recent results on neutral particles spectra from the lhcf experiment massimo bongi - infn (florence,...

Recent results on neutral particles spectra from the

LHCf experiment

Massimo Bongi - INFN (Florence, Italy)

LHCf Collaboration

13th ICATPP Conference onAstroparticle, Particle, Space Physics and Detectors for Physics

ApplicationsVilla Olmo - Como, Oct 3rd – 7th, 2011

Massimo Bongi – ICATPP – 3rd October 2011 – Como

High-energy cosmic rays

LHC

SPS

AUGER

Tevatron

E [eV]

Recent excellent observations (e.g. Auger, HiRes, TA) but the

origin and composition of HE CR is still unclear

2


Development of atmospheric showers

LHC forward (LHCf) experiment

1019 eV proton

The dominant contribution to the shower development comes from particles emitted at low angles (forward region).

Experimental tests of hadron interaction models are necessary

LHC gives us the unique opportunity to study hadronic interactions at 1017eV

7 TeV + 7 TeV→ Elab ≈ 1 x 1017 eV

3.5 TeV + 3.5 TeV → Elab ≈ 3 x 1016 eV

450 GeV + 450 GeV → Elab ≈ 4 x 1014 eV

The depth of the maximum of the shower Xmax in the atmosphere depends on energy and type of the primary particle

Several Monte Carlo simulations (different hadronic interaction models) are used and they give different answers about composition

3


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, JapanK.Yoshida Shibaura Institute of Technology, Japan

K.Kasahara, T.Suzuki, S.Torii Waseda University, JapanY.Shimizu JAXA, 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 and Universita’ di Firenze, ItalyK.Noda, A.Tricomi INFN and Universita’ di Catania, Italy

J.Velasco, A.Faus IFIC, Centro Mixto CSIC-UVEG, Spain

A-L.Perrot CERN, Switzerland

The LHCf collaboration

4


LHCf experimental set-up

96mm

ATLAS

140m

LHCf Detector (Arm1)

ATLASLHCb

CMS

ALICELHCf

Beam pipe

Protons Charged particles (+)

Charged particles (-)

Neutral particlesTAN

5


Arm1 detectorScintillating Fibers + MAPMT:

4 pairs of layers (at 6, 10, 30, 42 X0),tracking measurements (resolution <

200 μm)

Plastic Scintillator: 16 layers, 3 mm thick,

trigger and energy profile measurement

40mm

20mm

Absorber: 22 tungsten

layers, 44 X0, 1.55

• Sampling e.m.

calorimeters:

each detector has two

calorimeter towers

which allow to reconstruct 0

• Front counters:

thin plastic scintillators, 80x80 mm2

monitor beam condition

estimate luminosity

reject background due to beam -

residual gas collisions by coincidence

analysis

6


25mm

32mm

Arm2 detector

Plastic Scintillator: 16 layers, 3 mm thick,

trigger and energy profile measurement

Absorber: 22 tungsten

layers, 44 X0, 1.55

• Sampling e.m.

calorimeters:

each detector has two

calorimeter towers

which allow to reconstruct 0

• Front counters:

thin plastic scintillators, 80x80 mm2

monitor beam condition

estimate luminosity

reject background due to beam -

residual gas collisions by coincidence

analysis

Silicon Microstrip:4 pairs of layers (at 6, 12, 30, 42 X0),

tracking measurements (resolution ~ 40 μm)

7


ATLAS & LHCf

8


Arm1 detector Arm2 detector90mm290mm

9


What LHCf can measureEnergy spectra and transverse momentumdistribution of: gamma rays (E>100 GeV,

dE/E<5%) neutral hadrons (E>few 100 GeV,

dE/E~30%) π0 (E>600 GeV,

dE/E<3%)in the pseudo-rapidity range η>8.4

Multiplicity @ 14TeV Energy Flux @ 14TeV

Low multiplicity

High energy flux

(simulated by DPMJET3)

η

∞

8.5

Front view of calorimeters,

@100μrad crossing angle

Projected edge of beam pipe

mm

10


Event categoriesleading baryon

(neutron)

multi meson production

π0 photon

hadron event

π0 event

photon event

LHCf calorimeters

11


Summary of operations in 2009 and 2010

With stable beams at 450GeV+450GeVTotal of 42 hours for physics (6th–15th Dec. 2009, 2nd-3rd,27thMay 2010)

~ 105 showers events in Arm1+Arm2

With stable beams at 3.5TeV+3.5TeVTotal of 150 hours for physics (30th Mar.-19th Jul. 2010)

Different vertical positions to increase the accessible kinematical range

Runs with or without beam crossing angle

~ 4·108 shower events in Arm1+Arm2

~ 106 0 events in Arm1+Arm2

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

Removed detectors from tunnel in July 2010 (luminosity >1030 cm-2s-1)

Post-calibration beam test in October 2010

Upgrade to more rad-hard detectors to operate at 7TeV+7TeV in 2014

12


Photon energy spectra analysisE X P E R I M E N TA L D ATA

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

• Luminosity: (6.3÷6.5) x 1028 cm-2s-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 LO D ATA

• 107 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 LY 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. Particle identification (PID): longitudinal development of the shower

4. Selection of two pseudo-rapidity regions: 8.81 < η < 8.99 and η > 10.94

5. Combine spectra of Arm1 and Arm2 and compare with MC expectations 13


1 TeV π0 candidate event

25mmtower

32mmtower

scintillator layers – longitudinal development

silicon layers – transverse energy

Y view

X view

600 GeVphoton

420 GeVphoton

Energy reconstruction

PID

Hit position Multi-hit

identification

π0 mass reconstruction

14


Energy reconstruction Energy reconstruction: Ephoton = f( Σ Ei ) (i = layer index)

(Ei = A x Qi 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-in

correction

2 mm

Shower leakage-out

25mmtower

32mmtower

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-mstrip)

Arm1

Arm2

Small tower Large towerArm2

Multi-hit detection efficiency

Single-hit detection efficiency

16


Particle identification

500 GeV < EREC < 1 TeV

photon

hadron

44 X0

1.55 λ

L90%: longitudinal position containing 90% of the shower energy

Photon selection based on L90% cut Energy dependent threshold in order to

keep constant efficiency εPID = 90%

Purity P = Nphot/(Nphot+Nhad) estimated by

comparison with MC Event number in each bin corrected by P/εPID

MC photon and hadron events are

independently normalized to data

Comparison done in each energy

bin

LPM effects are switched on17


π0 mass reconstruction

m 140

R

I.P.1

1(E1)

2(E2)

140 mR

m ≈ θ√(E1xE2)

Energy scale can be checked by π0 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 π0 reconstruction is 4.2%

Conservative approach: no correction is applied to the energy scale, but an asymmetric systematic error is assigned

Arm2MC

Peak :135.0 ± 0.2MeV

18


Comparison between the two detectors

R1 = 5 mmR2-1 = 35 mmR2-2 = 42 mm

We define two common pseudo-rapidity and azimuthal regions for

the

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

η > 10.94, Δφ = 360˚ (small tower)

Normalized by the number of inelastic collisions

(assuming σine = 71.5 mb)

General agreement between the two detectors

(deviation in small tower within the error)

Δφ

Red points: Arm1 detector Blue points: Arm2 detectorFilled area: uncorrelated systematic uncertainties 19


Combined photon spectragray hatch: systematic error error bars: statistical error

20


Comparison with MCgray hatch: systematic error magenta hatch: MC statistical

error

DPMJET 3.04 QGSJET II-03 SYBILL 2.1 EPOS 1.99 PYTHIA 8.14521


Preliminary π0 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

towerm ≈ θ√(E1xE2)Eπ = E1+E2

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

energynew input data for model developersimplications 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 K0 particles

Other analysis: 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

23

Backup


AGASA SystematicsTotal ±18%

Hadr Model ~10% (Takeda et al., 2003)

Open Issues on UHECR spectrum

M NaganoNew Journal of Physics 11 (2009) 065012

Depth of the max of the shower Xmax in the atmosphere

AUGERHiRes

25


Front counters• Thin scintillators with 8x8cm2 acceptance,

which have been installed in front of each main detector.

• To monitor beam condition. • For background rejection of

beam-residual gas collisions by coincidence analysis

Schematic view of Front counter

26

Detector vertical position and acceptance Remotely changed by a manipulator( with accuracy of 50 mm)

Distance from neutral center Beam pipe aperture

Data taking modewith different positionto cover PT gap

N

L

G

All g from IP

Viewed from IP

Neutral flux center

N

L

7TeV collisions

Collisions with a crossing angle lower the neutral flux center thus enlarging Pt acceptance

27


Expected results @ 14 TeV collisions

n0

Energy spectra and transverse momentum distribution of:

• photons (E > 100 GeV): E/E < 5%

• neutral pions (E > 500 GeV): E/E < 3%

• neutrons (E > few 100 GeV): E/E ~ 30%

in the pseudo-rapidity range > 8.4

28


LHCf energy resolution

2.5 x 2.5 cm2 tower 2.0 x 2.0 cm2 tower

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

29


Arm1 position resolutionN

um

ber

of

even

tN

um

ber

of

even

t

x-pos[mm]

y-pos[mm]

200 GeV electrons

E[GeV]

E[GeV]

σX=172µm

σY=159µmσ X

[mm

]σ Y

[mm

]

30


Arm2 position resolutionPosition Resolution X Side

0

20

40

60

80

100

120

0 50 100 150 200 250

Energy (GeV)

Re

so

luti

on

(m

icro

ns

)

Data

Simulation Spread Out

Position Resolution Y Side

0

20

40

60

80

100

120

140

160

0 50 100 150 200 250

Energy (GeV)

Re

so

luti

on

(m

icro

ns

)

Data

Simulation Spread Out

x-pos[mm]

y-pos[mm]

Alignment has been taken into account

200 GeV electrons

E[GeV]

E[GeV]

σX=40µm

σY=64µmσ X

[µm

]σ Y

[µm

]

31


Estimation of pile-up

!)(

N

eNP

N

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

• The ratio of the pile-up event is:

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

2.3x1028cm-2s-1

• So the probability of pile-up is estimated to be 7.2%, with σ=71.5mb and

frev = 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

32


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

Beam sizes sx and sy measured directly by LHCf

33


p0 mass vs p0 energy

Arm2 data

No strong energy dependence of reconstructed

mass

34


2g invariant mass spectrum @ 7 TeV

Arm2 detector, all runs with zero crossing angleTrue η mass: 547.9 MeVMC reconstructed η mass peak: 548.5 ± 1.0 MeVData reconstructed η mass peak: 562.2 ± 1.8 MeV (2.6% shift)

35


Effect of mass shift

Energy rescaling NOT applied but included in energy error

Minv = 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%)

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)

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 (π0 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 spectra37


Background

Beam-Gas backgroundsSecondary-beam pipe backgrounds

1. Pile-up of collisions in one beam crossing Low Luminosity fill, L=2.3x1028cm-2s-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%

38


Arm1

Arm2

gamma-ray like hadron like

Acceptance is different for the two arms.Spectra are normalized by # of -ray and hadron like events.

Energy spectra at 900 GeV

PRELIMINARY

PRELIMINARY

Only statistical errors are

shown

39


Radiation damage studies

30 kGy

Dose evaluation on the

basis of LHC reports on

radiation environment at

IP1

~ 100 Gy/day @ 1030 cm-

2s-1 luminosity are

expected

~ 10 kGy during few

months operation lead to

~ 50% light output

decrease

continuous laser

calibration to monitor

scintillators and correct

for the decrease of light

output

test of Scintillating fibers and

scintillators

40

recent results on neutral particles spectra from the lhcf experiment massimo bongi - infn (florence,...

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