CLAS RTPC for 4 He Experiment & Light Nuclei Tagging S. Stepanyan (JLAB) For CLAS/eg6 group...

CLAS RTPC for 4He Experiment & Light Nuclei Tagging

S. Stepanyan (JLAB)

For CLAS/eg6 group

Exploring Hadron Structure with Tagged Structure Functions, Jefferson Lab, January 16-18, 2014

2

Outline

Experiments in CLAS/EG6 run – DVCS and meson spectroscopy in coherent scattering

Second generation RTPC RTPC calibrations with elastic scattering off 4He Preliminary results on coherent DVCS off 4He New Low-Energy Recoil Detector for CLAS12

S. Stepanyan, Exploring Hadron Structure with Tagged Structure Functions, Jefferson Lab, January 16-18, 2014

3


CLAS/Eg6 Run Meson Spectroscopy and DVCS (coherent and incoherent) on 4He Both experiments are making use of zero spin and isospin of the target Coherent DVCS on 4He will allow to extract real and imaginary parts of

Compton amplitude in model independent way from BSA measurment

Production of 0 and 0’ off 4He limits quantum numbers of exchange state and simplifies PWA analysis

Both experiments required detection and identification of recoil -particles 2nd Generation Radial Time Projection Chamber with 20 cm long, 6 atm, 4He

gaseous target located inside of the Hall-B superconducting solenoid (used for RTPC momentum analysis and Møller reduction)

Production data with 6.6 GeV polarized electrons, 1 GeV run for RTPC calibration

4

Target & RTPC assembly for eg6

New target cell, 6 mm ID & with 27 m wall thickness, target gas He @ 6 atm. (Bonus run with 50 m thick target cell)

He @ 1 atm

Working gas, NeDME @ 1 atm

Open geometry (has not been utilized effectively)

Improved backend readout and increase the trigger rate to 2.5 kHz

Total material thickness on the way of particles at 90o is ~39 m

2 aluminized mylar foils, 2 and 6 m thick


5

, N*

Elastic scattering on 4He at 1.2 GeV

RTPC calibration


6

Selection of elastic events


Inclusive electron W-distribution of all events

- vs. Z-RTPC distribution of elastic electron in CLAS and a track in RTPC

Difference between measured and calculated from elastic kinematics polar angle of recoil 4He

Difference between measured and calculated from elastic kinematics polar angle of recoil 4He

7

Δϕ CLAS-RTPC (°)

RTPC Efficiency: Detect Elastic 4He With electron is selected, look for RTPC track

with matching vertex and scattering angles Each Δ-quantity below has a cut on the others’

peaks Resolutions are roughly 8mm, 2°,3° on z,φ,θ

Test cut sensitivity, particularly Δθ Result: ~400K Exclusive Elastic Events


ΔZ CLAS-RTPC (cm) Δθ CLAS-RTPC (°)

W (GeV)

Pass

Fail Elastic Cuts

Inclusive

8

RTPC Efficiency: Measure Yields

The ration of the number of Exclusive and Inclusive Elastic events ( i.e. with and without 4He detection) will be the RTPC efficiency

Shown here is Gaussian signal and backgrounds Physical models of background (quasi-

elastic) and signal (radiated elastic peak) were also tried

Efficiency is not highly sensitive to yield extraction method so long as it is consistent for exclusive and inclusive final states


W (GeV)

Inclusive

Exclusive

Example Fits

9

RTPC Efficiency: Result

What is the best variable(s)? Ideally p,θ,ϕ,z simultaneously Very limited p/θ range for elastics (50

MeV/c, 5°) ϕ is tricky due to CLAS+RTPC

acceptance Z-vertex is also important

Calibration is more difficult at ends of the detector

Sensitive to field effects We find similar tracking efficiencies

for LEFT/RIGHT, although we know noise and # dead channels is different


Z-Vertex (cm)

RTP

C E

ffici

ency

Q2 (GeV2)

Yiel

d

LEFT

RIGHT

10

RTPC gain calibration with elastic events


PID in RTPC is based on a track energy loss in the drift volume of the detector – calibration of gains of individual pads are very important Large gain variation from pad-to-pad is due to non-uniformity of space between GEM plains

11

DVCS Exclusivity Variables: Simulation vs. Data


θX (°)

Missing PT (GeV) Coplanarity θ*He (°)

M2X (e4He) (GeV2)

EX (e4He) (GeV)

e4He e4He Full Exclusivity

Cuts|θcop| < 2°|θX| < 2°

PtX < 0.2 GeV|M2

X| < 0.02 GeV2

12

BSA in coherent DVCS -


0

1-d t-bins 83.7% beam polarization

is taken into account 1-σ MINOS uncertainties

13

– Significant trends in t and xB, similar to Guzey’s calculation• Model from EG6 proposal• Kinematics are close but not matched to data

Compton Form Factor HHe, Re and Im parts


EG6 Range1 < Q2 < 2.3 GeV2

0.05 < -t < 0.2 GeV2

0.1 < xB < 0.25

GS: Guzey & Strikman, Phys. Rev. C 68 (2003) 015204

14

Results: BSA and Generalized EMC RatioBeam Spin Asymmetry @ 90

Significantly non-zero and relatively flat ~25%

Consistent with HERMES ((eX, no 4He detection)

A. Airapetian et al, Phys. Rev. C 81 (2010) 035202


GS: Guzey & Strikman, Phys. Rev. C 68 (2003) 015204LT: Liuti & Taneja, Phys. Rev. C 72 (2005) 032201

Generalized EMC Ratio– Binning chosen to match published

e1dvcs kinematics for the denominator– We only cover eg1dvcs’s lowest t-bin– A hint of the predicted behavior

15

New LERD for CLAS12


N. Baltzel (ANL)

• Low-pressure wire chamber (LPWC), surrounded Si-strip layers, and scintillator fibers

• Insensitive to MIP, LPWC provides fast signal for triggering and PID

• All inside low-pressure vessel, vessel inside the solenoid (for simulation CLAS12 solenoid at 60% field has been used

• Momentum from tracking, PID from energy loss and time information

Lessons learned from GEM RTPCs:o big gain variations from pad-to-pad (two mechanically different

detector designs, in both the main problem is uniformity of diisdance between GEM planes) - limits PID based on dE/dX

o no triggering capability, limits trigger rates, target windows have big effect in the trigger

16

Low energy recoil detector and CLAS12 CD

Silicon TrackerScintillator Counters, t=60ps

5T SC Solenoid Magnet

Replace CLAS12 barrel tracker with LERD

Use CTOF to extend momentum range of LERD


17

Particle ID


18


Summary CLAS experiment for coherent photo- and electro-production on a spin and

isospin zero target, 4He, run in 2009 (with shorter than PAC approve beam time) Second generation RTPC à la Bonus detector has been deployed for detection

and identification of low energy recoil particles The new RTPC had few improvements – open geometry for a drift volume, lower material budget on a way particles, a much faster trigger rate …

Although Bonus and eg6 RTPCs have very different mechanical design, the non-uniformity of distances between GEM planes remind a main issue for pad gain uniformity and hence was the limiting factor in PID reach

For reliable detection and identification of wide verity of low energy particles - p, d, 3H, 3He, and 4He, a fast timing information from the detector is desirable

Fast timing information can be used in the trigger as well – trigger rate was a limiting factor for high luminosity running in eg6, since with only CLAS trigger the 60% of events did not have RTPC track, and 40% come from target windows

A new detector concept has been developed for CLAS12 based on LPMWC, Si-strips and scintillator fibers, simulations and conceptual design is in progress

19


Backup slides

20

Forward Central Detector Detector

Angular rangeTracks 50 – 400 350 – 1250

Photons 20 – 400 ---Resolutionp/p (%) < 1 @ 5 GeV/c < 5 @ 1.5 GeV/c(mr) < 1 < 10 - 20(mr) < 3 < 5 Photon detectionEnergy (MeV) >150 --- (mr) 4 @ 1 GeV ---Neutron detection

Neff < 0.7 (EC+PCAL) n.a.Particle ID

e/Full range ---p< 5 GeV/c < 1.25 GeV/c/K < 2.6 GeV/c < 0.65 GeV/c

K/pGeV/c < 1.0 GeV/cFull range ---

CLAS12 – Design ParametersForward Detector

Central Detector


21

Helium bag downstream window (15 m Al)

Target downstream window (15 m Al)

Target upstream window (4mm, 15 m thick Al)

4He at 1 atmTarget

gas

Passage of 100 nA 6 GeV through 30 cm long “straw” target

RTPC and high pressure helium target


CLAS RTPC for 4 He Experiment & Light Nuclei Tagging S. Stepanyan (JLAB) For CLAS/eg6 group...

Documents

Transcript of CLAS RTPC for 4 He Experiment & Light Nuclei Tagging S. Stepanyan (JLAB) For CLAS/eg6 group...