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 and Deuterium the detection of the spectator protons from 3 He and Deuterium  location/acceptance of RP;  impact of crab-cavities on forward scattered protons Lepton Beam: 3.the beam element free region around the IR 4.minimize impact of detector magnetic field on lepton beam  synchrotron radiation  synchrotron radiation 3.space for low Q 2 scattered lepton detection 4.space for the luminosity monitor in the outgoing lepton beam direction 5.space for lepton polarimetry Important EIC is a high luminosity machine 10 33 cm -2 s -1 such controlling systematics becomes crucial  luminosity measurement  lepton and hadron polarisation measurement

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 before or after IR

4. Example: Longitudinal Spin Structure 4 E.C. Aschenauer Can  and  G explain it all ? Contribution to proton spin to date: Gluon: 20% (RHIC) Quarks: 30% (DIS) MISS 50%  low x

5. E.C. Aschenauer 5 5 x 250 starts here 5 x 100 starts here hep-ph:1206.6014 (M.Stratmann, R. Sassot, ECA) cross section: pQCD scaling violations world data now eRHIC 5x100/250 GeV dramatic reduction of uncertainties:

6. can expect ~5-10% can expect ~5-10% uncertainties on ΔΣ and Δg uncertainties on ΔΣ and Δg BUT BUT need to control systematics need to control systematics current data w/ eRHIC data 6 E.C. Aschenauer total quark spin  spin  gluon spin  g ✔ orbital angular momentum can be extracted through exclusive reactions for details see D. Mueller, K. Kumericki S. Fazio, and ECA arXiv:1304.0077

7. Impact on ∫  g from systematic uncertainties E.C. Aschenauer 7 Need systematics ≤ 2% arXiv: 1206.6014 Dominant systematics: Luminosity Measurement  Relative Luminosity  needs to be controlled better then A LL  ~10 -4 at low x Absolut polarization measurements: electron P e and hadron P p relativeluminosity

8. Luminosity Measurement: physics processes E.C. Aschenauer 8 Goals for Luminosity Measurement:  Integrated luminosity with precision δL< 1%  Measurement of relative luminosity: physics-asymmetry/10  Fast beam monitoring for optimization of ep-collisions and control of mid-term variations of instantaneous luminosity  requires ‘alternative’ methods for luminosity determination

9. Polarization and Luminosity Coupling  Concept: Use Bremsstrahlung ep  ep  as reference cross section Use Bremsstrahlung ep  ep  as reference cross section  normally only single photon counting  Hera: reached 1-2% systematic uncertainty  eRHIC BUTs:  with 10 33 cm -2 s -1 one gets on average of 23 bremsstrahlungs photons/bunch for proton beam  A-beam Z 2 -dependence  this will challenge single photon measurement under 0 o  coupling between polarization measurement uncertainty and uncertainty achievable for lumi-measurement  no experience no polarized ep collider jet  have started to calculate a with the help of  have started to calculate a with the help of Vladimir Makarenk (NC PHEP BSU, Minsk), did these calculations for ZEUS and is now at CERN to work on CLIC-QED calculations  hopefully a is small E.C. Aschenauer 9 Important need to monitor not only polarisation level but also polarisation bunch current correlation

10. 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 10

11. Luminosity Detectors  zero degree calorimeter  high rate  measured energy proportional to # photons  subject to synchrotron radiation  alternative pair spectrometer 11 VacuumChamber L3L3L3L3  e + /e -  e-e-e-e- e+e+e+e+ Dipole Magnet very thin Converter L2L2L2L2 L1L1L1L1 SegmentedECal   The calorimeters are outside of the primary synchrotron radiation fan   The exit window conversion fraction reduces the overall rate   The spectrometer geometry imposes a low energy cutoff in the photon spectrum, which depends on the magnitude of the dipole field and the transverse location of the calorimeters

12. 12 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<  <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?

13. eRHIC Lepton Beam 13  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  eRHIC design 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

14. Lepton Polarization E.C. Aschenauer 14  Method: Compton backscattering 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 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 =0.184Result: Have achieved 1.4% uncertainty at HERA

15. E.C. Aschenauer 15 e p PolarimeterLaser laser polarisation needs to be monitored  Measure Polarisation at IP  overlap of bremsstrahlungs and compton photons  only possible if we have number of empty p-bunches = # cathods  luminosity loss  Measure after / before IP need to measure at location spin is fully longitudinal or transverse longitudinal or transverse  1/6 turn should rotate spin by integer number of π  After IP:  does collision reduce polarisation?  need to measure at location, where bremsstrahlung contribution is small  Before IP:  need to find room for photon calorimeter The lepton polarimeter: Location? Summary:  all of this needs to be carefully modeled  work to integrate eRHIC IR into EICroot has started Comptonphotondetector

16. Low Q 2 -tagger  e’-tagger:  detect low Q 2 scattered electrons  quasi-real photoproduction physics  possibly also detect lepton from lepton polarimeter compton scattering  design could follow the Hall-D tagger design pileup can be avoided by fine segmentation of tagger detectors E.C. Aschenauer 16 e’-detector EeEeEeEe Array of Scintillators very finely spaced might need less segmentation Scintillator  Calorimeter

17. Electron Tagger as Hall-D 17 Microscope Hodoscope support frame Taggerstrong-back Vacuum Chamber supports Magnet steel Vacuum chamber Coils Electron beam beam Photonbeam post-bremsstrahlungselectrons Hodoscope E.C. Aschenauer tagged scattered electrons from Bremsstrahlung from ~1 GeV to 6 GeV  photon energy 6 GeV to 12 GeV

18. Deliverables  Luminosity:  determine a in  0 (1+aP e P p ) through calculation  develop a MC for (un)polarised bremsstrahlung in ep/eA collisions  integrate luminosity detectors into the IR-design  develop detector performance requirements  follow up with detector R&D for calorimeter technology, i.e. Diamond  Polarimetry:  determine performance requirements for fast and “slow” polarisation measurement  integrate polarimeter into IR-design and as close as possible to IP  simulation package of polarimeter  Low Q 2 -tagger:  determine the detector performance requirements can scattered leptons from bremsstrahlung be separated from low- Q 2 DIS  segmentation of tagger-detectors  Integrate into IR-design E.C. Aschenauer 18 Goal to increase collaboration: Will seek collaboration with Luminosity and low-Q 2 tagger group from LHeC Request: 1 postdoc position for 2 years starting in FY14 travel funding for the group 10k$ / year

19. E.C. Aschenauer 19 BACKUP

20. What needs to be covered BY THE DETECTOR 20e’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

21. RHIC Hadron Polarisation 21 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

22. RHIC: Polarisation-Bunch Current Correlation E.C. Aschenauer 22 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

23. eRHIC: high-luminosity IR 23  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

24. Integration into Machine: IR-Design E.C. Aschenauer 24 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

25. Exclusive Reactions: Event Selection E.C. Aschenauer 25 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

26. 5x100 GeV 20x250 GeV t-Measurement using RP 26 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

27. Spectator proton tagging for He-3 E.C. Aschenauer 27  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

28. Kinematics of Breakup Neutrons 28 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

29. 29 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  work to integrate eRHIC IR into EICroot has started