From Raw Data to Physics Results

1. From Raw Datato Physics Results Grass 2009/08/07

2. Data Analysis Chain • Have to collect data from many channels on many sub-detectors (millions) • Decide to read out everything or throw event away (Trigger) • Build the event (put info together) • Store the data • Analyze them • do the same with a simulation • Compare data and theory

3. Trigger and veto-Schematic view of the LEPS exp.

4. M. Sumihama Ph.D. thesis, 2003 Trigger and veto-Tagging system If there happened BCS, the TAG got fired. 3.5 eV SSD :Silicon strip detector The precise hit position of recoil electron is measured by SSD layers. PS : Plastic scintillator If there are hits at PS associated with the hits in the SSD, we obtain the energy Ee’ with the hit position at SSD and obtain the photon energy by estimation. We select the events finding only one hit in the region covered by the fired scintillators to reduce the background events

5. Trigger and veto- around the spectrometer M. Sumihama Ph.D. thesis, 2003

6. Trigger and veto-Trigger counter (TRG) • The TRG is a plastic scitillation counter to identify the event signals from charged particles produced at the target. • The trigger counter is used as reference counter to measure the time-of flight with the RF signal. M. Sumihama Ph.D. thesis, 2003

7. Trigger and veto-Aerogel Cerenkov counter (AC) • Main background event are the e+e- pairs producted at the target and at TRG in a measurement of hadronic reaction. • When a particle with a velocityβ>1/n passes through a transparent material with a refractive index n, Cerenkov lights are emitted. --- n=1.03; β~0.97 M. Sumihama Ph.D. thesis, 2003

8. Trigger and veto- Time-of flights (TOF) • Time-of flights of charged particles are measured by a TOF wall. • This is one of trigger. M. Sumihama Ph.D. thesis, 2003

9. Trigger and veto-Upstream-veto counter • The photon beam partly converts to charged particles mainly by the e+e- pair production process in air, the residual gas or Al windows of the beam pipe. • This counter is a plastic scintillator located at 4m upstream from the target. M. Sumihama Ph.D. thesis, 2003

10. Trigger and Veto M. Sumihama Ph.D. thesis, 2003

11. Detectors :TPC（time projection chamber） J.Y. Chen Ph.D. defence

12. Raw data

13. Return to original the physics events vertex track J.Y. Chen Ph.D. defence

14. Return to original the physics events And then … ? J.Y. Chen Ph.D. defence

15. From Track to momentum • If a particle in a magnetic field Btesla has charge Qcoulombs and velocity vm/s, the magnetic force is F = BQv • The unit of Q is Coulombs (C), B is Tesla (T) and r is meters (m). If we multiply both sides of the equation by the speed of light, c = 3x108ms-1, then the units are now in Joules because: Momentum x Speed = Energy pc=BQrc (units:Joules(J)) http://lppp.lancs.ac.uk/motioninb/experiment.html

16. From Track to momentum • One electron volt, 1 eV = 1.6x10-19 J or, expressed another way, 1 J = (1/1.6x10-19)eV. Therefore the units of the equation, above, can be converted to eV as follows: • Q is equal to the charge on the particle moving in the magnetic field. For this exercise Q is equal to the charge on one electron or proton = 1.6x10-19 C. Therefore the equation above reduces to: pc=Brc (units: eV) • By substituting in the value for c, on the right hand side, we get pc=Br·3×108(units: eV)

17. From Track to momentum • or, because 1GeV = 1x109 eV pc=0.3Br (units:GeV) • Finally, by expressing the units in terms of c we obtain: p=0.3Br (units:GeV/c) • What we need to know are just B and r. • How could we know the radius?

18. From Track to momentum-How could we know the radius • AP = BP = CP = radii of the circle. • The machine applies Pythagoras theorem to pairs of the coordinates pairs to calculate AB, A and BC. • The cosine rule is then applied to ΔABC in order to calculate ∠ABC. • ΔBAP and ΔBCP are both isocoles. This can be used to show that: • ∠ABC = ∠BCP + ∠ BAP. • Thus ∠APC = 360 - 2 ∠ABC • The cosine rule is now applied to ΔACP to find the radius of the circle. c2 = a2 + b2 - 2ab cos C

19. Find rest masses by dE/dx J.Y. Chen Ph.D. defence

20. γ p B A C What happen? • We got what is B and C. pp K+K- pK π+ π– π0

21. γ p K- A K+ What is A?-invariant mass

22. Do we miss something? • Conservation of Baryon Number γ+p → X → K+ + K- γ+p → φ → K+ + K- NBarion 0 +1 → 0 → 0 + 0 • There are something else … γ+p → X +Y → K+ + K- γ+p → φ +Y → K+ + K- NBarion 0 +1 → 0 +1 → 0 + 0 +1 Q 0 +1 → 0 +1 → 0 + 0 +1 Wrong!!

23. What is Y?-missing mass • γ+p → φ +p → K+ + K- • NBarion 0 +1 → 0 +1 → 0 + 0 +1 • Q 0 +1 → 0 +1 → 0 + 0 +1 M0 of proton from PDG =0.938 GeV

24. Use the cross section ratio to find the number of colours

25. Result

26. End Thanks

28. Lancaster Particle Physics Package (LPPP). http://lppp.lancs.ac.uk/index.html