Simona Malace University of South Carolina Users Group Workshop and Annual Meeting, June 7–9 2010, JLAB

QCD calculations and Parton Distribution Functions (PDFs)  pQCD Leading Twist (LT) and standard PDFs extraction  how far pQCD LT can take us? (PDFs uncertainties)  efforts to push PDFs extraction at larger x - CTEQ6X and Alekhin et al.: PDFs at large x (from high W 2 DIS to low W 2 DIS) - PDFs extraction into the Resonance Region? (quark-hadron duality) - plans for future

DIS  First results from famous SLAC-MIT experiments: presented in 1968 in Vienna by Panofsky, published in 1969 Deep inelastic scattering (DIS) region resonance region “… theoretical speculations are focused on the possibility that these data might give evidence on the behavior of point-like, charged structures within the nucleon”

PDF  Decades of accumulated data + sophisticated QCD analyses => mapping of PDFs over a large kinematic range PDFs  connect hadron-parton processes  universal: many processes calculated with same set of PDFs  information as to the underlying structure of hadrons  Distribution of quarks and gluons (PDFs) inside the nucleon: fundamental characterization of its structure in QCD Q: How precisely? A: It depends…

 Two ideas of QCD + data: x dependence obtained from global fits to data Data: DIS ( ), neutrino DIS dimuon production, vector boson production, hadronic jet production,… input (PDF) perturbative Factorization: perturbative Evolution: LO NLO 1)pQCD, LT (leading twist) calculation  cannot use data from kinematic regions which require corrections beyond LT 2) data coverage not uniform across x  knowledge of PDFs not uniform across x

small large  No data at large x  large uncertainties for PDFs at large x

stage 1 stage 2 stage 3?  Stage 1 (last few decades): LT calculations  PDFs constrained up to x ~ 0.7 (CTEQ, MRST(MSTW), GRV, etc.)  Stage 2 (last decade): calculations beyond LT  PDFs constrained up to x ~  Alekhin et al. S. Alekhin, Phys. Rev. D 63, (2001) …. S. Alekhin, J. Blumlein, S. Klein, S. Moch, Phys. Rev. D 81, (2010)  CTEQ6X Accardi, Christy, Keppel, Melnitchouk, Monaghan, Morfín, Owens, Phys. Rev. D 81, (2010) Accardi et al., in preparation  CTEQ6X: future?  Stage 3 (future):

 Operator Product Expansion: leading twist (LT) beyond LT: higher twist (HT)  To extend to large x and low->intermediate Q 2 : 1) higher twist 2) target mass corrections (TMC) 3) nuclear corrections 4) quark-hadron duality 5) jet mass corrections (JMC) 6) Heavy quark mass corrections 7) Large x resummation 8) Large x DGLAP evolution 9) parton recombination at large x 10) perturbative stability at low Q2 11) … List from A. Accardi (talk at INT09) least

LT+TMC residual power corrections (HT)  NLO global fit to proton and deuteron data with Q 2 > 1.69 GeV 2 and W 2 > 3 GeV 2 : DIS from SLAC, JLab, FNAL Drell-Yan, W asymmetry data at higher x (Hall C E00-116) cut 0: Q 2 > 4 GeV 2, W 2 > GeV 2 (standard) cut 1: Q 2 > 3 GeV 2, W 2 > 8 GeV 2 cut 2: Q 2 > 2 GeV 2, W 2 > 4 GeV 2 cut 3: Q 2 > 1.69 GeV 2, W 2 > 3 GeV 2 CTEQ6X: A. Accardi et al., Phys. Rev. D 81, (2010)  TMC via colinear factorization (CF) method  HT: applied multiplicatively; same for proton as for neutron

no direct constraints from data  stronger suppression of d-quark PDF at large x (sensitive to the treatment of nuclear corrections)  greatly reduced experimental errors: 10-20% for x < 0.6 and up to 40-60% at larger x  u and d ~ stable with respect to choice of TMC if flexible enough param. of HT is used CTEQ6X: A. Accardi et al., Phys. Rev. D 81, (2010)

 d-quark constrained by Deuterium data: smearing function  d-quark extraction sensitive to the treatment of nuclear corrections  no nuclear corrections: strong enhancement of d-quark compared to ref.  nuclear corrections: strong suppression of d-quark compared to ref.  nuclear corrections (DMC): strong enhancement of d-quark compared to ref. Accardi et al., in preparation

 TMC: via “Georgi and Politzer” (OPE) [CTEQ6X: TMC via CF]  HT: applied additively; HT(proton) different from HT(neutron) [CTEQ6X: HT applied multiplicatively; HT(proton) same as HT(neutron)]  nuclear corrections + off-shell via Kulagin-Petti (K-P) [CTEQ6X(standard) = nuclear corrections, no off-shell corrections] S. Alekhin, J. Blumlein, S. Klein, S. Moch, Phys. Rev. D 81, (2010)  NNLO global fit to data with W 2 > 3.4 GeV 2 S. Alekhin, Phys. Rev. D 63, (2001) …

 F 2 p (direct constraints from data): very good agreement  within 5% up to x = 0.8  within 15% at x = 0.9  F 2 d (direct constraints from data): very good agreement  within 5% up to x = 0.8  F 2 n : good agreement  within 15% up to x = 0.7  within 20-25% at x = 0.8 CTEQ6X(standard)/ALEKHIN sensitive to nuclear corrections on-shell off-shell (K-P) Comparisons of full calculations

CTEQ6X(K-P off-shell)/ALEKHIN Comparisons of full calculations  F 2 p comparisons (direct constraints from data): mostly insensitive to off-shell corrections in CTEQ6X (x < 0.9)  F 2 d comparisons (direct constraints from data): mostly insensitive to off-shell corrections in CTEQ6X (x < 0.8)  F 2 n comparisons: ~ 15-20% change; CTEQ6X(K-P off-shell)/ALEKHIN closer to unity

Compare: relative contributions of various effects (HT)  TMC contributions same for both calculations (OPE)  nuclear corrections: similar treatment  HT contributions differ: more for F 2 n than F 2 p  Difference in HT for F 2 n correlated to difference in LT?

stage 1 stage 2 stage 3? 2 nd res. Region: Q 2 = 2 GeV 2 2 nd res. Region: Q 2 = 5 GeV 2  Use quark-hadron duality to access even larger x and provide good Q 2 coverage at large x for PDF studies  Need good (& extended) Q 2 coverage from data at fixed x for a thorough study of PDFs extraction at large x

Quark-Hadron Duality: experimental observation which could be a working hypothesis for extending PDFs at large x => needs to be verified and quantified  Duality between quark and hadron descriptions of observables in electron-hadron scattering  observed by Bloom and Gilman in proton F 2 (1969)  firmly established for proton F 2 and F L (JLAB)  studied in spin-dependent in semi-inclusive scattering (JLAB)  recently acknowledged in neutron F 2 (JLAB)  interpreted in OPE as cancellations of dynamical HT  … Random facts about quark-hadron duality

Calculate: 1 st 2 st 2 nd 2 st 3 rd 4 th DIS Region W min W max 1 st nd rd th DIS To what extent the resonance region data average to the QCD curve?

 To what extent the resonance region data average to a (stage 2) QCD curve (Alekhin03)?  Within 10% : globally, low W DIS, 4 th, 3 rd, 2 nd S.P. Malace et al., Phys. Rev. C 80, (2009)  1 st : special case  some models predict stronger violations of duality  calculation based on handbag diagram may break at low W  at the largest x where QCD curves poorly constrained => difficult to test duality

 Impulse Approximation – virtual photon scatters incoherently from individual nucleons New method New method : employs iterative procedure of solving integral convolution equations Y. Kahn, W. Melnitchouk, S.A. Kulagin, Phys. Rev. C 79, (2009) nuclear F 2 nucleon F 2 smearing function  Some arguments: quark-hadron duality in F 2 p could be the result of accidental cancellations between quark charges (do not occur for F 2 n )… Is quark-hadron duality an accident? Verify quark-hadron duality in F 2 n Need F 2 n in the resonance region…

quasielastic peak  Use proton and deuteron data at fixed Q 2 (matched kinematics) data  Data: SLAC at Q 2 = 0.6, 0.9, 1.7, 2.4 GeV 2 + data from Jlab (Hall C E00-116) at Q 2 = 4.5, 5, 5.5, 6.2, 6.4 GeV 2 S.P. Malace, Y. Kahn, W. Melnitchouk, C. Keppel, Phys. Rev. Lett (2010) model  QE extracted from data using model (form factors + same smearing function as for extraction)  Off-shell corrections: upper limit from model(MST) ~1.5%; assign 100% uncertainty to correction => contributes < 2% to total uncertainty on F 2 n

 F 2 n in resonance region: 3 resonant enhancements (fall with Q 2 at ~ rate as for F 2 p ) S.P. Malace, Y. Kahn, W. Melnitchouk, C. Keppel, Phys. Rev. Lett (2010)  F 2 n in resonance region appears to average to F 2 n from Alekhin09 S.P. Malace, Y. Kahn, W. Melnitchouk, in preparation

 2 nd and 3 rd RES regions: agreement within 15-20%, on average  1 st RES region: agreement worsens at the highest Q 2 (corresponds to the largest x)  globally remarkable agreement: within 10% W 2 : ( ) GeV 2 W 2 : ( ) GeV 2 W 2 : ( ) GeV 2 S.P. Malace, Y. Kahn, W. Melnitchouk, C. Keppel, Phys. Rev. Lett (2010)  To what extent the resonance region data average to a (stage 2) QCD curve (Alekhin09)?

A. Accardi, S.P. Malace, in preparation preliminary  Study sensitivity of quark-hadron duality ratios to various prescriptions for inclusion of:  HT: additive vs multiplicative; HT(proton) same/different than HT(neutron)  TMC: OPE, CF… etc. (in preparation for) Stage 3…

A. Accardi, S.P. Malace, in preparation preliminary  Study applicability of QCD calculation at low values of W; criterion: separation between target jet and current jet, (in preparation for) Stage 3…

A. Accardi, S.P. Malace, in preparation preliminary  Extend studies to larger Q 2 (in preparation for) Stage 3…

E (Hall C): approved by PAC35 Will extend proton and deuteron F 2 precision measurements to larger x and Q 2 by measuring H(e,e’) and D(e,e’) cross sections in the resonance region and beyond up to Q 2 ~ 17 GeV 2 and x ~ 0.99 Spokespeople: S.P. Malace (contact person), I.M. Niculescu, C. Keppel We aim for similar precision as for the lower energy run E00-116

 Expected kinematic coverage in the ratio deuteron to proton truncated moments from E

The 3rd International Workshop on Nucleon Structure at Large Bjorken x (HiX2010) This workshop will continue a series of meetings held previously at Temple University, Philadelphia (2000) and CPPM, Marseille (2004). We will have ~36 speakers (30 minutes talks); 30 speakers already confirmed Proceedings We can offer travel support for students

No connection to what I discussed up to this point…  E in Hall A: search for medium modifications of the proton structure in 4 He(e,e’p) 3 H   Induced polarization P y : my primary responsibility in the project S.P. Malace, M. Paolone, S. Strauch et al., in preparation Mike Paolone (Ph.D. in Dec. 2008): M. Paolone, S. Malace, S. Strauch et al., accepted for publication to Phys. Rev. Lett.