The PRIMEX Experiment: A Fundamental Test of the Chiral Anomaly Prediction in QCD. Erik Minges April 23 rd, 2010

Transcription

1 The PRIMEX Experiment: A Fundamental Test of the Chiral Anomaly Prediction in QCD Erik Minges April 23 rd, 2010

2 Outline Symmetry and conservation Laws Overview and examples PRIMEX physics motivation The Chiral Anomaly Experimental Setup PRIMEX first run results Prototype detector beamtest Energy calibration, shower profile, position resolution Conclusion

3 Symmetry What is it? Generalized to mean invariance A system which remains unchanged under a certain kind of transformation. Rotational symmetry of a pencil Symmetry Breaking Rotational Symmetry

4 Powerful tool in physics Symmetry cont. In 1905, Amalie Noether determined the connection between symmetry and conservation laws Noether s theorem For every continuous mathematical symmetry, there is a corresponding conservation law. it is only slightly overstating that physics is the study of symmetry. Philip Warren Anderson American Physicist and Nobel Laureate Contributions to theories of localization, antiferromagnetism, and high-temperature superconductivity

5 PRIMEX Experiment The PRIMEX experiment at Thomas Jefferson National Lab is to measure the lifetime of the π 0 particle with high precision. This experiment is a very important test of Quantum Chromodynamics (the theory to describe the strong interaction).

6 PRIMEX Physics Motivation Prediction of the 0 decay width in Chiral Anomaly is exact in the Chiral limit. However quarks have mass. Leads to correction in theory. Neutral Pion decay measured to test fundamental prediction of low energy QCD. 0 High precision measurement of decay rate, dominated by axial anomaly.

7 Chiral Anomaly Axial symmetry of the Classical Lagrangian of Quantum Chromodynamics is broken in the Chiral limit. Chiral limit is when the up, down quark masses vanish. This symmetry breaking is of pure Quantum mechanical origin due to quantization. The Lagrangian has continuous symmetry, but no conservation law associated with it i.e. - no conserved current

8 Confirmation of Quark Color In the chiral limit, the predicted decay amplitude A N (3f Where N C 3 is the number of quark colors in QCD and f MeV is the Pion decay constant. Precise predicted decay width C ) Number of quark colors will be directly measured by this experiment Number colors most fundamental parameter in Physics 2 GeV m 1 3 A eV

9 Primakoff Effect Virtual photon from nucleus of target interacts with tagged photon from incident photon beam. Virtual photon and tagged photon create neutral Pi meson Photopion production from Coulomb field of nucleus. Pion decay in forward direction, so need good central resolution. Pi zero has high branching ratio to decay into 2 gamma rays, which HYCAL can detect.

10 Experimental Setup Helium bag less particle interaction than air and cheaper than vacuum Magnet measure pair production to monitor photon flux and sweep out charged particles Electron beam passing through nucleus field and change momentum, produce Bremsstrahlung radiation Physics target (Primakoff) Radiator Measure energy and momentum of scattered electrons yield energy and momentum of gamma produced

11 Status of PRIMEX PrimEx-I () = 7.82eV2.2%2.1% Next toleading Order Chiral Anomaly Leading Order Chiral Anomaly

12 Analysis Results for the 6x6 PbWO 4 Crystal Prototype Detector Beam Test Center Crystals PbWO4 Surrounding Lead Glass

13 My Project for PRIMEX What is the need for an energy calibration? 36 PbWO 4 crystals detect incident beam energy via ADC Meaningful average pulse height signal from ADC requires calibration of each crystal using known incident beam energies How is the incident E beam beam energy found? x-y coordinate detector with 60 scintillating fibers on each axis Detects position of incident electrons. Each fiber approximately 2 mm in diameter e Dipole magnet s field yields incident energy of electrons Incident electron beam energy as a function of X fiber number is X * X * X X e

14 Relative Energy Calibration Alignment Each crystal needs to have the same response Align each individual crystal center Assume all incident energy is deposited at center of crystal Assume no energy is lost due to leakage into surrounding crystals Find mean ADC at center of crystal, divide by known incident energy E beam =A*(mean ADC) adc(1) for run 435 cut at (X=29) and (Y=31) mean ADC = 5413 i.e. For run 435 (centered on crystal 26) E beam = E(29) = (mean ADC) = so A = E-04!!!

15 Global Energy Calibration Absolute scale from 5x5 cluster size Shower interacts in several crystal Sum all deposited energy in surrounding crystals to account for leakage E beam = B*[ A i * (mean ADC) i ] i.e. For run 419 (centered on crystal 15) E beam = E(29) = A i * (mean ADC) I = so B = !!! with σ/e re = Now just take the average value of the four center crystals B avg =

16 Results - Ratio of Energies Deposited in a single module Error bars for (E re /E beam )associated with run 413 Maximum deposited energy is at center of crystal. Minimum deposited energy is at boundary of crystal. (As expected)

17 Results - Energy Resolution of the Prototype Error bars for (σ/e re )associated with run Energy resolution at center is greater than at boundaries of crystal. (As expected)

18 Results - Shower Profile The shower profile measures the dependence of the average pulse-height ratio for different crystal channels 1.) Adjacent Channel ratio A i /A i+1 2.) Adjacent Row ratio A j /A j+1 3.) Separated Channel ratio A i+1 /A i-1

19 Results - Adjacent Channel Ratio Run 435 for E26/E Boundary

20 Results - Adjacent Row Ratio Run 422 E3,9,15/E4,10,16 1 3, 9, 15 4, 10, 16 Boundary

21 Results - Separated Channels Ratio Run 435 for E28/E Center: 27

22 Reconstructed Position Method Center of Gravity Method Weight factor for cell Linear Weight where, Logarithmic Weight ) ( )* ( i N i i i i N i i cal E x E x ) ( i i E T i i i E E E ) ( N i E T E i T i i i E E W E ln 0, max 0 th i

23 Linear - Reconstructed Position 3x3 run 389 3x3 run

24 Linear - Reconstructed Position 5x5 run S shape indicates some systematic shift from the method incorporated.

25 Linear Position Resolution 3x3 run 389 3x3 run

26 Linear Position Resolution 5x5 run Position resolution worst at boundaries and best at center

27 Logarithmic Reconstructed Position ~ %3 error (leakage) 3x3 run 389 3x3 run ~ %3 error (leakage)

28 Logarithmic Reconstructed Position 5x5 run 413 (No systematic shift) 22 21

29 Logarithmic Position Resolution 3% error 3x3 run 389 3x3 run

30 Logarithmic Position Resolution 5x5 run 413 1% error 21 22

31 Linear or Logarithmic Weight? Linear weight - large systematic errors Radial energy fall off of showers is exponential Energy deposited in the module decreases exponentially as a function of the distance from the point of incidence.

32 Logarithmic Weight Ideal weight must employ a logarithmically weighted energy due to the exponential fall off of the shower profile The logarithmically weighting of the deposited energy signals produce the best results Which is what we were expecting from the results

33 Conclusion PRIMEX Experiment provide precision test on Chiral Anomaly prediction. Energy Resolution %1.7 at the center and %2.2 at boundaries Worse at edge of crystals Due to fluctuation of shower and energy leakage Reconstructed Position Center of gravity Linear has large systematic error Logarithmic is almost linear; small systematic shift

34 Thank You PrimEx! and my mentor: Dr. Gan - UNCW

35 Conservation Laws Symmetries in nature lead to conservation laws A particular measurable property of an isolated physical system does not change as the system evolves Corresponds to a conserved physical quantity. Conservation of energy, linear momentum, angular momentum, electric charge, probability, mass, etc. Usually derived from Lagrangian dynamics A reformulation of classical mechanics that combines conservation of momentum with conservation of energy.

36 Lagrangian Dynamics Lagrangian of a system is a classical method to derive Newton s second law of motion, F ma. Forces are hard to find. Lagrangian utilizes conservation of energy L xi, x i T xi, x i, t U xi, t, where is a generalized coordinate system L d L Lagrangian equation of motion: 0 xi dt x i Conservation Law If L x i L 0 x i x i C, where C is a constant.

37 Conservation Law second example Parity Violation Flip either one, or all spatial variable signs. Parity Example A mirror flips the original object by the vertical Parity of mirror = -1. Discontinuous symmetry > No conservation law. ),, ( ),, ( 1, ),, ( ),, ( 1, z y x z y x z y x z y x

38 Cross Section Cross section in particle physics expresses the likelihood of interaction between two particles. d Differential cross section, is the probability to observe a scattered particle per unit solid angle. d d d dns FN d t _ # Particles detected per second (Flux of incident particles)(# target particles)(detector area)