P3TMA Experimental Projects

Transcription

1 P3TMA Experimental Projects 3 credits Take S1 (from end of September to December); Enters in the average of the second semester. Projects currently available : Stern-Gerlach Experiment Quantum Entanglement Muon Magnetic Moment Measurement Parity Violation Organization: Groups of 2/3 students are formed at the beginning of the semester (students experiments are randomly associated). Each group will have to deal with one project during the semester (2 groups can work on a same experiment, independently). The task will consist in theoretical as well as experimental studies. A report has to be written at the end. The projects are described below:

2 The Stern & Gerlach experiment allows to study the magnetic properties of particles. This experiment consists in injecting a beam of particle through an inhomogeneous magnetic field. Because of the magnetic inhomogeneity, a magnetic strength acts on the magnetic moment of the particle leading to the separation of its spin quantum states. The experiment, originally performed in 1922 by Otto Stern and Walther Gerlach, permitted to discover the particle spin and demonstrated that particles have an intrinsic quantized angular momentum. This experiment strongly influenced the development of modern physics and removed many lingering doubts that Quantum Mechanics was true. The entanglement experiment gives the opportunity to verify that quantum mechanics is not found at fault in this context and raises issues on the concept of space and time and on the notion of information as well.the experimental device generates polarization-entangled photon pairs and provides analysis system for different data analysis for the measurement of correlation curves, for the discrimination between Bell states, for the violation of the Bell's inequalities and for the tomographic reconstruction of the 2-photon density matrix. The theoretical aspects deal with the Bell inequalities and their physical outcomes and both the description of entangled states in Quantum Mechanics and the correlated measurements. The Muon Magnetic Moment measurement experiment is similar to the one originally set by C Amsler in Zurich (1973). It uses muons produced in Cosmic Ray atmospheric showers (via π and K decay), which are polarized (25-40% in lab frame at sea level). The muons can stop in a target (here, copper), and then decay in the lab frame (= their rest frame). Here, the relevant Muon is μ +. It's possible, with a magnetic field, to make the Muon Spin precess before the decay, which will impact the observed time distribution of the issued positrons in a given direction, allowing to measure the Muon Magnetic Moment. The experimental setup is made of a copper target (4cm thick), surrounded by scintillator plates read by photomultipliers. Target and scintillators are inside coils which can generate a magnetic field. The purpose of the project is to operate the system, to fully characterize it, and to analyse the data taken during several months. Parity Violation. Up to 1954, physicists were believing that parity was always conserved. The τ - θ puzzle: τ +, θ +, same mass, same charge, same half life but different parity (in fact = K + ), lead, in 1956, Yang and Lee to suggest that τ - θ puzzle could be explained if parity is not conserved in Weak Interaction. In 1957 C. S. Wu confirmed that parity was violated in weak decays. The experimental project consists in the determination of Parity Violation by the study of Moeller scattering of electrons produced in a beta decay. This was initially proposed by Frauenfelder et al. in The experiment exploits the strong dependence of Moeller scattering cross section w.r.t. the relative orientation of the spins of the incident and target electrons, which serves as an analyser of the spin of the electrons issued by the beta decay (weak interaction), allowing to demonstrate the parity violation in the decay. The work consists in studying and characterizing the main components of the experimental setup (radioactive source, magnetic field, electron detectors), and in studying and quantifying the parity violation.

3 Entanglement experiment (supervision : S. Lazzarini) Fact : Quantum mechanics has transformed our vision of the world Non-locality - [A. Aspect et al. (1982)]= larger scales. Non separable states= quantum entanglement with photon pairs. QM has never been found at fault and puts into question both the concept of space, time and the notion of information. Nature itself is fundamentally non local "Nobody understands quantum theory" R.P. Feynman (Nobel prize 1965) Experimental projects: EPR Master P3TMA S. Lazzarini (CPT) 1 / 2

4 The issue : quantum entanglement and measurement Two groups of (at most) 3 students will be concerned by both the theoretical aspects and the measurements of entangled photon pairs. 1 EPR experiment : Consider a Bell state (entangled state) for a photon pair or for a e + e pair (Bohm) and perform the calulation given by QM for the measurement on each of both the components of the pair. 2 Learn about Bell inequality and its physical outcomes. 3 Specializing to the photon pairs with polarization according to the experimental device. 4 Show the violation of the Bell inequality by QM = no local hidden variables and highly strong quantum correlations. 5 Entanglement entropy and fidelity tests (comparison TH and EXP). 6 Write down a short article and conclude according to what would measure the entanglement experiment. Experimental projects: EPR Master P3TMA S. Lazzarini (CPT) 2 / 2

5 Muon Magnetic Moment Measurement Principles: Muons, produced in Cosmic Ray atmospheric showers (via π and K decay), are polarized (25-40% in lab frame at sea level). Theory: this will have to be proved. The muons can stop in a target (here, copper), and then decay in the lab frame = rest frame. Theory: computation of the angular distribution of the electron issued in the muon decay. It's possible, with a magnetic field, to make the Muon Spin precess. This will impact the angular distribution of the issued positrons (here the relevant Muon is µ + ) => measure of the Muon Magnetic Moment.

6 Experiment : goal : measure the Landé factor µ (g) for the muon. B ~ 35 G Muon Trigger+ electron detection Cu Target VETO No Field Amsler 1974 B Field τ ~ 2.10 µs t Muon trigger - electron detection DAQ One of our setups Scintillator plate Photomultiplier tube

7 Stern & Gerlach Experiment (Supervisor W. Gillard) - Stern & Gerlach: 1943 Nobel prize laureates Discover new fundamental property of particles : the Spin, Prove the quantum nature of particles, Remove any lingering doubts on Quantum Mechanic. - Aim: Probe fundamental quantum property of atoms and electrons Spin and Magnetic moment - How: Use non-uniform magnetic field to separate different spin quantum states Experimental Projects : SG Master P3TMA 2016/17 W. Gillard 1 / 2

8 Stern & Gerlach Experiment (Supervisor W. Gillard) precision measurements : - Optimize of the signal-to-noise ratio, - Calibrate the Stern & Gerlach device, - Investigate sources of systematic uncertainties, - Derive particle magnetic-moment based on your measurements. theoretical aspects : - Demonstrate the capability of the Stern & Gerlach experiment to separate different spin states, - Extend the calculation to a cascade of Stern & Gerlach devices with different magnetic field, orientation, - Investigate the possibility to use Stern & Gerlach devices to filter spin states. Each group will write down a scientific article to present its measurements and theoretical calculations to the quantum nature of spin. Experimental Projects : SG Master P3TMA 2016/17 W. Gillard 2 / 2

9 Parity Violation Jose Busto

10 Up to 1954, physicist believes that parity was always conserved. (Parity was well-tested in selection rules in atomic and nuclear physics, until 1954) The Tau Theta puzzle +, + + θ +, τ +, same mass, same charge, same half live but different parity ( θ +, τ + K + ) In 1956 Yang and Lee suggest that θ τ puzzle can be explained if parity is not conserved in Weak Interaction.

11 In 1957 C. S. Wu confirmed that parity was violated in weak decays + +ν

12 Proposed experiment Determination of Parity Violation by the study of Moeller scattering of electrons produced in a beta decay Frauenfelder et al Strongly dependence of Moeller scattering cross section on the relative orientation of the spins of the incident an target electrons 90 Sr Variable magnetic field

13 90 Sr B Fe D2 Study and characterize the main components of the experimental setup (radioactive source, magnetic field, electron detectors) Study and quantify the parity violation.