Luigi Benussi, Stefano Bianco, Luciano Passamonti Incontri di Fisica 2002 Laboratori Nazionali di...

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Luigi Benussi, Stefano Bianco, Luciano Passamonti Incontri di Fisica 2002 Laboratori Nazionali di Frascati dell’INFN DETECTION OF ELEMENTARY PARTICLES WITH FAST ELECTRONICS AND MEASUREMENT OF THEIR SPEED
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Page 1: Luigi Benussi, Stefano Bianco, Luciano Passamonti Incontri di Fisica 2002 Laboratori Nazionali di Frascati dell’INFN DETECTION OF ELEMENTARY PARTICLES.

Luigi Benussi, Stefano Bianco, Luciano Passamonti

Incontri di Fisica 2002Laboratori Nazionali di Frascati dell’INFN

DETECTION OF ELEMENTARY PARTICLESWITH FAST ELECTRONICS

AND MEASUREMENT OF THEIR SPEED

Page 2: Luigi Benussi, Stefano Bianco, Luciano Passamonti Incontri di Fisica 2002 Laboratori Nazionali di Frascati dell’INFN DETECTION OF ELEMENTARY PARTICLES.

Finuda

The Finuda experiment uses Kaons generated by decays to produce a new kind of nuclear matter: Hyper nucleus.

Atom’s nuclei are generally composed by protons and neutrons, which are called nucleons. Inside the nucleus, the nucleons are disposed in a precise way in levels nearer and nearer the nucleus area. These nucleons follow Pauli’s exclusion principle: two equal particles can’t lay in the same level with the same spin.

Finuda wants to circumvent this principle; after the interaction between electrons and positrons, Kaons are produced and when they interact with the nuclei they replaced one of the nucleons creating particle.

This new nucleus, called Λ hyper nucleus, contains, instead of a nucleon, a Λ particle. This particle can elude Pauli’s principle because it contains strangeness, a new quantum number, and will occupy the most internal level, studying the deepest part of the nucleus.

Λ Hyper nucleus isn’t stable; infact the Λ decays and the nucleus returns to his natural state after a short time. The features of this return depend on the characteristics of the hyper nucleus himself; in this way Finuda can understand which kind of particle has been produced.

Finuda structure is very complex: it is composed by a first apparatus which measures the trajectory of the K produced by φ, by a nuclear target and by a detector system which measures the point of creation of hypernucleus and some features of the particles ( position, speed, mass, electric charge and lifetime).

Page 3: Luigi Benussi, Stefano Bianco, Luciano Passamonti Incontri di Fisica 2002 Laboratori Nazionali di Frascati dell’INFN DETECTION OF ELEMENTARY PARTICLES.

What we want to do and how we will do it

Our goal is to measure high energy cosmic rays speed

Our tools are:

• Relativistic formulas• Plastic scintillators & phototubes• Electronics for discrimination and logic• Data Acquisition System (DAQ)• Analysis program

Page 4: Luigi Benussi, Stefano Bianco, Luciano Passamonti Incontri di Fisica 2002 Laboratori Nazionali di Frascati dell’INFN DETECTION OF ELEMENTARY PARTICLES.

What are cosmic rays ?Cosmic rays are particles, of different energies, that reach the earth from the space.These particles are produced by different sources like stars (also our sun), black holes, neutron stars, quasar. Cosmic rays are composed by several kind of particles, but must of them are hadrons, i.e. protrons.At see level large part of cosmic ray are muons which are produced by the interaction of the hadrons with the molecules of the atmoshepere.

The energy of cosmic rays ranges form few hundred of MeV/c2 to several hundred of GeV/c2. However the most probable energy for muons reaching the sea level is around 2 GeV/c2.

Page 5: Luigi Benussi, Stefano Bianco, Luciano Passamonti Incontri di Fisica 2002 Laboratori Nazionali di Frascati dell’INFN DETECTION OF ELEMENTARY PARTICLES.

Elementary relativistic formulae

The energy E of relativistic particles is given by the relationship

E2 = p2c2 + m2c4 (1)

In which p is the quantity of motion or momentum, m the mass of the particle, and c the speed of light in vacuum. for computational simplicity it is customary to set c = 1, and so

E2 = p2+ m2. (2)

The energy is measured in eV (electronVolt), which is the energy acquired by the electron crossing a potential difference of 1V. For the greatest values are used theprefixes Kilo (KV = 103 eV), Mega (MeV = 106 eV), Giga (GeV = 109 eV) and Tera (TeV = 1012 eV); while for the smallest values are used the prefixes milli (m = 10 -3 ), micro ( = 10-6), nano (n = 10-9 ) and pico (p = 10-12 ).

For very fast particles, Galilei transformations are replaced by Lorentz transformations.The fundamental relationships are:

= v/c (3)

in which v is the speed of the particle; and

= 1 / (1-2) (4)

because of Eq. 2 we also have

= p/E (5) = E/m (6)

in which E is the energy of the particle in motion and m the energy of the particle at rest.

Page 6: Luigi Benussi, Stefano Bianco, Luciano Passamonti Incontri di Fisica 2002 Laboratori Nazionali di Frascati dell’INFN DETECTION OF ELEMENTARY PARTICLES.

Propagation of errors

Statistical errors are defined as the fluctuation in a measurement, when the fluctuations are larger than the sensitivity of the instrument.

Systematical errors are due to biases in either the instrument or the procedure.

They produce a result always larger or smaller than the true value.

Be a physical quantity y a function of n quantities xi

y = f(x1,x2,...xn) (7)

The error Δy to assign to y because of errors Δxi is

y = x1±x2 Δy = Δx1+Δx2 (8)

y = x1 ּx2 Δy = x2Δx1+ x1Δx2 (9)

y = x1/x2 Δy = (x2Δx1+ x1Δx2 )/x22 (10)

Page 7: Luigi Benussi, Stefano Bianco, Luciano Passamonti Incontri di Fisica 2002 Laboratori Nazionali di Frascati dell’INFN DETECTION OF ELEMENTARY PARTICLES.

Computing the speed of cosmic rays

We know that the most part of the particles present in the cosmic rays are muons; so we canrelativistically calculate their speed.

E2= p2 + m2 (11) β= p / E (12)γ= E / m (13) Legend: E = energy

p = momentum m = mass And, according to Lorentz transformation, we can also say that

= v/c (14) = 1 /1-2 (15) Knowing the muon momentum pμ and mass mμ:

pμ = 2 GeV = 2000 MeV (16)mμ = 105.698389 ± 0.000034 MeV (17)

we can obtain the muon energy and from this, the value of β:

E =(4000000 + 11163.69517) MeV2 = 4011163.695 MeV2 = 2002.788979 MeV (18)β =2000 MeV / 2002.788979 MeV = 0.998607452 (19)

This value is very near to 1, as we wanted to demonstrate.

Page 8: Luigi Benussi, Stefano Bianco, Luciano Passamonti Incontri di Fisica 2002 Laboratori Nazionali di Frascati dell’INFN DETECTION OF ELEMENTARY PARTICLES.

Scintillators

Scintillators are materials capable to point out the passage of a particle or of a radiation bundle which cross them. The phenomenon on which they are based is the fluorescence and it has its origin in the energy exchange which happens when the particle interacts with the scintillator material. The whole instrument is wrapped by black adhesive tape, so that it is made insensible to environment light. The light produced by the scintillator is conveyed on the amplifier through an optical guide, whose function principle is the total reflection of the light inside itself. The guides are usually in transparent plexiglas with polished ending surfaces, and mirrored lateral surfaces, to avoid light loss.

Page 9: Luigi Benussi, Stefano Bianco, Luciano Passamonti Incontri di Fisica 2002 Laboratori Nazionali di Frascati dell’INFN DETECTION OF ELEMENTARY PARTICLES.

PhotomultipliersThe signal is amplified through the photomultiplier or phototube (PM), a device that converts a light pulse into an electric signal, basing its operation on the photoelectric effect. It is well-suited to work with the scintillators because it is able to convert the light signals, which usually consist of some hundreds of photons, in an acceptable electric impulse without the introduction of big noise quantity. The two more important parts of a phototube are a photosensible slab, called photocathode, in which the photoelectric effect happens, and a sequence (usually ten) of dinodes which are used to multiply the number of the electrons produced by the photocathode. These are some electrodes placed at a distance of 1 cm about, and with a voltage increasing from a dinode to another. The phototube ends with some connectors which are inserted in an apposite base of the power supply. When a primary electron, extracted by the light, which has stroke the photocathode, is led towards the first dinode by the potential difference between the photocathode and the dinode, gives up its energy to some of the atomic electrons of the dinode; these latter acquire energy sufficient to escape to the second dinode, which has a higher potential, and this process is repeated until the last dinode.In this way the few electrons gone out from the photocathode, after being passed through all the dinodes, have become many more. The whole process lasted few nanoseconds, and this feature gives the possibility to know the time in which the particles passage in the detector has happened, also with a good precision. So with a scintillator counter it is possible to determine not only the number of the particles which pass, but also the energy deposited by each single event because there is a relationship between the quantity of light produced by the originary process and the quantity of electrons which arrive to the anode.

Page 10: Luigi Benussi, Stefano Bianco, Luciano Passamonti Incontri di Fisica 2002 Laboratori Nazionali di Frascati dell’INFN DETECTION OF ELEMENTARY PARTICLES.

Particles counter

Particles counters are very important in nuclear physics. They consist of three main elements: a detector, which generates observable signals when it interacts (through energetic exchange) with a particle or with a radiation bundle; an amplifier, which increases the intensity of the signal produced by the detector; and an analyser, which selects and counts the number of signals made by the detector.

Page 11: Luigi Benussi, Stefano Bianco, Luciano Passamonti Incontri di Fisica 2002 Laboratori Nazionali di Frascati dell’INFN DETECTION OF ELEMENTARY PARTICLES.

DiscriminatorsThe discriminator is a device which is able to make a selection between the analogical pulse (the pulse which comes from phototube), rejecting the impulses with a voltage amplitude inferior to a certain threshold, which is chosen arbitrarily. Instead when the impulse overgoes the threshold voltage, the discriminator sends a digital signal whose features belong to an international standard called NIM, with a width regulated by the front panel, and a fixed voltage amplitude of . 0.8 V.The function of the discriminator is double: to eliminate the noise and to make the signal analysable by logical electronics elements (coincidence, scaler, TDC, etc…)It is very important to choose a threshold voltage not too low in order to avoid the noise, but, at the same time, it must not be too high to avoid a data loss.

Page 12: Luigi Benussi, Stefano Bianco, Luciano Passamonti Incontri di Fisica 2002 Laboratori Nazionali di Frascati dell’INFN DETECTION OF ELEMENTARY PARTICLES.

Time to Digital Converter (TDC)A TDC (time to Digital converter) is a electronic device used to measure the time elapsed between two digital signal.

The basic idea of a TDC is the following:

a digital signal enters inside the TDC circuit and gives the start to an internal clock to start to measure the time until the second digital signal enters the circuit and stops the clock. The output of a TDC is a integer number corresponding to the number of internal clock time units (typically nanoseconds) elapsed between start and stop

Page 13: Luigi Benussi, Stefano Bianco, Luciano Passamonti Incontri di Fisica 2002 Laboratori Nazionali di Frascati dell’INFN DETECTION OF ELEMENTARY PARTICLES.

Time to Digital Converter (TDC)A TDC (time to Digital converter) is a electronic device used to measure the time elapsed between two digital signal.

The basic idea of a TDC is the following:

a digital signal enters inside the TDC circuit and gives the start to an internal clock to start to measure the time until the second digital signal enters the circuit and stops the clock. The output of a TDC is a integer number corresponding to the number of internal clock time units (typically nanoseconds) elapsed between start and stop

start

Time

Page 14: Luigi Benussi, Stefano Bianco, Luciano Passamonti Incontri di Fisica 2002 Laboratori Nazionali di Frascati dell’INFN DETECTION OF ELEMENTARY PARTICLES.

Time to Digital Converter (TDC)A TDC (time to Digital converter) is a electronic device used to measure the time elapsed between two digital signal.

The basic idea of a TDC is the following:

a digital signal enters inside the TDC circuit and gives the start to an internal clock to start to measure the time until the second digital signal enters the circuit and stops the clock. The output of a TDC is a integer number corresponding to the number of internal clock time units (typically nanoseconds) elapsed between start and stop

Time

start

stop

Page 15: Luigi Benussi, Stefano Bianco, Luciano Passamonti Incontri di Fisica 2002 Laboratori Nazionali di Frascati dell’INFN DETECTION OF ELEMENTARY PARTICLES.

Time to Digital Converter (TDC)A TDC (time to Digital converter) is a electronic device used to measure the time elapsed between two digital signal.

The basic idea of a TDC is the following:

a digital signal enters inside the TDC circuit and gives the start to an internal clock to start to measure the time until the second digital signal enters the circuit and stops the clock. The output of a TDC is a integer number corresponding to the number of internal clock time units (typically nanoseconds) elapsed between start and stop

Time

start

stop

t

The TDC output is read by the Data Acquisition (DAQ) program and stored in a PC for further analysis

Page 16: Luigi Benussi, Stefano Bianco, Luciano Passamonti Incontri di Fisica 2002 Laboratori Nazionali di Frascati dell’INFN DETECTION OF ELEMENTARY PARTICLES.

The basic idea

L

Scintillators

Page 17: Luigi Benussi, Stefano Bianco, Luciano Passamonti Incontri di Fisica 2002 Laboratori Nazionali di Frascati dell’INFN DETECTION OF ELEMENTARY PARTICLES.

The basic idea

L

Scintillators

start

Page 18: Luigi Benussi, Stefano Bianco, Luciano Passamonti Incontri di Fisica 2002 Laboratori Nazionali di Frascati dell’INFN DETECTION OF ELEMENTARY PARTICLES.

The basic idea

L

Scintillators

start

stop

Page 19: Luigi Benussi, Stefano Bianco, Luciano Passamonti Incontri di Fisica 2002 Laboratori Nazionali di Frascati dell’INFN DETECTION OF ELEMENTARY PARTICLES.

The basic idea

L

Scintillators

t

If we measure the time that the cosmic ray takes to pass both scintillators, knowing the the distance L, we can calculate the particle speed using the well know relation:

V = s/t

where s=L and t = t

start

stop

Page 20: Luigi Benussi, Stefano Bianco, Luciano Passamonti Incontri di Fisica 2002 Laboratori Nazionali di Frascati dell’INFN DETECTION OF ELEMENTARY PARTICLES.

Experimental setup

The experimental set up consists of the following components: • 2 scintillation detectors, composed by a scintillator (30x30x0.5 cm3) Philips NE110, an optical guide (22cm), a photomultiplier Philips 56AVP and a voltage divider.

• Crate VME, equipped with Low threshold discriminator (mod.CAEN 417), Quad coincidence logic unit ( mod.CAEN 455), Quad scaler and present counter time ( mod.CAEN 145), 4ch programmable HV power supply (mod.CAEN 470) and Dual delay (mod.CAEN 108).

• Camac crate DDC, equipped with: Status A (mod.CAEN 236), TDC (mod.LeCroy 2228) and SCSI interface, connected to PC

• PC software: Microsoft Word, for the texts editing; LabVIEW 6.1, for the acquisition of data; Origin, for the elaboration of graphics; Internet explorer. The detectors are vertically aligned at a distance L, which can be adjusted. When a cosmic ray particle crosses the scintillator detector, it produces a light pulse which is converted to an electrical signal at the photomultiplier exit. The signal goes to a low threshold discriminator which transforms it into a digital signal. The digital signal is delayed of 200 ns for the top detector (PM1)and 100 ns for the bottom one(PM2), and the two delayed signals arrive to an coincidence logic unit that performs an AND operation. We need an AND operation because we must select only cosmic ray particles which cross both detectors, otherwise we would have gather also signals from particles which pass from every direction. The logic unit has three outputs: one of these goes to a scaler for the count of the coincidences, another goes to a Status A producing a signal which is fed to the coincidence VETO and stops the unit for a short time after each coincidence; the last one goes to the TDC common start. The same delayed signal of the PM2 detector goes to TDC common stop. The TDC and the Status A device, contained in the Camac Crate, exchange data with the PC via the SCSI interface.

Page 21: Luigi Benussi, Stefano Bianco, Luciano Passamonti Incontri di Fisica 2002 Laboratori Nazionali di Frascati dell’INFN DETECTION OF ELEMENTARY PARTICLES.

Experimental setup

Diagram

Page 22: Luigi Benussi, Stefano Bianco, Luciano Passamonti Incontri di Fisica 2002 Laboratori Nazionali di Frascati dell’INFN DETECTION OF ELEMENTARY PARTICLES.

Experimental setup