some preliminary thoughts: tracking & f l measurement

F_{L} systematic uncertainty: Comments Abhay

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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

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• 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.

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Data sets: ZEUS cross section: Ep = 460, 575, 920H1 preliminary at lower energies & published 9202.5 < 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

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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.

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Slides added by ELKE

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)

• indirect measurement from deviation of σr from “F2 only fit”• slope of y2/Y+ for different S at fixed x and Q2 strength of an EIC

strategies:

• FL starts only at O(αs) (due to helicity conservation)

this is theLO expression

longitudinal structure function FL -

cont’dbest 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)

1st feasibility study for

E. Aschenauer

5x50 - 5x325 running

TO DO:

refine & testhow well we can extract FL with high precision

FL “slopes”(examples)

selected open issues in flavor

structurestrangeness 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)

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)

we really need to determine it ! (as well as their u,d quark colleagues)

NNPDF collaboration

• substantial uncertainties• known issues with HERMES data at large x• hot topic:

flavor separation with semi-inclusive

DIS

at LO: extra weightfor each quark

actual analysis of data requires NLO QCD where x, z dependence is non-trivialallows for full flavor separation if enough hadrons are studied

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)

complications/additional opportunities:• 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)

1st studies done for charged kaonsAschenauer, MS

compute K+ yields at NLO with 100 NNPDF replicasz integrated to minimize FF uncertainties (work in progress)

PYTHIA agrees very well (despite different hadronization) --> confidence that we can use MC to estimate yields & generate toy data

actual uncertaintiesmuch smaller than points

one month of running

5×250 GeV

kaon studies – cont’d

to do: include also π± ; polarized SIDIS and impact on global fit

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

how about K- (relevant for separation)


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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

some preliminary thoughts: tracking & f l measurement

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