1. Physics Case For Electron Ion Collider Abhay Deshpande Abhay Deshpande AA Physics Capabilities of an EIC Detector Mini-Workshop at BNL September 19, 2002 Riken BNL Research Center http://www.bnl.gov/eic A

2. BNL Sept. 02Physics Case of EIC2 Crossing the x-Q 2 Barrier in DIS: Low-x surprises! Elastic e-p scattering (SLAC, 1950s) Q2 ~ 1 GeV 2 Finite Size of proton Inelastic e-p scattering (SLAC, 1960s) Q2 > 1 GeV 2 Parton structure of the proton Inelastic m-p scattering off p/d at CERN (1980s) Q2 > 1 GeV 2 Unpolarized EMC effect Inelastic e-p scattering at HERA/DESY (1990s) Q2 > 1 GeV 2 Unexpected rise of F 2, Study of pQCD and QCD through various physics processes, diffraction… What NEXT? Low x

3. BNL Sept. 02Physics Case of EIC3 Stern & Gehrlach (1921): Space quantization associated with direction Goudschmidt & Ulhenbeck (1926): Atomic fine structure and electron spin magnetic moment Stern (1933): Proton anomalous magnetic moment Kusch (1947): Electron anomalous magnetic moment Prescott & Yale-SLAC Collaboration (1978): EW interference in polarized e-d DIS, parity non-conservation EMC (1989): Proton spin crisis/puzzle Low x! E704, AGS pp scattering, HERMES ep (1999): ???? Transverse spin asymmetries ???? Physics with “Spin” full of Surprises!

4. BNL Sept. 02Physics Case of EIC4 Deep Inelastic Scattering Kinematics Observe scattered electrons and hadrons Observe spectator or remnant of the interaction??

5. BNL Sept. 02Physics Case of EIC5 Advantages of a Collider Experiment Historically polarized & un-polarized DIS  fixed target experiment However colliding beam configuration has advantages Better angular separation between scattered lepton & nucl. Fragments -- Better resolution for electro-magnetic probe -- Recognition of rapidity gap events (recent history of diffraction) Better measurement of nuclear fragments Higher Center of Mass (CM) energies reachable Tricky integration of beam pipe and accelerator components

6. BNL Sept. 02Physics Case of EIC6 The EIC w.r.t. Other Experimental Facilities New kinematic region to be explored EIC = eRHIC + EPIC Kinematic Reach for DIS: High Luminosity!

7. BNL Sept. 02Physics Case of EIC7 The EIC w.r.t. Other Facilities Large luminosity and high CM Energy makes EIC unique! Variable CM energy, ion species and polarizability of hadron beams enhances its versatility! TESLA-N

8. BNL Sept. 02Physics Case of EIC8 Scientific Frontiers Open to the EIC Nucleon structure:  Spin structure: polarized quark and gluon distributions the nucleon  Unplarized quark and gluon distributions in the nucleon  Correlations between partons Role of quarks and gluons in the nuclei Hadronization in nucleons and nuclei Partonic matter under extreme conditions

9. BNL Sept. 02Physics Case of EIC9 The EIC Detector  A “4  ” Detector Scattered electrons to measure kinematics of DIS Scattered electrons at small (~zero degree) angles to tag photo- production events Central hadronic final state for kinematics, jet measurements, quark flavor tagging, fragmentation studies…. Central hard photon and particle/vector meson detection (DVCS) Zero angle photon measurement to control radiative corrections and in e-A physics to tag nuclear de-excitations Missing E T for neutrinos in final state (W physics) Tagging forward nuclear fragments Tagging forward particles for diffractive physics & target depedence Variable energies & species of ions Polarized beam species: p, d, He High luminosity The EI Collider will provide:

10. BNL Sept. 02Physics Case of EIC10 Where do electrons and quarks go?  p q,e 10 GeV x 250 GeV 177 0 160 0 scattered electronscattered quark 10 GeV 5 GeV 90 0 5 GeV 10 0

11. BNL Sept. 02Physics Case of EIC11 Electron kinematics… some details… scattered electron 10 GeV x 250 GeV At HERA:  Electron method:  x/x ~  E/(y.E) Limited by calorimeter resolution  Hadron method: Limited by noise in calorimeter (E_noise/E_beam) At EIC:  Measure electron energy with tracker (< 20 GeV, large kin. region)  p/p ~ 0.005-0.0001  (2-4T Magnet)  Design low noise calorimeter  Crystal or SPACAL

12. BNL Sept. 02Physics Case of EIC12 Electron, Quark Kinematics scattered electronscattered quark 5 GeV x 50 GeV  p q,e

13. BNL Sept. 02Physics Case of EIC13 Physics with Unpolarized e-p Collisions Large kinematic region already covered by HERA but additional studies at the EIC are possible & desirable! Uniqueness of EIC: High luminosity, variable Sqrt(s), deuterons, improved detector & IP Will enable precision physics studies: d beams  neutron structure, d/u x  0, dbar(x)-ubar(x) precision  S (Q 2 ) flavor separation (charm, strangeness) slopes in dF 2 /dlnQ 2 precision gluon distribution x  0.001  0.5-1 exclusive reaction measurements transition region physics Q 2 =0  few GeV nuclear fragmentation region

14. BNL Sept. 02Physics Case of EIC14 Topics of Interest for polarized DIS Spin structure function g 1 p/g 1 n with high precision and at low x Bjorken sum rule with high precision  G(x,Q2) from pQCD analysis, Di-Jet/high pT hadron events in PGF processes Precise determination of  S from g 1 scaling violations alone… Polarized structure of the photon from photo-production studies Electroweak structure functions g 5 (+/-) from W(+/-) production in polarized ep scattering Flavor separation of PDFs through semi-inclusive DIS Transversity DVCS Contribution to GDH sum rule at very high υ Tgt/Current fragmentation Etc……. Many other measurements A robust program which would require a challenging detector & interaction region design

15. BNL Sept. 02Physics Case of EIC15 Spin Structure Function g 1 at low x A. Deshpande, V. W. Hughes ~5-7 days of data No present/future approved experiment will do as well. 3 years of data Studies included statistical errors & detector smearing

16. BNL Sept. 02Physics Case of EIC16 Low x Measurement of g1 of the Neutron A. Deshpande, V.W.Hughes With He +2 or Deuteron in hadron ring: g 1 n measurable ~2 weeks of EIC data (only the low x data shown) Shown is the present SMC data with various low x scenarios and uncertainties from possible HERA data in 3 years Combined with g 1 p this would enable a “hyperfine” test of Bjorken sum rule which is a fundamental result of QCD (~0.5-1.0 % accuracy estimated) EIC 1 inv.fb

17. BNL Sept. 02Physics Case of EIC17 Polarized Gluon Distribution Polarized Gluon distribution is being pursued at various various experimental facilities as we speak…. Each has its weaknesses and strong points. At the Electron Ion Collider this will be pursued with very different physics interactions: Different Systematics/Different Kinematics Deep Inelastic Scattering Kinematics with EIC: 1.Perturbative QCD analysis of the g1 spin structure of the data 2.2+1 Jet production in photon gluon fusion (PGF) process 3.2-high pT opposite charged hadron tracks (PGF) Photoproduction (real photon) Kinematics with EIC: 1.Single jet production in PGF 2.Di-Jet production in PGF 3.Open charm production 4.….

18. BNL Sept. 02Physics Case of EIC18 First Moment of the  G(x) A.Deshpande, V. W. Hughes & J. Lichtenstadt pQCD analysis of g 1 structure function at NLO gives the first moment of the polarized gluon distribution. Present value and uncertainty is: (at Q 2 = 1 GeV 2 ) 1.0 (stat) (exp.sys.) (theory/low-x) Major source of uncertainty from low x unmeasured region: Theory completely unconstrained in this region. If EIC data (~1 week) is obtained and the analysis is repeated, the theoretical uncertainties are estimated to improve by factor of ~3-5; the statistical uncertainty improves by factor ~5. Study to be repeated for 1-3yr data. +1.0 + 0.4 +1.4 - 0.4 - 0.2 - 0.5 Complimentary determination of  G to that from RHIC Spin

19. BNL Sept. 02Physics Case of EIC19 Other “direct” methods to get  G Photon-Gluon-Fusion (PGF) Photon Gluon Fusion in DIS: Di-Jet events 2-High-pT hadron events At high Sqrt(s) the theoretical interpretation is without ambiguities or uncertainties! Method already tried at HERA -- NLO calculations exist -- G(x,Q 2 ) extracted and published (H1 & ZEUS) -- Consistent with G(x,Q 2 ) from pQCD analysis of F 2 Signal: PGF Background QCD Compton

20. BNL Sept. 02Physics Case of EIC20 Result of Di-Jet analysis at NLO G. Radel & A. De Roeck, A. Deshpande, V. W. Hughes, J. Lichtenstadt Easy to differentiate between different scenarios of  G: Improves  G by factor of ~2-3? Combined analysis: Di-Jet + pQCD analysis of g1:  G constrained by these two together further improve the uncertainties by an additonal factor of ~3 Effectively a ~5% or better measurement of  G might be expected Statistical accuracy shown for EIC for 2 luminosities Detector smearing effects studied NLO analysis for Di-Jet considered in the past

21. BNL Sept. 02Physics Case of EIC21  G(x)/G(x) EIC vs. Rest of the World EIC Di-Jet DATA 2fb -1 Good precision Clean measurement Range 0.01 <x< 0.3 Constrains shape!!

22. BNL Sept. 02Physics Case of EIC22 Polarized Parton Distribution of the Photon Photoproduction studies with single and di-jet and one and 2 high pT opposite charged hadrons. At high enough energies the photon can resolve itself into its parton content With polarized protons asymmetries related to the spin structure of the photon can be extracted! A UNIQUE measurement! Asymmetries sensitive to the gluon structure as well! Resolved PhotonDirect Photon

23. BNL Sept. 02Physics Case of EIC23 Spin structure of polarized photon! M. Stratmann & W. Vogelsang Statistical uncertainty with 1 inv.fb. ~2wks running for EIC Single and double jet asymmetries ZEUS Acceptance cuts Will resolve the photon pdfs easily! Direct Photon Resolved Photon

24. BNL Sept. 02Physics Case of EIC24 Parity Violating Structure Functions g 5 Unique measurement with EIC polarized HERA Experimental Signature: missing (neutrino) momentum: huge asymmetry in detector Complementary measurement to RHIC SPIN For EIC kinematics

25. BNL Sept. 02Physics Case of EIC25 Measurement Accuracy PV g 5 with EIC J. Contreras & A. De Roeck Assume: 1) Input GS Polarized PDFs 2) xF3 is measured well by that time 3) 4fb-1 luminosity If e+ and e- possible then one can have g5(+) as well. Separate flavors Delta u, Delta d etc.

26. BNL Sept. 02Physics Case of EIC26 Drell-Hearn-Gerasimov Sum Rule S. Bass, A. De Roeck, A. Deshpande DGH sum rule: At EIC  range: GeV-few TeV range Although contribution to integral is small: explore energy dependence of cross-section. Complementary to JLAB, MAMI Experimental effort Electron Tagger: Inclusive Photoproduction measurement

27. BNL Sept. 02Physics Case of EIC27 DVCS/Vector meson production Hard exclusive DIS process  (default) but also pions, vector mesons…. Remove a parton & put another one back in  Microsurgery of Baryons! Claim: Possible access to skewed/off forward PDFs Polarized structure: Access to quark orbital angular momentum(??) ? H(x, ,t), E(x, ,t)  J q =  q +L q ? An ongoing debate….R. Jaffe/X.Ji …… Will need a large kinematic coverage in the data  EIC’s variable energy scheme should help ??

28. BNL Sept. 02Physics Case of EIC28 Deeply Virtual Compton Scattering at EIC D. Hasell, R. Milner et al. DVCS has been observed at HERA (ZEUS,H1), recently by HERMES and later by Jlab Potential for getting to Nucleon Angular Momentum??? Reflection of processes in the nucleon Could be measured with EIC with considerable x,Q 2 range.  Extrapolations and generalizations involved may become clearer by then? EIC: 5 GeV e on 50 GeV proton: Much large range possible….

29. BNL Sept. 02Physics Case of EIC29 DVCS at EIC (preliminary) 10 x 250 GeV Q 2 > 1 GeV 2 20<W<95 GeV 0.1<|t|<1.0 GeV 2 Full curve: all events Dashed curve: accepted events Q 2 >1 GeV 2 : 50K events/fb -1 A. Sandacz Acceptance enhanced ZEUS-like detector Add Roman pots a la PP2PP at RHIC

30. BNL Sept. 02Physics Case of EIC30 Target & Current Fragmentation Region T. Londergan & P. Moulders Target and current fragments separated naturally in a collider mode compared to the fixed target experiment Exclusive/Semi-Inclusive measurements need high luminosity EIC will have both capabilities Numerous measurements leading to detailed study of different fragmentation functions using the different species of beams at EIC both in polarized and unpolarized DIS.

31. BNL Sept. 02Physics Case of EIC31 Polarized & Unpolarized Strange Quark Distribution Measurements Assuming that u and d quark distributions are measured by the time EIC comes along…. A detector with a good particle ID for pion/kaon… separation could access strange quark distribution Upper left plot shows statistical accuracy for Asymmetries measured for events with Kaons with 1fb -1 luminosity at EIC Lower left plot shows the accuracy on strange quark distribution possible E. Kinney, U. Stoesslein

32. BNL Sept. 02Physics Case of EIC32 Collider helps: Target Fragmentation Studies D. De Florian, G. M. Shore & G. Veneziano Experimetal Measurement: Different targets,Forward detectors, Detect positive & negative hadrons, Provide good PID

33. BNL Sept. 02Physics Case of EIC33 Low x Physics with e-A Collider …and extend into a novel high parton density region: Color Glass Condensate Study e-A in a collider mode for the first time! QCD in a different environment! Clarify & reinforce the physics studied so far from e-A/  -A in fixed target experiments including target fragmentation region….. Physics to be explored can be broadly categorized into three x regions 1) High x 2) Intermediate x 3) Low x

34. BNL Sept. 02Physics Case of EIC34 Why e-A in Collider Mode? Highest energy fixed target experiment (NMC @ CERN, E665 @ FNAL) used secondary muon beams and achieved Beam intensities: Target thinkness: 600 gm/cm2 Luminosity: Electron DIS experiments at SLAC & DESY: Large beam currents but limited beam energies: Thick targets do not allow a good measurement of the target fragments! ONLY INCLUSIVE MEASUREMENTS An e-A Collider with appropriately chosen beam energies can overcome all these limitations! Ee ~5-10 GeV, E A ~100 GeV/nucleon Luminosity > per e-N This corresponds to approx. 85pb-1 per day!

35. BNL Sept. 02Physics Case of EIC35 Experimental Hints of the Unusual in Nuclei M. L. Leicht et al. for FNAL E866 800 GeV Proton-fixed target A collisions: Comparison of Drell-Yan di-muon production vs production and then decay of J/Y and Upsilon Nuclear medium enhances high parton density effects! Also more recent results from RHIC…

36. BNL Sept. 02Physics Case of EIC36 DIS on Nuclei is Different! E665, NMC & SLAC Collaborations Fermi motion EMC effect Enhancement Shadowing Saturation? Region of Shadowing and saturation hardly have data with Q 2 > 1 GeV 2 An e-A Collider will measure these regions! F 2 D/F 2 A Low Q 2 !

37. BNL Sept. 02Physics Case of EIC37 Statistical Precision possible with EIC T. Sloan Statistical Precision Possible with EIC: NMC data F 2 (Ca/D) EIC data with L=1 pb -1 Recall expected rates at EIC are ~85 pb -1 /day Also extends the measurements in to the low x region keeping the Q 2 >1 GeV 2 ! Region of saturation? EIC 1 inv. pb T. Sloan

38. BNL Sept. 02Physics Case of EIC38 Why high Q2 important at low x? Before HERA: for Lack of high Q2 a stumbling block for understanding QCD. Although low x, the coupling constant too large to make predictions and extract information in this region from theory. Lack of high Q2 a stumbling block for understanding QCD. HERA: Ep = 820-925 GeV, Ee=27.6 GeV, = 300 GeV For At HERA in good portion of low x region of interest. Coupling weak: computations in conventional pQCD possible & tested with data but interpretation is ambiguous. Hard (BFKL) Pomeron: In QCD it comes from gluon ladder diagrams 1) LO BFKL predicts cross sections rising faster than the HERA data 2) NLO corrections large and negative: Resummations necessary! Confusion! Interest! Formulate QCD at small x: High Parton Density Physics

39. BNL Sept. 02Physics Case of EIC39 Lessons from HERA: Hints of something new? At high Q2 (>>10 GeV2), the rise of gluon structure function at small x is well understood in pQCD framework. extracted reliably! extremely low x!However this is not extremely low x! In region Q2 (1-10) GeV2 issues less clear: Although fits accommodate data well, the interpretation problematic! Gluon too small, and sea quark distribution more than glue! Is the pQCD approach breaking down? If so Why?

40. BNL Sept. 02Physics Case of EIC40 What could be wrong with the low Q 2 evaluations of HERA pQCD fits? Coupling strength is still weak in 1-10 GeV 2 region! Screening effects due to large parton densities need to be considered specially! Phenomenological models that take these into account Explain inclusive and diffractive data together! Evidence of possible high parton density phenomena

41. BNL Sept. 02Physics Case of EIC41 In Summary…. As parton densities become too high, standard pQCD breaks down. Even though the coupling is weak, the physics may be non- perturbative due to high field strengths generated by large number of partons A novel state of matter? To experimentally explore this novel state of matter an e-A collider with LARGE luminosity and HIGH energy beams is essential!

42. BNL Sept. 02Physics Case of EIC42 High Parton Density Matter(HPDM) For a fixed external probe the number of partons per unit area grows rapidly with increasing energy (decreasing x) QCD field strengths grow as Small coupling implies large field strengths… non-linearities of theory are manifest and significantly change the properties of distributions in high energy collisions. Calculations indicate that the rapid rise of gluon distributions (as seen at HERA) will saturate.. i.e. grow slowly….. perhaps as slowly as ~ln(1/x). Will form a “Color Glass Condensate ! ”

43. BNL Sept. 02Physics Case of EIC43 Color Glass Condensate….(CGC) L. McLerran, R. Venugopalan et al. Why Glass? At small x, partons are rapidly fluctuating gluons interacting weakly with each other, but strongly coupled to the high x parton color charges which act as random-static-sources of color charge. Analogous to a spin glass system of condensed matter: a disordered state of spins is coupled to random magnetic impurities. Why Condensate? Gluon occupation number very large. They form a condensate. Being bosons large numbers can occupy the same state. A Bose-Einstein condensate leads to a huge overpopulation of the ground states A new state of matter at high energies would display dramatically different, yet simple, property of glassy condensates.

44. BNL Sept. 02Physics Case of EIC44 Inclusive Signatures Of CGC/HDPM The structure function F 2 (x,Q2), dF 2 /dlnQ2, dF 2 /dlnx. dF 2 /dlnQ 2 at fixed x @ high Q 2 is the Gluon Distribution. Predictions from saturation models VERY DIFFERENT from those in conventional pQCD EIC: Large luminosity and substantial x-Q 2 coverage: Precise measurements possible! Longitudinal structure function F L = F 2 –2xF 1 Needs variable beam energies  Possible @ EIC/eRHIC – Provides independent measurement of the gluon distribution Measurement of Nuclear Shadowing Quark Shadowing (F 2 A/A*F 2 N) in fixed tgt experiments: Observed Gluon Shadowing (GA/A*GN) indirect evidence through pQCD fits but are at low Q 2 ! Gluon shadowing expected to be VERY LARGE at low x and perturbatively reliable Q 2 s. EIC with high energy can do precise measurements! In addition, direct measurements possible using semi-inclusive channels (see next slide) Relation between Shadowing and Diffraction Relation between diffraction off nucleons and shadowing in nuclei will be very different in high parton density environment. EIC with different hadron beams will explore this.

45. BNL Sept. 02Physics Case of EIC45 Semi-Inclusive Signatures of CGC Hard Diffraction: Large rapidity gap between fragmentation region of electron and that of the target. At HERA 7-10% of the cross section corresponds to hard diffraction! Models with Saturation effects can explain this. These models predict that in eA scattering, the hard diffractive cross section could be huge! (~30-40%).  EIC will clearly see this! Coherent & Inclusive vector meson production: For light vector mesons, the diffractive cross-section is ~1/2 inclusive cross-section. For heavier vector mesons, this factor decreases (finally to 1/ln(Q2)). EIC will measure (for different A)  J  cross sections Gluon distribution measurements using jets and other semi-inclusive probes Large multiplicity fluctuations on event-by-event basis

46. BNL Sept. 02Physics Case of EIC46 Implications of EIC for A-A and p-A Collisions Goal of RHIC is to discover and study properties of QGP Possible scenario: QGP formed when CGC “shatters”! Bottom line: gluon distribution in nuclei important for initial conditions for QGP formation in A-A collisions. Physics of p-A complementary to that of e-A Consequences of the absence of evidence of CGC Should we be probing even deeper? We learnt something already! A) What was it that we saw hints of at HERA? B) Is there a possibility that such a state of matter indeed does not exist? What does this mean for QCD at high energies?

47. BNL Sept. 02Physics Case of EIC47 A Case for the EIC Explore a new regime of QCD: An e-A collider will provide a unique opportunity to explore fundamental and universal aspects of QCD. Measurements would be essential to fully understand the QGP already being pursued at RHIC now, and that would be studied at RHIC later…. And in future at LHC. An e-A collider will allow us to explore with great precision inclusive measurements that have not been pursued beyond the fixed target experimental era. It would also enable, for the first time, a wide range of semi- inclusive and exclusive measurements in the nuclear environment.

48. BNL Sept. 02Physics Case of EIC48 A Case for the EIC (Continued)… A polarized e-p scattering facility with variable sqrt(s) will allow a) at high sqrt(s) a new region in the x-Q2 to be explored for the pol. DIS. It will address issues that no other present or future approved facility will address b) in the already measured x-Q2 range the high luminosity of EIC will allow us to settle lots of yet uncertain issues regarding the nucleon spin related to semi-inclusive and exclusive measurements… http://www.bnl.gov/eic DETECTOR DESIGN SHOULD BEGIN IN EARNEST

49. BNL Sept. 02Physics Case of EIC49 Time Line for EIC (past) September 2000: Electron Ion Collider grew out of a joining of forces from two communities: 1) Polarized eRHIC (ep and eA at RHIC) -- BNL, DESY, UCLA, Yale & CERN fixed target & HERA Collider Experiment Community 2) Electron Polarized Ion Collider (EPIC) (3-5 GeV e X 30-50 GeV polarized light ions.) -- Colorado, IUCF, MIT/Bates, IUCF & HERMES Community February 2002: A white paper was submitted to NSAC Long Range Planning Review  Received enthusiastic support as a next R&D project beyond RHIC II at BNL ** Steering Committee 7 prominent scientists from DoE labs and DoE supported university groups & 1 contact person ** Physics Working Group, Accelerator Working Group (BNL-MIT-Budker Institute)  Detector simulations about to begin with various detector concepts in mind

50. BNL Sept. 02Physics Case of EIC50 EIC Time Line… (future)…. “Predictions are very difficult to make, especially when they are about the future…..” - Albert E. Expected presentation & approval in next LRP (2006) R&D money for detector could start (2007) Construction of IR and Detector components (2008) 3 yrs for construction of IR & Detector (??) without interfering with the on going RHIC program First collisions (2011) ?? If you know how to get it done earlier… -- I am listening….

51. BNL Sept. 02Physics Case of EIC51 EIC at BNL vs. What else is there? MachineLuminosity/year (pb -1 ) Sqrt(s) (GeV) HERA III150300-320 EIC200030-100 THERA40-2501000-16000 HERA III after 2006(?), new detector or/and H1 detector effort in progress  No effort towards polarized protons yet, none on nuclei but seems possible  Primary focus of new detector: low angle e-p scattering EIC needs polarized electron beam facility & an experiment THERA= TESLA * HERA  Need TESLA, polarized protons/nuclei in HERA, new detectors and interaction point design > 2015-8 What is important? High CM or High Luminosity?  Depends on what physic one wants to do….

52. BNL Sept. 02Physics Case of EIC52 Low x Resummation The g1p at low x dominated by double logarithmic terms like For Unpolarized case: (J. Bartels et al. Z. Phy. C70 (1996) 236; C72 (1996) 627) Predictions for g1p using LO DGLAP equations + Resummed terms in splitting and coefficent function are now available. (J. Kwiecinski & B. Ziaja, HERA Workshop proceedings DESY-1999-02) Data from EIC would easily be able to distinguish between the LO, DGLAP or LO+Resummed term scenario.

53. BNL Sept. 02Physics Case of EIC53 Low x Resummation Scenario and EIC Data A. Deshpande, A. De Roeck, J. Kweicinski & B. Ziaja Shown are: a) LO calculation for g1p b) LO DGLAP + Resummed calculation c) HERA measurements with 3yrs running d) EIC uncertainty ~2wks Otherwise this physics could be pursued robustly only at TELSA*HERA Collider at DESY EIC