2. E.C. Aschenauer Why run top-energy p+p in run-16 2 Transverse momentum dependent parton distribution functions  initial state effects  important in calculating cross-sections in a range of processes  provide a way to image the proton in transverse and longitudinal momentum space (2+1d)  provide access to spin-orbit correlations  provide constrains to quark-gluon-quark correlations  are important to describe the gluon distribution at low-x  CGC  the most popular explanation for the large A N seen in transverse p+p of special interest: The Sivers function, of special interest: The Sivers function, it describes the correlation of the parton transverse momentum with it describes the correlation of the parton transverse momentum with the transverse spin of the nucleon. the transverse spin of the nucleon. Transverse momentum dependent fragmentation functions  final state effects  describe a correlation of the transverse spin of a fragmenting quark and the transverse momentum of a hadron  Collins FF  Collins FF

3. 3 Q  QCD Q T /P T <<<< Collinear/twist-3 Q,Q T >>  QCD p T ~Q Transversemomentumdependent Q>>Q T >=  QCD Q>>p T Intermediate Q T Q>>Q T /p T >>  QCD Sivers fct. Efremov, Teryaev; Qiu, Sterman Need 2 scales Q 2 and p t Remember pp: most observables one scale Exception: DY, W/Z-production Need only 1 scale Q 2 or p t But should be of reasonable size should be applicable to most pp observables A N (  0 /  /jet) E.C. Aschenauer related through Why run top-energy p+p in run-16

4. E.C. Aschenauer 4 Initial State Final State  A N as function of rapidity, E T, p T and x F for inclusive jets, p T and x F for inclusive jets, direct photons direct photons  A N for heavy flavour  gluon  A N as a function of rapidity, p T for W +/-, Z 0, DY p T for W +/-, Z 0, DY  A UT as a function of the azimuthal dependence of the correlated hadron dependence of the correlated hadron pair on the spin of the parent quark pair on the spin of the parent quark (transversity x interference FF) (transversity x interference FF)  Azimuthal dependences of hadrons within a jet (transversity x Collins FF) a jet (transversity x Collins FF)  A N as function of rapidity, p T and x F for inclusive identified hadrons inclusive identified hadrons (transversity x Twist-3 FF) (transversity x Twist-3 FF) TMD, TWIST-3, Collinear Why run top-energy p+p in run-16

5. 5 DIS:  q-scattering attractive FSI pp:qqbar-anhilation repulsive ISI QCD:QCD:QCD:QCD: Sivers DIS = - Sivers DY or Sivers W or Sivers Z0 Measure non-universality of sivers-function E.C. Aschenauer All three observables can be addressed through a 500 GeV Run A N (direct photon) measures the sign change in the Twist-3 formalism Critical test of factorization in QCD no sign change  need to rethink QCD factorization Why run top-energy p+p in run-16

6. much stronger then any other known evolution effects needs input from data to constrain non-perturbative part in TMD evolution current data extremely limited further constraints cannot come from fixed target SIDIS  too small lever arm in Q 2 & p t NOTE: the same evolution applies to TMD FFs, i.e. Collins and to e + e -, SIDIS  eRHIC E.C. Aschenauer 6 Z. Kang: original paper arXiv:1401.5078 Z.-B. Kang & J.-W. Qui arXiv:0903.3629 before evolution after evolution ÷ ~10 ÷ ~10 4 < Q < 9 GeV 0 < q T 1 GeV DY 500 GeV 200 GeV Z.-B. Kang & J.-W. Qui Phys.Rev.D81:054020,2010 ÷ ~4 ÷ ~4 Z. Kang et al. arXiv:1401.5078 before evolution after evolution Why run top-energy p+p in run-16

7. E.C. Aschenauer 7  What is the sea-quark Sivers fct.?  W’s ideal  rapidity dependence of A N separates quarks from antiquarks  no constraint from existing SIDIS data Z. Kang A N (W +/-,Z 0 ) accounting for sea quark uncertainties through positivity bounds all plots after evolution (arXiv:1401.5078) Why run top-energy p+p in run-16

8. E.C. Aschenauer 8 proof of principle analysis by STAR (S. Fazio for the collaboration, DIS-2014) Need to reconstruct W kinematics as lepton asymmetry cannot be resolved due to resolution effects Apply analysis technique developed at the Tevatron and used at LHC i.e. CDF PRD 70, 032004 (2004) Philosophy: W  l+  as  is not seen  reconstruct W through lepton and recoil Why run top-energy p+p in run-16

9. E.C. Aschenauer 9 Analysis Strategy to fully reconstruct Ws: Follow the analysis steps of the A L  W candidate selection via high p t lepton Data set: 2011 transverse 500 GeV data (25 pb -1 ) In transverse plane: In transverse plane: Recoil reconstructed using tracks and towers: Recoil reconstructed using tracks and towers: Part of the recoil not within STAR acceptance Part of the recoil not within STAR acceptance  correction through MC (Pythia)  correction through MC (Pythia)  MC-correction  MC-correction Why run top-energy p+p in run-16

10. W Rapidity reconstruction: W longitudinal momentum (along z) can be calculated from the invariant mass: W longitudinal momentum (along z) can be calculated from the invariant mass: Neutrino longitudinal momentum component from quadratic equation Neutrino longitudinal momentum component from quadratic equation E.C. Aschenauer Why to run transvers pp in run-16 10 GOOD data/MC agreement Systematics determined through a MC challenge method input asymmetries from arXiv:1401.5078 and reconstruct it back Measuring the sign change through DY STAR is investigating in detail if sensitive DY measurements are possible using several forward-upgrade scenarios The biggest challenge is QCD-background suppression of 10 6 -10 7 10 6 -10 7 QCD DY

11. E.C. Aschenauer Why to run transvers pp in run-16 11 Assumptions: integrated delivered luminosity of 400 pb -1  7 weeks transversely polarized p+p at 510 GeV  electron lenses are operational and dynamic  -squeeze is used throughout the fill throughout the fill  smoothed lumi-decay during fills  reduced pileup effects in TPC  high W reconstruction efficiency Will provide data to constrain TMD evolution sea-quark Sivers fct sea-quark Sivers fct test sign-change if TMD evolution ÷ ~5 or less test sign-change if TMD evolution ÷ ~5 or less

12. E.C. Aschenauer Why to run transvers pp in run-16 12  HP13 is being pursued also by others, notably COMPASS  knowledge about TMD evolution influences many other projects/plans  physics of RHIC forward upgrades  pp/pA-LoI  flavor separation of transversity and Sivers fct.  A N for DY  TMD physics of an EIC  STAR will not benefit from a luminosity increase for these measurements  TPC is pile-up limited  luminosity numbers in the pp/pA LoI charge correspond to ~5 multiple interactions per bunch  needs LHC technologies/techniques interactions per bunch  needs LHC technologies/techniques  no new SIDIS input to constrain non-perturbative component in TMD-evolution before EIC TMD-evolution before EIC

13. Note: similar capabilities with PHENIX MPC-EX E.C. Aschenauer 13 A N for direct photon production: STAR FMS-PreShower: 3 layer preshower in front of the FMS,   distinguish photons, electrons/positrons and charged hadrons  installed for RUN-15  sensitive to sign change, but in TWIST-3 formalism  not sensitive to TMD evolution  no sensitivity to sea-quarks; mainly u v and d v at high x  collinear objects but more complicated evolutions than DGLAP  indirect constraint on Sivers fct. Not a replacement for a A N (W +/-, Z 0, DY) measurement but an important complementary piece in the puzzle Why run top-energy p+p in run-16

14. E.C. Aschenauer 14 A N (W +/-,Z 0 )A N (DY)AN()AN() sensitive to sign change through TMDs yes no sensitive to sign change through Twist-3 T q,F (x,x) no yes sensitive to TMD evolution yes no sensitive to sea- quark Sivers fct. yes no need detector upgrades noyes at minimum: FMS postshower yes installed for run-15 biggest experimental challenge integrated luminositybackground suppression & integrated luminosity need to still proove analysis on data A N (W +/-,Z 0 ) clean and proven probe sensitive to all questions in a timely way without the need for upgrades in a timely way without the need for upgrades Why run top-energy p+p in run-16