status of the primex experiment: a precision measurement of the neutral pion lifetime 7 th european...
TRANSCRIPT
![Page 1: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/1.jpg)
Status of the PrimEx Experiment:A Precision Measurement of the Neutral
Pion Lifetime
7th European Conference on “Electromagnetic Interactions with Nucleons and Nuclei”
Milos Island, GreeceSeptember 12-15, 2007
Dan DaleIdaho State University
![Page 2: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/2.jpg)
Participating Institutions
North Carolina A&T State University University of MassachusettsUniversity of Kentucky Idaho State UniversityJefferson Lab Hampton UniversityMIT University of North Carolina at WilmingtonCatholic University of America Arizona State UniversityUniversity of Virginia ITEP, RussiaIHEP, Russia Norfolk State UniversityUniversity of Illinois Kharkov Inst. of Physics and TechnologyChinese Institute of Atomic Energy IHEP, Chinese Academy of Sciences George Washington University Yerevan Physics Institute, ArmeniaSouthern University at New Orleans Tomsk Polytechnical University, RussiaUniversity of Sao Paulo
![Page 3: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/3.jpg)
A High Precision Measurement of
• Physics motivation• The Primakoff effect• Experimental setup• Towards high precision• Current analysis event selection radiative width extraction • Summary
![Page 4: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/4.jpg)
The axial anomaly
Leading order corrections (Donoghue, 1989)
Corrections O(p4)
![Page 5: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/5.jpg)
Current experimental and theoretical status
Expected PrimEx error bar,arbitrarily projected to theleading order chiral anomaly
decay
wid
th (
eV
)
Next to LeadingOrder, +- 1%
![Page 6: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/6.jpg)
Sum rule approach to axial-vector-vector (AVV) form factor.
f – f caused by strong interaction shown to be small.
Eta width only input parameter. o mixing included.
o eV
Recent Theoretical Advances(B.L. Ioffe and A.G. Oganesian, Phys. Lett. B647, p. 389, 2007)
![Page 7: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/7.jpg)
![Page 8: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/8.jpg)
![Page 9: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/9.jpg)
The Primakoff Effect
Radiative width Known, measured quantities
![Page 10: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/10.jpg)
Angular distributionenables separation ofamplitudes
![Page 11: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/11.jpg)
For high precision:
• Measure angular distribution well to separate various amplitudes
new state of the art o detector
• Measure on a variety of targets to test validity of background extraction (Primakoff
• Tight photon energy (peak4and flux control
photon tagging
• Measure QED processes (Compton and pair production) to validate setup and analysis techniques.
![Page 12: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/12.jpg)
incident electrons
Tagged photon beam
![Page 13: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/13.jpg)
Bremsstrahlung photon tagging
Electron beam
Post-brems electrons
![Page 14: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/14.jpg)
Tagging Ratios
![Page 15: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/15.jpg)
Photon Calorimetry – the HYCAL calorimeter
1152 PbWO4 and 576 lead glass modules
1.6% energy resolution
1-2 mm position resolution
![Page 16: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/16.jpg)
In-beam calibration
![Page 17: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/17.jpg)
![Page 18: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/18.jpg)
Effect of periodicityof detector modules.
![Page 19: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/19.jpg)
Energy resolution – lead tungstate
![Page 20: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/20.jpg)
![Page 21: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/21.jpg)
Luminosity analysis efforts
• Electron counting (absolute flux)
• Pair spectrometer (relative tagging ratios)
• TAC (absolute tagging ratios)
• Target thickness
• Known cross sections (pair production,
Compton)
![Page 22: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/22.jpg)
Online Flux Monitoring
e+ - e - pair spectrometer
dipolemagnet
plastic scintillators
![Page 23: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/23.jpg)
Stability of relative tagging ratios
Monitored during production data taking.
![Page 24: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/24.jpg)
Stability of relative tagging ratios
Stable to 1%.
![Page 25: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/25.jpg)
Relative tagging ratios versus rate
Independent of rate!
![Page 26: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/26.jpg)
Pair production cross section
(1)Bethe-Heitler (modified by nuclear form factor).
(2)Virtual Compton scattering.
(3)Radiative effects.
(4)Atomic screening.
(5)Electron field pair production.
![Page 27: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/27.jpg)
Compton Scattering--Stability of Setup
![Page 28: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/28.jpg)
Angular distribution for CarbonPrimakoff Peak
![Page 29: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/29.jpg)
UMass Analysis
HYCAL – Tagger timing
Invariant Mass Elasticity
Total Probability = Timing x Mass x Elasticity
Event selection:
Normalized probabilitydistributions for
![Page 30: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/30.jpg)
Elasticity versus invariant mass
Hybrid mass
![Page 31: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/31.jpg)
UMass Analysis: Radiative Width for Carbon
Primakoff peak
Nuclear coherent andPrimakoff – NC interference
![Page 32: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/32.jpg)
MIT/JLab Analysis: Event Selection
Invariant mass
HYCAL – Tagger timing
Elasticity
![Page 33: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/33.jpg)
Angular distributions and background
Carbon Lead
![Page 34: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/34.jpg)
MIT/JLab Analysis: Radiative Widths for Carbon and Lead
Carbon: = 8.20 ± 0.15 eV ± 0.20 eV Lead: = 8.11 ± 0.16 eV ± 0.20 eV
![Page 35: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/35.jpg)
ITEP/NCA&T Analysis: Radiative Width for Carbon
= 7.98 ± 0.18eV
All possible cluster combinations.Elasticity imposed.HYCAL – tagger timing < 4 nsec.
![Page 36: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/36.jpg)
ITEP/NCA&T Analysis: Radiative Width for Lead
= 7.94 ± 0.18eV
![Page 37: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/37.jpg)
ITEP/NCA&T Analysis: Radiative Width Combined Fit for Carbon and Lead
= 7.95 ± 0.13eV
Carbon
Lead
![Page 38: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/38.jpg)
![Page 39: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/39.jpg)
Summary IUMass AnalysisCarbon 8.41 eV ± 0.15 eV ± 1.8%
MIT/JLab Analysis: Carbon: = 8.20 eV ± 0.15 eV ± 0.20 eVLead: = 8.11 eV ± 0.16 eV ± 0.20 eV
ITEP/NCA&T Analysis:Carbon: = 7.98 eV ± 0.18 eVLead: = 7.94 eV ± 0.18 eVCombined fit, Carbon and Lead: = 7.95 eV ± 0.13 eV
![Page 40: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/40.jpg)
Summary
• The neutral pion lifetime is a stringent test of confinement scale QCD.
• High precision of the experiment has pushed the limits of photon calorimetery, luminosity monitoring, and QED calculations.
• Experimental systematic errors controlled by pair production and Compton scattering.
• High quality data taken in late 2004. Three quasi-independent analyses.
• Our preliminary result is:
= 7.93 eV ± 2.1% (stat) ± 2.0% (stat)
• In good agreement with ChPT predictions.• Further studies of backgrounds underway.
![Page 41: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/41.jpg)
Extra Slides
![Page 42: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/42.jpg)
PDF1: HYCAL – Tagger timing
![Page 43: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/43.jpg)
PDF 3: Invariant mass
![Page 44: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/44.jpg)
PDF 2: Elasticity
![Page 45: Status of the PrimEx Experiment: A Precision Measurement of the Neutral Pion Lifetime 7 th European Conference on “Electromagnetic Interactions with Nucleons](https://reader030.vdocuments.net/reader030/viewer/2022032612/56649efa5503460f94c0b80e/html5/thumbnails/45.jpg)
Previous Experiment: The Direct Method(Phys. Lett., vol 158B, no. 1, 81, 1985)
o`s produced by 450 GeV protons in tungsten foils.
o decays observed by detection of 150 GeV/c positrons produced by decay rays converting in foils.
Y(d) = N[A + B(1-e-d/)]
Dalitz decay, conversion in first foil