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Some preliminary thoughts: Tracking & F L measurement

Some preliminary thoughts: Tracking & F L measurement. (Zeus-prel-10-001) Inclusive cross section Data from H1 and ZEUS Beam energies: E p = 920, 460, 575 GeV Takes correlations of systematics in to account resulting in improved accuracy

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Some preliminary thoughts: Tracking & F L measurement

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  1. Some preliminary thoughts: Tracking & FL measurement (Zeus-prel-10-001) • Inclusive cross section Data from H1 and ZEUS • Beam energies: Ep = 920, 460, 575 GeV • Takes correlations of systematics in to account resulting in improved accuracy • FL is extracted in the region of 2.5<Q2<800 GeV2 F_{L} systematic uncertainty: Comments Abhay

  2. At low Q2 the total DIS cross section is defined by two structure functions: • F2 is dominant, FL is only visible at high “y” • Measurements at fixed (x,Q2) but different y allow solving for F2 & FL simultaneously. F_{L} systematic uncertainty: Comments Abhay

  3. Data sets: ZEUS cross section: Ep = 460, 575, 920 H1 preliminary at lower energies & published 920 2.5 < Q2 <800 GeV2 and 0.85 < y < 0.1 • The data from y < 0.35 binned “together” Electron method to determine the event kinematics: optimal for high y F_{L} systematic uncertainty: Comments Abhay

  4. Systematic uncertainties: • EM & Hadronic energy scales • Detector alignment • Background subtraction • Electron reconstruction efficiency A Study for US to pursue: (example) Vary the one of the above (blue for example) in the GEANT code and compare the extracted values of x,y,Q2 as the reconstructed E’ and Q’ change as a result. • Elke, Marcus D. have shown a plot for FL at the INT workshop. We could initiate a study from that point onwards. F_{L} systematic uncertainty: Comments Abhay

  5. Slides added by ELKE F_{L} systematic uncertainty: Comments Abhay

  6. unpolarized DIS at an EIC • precision data for F2 may help to resolve some issues with old fixed target data • (nice to have, but only “incremental” with little impact; cannot beat HERA at small x) • longitudinal structure function FL- basically missed at HERA (fixed Ee, Ep) interesting for several reasons: • hard to get; recall •  contributes mainly at large y (= low x for a given Q2) strategies: • indirect measurement from deviation of σr from “F2 only fit” • slope of y2/Y+for different S at fixed x and Q2strength of an EIC • FL starts only at O(αs) (due to helicity conservation) this is the LO expression

  7. longitudinal structure function FL - cont’d best motivation for a precise measurement at the EIC in 10+ years is not to determine the gluon density but to understand pQCD series • known up to three loops (NNLO) Moch, Vermaseren, Vogt • leading small x term • appears first at NNLO • sensitivity to small x term • at lowish Q2 values (few GeV2)

  8. 1st feasibility study for E. Aschenauer 5x50 - 5x325 running FL “slopes” (examples) TO DO: refine & test how well we can extract FL with high precision

  9. selected open issues in flavor structure strangeness was identified to be one of the least known quantities – both unpolarized and polarized – where significant progress is unlikely w/o the EIC DSSV (incl. all latest COMPASS data) NNPDF collaboration data • surprise: Δs small & positive from SIDIS data • but 1st moment is negative and sizable due • to “constraint” from hyperon decays (F,D) • (assumed SU(3) symmetry debatable M. Savage) • drives uncertainties on ΔΣ (spin sum) • substantial uncertainties • known issues with HERMES data at large x • hot topic: we really need to determine it ! (as well as their u,d quark colleagues)

  10. flavor separation with semi-inclusive DIS at LO: extra weight for each quark allows for full flavor separation if enough hadrons are studied complications/additional opportunities: actual analysis of data requires NLO QCD where x, z dependence is non-trivial • PDF information entangled with fragmentation functions • should be not a problem: already known pretty well (DSS), more data (Belle, LHC, …) • EIC: if needed, can play with x & z integration/binning to reduce uncertainties • (needs to be studied in more detail) relevant quantities/measurements: • (un)polarized SIDIS cross sections (we don’t want to study asymmetries anymore at an EIC) • for u, ubar, d, dbar, s, sbar separation need H = π+, π-, K+, K- (nice to have more)

  11. 1st studies done for charged kaons Aschenauer, MS compute K+ yields at NLO with 100 NNPDF replicas z integrated to minimize FF uncertainties (work in progress) 5×250 GeV actual uncertainties much smaller than points one month of running PYTHIA agrees very well (despite different hadronization) --> confidence that we can use MC to estimate yields & generate toy data

  12. kaon studies – cont’d how about K- (relevant for separation) next step: assess impact of data on PDFs with “reweighting method” (using full set of stage-1 energies: 5×50 – 5×325) Giele, Keller; NNPDF to do: include also π±; polarized SIDIS and impact on global fit

  13. Tools available for simulation: • Monte Carlos generators • DJANGOH simulates FL with radiative corrections for proton and nuclei • have a root-routine, which can re-weight events with momentum, Energy, • angular resolution functions as well as acceptance • will also include functions, which describe PID responses • Tom B. is working on a nice easy to use full simulation of the detector F_{L} systematic uncertainty: Comments Abhay

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