CLAS12 European Workshop

 

February 25-28, 2009- Genova, Italy

Analyzing CLAS / Hall B Data to Extract New Results on QCD Nuclear Physics

An Initiative to Maximize the Return on Already Collected Data

M. Strikman, L. Weinstein, S. Kuhn, S. Stepanyan,E. Piasetzky, K. Griffioen, M. Sargsian

Eli Piasetzky

Tel Aviv University, ISRAEL

MEGIDDO: THE FLAGSHIP OF TEL AVIV UNIVERSITY DIGS

A mound with 32 cities one on top of the other

1903-1905 Schumacher

1920-1939 University of Chicago

1960s,1970s The Hebrew University

1994 - Tel Aviv University

1903-1905 Schumacher

1920-1939 University of Chicago

1960s,1970s The Hebrew University

1994 - Tel Aviv University

The physics driving the proposed analysis

Short Range Correlations (SRC)

Hadronization

Nuclear Matter in non - equilibrium condition

Nuclear transparency

Detailed study on few body systems (Deuteron, 3He)

Nucleon Short Range Correlations (SRC)

1.f

Nucleons

2N-SRC

1.7f

o = 0.16 GeV/fm3

5o

~1 fm

1.7 fm

What SRC in nuclei can tell us about:

High – Momentum Component of the Nuclear Wave Function.

The Strong Short-Range Force Between Nucleons.

Cold-Dense Nuclear Matter (from deuteron to neutron-stars).

A~1057

tensor force, repulsive core, 3N forces

What did we learn recently about SRC ?

The probability for a nucleon to have momentum ≥ 300 MeV / c in medium nuclei is ~25%

More than ~90% of all nucleons with momentum ≥ 300 MeV / c belong to 2N-SRC.

The probability for a nucleon with momentum 300-600 MeV / c to belong to np-SRC is ~18 times larger than to belong to pp-SRC.

2N-SRC mostly built of 2N not 6 quarks or NΔ ΔΔ.All the non-nucleonic components can not exceed 20% of the 2N-SRC.

Three nucleon SRC are present in nuclei.

. PRL. 96, 082501 (2006)

PRL 162504(2006); Science 320, 1476 (2008).

CLA

S /

HA

LL B

EV

A /

BN

L an

d Jl

ab /

HA

LL A

The dominant NN force in the 2N-SRC is the tensor force.

1

2

4

3

1

6

5 2

3

6

5

4

PRL 98,132501 (2007).

np-SRC dominance ~18 %

12C

2N-SRC Results (summary)

The uncertainties allow a few percent of:

more than 2N correlations

Non - nucleonic degrees of freedom

2N –SRC dominance

18±5%

1±0.3%

12C

Sensitivity required: 1% of (e,e’p) 5% of (e, e’ p) with Pmiss>300 MeV/c

Looking for non-nucleonic degrees of freedom

The signature of a non-nucleonic SRC intermediate state is a large branching ratio to a non-nucleonic final state.

... cba NNNSRC

c,...b, ,a

Breaking the pair will yield more backward Δ, π , k

1.f

Nucleons

2N-SRC 5o

~1 fm

For the non –nucleonic component:

Search for cumulative Delta 0(1232) and Delta + + (1232)

isobars in neutrino interactions with neon nuclei

Ammosov, et al.

Journal of Experimental and Theoretical Physics Letters, Vol. 40, p.1041 (1984).

Δ’s rates 5-10% of recoil N rates

Nucl-th 0901.2340

a measurement of (e,e’ pback) by the Yerevan group

src

How to search for pre-existing Δs in CLAS data?

(e, e’ Δback) and (e, e’ N Δback) Search for backward emitted Δ, both

to separate initial state from background multistep processes

a) Look at x<1 and x>1b) Vary Q2 and ω

Search for forward emitted Δ++ at x>1

By studying the dependence on x and A we can separate the charge exchange Δ++ production (main effect for α =1 increasing with A ) and scattering off primordial Δ++ ( larger x).

Look for Δ++ at large x, corresponding to the larger expected Δ - momentum in the nucleus.

~800 MeV/c~800 MeV/c

~800 MeV/c~400 MeV/c

Colinear geometry :

3N-SRC

Needs to detect two recoil nucleons

0.3-1 GeV/c p and n

3N –SRC arise from two mechanisms:

pair interactions

3N force 0

,

321

3,21

ppp

pppp F

Isospin ratios and selected kinematics may allow to separate them

19±4%

0.6±0.2%2N

3N

1N >> 2N - SRC >> 3N – SRC.

0.6 / 19 ~ 3%

(large uncertainty on this ratio)

How to search for these in the CLAS data?

Inclusive measurement of two backward recoil nucleons

(e, 2Nback)

In coincidence with the scattered electron

(e, e’ 2Nback)

208Pb(e,e’) / 3He(e,e’) Is there a reduction of the a2 for neutron rich nuclei ? a step toward neutron stars

System A Z N

3He 3 2 1 1.33

4He,12C,40Ca 1

56Fe 56 26 30 0.93

48Ca 48 28 20 0.83

197Au 197 79 118 0.8

208Pb 208 82 126 0.79

n-star 0.05 0.95 0.1

0.1 0.9 0.2

A

nn pn 1

A2(A / d)

Available data:

1.7

3.33 (±2%)

4.27 (±6%)

5.10 (±6%)

a2(A/d)

Extrapolation factor ~10

)',()/',( 1212 peeCppeeC

Measured ratio

Extrapolated ratio

The limited acceptance allows determination of only two components of the pair c.m. momentum with very limited acceptance.

Even the triple coincidence SRC experiment could be done better with a larger acceptance detector.

R.B. Wiringa, R. Schiavilla, Steven C. Pieper, J. Carlson . Jun 2008. arXiv:0806.1718 [nucl-th]

Can we look for a signature of the l=2 pair in the relative angular distribution of the pair ? Can we learn more on the CM motion of the pair ?

Detailed study of the Fermi sea level ( the SRC onset).

The transition from single particle to SRC phases

Available now: 12C only

Available now : Q2=2 only

very limited CM momentum range (in 2 direction) onlyAvailable now: 12C only

Detailed study on few body systems (Deuteron, 3He)

These are interesting by themselves but also are important doorwayto study complex nuclei. The clearly determined kinematics offered by these systems can be useful.

2N-SRC are dominant with T=0 np pairs. Fingerprints of the deuteron can be used to study 2N-SRC in nuclei.

Effects related to EMC and CT can be tested on few body systems

Search for ΔΔ admixtures in the deutron

Important also for the study of non-nucleonic componnetsof SRC in nuclei.

Measurements of tagged structure functions (electron scattering in coincidence with a fast backward proton or neutron)

Important also for the study of EMC with the 12 GeV upgrade

Measurements of the spin structure of SRC in the deuteron using polarized electron scattering off polarized or unpolarized deuteron

Important also for the study of SRC in nuclei

Some examples:

Detailed study of FSI as a function of the final state particles, momenta, and Q2

Important also for the study of CT, hadronization and medium modification to the nucleon form factors.

Q1: Is the strong interaction of small neutral (colorless) objects suppressed ?

Q2: Can we produce small hadrons (PLC) ?

Q3: Can we freeze the PLC long enough to observe the suppression of its interaction ?

If the answers to all the questions above is positive we can expect a phenomenon known as Color Transparency.

Q4: Where is the onset of CT ? (CT is a necessary condition for factorization of exclusive hard processes)

Q5: What is the time / space structure of the transition from the PLC to a ‘normal’ hadron ?

Color Transparency

PLC

(e, e’ π)DATA: Jlab / Hall C B. Clasie et al. PRL 242502 (2007).

solid : Glauber (semi-classical)dashed : Glauber +CT (quantum diff.) Larson et al , PRC 74, 018201 (2006)

dot-dash : Glauber (Relativistic)dotted : Glauber +CT (quantum diff.) +SRC Cosyn et al. PRC 74, 062201R (2006)Also: PRC 77, 034602 (2008)

no CT

no CT

with CT

With CT

with CT

no CTno CT

no CT

with CT

with CT

Dashed area: from Pion nucleus scatteringCarroll et al., PLB 80, 319 (’79)

Coherence length: 0.2-0.5 fm

22 GeV 7.0M ,/1 cfm

Data from Hall C indicate that maybe the onset of CT is low enough to look for CT effects at the current JLab energy range

If CT is relevant at JLab energies one can look for suppression of the pion cloud and its interaction with the nuclear medium close to the point where a hadron is being produced in a hard process.

e e’

dStudy A(e, e’ Δ0) as a function of Q2 and A

A

ee’

s11

Hadronization

Measure the multiplicity and the type of emitted particles in a large acceptance “backward direction ” in coincidence with the forward (large z) leading π +, π -, k +, k - particle.

Difference in hadronization of different quarks

Difference between hardonization in a free space and nuclear medium

Nuclear Matter in non - equilibrium condition

Using hard processes to remove a single or a few nucleons from the nucleus creates a non-stable state.

How does such a non-stable state decay to a stable system?

Data sets: E > 1 GeV, A>1, electron or photon beams

Plan of action

White paper, seek for funding - Jan 2009

Exploration: 2009

Narrow down the effort to the most promising analysis projects

1full time experience postdoc at JLab.

Use existing data summary files

1st stage analysis: developing analysis tools, Re-cooking

3full time experienced researchers at JLab. and up to 6 students

Create new data summary files

2010-2011

Full analysis effort at Jlab. and home institutes

Use the new data summary files

2011-2015

3full time experimental and 1 theoretical researcher at JLab. and up to 6+1 students

Organization

“steering committee”

Core of postdocs and students at Jlab

Groups of Postocs and students at the universities

Weekly conferences calls

Two annual meetings

Open for everyone interested , Please join the initiative

How to search for these in the CLAS data?

Inclusive measurement of two backward recoil nucleons

(e, 2Nback)

In coincidence with the scattered electron

(e, e’ N) x>2

(e, e’ 2Nback)

qEN MAX (A-1 recoil)

Notice that FSI will not fill the gap

208Pb ? Is there a reduction of the a2 for neutron reach nuclei ? a step toward neutron stars

A large acceptance detector allows tagging of the DIS event

EMC

High nuclear density tagging :

A recoil high momentum nucleon to the backward hemisphere is a signature of 2N-SRC i.e large local nuclear density.

Due to the dominance of np-SRC pairs: a recoil neutron tags the proton structure function a recoil proton tags the neutron structure function

Flavor tagging :

Identifying a π + or π - with a large z can point to the flavor of the struck quark ( u or d).

Recoil and forward tagging allows the study of u, d in p, n

How to search for these in the CLAS data?

(e, e’ Δback)

or even

(e, e’ p Δback) (e, e’ n Δback)

XB>1 and XB<1

How to search for these in the CLAS data?

By studying the dependence on x and A we can separate the charge exchange Δ++ production (main effect for α =1 increasing with A ) and scattering off primordial Δ++ ( larger x).