13th ICATPP Conference on Astroparticle, Particle, Space Physics and Detectors for Physics Applications Villa Olmo - Como, Oct 3 rd – 7 th , 2011

Recent results on neutral particles spectra from the LHCf experiment

Massimo Bongi - INFN (Florence, Italy) LHCf Collaboration

High-energy cosmic rays

SPS Tevatron LHC Recent excellent observations (e.g. Auger, HiRes, TA) but the origin and composition of HE CR is still unclear AUGER

Massimo Bongi – ICATPP – 3 rd October 2011 – Como

E [eV]

2

Development of atmospheric showers

 The depth of the maximum of the shower X max energy and type of the primary particle in the atmosphere depends on  Several Monte Carlo simulations (different hadronic interaction models) are used and they give different answers about composition 10 19 eV proton Experimental tests of hadron interaction models are necessary The dominant contribution to the shower development comes from particles emitted at low angles (forward region).

LHC gives us the unique opportunity to study hadronic interactions at

10 17 eV

7 TeV + 7 TeV 3.5 TeV + 3.5 TeV 450 GeV + 450 GeV → → → E lab ≈ 1 x 10 17 eV E lab ≈ 3 x 10 16 eV E lab ≈ 4 x 10 14 eV

LHC forward (LHCf) experiment

Massimo Bongi – ICATPP – 3 rd October 2011 – Como 3

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

Kobayashi-Maskawa Institute, Nagoya University, Japan

K.Yoshida

K.Kasahara, T.Suzuki, S.Torii

Y.Shimizu

T.Tamura

Shibaura Institute of Technology, Japan Waseda University, Japan JAXA, Japan 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 and Universita’ di Firenze, Italy

K.Noda, A.Tricomi

INFN and Universita’ di Catania, Italy

J.Velasco, A.Faus

A-L.Perrot

IFIC, Centro Mixto CSIC-UVEG, Spain

Massimo Bongi – ICATPP – 3 rd October 2011 – Como

CERN, Switzerland

4

LHCf experimental set-up

ALICE LHCf CMS LHCb ATLAS Protons Charged particles (+) Neutral particles TAN Beam pipe Charged particles (-)

ATLAS

96mm 140m

LHCf Detector

(Arm1)

Massimo Bongi – ICATPP – 3 rd October 2011 – Como 5

•

Arm1 detector

Sampling e.m. calorimeters:

Scintillating Fibers + MAPMT: 4 pairs of layers (at 6, 10, 30, 42 X 0 ), tracking measurements (resolution < 200 μm) each detector has two calorimeter towers which allow to reconstruct  0

40mm

•

Front counters:

thin plastic scintillators, 80x80 mm 2  monitor beam condition   estimate luminosity reject background due to beam - residual gas collisions by coincidence analysis

20mm

Absorber: 22 tungsten layers, 44 X 0 , 1.55  Plastic Scintillator: 16 layers, 3 mm thick, trigger and energy profile measurement Massimo Bongi – ICATPP – 3 rd October 2011 – Como 6

•

Arm2 detector

Sampling e.m. calorimeters:

Silicon Microstrip: 4 pairs of layers (at 6, 12, 30, 42 X 0 ), tracking measurements (resolution ~ 40 μm) each detector has two calorimeter towers which allow to reconstruct  0 •

Front counters:

thin plastic scintillators, 80x80 mm 2  monitor beam condition   estimate luminosity reject background due to beam - residual gas collisions by coincidence analysis

32mm 25mm

Absorber: 22 tungsten layers, 44 X 0 , 1.55  Plastic Scintillator: 16 layers, 3 mm thick, trigger and energy profile measurement Massimo Bongi – ICATPP – 3 rd October 2011 – Como 7

ATLAS

&

LHCf Massimo Bongi – ICATPP – 3 rd October 2011 – Como 8

Arm1 detector

Massimo Bongi – ICATPP – 3 rd October 2011 – Como

Arm2 detector

9

What LHCf can measure

Energy spectra and transverse momentum distribution of:  gamma rays (E>100 GeV, dE/E<5%)   neutral hadrons (E>few 100 GeV, dE/E~30%) π 0 (E>600 GeV, dE/E<3%)

in the pseudo-rapidity range η >8.4

Front view of calorimeters, @100μrad crossing angle Projected edge of beam pipe 8.5

η

Multiplicity @ 14TeV Energy Flux @ 14TeV

∞

mm

Low multiplicity High energy flux

(simulated by DPMJET3) Massimo Bongi – ICATPP – 3 rd October 2011 – Como 10

Event categories

leading baryon (neutron) LHCf calorimeters hadron event multi meson production π 0 photon π 0 event Massimo Bongi – ICATPP – 3 rd October 2011 – Como photon event 11

Summary of operations in 2009 and 2010 With stable beams at 450GeV+450GeV

Total of 42 hours for physics (6 th –15 th Dec. 2009, 2 nd -3 rd ,27 th May 2010) ~ 10 5 showers events in Arm1+Arm2

With stable beams at 3.5TeV+3.5TeV

Total of 150 hours for physics (30 Different vertical positions to increase the accessible kinematical range ~ 4·10 8 shower events th in Arm1+Arm2 Mar.-19 Runs with or without beam crossing angle th Jul. 2010) ~ 10 6  0 events in Arm1+Arm2

Status

Completed program for 450GeV+450GeV and 3.5TeV+3.5TeV

Removed detectors from tunnel in July 2010 (luminosity >10 30 cm -2 s -1 ) Post-calibration beam test in October 2010 Upgrade to more rad-hard detectors to operate at 7TeV+7TeV in 2014 Massimo Bongi – ICATPP – 3 rd October 2011 – Como 12

• • • • •

Photon energy spectra analysis

E X P E R I M E N T A L D A T A

p-p collisions at √s=7 TeV, no crossing angle (Fill# 1104, 15 th May 2010 17:45-21:23) Luminosity: (6.3

÷ 6.5) x 10 28 cm -2 s -1 (3 crossing bunches) Negligible pile-up (~0.2%) DAQ Live Time: 85.7% (Arm1), 67.0% (Arm2) Integrated luminosity: 0.68 nb -1 (Arm1), 0.53 nb -1 (Arm2) • •

M O N T E C A R L O D A T A

10 7 inelastic p-p collisions at √s=7 TeV simulated by several MC codes: DPMJET 3.04

, QGSJET II-03 , SYBILL 2.1

, EPOS 1.99

, PYTHIA 8.145

Propagation of collision products in the beam pipe and detector response simulated by EPICS/COSMOS

A N A L Y S I S P R O C E D U R E

1.

Energy Reconstruction: total energy deposition in a tower (corrections for light yield, shower leakage, energy calibration, etc.) 2.

Rejection of multi-hit events: transverse energy deposit 3.

4.

5.

Particle identification (PID): longitudinal development of the shower Selection of two pseudo-rapidity regions: 8.81 < η < 8.99 and η > 10.94

Combine spectra of Arm1 and Arm2 and compare with MC expectations Massimo Bongi – ICATPP – 3 rd October 2011 – Como 13

1 TeV π

0

candidate event

scintillator layers – longitudinal development

  Energy reconstruction PID

600 GeV photon 25mm tower 420 GeV photon 32mm tower silicon layers – transverse energy X view

 π 0 mass reconstruction

Y view

  Hit position Multi-hit identification Massimo Bongi – ICATPP – 3 rd October 2011 – Como 14

  

Energy reconstruction

Energy reconstruction: E photon (E i = A x Q i = f( Σ E i ) (i = layer index) determined at SPS; f() determined by MC and checked at SPS) Impact position from lateral distribution Position dependent corrections: • • • light collection non-uniformity shower leakage-out (and 2 mm edge cut) shower leakage-in

Light collection non-uniformity Shower leakage-out Shower leakage-in 32mm tower correction 2 mm

Massimo Bongi – ICATPP – 3 rd October 2011 – Como

25mm tower

15

Multi-hit rejection

 Rejection of multi-hit events is mandatory especially at high energy (> 2.5 TeV)  Multi-hit events are identified thanks to position sensitive layers in Arm1 (SciFi) and Arm2 (Si m strip)

Arm2

Small tower Large tower

Multi-hit detection efficiency Single-hit detection efficiency

Massimo Bongi – ICATPP – 3 rd October 2011 – Como Arm1 Arm2 16

    

Particle identification

L 90% : longitudinal position containing 90% of the shower energy Photon selection based on L 90% cut

500 GeV < E REC < 1 TeV

Energy dependent threshold in order to keep constant efficiency ε PID = 90% Purity P = N phot /(N phot +N had ) estimated by comparison with MC Event number in each bin corrected by P/ ε PID

photon hadron

44 X 0 1.55 λ    MC photon and hadron events are independently normalized to data Comparison done in each energy bin LPM effects are switched on Massimo Bongi – ICATPP – 3 rd October 2011 – Como 17

π

0

mass reconstruction

 Energy scale can be checked by π 0 identification    Mass shift observed both in Arm1 (+7.8%) and Arm2 (+3.7%) Many checks have been done to understand the energy scale difference: the estimated systematic uncertainty on π 0 reconstruction is 4.2% Conservative approach: no correction is applied to the energy scale, but an asymmetric systematic error is assigned

m ≈ θ√(E

1

xE

2

)

Arm2 MC

Peak : 135.0 ± MeV 0.2

R



1 (E 1 )



2 (E 2 )

 

R

140 m

140 m



I.P.1

Massimo Bongi – ICATPP – 3 rd October 2011 – Como 18

Comparison between the two detectors

 We define two common pseudo-rapidity and azimuthal regions for the

R1 = 5 mm

two detectors: 8.81 < η < 8.99, Δφ = 20˚ (large tower)

R2-1 = 35 mm R2-2 = 42 mm

η > 10.94, Δφ = 360˚ (small tower)  Normalized by the number of inelastic collisions (assuming σ ine = 71.5 mb)  General agreement between the two detectors (deviation in small tower within the error)

Δφ Red points: Arm1 detector Blue points: Arm2 detector

rd

Filled area: uncorrelated systematic uncertainties

19

Combined photon spectra

error bars: statistical error gray hatch: systematic error Massimo Bongi – ICATPP – 3 rd October 2011 – Como 20

Comparison with MC

magenta hatch: MC statistical error gray hatch: systematic error

DPMJET 3.04

QGSJET II-03 SYBILL 2.1

PYTHIA 8.145

21

Preliminary π

0

spectra

 Mass range selection: +/- 10 MeV around  the measured peak Acceptance depends on energy and transverse momentum (lowest energy is limited by maximum angle between photons)  Comparison with MC is on-going  Extend the analysis to events with two photons in the same tower

m ≈ θ√(E

1

xE

2

) E

π

= E

1

+E

2

Massimo Bongi – ICATPP – 3 rd October 2011 – Como 22

  

Summary and outlook

Single photon analysis at 3.5 TeV + 3.5 TeV:

• first comparison of various hadronic interaction models with experimental data in a challenging phase space region • • very safe estimation of systematics no model perfectly reproduces LHCf data, especially at high energy  new input data for model developers  implications for HE CR physics under study

Neutral pion analysis at 3.5 TeV + 3.5 TeV is in progress:

• compare pion spectra with MC • • include events with two gammas hitting the same tower the same analysis can be extended to η and K Other analysis: 0 particles complete the analysis at 450 GeV + 450 GeV, neutrons, transverse momentum distributions, extend pseudo-rapidity range,…  We are upgrading the detectors to improve their radiation hardness (GSO scintillators): • we will come back on the LHC beam for the 7 TeV + 7 TeV runs • discussion is under way to come back for possible p-Pb runs in 2013 Massimo Bongi – ICATPP – 3 rd October 2011 – Como 23

Backup

Open Issues on UHECR spectrum

AGASA Systematics Total ±18% Hadr Model ~10% (Takeda et al., 2003) M Nagano

New Journal of Physics

11 (2009) 065012

Depth of the max of the shower X max the atmosphere in HiRes

Massimo Bongi – ICATPP – 3 rd October 2011 – Como

AUGER

25

Front counters

•

Thin scintillators with 8x8cm

2

acceptance, which have been installed in front of each main detector.

Schematic view of Front counter • •

To monitor beam condition. For background rejection of beam-residual gas collisions by coincidence analysis

Massimo Bongi – ICATPP – 3 rd October 2011 – Como 26

Detector vertical position and acceptance

Remotely changed by a manipulator( with accuracy of 50 m m)

Viewed from IP G Distance from neutral center Data taking mode with different position to cover P T gap Beam pipe aperture N L Neutral flux center

All  from IP

7TeV collisions L Collisions with a crossing angle lower the neutral flux center thus enlarging P t acceptance N

27

Expected results @ 14 TeV collisions

 Energy spectra and transverse momentum distribution of: • photons (E > 100 GeV):  E/E < 5% • neutral pions (E > 500 GeV): • neutrons (E > few 100 GeV): in the pseudo-rapidity range   E/E < 3%  E/E ~ 30% > 8.4



0

Massimo Bongi – ICATPP – 3 rd October 2011 – Como

n

28

LHCf energy resolution

2.5 x 2.5 cm 2 tower 2.0 x 2.0 cm 2 tower

Energy resolution < 5% at high energy, even for the smallest tower

Massimo Bongi – ICATPP – 3 rd October 2011 – Como 29

Arm1 position resolution

200 GeV electrons σ X =172µm x-pos[mm] σ Y =159µm E[GeV] y-pos[mm]

Massimo Bongi – ICATPP – 3 rd October 2011 – Como

E[GeV]

30

Arm2 position resolution

200 GeV electrons Position Resolution X Side 120 Data Simulation Spread Out 100 80 σ X =40µm 60 40 20 x-pos[mm] 0 0 200 250 50 E[GeV] 100 Energy (GeV) 150 Position Resolution Y Side σ Y =64µm 160 140 120 100 80 60 40 20 y-pos[mm]

Alignment has been taken into account rd

0 0

October 2011 – Como

50 E[GeV] 100 Energy (GeV) 150 Data Simulation Spread Out 200 250

31

Estimation of pile-up

• When the circulated bunch is 1x1, the probability of N collisions per crossing is:

P

(

N

)  

N e

 

N

!

• The ratio of the pile-up event is:

R

pileup =

P

(

N P

(

N

³ 2) ³ 1) = 1 (1 + l -

e

l )

e

l • The maximum luminosity per bunch during runs used for the analysis is l =

L

×

f

rev s 2.3x10

28 cm -2 s -1 • So the probability of pile-up is estimated to be 7.2%, with σ=71.5mb and f rev = 11.2 kHz • Taking into account our calorimeter acceptance for an inelastic collision (~0.03) only 0.2% of events have multi-hit due to pile-up Massimo Bongi – ICATPP – 3 rd October 2011 – Como 32

•

Luminosity estimation

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 VDM scan

L

VDM =

n

b

f

rev 2

I

1

I

2 ps

x

s

y

Beam sizes s x directly by LHCf and s y measured Massimo Bongi – ICATPP – 3 rd October 2011 – Como 33



0

mass vs



0

energy

Arm2 data No strong energy dependence of reconstructed mass Massimo Bongi – ICATPP – 3 rd October 2011 – Como 34

2



invariant mass spectrum @ 7 TeV

Arm2 detector, all runs with zero crossing angle True η mass: 547.9 MeV MC reconstructed η mass peak: 548.5 ± Data reconstructed η mass peak: 562.2 ± 1.0 MeV 1.8 MeV (2.6% shift) Massimo Bongi – ICATPP – 3 rd October 2011 – Como 35

Effect of mass shift



Energy rescaling

NOT

error applied but included in energy



M

inv

= θ √(E

1 – (ΔE/E) calib – Δθ/θ = 1% = 3.5%

x E

2

)

– (ΔE/E) leak-in = 2% => ΔM/M = 4.2% ; not sufficient for Arm1 (+7.8%) 135MeV ± 3.5% Gaussian probability ± 7.8% flat probability

Quadratic sum of two errors is given as energy error

145.8MeV

(to allow both 135MeV and

(Arm1 observed)

observed mass peak)

Massimo Bongi – ICATPP – 3 rd October 2011 – Como 36

• • • • • •

Systematic uncertainties

Energy reconstruction (detector response, from beam test at SPS): 3.5% Multi-hit rejection (estimated by comparing true MC and reconstructed MC spectra after MH cut): from 1% for E < 1.5 TeV to 20% at E = 3 TeV PID (by comparing 2 different approaches): 5% for E < 1.7 TeV, 20% for E > 1.7 TeV Beam center position (by comparing position measured by LHCf and by Beam Position Monitors): 5 ÷ 20 % varying with energy and pseudo-rapidity Luminosity (Front Counter measurement during Van der Meer scans): 6.1%, it causes an energy independent shift of spectra, not included in photon spectra Energy shift (π 0 mass shift, asymmetric): 7.8% Arm1, 3.7% Arm2 Total energy scale systematic : -9.8% / +1.8% for Arm1 -6.6% / +2.2% for Arm2 Systematic uncertainty on spectra is estimated from the difference between normal spectra and energy scaled spectra Massimo Bongi – ICATPP – 3 rd October 2011 – Como 37

Background

1. Pile-up of collisions in one beam crossing  Low Luminosity fill, L=2.3x10

28 cm -2 s -1  7.2% pile-up at collisions, 0.2% at the detectors. 2. Collisions between secondary's and beam pipes  Very low energy particles reach the detector (few % at 100GeV) 3. Collisions between beams and residual gas  Estimated from data with non-crossing bunches.

 ~0.1% Secondary-beam pipe backgrounds Beam-Gas backgrounds Massimo Bongi – ICATPP – 3 rd October 2011 – Como 38

Energy spectra at 900 GeV

gamma-ray like hadron like

Arm1 Arm2

Acceptance is different for the two arms.

Spectra are normalized by # of



-ray and hadron like events.

Only statistical errors are shown

Radiation damage studies



test of Scintillating fibers and scintillators

 Dose evaluation on the basis of LHC reports on radiation environment at IP1  ~ 100 Gy/day @ 10 30 cm -2 s -1 luminosity are expected  ~ 10 kGy during few months operation lead to ~ 50% light output decrease  continuous laser calibration to monitor scintillators and Massimo Bongi – ICATPP – 3 rd 30 kGy correct for the decrease of light output October 2011 – Como 40