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VHE  cosmic  rays:  experimental  

Cosmic  Rays  

  History –  1912: First discovered –  1927: First seen in cloud chambers –  1962: First 1020 eV cosmic ray seen

  Low energy cosmic rays from Sun –  Solar wind (mainly protons) –  Neutrinos

  High energy particles from sun, galaxy and perhaps beyond –  Primary: Astronomical sources. –  Secondary: Interstellar Gas. –  Neutrinos pass through atmosphere and earth –  Low energy charged particles trapped in Van Allen Belt –  High energy particles interact in atmosphere. –  Flux at ground level mainly muons

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Cosmic  Ray  Spectrum  

  Flux  follows  power  law  –  E-­‐2.7  below  knee  –  E-­‐3.2  below  ankle  

  Energies  up  to  1021  eV  

  Cosmic  Rays  at  the  surface  – Mostly  muons  –  Average  energy  3  GeV  –  Integrated  Flux  1  per  cm2  per  minute  for  a  horizontal  detector  

Ultra  High  Energy  Cosmic  Rays  

  Cosmic  rays  at  the  highest  energy  have  galac�c  or  even  extra-­‐galac�c  origin  

  The  universe  is  filled  with  the  cosmic  microwave  background.  Remnant  of  the  Big  Bang  

  Photon  temperature  ~2.7K  

Do  you  believe  this  result    from  the  AGASA  experiment?  

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Exercise  

Consider  a  high  energy  proton  interac�on  with  a    photon  of  the  cosmic  microwave  background.  These  photons  are  in  thermal  equilibrium  with  T~2.7  K.  Find  the  minimum  energy  the  proton  would  need  for  the  following  reac�on  to  occur:    

   p  +  γ  →  Δ+      (→  p  +  π0)    Masses:  p:  938  MeV,  Δ:  1232  MeV  =M,  π0:  135  MeV    Hint:  P2  =  M2      (P  =  4-­‐vector),  Lorentz  invariant                      Assume  head-­‐on  collisions    If  the  CMB  photon  density  is  420/cm3,  and  the  cross  sec�on  of  the  process  is  0.6  mb,  compute  the  mean  free  path.  

  Taking  as  a  central  value  for  the  temperature  of  the  Universe  T  =  2.7  K,  by  applying  Wien’s  one  can  obtain  the  peak  value  for  the  wavelength,  and  then  and  for  the  energy:          Epeak  =  1.2  meV  

       

  Mean  free  path    

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GZK  Cutoff  Auger  

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Large  mean  free  path…  Transparency  of  the  Universe  

15  ly  

1.5  Mly  

500    Mly  

Nearest  Stars  

Nearest  Galaxies  

Nearest  Galaxy  Clusters  

Milky  Way  

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E      α    B  R  

S.  Swordy  

Cosmic rays flux vs. Energy

UHECR    •   one  par�cle  per  century  per  km2  

•   many  interes�ng  ques�ons  

  (nearly) uniform power-law spectrum spanning 10 orders of magnitude in E and 32 in flux!

  structures : ~ 3 – 5 1015 eV: knee change of source? new physics? ~ 3 1018 eV: ankle transition galactic – extragalatic? change in composition?

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Questions

  How  cosmic  rays  are  accelerated  at                                              ?    What  are  the  sources?      How  can  they  propagate  along  astronomical  distances  at  such  high  energies?    Are  they  substan�ally  deflected  by  magne�c  fields?    Can  we  do  cosmic  ray  astronomy?    What  is  the  mass  composi�on  of  cosmic  rays?  

 

eV 1019>E

Detection techniques

Par�cles  at  ground  level  •   large  detector  arrays  (scin�llators,  water  Cherenkov  tanks,  etc)  •   detects  a  small  sample  of  secondary  par�cles  (lateral  profile)  •   100%  duty  cicle  •   aperture:  area  of  array    (independent  of  energy)  •   results  on  primary  energy  and  mass  composi�on    are  model  dependent  (rely  on  Monte  Carlo  simula�ons  based  on  extrapola�ons  of  the  hadronic  models    constrained  at  low  energies  by  accelerator  physics)  

ex: AGASA

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Detection techniques

Fluorescence  of  N2  in  the  atmosphere  •   calorimetric  energy  measurement  as  func�on  of  atmospheric  depth  •   only  for  E  >  1017  eV  •   only  for  dark  nights  (10%  duty  cicle)  •   requires  good  knowledge  of  atmospheric  condi�ons  •   aperture  grows  with  energy,  varies  with  atmosphere  

ex: HiRes

The Auger Observatory: Hybrid design   A  large  surface  detector  array  combined  with  fluorescence  detectors  results  in  a  unique  and  powerful  design.  

  Simultaneous  shower  measurement  allows  for  transfer  of  the  nearly  calorimetric  energy  calibra�on    from  the  fluorescence  detector  to  the  event  gathering  power  of  the  surface  array.  

  A  complementary  set  of  mass  sensi�ve  shower  parameters  contributes  to  the  iden�fica�on  of  primary  composi�on.  

  Different  measurement  techniques  force  understanding  of  systema�c  uncertain�es  in  each.  

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Loca�on  of  the  Auger  experiment  

 4  fluorescence    buildings,  each  with  6  telescopes    1st  4-­‐fold  on  20  May  2007    1600  tanks    

HYBRID  DETECTOR  

Pierre Auger South Observatory 3000 km2

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A  surface  array  sta�on  

Communica�ons    antenna   GPS  antenna  

Electronics  enclosure   Solar  panels  

Ba�ery  box  

3  photomul�plier  tubes  looking  into  the  water  collect  light  le�  by  the  

par�cles  

Plas�c  tank  with  12  tons  of  very  pure  water  

The fluorescence detector

Los  Leones    telescope  

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The  fluorescence  telescope  

30  deg  x  30  deg    view  per  telescope  

20  May  2007        E  ~  1019  eV  

First hybrid qudriple event!

Signal in all four FD detectors and 15 SD stations!

First 4-fold hybrid on 20 May 2007

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θ~  48º,  ~  70  EeV  

Flash  ADC  traces  Flash  ADC  traces  

Lateral  density  distribu�on  

 

 

   

 

 

 

 

Typical  flash  ADC  trace  

at  about  2  km  

Detector  signal  (VEM)  vs  �me  (µs)  

PMT  1  

PMT  2  

PMT  3  

-­‐0.5    0        0.5      1.0      1.5    2.0    2.5    3.0  µs    

18  detectors  triggered  

 Hybrid  Event  

longitudinal profile

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θθ  =  79  °  

Inclined  Events  offer  addi�onal  aperture  

Energy spectrum from Auger Observatory

  Based  on  fluorescence  and  surface  detector  data    Model-­‐  and  mass-­‐independent  energy  spectrum    Power  of  the  sta�s�cs  and  well-­‐defined  exposure  of  the  surface  detector  

  Hybrid  data  confirm  that  SD  event  trigger  is  fully  efficient  above  3x1018  eV  for  θ<60o  

  Uses  energy  scale  of  the  fluorescence  detector  (nearly  calorimetric,  model  independent  energy  measurement)  to  calibrate  the  SD  energy.  

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  SD  parameter  S1000:  interpolated  tank  signal  at  1000  meters  from  the  lateral  distribu�on  func�on    Determined  for  each  SD  event    It  is  propor�onal  to  the  primary  energy  

Energy calibration

  Reduced measurement uncertainty (shower fluctuations dominate)   VEM = vertical equivalent muons from self calibration of the tank signal (from

ambient muons)

Energy calibration

Fractional difference between the SD and FD energy for the hybrid events;

  Small relative dispersion   includes uncertainties in both the FD

energy and the SD signal

  S(1000) is intrinsecally a very good energy estimator   Reliable energy measurements

when properly calibrated

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  The agreement between the spectra derived using three different methods is good

Energy spectra from Auger

Astrophysical  models  and  the  Auger  spectrum  

models assume: an injection spectral index, an exponential cutoff at an energy of Emax times the charge of the nucleus, and a mass composition at the acceleration site as well as a distribution of sources.

Auger data: sharp suppression in the spectrum with a high confidence level!

Expected GZK effect or a limit in the acceleration process?

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Composition from hybrid data

  UHECR:    observatories  detect  induced  showers  in  the  atmosphere  

  Nature  of  primary:  look  for  diferences  in  the  shower  development  

  Showers  from  heavier  nuclei  develop  earlier  in  the  atm  with  smaller  fluctua�ons  –  They  reach  their  maximum  development  

higher  in  the  atmosphere    (lower  cumulated  grammage,    Xmax  )  

  Xmax    is  increasing  with  energy  (more  energe�c  showers  can  develop  longer  before  being  quenched  by  atmospheric  losses)  

Composition from hybrid data

Xmax resolution ~ 20 g/cm2

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composition from hybrid data

  The results of all three experiments are compatible within their systematic uncertainties.   The statistical precision of Auger data exceeds that of preceding experiments

test of hadronic models

  Assump�on:  universality  of  the  electromagne�c  shower  evolu�on  

Lateral  distribu�on  func�on  

Longitudinal  profile  

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Cosmic  Rays  

Cosmic  Rays  and  LHC  

 accelerators  

     satellites,        balloons    

air  shower          arrays   Auger  

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Cosmic  Rays  and  LHC  

 accelerators  Current  models          tuned  here  

LHC provides a significant lever arm providing constraints for UHECR simulations !

     satellites,        balloons    

air  shower          arrays   Auger  

§  LHC  detectors  cover  all  wide  rapidity  range    

§  EAS  models  bracket  accelerator  data  §  no  model  perfect,  but  EAS  models  seem  to  do  be�er  than  HEP  

models            

 

§  HEP                    High  Energy  Physics  

models  

§  EAS                                            Extensive  Air  Shower  

models    

Small-­‐x  region  (LHC  as  a  pathfinder  for  CR,  and  vice-­‐versa)  

(Spiering)  

η = ln tan ϑ2$

% &

'

( )

$

% &

'

( )

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Cross  sec�ons:  something  not  understood  in  Auger    

Shower  Maximum  Xmax  

These  suggest  high  cross  sec�on  and  high  mul�plicity  at  high  energy.  

 Heavy  nuclei?          

 Or  protons  interac�ng  differently  than  expected?  

Informa�on  lacking  for  the  EHE  (anisotropic?)  energy  regime!  

   

(Pimenta)

Cosmic  Rays  and  LHC:  total  cross  sec�on  

§  Test  Glauber  model  §  Tune  EAS  simula�ons  

(Pro

ton-

Prot

on)

[m

b]in

elσ

30

40

50

60

70

80

90

100

110

[GeV]s310 410 510

ATLAS 2011

CMS 2011

ALICE 2011

TOTEM 2011

UA5

CDF/E710

Auger 2012 (Glauber)

QGSJet01

QGSJetII.3

Sibyll2.1

Epos1.99

Pythia 6.115

Phojet

pp inel. cross section at sqrt(s)=57 TeV

If  protons,  the    X-­‐sec�on  rises  at  ~100  TeV  =>  A  new  physics  scale?  

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§  High-­‐mul�plicity  cosmic  event  in  ALICE                  à  §  Density  of  ~18  muons/m2  (within  the  TPC  volume)  

§  Similar  enigmas  in  underground  experiments  §  Muon  numbers  in  EAS  about  50-­‐100%  higher  than  MC  

predic�ons  

§  `  

§  à  Upgrade  EAS  experiments  with  muon  counters  

 

Auger  

Extreme  muon  mul�plici�es    

   N19  ~  Nµ  

photon limits    

A = Agasa HP = Haverah Park Y = Yakutsk

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Direct  hints  of  cosmic  accelerators?  

       B      R      E  (eV)    IGM  10-­‐4  µG        ISM    3  x  1  µG  100  kpc    SNR    30  µG    1  pc      3  x  1016  

 SMBH  300  µG  104  pc    >  1021          GRB  109  G      10-­‐3  AU  0.2  x  1021  

41  

!!

E1!PeV

≅B

1!µG×

R1!pc

E1!PeV

≅ 0.2 B1!G

×R

1!AU

Angular resolution Surface detector

Hybrid data: better angular resolution, ~ 0.7o @ 68% c.l. in the EeV energy range

Events with E > 10 EeV : 6 or more SD stations

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Galactic center

  Galac�c  Center  is  a  “natural”  site  for  cosmic  ray  accelera�on  –  Supermassive  black  hole  –  Dense  clusters  of  stars  –  Stellar  remnants  –  SNR  (?)  Sgr  A  East  

  excess  should  be  consistent  with  a  point  source  

Chandra  

Source at the Galactic center AGASA  

)4.5( 6.413

506expectedobserved

σ+=

20o  scales  

1018  –  1018.4  eV      

N.  Hayashida  et  al.,  Astropar�cle  Phys.  10  (1999)  303  

Significance  (σ)  

•   Cuts  are  a  posteriori    •   Chance  probability  is  not  well  defined  

22%    excess  

)280,15(),( °°−=αδ

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Source at Galactic center

J.A.  Bellido  et  al.,  Astropar�cle  Phys.  15  (2001)  167  

)2.9( 8.118.21

expectedobserved

σ+=

85%    excess  

1018  –  1018.4    eV      

5.5o  cone  )274,22(),( °°−=αδ

§  test  of  AGASA:  obs/exp  =  2116/2159.5              R  =  0.98  ±  0.02  ±  0.01            

       NOT  CONFIRMED  (with  3x  more  stats)    §   test  of  SUGAR:    obs/exp  =  286/289.7    

     R  =  0.98  ±  0.06  ±  0.01              NOT  CONFIRMED  (with  10x  more  stats)    §   Galac�c  Center  as  a  point  source  (σ=1.5°):                                                              obs/exp  =  53.8/45.8                                          R  =  1.17  ±  0.10  ±  0.01                                                NO  SIGNIFICANT  EXCESS    §   upper  limit  on  the  flux  of  neutrons  coming  from  GC:       §  Galac�c  Plane:  NO  SIGNIFICANT  EXCESS    

astro-ph/0607382 (Astropart. Phys., 2007)

Φs  <  0.08  ξ  km-­‐2  yr-­‐1        at  95%  C.L.  

5°, top-hat AGASA SUGAR

G.P.

results for the galactic center

(check proceedings ICRC 07 for an update)

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Overdensity search (galactic center)

Li,  Ma  ApJ  272,  317-­‐324  (1983)  

significance  

All  distribu�ons  consistent  with  isotropy    

1 EeV < E <10 EeV

0.1 EeV < E < 1 EeV

anisotropy searches

  All-­‐sky  blind  searches  for  sources:    NO  EXCESS  FOUND    Angular  coincidences  between  Auger  events  and  BL  Lac  objects  (as  possibly  seen  by  HiRes):  see  later;  

  Search  for  clustering  (as  seen  by  AGASA),  1  significant  excess  observed  (Cen  A)  

  Scan  in  angle  and  energy:  hints  of  clustering  at  larger  energies  and  intermediate  angular  scales  –  Large  scale  distribu�on  of  nearby  sources?  –  Chance  probability  of  such  a  signal  from  an  isotropic  flux  ~  2%  (marginally  

significant)  

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Origin  of  EHE:  the  2007  evidence  for  the  emission  of    EHE  hadrons  by  AGN  almost  disappeared  (apart  from  CenA)  

  The  “direct”  measurement  by  AUGER  (E  >  60  EeV)  

  Orphan  flares  in  TeV  band  (?)    The  produc�on  region  of  gammas  from  flares  in  M87  is  accompanied  by  radio  ac�vity  very  close  to  the  BH,  where  there  is  abundance  of  protons  –  If  SNRs  O(10  SM)  can  explain  CR  at  O(1  PeV),      BH  O(109  SM)  “might”  explain  CR  up  to  O(1023  eV)  

27 events as of November 2007 84 events now; 28 correlate with AGN

Correlation significant only around CenA

50  

One  should  be  careful  about  astrophysics  with  CR  …  

  Auger  observa�ons  confirm  

the  GZK  cutoff  

  Role  of  magne�c  fields  

–  Galac�c  astrophysics  impossible  (BMW~1µG)  

–  Extragalac�c  astrophysics  very  difficult:    

Anisotropy

 Angular  spread  

!!

E1!EeV

≅B

1!µG×

R1!kpc

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other physics topics to be explored    

  Neutrinos    Gamma  ray  burst  detec�on    Measurement  of  the  primary  cosmic  ray  cross  sec�on;    and  many  others  ...  

 

Conclusions, perspectives

  The  EHE  CR  physics  is  substan�ally  dominated  by  the  Auger  experiment    No  significant  correla�on  of  EHE  CR  with  known  sources  (apart  CenA)    Marginal  direc�on  correla�on  with  CenA  

  Hadronic  models  validated  

  Something  strange  might  happen  around  10^20  eV;  change  of  composi�on  does  not  seem  enough  to  explain  it