1 From Raw Data to 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 Schematic view of the LEPS exp. Trigger and veto -Schematic view of the LEPS exp.

4 Trigger Tagging system Trigger and veto -Tagging system 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 E e ’ 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 If there happened BCS, the TAG got fired. 3.5 eV M. Sumihama Ph.D. thesis, 2003

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

6 Trigger 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 veto 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 velocity β>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 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 veto 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 track vertex 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 B tesla has charge Q coulombs and velocity v m/s, the magnetic force is F = BQv Momentum x Speed = EnergyThe 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 = 3x10 8 ms -1, then the units are now in Joules because: Momentum x Speed = Energy pc=BQrc (units:Joules(J))

16 From Track to momentum One electron volt, 1 eV = 1.6x J or, expressed another way, 1 J = (1/1.6x )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 = 1.6x 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 · 3×10 8 (units: eV)

17 From Track to momentum or, because 1GeV = 1x10 9 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: c 2 = a 2 + b 2 - 2ab cos C ∠ ABC = ∠ BCP + ∠ BAP. Thus ∠ APC = ∠ ABC The cosine rule is now applied to ΔACP to find the radius of the circle.

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

20 What happen? We got what is B and C. A B C γ p pp pK K+K-K+K- π + π – π 0

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

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

23 What is Y? -missing mass M 0 of proton from PDG =0.938 GeV γ+p → φ +p → K + + K - N Barion 0 +1 → 0 +1 → Q 0 +1 → 0 +1 →

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

25 Result

26 End Thanks

27

28 Lancaster Particle Physics Package (LPPP).