Forward spin + cold nuclear measurements and forward Calorimetry Korea-Japan workshop, Hanyan University 2015/10/20 Ralf Seidl (RIKEN)

Remaining spin/CNM questions at RHIC What causes these large single transverse spin asymmetries? Final state effects (transversity x higher twist fragmentation functions, partially related to Collins FF) Initial state effects (higher twist correlation function related to Sivers function) Other source such as diffraction Spin asymmetries in pA to get sensitivity to gluon saturation Diffractive Meson measurements in pp and pA to access GPD E and gluon saturation 2019/1/2 fsPHENIX

Transvsere spin questions continued Final state effects (eliminate initial state effect): directly access Collins asymmetries via jet + hadron asymmetries, also allows to reach unmeasured transversity x region Non Collins related final state effects: ? Initial state effects (eliminate final state effects): Direct photon and Jet asymmetries Is part of initial smallness due to u and d cancellation? Diffractive effects via proton tagging (Roman pots) Some answers will be there before 2020+ 2019/1/2 fsPHENIX

Jet asymmetries Only jet result so far with rather smaller asymmetries: Very little initial state effect or Cancellation of up and down “Sivers” contributions? AnDY 2019/1/2 fsPHENIX

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Collins asymmetries Measure AN for hadrons(pions) within a Jet Directly sensitive to Transversity X Collins Existence known from HERMES and COMPASS Also shown at higher PT at mid rapidity in STAR Forward rapidity for higher x extension 2019/1/2 fsPHENIX

x1 x2 ranges in rapidity slices 200 GeV p – p x1 x2 ranges in rapidity slices Baseline for TTPMC: 200 GeV pp Hard light processes (ckin > 1GeV), Hadrons in 1-4 rapidity range with Pt> 1GeV 2019/1/2 fsPHENIX

Expected asymmetries arXiv: 1505.05589 Transvsersity to higher x could be nicely accessed in forward region Still large uncertainties Particle identification expensive 2019/1/2 fsPHENIX

fsPHENIX Main requirements: Jet reconstruction (HCAL) Tracking for momentum and charge (GEMs) reconstruction Maybe muon identification (old MUID +X) Photon and electron reco/id ( MPC+EX? ) 2019/1/2 fsPHENIX

Sideview of ePHENIX 2019/1/2 fsPHENIX

The fHCAL General constraints are: z<4.5 m due to Quad magnet for EIC Return the flux of the BaBar solenoid Rapidity around 1.2-4, likely staged with forward first Follow EIC/STAR proposal by UCLA group (O.Tsai): Scintillator/Absorber sandwich detector WLS transport the light to the back  SiPMT readout 2019/1/2 fsPHENIX

STAR/UCLA prototype Taken from STAR pp/pA proposal, FNAL test beam in March 2014 2019/1/2 fsPHENIX

Diffraction Generally large rapidity gap in final state yields or (at least) one proton intact Most common interaction: Pomeron (two gluon) Because two gluon interaction sensitive to gluon density2 For spin asymmetries helicity flip needed  odderon? Experimentally: roman pots t = (p-p’)2 z = Mx2/W: momentum fraction of the exchanged object w.r.t. the hadron exact kinematics not known  factorization is violated 2019/1/2 fsPHENIX

STAR roman pots 2019/1/2 fsPHENIX

UPC in polarized pp↑ or Ap↑ Get quasi-real photon from one proton Ensure dominance of g from one identified proton by selecting very small t1, while t2 of “typical hadronic size” small t1  large impact parameter b (UPC) Two possibilities: Final state lepton pair  timelike compton scattering timelike Compton scattering: detailed access to GPDs including Eq/g if have transv. target pol. Challenging to suppress all backgrounds p p’ p p’ Z2 Au Au’ p p’ Final state lepton pair not from g* but from J/ψ Done already in AuAu Estimates for J/ψ (hep-ph/0310223) transverse target spin asymmetry  calculable with GPDs information on helicity-flip distribution E for gluons golden measurement for eRHIC polarized p↑A: gain in statistics ~ Z2 2019/1/2 fsPHENIX

RHIC as gA collider: UPC Ultra-peripheral (UPC) collisions: b > 2R → hadronic interactions strongly suppressed High photon flux ~ Z2 → well described in Weizsäcker-Williams approximation → high σ for -induced reactions e.g. exclusive vector meson production Coherent vector meson production: • photon couples coherently to all nucleons • pT ~ 1/RA ~ 60 MeV/c • no neutron emission in ~80% of cases Incoherent vector meson production: • photon couples to a single nucleon • pT ~ 1/Rp ~ 450 MeV/c • target nucleus normally breaks up 2019/1/2 fsPHENIX

Why UPC? Quarkonia photoproduction allows to study the gluon density G(x,Q2) in A as well as G(x,Q2, bT) LO pQCD: forward coherent photoproduction cross section is proportional to the squared gluon density Quarkonium photoproduction in UPC is a direct tool to measure nuclear gluon shadowing 2020+ UPC: “proton-shine”-case: Requires: RP-II* and 2.5 pb-1 p+Au Fourier transform of s vs. t  g(x,Q2,b) 2019/1/2 fsPHENIX

UPC at STAR R. Debbe 2 tracks in STAR and one neutron in each ZDC Au+Au  n+n+e+e- no attempt for a Fourier transform of s vs. t has been made  g(x,Q2,b) 2019/1/2 fsPHENIX

Other spin/CNM aspects More DY and direct photon measurements in pp (Sivers sign change) and pA (saturation effects, clean initial state ) Nuclear fragmentation functions (jets+hadrons, preferably identified) Incremental measurements: More ALL measurements for (di)jets and hadrons 2019/1/2 fsPHENIX

Summary and Outlook Jet asymmetry enhancement via hadron selection; requires at least hadronic calorimetry and tracking Forward Collins (hadrons in jets) interesting for intermediate to higher x at reasonable scale; requires hadronic calorimetry, tracking and better also hadron id Need forward Hadronic calorimeter and tracking Diffraction and UPC very interesting for gluon PDFs, three-dimensional PDF and GPD E Roman pots needed for diffractive measurements Some Ecal (restacked MPC-EX?) for photon/electron measurements? 2019/1/2 fsPHENIX

Backup 2019/1/2 fsPHENIX