n p MeAsurement of F2 /F2 , d/u RAtios and A=3 EMC Effect in Deep Inelastic Scattering Off the Tritium and MirrOr Nuclei (JLab Conditionally Approved Experiment C12-10-103)

Makis Petratos Kent State University For the JLab MARATHON Collaboration

PAC37 – January 2011 Jefferson Lab

PAC30: Physics goals of experiment: “Highlights of 12 GeV Program”

Conditional approval based on on “review of safety aspects of 3H target”

PAC36: Physics again very highly rated. Conditional approval based on detailed SBS detector design

3H target conditional approval removed Electron- Deep Inelastic Scattering (DIS): Interaction is mediated via exchange of a virtual photon absorbed by one of the nucleon’s . Nucleon breaks up into several X hadrons. X e’

γ★

Q2

e N DIS and Parton Model

• Cross Section – Nucleon structure functions F1 and F2: d  2 F ( ,Q2 ) 2F ( ,Q2 )   2 cos2   1 sin 2  2 4   2  2  ddE' 4E sin  2    M 

 F M  v2    E  E' R  L  2 1  1  F  Q2  2 2 T 1   Q  4EEsin ( / 2) • Quark-Parton Model (QPM) interpretation in terms of 2 quark probability distributions qi(x) (large Q and ν): 1 2 F (x)  x e2q (x) F1(x)  ei qi (x) 2  i i 2 i i • Bjorken x: fraction of nucleon momentum carried by struck quark: x  Q2 / 2M

n p F2 /F2 in Quark Parton Model • Assume isospin symmetry: u p (x)  d n (x)  u(x) u p (x)  d n (x)  u(x)

d p (x)  un (x)  d(x) d p (x)  u n (x)  d (x)

p n p n s (x)  s (x)  s(x) s (x)  s (x)  s(x) • and structure functions:

p 4 1 1  F  x (u  u)  (d  d )  (s  s) 2   9 9 9  n 4 1 1  F2  x (d  d )  (u  u)  (s  s) 9 9 9  • Nachtmann inequality: n p 1/ 4  F2 / F2  4

SLAC Measurements End Station A 1968-1972

Friedman, Kendal, Taylor Nobel 1991

n p F2 /F2 extracted from proton and deep inelastic data using Hamada-Johnston potential in a Fermi-smearing model.

Data in disagreement with SU(6) prediction: 2/3=0.67! SLAC/MIT and (later) CERN Data n p • Nachtmann inequality satisfied: 1/ 4  F2 / F2  4

n p • For x → 0 : F2 /F2 → 1: Sea quarks dominate with: u  u  d  d  s  s

n p • For x → 1 : F2 /F2 → 1/4: High momentum partons in proton (neutron) are up (down) quarks, and: s  s  0

• For medium and high x, safe to assume that (with d and u denoting now quark plus antiquark distributions): F n [1 4(d / u)] 2  F p [4  (d / u)] 2 Theory Overview (I)

• SU(6)-breaking Diquark Model (Close/Feynman, 1970’s) n p • Phenomenological explanation: fall off of F2 /F2 and its x=1 limit easily explainable using SU(6) nucleon wave function (Close, 1973) or Regge theory (Feynman, 1975) and assuming that the spectator diquark configuration with total spin s=1 is suppressed relative to that with s=0. • Limit at x=1 in agreement with the SLAC/CERN data. • Constituent Quark Model (Isgur and Carl, 1980-2000) • Suppression fully understood in the hyperfine-perturbed quark model: color-magnetic hyperfine interaction generated by

exchange is proportional to quark spin dot products si·sj. Force is repulsive(attractive) for parallel(antiparallel) spins and allows the u(x) and d(x) quark momentum distributions to be different. • Limit for x=1 in agreement with the diquark model and data.

Theory Overview (II)

• Perturbative QCD (Farrar and Jackson, 1975) • Simple consideration of isospin and helicity structure of nucleon’s quark wave function within perturbative QCD dictates that for diquark spin alignment (s=1) only exchange of longitudinal is permitted, resulting in suppression of n p Compton scattering amplitude, which causes the F2 /F2 fall off. • Problem: pQCD x=1 limit different than that of quark/diquark model! • QCD Counting Rules (Brodsky et al., 1995) • Early pQCD findings substantiated within first-principles calcu- lations of Counting Rules of QCD predicting the high-x behavior of quark distributions: q(x)~(1-x)2n-1+2Δh, where n is the minimum number of not interacting (spectator) quarks and Δh is the difference in helicity between the struck quark and the nucleon. • Same x=1 limit as pQCD.

n n F2 / F2 , d/u Ratios and A1 Limits for x→1

n p n p F2 /F2 d/u A1 A1

SU(6) 2/3 1/2 0 5/9

Diquark Model/Feynman 1/4 0 1 1

Quark Model/Isgur 1/4 0 1 1

Perturbative QCD 3/7 1/5 1 1

QCD Counting Rules 3/7 1/5 1 1

A1: Asymmetry measured with polarized and . Equal in QPM to probability that the quark spins are aligned with the nucleon spin. Extensive experimental programs at CERN, SLAC, DESY and JLab.

Extensive recent review on the valence/high-x structure of the nucleon: R. J. Holt and C. D. Roberts, Rev. Mod. Phys. 82, 2991 (2010). EMC Effect

• Nuclear F2 structure function per nucleon is different than that of deuterium: large x and A dependence. • Quark distribution functions modified in the nuclear medium. • Possible explanations include: • Binding effects beyond nucleon Fermi motion • Enhancement of field with increasing A • Influence of possible multi-quark clusters • Change in the quark confinement scale in nuclei • No universally accepted theory for the effect explanation. • A=3 data will be pivotal for understanding the EMC effect. • Theorists: Ratio of EMC effect for 3H and 3He is the best quantity for quantitative check of the theory, free of most uncertainties.

A Dependence EMC Effect

SLAC E139, 1984 J. Gomez et al.

Nucleon momentum probability distributions in nuclei different than those in deuterium. Effect increases with mass number A. Binding/EMC Effect in Deuteron • Deuteron structure function convolution: Calculated in a covariant frame-work in terms of free nucleon structure functions (Melnitchouk and Thomas 1996) : F d (x,Q2 )  f (y) F p (x,Q2 )  F n (x,Q2 ) dy 2  2 2 Spectral function f(y) accounts for Fermi Motion AND Binding/Off-Shell Effects, where y is the fraction of the nucleus momentum carried by the struck nucleon.

• Density Model: EMC effect for deuteron scales with nuclear charge density as for heavy nuclei (Frankfurt and Strikman 1988, applied by Whitlow et al. 1992) : F d  F A  2 1 d 2 1 p p  d  F2  F2  A  d  F2 

SLAC DIS Data

Whitlow: Density Model

M&T: Convolution Model

Bodek: Fermi-Smearing Paris N-N potential

n/ p Standard analysis of F2 F2 from proton and deuteron data shows large uncertainty at high-x values depending on nucleon-nucleon potential used. The three analysis methods indicate tremendous uncertainties in high-x n p behavior of F2 /F2 and d/u ratios … d/u essentially unknown at large x! Most recent CTEQ6X analysis shows similar large uncertainties at high x: A. Accardi et al., Phys. Rev D81, 034016 (2010). 3 3 Nucleon F2 Ratio Extraction from He/ H • Form the “SuperRatio” of EMC ratios for A=3 mirror nuclei: 3He 3H 3 3 F 3 F  R( He) R( He)  2 R( H)  2 R  2F p  F n F p  2F n R(3H ) 2 2 2 2 3 3 • If R=σL/ σT is the same for He and H, measured DIS cross section ratio must be equal to the structure function ratio as calculated from above equations: 3 He 3  F He 2F p  F n  2  R 2 2 3 H 3 H F p  2F n  F2 2 2

• Solve for the nucleon F2 ratio and calculate R* (expected to be very close to unity) using a theory model: 3 3 F n 2R  F He / F H 2  2 2 p 3He 3H  F2 2F2 / F2  R 3He and 3H Structure Functions • Nucleon structure function in nucleus A in the Impulse Approximation: extension of deuteron model (Melnitchouk and Thomas): F NA (x)  dy [ f (y)] F N (x / y)  f  F N 2  N / A 2 N / A 2

• For 3He: 3He p n F2  2 f 3  F2  f 3  F2 p/ He n/ He • With isospin symmetry: f 3  f 3  f n/ H p/ He p

f 3  f 3  f p/ H n/ He n

• Then for 3H: 3H p n F2  fn  F2  2 f p  F2

• Charge symmetry breaking effects are small! SuperRatio R* = R(3He)/R(3H) has been calculated by three expert groups to deviate from 1 only up to ~1.5% taking into account all possible effects:

* I. Afnan et al., Phys. Lett. B493, 36 (2000); Phys. Rev. C68, 035201 (2003) * E. Pace, G Salme, S. Scopetta, A. Kievsky, Phys. Rev. C64, 055203 (2001) * M. Sargsian, S. Simula, M. Strikman, Phys. Rev. C66, 024001 (2002)

The Experiment • 3He/3H DIS measurements can be best run in Hall A: • Beam Energy: 11.0 GeV – Beam Current: 25 µA • Small angles (15o - 25o): use Left HRS system • Large angles (42o - 57o): use BigBite system • Standard electron detection packages for both systems • ~700 hours for d/u measurement (@ 100% efficiency)

• ~300 hours for R=σL/σT measurement (@ 100% efficiency) • Desirable to check that the ratio R is the same for 3He and 3H with Rosenbluth separation of cross section versus ε (degree of γ* longitudinal polarization) using the Left HRS

system. Need dedicated 3.3, 5.5, 7.7 GeV energies. • Need target system with helium/tritium/deuterium cells. n p • Normalize F2 /F2 results to low-x data (no theory error) from SLAC (overall normalization uncertainty ±0.01).

The Tritium Target System • Five-cell target structure (1H, 2H, 3H, 3He, Al Dummy): • All cells: 25 cm long, 1.25 cm diameter, 25 µA max current • 3H cell: 10 atm, 1000 Ci activity • 1H, 2H, 3He cells: 25 atm

• Cells will be filled at STAR Facility of Idaho National Lab. • Target will be shipped to JLab using commercial services. • System will be enclosed in secondary “sealed” containment vessel (no reliance on fast valves). • A catastrophic leak will be vented through stack above Hall A. • Resulting emission will keep tritium levels at the JLab site boundary below regulatory limits. • More work to be done BUT Jlab review did not find a show stopper for further development and operation of target at Jlab.

Tritium Target at JLab

Tritium Target Task Force 1000 Ci E. J. Beise (U. of Maryland) B. Brajuskovic (Argonne) R. J. Holt (Argonne) W. Korsch (U. of Kentucky) A. T. Katramatou (Kent State U.) D. Meekins (JLab) JLab Review: June 3, 2010: T. O’Connor (Argonne) “No direct show stopper” G. G. Petratos (Kent State U.) R. Ransome (Rutgers U.) Details: Conceptual Design of a 3H Gas Target for JLab, P. Solvignon (JLab) Tritium Target Task Force, Roy J. Holt et al., May 2010. B. Wojtsekhowski (JLab)

The BigBite Spectrometer • 40-50 msr solid angle, ~1.0% momentum resolution. • Successfully employed in previous Hall A experiments with similar luminosities. Existing detectors: • Drift Chamber set and Scintillator Hodoscope package • Pb-glass Calorimeter and Gas Threshold Cherenkov Detector • Calorimeter: excellent resolution: ~8%/E1/2 • Improve Cherenkov Detector: i) Double radiator length (from 40 to 80 cm) and ii) Recoat all mirrors and Winston cones at CERN shop. Expect to triple number of photoelectrons (>20)! • To minimize background through dipole (dominant source): install lead collimator in front of dipole magnet. • To develop reliable Monte Carlo Model: set up TOSCA model and cross check it with basic magnetic measurements. Side View BigBite Spectrometer

BigBite Spectrometer Cherenkov Detector R=σL/σT Measurements SLAC/CERN data show that the ratio R=σL/σT is the same for all nuclei within experimental errors

3He/3H JLab data will be of better precision than SLAC data [wider angular (ε) range!] n p Possible Jlab - Hall A Data for F2 /F2 and d/u Ratios EMC Effect for A=3 Mirror Nuclei

Hall A data on 3H, 3He will be of similar precision to Hall C data n p F2 /F2 Ratio and EMC Effect are Elementary Undergraduate Nuclear-Particle Textbook Physics! Summary • DIS off 3He and 3H with the 11 GeV JLab beam can provide: n p • Best measurements of F2 /F2 and d/u ratios • Discrimination between differing predictions of Quark Model and Perturbative QCD/Quark Counting Rules • Understanding of SU(6) symmetry breaking • Crucial EMC effect data for both A=3 systems • Input to light-nuclei structure theory • Input to structure function parametrizations needed for inter- pretation of high energy collider and neutrino oscillations data • Textbook Physics experiment. • Opportunities for other large Q2 measurements: x>1 etc. • NEED: (primarily) a safe, low-activity tritium target! Request full approval to proceed with realistic target design based on recommendations of safety review committee.

Beam Time Request (Hours)

n p Target F2 /F2 R=σL/σT BBS/HRS Changes

3He 184 3H 275 D 198 Sub-Total 657 45 3He 117 3H 180 Sub-Total 297

TOTAL 999 hrs 42 days