Physics with low energy recoil detector and options for instrumentation for the CLAS12

Physics with low energy recoil detector and options for instrumentation for the CLAS12

S. Stepanyan (JLAB)

CLAS12 European Workshop

February 25-28, 2009, Genova, Italy

CLAS12 European Workshop February 25-28, 2009, Genova, Italy

2

Few physics topics with low energy recoil ( ) detector

• neutron structure

• nuclear structure (see also K. Joo’s talk)

• meson spectroscopy

Options for a recoil detector

• RTPC

• LPMWPC&SSD

4A


3

Neutron target and accessible physics

PDF at large x d/u at large x quark-hadron duality on neutron neutron elastic scattering neutron DVCS

S. Bueltman et al., E12-06-113

Free neutrons decay in 15 min Can we explore the structure of the neutron if all we have are

neutrons bound in nuclei? – nuclear model uncertainties

Low energy spectator tagging can be a solution for a neutron target:

nnBeBe

ndH

npH

s

s

89

3

2


4

d/u ratio at x 1

F2n

F2p

14d /u

4 d /u

d

u

4 F2n F2p 1

4 F2n F2p

F2n/F2p = F2d/F2p -1

???


5

Modifications to Simple Spectator Picture

Final State Interactions

“BoNuS”

Binding Effects


6

Spectator Tagging with BoNuS RTPC

2/

ˆ;,

D

SSSSSS M

qpEpEp

pn MD ES ,p S ;

n 2 S

W 2 M 2 2M Q2

22

222

)2(2*

)(2*

QMM

QqpEMppqpW

S

nsDnnn

x Q 2

2 pnq

Q 2

2M (2 S )

*

E = 4.223 GeV

e

p

n

<Q2> = 1.19 (GeV/c)2


7

Coherent DVCS Nuclear GPDs - partonic structure of nuclei, momentum and spatial distribution of quarks in nuclei,

generalized EMC effect

Incoherent DVCS bound nucleon GPDs – nuclear medium effects,

modification with respect to free nucleon ones

DVCS on nuclei

Coherent DVCS Incoherent DVCS

Both will require low energy recoil detector


8

Coherent and incoherent were not cleanly separated.

Nuclear DVCS


9

For nucleon DVCS:

CLAS experiment E08-024 (K. Hafidi et al.)

m{H 4 He}

e{H 4 He}

ALU () 0()

1()2() 3()(2 2 )

4He nucleusFC I H


10

Meson spectroscopy

(1232)N(1520)

N(1680)

Strong kinematical cuts and a complex PWA are required

Production on hydrogen - physics background from associated baryon resonance production

, N*

CLAS/g6: p’n++-

a2(1320)


11

Spectroscopy in coherent production on nuclei

Method to eliminate the baryon background

044

33

33

MHeHe

MHHe

MHeH

All three charged modes can be studied using gas targets 3H, 3He, and 4He


12

Example: coherent production on 4He

eHHe 404*

eHHe 404 '*

);(' 0

0 andwith

Scattering off a spin and isospin zero target works as a spin and parity filter

JLAB experiment E07-009, Stepanyan et al.


13

Coherent production of 0 and 0’ off 4He

Only C=-1 -exchanges is allowed, Natural Parity Exchange (NPE)

22

0

AAAd

d

C

),(Im212 0

2/1max

0 1

LL

L

L

DLLA

;0;00 AA

),(Im212 101

2/1max

1

LL

L

DLLA

22

2

2111 sinsin)1cos5(

2

7

2

1cos53

FDPd

d

C

The helicity of the produced state will be that of the incoming photon, =, production of 0 (0’) in S-wave is forbidden

Test for above assumptions


14

CLAS12 central detector

Silicon Vertex Tracker

Scintillator Counters, t=50ps

5T SC Solenoid Magnet

Low (200 MeV/c) energy protons in CLAS12 CD (M. Ungaro, GEMC)


15

CLAS12 Central detector

Protons Deuterons

Specialized detector is needed for a broad physics program requiring low energy recoil detection


16

BoNuS* RTPC**

*BoNuS = Barely off-shell Nucleon Scattering**RTPC = Radial Time Projection Chamber

BoNuS

Region

VIPs

0.07 0.2 GeV/c

D (r p )

2

Gas Electron Multiplier

Drift Region

Helium/DME at 80/20 ratio

Readout pads and electronics

7 atm D2 gas


17

Performance and limitations of BoNuS RTPC

dE/dx from charge along the tracke- reconstructed in CLAS & RTPC

z

=8mm

=4º=1.4ºReasonable 3-vector reconstruction

Reasonable PID for a proton

Low rate of DAQ - ~500Hz

Poor PID for high mass fragments – gain uniformity of GEM pads


18

BoNuS-II (for EG6 run in October)

Lightweight (carbon-foam composite structure) rungs for stress-free, self support of GEMs – to avoid “wrinkles”

Target region - new cell – ID 4mm, 30m thick wall

Ground and cathode foils, each 6m thick

Open, 2 geometry – only 80% is accessible due to the GEM and readout pad sizes


19

Expected performance of BoNuS-II

Expected PID with fully calibrated RTPCBetter gain uniformity – better PID: new GEM foils stress free support calibration system (-source and

elastic scattering)

Lower momentum threshold (250 MeV for ’s)

thinner target walls

Increased DAQ rate - 0.5 kHz to 5 kHz new RCUs, crate, backplane … work

is done at INFN Genova (R. De Vita, M. Battaglieri, S. Minutoli)


20

DAQ with new Readout Control Unit board

Lo

cal M

onito

ra

nd

Co

ntr

ol BOARD

Controller

RCU

DCS ( 1 MB/s )

DDL ( 200 MB/s )

Front-end bus( 200 MB / s )

Control Network(I2C-serial link)

Bu

s c

on

tro

ller

( c

on

f. &

R/O

)

FEC128 ch

1

1

2

2

13

13

DCS int.(Ethernet)

DAQ int.(DDL-SIU)

Trigger int.(TTC-RX)

FEC128 ch

FEC128 ch

FEC128 ch

FEC128 ch

FEC128 ch

Rx - PASA - ALTRO

DE

TE

CT

OR

TTC optical Link

(Clock, L1 and L2 )

Data Proc.and MemoryTx

Triggerand Timing

circuit

Max event rate 7 kHz


21

LPAC&SSD* (NIKHEF NIM A409, 1998)

* Low-pressure avalanche chamber and silicon strip detectors

MeV

H 3.2

2H 4.2

3H 4.9

3He 11

4He 13

H 2H 3H 3He 4He

8.8 12 14 31 35 MeVIsobutane@ 7 mbar

SiX E or E, x

SiY E or E, y

Sci E

AC E, t(t=100ps), y

Entrance foil – 1m


22

LPMWPC (JLAB FF detector NIM A426, 1999)

Two windowless gas proportional counters with three electrodes, operating as a parallel plate (wire planes) avalanche counter

Silicon strip detectors to measure full energy

Options for running the chamber with helium, helium/heptane (99%/1%), or helium/hydrogen (86%/15%) are under studies (YerPhI/Idaho)

Detector was developed by YerPhI group for detection of fission fragments for studies of the absolute photofission cross sections at MAX-lab (Lund, Sweden) and for hypernuclear experiments in Hall C at JLAB


23

Test of LPMWPC in Hall B Two symmetric arms placed on top and bottom of the beam centerline

The inner chambers active area - 10.5 x 21cm2

Distance of the anode plane from the beam line - 3 cm.

The outer chambers - 21 x 21 cm2

Target - 209Bi with a thickness of 2 mg/cm2.


24

RTPC and LPMWPCBoNuS RTPC LPMWPC&SSD

Rate High High

Background Insensitive to MIP Insensitive to MIP

Momentum resolution Dp/p~20%, full trajectory fitting

Two point position recopnstruction

Minimum energy ~6 MeV for Defined by target, can be ~1 MeV for

Efficiency ~100% ~100%

Time resolution None ~200ps

Use in the trigger No Yes

Solid targets No, high accidental rates, long drift time

Yes, good for heavier fragments


25

Summary

Broad physics program, ranging from nucleon and nuclear structure to meson spectroscopy, can be accessed with CLAS12 and a low energy recoil detector

Exploration of some of these physics topics is started with CLAS and BoNuS RTPC

2nd generation RTPC will have much improved characteristics for PID and data rate (3rd generation detector for CLAS12 can have ~2 azimuthal coverage)

Option with LPMWPC must be carefully studied, specially for the detection of -s and the heavier fragments from solid targets


26

Backup slides


2727

CLAS12

cGeVPth /9.4

cGeVPth /7.2

Low Threshold Cherenkov Counters

High Threshold Cherenkov Counter (HTCC)

Pre-shower calorimeters

Electromagnetic calorimeters

CLAS12 Torus

Drift Chambers

TOF Counters

Central Detector

CLAS12 Solenoid


28

S. Liuti & S. K. Taneja PRC72, 2005

Gomez et al., PRD49, 1994

Medium Modification

4He/D

• The deviations from unity is mostly due to convolutions with k.

• The asymmetry ratio for DVCS enhances the EMC effect.

EMC effect


29

Electroproduction at “0” degrees [photoproduction]

Reaction ep’pX at 5.76 GeV

(e1-6 and e1-DVCS experiments)Missing transverse momentum distribution for |MX|2<0.1 GeV

Invariant mass of 2 photon pairs in the reaction ep’p(e’)1.0

22

X

yX

X

xX

P

P

P

P

Data were taken with loosely defined electron trigger


30

Reaction ep’p(e’) andep’p(e’)

CLAS e1-6 CLAS DVCS

Note:- data were taken with unfavorable trigger conditions- transferred momentum squared, |t|>0.2 (GeV/c)2 (proton momentum >0.4 GeV/c) - spectra contain the baryon background


31

Event display of RTPC: BoNuS data on D2 and 4He

Deuterium Target Helium Target

2xQD < QHe

Physics with low energy recoil detector and options for instrumentation for the CLAS12

Documents

coherent production

production of p0h p0h

low energy recoil detection

neutron target

nucleon dvcs

recoil detectorrtpclpmwpcssd

nuclear dvcs

physics topics