1020eVDebate in AGASA, HiRes results in 10 years ago

Proton at rest100MeV photon

3K CMB1020eV proton

GZK Cutoff mechanism

Observations (10 years ago and now)

5

Auger, HiRes (final), TA indicate GZK-like 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

6

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 at accelerators are indispensable. 7

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① Inelastic cross section

② Forward energy spectrum

If large k rapid developmentIf small k deep penetrating

If large s rapid developmentIf small s deep penetrating④ 2ndary interactions

③ Inelasticity k (1-Eleading)/E0

If softer shallow developmentIf harder deep penetrating

What should 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

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, 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

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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 (-)

√s=14TeV ]

Elab=1017eV

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)

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 Arm216

η

∞

8.7

θ[μrad]

0

310

0 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 2009-2010

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Summary of Operations in 2009 and 2010With Stable Beam at 900 GeV Total of 42 hours for physics About 105 showers events in Arm1+Arm2

With Stable Beam at 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+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 2014

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2009-2010 run summary (7TeV)

106

107

108

Integrated showers at 7TeV

# of

sho

wer

s

Det

ecto

r rem

oved

High luminosity (L=3~20e29cm2s-1)(1e11ppb, b*=3.5m,Nb=1~8)100mrad crossing

Arm1 p0 stat.

Low luminosity (L=2~10e28cm2s-1)(1~2.5e10ppb, *b =2m,Nb=1~4) No crossing angle

500K

1000K

# of

p0

900GeV

4/1 5/27 7/22

4/4 5/30 7/25

Analysis for single photon spectra

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(Photons are mostly decay products of π0 and η)

arXiv:1104.5294v2PLB Received

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 22

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

Silicon X

Silicon Y

Small calorimeter

Largecalorimeter

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)

25Light collection non-uniformity Shower 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)

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Double hit in a single calorimeter

Single hit detection efficiency

Small tower Large tower

Double hit detection efficiency

Arm1

Arm2

Analysis Step.3 PID (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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photonhadron

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.5 Spectra in Arm1, Arm2 common rapidity Energy scale error not included in plot (maybe correlated) Nine = σine ∫Ldt (σine = 71.5mb assumed)

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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

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TRUEMEASURED TRU

E/M

EASU

RED

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

Comparison with Models

33DPMJET 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. DPMJET3, PYTHIA8: good agreement in 0.5-1.5TeV 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

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

π0 spectrum at Elab = 1019eV

QGSJET II originalArtificial modification

Longitudinal AS development

Ignoring X>0.1 meson

X=E/E0

30g/cm2

Future

37

Next stepAnalysis

– π0 energy spectrum• Fundamental in EM component of air shower

– PT spectrum for photon and π0

• 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

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LHCf stands forLong-island Hadron Collider forward??

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Potential Advantages– Having ZDC installation slots close to IP • possible wide rapidity coverage• π0->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

π0 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 2014.LHC p-Pb run in study.Measurements at other accelerators in study.

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Backup

43

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

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

44Single / (single+multi), Arm1 vs Arm2Effect of Δεmulti to single photon spectra

Uncertainty in Step.3Imperfection in L90% 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 BGBeam pipe BGBeam 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?

47Effect 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 π0 spectra at LHC energy– Try&Error to find artificial π0 spectra to explain LHCf photon

measurements– Analysis of π0 events 48

Very similar!?

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

Last forward experiment at hadron collider – UA7 -

No sizable violation of Feynman scaling in forward√s = 630GeV, Elab = 2x1014 eV 49

π0 energy flow at 500GeV p-p collisions predicted by PYTHIA8

50

50mm/20m (2.5mrad acceptance)200mm/25m (8mrad acceptance)

400mm/20m (20mrad acceptance)

Geometrical acceptance and rapidity coverage