From Raw Data to Physics Results

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From Raw DataRaw Data

to Physics ResultsPhysics Results

Grass2009/08/07

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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

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Trigger and veto

-Schematic view of the LEPS exp.Schematic view of the LEPS exp.

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TriggerTrigger and veto

-Tagging systemTagging 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 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

If there happened BCS, the TAG got fired.

3.5 eV

M. Sumihama Ph.D. thesis, 2003

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Trigger and veto

- around the spectrometer

M. Sumihama Ph.D. thesis, 2003

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TriggerTrigger 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

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Trigger and vetoveto-Aerogel Cerenkov counter (AC)• Main background event are the e+e- p

airs 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

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TriggerTrigger 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

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Trigger and vetoveto

-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

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Trigger and VetoTrigger and Veto

TOFTRGUPvetoTAGTOFACTRGUPvetoTAG

trig. ee trig. Hadron

-

M. Sumihama Ph.D. thesis, 2003

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Detectors :TPC （ time projection chambe

r ）

J.Y. Chen Ph.D. defence

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Raw data

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Return to original the physics events

track

vertex

J.Y. Chen Ph.D. defence

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Return to original the physics events

And then … ?And then … ?J.Y. Chen Ph.D. defence

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From Track to momentum• If a particle in a magnetic field B tesla has charge Q coulombs an

d velocity v m/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 = EnergyMomentum x Speed = Energy

pc=BQrc (units:Joules(J))

http://lppp.lancs.ac.uk/motioninb/experiment.html

):(units

1

2

smKgBQrporBQrmv

BQvrv

m

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From Track to momentum• One electron volt, 1 eV = 1.6x10-19 J or, expressed another way, 1 J = (1/1.6

x10-19)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)

•

(eV)) ltsElectronvo:(units . 191061

BQrc

pc

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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?

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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 pai

rs 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:

c2 = a2 + b2 - 2ab cos C

• ∠ABC = ∠BCP + ∠ BAP. • Thus ∠APC = 360 - 2 ∠ABC• The cosine rule is now applied to ΔACP to find

the radius of the circle.

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Find rest masses by dE/dx

J.Y. Chen Ph.D. defence

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What happen?

• We got what is B and C.

A

B

C

γ p

pp

pKK+K-

π + π – π0

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What is A?

-invariant mass

Az

Ay

Ax

A

Kz

Ky

Kx

K

Kz

Ky

Kx

K

P

P

P

E

P

P

P

E

P

P

P

E

A K K

A

K-

K+

γ p

222

222

2222

)()()(

)()()(

)()()()(

Ap

AA

Kz

Kz

Ky

Ky

Kx

Kx

Ap

Kx

Kx

Ax

Kp

KKp

KKKA

PEM

PPPPPPP

PPP

PMPMEEE

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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!!

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What is Y?-missing mass

Yz

Yy

Yx

Y

Kz

Ky

Kx

K

Kz

Ky

Kx

Kp

P

P

P

E

P

P

P

E

P

P

P

EM

E

EY K K p

0

0

0

0

0

M0 of proton from PDG =0.938 GeV

γ+p → φ +p → K+ + K- NBarion 0 +1 → 0 +1 → 0 + 0 +1 Q 0 +1 → 0 +1 → 0 + 0 +1

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Use the cross section ratio to find the number of colours

f fc-ff zN

qqR 2

)ee(

)e(e

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Result

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End

Thanks

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