1 / 31

Nucleon Structure at Large Bjorken x

Nucleon Structure at Large Bjorken x . Simona Malace University of South Carolina. Users Group Workshop and Annual Meeting , June 7–9 2010, JLAB. Outline. QCD calculations and Parton Distribution Functions (PDFs) pQCD Leading Twist (LT) and standard PDFs extraction

maris
Download Presentation

Nucleon Structure at Large Bjorken x

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Nucleon Structure at Large Bjorken x SimonaMalace University of South Carolina Users Group Workshop and Annual Meeting, June 7–9 2010, JLAB

  2. Outline • QCD calculations and Parton Distribution Functions (PDFs) • pQCDLeading 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 Alekhinet al.: PDFs at large x (from high W2 DIS to low W2 DIS) • - PDFs extraction into the Resonance Region? (quark-hadron duality) • - plans for future

  3. Quarks inside the Nucleon? • First results from famous SLAC-MIT experiments: presented in 1968 in Vienna by Panofsky, published in 1969 DIS resonance region Deep inelastic scattering (DIS) 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”

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

  5. Standard PDF extraction in QCD • Two ideas of QCD + data: x dependence obtained from global fits to data Factorization: • perturbative input (PDF) • perturbative + NLO Evolution: LO + Data: DIS ( ), neutrino DIS dimuon production, vector boson production, hadronic jet production,… 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

  6. PDFs Uncertainties • No data at large x  large uncertainties for PDFs at large x data used example: CTEQ6 W2 > 12.25 small large data not used Q2> 4

  7. Extraction of PDFs in QCD • 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 ~ 0.8-0.9 • Alekhinet al. W2 > 12.25 RES. region stage 2 W2 > 3 stage 1 • S. Alekhin, Phys. Rev. D 63, 094022 (2001) • …. • S. Alekhin, J. Blumlein, S. Klein, S. Moch, Phys. Rev. D 81, 014032 (2010) • CTEQ6X Accardi, Christy, Keppel, Melnitchouk, Monaghan, Morfín, Owens, Phys. Rev. D 81, 034016 (2010) Accardiet al., in preparation stage 3? • Stage 3 (future): • CTEQ6X: future?

  8. Corrections beyond Leading Twist • Operator Product Expansion: beyond LT: higher twist (HT) leading twist (LT) • To extend to large x and low->intermediate Q2: 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) … least List from A. Accardi (talk at INT09)

  9. PDFs Extraction: Calculations beyond LT (Hall C E00-116) CTEQ6X: A. Accardiet al.,Phys. Rev. D 81, 034016 (2010) residual power corrections (HT) LT+TMC • TMC via colinear factorization (CF) method • HT: applied multiplicatively; same for proton as for neutron • NLO global fit to proton and deuteron data with Q2 > 1.69 GeV2 and W2 > 3 GeV2: DIS from SLAC, JLab, FNAL Drell-Yan, W asymmetry data at higher x cut 0: Q2 > 4 GeV2, W2 > 12.25 GeV2(standard) cut 1: Q2 > 3 GeV2, W2 > 8 GeV2 cut 2: Q2 > 2 GeV2, W2 > 4 GeV2 cut 3: Q2 > 1.69 GeV2, W2 > 3 GeV2

  10. PDFs Extraction: Calculations beyond LT CTEQ6X: A. Accardiet al.,Phys. Rev. D 81, 034016 (2010) • 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 no direct constraints from data • u and d ~ stable with respect to choice of TMC if flexible enough param. of HT is used

  11. PDFs Extraction: Calculations beyond LT CTEQ6X: A. Accardiet al.,Phys. Rev. D 81, 034016 (2010) • d-quark constrained by Deuterium data: • 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. smearing function Accardiet al., in preparation

  12. PDFs Extraction: Calculations beyond LT S. Alekhin, Phys. Rev. D 63, 094022 (2001) … S. Alekhin, J. Blumlein, S. Klein, S. Moch, Phys. Rev. D 81, 014032 (2010) • NNLO global fit to data with W2 > 3.4 GeV2 • 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]

  13. CTEQ6X vs ALEKHIN et al. off-shell (K-P) on-shell Comparisons of full calculations CTEQ6X(standard)/ALEKHIN • F2p (direct constraints from data): very good agreement • within 5% up to x = 0.8 • within 15% at x = 0.9 • F2d (direct constraints from data): very good agreement • within 5% up to x = 0.8 • F2n: good agreement • within 15% up to x = 0.7 • within 20-25% at x = 0.8 sensitive to nuclear corrections

  14. CTEQ6X vs ALEKHIN et al. Comparisons of full calculations CTEQ6X(K-P off-shell)/ALEKHIN • F2p comparisons (direct constraints from data): mostly insensitive to off-shell corrections in CTEQ6X (x < 0.9) • F2dcomparisons (direct constraints from data): mostly insensitive to off-shell corrections in CTEQ6X (x < 0.8) • F2ncomparisons: ~ 15-20% change; • CTEQ6X(K-P off-shell)/ALEKHIN closer to unity

  15. CTEQ6X vs ALEKHIN et al. Compare: relative contributions of various effects (HT) • TMC contributions same for both calculations (OPE) • nuclear corrections: similar treatment • HT contributions differ: more for F2n than F2p • Difference in HT for F2n correlated to difference in LT?

  16. PDFs extraction: into the Res. Region? • Need good (& extended) Q2 coverage from data at fixed x for a thorough study of PDFs extraction at large x stage 1 W2 > 12.25 W2 > 3 stage 2 resonances stage 3? • Use quark-hadron duality to access • even larger x and provide good • Q2coverage at large x for PDF studies 2nd res. Region: Q2 = 2 GeV2 2nd res. Region: Q2 = 5 GeV2

  17. Quark-Hadron Duality • Duality between quark and hadrondescriptions of observables in electron-hadron scattering Random facts about quark-hadron duality • observed by Bloom and Gilman in proton F2 (1969) • firmly established for proton F2 and FL (JLAB) • studied in spin-dependent in semi-inclusive scattering (JLAB) • recently acknowledged in neutron F2 (JLAB) • interpreted in OPE as cancellations of dynamical HT • … Quark-Hadron Duality: experimental observation which could be a working hypothesis for extending PDFs at large x => needs to be verified and quantified

  18. Quantifing Quark-Hadron Duality Region WminWmax 1st 1.3 1.9 2nd 1.9 2.5 3rd 2.5 3.1 4th 3.1 3.9 DIS 3.9 4.5 To what extent the resonance region data average to the QCD curve? DIS 4th 3rd 2st 2nd 2st 1st Calculate:

  19. Quark-Hadron Duality in F2p • To what extent the resonance region dataaverage to a (stage 2)QCD curve (Alekhin03)? • Within 10% : globally, low W DIS, 4th, 3rd, 2nd • 1st : 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 S.P. Malaceet al., Phys. Rev. C 80, 035207 (2009)

  20. Quark-Hadron Duality in F2n • Some arguments: quark-hadron duality in F2p could be the result of accidental cancellations between quark charges (do not occur for F2n)… • Is quark-hadron duality an accident? Verify quark-hadron duality in F2n Need F2n in the resonance region… New method : employs iterative procedure of solving integral convolution equations Y. Kahn, W. Melnitchouk, S.A. Kulagin, Phys. Rev. C 79, 035205 (2009) • Impulse Approximation – virtual photon scatters incoherently from individual nucleons nuclear F2 smearing function nucleon F2

  21. Extraction of F2n from Data • Use proton and deuteron data at fixed Q2 (matched kinematics) data data model model • Data: SLACatQ2 = 0.6, 0.9, 1.7, 2.4GeV2+ data fromJlab(Hall C E00-116)at Q2= 4.5, 5, 5.5, 6.2, 6.4 GeV2 quasielastic peak • 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 F2n S.P. Malace, Y. Kahn, W. Melnitchouk, C. Keppel, Phys. Rev. Lett. 104 102001 (2010)

  22. F2n in the Resonance Region • F2n in resonance region: 3 resonant enhancements (fall with Q2 at ~ rate as for F2p) • F2n in resonance region appears to average to F2n from Alekhin09 S.P. Malace, Y. Kahn, W. Melnitchouk, C. Keppel, Phys. Rev. Lett. 104 102001 (2010) S.P. Malace, Y. Kahn, W. Melnitchouk, in preparation

  23. Quark-Hadron Duality in F2n • To what extent the resonance region dataaverage to a (stage 2)QCD curve (Alekhin09)? W2 : (1.3-1.9) GeV2 • 1st RES region: agreement worsens at the highest Q2 (corresponds to the largest x) W2 : (1.9-2.5) GeV2 • 2nd and 3rdRES regions: agreement within 15-20%, on average W2 : (2.5-3.1) GeV2 • globally remarkable agreement: within 10% S.P. Malace, Y. Kahn, W. Melnitchouk, C. Keppel, Phys. Rev. Lett. 104 102001 (2010)

  24. Plans for Future: Quark-Hadron Duality (in preparation for) Stage 3… A. Accardi, S.P. Malace, in preparation • 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. preliminary

  25. Plans for Future: Quark-Hadron Duality (in preparation for) Stage 3… A. Accardi, S.P. Malace, in preparation • Study applicability of QCD calculation at low values of W; criterion: separation between target jet and current jet, preliminary preliminary

  26. Plans for Future: Quark-Hadron Duality (in preparation for) Stage 3… A. Accardi, S.P. Malace, in preparation • Extend studies to larger Q2 preliminary

  27. Plans for Future: E12-10-002 @ 12 GeV Spokespeople: S.P. Malace (contact person), I.M. Niculescu, C. Keppel E12-10-002 (Hall C): approved by PAC35 Will extend proton and deuteron F2precision measurements to larger x and Q2by measuring H(e,e’) and D(e,e’) cross sections in the resonance region and beyond up to Q2 ~ 17 GeV2 and x ~ 0.99 We aim for similar precision as for the lower energy run E00-116

  28. Plans for Future: E12-10-002 @ 12 GeV • Expected kinematic coverage in the ratio deuteron to proton truncated moments from E12-10-002

  29. Plans for Future: E12-10-002 @ 12 GeV • Expected kinematic coverage in the ratio deuteron to proton truncated moments from E12-10-002

  30. Plans for Future The 3rd International Workshop on Nucleon Structure at Large Bjorkenx (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 http://conferences.jlab.org/HiX2010/

  31. Plans for Future: Py in 4He(e,e’p)3H No connection to what I discussed up to this point… • E03-104 in Hall A: search for medium modifications of the proton structure in4He(e,e’p)3H Mike Paolone(Ph.D. in Dec. 2008): M. Paolone, S. Malace, S. Strauchet al., accepted for publication to Phys. Rev. Lett. • Induced polarization Py: my primary responsibility in the project http://www.jlab.org/intralab/calendar/phys_seminar/2010/Malace_talk.pdf S.P. Malace, M. Paolone, S. Strauchet al., in preparation

More Related