Cosmic Ray Research activities at the Physics Department, Gauhati University

1. Cosmic Ray Research activities at the Physics Department, Gauhati University KalyaneeBoruah 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

2. Plan of my talk Review of work by GUCR group and important findings Mini-array concept & early work Radio-emission from EAS Application of CORSIKA Simulation New proposal to study atmospheric effects.

3. 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

4. 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

5. 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.

6. 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.

7. 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).

8. 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.

9. 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.

10. 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.

11. Mini array Concept – Arrival time spread (thickness of shower front in ns) increases with core distance 11

12. 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.

13. BLOCK DIAGRAM OF THE EXPERIMENTAL SETUP

16. 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

17. 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.

18. 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)

21. 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.

22. 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

23. 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.

24. 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 (10-100MHz)-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.

25. Geomagnetic charge Segmentation LF radio emission Kahn & Lerche’s Model.

26. transition radiation emission from a charge e

27. 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.

29. 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..

30. Geometrical Model

31. SIMULATION • Theexcess 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.

32. (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.

33. 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.

34. 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.

35. Photographic view of the Experimental Setup.

36. Application of CORSIKA Simulation • Mass Composition • Study of model dependence • Gamma hadron discrimination • Neutrino shower

37. 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.

39. Mass Composition study Lateral density distribution of cherenkov photons for proton & Helium primary of energy 10^17 eV.

40. Mass Composition study Lateral density distribution of cherenkov photons for Oxygen & Iron primary of energy 10^17 eV.

41. Mass Composition study Parameterization for lateral density distribution at 1017eV

42. Study of model dependence

43. Study of model dependence

44. Study of model dependence

45. Gamma hadron discrimination

46. Gamma hadron discrimination

47. Gamma hadron discrimination

48. Gamma hadron discrimination

49. Gamma hadron discrimination Application of Principal Component Analysis (PCA) method for Gamma-hadron separation

50. Neutrino shower