Recently essential efforts were made to improve measurement routine with X-ray films exposed in the X-ray emulsion chambers at the Pamirs. Analysis of X-ray emulsion response upon recorded events show that γ-family energy and intensity in early publications were over estimated. The main physical results of the new analysis are presented

A.E. Morozov

A.S. Borisov

E.A. Kanevskaya

M.D. Smirnova

M.G Kogan

R.A. Mukhamedshin

S.E Pyatovsky

V.G. Denisova

V.M. Maximenko

V.S. Puchkov

Z.M. Guseva

EPJ Web of Conferences

English

Crossref

Revised data on γ-families observed in Χ-ray emulsion chambers of the 
Experiment PAMIR
A.S.Borisov1, Z.M.Guseva1, V.G.Denisova1, E.A.Kanevskaya1, M.G.Kogan1, V.M.Maximenko1, A.E.Morozov1, 
R.A.Mukhamedshin2, V.S.Puchkov1, S.E.Pyatovsky1, M.D.Smirnova1
1 Lebedev Physical Institute, Russian Academy of Sciences, Leninsky pr. 53, Moscow, 119991 Russia
2 Institute for Nuclear Research, Russian Academy of Sciences, pr 60-letiya Oktyabrya 7a, Moscow, 117312 Russia
Abstract. Recently essential efforts were made to improve measurement routine with Χ-ray films exposed in 
the Χ-ray emulsion chambers at the Pamirs. Analysis of Χ-ray emulsion response upon recorded events show 
that γ-family energy and intensity in early publications were over estimated. The main physical results of the  
new analysis are presented.
1 Introduction
Over  many  years  the  collaboration  of  the  Experiment 
PAMIR [1] investigated high-energy nuclear interactions 
in cosmic rays with  Χ-ray emulsion chambers  (ΧREC) 
exposed at the Pamirs at an altitude of 4370 m above sea 
level  (600  g/cm2).  Various  components  of  nuclear-
electromagnetic cascades (NEC) induced by protons and 
nuclei of primary cosmic rays (PCR) at an energy E0≥1015 
eV are recorded. The investigations are concerned mainly 
with  «families»,  i.e.  bundles  of  the  most  energetic 
secondary particles (threshold for particle detection in the 
XREC is 1–2 TeV ) in the core of just the same NEC. 
The  secondaries  are  hadrons  and  particles  of 
electromagnetic nature (γ-rays and electrons ) which, for 
brevity, hereafter are referred to as γ-rays.
In this paper we consider families recorded in a thin 
XREC  with  lead  absorber  (Г-block);  its  structure 
schematically is as follows: 4 cm Pb + X-ray film + 1 cm 
Pb + X-ray film + 1 cm Pb + X–ray film. The XREC of 
this type were exposed either as a single Γ-block or as an 
upper  part  of  a  compound  experimental  set-up  with 
hadron blocks. The main fraction of particles recorded in 
Γ-block  are  γ-rays,  and  the  corresponding  families  are 
called γ-families.
The  characteristics  of  γ-family  are  sensitive  to  a 
composition and energy spectra of the PCR. The analysis 
is  based  on  comparison  of  experimental  data  with 
simulations.
The proper improvement  of measurement  procedure 
with Χ-ray films exposed in the XREC was made in order 
to increase an accuracy of physical results.
2 Experimental data
The  present  analysis  is  based  on  γ-families  recorded 
during  a  total  XREC  exposure  ST=2635 m2.year  and 
selected by following criteria: a) total energy of γ-rays in 
the family  ΣEγ≥100 TeV; b)  energy  of  γ-rays  and their 
incidence angle (with respect to vertical) Eγ≥4 TeV and 
θγ≤45⁰, respectively; c) deviation of separate  γ-rays from 
the  energy-weighted  center  of  a  family  in  the  target 
diagram  plane  at  the  observation  level  Rγ≤15  cm;  d) 
number of  γ-rays in the family satisfying above criteria 
nγ ≥ 3.  The  total  number  of  selected  and  analyzed  γ-
families is Nfam=1003.
Among  γ-families  with total  energy  ΣEγ≥500 TeV 
there are events, in which closely related electromagnetic 
cascades in the central part of γ-family overlap and make 
up a large diffusive dark spot with high optical density 
(halo). There are γ-families with single-center and multi-
center halo (fig.1).
The 61  γ-families with halo were recorded over an 
exposure ST=3000 m2 year and also used in our analysis. 
Model calculations show that single-center halo produced 
mainly by protons, while multicenter halo are produced 
by heavy nuclei.
EPJ Web of Conferences
DOI: 10.1051/
C© Owned by the authors, published by EDP Sciences, 2013
,
epjconf 201/
04007 (2013)
35204007
52
 This  is  an  Open Access  article distributed under the terms of the Creative Commons Attribution License 2 0 , which . permits unrestricted  use,  distributi
and reproduction in any medium, provided the original work is properly cited. 
on,
Article available at http://www.epj-conferences.org or http://dx.doi.org/10.1051/epjconf/20125204007
a) b)
Fig.1. a)  Example  of  γ-family on the  X-ray  film; 
b) scanner image of the halo event called «FIANIT».
The criteria for selection of γ-families with halo are 
as follows:
a) ΣEγ≥500 TeV;
b) the area of halo SD=0.5 bounded by isodense with 
optical density D=0.5.
SD=0.5≥4 mm2 – for single-center halo, and ΣSi D=0.5≥4 
mm2, if Si D=0.5≥1 mm2 – for multi-center halo.
Model calculations show that  γ-families with  ΣEγ=100–
400  TeV  are  produced  mainly  by  PCR  particles  with 
E0=1015–1016eV, while halo γ-families with ΣEγ≥500 TeV 
are produced by PCR with E0≥1016 eV.
3 Model calculations
Artificial events of γ-families were sampled by code MC0 
of  quark-gluon-string  model  [2],  which  was  elaborated 
for  Experiment  PAMIR  and  satisfactorily  reproduced 
main  characteristics  of  γ-families  with  ΣEγ>100  TeV. 
Spectrum of PCR at an energy E0=2·1014–3·1018 eV was 
taken from experimental  data of  KASKADE and Tibet 
[3].  Mass  composition  in  MC0  model  is  presented  in 
Table  1.  Calculations  revealed  that  about  80%  of  all 
events are produced by primary protons, 10% by helium 
nuclei  and  no  more  than  10% by  heavier  nuclei.  This 
conclusion is almost independent of the models and thus 
provides a possibility to estimate the fraction of protons 
in PCR in the range of E0=1015–1017 eV.
Table 1. Mass composition in MC0 model.
Е, eV 1015 1016 1017
p, % 33 26 20 
α, % 22 17 15 
Detailed  analysis  of  a  response  of  the  XREC  to 
events  recorded  Χ-ray  films  is  based  on  simulation  of 
measurement  procedure  by  code  GEANT3.21.  The 
contribution of under threshold electromagnetic cascades, 
the mutual influence of neighboring cascades in γ-family, 
identification of cascades against background by Raleigh 
criterion are taken into account. The analysis show that in 
our early publication there was overestimation of family 
energy approximately by 20%.
4 Spatial distribution and structure of γ-
families
Analysis  of  spatial  distribution  in  γ-families  show that 
due to fluctuation, a large number of γ-families with ΣEγ 
close to threshold (ΣEγthr=100 TeV) have broader spatial 
distributions than average one (with Rf=ΣRγ/nγ larger by 
15%). Experimental value of <Rf> for range of ΣEγ=100–
400  TeV  is  <Rf>=1.94±0.06  cm,  while  model  values 
<RfMC0>=2.01±0.03  cm,  <Rfp>=1.79±0.03, 
<RfHe>=2.37±0.09, <RfFe>=4.15±0.18 cm.
Comparison  <Rf>  and  <RfMC0>  indicates  that 
experimental  γ-families at energy range E0=1015–1016 are 
produced  mainly  by  protons.  At  the  same  time 
contribution of helium nuclei less than 15%.
To prove the suggestion that  at  energy E0>1016eV 
most events with halo are generated by primary protons 
we compare the fraction of  γ-families with multi-center 
halo in the experiment and calculations (Table 2).
Table  2. Fraction  of  γ-families  with  multi-center  halo 
generated by different nuclei.
p He C Fe PAMIR
0.25
±0.03
0.45
±0.09
0.59
±0.11
0.70
±0.12
0.23
±0.07
It  is  evident  that  recorded  γ-families  with  halo 
almost  entirely  are  generated  by  primary  protons  with 
possible little addition of He.
5.  Dependence  of  g-family  flux  on  the 
PCR mass composition
The intensities of the γ-families in MC0 model and Pamir 
experiment are presented in Table 3.
Table 3. Energy range: 1015 ÷ 1016 eV.
MC0
PAMIR* (with 
chamber 
response)
If(ΣЕg >100 TeV, 600 g/см2,
θ=0), m-2×year-1×sr-1
0.71
± 0.02
0.39
± 0.03
To  match  this  experimental  value  of  γ-families 
intensity  in  the  interval  of  E0=1015-1016 eV  and 
calculations  of  code  MC0  fraction  of  protons  in  the 
model should be reduced  from 33% to (18±2)% if  the 
ejected  part  of  protons is  substituted  by nuclei  of  iron 
group or to (16±2)%if the ejected protons are substituted 
by helium nuclei. The similar conclusion with the same 
quantitive estimation of the proton fraction in PCR was 
made for the energy E0>1016 eV by analysis of γ-families 
with halo.
Thus  proton  fraction  in  PCR  in  the  energy  range 
1015 ÷ 1017 eV in Pamir experiment is about (16 ÷ 18)%, 
Table 4.
04007-p.2
EPJ Web of Conferences
Table  4. Fraction  of  protons  in  the  energy  range 
1015 ÷ 1017 eV.
MC0 PAMIR* (allowing for chamber response)
33% (16 ÷ 18)% ± 2%
6. Conclusions
1) γ-families  in  the  Experiment  PAMIR at  an primary 
energy E0=1015-1016 eV are produced by primary pro-
tons with a small amount (∼10%) of helium;
2) the fraction of protons in the PCR composition at an 
energy E0=1015-1016 eV is about 15-20% and do not 
change appreciably up to E0=1017 eV.
The  article  was  supported  by  the  State  contract 
N 11.519.11.5022.
References
1. S.G.Bayburina  et  al.  Trudy  FIAN  (Transactions  of 
Lebedev  Physical  Institute),  V.154,  pp.1  –  141 
(1984).
2. G.F.Fedorova,  R.A.Mukhamedshin,  Bull.  Soc.  Sci. 
Lett. Lodz, Ser Rech. Def., 1994, vol.XVI, pp. 137-
152.
3. H.Ulrich et al., Proc. 27th ICRC, Hamburg, 2001, vol. 
1, pp. 97-100.
4. V.S.Puchkov et al. Nuclear Phys. B. (Proc. Suppl.), 1, 
2009, V.196, P.110.
04007-p.3
ISVHECRI 2012


Revised data on γ-families observed in X-ray emulsion chambers of the Experiment PAMIR

Revised data on γ-families observed in Χ-ray emulsion chambers of the Experiment PAMIRA.S.Borisov1, Z.M.Guseva1, V.G.Denisova1, E.A.Kanevskaya1, M.G.Kogan1, V.M.Maximenko1, A.E.Morozov1, R.A.Mukhamedshin2, V.S.Puchkov1, S.E.Pyatovsky1, M.D.Smirnova11 Lebedev Physical Institute, Russian Academy of Sciences, Leninsky pr. 53, Moscow, 119991 Russia2 Institute for Nuclear Research, Russian Academy of Sciences, pr 60-letiya Oktyabrya 7a, Moscow, 117312 RussiaAbstract. Recently essential efforts were made to improve measurement routine with Χ-ray films exposed in the Χ-ray emulsion chambers at the Pamirs. Analysis of Χ-ray emulsion response upon recorded events show that γ-family energy and intensity in early publications were over estimated. The main physical results of the  new analysis are presented.1 IntroductionOver  many  years  the  collaboration  of  the  Experiment PAMIR [1] investigated high-energy nuclear interactions in cosmic rays with  Χ-ray emulsion chambers  (ΧREC) exposed at the Pamirs at an altitude of 4370 m above sea level  (600  g/cm2).  Various  components  of  nuclear-electromagnetic cascades (NEC) induced by protons and nuclei of primary cosmic rays (PCR) at an energy E0≥1015 eV are recorded. The investigations are concerned mainly with  «families»,  i.e.  bundles  of  the  most  energetic secondary particles (threshold for particle detection in the XREC is 1–2 TeV ) in the core of just the same NEC. The  secondaries  are  hadrons  and  particles  of electromagnetic nature (γ-rays and electrons ) which, for brevity, hereafter are referred to as γ-rays.In this paper we consider families recorded in a thin XREC  with  lead  absorber  (Г-block);  its  structure schematically is as follows: 4 cm Pb + X-ray film + 1 cm Pb + X-ray film + 1 cm Pb + X–ray film. The XREC of this type were exposed either as a single Γ-block or as an upper  part  of  a  compound  experimental  set-up  with hadron blocks. The main fraction of particles recorded in Γ-block  are  γ-rays,  and  the  corresponding  families  are called γ-families.The  characteristics  of  γ-family  are  sensitive  to  a composition and energy spectra of the PCR. The analysis is  based  on  comparison  of  experimental  data  with simulations.The proper improvement  of measurement  procedure with Χ-ray films exposed in the XREC was made in order to increase an accuracy of physical results.2 Experimental dataThe  present  analysis  is  based  on  γ-families  recorded during  a  total  XREC  exposure  ST=2635 m2.year  and selected by following criteria: a) total energy of γ-rays in the family  ΣEγ≥100 TeV; b)  energy  of  γ-rays  and their incidence angle (with respect to vertical) Eγ≥4 TeV and θγ≤45⁰, respectively; c) deviation of separate  γ-rays from the  energy-weighted  center  of  a  family  in  the  target diagram  plane  at  the  observation  level  Rγ≤15  cm;  d) number of  γ-rays in the family satisfying above criteria nγ ≥ 3.  The  total  number  of  selected  and  analyzed  γ-families is Nfam=1003.Among  γ-families  with total  energy  ΣEγ≥500 TeV there are events, in which closely related electromagnetic cascades in the central part of γ-family overlap and make up a large diffusive dark spot with high optical density (halo). There are γ-families with single-center and multi-center halo (fig.1).The 61  γ-families with halo were recorded over an exposure ST=3000 m2 year and also used in our analysis. Model calculations show that single-center halo produced mainly by protons, while multicenter halo are produced by heavy nuclei.EPJ Web of ConferencesDOI: 10.1051/C© Owned by the authors, published by EDP Sciences, 2013,epjconf 201/04007 (2013)3520400752 This  is  an  Open Access  article distributed under the terms of the Creative Commons Attribution License 2 0 , which . permits unrestricted  use,  distributiand reproduction in any medium, provided the original work is properly cited. on,Article available at http://www.epj-conferences.org or http://dx.doi.org/10.1051/epjconf/20125204007a) b)Fig.1. a)  Example  of  γ-family on the  X-ray  film; b) scanner image of the halo event called «FIANIT».The criteria for selection of γ-families with halo are as follows:a) ΣEγ≥500 TeV;b) the area of halo SD=0.5 bounded by isodense with optical density D=0.5.SD=0.5≥4 mm2 – for single-center halo, and ΣSi D=0.5≥4 mm2, if Si D=0.5≥1 mm2 – for multi-center halo.Model calculations show that  γ-families with  ΣEγ=100–400  TeV  are  produced  mainly  by  PCR  particles  with E0=1015–1016eV, while halo γ-families with ΣEγ≥500 TeV are produced by PCR with E0≥1016 eV.3 Model calculationsArtificial events of γ-families were sampled by code MC0 of  quark-gluon-string  model  [2],  which  was  elaborated for  Experiment  PAMIR  and  satisfactorily  reproduced main  characteristics  of  γ-families  with  ΣEγ>100  TeV. Spectrum of PCR at an energy E0=2·1014–3·1018 eV was taken from experimental  data of  KASKADE and Tibet [3].  Mass  composition  in  MC0  model  is  presented  in Table  1.  Calculations  revealed  that  about  80%  of  all events are produced by primary protons, 10% by helium nuclei  and  no  more  than  10% by  heavier  nuclei.  This conclusion is almost independent of the models and thus provides a possibility to estimate the fraction of protons in PCR in the range of E0=1015–1017 eV.Table 1. Mass composition in MC0 model.Е, eV 1015 1016 1017p, % 33 26 20 α, % 22 17 15 Detailed  analysis  of  a  response  of  the  XREC  to events  recorded  Χ-ray  films  is  based  on  simulation  of measurement  procedure  by  code  GEANT3.21.  The contribution of under threshold electromagnetic cascades, the mutual influence of neighboring cascades in γ-family, identification of cascades against background by Raleigh criterion are taken into account. The analysis show that in our early publication there was overestimation of family energy approximately by 20%.4 Spatial distribution and structure of γ-familiesAnalysis  of  spatial  distribution  in  γ-families  show that due to fluctuation, a large number of γ-families with ΣEγ close to threshold (ΣEγthr=100 TeV) have broader spatial distributions than average one (with Rf=ΣRγ/nγ larger by 15%). Experimental value of <Rf> for range of ΣEγ=100–400  TeV  is  <Rf>=1.94±0.06  cm,  while  model  values <RfMC0>=2.01±0.03  cm,  <Rfp>=1.79±0.03, <RfHe>=2.37±0.09, <RfFe>=4.15±0.18 cm.Comparison  <Rf>  and  <RfMC0>  indicates  that experimental  γ-families at energy range E0=1015–1016 are produced  mainly  by  protons.  At  the  same  time contribution of helium nuclei less than 15%.To prove the suggestion that  at  energy E0>1016eV most events with halo are generated by primary protons we compare the fraction of  γ-families with multi-center halo in the experiment and calculations (Table 2).Table  2. Fraction  of  γ-families  with  multi-center  halo generated by different nuclei.p He C Fe PAMIR0.25±0.030.45±0.090.59±0.110.70±0.120.23±0.07It  is  evident  that  recorded  γ-families  with  halo almost  entirely  are  generated  by  primary  protons  with possible little addition of He.5.  Dependence  of  g-family  flux  on  the PCR mass compositionThe intensities of the γ-families in MC0 model and Pamir experiment are presented in Table 3.Table 3. Energy range: 1015 ÷ 1016 eV.MC0PAMIR* (with chamber response)If(ΣЕg >100 TeV, 600 g/см2,θ=0), m-2×year-1×sr-10.71± 0.020.39± 0.03To  match  this  experimental  value  of  γ-families intensity  in  the  interval  of  E0=1015-1016 eV  and calculations  of  code  MC0  fraction  of  protons  in  the model should be reduced  from 33% to (18±2)% if  the ejected  part  of  protons is  substituted  by nuclei  of  iron group or to (16±2)%if the ejected protons are substituted by helium nuclei. The similar conclusion with the same quantitive estimation of the proton fraction in PCR was made for the energy E0>1016 eV by analysis of γ-families with halo.Thus  proton  fraction  in  PCR  in  the  energy  range 1015 ÷ 1017 eV in Pamir experiment is about (16 ÷ 18)%, Table 4.04007-p.2EPJ Web of ConferencesTable  4. Fraction  of  protons  in  the  energy  range 1015 ÷ 1017 eV.MC0 PAMIR* (allowing for chamber response)33% (16 ÷ 18)% ± 2%6. Conclusions1) γ-families  in  the  Experiment  PAMIR at  an primary energy E0=1015-1016 eV are produced by primary pro-tons with a small amount (∼10%) of helium;2) the fraction of protons in the PCR composition at an energy E0=1015-1016 eV is about 15-20% and do not change appreciably up to E0=1017 eV.The  article  was  supported  by  the  State  contract N 11.519.11.5022.References1. S.G.Bayburina  et  al.  Trudy  FIAN  (Transactions  of Lebedev  Physical  Institute),  V.154,  pp.1  –  141 (1984).2. G.F.Fedorova,  R.A.Mukhamedshin,  Bull.  Soc.  Sci. Lett. Lodz, Ser Rech. Def., 1994, vol.XVI, pp. 137-152.3. H.Ulrich et al., Proc. 27th ICRC, Hamburg, 2001, vol. 1, pp. 97-100.4. V.S.Puchkov et al. Nuclear Phys. B. (Proc. Suppl.), 1, 2009, V.196, P.110.04007-p.3ISVHECRI 2012

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Revised data on γ-families observed in X-ray emulsion chambers of the Experiment PAMIR

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