RICAP 2013
Muon puzzle in cosmic ray experiments
and its possible solution
Anatoly Petrukhin
National Research Nuclear University MEPhI,
Moscow, Russia
Outline
1. Introduction
2. Muon bundle investigations
3. VHE muon investigations
4. Possible explanation
5. How to check the new approach
5. Conclusion
Introduction
What does mean “muon puzzle”?
Short answer:
Excess of muons in different experiments compared
to expectations from corresponding calculations and
simulations.
The term “muon puzzle” was finally formulated at
International Symposium on Future Directions in UHECR
Physics in CERN, 13-16 February, 2012.
Short conclusions of talks
P. Sokolsky:
Muon content in showers in HiRes/MIA higher then expected
Pierre Auger Observatory:
Deficit of muons in simulations.
Harder muon spectra in data.
M. Fukushima:
Air shower at UHE is poorly understood, esp. muon (had)
sector is un-healthy.
T. Pierog:
Discrepancy (baryon and pion spectra) between models =
= Large differences in the number of muons.
P. Lipari:
The “muon problem”.
Muon bundle investigations
LEP Detectors (CERN)
ALEPH
130 m depth (E  70 GeV)
Hadron calorimeter, TPC
5 scintillator stations
DELPHI
100 m depth (E  50 GeV)
Hadron calorimeter, TPC, TOF
L3
40 m depth (E  15 GeV)
Drift chambers, timing
scintillators, EAS surface array
Multi-muon events (muon bundles)
C. Grupen et al., Nuclear Physics B (Proc. Suppl.)
175-176 (2008) 286,
ALEPH
J. Abdallah et al., Astroparticle Physics 28 (2007) 273.
DELPHI
General view of NEVOD-DECOR complex
(Russian-Italian Project)
Coordinate-tracking
detector DECOR
(~115 m2)
Cherenkov water
detector NEVOD
(2000 m3)
Side SM: 8.4 m2 each
• σx  1 cm; σψ  1°
A typical muon bundle event in Side DECOR
( 9 muons, 78 degrees)
Run 8 --- Event 219242 ----06-12-2004 23:25:26.27 Trigger(1-16):01110100 00000000 Weit_Time:109.072 msec
3468:0
3319:1
3290:2
3094:3
3621:0
3336:1
3270:2
3294:3
3514:0
3384:1
3110:2
3158:3
3649:0
3511:1
3353:2
3378:3
7190:0
3453:1
3239:2
3388:3
4073:0
3360:1
4413:2
3888:3
3623:0
3554:1
3470:2
3444:3
3564:0
3299:1
3058:2
3303:3
0:3264
1:3216
2:3072
3:3207
0:2987
1:3147
2:3051
3:3146
0:3596
1:3446
2:4148
3:3509
0:3476
1:3205
2:3331
3:3000
0:3705
1:3597
2:3600
3:3859
0:3405
1:3394
2:3410
3:3626
0:3521
1:3532
2:3429
3:3159
0:3871
1:3568
2:3545
3:3697
SM=0
SM=1
SM=2
SM=3
SM=4
SM=5
SM=6
SM=7
Y-projection
X-projection
Plate1:Step=25nsec
0
1
2
3
4
5
6
7
Plate2:Step=25nsec
0
1
2
3
4
5
6
7
A “record” muon bundle event
Run 242 --- Event 847205 ----05-05-2003 06:11:04.43 Trigger(1-16):01110101 00111100 Weit_Time:30.065 msec
4873:0
3644:1
3754:2
3814:3
3859:0
4199:1
3877:2
5106:3
3562:0
3149:1
3376:2
3672:3
4000:0
4098:1
4109:2
4255:3
3786:0
3732:1
3712:2
4030:3
4000:0
3388:1
3477:2
4119:3
4050:0
4120:1
4164:2
5038:3
3961:0
3769:1
3844:2
4323:3
3352:0
3438:1
3922:2
4134:3
3181:0
3942:1
5269:2
0:3923
1:3332
2:3387
3:3266
0:3054
1:3101
2:3351
3:3591
0:3570
1:3435
2:3511
3:3948
0:3619
1:3601
2:3894
3:3760
0:3750
1:3582
2:3655
3:3992
0:3641
1:3639
2:3849
3:4104
0:3609
1:3508
2:3684
3:3647
0:4245
1:3814
2:4037
3:4338
SM=0
SM=1
SM=2
SM=3
SM=4
SM=5
SM=6
SM=7
Y-projection
SM=8
SM=9
X-projection
Pla
0
1
2
3
4
5
6
7
Pla
0
1
2
3
4
5
6
7
Muon bundle event (geometry reconstruction)
Nlam=31,N5=30,N6=31,NR1=0 ,NR2=0
NGroup2=132
N1=30,N3=26 nCup= 3 SumAmp=5.57e+04
N2=30,N4=28 nCdow n= 3 NPMT=175 ETel= 0.0% ERec= 49.7%
Date=05-05-03 06:11:04.043 Nevent= 847205 fm=123.1 tm= 79.7
θ = 50º : 1016 – 1017 eV
Low angles: around the “knee”
1015 eV
1015
1016
eV
1017
eV
Fe
p
 = 1.92 + 0.02
 = 2.13 + 0.05
10-4
35 o
solid: QGSJET01
dashed: SIBYLL
0.01
0.1
D, m - 2
1016 eV
1017 eV
eV
D 3 dF/dD, 1 / ( s sr m 4 )
D 3 dF/dD, 1 / ( s sr m 4 )
10-3
1
Fe
 = 2.13 + 0.05
10-4
p
50 o
solid: QGSJET01
dashed: SIBYLL
10-5
0.01
10
θ = 65º : 1016 – 1018 eV
0.1
D, m - 2
1
10
Large angles: around 1018 eV
10-4
 1 = 2.11 + 0.02
Fe
1017 eV
1018 eV
1017 eV
D 3 dF/dD, 1 / ( s sr m 4 )
D 3 dF/dD, 1 / ( s sr m 4 )
1016 eV
 2 = 2.31 + 0.09
p
10-5
65 o
 = 0.20 + 0.09
10-6
0.1
Fe
1019 eV
 = 2.25 + 0.04
78 o
p
10-7
solid: QGSJET01
dashed: SIBYLL
10-6
0.01
1018 eV
solid: QGSJET01
dashed: SIBYLL
D, m - 2
1
10
0.01
0.1
D, m - 2
1
10
Muons in Auger
VHE (> 100 TeV) muon investigations
Baksan underground scintillation telescope
Preliminary results of muon energy spectrum investigations
in Baksan Underground Scintillation Telescope (BUST)
[A.G. Bogdanov et al., Astropart. Phys. 36 (2012) 224]
IceCube results
Bundle
Data
High pT
Muon
High pT Muons
Single Showers
Double Coincident
CRs
Patrick Berghaus, Chen Xu, 32nd ICRC, 2011, Beijing
Muon energy spectrum - 2011
Possible explanation
How to explain results of muon
investigations?
Of course, excess of muon bundles can be explained by changing
of interaction model (existing attempt - EPOS).
But it is more difficult to explain the excess of VHE muons, since
very quick processes of muon generation are required.
Also it is necessary to explain of other unusual phenomena which
were detected in cosmic rays:
-unusual events in hadron experiments (halo, alignment,
Centauros, penetrating cascades, etc.);
- some deviations in EAS (“young” and “old” showers, large Pt,
N/Ne-ratio behavior, etc.).
It is important to mark that all unusual phenomena appear at
primary energies between 1015 - 1016 eV.
Possible new model
Production of blobs of quark-gluon matter (QGM)
with large orbital momentum.
This model ensures two main conditions:
- threshold behavior, since for that high temperature
(energy) is required;
- large cross section, since the transition from quarkquark interaction to some collective interaction of many
quarks occurs:

2
     R  or   R1  R2 
2
2
where R, R1 and R2 are sizes of quark-gluon blobs.
Centrifugal barrier
Appearance of a globally polarized QGM with a large
orbital angular momentum in non-central ion-ion collisions
was predicted by Zuo-Tang Liang and Xin-Nian Wang.
In this case, such state of quark-gluon matter can be
considered as a usual resonance with a large centrifugal
barrier.
Centrifugal barrier V ( L)  L2 2mr 2 will be large for
light quarks but small for top-quarks.
Centrifugal barrier for different masses
Consequences of top-quark production
Top-quarks decay: t  t   W

W   b  b 

W –bosons decay into hadrons (~70%) and leptons (~30%).
In the first case, the increase of the number of secondary
pions will lead to increasing muon number (muon
multiplicity).
In the second case, the decay W  gives the excess of
VHE muons in cosmic rays.
Muon energy spectrum
3
10
p, CORSIKA
pp, PYTHIA+CORSIKA
pp->tt, PYTHIA+CORSIKA
2
10
15
E = 10 eV, H1int = 23.5 km
1
dN/dlgE
10
0
10
-1
10
-2
10
-3
10
0
1
2
3
lg(E, GeV)
4
5
How to check the new approach?
How to check the new approach at LHC?
It is very interesting, but the first results of LHC experiments
confirm the new approach.
There are a good agreement of obtained results with
predictions for pp-interactions but it is observed some
deviations for nuclei-nuclei interactions.
The last circumstance is very important, since in cosmic
rays most part of interactions are nuclei-nuclei collisions.
ATLAS observes striking imbalance of jet energies in heavy ion collisions
(CERN Courier, January/February 2011)
Highly asymmetric dijet event
Dijet asymmetry distributions
How to explain ATLAS results in frame
of the considered approach?
tW++b
In the top-quark center-of-mass system:
Tb ~ 65 GeV,
TW ~ 25 GeV.
If to take into account fly-out energy, Tb can be more
than 100 GeV.
In the case, if b gives a jet and W  ~ 20 , the ATLAS
experiment’s picture will be obtained.
How to check the new approach in CR?
There are two possibilities to check new interaction model:
• detailed measurements of inclusive muon energy spectrum
near and above 100 TeV (for that, IceCube and other large
detectors can be used);
• measurements of the energy deposit of muon bundles and
changes of its behavior with increasing PCR energy (for that,
NEVOD-DECOR complex must be complimented by an usual
EAS array for independent evaluation of PCR energy).
This array will be constructed from Italian scintillation
detectors which were used in KASCADE-Grande experiment.
This work will be fulfilled in collaboration with Torino Section
of INFN (A.Chiavassa).
Shower array around NEVOD-DECOR
НЕВОД
Expected results of muon energy
deposit measurements
E1
Conclusion
Considered approach of production of blobs of
QGM with large orbital momentum in nuclei-nuclei
interactions allows solve not only “muon puzzle” but
explain other unusual events observed in CR
experiments (halo, alignment, Centauros,
penetrating cascades, etc).
Seemingly, this is a good idea which with a high
probability is realized in Nature.
Thank you for attention!