Some consequences for LHC experiments from the results of cosmic ray investigations above the knee

0.43 MB·English

by  A. A. Petrukhin

XVI International Symposium on Very High Energy Cosmic Ray Interactions
ISVHECRI 2010, Batavia, IL, USA (28 June - 2 July 2010) 1
Some consequences for LHC experiments from the results of cosmic
ray investigations above the knee
A.A.Petrukhin
NationalResearchNuclearUniversityMEPhI,Moscow115409,Russia
Experimentaldata obtainedincosmicrayinvestigations atenergiesabove theknee arediscussed. Allfeatures
observed at these energies starting from the knee, changes of mass composition and concluding with various
typesofunusualeventsareanalysedintheframeworkofthenewhadroninteractionmodelproducingblobsof
quarkgluonmatter. Consequences forLHCexperimentsareconsidered.
1
1
0
2 1. INTRODUCTION hadron experiments these are: halos, alignment, pen-
etrating cascades, long-flying component, Centauros
n
a Forthcoming experiments at the LHC in the inter- and Anti-Centauros; in muon experiments: excess of
J val2 14TeVforp-pinteractionssharplyincreasethe muonsintheirenergyspectrumatenergiesmorethan
0 inter÷est in various predictions (theoretical and exper- several tens TeV, observation of VHE (> 100 TeV)
1 imental) for this energy region. muonsinvariousexperiments. Ofcourseeachofthese
It is known that many physicists predict the ap- events can be explained by large physical or statisti-
E] pearance of new particles and states of matter in the calfluctuations, but it is practically impossible to ex-
H TeV energy region,but none of them predicts the ap- plain in this way the full set of these unusual events
pearanceofthesenewobjectswithlargecrosssection. and phenomena. In addition, and this is very impo-
.
h Values of usually predicted cross-sections are evalu- tent, practically all these unusualevents are observed
p ated in nb or even pb. Of course processes with such at energies above the knee. Attempts to find simi-
- smallcrosssectionscannotbeobservedincosmicrays. lar events in accelerator experiments at beam ener-
o
r In cosmic ray experiments, the interval 2 14 TeV gies which correspond to cosmic ray energies below
st in the center of mass system corresp÷onds to the knee did not give positive results. Therefore it is
a 2 1015 1017 eV in laboratory system, but namely possible to consider these events as evidence of new
[ in×this e÷nergy region the following phenomena were physics at energies above the knee.
1 observed: the knee in energy spectrum, change of Ifitisbelievedthatthehadroninteractionmodelis
v mass composition and appearance of various unusual not changed in the TeV energy region, all changes in
0 events. For their observations in cosmic ray experi- EAS parameter measurements versus primary parti-
0 ments a rather large cross section for new processes cle energy can be explained by changes of the cosmic
9
is required. If these results obtained in cosmic rays ray energy spectrum and/or mass composition (cos-
1
arereallyphysical(notmethodicalorerroneous)then mophysical approach). For that, existing models of
.
1 corresponding phenomena can be found in LHC ex- acceleration of particles in the Galaxy, and keeping
0 periments. them within it, predict that at knee energies protons
1
begintoreachtheiraccelerationenergylimitandleave
1
theGalaxy. Then,withthe increaseofenergypernu-
:
v cleus, helium nuclei begin to leave the Galaxy, etc.
2. RESULTS OF CR EXPERIMENTS AT
i
X Intheframeworkofthesecosmophysicalmodelsthe
LHC ENERGIES
mass composition of cosmic rays must be changed in
r
a favour of heavy nuclei, first slowly then more quickly
These results can be separated into two basic
up to iron nuclei. But the experimental situation is
groups:
the opposite. Evaluations of the averagelogarithm of
mass number lnA based on N /N -ratio (Figure 1
unusual events, which cannot be explained in h i µ e
• theframeworkofexistingtheoreticalmodelsand [3]) and Xmax (Figure 2 [4]) measurements give first
arelativelysharpandstronggrowthofthis value and
approaches;
then a slow decrease down to protons. In this situa-
tionconsiderationofanalternativeexplanationofthe
changesofmeasuredEASparametersasafunc-
• behaviour of the measured EAS parameters (nuclear-
tion of energy, which can be interpreted as
physical approach) is rather substantiated.
changes in the interaction model.
Inthenuclear-physicalapproach,itisassumedthat
Various types of unusual events were detected in the primary cosmic ray energy spectrum and mass
hadronexperimentsathighaltitudes andinmuonin- compositionabovethekneearenotseriouslychanged.
vestigations. Theywerediscussedinmanypapers(see All changes in the measured EAS parameters (the
f.e. [1,2])thereforeinthispaperweonlylistthem. In kneeinEASsizespectrum,theincreaseoftheN /N -
µ e
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XVI International Symposium on Very High Energy Cosmic Ray Interactions
2 ISVHECRI 2010, Batavia, IL, USA (28 June - 2 July 2010)

Figure 1: Results of mean logarithmic mass evaluations
from Nµ/Ne-ratio measurements [3]. Figure 2: Results of Xmax measurements [4].
ratio,the decreasingofXmax elongationrate,etc)are where mN is nucleon mass, mc is compound mass of
produced by the inclusion of new physical processes. many interacting quarks in nuclei of nitrogen or oxy-
gen (mc mN). A sharp change of √s leads to a cor-
≥
responding change of the value of orbitalmomentum,
3. HADRON INTERACTION MODEL WITH L, and the centrifugal barrier
QGM PRODUCTION
V(L)=L2/(2mr2). (2)
Toexplainallunusualeventsandphenomenafroma
Thisbarrierwillbehighforlightparticles(u,d,s,c,
singlepointofviewanewinteractionmodelmustsat-
b-quarks) but low for heavy particles (t-quarks). The
isfy the following requirements: threshold behaviour production of tt¯-quark pairs with large mass changes
of cross section (unusual events begin to appear at the EAS development. Decays of top-quarks t(t¯)
energies more than severalPeV), large value of cross- W+(W−)+b(¯b) and consequent decays of W-boso→ns
section (to be observed in cosmic ray experiments),
andb-quarksgiveanexcessofveryhighenergymuons
largeorbitalmomentum (to explain alignment), large
and neutrinos and also multiple hadrons with large
yield of leptons (to explain VHE muon excess) and
transferred momenta.
wideningpossibilitiesofEASdevelopment(toexplain
Thepossibilityofexplainingvariousunusualevents
changes in measurements of Ne, Nµ/Ne, Xmax and in the framework of the new model was discussed in
other parameters).
papers [2, 6]. The role of VHE muons in explaining
The production of quark-gluon plasma (better to
thepenetratingcascadesobservedinthePamirexper-
speak about quark-gluon matter – QGM) provides
iment[7]wasdiscussedin[2]andinmoredetailin[8].
the fulfilment of conditions listed above: threshold
As a whole a model of QGM production can explain
behaviour,sincehightemperature(energy)foritsap-
all unusual events observed in cosmic rays.
pearance is required; large cross section, since in this
casetransitionfromquark-quarkinteractiontothein-
teraction of many quarks and gluons occurs and the
4. DESCRIPTION OF THE COSMIC RAY
geometrical cross section changes from πλ2 to πR2,
ENERGY SPECTRUM IN THE
where R is the size of the QGM blob which is not
less than the nucleonradius; large orbitalmomentum FRAMEWORK OF THE QGM MODEL
inperipheralion-ioncollisions,since,aswas shownin
[5],thequark-gluonplasmaasagloballypolarizedob- In the framework of this model, hadrons will be
ject is produced with orbital momentum, L, which is produced at higher altitudes in the atmosphere than
proportional to √s, and correspondingly a large cen- usual. Decays of W-bosons into leptons and hadrons
trifugal barrier appears. give very large fluctuations in EAS development,
The two last points are very importantfor explain- changetheaveragetransitioncurveandcanleadtoan
ing various phenomena observed in cosmic rays. The underestimation of the EAS energy and appearance
transition to collective interactions of many quarks of other phenomena: young and old showers, large
drastically changes the energy in the center of mass transferred momenta, changes of Xmax and Nµ/Ne-
system ratio,etc. To evaluate the EAS energy it is necessary
to take into account the energy carried away by top-
√s=p2mNE1 p2mcE1, (1) quarks. Of course some part of this energy will be
→
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XVI International Symposium on Very High Energy Cosmic Ray Interactions
ISVHECRI 2010, Batavia, IL, USA (28 June - 2 July 2010) 3
Figure 4: New version of thecontribution of various
cosmicraycomponentsinthemeasuredenergyspectrum.

Figure 3: The all-particle energy spectrum of primary
110055
cosmic rays and its explanation in theframework of the
cosmophysical approach [9].
]
1
-r
s
1
re-injected into EAS development. But in a first ap- -s
2
proximation,tosimplifyconsiderationitispossibleto -m
assume that all the energy, εt, carried away by top- 1.7 110044
V
quarks is missing. Then the energy in the centre of e
mass system is decreased (√s εt, where εt > 2mt) [G
andcorrespondinglythe EASe−nergywill be less than E)
(
the energy of the primary particle F
7
(√2mcE1 εt)2 2.E 110033
EEAS = − . (3)
2mc
By this reason we obtain the steepening of the ob-
11001133 11001144 11001155 11001166 11001177 11001188 11001199 11100021222000 11002211
served spectrum.
E[eV]
Sincefortheproductionofquark-gluonmatter,not
only is high temperature (energy) required but also
Figure 5: Calculated spectrum and experimental data.
high density, it is reasonable to assume that at first
QGMwillbeproducedinnucleus-nucleusinteractions
but not in proton-nucleus interactions. This means
So, in this approach the knee is the result of our
that in cosmic rays the first component (at the same
interpretation of observationaldata.
energy per nucleus) which will interact with the pro-
For more detailed comparison of predictions of the
duction of QGM will be iron nuclei (or heavier ones),
QGM model with experimental data, corresponding
thenmorelighternuclei,andfinallythelastonespro-
calculationswereperformed. Thekeyquestionforthis
tons.
model is a value of threshold energy at which QGM
The difference between cosmophysicaland nuclear-
blobsbegintobe producedandtheirmassforvarious
physicalapproachesto the interpretationof results of
nuclei. Goodresultswere obtainedwiththe following
EAS measurements is demonstrated in Figure 3 and
dependences
Figure4. TheFigure3from[9]illustratesthechanges
of the contribution of various cosmic ray components Eth =Eknee(56/A)0.5, (4)
intotheall-particleenergyspectrumintheframework
of the cosmophysical approach. Figure 4 illustrates
the contribution of various components in the same mc =2mNA0.25. (5)
spectrumintheframeworkofthenuclear-physicalap-
proach. Comparison with experimental data is shown in
Figure 4 is constructed by the analogy of Figure 3. Figure 5.
The curves in this figure are not a result of calcu- The energy spectrum obtained in the framework of
lations; they only illustrate the principal change of the simplest model surprisingly well describes the ex-
the approach. In Figure 3, real changes of primary perimental data. Observed changes of composition
spectra of different cosmic ray species are shown. In are also explained. A sharp increase of average mass
Figure 4, the results of measurements of different cos- above the knee is the result of additional detection
micrayspeciesareshown,whicharereallynotrelated of EAS from heavy nuclei. At higher energies a slow
with changes of their spectrum slope. transitiontomorelightnuclei(upto protons)begins.
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XVI International Symposium on Very High Energy Cosmic Ray Interactions
4 ISVHECRI 2010, Batavia, IL, USA (28 June - 2 July 2010)
function of the energy and mass of beam particles. It
isimportantthatforheavynucleithethresholdenergy

must be less than for light nuclei.
E
? Inthiscasethesituationissimilartoexperimentsin
cosmicrays,inwhichtheenergydepositofEASmuon

componentbelowandabovethekneewillbemeasured
? (Figure 6). If the new state of matter appears at the
knee energy the energy deposit and also behaviour of
the knee E other EAS characteristics must be changed.
Figure 6: Possible behaviourof the EAS muon energy
deposit above theknee.
6. CONCLUSION
Results of composition changes obtained by means of
Ofcoursethe consideredmodelofnewphysicscon-
N measurements are also explained. The number of
µ
nectedwithQGMblobproductioncannotbetheonly
muons is increasing as a result of muon production
one and other possibilities exist. But the need to ob-
not only in the usual scheme of EAS development,
tain a large cross-section and to suppress decays of
but also through decays of heavy particles.
new heavy particles (or state of matter) into light
quarksmakesachoiceinfavourofQGMveryalluring.
5. CONSEQUENCES FOR LHC
EXPERIMENTS
Acknowledgments
If the considered nuclear-physical approach is cor-
rect then the following predictions can be made for
LHC experiments directed in the search for new The author thanks Alexey Bogdanovand Rostislav
physics. Kokoulin for big help in the fulfilment of this work.
Firstly,for searchesofquark-gluonmatter with the TheworkwassupportedbyMinistryofEducationand
described properties it is necessary to use nucleus- Science of the Russian Federation and RFBR (grant
nucleus collisions. For pp-interactions the threshold 09-02-12270-ofi-m).
energy can be more than 1017 eV for cosmic raysand
more than 14 TeV for LHC (unfortunately in cosmic
ray experiments it is impossible to check this circum-
stance). To correspond to conditions of cosmic ray
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