Transcript Cosmic Ray Research activities at the Physics Department

Cosmic Ray Research activities
at the Physics Department,
Gauhati University
Kalyanee Boruah
Professor in Physics, GU
8th. Winter Workshop and School on Astroparticle
Physics (WAPP 2013), 17-19 Dec, 2013
Centre for Astroparticle Physics and Space Science,
Bose Institute, Mayapuri, Darjeeling
Plan of my talk
1.Review of work by GUCR group and
important findings
2.Mini-array concept & early work
3.Radio-emission from EAS
4.Application of CORSIKA Simulation
5.New proposal to study atmospheric effects.
Review of Cosmic rays Research by GU
Cosmic Ray (GUCR) Group (1970-present)
• First Stage : 1970-82 :
EAS array with GM trays (up to primary
energy 1016eV), Cerenkov detector
(Photomultiplier Tube & parabolic mirror) &
radio antenna. Pulses were recorded by
photographic method. LF radio-emission
(30,40 & 60 MHz) detected using wide band
half wave dipole antenna & HF (80,110 &
220MHz) using Yagi antenna. Analytical &
MonteCarlo simulation of cerenkov emission
Important Findings (1970-1982)
Measured Cerenkov pulse height and EAS rate
spectrum in agreement with Monte Carlo
simulation with pure proton composition at about
10^16eV primary energy.
Correlation study between pairs of (LF,MF) radio
frequencies showed positive correlation when both
frequencies are above or below the theoretical
cutoff frequency (75MHz), while negative
correlation between higher and lower frequency
pairs, showing different emission mechanisms.
Radio field strength increases at low frequency
Review of Cosmic rays Research…
Second stage : 1982-94
: Conventional EAS array with plastic scintillators
(up to Ep= 1017eV) with DST & ASTEC funding.
More optical cerenkov and radio antenna with
receivers installed.
Microprocessors used for controlling and
automatic data recording.
Fortran programs developed for simulating EAS in
detail using Monte Carlo technique.
Theoretical study of radio and cerenkov emission.
Important Findings (1982-1994)
Measurement of lateral distribution of Cerenkov
emission indicated proton enhancement above
10^16eV primary energy.
Rise of field strength of radioemission with lowering
of radio frequency to VLF (Very Low Frequency)
region. This could not be explained by any of the
existing theories, but by a new method called
Transition Radiation phenomenon that occurs
when a charged particle crosses a boundary
between two media of different dielectric properties.
Review of Cosmic rays Research…
Third stage : 1994- present
• 1994-2004 :DAE-BRNS project of UHE
cosmic ray detection by miniarray of eight
scintillation detectors covering 2 sq m area.
Microprocessor based & computer controlled
data acquisition system. (published in NIM &
AstroparticlePhysics.)
• Theoretical simulation of hadronic interaction,
Higgs production (published in PRD) .
• Fabrication of RPC detectors for cosmic ray
detection(ISRO Project & ICTP-TWAS grant).
Review of Cosmic rays Research… 2004-13 :
• Study of 30kHz radio-emission using loop
antenna with miniarray.
• Study of low cost, efficient RPC design.
• Simulation using CORSIKA code for study of
charm production, model dependence, mass
composition, LF radioemission, gamma hadron
discrimination & neutrino production.
• Work on digital signal processing for analysing
radio pulses recorded in association with EAS.
• Design of FPGA based trigger, monitoring &
control system for particle detector array in
collaboration with Dept. of Instrumentation, GU.
Important Findings (1994-present)
• GU miniarray could detect UHE cosmic rays of
primary energy 1017-1018 eV.
• Efforts have been made to detect radio
emission associated with UHE cosmic ray air
showers as detected by the miniarray detector,
using loop antenna, placed close to the
miniarray. However, when triggered by miniarray
pulse, no coincidence was observed. On the
other hand when the miniarray channel was
decoupled, radio-radio coincidence could be
observed.
The new findings may be explained by a model
based on mechanism of transition radiation,
which shows that the radio antenna picks up
signal emitted by excess charged particles after
striking ground. Calculations based on CORSIKA
simulation shows that this effect is detectable
near the core of an EAS, where particle density is
large. Mini array being effective at a large
distance >300m from the core requires a
distance and a time delay(~10μs) . Their
acceptance area are not overlapping. Therefore,
the mini-array and the loop antenna cannot be
placed close to each other.
Mini array Concept – Arrival time spread (thickness
of shower front in ns) increases with core distance
11
Mini-array method
• A mini-array is a low cost and an
unconventional particle detector array
capable of detecting UHE cosmic ray air
shower using Linsley’s effect, i.e, increase
of shower disk thickness with core distance.
• Gauhati University mini-array (operated
during 1994 to 2007) consisted of eight
closely spaced plastic scintillators, and
could detect Cosmic rays of primary energy
1017–1018 eV.
BLOCK DIAGRAM OF THE
EXPERIMENTAL SETUP
Thickness of shower front ‘σ’ in ns
•Linsley derived the empirical formula, using
experimental data of Volcano Ranch Array
σ(r) = Brβ . . . . , (1)
where B = 0.0158 and β = 1.5
• Capdevielle et al. derived the same from
their simulation with CORSIKA (near
vertical shower )
σ(r) = B(1+r/c)β . . . . , (2)
where B = 2.6, c = 25 and β = 1.4
Lateral Distribution Function
• LDF as used for earlier miniarray, for large
shower and large core distances is given by
ρ(r) = CNr-n.
Where, C= 853, N= shower size & n= 3.8.
• GU miniarray detector system is designed
specially to measure both charged particle
density and arrival time spread at the
detector level. Core distance ‘r’ and shower
size ‘N’ are derived as secondary
parameters.
Effective area of the miniarray
The effective area of mini array A(N) is an
annular ring with inner radius rmin
Determined by minimum time spread σ1
& outer radius rmax determined by density
threshold ρ1 as selected
A(N) = π( rmax2 - rmin 2)
Radio-emission : Historical development
Theory
1960- Askaryan predicted
radio Cerenkov from –ve
charge excess.
1966- Kahn & Lerche
developd geomagnetic
charge separation model
of dipole & transverse
current through the
atmosphere.
Experiment
1965- Jelley detected
44MHz radio pulse
associated with EAS =>
Intensive research
VLF(few kHz) to VHF
(hundreds of MHz).
1967- Allan found
polarization depends on
geomagnetic field.
1970 - Experimental work ceased due to technical problem,
man-made interference & advent of alternative techniques.
1970-84 : Work done by GUCR Group
Correlation study between pairs of (LF,MF)
radio frequencies showed positive
correlation when both frequencies are
above or below the theoretical cutoff
frequency (75MHz), while negative
correlation between higher and lower
frequency pairs, showing different
emission mechanisms.
Radio field strength increases at low
frequency
Later development
• 1985 – Nishimura proposed Transition Radiation (TR)
mechanism to explain high field strength at low
frequency (LF)
• 2001- Askaryan type charge excess mechanism plays
a major role in dense media such as ice & used to
detect neutrino induced shower (RICE)
• 2003- Falcke & Gorham proposed coherent
geosynchrotron radiation from highly relativistic
electron positron pairs gyrating in earth’s magnetic
field.
• 2004- Huege & Falcke: analytic calculation using
synchrotron theory from individual particle is applied to
air showers. Detailed Monte Carlo simulation is used to
study dependence on shower parameters.
Present understanding
• UHECRs produce particle showers in atmosphere
• Shower front is ~2-3 m thick ~ wavelength at 100 MHz
• e± emit synchrotron in geomagnetic field ~ 0.3G (10100MHz)-Geosynchrotron emission.
• Emission from all e± (Ne) add up coherently
• Radio power grows quadratically with Ne.
• The mechanisms for the highest and the lowest
frequencies are found to be very different.
• VHF emission is well explained by geo synchrotron
mechanism, but VLF (<1MHz) emission is yet unclear,
may be explained by Transition radiation mechanism.
Geomagnetic charge Segmentation
LF radio emission
Kahn & Lerche’s Model.
transition radiation emission from a charge e
Transition Radiation
• The existence of Transition radiation was
first suggested by Frank & Ginzburg(1946)
• emitted when a uniformly moving charged
particle traverses the boundary separating
two media of different dielectric properties.
• Later, Garibian deduced wave solutions in
the radiation zone, a method used by
Dooher (1971) to calculate Transition
radiation from magnetic monopoles.
• We extend and apply TR theory to develop
a prototype model for radioemission
following Dooher’s approach.
Theoretical Model:
• This method involves solving Maxwell’s
equations and resolving field vectors into Fourier
components with respect to time as suggested
by Fermi [1940]. The magnetic field component
of the Transition Radiation field is effective in
producing induced current in the loop antenna.
• A FORTRAN program is written to calculate the
arrival time of the transition radiation at the
position of the loop antenna, from different
elements of the shower front after striking
ground, and the corresponding induced field
strength , using charge excess derived from
CORSIKA simulation..
Geometrical Model
SIMULATION
• The excess charge distribution at the ground level
are estimated using CORSIKA simulation code.
• The particle output file from CORSIKA is first
decoded with available FORTRAN code and the
decoded output is further processed with a C++
program to get the excess of e- over e+.
• The whole ground area (assumed plane) is divided
into elements of area 10m × 10m. Negative charge
excess and their average arrival time are recorded
for each element using a Fortran program.
• Another program is written to evaluate the inducing
electric field at the loop antenna due to k th element
on the ground and the corresponding arrival time, to
get the pulse profile. This information is transformed
to the frequency domain by using DFFT.
(a)
(b)
(a) Radio pulse profiles and (b) dependence of peak
field strength on primary energy at 300 m lateral
distance from the shower centre.
Comparison with REAS 3 and experimental observation
due to Hough et al. at 1017 eV (left) and Comparison with
earlier GUCR model at 1018 eV.
Radio emission Result
• We have used a simple geometrical model for
production of TR from cosmic ray EAS using charge
excess distribution as calculated from CORSIKA
Simulation. The model helps to establish the
observed higher field strength at lower frequency.
• Also information about primary energy and mass
composition may be obtained from measurement of
radio frequency and field strength.
• Loop antenna for detection of LF radio-emission
associated with giant EAS may be operated along
with miniarray suitable for UHE giant EAS detection
by suitably adjusting the time delay due to TR.
Photographic view of the Experimental Setup.
Application of CORSIKA Simulation
1. Mass Composition
2. Study of model dependence
3. Gamma hadron discrimination
4. Neutrino shower
CORSIKA SIMULATION
• Success of an air shower experiment in
respect of design and measurement depends
on accurate theoretical simulation work.
• Standard EAS simulation code CORSIKA
is a detailed Monte Carlo program to study the
EAS in the atmosphere initiated by photons,
protons, nuclei and many other particles. It
recognizes more than 50 elementary particles
& gives type, energy, momentum, location,
direction and arrival times of all secondary
particles that are created in an air shower and
pass selected observation level.
Mass Composition study
Lateral density distribution of cherenkov photons for
proton & Helium primary of energy 10^17 eV.
Mass Composition study
Lateral density distribution of cherenkov photons for
Oxygen & Iron primary of energy 10^17 eV.
Mass Composition study
Parameterization for lateral density distribution at 1017eV
Study of model dependence
Study of model dependence
Study of model dependence
Gamma hadron discrimination
Gamma hadron discrimination
Gamma hadron discrimination
Gamma hadron discrimination
Gamma hadron discrimination
Application of Principal Component Analysis (PCA) method for
Gamma-hadron separation
Neutrino shower
Neutrino shower
Neutrino shower
Neutrino shower
Neutrino shower
Neutrino shower
New Proposal : Simulation
and Design
of the water Cerenkov array
Scientific background
Based on our success in detecting High Energy
cosmic ray showers using various detectors,
and expertise in Cerenkov and Scintillation
detectors operating with microprocessor and
computer based high speed data acquisition
system, we now propose to set up a small air
shower array consisting of water Cerenkov
detectors at the roof top of Physics building of
Gauhati University. Water Cerenkov method
was used by us to calibrate our air Cerenkov
detectors.
Motivation
The atmosphere acts as a part of the detector for
recording an EAS. However, for showers arriving
detector level after crossing the maximum
development, absorption effect of the atmosphere is
dominant. The shower maximum for about 100 TeV
is near 500 gr/cm2 (~5200m above sea level) and
most of EAS arrays in this energy range are at heights
below the shower maximum height, specially for
higher zenith angle EAS events. Therefore, for ground
based observation of cosmic gamma source, we need
to consider the atmospheric absorption effect.
The mechanism of the development of
EAS events in the atmosphere affects
directly the characteristics of the
secondary particles. So it is very
important to investigate theoretically the
characteristics of the secondary
particles, such as longitudinal and lateral
distribution, arrival time distribution,
zenith angle distribution etc. and to
recognize the factors affecting the
observable parameters.
The whole EAS phenomenon may be
simulated using Monte Carlo Technique
and different characteristics may be
studied more accurately.
• Here, we have applied results of
CORSIKA simulation code to design the
proposed detector array in terms of
detector size, position and separation.
Longitudinal Distribution of electrons
Lateral Distribution of electrons
The theory of lateral Distribution of the shower
particles was developed by Nishimura, Kamata &
Greisen and is known as NKG formula
Shower sizes at ground level ‘Ne’ are derived
from CORSIKA Simulation, for different primary
energy and mass compositions and densities at
different core distances calculated. The
threshold condition is determined when the core
strikes the centre of the array.
Detector Design
We aim to study some factors related with
atmosphere by using a small array of Water
Cerenkov Detectors (WCD) and by comparison of
measurements with simulation results. A minimum
of four particle detectors are necessary for
measurement
of
air
shower
parameters.
Preliminary calculation using CORSIKA shows that
an array of four WCDs of area 1sq m [radius 56cm]
each, positioned at the corners of a square of side
5m may be used to detect primary particle of
threshold energy 100TeV. A change in the cross
sectional area of WCDs or a change in the length of
the side would change the energy threshold.
<--------------------------5m ------------------------>
The array is proposed to be located on the roof
of the Physics Department of Gauhati
University. The signal output from the PMTs
are to be discriminated for suitable trigger and
connected to Time to Amplitude Converter
(TAC). The time lag of three of the WCDs with
reference to the fourth one are to be
recorded. These data are to be used for
measuring zenith angle distribution which
may be correlated with atmospheric thickness
and pressure.
References
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4.
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A.M. Hillas, Phys. Report C 20 (1975) 79.
J. Linsley, L. Scarsi, Phys. Rev. Lett. 9 (1962) 123.
J.N. Capdevielle et al., in: Proc. 28th Int. Cosmic RayConf. Tsukuba,
Japan, vol. 2, 2003, p. 217.
5. T. Bezboruah, K. Boruah, P.K. Boruah, Nucl. Inst. Meth.Phys. Res. A
410 (1998) 206.
6. TBezboruah, KBoruah, PKBoruah, Astroparticle Phys.11 (1999) 395.
7. D. Heck, J. Knapp, J.N. Capdevielle, G. Schatz, T. Thouw, Report
FZKA 6019, Forschungszentrum Karlsruhe, (1998).
8. J. van Buren , Report FZKA 7292 (2007), Forschungszentrum
Karlsruhe GmbH, Karlsruhe.
9. Todor Stanev, High Energy Cosmic Rays (2009), Springer.
10.M. Khakian Ghomi et al., 30th ICRC, V.4, P.15-18, HE0263 (2007)
11.Sheidaei, F., et al. , arXiv:0705.4234v1 [hepex] 29 May 2007
12.M Khakian Ghomi, M Bahmanabadi, J Samimi, 2005, A&A, 434, 459