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
ECRS 2008 A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ 2
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
ECRS 2008 A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ 3
• 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
ECRS 2008 A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ 4
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, ...)
ECRS 2008 A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ 5
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)
ECRS 2008 A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ 6
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
ECRS 2008 A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ 7
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)
ECRS 2008 A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ 8
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
ECRS 2008 A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ 9
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
ECRS 2008 A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ 10
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
ECRS 2008 A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ 11
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
ECRS 2008 A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ 12
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
ECRS 2008 A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ 13
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
ECRS 2008 A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ 14
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
ECRS 2008 A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ 15
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)(
ECRS 2008 A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ 16
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
ECRS 2008 A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ 17
Inelastic p-air cross section(statistical errors only in the plot)
ECRS 2008 A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ 18
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
ECRS 2008 A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ 19
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
ECRS 2008 A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ 20
Total p-p cross section
ECRS 2008 A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ 21
Total p-pbar cross section
ECRS 2008 A.Surdo: Measurement of the p-air inelastic cross section with ARGO-YBJ 22
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.