Status of TPC experiment ---- Online & Offline M. Niiyama H. Fujimura D.S. Ahn W.C. Chang.

Status of TPC experiment ----Online & Offline

M. NiiyamaH. FujimuraD.S. AhnW.C. Chang

• From cosmic ray test, 1 track resolution is - 300 um in pad plane w/ magnet- 700 um in drift direction w/o magnet.

• If we apply magnetic field, residual in drift direction shifts layer by layer. Possible reason are

- circle fitting is not suitable for our solenoid magnet. -> runge kutta is needed - E x B effect disturbs drift property of electrons in TP

C. Bx at z=350mm is 0.5T -> simulation of drift property is needed.

Results from cosmic ray test

Bx at z=350mm

E // B Cycloid Motion

E&M Calculation

Install & Geometry

151.6 cm 40.7cm

20cm

32.4cm

Collimator Shield target

TPC

solenoid

Pb

Top view

Dip

ole m

agn

et

37.5 cm

dipole magnet

Downstream scintillators

Side 　 scintillators

Ｓｈｉｅｌｄ

Ｃｏｌｌｉｍａｔｏｒ

Ｕｐｖｅｔｏ　

ＥＸＰ．ＨＵＴＣＨ（ February ）

February run

dipole magnet

Downstream scintillators

Side 　 scintillators

Ｓｈｉｅｌｄ

Ｃｏｌｌｉｍａｔｏｒ

Ｕｐｖｅｔｏ　

ＥＸＰ．ＨＵＴＣＨ（Ｍａｒｃｈ）

Ｓｔａｒｔ　ｃｏｕｎｔｅｒ

ＴＯＦ　Ｗａｌｌ

Ｖｅｔｏ　＠ＴＯＦ

March run

Trigger condition

• Run in Feb, to know performance of TPC

tag x (up-veto) x (8scinti M>=2) x (TPC side scinti M>=1)

95Hz at 400kHz tagger• Run in Mar, Particle ID by spectrometer calibration of TPC.

gamma-> pi+ pi- p, trigger is similar as K0 exp.

- tag x (ATG) x (TOF M>=2) x (veto after TOF)

x (TPC side scinti M>=1)

Eye scanning

• At least one particle comes from target holder• Reject if two tracks overlap each other

Scanning criteria

Analysis

• dE is measured by pad rows• By correction by dip angle between pad plane and track was

applied.• Truncated mean was used to suppress Landau distribution.

- for each track, to get truncated mean,

- cut the Landau tail of the distribution

- keep 60% of the sample, which have the most lowest amplitude

- get the mean value of the remaining distribution

truncated mean• Circle fitting in pad plane, line fitting in arclength z plane• dE/dx value of given tracks• Cut condition ; chi2 for pad plane and arclength z plane

Momentum/charge

(dE

/dx

Tru

nca

ted

me

an)

*co

s(la

mb

da)

• Calibration of gain is not finished.• Runge-Kutta tracking is not yet used. Just circle fitting for p_t determination

proton

Pions or electrons

1000 events eyescan

DAQ and Offline Analysis

1200-channel FADC Modules (10 bits, 40 MHz, pedestal-subtraction) for TPC

DAQ Speed

Goal: 100 Hz. In total 3 SUN SPARC (collector) to read out data in

parallel. Feb run:15Hz.

# of words read =10000-30000 word, for 1 IRQ( = 4events), 1 module

Unstable pedestal: drifting with temperatures. (Air-condition is desirable.)

March Run: 20Hz On-board width-cut for discrete pulses (<4 time bins). Tag*\bar{up}*ATG*\bar{e+e-}*(TOF M>=1) * (TPC side M>=2) # of words = 3000, 1 IRQ( = 4events) for 1 module

Where is the bottle neck of DAQ speed? Reduce the number of sampling to 600. Reduce the CLOCK from 40 MHz to 20 MHz. Look for the other possible source in collector or builder.

Determination of Particle Trajectory

TPC analyzer 1

Pad 1

pulse1 Pulse2 ……….

ADCTDC

ADCTDC

Pad 2

pulse1 Pulse2 ……….

ADCTDC

ADCTDC

If overlap in time direction was foundin adjacent pad they are include in a cluster.

Pad 3

pulse1 Pulse2 ……….

ADCTDC

ADCTDC

Continue in all pads in layer while overlap is found

In one layer

Pad#

Time

TPC analyzer 2

In one layer

Cluster Hit

x, y, z coordinateADC

To reduce # of hits to be searched by find track. Select hits of enough large ADC.

BoneHit

x, y, z coordinateADC

TrackFinder

Under construction

TrackFinder

Track pattern recognition: Segment the acceptance into sub-volumes in

(r,,z). Nose-finding algorithm: pick up hits on the

most outer layer and search the nearest hit in the neighboring sub-volume inwards.

Construct track-candidates: after conformal mapping, make the cut on the chi2 values of a straight line fit.

Track Parameters for RK fitting: Assuming uniform B field. Circle fitting on the transverse plane: (x0,y0)

and (Px0,Py0) Slope of arclength vs z: (z0) and Pz0.

Runge-Kutta Fit with real B field map.

TPC Analyzer

Input file: MC ntuples or real data. Output ntuples: hits information and

track parameters. Test with MC ntuples. Test with real data.

Conclusion

TPC has started operation in this Feb. We are taking data now with triggers from

both tracks in TPC and spectrometer. Struggling with large data size and slow

DAQ speed. Need to improve it significantly.

Need to demonstrate the ability of track-finding and PID.

We need helps from other LEPS members for data-taking and offline analysis.