# Presentation: 675322

## Hadrons in the Nuclear MediumRolf EntJefferson Lab

**Hadrons in the Nuclear Medium**Rolf EntJefferson Lab

**Science & Technology Review**
**June 2004**

- The Baryon-Meson versus Quark-Gluon Description
- Nuclear Effects in Structure Functions
- Tagged Structure Functions
- Using the Nucleus as a Laboratory
- Summary

## Campaigns and Performance Measures

**The Structure of the Nuclear Building Blocks**** **
- How does the NN Force arise from the underlying quark and gluon structure of hadronic matter?
**The Structure of Nuclei**
- What is the structure of nuclear matter?
- At what distance and energy scale does the underlying quark and gluon structure of nuclear matter become evident?
- DOE Performance Measure:
- ... and compare free proton and bound proton properties via measurement of polarization transfer in the 4He(e,e’p)3H reaction.

- _QCD Lagrangian: quarks and gluons_
- 	Nuclear Physics Model is an effective (but highly successful!)
- 	model using free nucleons and mesons as degrees of freedom.

- Are these, under every circumstance, the best effective degrees of freedom to chose?

## JLab Data Reveal Deuteron’s Size and Shape

- The nucleon-based description works down to < 0.5 fm

- Combined Data ->
- Deuteron’s Intrinsic Shape

## Is there a Limit for Meson-Baryon Models?

- Not really but ...

- ... there might be a more economical QCD description.

## Transition to the Quark-Gluon Description

- d/dt  f(cm)/sn-2
-   where   n = nA + nB + nC + nD
- 	s = (pA+pB)2, t=(pA-pC)2
- d  pn  n=13  d/dt  s-11

**Conventional**
**Nuclear Theory**

**p****A**

**p****B**

**p****C**

**p****D**

-  Scaling behavior (d/dt  s-11)  for PT > 1.2 GeV/c  (see  )
-  quark-gluon  description sets in at scales below ~0.1 fm

## Exploring the Transition Region

- Now nearly complete angular distributions of D(,p)n up to E = 3 GeV with CLAS
- Excellent fit of data with d/dt  s-11 if starting fit at pT ~ 1.0-1.3 GeV/c.

## 	Hadrons in the Nuclear Medium 

-  Nucleons and Mesons are not the fundamental entities
-   of the underlying theory.
-  At high densities a phase transition must occur to  a
-   quark-gluon plasma.
-  At nuclear matter densities of 0.17 nucleons/fm3,
-   nucleon wave functions overlap considerably.
-  EMC effect: Change in the inclusive deep-inelastic
-   structure function of a nucleus relative to that of
-   a free nucleon.

## Quarks in Nuclear Physics

**Quarks in Nuclear Physics**

- Quark-Meson Coupling (QMC) Model (Thomas et al.): quark’s response to mean scalar and vector field (similar to quantum hadrodynamics for nucleon’s response)  quark substructure of nucleon irrelevant for bulk properties of nucleus, but is relevant for form factor 	and 		structure functions

- F2A/F2D

- (GE/GM)QMC/(GE/GM)free

- Q2 (GeV/c)2

- x

- Effects are Precursor of Quark Gluon Plasma

-  0

## ?

- European Muon Collaboration: muon scattering to measure nuclear structure functions (1982)

- 2F2A/F2D

-  Depletion of the nuclear structure function F2A(x) in the valence-quark regime
-                                                                                              0.3 < x < 0.8
-  Specific cause for depletion remains unclear: conventional nuclear effects or
-                                                                           nucleon swelling?
-  J. Smith & G.A. Miller (2003): chiral quark soliton model of the nucleon
-                   *claim:* Conventional nuclear physics does not explain full EMC effect

## EMC Effect in 3He and 4He

**EMC Effect in ****3****He and ****4****He**

- The Nuclear EMC effect shows that quarks behave differently in nuclear systems.
- It has been extensively measured in A>8 nuclei.

## EMC Effect in 3He and 4He

- The Nuclear EMC effect shows that quarks behave differently in nuclear systems.
- It has been extensively measured in A>8 nuclei, but current data do not differentiate
- between models with either an A-dependence or a -dependence.
- 		 Measure the shape in very light nuclei to distinguish
- 		 Test models of the EMC effect in exact few-body calculations

- SLAC fit to heavy nuclei
- (scaled to 3He)

- Calculations by Pandharipande and Benhar for 3He and 4He

## EMC Effect in 3He and 4He

- The Nuclear EMC effect shows that quarks behave differently in nuclear systems.
- It has been extensively measured in A>8 nuclei, but current data do not differentiate
- between models with either an A-dependence or a -dependence.
- 		 Measure the shape in very light nuclei to distinguish
- 		 Test models of the EMC effect in exact few-body calculations

- SLAC fit to heavy nuclei
- (scaled to 3He)

- Calculations by Pandharipande and Benhar for 3He and 4He

- Projected uncertainties for an experiment to run this year (November)

## EMC Effect in R = L/T

**EMC Effect in R = ********L****/********T**

- EMC Effect is measured as ratio of F2A/F2D
- In Bjorken Limit: F2 = 2xF1 (transverse only)
- There should be medium effects also in FL, or in R = L/T !

*E. Garutti, Ph.D UvA 2003, *

- HERMES: RA = RD within 25%

- JLab: Rp @ low Q2, RD + RA soon

-  Should be able to see effects, if any.

## R in Nuclei – Link with Neutrino Community

- Mass difference between neutrino flavors: M2 ~ E/L, with E the  energy and L the distance source-detector

- L was fixed when M2 was thought to be larger 
-  energy of interest ~ few GeV ~ JLab energy!

-  physics derived from Monte Carlo models folding poorly known beam properties with the best known response of a detector to the creation of various particles in  interactions 
- All conventional Nuclear Physics needs to be known for few-GeV probes and included, both for the axial and vector couplings

- Approach I    : High Luminosity few-GeV  Experiments
- Approach II  : Electron scattering experiments to constrain Monte Carlo
- Approach III: Do both to extract axial information from difference

- Neutrino community (Bodek et al.) involved in:
- 	I)   Approved experiment to measure R = L/T in Nuclei
- 	      in Hall C
- 	II) Analysis of existing data on low-energy transparencies
- 	      and multi-pion production in Hall B

## A nuclear medium has an average density, ρo, of 0.17 GeV/fm3. 
A typical distance for 2 nucleons participating in a short-range correlation (SRC) is  ~1.0 fm  the local density can increase by a factor of ~4: this is comparable to the density of neutron stars.
Nucleons participating in a SRC are deeply bound, i.e. their structure should be modified, like their shape or quark distributions. 
x = Q2/2M > 1  can be used to select quarks inside nucleon participating in a SRC  superfast quarks!

**A typical distance for 2 nucleons participating in a short-range correlation (SRC) is  ~1.0 fm**** ******** ****the local density can increase by a factor of ~4: this is comparable to the density of ****neutron stars****.**
**Nucleons**** ****participating in a SRC are deeply bound, i.e. their structure ****should be modified****, like their shape or quark distributions.**** **
**x = Q****2****/2M******** > 1 ******** can be used to select quarks inside nucleon participating in a SRC**** ******** superfast quarks!**

**Nucleus**

**Neutron**

**Proton**

******o ****= 0.17 GeV/fermi****3**

****** ******** ****4********o**

**EMC Effect at large x (> 1)**

## EMC Effect at large x (> 1)

- E89-008 @ 4 GeV:
- Iron cross sections vs (,Q2)
- Structure Functions vs 

**x (as Q****2**** ********    ) **

- 

- “scaling” regime sets in at Q2 > 3

- X   = 1
- Q2 = 3

- }

-  = 0.80

- F2Fe/A

- F2Fe/A

## EMC Effect at large x (> 1) – cont.

**EMC Effect at large x (> 1) – cont.**

- SLAC NE3

- E89-008
-      (1996)

- E02-019
- (experiment to start data taking June 26th)

- Q2 > 3!

- Note: x = 3,   Q2 =  5  nucleon with 1.78+ GeV/c!
- 	*(similar for x = 1.5, Q**2** = 10)*

- Acceptance plot of (x,Q2) of SLAC and JLab experiments

- x

## Tagged Structure Functions

**Modification of the off-shell scattering amplitude (Thomas, Melnitchouk)**

**Suppression of “point-like configurations”**

**Color delocalization**

- P = 320 MeV/c
- M* ~ 823 MeV

**Tagged Structure Functions**

- Goal: Tag nucleon (here, neutron) participating in SRC directly

- D(e,e’ps)n

- Already measured in CLAS for 300 < P < 600 MeV/c (proton angles > 107o)

## Preliminary Results: x* (= Q2/2pnq) dependence

- Q2 = 1.8 GeV2
- Proton angles  > 107.5O
- Several different proton momenta
- Vertical axis: structure function F2n(x*,Q2)

- x*

- 300 MeV/c
-         M* = 0.84 GeV

- 340 MeV/c
-       M* = 0.81 GeV

- 390 MeV/c
-       M* = 0.77 GeV

- 460 MeV/c
-            M* = 0.70 GeV

- 560 MeV/c
-        M* = 0.54

- 0.2

- 0.7

- x*

- 0.2

- 0.7

- x*

- 0.2

- 0.7

- F2n(x*,Q2)

## 	Hadrons in the Nuclear Medium 

-  Nucleons and Mesons are not the fundamental entities
-   of the underlying theory.
-  At high densities a phase transition must occur to  a
-   quark-gluon plasma.
-  At nuclear matter densities of 0.17 nucleons/fm3,
-   nucleon wave functions overlap considerably.
-  EMC effect: Change in the inclusive deep-inelastic
-   structure function of a nucleus relative to that of
-   a free nucleon.

## Polarization transfer in 4He(e,e’p)3H

-     *(see also talk by Kees de Jager)*
-  Bound nucleons  evaluation
-                                   within model
-  Reaction mechanism effects
-    minimal for A(e,e’p) about **P****m** = 0
-  Form Factors in the Nucleus

**Polarization transfer in ****4****He(e,e’p)****3****H**

- E93-049 (Hall A): Measured 4He(e,e’p)3H in quasi-elastic kinematics
- 	for Q2 = 0.5, 1.0, 1.6 and 2.6 (GeV/c)2 using Focal Plane Polarimeter
- Extracted “Superratio”: (P’x/P’z) in 4He/(P’x/P’z) in 1H

- RPWIA

- RDWIA

-  GE       P’x (Ei + Ef)        e
-   GM      P’z     2m            2

- __      __  _____        __

- = -                   tan

-  GE       P’x (Ei + Ef)        e
-   GM      P’z     2m            2

- __      __  _____        __

- = -                   tan

- ~

- ~

## Polarization transfer in 4He(e,e’p)3H

- E93-049 (Hall A): Measured 4He(e,e’p)3H in quasi-elastic kinematics
- 	for Q2 = 0.5, 1.0, 1.6 and 2.6 (GeV/c)2 using Focal Plane Polarimeter
- Extracted “Superratio”: (P’x/P’z) in 4He/(P’x/P’z) in 1H

- Compared to calculations by Udias without and with inclusion of medium effects predicted by Thomas *et al*. (Quark Meson Coupling model).

- Medium Modifications of Nucleon Form Factor

- RPWIA

- RDWIA

- +QMC

## Polarization transfer in 4He(e,e’p)3H

- E93-049 (Hall A): Measured 4He(e,e’p)3H in quasi-elastic kinematics
- 	for Q2 = 0.5, 1.0, 1.6 and 2.6 (GeV/c)2 using Focal Plane Polarimeter
- Extracted “Double Superratio”: [(P’x/P’z) in 4He/(P’x/P’z) in 1H]/[PWIA ratio]
- After corrections for FSI effects: deviation from 1 a measure of the medium dependence of GEp/GMp

- Compared to calculations by Udias without and with inclusion of medium effects predicted by Thomas *et al*. (Quark Meson Coupling model).

- Medium Modifications of Nucleon Form Factor

## Polarization transfer in 4He(e,e’p)3H

**Polarization transfer in ****4****He(e,e’p)****3****H**

- E93-049 (Hall A): Measured 4He(e,e’p)3H in quasi-elastic kinematics
- 	for Q2 = 0.5, 1.0, 1.6 and 2.6 (GeV/c)2 using Focal Plane Polarimeter
- Extracted “Double Superratio”: [(P’x/P’z) in 4He/(P’x/P’z) in 1H]/[PWIA ratio]
- After corrections for FSI effects: deviation from 1 a measure of the medium dependence of GEp/GMp

- Compared to calculations by Udias without and with inclusion of medium effects predicted by Thomas *et al*. (Quark Meson Coupling model).
- New proposal approved by PAC24

- Medium Modifications of Nucleon Form Factor

## Hadrons in the Nuclear MediumRolf EntJefferson Lab

**Hadrons in the Nuclear Medium**Rolf EntJefferson Lab

**Science & Technology Review**
**June 2004**

- The Baryon-Meson versus Quark-Gluon Description
- Nuclear Effects in Structure Functions
- Tagged Structure Functions
- Using the Nucleus as a Laboratory
- 	Any signatures for the onset of non-hadronic
- 	degrees of freedom and QCD dynamics?

## Nuclear Transparency

**Nuclear Transparency**

** **

**Ratio of cross-sections for exclusive processes **
**from nuclei to  nucleons is termed as ****Transparency**

**= free (nucleon) cross-section**

**parameterized as = **

**Experimentally   ********  =  0.72 – 0.78, for  ********p******** **** **

**Nucleons**

**Nuclei**

**A + B’ ******** C + D + X**

**A + B ******** C + D **

**N**

**Exclusive Processes**

******(A)**

******o**

**T  =**

******o**

******(A)**

## Total Hadron-Nucleus Cross Sections

**Hadron– Nucleus**
**total cross section**

**Fit to**

****

****

****

**p**

**p**

**_**

**Hadron momentum**
**60, 200, 250 GeV/c**

**  ****< 1  interpreted as due to the strongly interacting nature of the probe **

****

- A. S. Carroll * et al. *Phys. Lett  80B 319 (1979)

** ********  ****=  0.72 – 0.78, for p, ********k**

## Nuclear Transparency

** **

**Traditional nuclear physics calculations (Glauber calculations) predict transparency to be ****nearly**** energy independent .**

**T**

**1.0**

**5.0**

**Energy (GeV)**

_**Ingredients**_

** ******h-N cross-section
-  Glauber multiple
-    scattering approximation
-  Correlations & FSI effects.

- hN

- For light nuclei  very precise calculations of T are possible.

## Search for Color Transparency in Quasi-free A(e,e’p) Scattering

- From fundamental considerations (quantum mechanics, relativity, nature of the strong interaction) it is predicted (Brodsky, Mueller) that fast protons scattered from the nucleus will have decreased final state interactions

- Hall C – E94-139

- Constant value line fits give
- good description 2/df = 1
- Conventional Nuclear Physics  Calculation by Pandharipande *et al.* (dashed) also gives good description
- 	No sign of CT yet

## A(e,e’p) Results  -- A Dependence

**Fit to  ******

****

- o

****** ****= constant = 0.75**

**for  Q  > 2  (GeV/c) **

**2 **

**2 **

****

- Close to proton-nucleus total cross section data!

## qqq vs qq systems

** ****There is no unambiguous, model independent, **
**   ****evidence for ****CT**** in ****qqq**** systems.**
** ****Small size is more probable in ****2**** quark system **
**   ****such as ****pions**** than in protons.**
** ****Onset of ****CT**** expected at lower ****Q****2**** **** in ****qq**** system.**
** ****Formation length **** ****is ****~ 10 fm**** at moderate ****Q****2**** **** in **
**   ****qq**** system (******** larger than nuclear radius)**
** ****Onset of CT related to onset of factorization required**
**   ****for access to GPDs in deep exclusive qq production**

**(B. Blattel et al., PRL 70, 896 (1993)**** **

## A(,dijet) Data from FNAL

**Coherent ******** diffractive dissociation**
**with 500 GeV/c pions on Pt and C.**

**+**

**Fit to ********A**

**0**

****

******> 0.76 from pion-nucleus **
**total cross-section.**

- Aitala *et al., *PRL **86 ** 4773 (2001)

- Claim: Full CT effect observed by Q2 ~ 10 (GeV/c)2
- A(e,e’) and A(e,e’) experiments at JLab pushing Q2 range
- A(,-p) pushing t range

## Results from E94-104 ( n -> - p in 4He)

- Calculations use Glauber theory and correlations from Argonne v14 and Urbana VIII
- CT estimated from quantum diffusion model, normalization can be chosen arbitrarily
- Data show t-dependence seemingly at variance with traditional nuclear physics
- Clear need for extension to higher t-values

## A Pion Transparency Experiment 

**JLab  Experiment  E01-107:  A(e,e’********) on H, D, C, Cu, Au **

- Measurable effect predicted
- for Q2  <  5 (GeV/c)2
- (Miller et al., Ralston et al.)

- Projected uncertainties for experiment to start this July (E = 5.75 GeV)

## CT and Quark Propagation through Nuclei

- Search for Color Transparency
- Measure  absorption vs. Q2 at fixed coherence length lc
- Compare absorption in deuterium, carbon, aluminum, and iron

- Quark Propagation through Nuclei
- Measure attenuation and transverse momentum broadening of hadrons (p, K) in DIS kinematics
- Compare absorption in deuterium, carbon, iron, tin, and lead

- E02-110

- E02-104

- EG2

## CLAS EG2 - Online Results (2003)

- K0 short, D+Fe

- K0 short, D+Pb

- (Simple vertex cut)

- (Simple vertex cut)

- 27 M D+Pb electrons
-  (5% of total)

- Q2

- W

## Summary

- In principle both baryon-meson and quark-gluon descriptions of the nucleus should work, question is rather what is the most efficient description of observables?

- JLab is pushing both descriptions to the limit:
- A description of the deuteron elastic scattering data in terms of conventional nuclear physics works to much smaller distance scales (0.5 fm) than expected.
- Deuteron photodisintegration experiments reveal the underlying quark-gluon degrees of freedom at a distance scale smaller than 0.1 fm.
- First indication that a nucleus is not merely a set of nucleons, the nuclear EMC effect, is under scrutiny for cases where nucleons are strongly bound (x > 1, tagged structure functions). Can alternatively view this as scattering from superfast quarks.
- A second indication is given by the observed medium dependence of proton form factors, considered a precursor of the onset of a quark gluon plasma.
- Proton transparency data can be well described by conventional nuclear physics;
- But have seen hints of QCD dynamics (Color Transparency) in meson production data. Full effects of CT may be anticipated at Q2 < 10 here, presently under investigation.

- Data show beautiful balance between conventional nuclear physics descriptions and QCD effects.

- This topic: some experiments complete, many ran/to run in FY’03 and ‘04