1. ECT* workshop “Flavor structure of the nucleon sea” Trento July 1 st, 2013 Ralf Seidl (RIKEN)

2. Outline Real W production to access sea quarks and helicities Current sea helicities W production and expected sensitivites RHIC, PHENIX, STAR and recent polarized runs Central W measurements Cross section measurements Asymmetries Forward W measurements Upgrades Asymmetries Outlook 7/01/2013 R.Seidl: RHIC W results2

3. Most recent global analysis : DSSV NLO analysis Inclusion of SIDIS data before COMPASS Inclusion of RHIC A LL data( from 200GeV) Using most recent NLO fragmentation functions (DSS) Large uncertainties still for sea quarks Decay data forces  s to become negative at small x RHIC data results in node to  g 7/01/2013 R.Seidl: RHIC W results 3 de Florian et al., PRL101, 072001 (2008)

4. Real W production as access to quark helicities Maximally parity violating V- A interaction selects only lefthanded quarks and righthanded antiquarks:  Having different helicities for the incoming proton then selects spin parallel or antiparallel of the quarks  Difference of the cross sections gives quark helicities  q(x) No Fragmentation function required Very high scale defined by W mass 7/01/2013 R.Seidl: RHIC W results 4 Bourrely, Soffer Nucl.Phys. B423 (1994) 329-348

5. Quark and antiquark helicities probed in W production Building single spin asymmetries of decay lepton Positive lepton asymmetries sensitive to  u (x) and  d (x) Negativ lepton asymmetries sensitive to  d (x) and  u (x) 7/01/2013 R.Seidl: RHIC W results 5 But unfortunately we don’t have a 4  detector, Need to find the Ws inclusively via their decay leptons

6. Sea quark polarization via W production  Single spin asymmetry proportional to quark polarizations Large asymmetries Forward/backward separation smeared by W decay kinematics 7/01/2013 R.Seidl: RHIC W results6 e-e- e+e+ ++ ++ -- --

7. W vs lepton asymmetries Clear correlation for W: valence quark polarization  forward sea quark  backward However, not for decay muon/electron: enhanced for W -, mixed for W + reversed effect for neutrino asymmetry neutron target reverses that due to isospin asymmetry  run He3 collisions eventully? x is not affected by this; still forward is larger x, backward smaller x 7/01/20137  u/u  d/  d  d/d u/uu/u u/uu/u  u/u  d/  d  u/u  d/  d u/uu/u  d/d

8. W kinematics 7/01/2013R.Seidl: RHIC W results8

9. Pythia: quark flavors and x ranges 7/01/2013 R.Seidl: RHIC W results 9 W -   case: almost entirely forward d quarks and backwards  u W +   case: predominantly forward  d quarks and backwards u Central Forward

10. Expected sea quark sensitivities Inclusion of W channels into global analysis DSSV prepared Expected impact with about 200 pb -1 in PHENIX and STAR in -2 <  <2 estimated 7/01/2013 R.Seidl: RHIC W results 10 Reduction of uncertainties in sea quark polarizations of above x~0.1 substantial deFlorian, Vogelsang: Phys.Rev. D81 (2010) 094020

11. 11 Relativistic Heavy Ion Collider 2 Spin Experiments PHENIX Electron detection |  | <0.35 (EMCal, Drift chambers, RICH, VTX) Muon arms 1.2 < |  | < 2.4 (MuonTracker, ID, RPCs, FVTX) STAR Electron detection -1 <  < 1 (2) (TPC,EmCals) RHIC Characteristics 2 counter-circulating rings 3.8 km in circumference Top Energies (each beam): 7-100GeV / Au-Au 31-255GeV / p-p Mixed Species (d+Au) 7/01/2013 R.Seidl: RHIC W results

12. 12 RHIC Polarized Proton Collider Polarized Source 200 MeV Polarimeter AGS Internal Polarimeter RHIC pC Polarimeters Absolute Polarimeter (H jet) AGS pC Polarimeter Siberian Snakes Helical Partial Snake local polarimetry spin rotators around IPs at PHENIX and STAR local polarimetry 7/01/2013 R.Seidl: RHIC W results RunEnergyPolarizationLongitudinal [GeV][%]L [pb -1 ]LP 4 [pb -1 ]LP 2 [pb -1 ] 200950036398.60.321.3 20115005254181.45.0 20125105557303.19.8 2013510545515613.945.0

13. 7/01/2013 R.Seidl: RHIC W results13

14. Central W analysis General Strategy: Find the Jacobian Peak ( ~0.5 M W ) in Energy or Pt spectrum for electrons Clean up backgrounds by E/P and isolation criteria including away side (neutrino direction) if possible 7/01/2013 R.Seidl: RHIC W results 14

15. Raw electron yields Raw electron Pt or energy spectra and after successively applying shower shape and isolation selection criteria 7/01/2013 R.Seidl: RHIC W results 15 STAR

16. Jacobian peaks and background fraction After all cuts sizeable signals and little background remain 7/01/2013 R.Seidl: RHIC W results 16

17. W Cross sections Correcting acceptance and efficiencies one can obtain the absolute W/Z cross sections: Excellent agreement of the scale dependence from RHIC to LHC 7/01/2013 R.Seidl: RHIC W results 17 PRL 106:062001(2011) PRD 85 (2012) 092010

18. First W results In 2009: First exploratory RHIC run at 500 GeV Both, PHENIX and STAR obtained first central rapidity results, PRL 106:062001(2011) PRL 106:062002(2011) Real W production can be used to access the sea quark polarization! 7/01/2013 R.Seidl: RHIC W results18 PHENIX

19. Central W asymmetries 7/01/2013 R.Seidl: RHIC W results 19 Stevens, arXiv:1302.6639

20. 7/01/2013 R.Seidl: RHIC W results20

21. Forward W analysis W momentum cannot be ignored Jacobian peak only visible for forward moving W + decaying at close to 90 degrees Need to understand and suppress backgrounds lacking distinct signal signature 7/01/2013 R.Seidl: RHIC W results 21 Pythia 6.4, muons in rapidities 1.2 – 2.4

22. Forward Tracking into the Endcap: STAR FGT Upgrade FGT: 6 light-weight triple-GEM disks using industrially produced GEM foils (Tech-Etch Inc.) Needed for charge separation: Goal: resolution of ~100  m η=1 η=2 FGT e +/- 2mm Sagitta (cm) TPC Barrel EMCc Endcap EMC Lightweight, Triple-GEM Detector Slides courtesy of A.Vossen and A. Ogawa 7/01/2013 R.Seidl: RHIC W results22

23. STAR Forward GEM Tracker Commissioning Run 12 Strip Layout Single Track Event Display Run 12 configuration x [cm] y [cm] Slides courtesy of A.Vossen and A. Ogawa 7/01/2013 R.Seidl: RHIC W results23

24. STAR FGT Installation for Run13 Slides courtesy of A.Vossen and A. Ogawa 7/01/2013 R.Seidl: RHIC W results24

25. PHENIX Muon trigger upgrade σ(tot)=60mb, L=3x10 32 cm -2 s -1 (500GeV) collision rate = 18MHz (after luminosity upgrade) DAQ rate limit < 2kHz (for muon Arm) Therefore, required rejection ratio > 9000 But, MuID-trigger rejection ratio (500GeV) < 100 A higher momentum trigger is needed 7/01/2013 R.Seidl: RHIC W results 25 PYTHIA5.7 W dominant region current trigger (MuID) threshold

26. PHENIX Muon Trigger Upgrade detectors 26 MuID trigger selecting muon momentum > 2GeV/c MuTR FEE upgrade fast selection of high-momentum-tracks RPC provide timing information and rough position information μμ MuID MuTR RPC absorber R.Seidl: RHIC W results 7/01/2013

27. RPC Muon Trigger Upgrade R.Seidl: RHIC W results27 digitized hit signal Level-1 trigger digitized hit signal digitized hit signal B MuTr timing information rough position information sagittaLevel-1 trigger board Level-1 RPCproject MuTRGproject 7/01/2013

28. PHENIX Forward W trigger upgrade installation and commissioning 7/01/2013 R.Seidl: RHIC W results 28

29. Forward Muon Backgrounds Real muons from heavy flavor and DY decays get smeared to higher transverse momenta Low energetic hadrons (huge cross section) decay within the muon tracker, mimicking a straight track Raw yields 3 orders above signal 7/01/2013 R.Seidl: RHIC W results 29

30. Reducing the background components Apply sensitivity to multiple scattering to reduce hadronic backgrounds Initially (2011) cut based removal of backgrounds Improved by using likelihood based pre- selection and unbinned max likelihood fit 7/01/2013 R.Seidl: RHIC W results 30 W Simulation Data

31. Multivariate analysis Define Wness likelihood using 5 kinematic variables based on signal MC and data ( = mostly BG) 7/01/2013 R.Seidl: RHIC W results 31 After preselecting W like events (>0.92) perform unbinned max likelihood fit in independent variables rapidity and effective bending angle f > 0.92

32. Forward W asymmetries After extracting S/BG ratios ( in 2012 preliminary data ~0.3) extract asymmetries and correct for BG (BG asymmetries are consistent with zero ) Inclusion of FVTX information will improve BG rejection (isolation, multiple scattering) 2011 and 2012 Analysis will be finalized soon 2013 data analysis is ongoing 7/01/2013 R.Seidl: RHIC W results 32

33. Outlook 7/01/2013 R.Seidl: RHIC W results 33 RHIC Spin NSAC write-up: Aschenauer et. al: arXiv:1304.0079

34. Expected impact of full data set Substantial uncertainty improvement of the sea quark helicities DSSV framework ready to include W asymmtries (see M. Stratmann’s talk) NNPDF in the process of including W asymmetries (see A. Guffanti’s talk) 7/01/2013 R.Seidl: RHIC W results 34

35. 7/01/2013 R.Seidl: RHIC W results35

36. pp @ 500 GeV 3 He p @ 432 GeV W Outlook 3 He p collisions 36 caveat: A L study assumes 216 GeV 3 He beam but 325 GeV × Z/A was too optimistic conservative: 250 GeV × 2/3 = 166 GeV does not affect A L much but cross section smaller caveat: A L study assumes 216 GeV 3 He beam but 325 GeV × Z/A was too optimistic conservative: 250 GeV × 2/3 = 166 GeV does not affect A L much but cross section smaller Marco Stratman (BNL) 7/01/2013 R.Seidl: RHIC W results

37. Forward W decays Forward W decays advantages: largest sensitivity to the anti-u quark polarization some sensitivity to the anti-d quark polarizaiton (due to decay kinematics) With high statistics possibility to test d pol sign change But no Jacobian peak, experimentally more difficult 7/01/2013 R.Seidl: RHIC W results 37 uu dd dd uu Pythia 6.4

38. Decay kinematics due to helicity conservation 7/01/2013 R.Seidl: RHIC W results 38 W+W+ W-W-

39. Sea quark polarization via W production Parity violation of weak interaction selects: lefthanded quarks and righthanded antiquaks  proton spin selects (anti)parallel quark/antiquark spins  Single spin asymmetry proportional to quark polarizations 7/01/2013 R.Seidl: RHIC W results39 e-e- e+e+ ++ ++ -- --

40. Sea quark polarization via W production Parity violation of weak interaction selects: lefthanded quarks and righthanded antiquaks  proton spin selects (anti)parallel quark/antiquark spins  Single spin asymmetry proportional to quark polarizations Large asymmetries 7/01/2013 R.Seidl: RHIC W results40 e-e- e+e+ ++ ++ -- --

41. Forward W analysis W momentum cannot be ignored Jacobian peak only visible for forward moving W + decaying at close to 90 degrees Need to understand and suppress backgrounds lacking distinct signal signature 7/01/2013 R.Seidl: RHIC W results 41 Pythia 6.4, muons in rapidities 1.2 – 2.4