1. E.C. Aschenauer1

2. Requirements from Physics on IR E.C. Aschenauer 2 Summarized at: https://wiki.bnl.gov/eic/index.php/IR_Design_Requirements Hadron Beam: 1.the detection of neutrons of nuclear break up in the outgoing hadron beam direction  location/acceptance of ZDC 2.the detection of the scattered protons from exclusive and diffractive reaction in the outgoing proton beam direction the detection of the spectator protons from 3 He in polarized e+ 3 He collisions the detection of the spectator protons from 3 He in polarized e+ 3 He collisions (and in e+d) (and in e+d)  location/acceptance of RP Lepton Beam: 3.the beam element free region around the IR and the requirements on the magnetic field of the detector 4.space for low Q 2 scattered lepton detection 5.space for the luminosity monitor in the outgoing lepton beam direction 6.space for lepton polarimetry

3. eRHIC-Detector Design Concept 3 To Roman Pots Upstream low Q 2 tagger ECAL W-Scintillator PID: -1<  <1: DIRC or proximity focusing Aerogel-RICH 1<|  |<3: RICH Lepton-ID: -3 <  < 3: e/p 1<|  |<3: in addition Hcal response &  suppression via tracking 1<|  |<3: in addition Hcal response &  suppression via tracking |  |>3: ECal+Hcal response &  suppression via tracking -5<  <5: Tracking (TPC+GEM+MAPS) DIRC/proximity RICH   E.C. Aschenauer ToLumidetector e-Polarimeter where to put

4. Exclusive Reactions: Event Selection E.C. Aschenauer 4 leading protons are never in the main detector acceptance at EIC (stage 1 and 2) eRHIC detector acceptance e’ (Q 2 ) e L*L*L*L* x+ξ x-ξ H, H, E, E (x,ξ,t) ~ ~  p p’ t proton/neutron tag method o Measurement of t o Free of p-diss background o Higher M X range o to have high acceptance for Roman Pots / ZDC challenging Roman Pots / ZDC challenging  IR design  IR design Diffractive peak Need for roman pot spectrometer ANDZDC

5. 5x100 GeV 20x250 GeV t-Measurement using RP 5 Accepted in“Roman Pot” at 20m Quadrupoles acceptance 10s from the beam-pipe high ‐ |t| acceptance mainly limited by magnet aperture high ‐ |t| acceptance mainly limited by magnet aperture low ‐ |t| acceptance limited by beam envelop (~10σ) low ‐ |t| acceptance limited by beam envelop (~10σ) |t| ‐ resolution limited by |t| ‐ resolution limited by – beam angular divergence ~100μrad for small |t| – uncertainties in vertex (x,y,z) and transport – ~<5-10% resolution in t (follow RP at STAR) Simulation based on eRHIC-IR Generated Quad aperture limited RP (at 20m) accepted 20x250 E.C. Aschenauer

6. Spectator proton tagging for He-3 E.C. Aschenauer 6  Momentum smearing mainly due to Fermi motion + Lorentz boost due to Fermi motion + Lorentz boost  Angle 99.9%) after IR magnets at 20m  after IR magnets  RP acceptance  +10  beam clearance  90% tagging efficency

7. Kinematics of Breakup Neutrons 7 Results from GEMINI++ for 50 GeV Au +/-5mrad acceptance totally sufficient Results: With an aperture of ±5 mrad we are in good shape enough “detection” power for t > 0.025 GeV 2 enough “detection” power for t > 0.025 GeV 2 below t ~ 0.02 GeV 2 photon detection in very forward direction below t ~ 0.02 GeV 2 photon detection in very forward direction  all accounted in IR design Question: For some physics needed rejection power for incoherent: ~10 4 For some physics needed rejection power for incoherent: ~10 4  Critical: ZDC efficiency E.C. Aschenauer

8. Luminosity Measurement  Concept: Use Bremsstrahlung ep  ep  as reference cross section Use Bremsstrahlung ep  ep  as reference cross section  normally only  is measured  Hera: reached 1-2% systematic uncertainty E.C. Aschenauer 8

9. Polarization and Luminosity Coupling  Concept: Use Bremsstrahlung ep  ep  as reference cross section Use Bremsstrahlung ep  ep  as reference cross section  normally only  is measured  Hera: reached 1-2% systematic uncertainty  eRHIC BUTs:  with 10 34 cm -2 s -1 we get on average 200 bremsstrahlungs photons  only pair spectrometer concept will work photons  only pair spectrometer concept will work  coupling between polarization measurement uncertainty and uncertainty achievable for lumi-measurement  no experience no polarized ep collider jet  have started to estimate a with the help of our theory friends  hopefully a is small E.C. Aschenauer 9 Important need to monitor not only polarisation level but also polarisation bunch current correlation for both beams

10. eRHIC Lepton Beam 10  How to generate 50 mA of polarized electron beam? Polarized cathodes are notorious for dying fast even at mA beam currents are notorious for dying fast even at mA beam currents  One possibility is using the idea of a “Gatling” electron gun with a combiner?  20 cathodes  20 cathodes  one proton bunch collides always with electrons from one specific cathode  one proton bunch collides always with electrons from one specific cathode Important questions:  What is the expected fluctuation in polarisation from cathode to cathode in the gatling gun  from Jlab experience 3-5%  What fluctuation in bunch current for the electron do we expect  limited by Surface Charge, need to see what we obtain from prototype gun  Do we expect that the collision deteriorates the electron polarisation. A problem discussed for ILC A problem discussed for ILC  influences where we want to measure polarisation in the ring  How much polarisation loss do we expect from the source to flat top in the ERL.  Losses in the arcs have been significant at SLC  Is there the possibility for a polarisation profile for the lepton bunches  if then in the longitudinal direction can be circumvented with 352 MHz RF Challenge: Integrate Compton polarimeter into IR and Detector design together with Luminosity monitor and low Q 2 -tagger  longitudinal polarisation  Energy asymmetry  segmented Calorimeter  to measure possible transverse polarisation component  position asymmetry E.C. Aschenauer

11. 11 E.C. Aschenauer Detector and IR-Design All optimized for dedicated detector Have +/-4.5m for main-detector  p: roman pots / ZDC  e: low Q 2 -tagger e eRHIC-Detector: collider detector with -4<h<4 rapidity coverage and excellent PID p eRHICDetector 100$-question: Can we combine low Q 2 -tagger lumi-monitor and compton polarimeter in one detector system?

12. Lepton Polarization  Method: Compton backscattering E.C. Aschenauer 12 572 nm pulsed laser 572 nm pulsed laser laser transport system: ~80m laser transport system: ~80m laser light polarisation measured laser light polarisation measured continuously in box #2 continuously in box #2

13. Polarimeter Operation E.C. AschenauerDESY Schichtgaenger Ausbildung 2006 13 Multi-Photon Mode Advantages: - eff. independent of brems. bkg and photon energy cutoff - dP/P = 0.01 in 1 min Disadvantage: - no easy monitoring of calorimeter performance A m = (   –    (   +       = P e P A p A p = (   –    (   +     = 0.184 (if detector is linear) Laser Compton scattering off HERA electron Pulsed Laser – Multi Photon Flip laser helicity and measure energy sum of scattered photonsResult: Have achieved 1.4% uncertainty at HERA

14. E.C. Aschenauer 14 e p PolarimeterLaser laser polarisation needs to be monitored  Allows to measure polarisation right at IR, but only for non-colliding bunches  need as many non-colliding bunches as cathods  no bremsstrahlungs background  ECal: needs to be radiation hard (sees synchrotron radiation fan)  possible technology diamante calorimeter  ILC FCal  will be used to detect compton photons  e’-tagger:  detect low Q 2 scattered electrons  quasi-real photoproduction physics  detect lepton from compton scattering  pair spectrometer: only possible high precision luminosity measurement ~ ECAL small θ e’-tagger pairspectrometer A possible layout for all in one Summary:  all of this needs to be carefully modeled  need urgently model of eRHIC IR region so we can include it in our GEANT-model

15. E.C. Aschenauer 15 BACKUP

16. RHIC Hadron Polarisation 16 Account for beam polarization decay through fill  P(t)=P 0 exp(-t/  p ) growth of beam polarization profile R through fill pCarbonpolarimeter x=x0x=x0x=x0x=x0 ColliderExperiments correlation of dP/dt to dR/dt for all 2012 fills at 250 GeV Polarization lifetime has consequences for physics analysis  different physics triggers mix over fill  different  different Result: Have achieved 6.5% uncertainty for DSA and 3.4 for SSA will be very challenging to reduce to 1-2% E.C. Aschenauer

17. RHIC: Polarisation-Bunch Current Correlation E.C. Aschenauer 17 Data from 2012-Run: Small anti-correlation between polarisation and bunch current at injection which washes out at collision energies Improvements of hadron polarisation measurements: continuously monitor molecular fraction in the H-Jet find longer lifetime and more homogenious target material for the pC polarimeters can we calibrate energy scale of pC closer to E kin (C) in CNI alternative detector technology for Si-detectors to detect C

18. What needs to be covered BY THE DETECTOR 18e’t (Q 2 ) e L*L*L*L* x+ξ x-ξ H, H, E, E (x,ξ,t) ~ ~  J  p p’ Inclusive Reactions in ep/eA:  Physics: Structure Fcts.: g 1, F 2, F L  Very good electron id  find scattered lepton  Momentum/energy and angular resolution of e’ critical  scattered lepton  kinematics Semi-inclusive Reactions in ep/eA:  Physics: TMDs, Helicity PDFs  flavor separation, dihadron-corr.,…  Kaon asymmetries, cross sections  Kaon asymmetries, cross sections  Excellent particle ID  ±,K ±,p ± separation over a wide range in   full  -coverage around  *  Excellent vertex resolution  Charm, Bottom identification Exclusive Reactions in ep/eA:  Physics: GPDs, proton/nucleus imaging, DVCS, excl. VM/PS prod.  Exclusivity  large rapidity coverage  rapidity gap events  ↘ reconstruction of all particles in event  high resolution in t  Roman pots E.C. Aschenauer

19. eRHIC: high-luminosity IR 19  10 mrad crossing angle and crab-crossing  High gradient (200 T/m) large aperture Nb 3 Sn focusing magnets  Arranged free-field electron pass through the hadron triplet magnets  Integration with the detector: efficient separation and registration of low angle collision products  Gentle bending of the electrons to avoid SR impact in the detector Proton beam lattice © D.Trbojevic, B.Parker, S. Tepikian, J. Beebe-Wang e p Nb 3 Sn 200 T/m G.Ambrosio et al., IPAC’10 eRHIC - Geometry high-lumi IR with β*=5 cm, l*=4.5 m and 10 mrad crossing angle  10 34 cm -2 s -1 20x250 20x250 Generated Quad aperture limited RP (at 20m) accepted E.C. Aschenauer

20. Integration into Machine: IR-Design E.C. Aschenauer 20 space for low-  e-tagger Outgoing electron direction currently under detailed design  detect low Q 2 scattered leptons  want to use the vertical bend to separate very low-  e’ from beam-electrons  can make bend faster for outgoing beam  faster separation  for 0.1 o <  <1 o will add calorimetry after the main detector

21. 21DESY Schichtgaenger Ausbildung 2006 E.C. Asc hena uer Principle of P e Measurement with the LPOL Calorimeter position NaBi(WO 4 ) 2 crystal calorimeter e (27.6GeV) (2.33 eV) (2.33 eV) back scattered Compton photons Calorimeter (E  ) Segmentation: position detection of Compton photons Compton Scattering: e+  e ’ +  Cross Section: d  /dE  = d  0 /dE  [ 1+ P e P A z (E  ) ] d  0, A z : known (QED) P e : longitudinal polarization of e beam P : circular polarization (  1) of laser beam Compton edge: Asymmetry: