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Marco Stratmann

What can be done with possible He3 W-boson A L data. Marco Stratmann. Regensburg / Wurzburg. RSC meeting, Ames, Iowa, May 14 th - 16 th , 2010. quick reminder: A L for W bosons . key measurement at RHIC. based on parity violation: W’s couple only to one parton helicity. study

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Marco Stratmann

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  1. What can be done with possible He3 W-boson AL data Marco Stratmann Regensburg / Wurzburg RSC meeting, Ames, Iowa, May 14th- 16th, 2010

  2. quick reminder: AL for W bosons key measurement at RHIC • based on parity violation: W’s couple only to one partonhelicity study single spin asymmetries • neat handle on flavor separation in global analysis; • large asymmetries; large scale Q=MWwhere pQCD works • RHIC: can detect only decay leptons; lepton rapidity most suited observable • strong correlation with x1,2 • allows for flavor separation for x > 0.07 • new versatile NLO MC code “CHE” available de Florian, Vogelsang, arXiv:1003.4533 • easily implemented in global analysis

  3. expectations for ALein pp collisions de Florian, Vogelsang t large u large t large u large strong sensitivity to limited sensitivity to

  4. W program in pp collisions: what can we learn? • “CHE” integrates nicely into DSSV global analysis code based on Mellin moments Δχ2 = 2% uncertainty bands of DSSV analysis simulated impact of RHIC W boson data on global fit • reduction of uncertainties • for 0.07 < x < 0.4 • can test consistency of • low Q2 SIDIS data in • that x regime de Florian, Vogelsang

  5. ALW: pp vsHe3-p collisions pp @ 500 GeV He3-p @ 432 GeV

  6. discussion – pros and cons pros polarized He-3 mainly a neutron target: 0.865 n + 2*(-0.027) p • important information for flavor • separation complementary to pp cross section enhanced (nuclear “target”) cons need maximum possible c.m.s. energy: 216 GeV protons on 216 GeV/n He-3 (feasible? – otherwise W cross section too small) unpolarized He-3 a combination of p and n  no longerprobingΔq/q as in pp; but irrelevant “complication“ in a global analysis need significant running time/luminosity for both pp and He-3 O(few hundred pb-1) each; but some “synergy effects” of combined set in global fit

  7. conclusions certainly an interesting avenue to arrive at a full u,d flavor separation at RHIC if we want to pursue this further, we can play with “pseudo data” not a free lunch – significant integrated luminosity needed would compete with other goals: more 200GeV running; transverse spin; … most likely, AL on its own does no justify the effort need a stronger physics case for He-3 at RHIC

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