E.C. Aschenauer arXiv: arXiv:

E.C. Aschenauer eRHIC NSAC Cost Review Requirements from Physics:  High Luminosity ~ cm -2 s -1 and higher  Flexible center of mass energy 20 to 100 GeV upgradable to 140 GeV  Electrons and protons/light nuclei (p, He 3 or D) highly polarized  Wide range of nuclear beams (D to Au, U, Pb)  a wide acceptance detector with good PID (e/h and , K, p)  wide acceptance for protons from elastic reactions and neutrons from nuclear breakup neutrons from nuclear breakup

3 low Q 2 taggerandluminositydetector Hadron PID: -1<  <1: proximity focusing LiF (Aerogel)-RICH (CLEO) + TPC: dE/dx 1<|  |<3: Dual-radiator RICH (Aerogel + C 4 F 10 ) (modeled: LHC-b RICH-I) 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 -4<  <4: Tracking (TPC+GEM+MAPS) MAPS: CMOS Monolithic Active Pixel Sensors   E.C. Aschenauer eRHIC NSAC Cost Review 2015 To Roman Pots & Zero Degree Calorimeter hadron beam lepton beam Machine clear space +/- 4.5 m around IP detector components down to 2 o Detector magnet aligned with lepton beam backgrounds due to synchrotron and beam gas events have to be kept at a minimum Detector fully model in Geant Hcal  -vertex Ecal GEM RICH TPC

E.C. Aschenauer eRHIC NSAC Cost Review eRHIC: Interaction Region and ancillary detector systems: hadron and lepton polarimeters luminosity detector low Q 2 tagger ZDC and Roman Pot systems all needed from the beginning

E.C. Aschenauer 5 Summarized at: Hadron Beam: 1.the detection of neutrons of nuclear break up in the outgoing hadron beam direction  location/acceptance of ZDC  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; 3.space for hadron and local polarimetry Lepton Beam: 1.minimize impact of detector magnetic field on lepton beam  synchrotron radiation 2.space for low Q 2 scattered lepton detection 3.space for the luminosity monitor in the outgoing lepton beam direction 4.space for lepton polarimetry Important eRHIC is a high luminosity machine cm -2 s -1 such controlling systematics becomes crucial  luminosity measurement  lepton and hadron polarization measurement eRHIC NSAC Cost Review 2015

6 Large Rapidiy Gap method o M X system and e’ measured o Proton dissociation background o High acceptance in  for detector two methods: to select events Need for HCal in the forward region E.C. Aschenauer eRHIC NSAC Cost Review 2015 Cuts: Q 2 >1 GeV, GeV, 0.01<y<0.85 DVCS – photon kinematics: 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 Need for Roman Pots (RP) and Zero Degree Calorimeter (ZDC) detector acceptance:  >4.5 increasing Hadron Beam Energy: influences max. photon energy at fixed  photons are boosted to negative rapidities (lepton direction)

 expected beam width calculation  from table 3-1 in design report and the attached figure obtained from Dejan of the beta function  beta_x = 2014m (at z=18m)  beta_y = 3465m (at z=18m)  epsilon (normalized) = 0.2e-6m  gamma = 270 (for 250GeV protons)

E.C. Aschenauer eRHIC Brainstorming Meeting, BNL, Aug < Q 2 < GeV < x < ~ 1 year for EIC-WP eRHIC EIC-WP Plot slope generated exponential in t dipole-fit:    dof = 17.2  statistics for t > 0.8 basically not existent not existent  cannot distinguish exp. from dipole shape exp. from dipole shape Study by S. Fazio remember: t ~ p t 2 of the forward going scattered proton going scattered proton p t = p cosΘ acceptance in theta limited by beam acceptance and beta-fct by beam acceptance and beta-fct as the beam stay clear region is as the beam stay clear region is defined by them defined by them

|t| > GeV 2 5 GeV x 100 GeV E.C. Aschenauer 9 high t  low b uncertainty does not yet accounted that exp. shape cannot be determined from dipole the t dependence can be transformed to a b t dependence through a Fourier transform

E.C. Aschenauer eRHIC NSAC Cost Review difference in unfolded b t spectrum based on lowest t accessible p t > 300 MeV vs. 200 MeV even higher p t cuts would be bad

E.C. Aschenauer 11 Results from GEMINI++ for 50 GeV Au +/-5mrad acceptance seems sufficient eRHIC NSAC Cost Review 2015 Important: For coherent VM-production rejection power For coherent VM-production rejection power of incoherent needed up to 10 4 of incoherent needed up to 10 4  ZDC detection efficiency is critical  ZDC detection efficiency is critical Can we reconstruct the eA collision geometry:

eRHIC NSAC Cost Review 2015 Concept: Use Bremsstrahlung ep  ep  as reference cross section  different methods: o Bethe Heitler, QED Compton, Pair Production  Hera: reached 1-2% systematic uncertainty Goals for Luminosity Measurement:  Integrated luminosity with precision δL< 1%  Measurement of relative luminosity: physics-asymmetry/10 eRHIC challenges:  with cm -2 s -1 one gets on average 23 bremsstrahlungs photons/bunch for proton beam  A-beam Z 2 -dependence  this will challenge single photon measurement under 0 o E.C. Aschenauer 12 zero degree photon calorimeter high rate  measured energy proportional to # photons  subject to synchrotron radiation additional pair spectrometer low rate   The calorimeters are outside of the primary synchrotron radiation fan   The spectrometer geometry  low energy cutoff in the photon spectrum,  depends on dipole field and calorimeter transverse location

 Two estimates of the expected angular distrubition of Bremsstrahlung photons  Bethe-Heitler calculation  DJANGOH MC simulation relative scaling (please ignore numbers on yaxis) Bethe-HeitlerDJANGOH typical angle of emission is less than 0.03mrad typical angle of emission is less than 0.03mrad though there is a fairly long tail to the distribution though there is a fairly long tail to the distribution roughly factor of 10 less than contribution from beam divergence for top energy ep collisions (see next slide) roughly factor of 10 less than contribution from beam divergence for top energy ep collisions (see next slide)

 calculation of the angular beam divergence (in radians)  sigma_theta = angular beam divergence  epsilon = (normalized) emittance (taken from table 3-1 of the design report)  gamma = lorentz factor  beta* = beam optics parameter at IP (5cm taken from table 3-1)  for 20x250 GeV e+p collisions  for other beam conditions

 considering the added effect if the IP moves a bit and is off center  look at DJANGOH ep->ep  events fed into EicRoot  both curves include crossing angle (10 mrad) and angular beam divergence (0.1mrad) and a flat z vertex spread of +/- 2.5cm  black has all events at (0,0) (x,y) vertex  red has events with (x,y) vertex distributed flat with +/- 0.5cm  note that in this definition, the electron going direction is 0 degrees

 will need roughly +/- 1 to 2 mrad of aperture for bremsstrahlung photons for lumi measurement  depends strongly on beam optics, not so much on the actual physics process  do we have that much space?  I think yes in the current design (depending on exactly how far down the lumi system is installed)

E.C. Aschenauer EIC R&D Meeting January e-Beam Hadrons synrad Matching  16 mrad bends “D0” Cryostat Cryostat CryostatCryostat Cryostat Cryostat Plan View of IR Layout 10 mrad crossing DetectorRegion(e-beamaligned) Philosophy: detect forward particles in the warm section between the IR magnets and Crab Cavities ZDC RomanPots Design: compromises physics and machine requirements low Q 2 tagger (not to scale)

E.C. Aschenauer eRHIC NSAC Cost Review Extended IR region and by pass modeled in Geant low Q 2 -tagger RP gain acceptance with a gain acceptance with a station very far down (>40m) station very far down (>40m) still need to model this still need to model this seems to be lost in magnet yoke seems to be lost in magnet yoke can work with CAD to improve can work with CAD to improve -6 < θ < -5 mrad -5 < θ < -4 mrad -4 < θ < -3 mrad -3 < θ < -2 mrad -2 < θ < -1 mrad -1 < θ < 0 mrad 0 < θ < 1 mrad 0 < θ < 1 mrad e-polarimeter and luminosity detector are next to be integrated in IR and modeled in Geant

Polarized hydrogen Jet Polarimeter (HJet) Source of absolute polarization (normalization for other polarimeters) Slow (low rates  needs looong time to get precise measurements) Proton-Carbon Polarimeter RHIC and AGS Very fast  main polarization monitoring tool Measures polarization bunch profile and lifetime Needs to be normalized to HJet Local Polarimeters at Experiments sits between spin rotators Critical to define spin direction at experiments  can use the concept of pC All of these systems are necessary for the proton beam polarization measurements and monitoring E.C. Aschenauer 19 eRHIC NSAC Cost Review 2015 All the equipment is existing from RHIC with years of operating experience NEED to make sure the methods continue to work

572 nm pulsed laser 572 nm pulsed laser laser transport system laser transport system laser light polarization laser light polarization measured continuously measured continuously Considerations:  Measure Polarization directly at IP  overlap of bremsstrahlungs and compton photons  location, where bremsstrahlung contribution is small and synchrotron radiation is minimized  Measure after / before IP need to measure at location spin is fully longitudinal or transverse or transverse  1/6 turn should rotate spin by integer number of π  constrain on location  Polarimeter technology needs to allow to have precision to measure polarisation correlated to bunch #, gatling gun cathode #, colliding proton bunch # correlated to bunch #, gatling gun cathode #, colliding proton bunch #  need to still integrate electron polarimeter fully into machine lattice / IR E.C. Aschenauer eRHIC NSAC Cost Review  Method: Compton backscattering longitudinal polarization  Energy asymmetry longitudinal polarization  Energy asymmetry transverse polarization  position asymmetry transverse polarization  position asymmetry  segmented Calorimeter  to measure both components HERA LPol: achieved systematic uncertainty 1.4%