Importance of bunch-by- bunch polarization information for EIC physics

1. Importance of bunch-by-bunchpolarization information for EIC physics E.C. Aschenauer arXiv: 1212.1701 & 1108.1713

2. Requirements to realize the EIC PHYSICS Program • Requirements from Physics: • High Luminosity ~ 1033 cm-2s-1 and higher • Flexible center of mass energy • Electrons and protons/light nuclei (p, He3 or D) highly polarised • Wide range of nuclear beams (D to U) • a wide acceptance detector with good PID (e/h and p, K, p) • wide acceptance for protons from elastic reactions and • neutrons from nuclear breakup • Important • EIC is a high luminosity machine >1033 cm-2s-1 • such controlling systematics becomes crucial • luminosity measurement • lepton and hadron polarization measurement EIC User Meeting 2014

3. g1p the way to find the Spin cross section: hep-ph:1206.6014 (M.Stratmann, R. Sassot, ECA) pQCD scaling violations 5 x 250 starts here 5 x 100 starts here current data w/ eRHIC data world data EIC User Meeting 2014

4. Impact on ∫Dg from systematic uncertainties arXiv: 1206.6014 • Dominant systematics: • Luminosity Measurement  Relative Luminosity • needs to be controlled better then ALL • ~10-4 at low x • Absolut polarization measurements: • electron Peand hadron Pp relative luminosity Need systematics ≤ 2% EIC User Meeting 2014

5. Impact on correlated Systematic uncertainty in p+pp0 ALL on DG arXiv:1402.6296 relative luminosity 2009: Relative Luminosity uncertainty same size as physics asymmetry R=1.18x10-3 + 0.21x10-3 ALL= 0.4 – 4 x 10-3 EIC User Meeting 2014

6. Reasons why polarization / Current CAN vary From Bunch to Bunch • Polarisation: • Hadrons in a storage ring: • source instabilities • Beam-Beam effects • bunch-to-bunch emittancevariation, Characteristic scale can be seen from AGS • RHIC polarization profile variation for different bunches after acceleration • leptons in a storage ring: • Beam-Beam effects • source instabilities • leptons in eRHIC • What is the expected fluctuation in polarisation from cathode to cathode • in the gatling gun • from Jlab experience 3-5% • Is there the possibility for a polarization profile for the lepton bunches • if then in the longitudinal direction can be circumvented with 352 MHz RF • Current: • Hadrons & leptons in a storage ring: • Variations in transfer efficiency from pre-accelerator to main ring • beam-beam interaction is important, it affects the bunch lifetime during the store • leptons in eRHIC • What fluctuation in bunch current for the electron do we expect • limited by Surface Charge, need to see what we obtain from prototype gun EIC User Meeting 2014

7. RHIC Hadron Polarimetry • Polarized hydrogen Jet Polarimeter (HJet) • Source of absolute polarization (normalization of other polarimeters) • Slow (low rates  needs looongtime to get precise measurements) • Proton-Carbon Polarimeter (pC) @ RHIC and AGS • Very fast  main polarization monitoring tool • Measures polarization profile (polarization is higher in beam center) and lifetime • Needs to be normalized to HJet • Local Polarimeters (in PHENIX and STAR experiments) • Defines spin direction in experimental area • Needs to be normalized to HJet All of these systems are necessary for the proton beam polarization measurements and monitoring EIC User Meeting 2014

8. RHIC Hadron polarisation and BUNCh Current Fill 17520 in 2013: Beginning Fill 17520 in 2013: End P↓ P↑ EIC User Meeting 2014

9. RHIC Hadron polarisation and BUNCh Current Fill 17571 in 2013: Beginning Fill 17571 in 2013: End P↓ P↑ EIC User Meeting 2014

10. RHIC: Polarisation-Bunch Current Correlation Data from 2012-Run: Small anti-correlation between polarisation and bunch current at injection which washes out at collision energies PSTP-2013, Charlotesville, VA

11. RHIC Hadron Polarisation Account for beam polarization decay through fill  P(t)=P0exp(-t/tp) growth of beam polarization profile R through fill pCarbon polarimeter Collider Experiments x=x0 Result: Have achieved 6.5% uncertainty for DSA and 3.4 for SSA will be very challenging to reduce to 1-2% 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 <P> EIC User Meeting 2014

12. Possible Improvements to RHIC Hadron Polarimetry EIC User Meeting 2014 • H-Jet: • continuously monitor molecular fraction in the H-Jet • currently dominant systematics • factor 10 lower bunch current for eRHIC precision per fill • pC-polarimeters • find longer lifetime and more homogenious target material for the pCpolarimeters • can we calibrate energy scale of pC closer to Ekin(C) in CNI • alternative detector technology for Si-detectors to detect C • smaller emittance of beam • reduced/eliminate x-y polarisation profile • harder to measure • polarised Deuterium and He-3 polarimetry will be challenging • to use CNI you need to make sure D and He-3 did not break up • local polarimetry @ eRHIC • integrate a pC-polarimeter between the spin-rotators • disappearance of asymmetry means full longitudinal polarisation

13. Lepton Polarization Result: Have achieved 1.4% uncertainty at HERA • 572 nm pulsed laser • laser transport system: ~80m • laser light polarisation measured • continuously in box #2 EIC User Meeting 2014 Method: Compton backscattering, i.e. HERA LPOL

14. eRHIC lepton polarimeter Polarimeter Laser Compton photon detector laser polarisation needs to be monitored # of cathods in gattling gun: 20 golden number This guarantees that a hadron bunch collides always with the electrons produced from one particular cathode, avoiding/reducing significantly harmful beam-beam effect of electron beam parameter variations on the hadrons e p • Measure Polarization at IP • overlap of bremsstrahlungsand compton photons • only possible if we have number of empty p-bunches = # cathods • luminosity loss • need to know polarisation is fully longitudinal • segmented Calorimeter • longitudinal polarization  Energy asymmetry • transverse polarization component  position asymmetry • Measure after / before IP need to measure at location spin is fully • longitudinal or transverse • 1/6 turn should rotate spin by integer number of π • After IP: • does collision reduce polarization  problem at ILC  for eRHIC very small • need to measure at location, where bremsstrahlung contribution is small • Before IP: • need to find room for photon calorimeter • Want to measure both the compton photon and the scattered lepton EIC User Meeting 2014

15. Polarization and Luminosity Coupling 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 EIC User Meeting 2014 • Concept: Use Bremsstrahlung ep epg as reference cross section • different methods: Bethe Heitler, QED Compton, Pair Production • Hera: reached 1-2% systematic uncertainty • eRHIC BUTs: • with 1033cm-2s-1 one gets on average of 23 bremsstrahlungs photons/bunch for proton beam  A-beam Z2-dependence • this will challenge single photon measurement under 0o • 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 Vladimir Makarenk (NC PHEP BSU, Minsk), the CERN CLIC-QED calculations expert • hopefully a is small

16. Summary EIC User Meeting 2014 • The need for bunch by bunch polarisation information was documented • there is need to monitor not only the polarization level but also polarization bunch current correlations • the polarimetertechnology needs to allow for this information • the known challenges to measure polarisation have been discussed • but EIC will be the first polarisedep collider, therefore there might be surprising effects influencing hadron and lepton polarisation • the unknown unknowns

17. BACKUP EIC User Meeting 2014

18. Luminosity Measurement: physics processes • Bremsstrahlung ep egp: • Bethe-Heitler (collinear emission): • very high rate of ‘zero angle’ photons and electrons, but • sensitive to the details of beam optics at IP • requires precise knowledge of geometrical acceptance • suffers from synchrotron radiation • sperature limitation • pile-up • QED Compton (wide angle bremsstrahlung): • lower rate, but • stable and well known acceptance of central detector •  Methods are complementary, different systematics HERA Concept: • normally only g is measured • Hera: reached 1-2% systematic uncertainty • NC DIS: • in (x,Q2) range where F2 is known to O(1%) • for relative normalisation and mid-term yield control EIC User Meeting 2014

19. Luminosity Detectors Dipole Magnet very thin Converter Vacuum Chamber g e- g e+/e- e+ Segmented ECal L3 L1 L2 • 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 EIC User Meeting 2014 • zero degree calorimeter • high rate  measured energy proportional to # photons • subject to synchrotron radiation • alternative pair spectrometer

20. Requirements from Physics on IR • Summarized at: • https://wiki.bnl.gov/eic/index.php/IR_Design_Requirements • Hadron Beam: • the detection of neutrons of nuclear break up in the outgoing hadron beam direction  location/acceptance of ZDC • the detection of the scattered protons from exclusive and diffractive reaction in the outgoing proton beam direction • the detection of the spectator protons from 3He and Deuterium • location/acceptance of RP; • impact of crab-cavities on forward scattered protons • Lepton Beam: • the beam element free region around the IR • minimize impact of detector magnetic field on lepton beam •  synchrotron radiation • space for low Q2 scattered lepton detection • space for the luminosity monitor in the outgoing lepton beam direction • space for lepton polarimetry • Important • EIC is a high luminosity machine 1033 cm-2s-1 • such controlling systematics becomes crucial • luminosity measurement • lepton and hadron polarization measurement EIC User Meeting 2014

21. eRHIC Lepton Beam • eRHIC design is using the idea of a “Gatling” electron gun with a combiner?  20 cathodes  one proton bunch collides always with electrons from one specific cathode • Challenge: • Integrate Compton polarimeter into IR and Detector design • together with Luminosity monitor and low Q2-tagger • longitudinal polarization  Energy asymmetry • segmented Calorimeter  to measure possible transverse polarization component  position asymmetry • 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 polarization. • A problem discussed for ILC •  influences where we want to measure polarization in the ring • How much polarization 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 polarization profile for the lepton bunches • if then in the longitudinal direction can be circumvented with 352 MHz RF EIC User Meeting 2014