Nucleons in the Nuclear Environment

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2 Nucleons in the Nuclear Environment "The next seven years..." John Arrington Argonne National Lab Topic: Study of nucleons (hadrons, quarks) in nuclei 1 - The EMC effect and related measurements 2 - Color Transparency 3 - Quark propagation 4 - J/ψ production [P. Bosted] [D. Dutta] [W. Brooks] [S. Kuhn, S. Strauch, J. Watson] Jefferson Lab User s Group Annual Meeting, June 18, 2004 "Beam in 30 minutes or it s free"

3 Nucleons in the Nuclear Environment "The next seven years..." John Arrington Argonne National Lab Bigger question: Does QCD matter in the real world? In the lab (GeV accelerators), matter is quarks In the real world, matter is hadrons Questions for JLab: How do nucleons interact with the nucleus? How do other (exotic?) hadrons interact with the nucleus? How do quarks interact with the nucleus? Jefferson Lab User s Group Annual Meeting, June 18, 2004 "Beam in 30 minutes or it s free"

4 Two "Realms" of Nuclear Physics QCD land quarks + gluons + color Strongly attractive at all distances: 1 GeV/cm = 18 tons! >10 12 times the coulomb attraction in hydrogen Real world nucleons + mesons + strong interaction Matter consists of colorless bound states of QCD Quark interactions cancel at large distances, making the interactions of hadrons finite. Don t observe quarks, gluons, or color in traditional nuclear physics V(r) [GeV] V(r) ~1 fm potential between two quarks Quarks have been swept under a very heavy (18 ton) rug r [fm] Potential between two nucleons r [fm]

5 When do quarks matter? To peek under the rug, we have to shift the 18 ton weight at least a little bit High energy Cosmic rays SLAC, DESY, LHC early universe LHC RHIC SPS thermal freeze-out 0.3 hadron gas chemical freeze-out AGS SIS quark-gluon plasma atomic nuclei neutron stars NET BARYON DENSITY (0.17 GeV/fm 3 ) 1 deconfinement chiral restoration 2 5 JLAB12 We do see density-dependent effects in nuclear structure (EMC effect) Do these effects have anything to do with the quarks? 8 temperature T (MeV) The Titanic High temperatures Early universe RHIC? High densities Neutron stars Nuclei?? JLab???? The Iceberg

6 Medium modifications to nucleon structure? Depletion of the structure function for 0.3<x<0.8 EMC effect for Iron (Copper) The magnitude of the effect increases with size/density The x-dependence is identical for all nuclei It has been clear for some time that binding, Fermi motion play important roles. Do we need something more than conventional nuclear physics? Recently shown that... The EMC effect cannot be explained by conventional nuclear physics... most recently - J. Smith and G. A. Miller, PRC 65: (2002) Unless it can be explained by conventional nuclear physics. most recently - J. Rozynek and G. Wilk, NPA 721, 388 (2003)

7 What else do we know about medium modifications? The EMC effect cannot be explained by conventional nuclear physics... most recently - J. Smith and G. A. Miller, PRC 65: (2002) Unless it can be explained by conventional nuclear physics most recently - J. Rozynek and G. Wilk, NPA 721, 388 (2003) arxiv:nucl-th/ v1 21 Aug 2002 The Coulomb Sum Rule is fulfilled... J. Jourdan, NPA 603, 117 (1996) J. Carlson et al., PLB 553, 191 (2003) Quasielastic response is (basically) nothing more than nucleon elastic scattering + nucleon distribution in nucleus

8 What else do we know about medium modifications? The EMC effect cannot be explained by conventional nuclear physics... most recently - J. Smith and G. A. Miller, PRC 65: (2002) Unless it can be explained by conventional nuclear physics most recently - J. Rozynek and G. Wilk, NPA 721, 388 (2003) The Coulomb Sum Rule is fulfilled... J. Jourdan, NPA 603, 117 (1996) J. Carlson et al., PLB 553, 191 (2003) Except that maybe it isn t. J. Morgenstern, Z.-E. Meziani, PLB 515, 269 (2001) SL (q eff ) Integrated quasielastic response suppressed by ~30-40% He Fig Ca 56 He Ca 48 Ca 56 Fe 208 Pb Fe 208 Pb 56 Fe 56 Fe q eff (MeV/c) a) b)

9 What else do we know about medium modifications? The EMC effect cannot be explained by conventional nuclear physics... most recently - J. Smith and G. A. Miller, PRC 65: (2002) Unless it can be explained by conventional nuclear physics most recently - J. Rozynek and G. Wilk, NPA 721, 388 (2003) The Coulomb Sum Rule is fulfilled... J. Jourdan, NPA 603, 117 (1996) J. Calrson et al., PLB 553, 191 (2003) Except that maybe it isn t. J. Morgenstern, Z.-E. Meziani, PLB 515, 269 (2001) Nucleon form factors are modified in nuclei... G. Van der Steenhoven, et al., PRL 57, 182 (1986) [form factor ratio in nuclei] G E /G M modified for nucleons in a nucleus

10 What else do we know about medium modifications? The EMC effect cannot be explained by conventional nuclear physics... most recently - J. Smith and G. A. Miller, PRC 65: (2002) Unless it can be explained by conventional nuclear physics most recently - J. Rozynek and G. Wilk, NPA 721, 388 (2003) The Coulomb Sum Rule is fulfilled... J. Jourdan, NPA 603, 117 (1996) J. Carlson et al., PLB 553, 191 (2003) Except that maybe it isn t. J. Morgenstern, Z.-E. Meziani, PLB 515, 269 (2001) Nucleon form factors are modified in nuclei... G. Van der Steenhoven, et al., PRL 57, 182 (1986) [form factor ratio in nuclei] Unless they aren t. T. D. Cohen, J.W. Van Orden, A. Picklesimer, PRL 59, 1267 (1987) [form factor ratio in nuclei] I. Sick, NPA 434, 677 (1985) R.W. McKeown, PRL 56, 1452 (1986) [y-scaling limits] DEAD END?

11 What do we really know about medium modifications? The EMC effect cannot be explained by conventional nuclear physics... most recently - J. Smith and G. A. Miller, PRC 65: (2002) Unless it can be explained by conventional nuclear physics most recently - J. Rozynek and G. Wilk, NPA 721, 388 (2003) The Coulomb Sum Rule is fulfilled... J. Jourdan, NPA 603, 117 (1996) J. Carlson et al., PLB 553, 191 (2003) Except that maybe it isn t. J. Morgenstern, Z.-E. Meziani, PLB 515, 269 (2001) Nucleon form factors are modified in nuclei... G. Van der Steenhoven, et al., PRL 57, 182 (1986) [form factor ratio in nuclei] Unless they aren t. The effects are small The experiments are hard T. D. Cohen, J.W. Van Orden, A. Picklesimer, PRL 59, 1267 (1987) [form factor ratio in nuclei] I. Sick, NPA 434, 677 (1985) R.W. McKeown, PRL 56, 1452 (1986) [y-scaling limits] The theory is very complicated Jefferson Lab needs to do more than just improve a few measurements...

12 What can Jefferson Lab do? 1) Improve a few measurements EMC effect Coulomb sum rule y-scaling limits on nucleon swelling (better facility) 2) Make new measurements (better techniques) Form factor modification by polarization transfer 3) Invent new techniques (brand new ideas) Measure EMC effect as a function of local density Probe high-density components of nucleus (SRCs)

13 E (4 GeV) - EMC effect in the resonance region 1.2 < W 2 < 3.0 Q 2 4 GeV 2 Identical nuclear dependence in DIS and resonance regimes! EMC effect - purely hadronic? Consequence of precise duality? Relaxing the DIS limit appears to yield identical results, with improved precision at large x Indication of different shape for Carbon at large x Any deviation from the DIS result should be even smaller at 6 GeV

14 EMC effect in very light nuclei F 2 (A)/F 2 (D) - Vary with A or <ρ A >? x-dependence same for all nuclei? New measurements planned for 3 He and 4 He: Provide more information on the A-dependence Allow comparison to models in exact few-body calculations The shape in 3 He, 4 He will provide a new way to test the existing models SLAC fit to heavy nuclei (scaled to 3 He) Calculations by Pandharipande and Benhar for 3 He and 4 He E01-001, Hall C, September 2004

15 Extending EMC effect measurements to F 2 and R=σ L /σ T Preliminary R A /R D from HERMES R p from JLab [E99-118] [also E94-110, E00-002] Additional experiments approved to measure R D [E02-109] and R A [E04-001] Are nuclear effects identical in F L and F 2?

16 Beyond "The EMC Effect" Some models, e.g. Quark-Meson Coupling model (Thomas, et al.), predict modified nucleon form factors as a consequence (or cause) of the EMC effect 15-20% 30-35% If nucleon modification explains the EMC effect, why probe nuclei? Probe nucleons! Previous attempts to look for nucleon form factor modification had mixed results - Nuclear effects large for quasielastic cross section measurements - Almost no sensitivity to G E at large Q 2 (e.g. y-scaling limits) JLab luminosity, polarization, polarimetry --> Study in-medium form factors using the polarization transfer technique

17 Polarization transfer in 4 He(e,e p) 3 He E (Hall A): Compare R=G E /G M of a bound proton to G E /G M of a free proton Nuclear effects are small (dotted and dashed lines) Data are systematically ~10% below calculations without modification Indication of modified form factors in a nucleus E approved by PAC24 to make additional, high precision measurements [S. Strauch - Details on the physics, experiment, models]

18 Crazy New ideas: Probe even higher densities early universe LHC RHIC SPS thermal freeze-out hadron gas chemical freeze-out AGS SIS quark-gluon plasma temperature T (MeV) deconfinement chiral restoration atomic nuclei neutron stars Average nuclear density is a few times smaller than the critical density NET BARYON DENSITY (0.17 GeV/fm 3 ) Low JLAB12 temperature high density A nucleus is a dynamic system, with local fluctuations in density These fluctuations provide a small high-density component (short-range correlations) * This may be origin of EMC effect, medium modifications * We can try to isolate SRCs to probe high density matter If SRCs are the source of the EMC effect, why probe nuclei? Probe SRCs instead!

19 High Density Configurations Nucleons are already closely packed in nuclei Ave. separation ~1.7 fm in heavy nuclei nucleon charge radius ~ 0.86 fm Nucleon separation is limited by the short range repulsive core Average nuclear density V(r) Potential between two nucleons 0 ~1 fm r [fm] For a 1 fm separation (typical for SRCs), the central density is ~4x nuclear matter. Comparable to neutron star densities! Warning: portions of the person seated next to you are at neutron star densities and may collapse without warning 1.7 fm separation 1.2 fm separation 3x nuclear matter 0.6 fm separation >5 times nuclear matter densities

20 2 < ; " How to isolate SRCs? - A(e,e ) at x>1 Inclusive Q scattering 2 <1.4 from nuclei at x>1 3 Deuteron and Iron fits to 4 GeV data (y-scaling analysis) is dominated by quasielastic scattering In 1 a PWIA analysis, you can extract the nucleon momentum distribution 1.5 R He4 He3 0.5 Momentum Q 2 >1.4 distribution at very Deuteron and nuclear matter calculations. high momentum has same shape for deuteron and heavy nuclei R He4 He3 1 2N short-range correlations Hall C: E (4 GeV) E projected (5.7 GeV) X B Hall B: Ratio of A/ 3 He and SLAC, Hall C: A/ 2 H Ratio constant for x>1.5, Q 2 >1.4 2: F Fe 2 /A 10-1 F2 /A x= Q 2 < R Fe He3 MF+multi-nucleon Frankfurt and Strikman 10-4 x=1.5 #%$ " "! 10-5 MF+2N Frankfurt, Day, Sargsian, and Strikman Q 2 > $ *+, )( #!' & 10-7 R Fe He3 Mean field $ / 10-8 $ )" & & & 0 1!) ' $ ) ( Q 2, GeV 2 X B 2?> ; 2: = 6

21 How to probe SRCs? - A(e,e ) at x>1 Inclusive x>1 --> isolate SRC Inclusive DIS --> quark PDFs JLab 12 GeV --> DIS scattering at x>1 --> PDF for SRC Expect any quark-mixing between nucleons to increase strength at large x F 2 (x) Red curve: 2 H = p + n Blue curve: 2 H = 0.95(p+n) (6q) Deuteron provides cleanest signature (we understand deuteron as p+n) Inelastic dominated for JLab 12 kinematics Heavy nuclei may yield larger signals, but need better understanding of SRCs for hadronic baseline SRCs provide a high-density component in nuclei Important to understand their impact on nuclear structure More than just as a baseline when looking for exotic effects

22 Studies of Short-Range Correlations Inclusive A(e,e ) at large x A(e,e p) at large P m and A(e,e NN) Sensitive to nucleon momentum distribution Sensitive to 2-N vs. multi-nucleon SRCs Very large kinematic range Sensitive to size of SRCs Sensitive to the full spectral function Sensitive to 2-N vs. multi-nucleon SRCs More limited kinematic range Sensitive to details of SRCs Completed measurements: SLAC, JLab Halls B,C Completed measurements: JLab Halls A, B, C a) pn b) Data PWIA 5 pn 1 Body Full cross section (fb/(mev/c) ) E (Sep 2004) E SLAC 0 30 pp c) cross section (fb/(mev/c) ) Scaling region Q 2 > 3 GeV 2 E will expand kinematic range, add 3 He and 4 He to better study 2N vs. multi-nucleon correlations P rel (GeV/c) d) P tot (GeV/c) E extended 16 O(e,e p) measurements pp Hall B, 3 He breakup E will measure A(e,e NN) for heavier nuclei at high Q 2 [Details - J. Watson]

23 Probing SRCs, part 2: Tagged EMC effect 1.05 Strike neutron in 2 H, tag proton x=0.3 x=0.6 R n Proton at θ 180 o --> spectator (reconstruct initial nucleon) Proton at low momentum --> suppress FSI, off-shell effects Small P S --> ~free neutron Large P S --> Isolate SRCs (high-density configuration) Spectator proton acts as a knob we can use to vary the density of the pair R n = F bound 2 / F free p (MeV/c) 0.4 For low spectator momentum, R 1 Nuclear effects much larger for high-momentum spectators EMC effect: structure of a nucleus as a function of average nuclear density 0.5 Tagged EMC effect: structure of a SRC as a function of local density ~EMC effect for Carbon

24 Preliminary results (high spectator momentum - high density) in <40 minutes [S. Kuhn] E03-012: BoNuS (low spectator momentum - free neutron) 2005

25 Nucleons in High Density Matter: the EMC effect and beyond Improved experiments of the EMC effect Improved precision for EMC effect at large x EMC effect in few-body nuclei (better calculations, different shape) Better measurements of Coulomb sum rule Better limits on nucleon swelling New experiments, not possible before JLab EMC effect for both F 2 and R Nucleon form factors inside of a nucleus Hall B: use CLAS to tag high-p spectators independent low-p tagger (BONUS) New ways to measure nucleon modification Probe internal structure of high density configuration Tag high-momentum spectator to isolate high density SRCs, low-momentum spectator to isolate almost free nucleons Measure distribution of superfast quarks (DIS at x>1) This is not your father s Oldsmobile EMC effect

26 "Nucleons in the Nuclear Environment" Why stop with nucleons? We can put other stuff in nuclei How do other (exotic?) hadrons interact with the nucleus? Point-like configurations - Color Transparency Intrinsically small hadrons - sub-threshold J/ψ production How do quarks interact with the nucleus? Quark propagation, quark hadronization in a hadronic medium Examine QCD in other extreme cases Look for QCD (color) degrees of freedom in nuclei

27 Color Transparency pqcd predicts that a hadron in a point-like configuration (PLC) will have a very small color interaction due to the cancellation of the color charge Standard example: Proton knockout reaction -Form PLC in hard, exclusive interaction [requires high-q 2. How high?] -PLC travels through nucleus [requires PLC to survive ~1 fm or more] -PLC has reduced interaction with nucleus --> reduced absorption [extract transparency = σ A / σ H as function of Q 2 ] A well designed set of experiments can study the formation, evolution, and interaction of this exotic QCD state

28 Color Transparency: Mesons vs. Baryons CT in a qqq system: -No analogous state in QED CT in a qq system: -Analogous to small electric dipole -Two quarks --> expect easier formation of PLC expect slower evolution back to normal size Transparency vs. Q 2 : Vary PLC formation, lifetime, Color Transparency Transparency vs. A: Study Lifetime (evolution) of the PLC CT in mesons vs. baryons: Separate CT from PLC formation/lifetime So far, no unambiguous evidence for CT in baryons Limited evidence in meson (π, ρ) attenuation [HERMES, JLab] Signal in jet production at FNAL Indicates full CT by Q 2 10 GeV 2 Different mechanism for PLC formation then in knockout reactions [More details - D. Dutta]

29 Color Transparency: Rescattering vs. attenuation Without rescattering, A(e,e p) maps out spectral function Rescattering dominates for large P m D(e,e p) JLAB 12 GeV No CT CT (I) CT (II) Cross Section Ratio > Larger signal Q 2 (GeV 2 ) --> Insensitive to PLC evolution beyond ~1 fm Large kinematic range at 12 GeV, already have some results from Hall B [K. Egiyan - thurs. morning]

30 Color Transparency in meson rescattering 0.11 Meson --> PLC formation is easier D(e,e ρ) 0.1 Rescattering --> ~independent of PLC evolution R=σ(-t=0.8)/σ(-t=0.4) 0.06 JLab12: Hall B Q 2 (GeV/c) we can disentangle the relevant effects By combining different measurements... PLC formation PLC evolution Reduced color interaction Meson vs. Baryon Knockout vs. Rescattering Q 2 - and A-dependence

31 Quark propagation through Nuclei Inclusive DIS measurements are "fire and forget" High energy virtual photon hits "free" quark --> scaling, quark distribution functions, etc... The "free" quark disappears into the ether after it is struck We create and then discard a tagged quark beam inside of a target nucleus by requiring that the reaction be a QCD-free zone Inclusive scattering from partons is clean and simple, QCD is not We could use this beam to study... Quark interaction (energy loss, rescattering) with high-density hadronic matter Effect of the nuclear medium on quark hadronization If DOE offered us an accelerator with these parameters, we would be crazy to pass it up, even if it takes some hard work to interpret all of the measurements!

32 HERMES has made such measurements, but with relatively low luminosity, and (for the first few years) mostly for the proton and deuteron E (Hall B, spring 2004): Measured production of π 0, π +/-, K +/-, p from deuterium, carbon, iron, tin, lead as a function of ν, q, z, p T to study attenuation, hadronization, and transverse momentum broadening

33 Quark propagation through Nuclei HERMES has made such measurements, but with relatively low luminosity, and (for the first few years) mostly for the proton and deuteron E (Hall B, spring 2004): Measured production of π 0, π +/-, K +/-, p 6 hadrons from deuterium, carbon, iron, tin, lead x 5 targets as a function of ν, q, z, p T x 4 variables to study attenuation, hadronization, x 3 topics and transverse momentum broadening [360 details - W. Brooks] E02-104: A dedicated, high-luminosity study of quark propagation at 5 GeV 12 GeV upgrade Larger kinematic range Simpler interpretation Expect factorization to be a better approximation at higher energy

34 J/ψ production Intrinsically small size c-c pair Unusual bound state of QCD Small size --> weaker interaction color Van der Waals interaction Probe of color interaction Virtually no charm quarks in nucleons Quark exchange suppressed 2-gluon exchange dominates - sensitive to short range effects (e.g.hidden color) Probe of exotic color configurations in nuclei Little is known about it s interactions J/ψ suppression an important signature for QGP formation J/ψ propagation in cold hadronic matter well known Exotic effects have been observed at charm threshold Possible source of apparent CT signature in Brookhaven (p,2p) data? Large asymmetry in double-polarized proton-proton scattering [Details - P. Bosted]

35 J/ψ production in Nuclei Small size --> weaker interaction color Van der Waals interaction Measure J/ψ production for various nuclei Attenuation --> ψ-n cross section E03-008(Hall C): y g g Current data come from high energy measurements - need to disentangle attenuation from formation/coherence length effects Unusual reaction mechanism --> sensitive to small components of nuclear structure ψ Observe in sub-threshold production from SRC γ Probe hidden color in nucleus Is having every nucleon be in a color singlet state the only way for a nucleus to be in a color singlet state?

36 Does QCD matter in the "real world"? Experiments in nuclei open up unique new windows on QCD in nuclei (nuclear structure): - Quark degrees of freedom in matter at high density - Color degrees of freedom in nuclei (hidden color) Program is not limited to learning about the "real world": early universe LHC RHIC SPS thermal freeze-out hadron gas chemical freeze-out AGS SIS quark-gluon plasma temperature T (MeV) 0.3 atomic nuclei neutron stars NET BARYON DENSITY (0.17 GeV/fm 3 ) 1 deconfinement chiral restoration 2 5 JLAB12 - Provide detailed information on the EMC effect, nucleon modification in nuclei, Color Transparency, quark energy loss, J/ψ production and interaction, etc... - In the end, these all tell us something about QCD 8 Finally, this physics has applications to other areas of fundamental research: - Complements RHIC/LHC studies of QCD at high temperature - ν-oscillation and scattering measurements: need form factors, structure function, models of nuclear effects to interpret results - J/ψ production and attenuation are input to QGP searches - Cold, dense matter important for neutron stars/astrophysics