ECRS 2008A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ 1 Measurement of the proton-air inelastic cross section with ARGO-YBJ

ECRS 2008 A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ 1

Measurement of the proton-air

inelastic cross section with ARGO-YBJ

A. Surdo

Istituto Nazionale di Fisica NucleareLecce – Italy

on behalf of ARGO-YBJ Collaboration

21° European Cosmic Ray Symposium9-12 September 2008 – Kosice, Slovakia


Introduction

Inelastic proton-air (and total p-p) cross section can be derived from cosmic ray measurements through several methods

• Direct method:

measure the distribution of X1, the 1st interaction point of p-air collisions, to directly measure the mean free path p-air

feasible (in principle) at relatively low energies only

• Indirect methods:

(a) for fixed primary energy and zenith angle, measure the exponential tail of the shower maximum depth (Xmax) distribution

ARGO-YBJ approach

(b) for fixed primary energies, measure the exponential zenith angle distribution of the shower intensity

slope parameter () connected to p-air


• Collaboration between: Istituto Nazionale di Fisica Nucleare (INFN) – Italy Chinese Academy of Science (CAS)

• Site: Cosmic Ray Observatory @ Yangbajing (Tibet), China

High Altitude Cosmic Ray Laboratory @ YangBaJing

Site Altitude: 4,300 m a.s.l. , ~ 600 g/cm2

Site Coordinates: longitude 90° 31’ 50” E, latitude 30° 06’ 38” N

The ARGO-YBJ experiment


ARGO-YBJ is a full-coverage Extensive Air Shower detector with several main goals:

ARGO-YBJ physics objects

VHE-Ray Astronomy: search for point-like (and diffuse) galactic and extra-galactic sources at few hundreds GeV energy threshold

Poster by D. Martello Search for GRB’s (full GeV / TeV energy range)

Talk by T. Di Girolamo

Sun and Heliosphere physics (Eth 10 GeV)

Cosmic ray physics: anti-p / p ratio at TeV energy spectrum and composition (Eth few TeV) study of the shower space-time structure fundamental physics issues (p-air cross section, ...)


ARGO-YBJ detector

Central carpet:

130 Clusters1,560 RPCs

124,800 Strips(5,600m2 active area)

Strip = spatial pixel (6.5 x 62 cm2)

Pad = time pixel

Time resolution ~1 ns

78 m

111 m

99 m

74 m

RPC

+ Analog RPC charge read-out

+ 0.5 cm lead converter (2009)

10 Pads = 1 RPC (2.80 1.25 m2)

12 RPC =1 Cluster ( 5.7 7.6 m2 ) 8 Strips = 1 Pad

(56 62 cm2)


Currently completed and in data taking

Inclusive trigger Npad > 20 (“shower mode” trigger) on the central carpet.

Trigger rate 4 kHz and data flow 7 MB/s.

ARGO-YBJ detector


Measurement of the Flux attenuation

h0

1sec)0()(

oh

eII

Use the shower frequency vs (sec -1)

The absorption length is connected to int

through:

The parameter k takes into accounts how the primary energy is dissipated in the shower

k determined by simulations, depends on:

interaction model

shower fluctuations

actual set of experimental observables

……..

p-Air (mb) = 2.41·104 / int(g/cm2)

for fixed energy and shower age (h0=vert. depth).

= k int

Warning

• Constrain XDO = Xdet – X0 or

better XDM = Xdet – Xmax

• Select deep showers (large

Xmax, i.e. small XD0 or XDM)


Analysis general criteria• Exploit peculiar detector features:

space/time granularity, full-coverage technique, high altitude (h0 600 g/cm2)

• Select deep showers (large XMax, i.e. small XD0 or XDM) in order to minimize the impact of shower development fluctuations

detailed space-time patternfor unique EAS reconstruction

3-D view of a detected shower Top view of the same shower


Event selection

Basic cuts:

a. Shower fully reconstructed (0<zen<40°) through conical fit

b. Shower “detected size” (Nstrip) > 400

c. Core reconstructed inside a fiducial area (64 x 64 m2)

+

more specific cuts, based on extension of the detected shower, hit density near the reconstructed core and lateral profile, in order to:

• reduce the contamination of external core events

• put a constraint on the maximum XDM value

Finally:

strip multiplicity (Nstrip) used to set primary energy intervals


CORSIKA showers, by p and He primaries

Energy ranges: p (0.3-3000)TeV

He (1-3000)TeV

Zenith angle range: 0<<45°

QGSJET interaction model

Use of information on the longitudinal shower profile (Xmax,…)

Full detector response simulation based on GEANT package

Proper choice of the sampling area including the detector

Same analysis chain as for real data

Monte Carlo simulation


Cuts in-dependence on the zenith angle

No significant zenith angle dependence below 30 degrees.

A slight shift might be seen above 40 degrees.

In this analysis we stop at 40 degrees

Energy XDM = XDet –XMax


The energy scale Use of the strip multiplicity (Nstrip) for the estimation of shower size

up to 100 TeV primary energy

> For Nstrip fold the MC energy distribution

with parametrized p-air distribution of int.

> Get the energy corresponding to <int> (ELog).

Average int also used to evaluate k factor: k = (MC)obs/(MC)

int

Log(E/TeV) int (g/cm2) (MC)int


Nstrip Elog (TeV) (MC)int (g/cm2) k

400 ÷ 1000 4.0 78.53 ± 2.1 2.01 ± 0.06 ± 0.05

1000 ÷ 2000 8.3 76.15 ± 1.8 1.53 ± 0.02 ± 0.04

3000 ÷ 4000 19.8 73.45 ± 1.5 1.59 ± 0.04 ± 0.03

6000 ÷ 8000 38.7 71.44 ± 1.3 1.68 ± 0.06 ± 0.03

8000 ÷ 12000 53.5 70.51 ± 1.2 1.71 ± 0.07 ± 0.03

> 8000 76.7 69.50 ± 1.6 2.05 ± 0.06 ± 0.05

Analysis of MC data:

sec distributions

((MC)obs=h0/|Slope|)

and k factors

k MCobs/

(MC)int


Analysis of real data: sec distributions

CR-air (mb) = 2.41·104/(exp)int (g/cm2)

Slopehobs 0(exp) kobs

(exp)int

(exp) from MC


Heavy primaries contribution

Hoerandel AP 19 (2003) 193 taken as reference.

JACEE and RUNJOB for the evaluation of systematic error

proton

helium

Z

TeV

EE

dE

dNZ

0)(


Nstrip Elog (TeV) Helium correction pAir (mb)

400 ÷ 1000 4.0 1.00 ± 0.04 ± 0.01 261 ± 13 ± 8

1000 ÷ 2000 8.3 1.00 ± 0.02 ± 0.01 278 ± 7 ± 7

3000 ÷ 4000 19.8 1.00 ± 0.04 ± 0.01 303 ± 15 ± 7

6000 ÷ 8000 38.7 0.96 ± 0.05 ± 0.03 288 ± 19 ± 11

8000 ÷ 12000 53.5 1.00 ± 0.05 ± 0.03 289 ± 19 ± 10

> 8000 76.7 0.95 ± 0.04 ± 0.04 322 ± 17 ± 16

Heavy primaries contribution

Correction on reconstructed at 80 TeV

Above 1 TeV:

primary Helium fraction ≈ 40%

After analysis cuts: ≈ 15-20%

Heavier primaries can be neglected


Inelastic p-air cross section(statistical errors only in the plot)


Nstrip Elog (TeV) pAir (mb) pp (mb)

400 ÷ 1000 4.0 261 ± 13 ± 8 38 ± 3 ± 3

1000 ÷ 2000 8.3 278 ± 7 ± 7 42 ± 2 ± 3

3000 ÷ 4000 19.8 303 ± 15 ± 7 49 ± 4 ± 3

6000 ÷ 8000 38.7 288 ± 19 ± 11 44 ± 5 ± 4

8000 ÷ 12000 53.5 289 ± 19 ± 10 45 ± 5 ± 4

> 8000 76.7 322 ± 17 ± 16 55 ± 6 ± 5

Several available models to obtain totp-p from inel

p-air:

• Glauber – Matthiae theory• Durand – Pi• Wibig – Sobczynska• ….

Models agree within few % in our energy range

systematic error: 5%

From p-air to p-p cross section


Systematic uncertainties

Variations of the atmospheric depth (pressure)

h0MC = 606.7 g/cm2 (4300m a.s.l. standard atm.),

h0MC / <h0> = 0.988 ± 0.007 impact on cross section analysis: 1%

Uncertainty on (MC)int: RMS of MC distribution 2÷3 %

Uncertainty on the contribution of heavy neclei: comparing slopes

from different (p+He) fluxes (Hoerandel, Jacee, RunJob) 1÷4 %

Uncertainty on “p-air to p-p”: comparing different models 5 %

Statistical and systematic errors independently propagated


Total p-p cross section


Total p-pbar cross section


Summary and outlook

• The flux attenuation technique has been successfully used in ARGO-YBJ experiment, by exploiting the detector features and location.

• The inelastic proton-air (and the total p-p) cross section has been measured in a scarcely explored energy region and results are in agreement with previous ARGO results.

• More checks on systematics are in progress (shower fluctuations, interaction models, heavy primaries contribution, …).

• Shower age and energy determinations will be improved by the use

of timing (rise time, front curvature,..) and topological information

• In the future, the analysis will be extended to higher energies (up to 1PeV), thus covering a region with few experimental data, by exploiting the analog RPC readout.

Documents

ECRS 2008A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ 1 Measurement of the proton-air inelastic cross section with ARGO-YBJ