Physics Driven Machine Requirements for the Electron Ion Collider (EIC) Rolf Ent, QCDFP BNL, 07/17/06 Will step-by-step go over (some) machine.

Physics Driven Machine Requirements for the Electron Ion Collider (EIC) Rolf Ent, QCDFP Meeting @ BNL, 07/17/06 Will step-by-step go over (some) machine requirements Occasionally, my personal (and naïve) view Short Intro on Main Science of EIC to guide this - What are the Energy Requirements? - What Kind of Nuclei are Essential? - What are the Polarization Requirements? - Does one need Positrons? - What are the Implications for the Interaction Region? - What are the Implications for the Detector? - Are there any constraints on the Bunch Spacing???

EIC: Electron Ion Collider e-e- e+e+ p Polarized electrons Polarized protons Ions (e.g. Au) Polarized light ions D, 3 He Effective neutron Polarized positrons (Variable  s) Urgency to establish next- generation ep/eA collider facility Fundamental QCD studies Nucleon spin structure and Partonic structure of nucleus Urgency to establish next- generation ep/eA collider facility Fundamental QCD studies Nucleon spin structure and Partonic structure of nucleus eRHICRHIC RHIC Brookhaven National LaboratoryJefferson Laboratory ELIC Seeheim, Germany1997 MIT 2000 IUCF 1999 BNL 2002 BNL 1999 JLab 2004 Yale 2000 BNL 2006

NSAC Report 2002 Electron-Ion Collider … Ring-ring and linac-ring options

A large community believes a high luminosity polarized electron ion collider is the ultimate tool to understand the structure of quark-gluon systems, nuclear binding, and the conversion of energy into matter to such detailed level that we can use/apply QCD. An Electron Ion Collider will allow us to look in detail into the sea of quarks and gluons, to create and study gluons, and to discover how energy transforms into matter From DOE 20-year plan Spin Structure of the Nucleon - Gluon and sea quark polarization - The role of orbital momentum Partonic Understanding of Nuclei - Gluon momentum distributions in Nuclei - Fundamental explanation of Nuclear Binding - Gluons in saturation, the Colored Glass Condensate Precision Tests of QCD - Bjorken Sum Rule - Hard diffraction

JLab 12 GeV Upgrade: The 12 GeV Upgrade, with its 10 38 + luminosity, is expected to allow for a complete spin and flavor dependence of the valence quark region, both in nucleons and in nuclei. Electron Ion Collider (eRHIC/ELIC) Provide a complete spin and flavor dependence of the nucleon and nuclear sea, study the explicit role that gluons play in the nucleon spin and in nuclei, open the new research territory of “gluon GPDs”, and study the onset of the physics of saturation. Personal, biased view, as JLab person

Physics Driven Machine Requirements for the Electron Ion Collider (EIC) - What are the Energy Requirements? - What Kind of Nuclei are Essential? - What are the Polarization Requirements? - Does one need Positrons? - What are the Implications for the Interaction Region? - What are the Implications for the Detector? - Are there any constraints on the Bunch Spacing???

World Data on F 2 p Structure Function In general, Next-to-Leading- Order (NLO) perturbative QCD (DGLAP) fits do a good job of reproducing the data over the full measurement range. g EIC is the ultimate gluon (spin) machine

EIC – Science: Gluons, gluons, gluons EIC 12-GeV Longitudinal Structure Function F L Experimentally can be determined directly IF VARIABLE ENERGIES! Highly sensitive to effects of gluon

DESY data showed a collapse of the F 2 Structure Function data at small x and low Q 2 The Parton-Hadron Transition at Low Q 2 Revisited Parameterize the rise of F 2 as a function of Q 2 as = -  lnF 2 /  lnx Hadron-hadron scattering energy dependence Observe transition from partons to hadrons (constituent quarks) in data at a distance scale  0.3 fm ?? (Caldwell)

Luminosity of up to 1x10 33 cm -2 sec -1 (one-day life time) One day  50 events/pb Supports Precision Experiments Lower value of x scales as s -1 DIS Limit for Q 2 > 1 GeV 2 implies x down to 1.0(2.5) times 10 -4 Significant results for 200 events/pb for inclusive scattering If Q 2 > 10 GeV 2 required for Deep Exclusive Processes can reach x down to 1.0(2.5) times 10 -3 Typical cross sections factor 100- 1,000 smaller than inclusive scattering Significant results for 20,000- 200,000 events/pb  high luminosity essential Luminosity Considerations for EIC eRHIC ELIC (W 2 > 4) x Q 2 (GeV 2 ) W 2 <4 eRHIC: x = 10 -4 @ Q2 = 1 ELIC : x = 2.5x10 -4 12 GeV: x = 4.5x10 -2 Include low-Q 2 region

EIC – Science: Gluons, gluons, gluons EIC 12-GeV Glue in full glory again… How many gluons can you stuff in a unit area? At high enough density saturation must set in! Gluon density at low x rises as x -  ~ x -0.3 Gluon density in nucleus rises as A 1/3 Lower value of x scales as s -1 E.g., E cm = 100 GeV, A = 200 vs. E cm = 65 GeV, A = 40 gives factor of 2 in gluon density (did I do that right?), or a factor of 10 in lower x reach compared to the proton case. [HERA: E cm = 290 GeV, A = 1  factor of 4.2]

EIC – Science: Gluons, gluons, gluons Glue in full glory again… How many gluons can you stuff in a unit area? At high enough density saturation must set in! Gluon density at low x rises as x -  ~ x -0.3 Gluon density in nucleus rises as A 1/3 Lower value of x scales as s -1 E.g., E cm = 100 GeV, A = 200 vs. E cm = 65 GeV, A = 40 gives factor of 2 in gluon density (did I do that right?), or a factor of 10 in lower x reach compared to the proton case. Saturation: the Color Glass Condensate

Quarks in a Nucleus “EMC Effect” Space-Time Structure of Photon F 2 A /F 2 D 10 -4 10 -3 10 -2 10 -1 1 x Can pick apart the spin-flavor structure of EMC effect by technique of flavor tagging, in the region where effects of the space-time structure of hadrons do not interfere (large !) Nuclear attenuation negligible for > 50 GeV  hadrons escape nuclear medium undisturbed ELIC Need: reach shadowing region (eRHIC+ELIC ok), range in A (D-Ca fine)

eRHIC projections for nuclear quark distributions T. Sloan 1 pb -1

Sea-Quarks and Gluons in a Nucleus Drell-Yan  No Nuclear Modifications to Sea-Quarks found at x ~ 0.1 Where is the Nuclear Binding? Flavor tagging can also (in principle) disentangle sea-quark contributions Constraints on possible nuclear modifications of glue come from 1) Q 2 evolution of nuclear ratio of F 2 in Sn/C (NMC) 2) Direct measurement of J/Psi production in nuclear targets Compatible with EMC effect? Precise measurements possible of  Nuclear ratio of Sn/C?  J/Psi production F2F2 G

Nuclear Binding  Natural Energy Scale of QCD: O(100 MeV)  Nuclear Binding Scale O(10 MeV)  Does it result from a complicated detail of near cancellation of strongly attractive and repulsive terms in N-N force, or is there another explanation? How can one understand nuclear binding in terms of quarks and gluons? Complete spin-flavor structure of modifications to quarks and gluons in nuclear system may be best clue.

The Spin Structure of the Proton  From NLO-QCD analysis of DIS measurements  ≈ 0.2  G = 1.0±1.2  quark polarization  q(x)  first 5-flavor separation from HERMES  transversity  q(x)  a new window on quark spin  azimuthal asymmetries from HERMES and JLab  future: flavor decomposition  gluon polarization  G(x)  RHIC-spin and COMPASS will provide some answers!  orbital angular momentum L  how to determine?  GPD’s ½ = ½  +  G + L q + L g We want to solve this puzzle!  need large range in x and Q 2 and high luminosity for precision!

World Data on F 2 p World Data on g 1 p  50% of momentum carried by gluons  20% of proton spin carried by quark spin The dream is to produce a similar plot for x  g(x) vs x

Bjorken Sum Rule: Γ 1 p - Γ 1 n = 1/6 g A [1 + Ο(α s )] Precision QCD Test, tested to 10-15% Work in progress… 2-3% at EIC? Needs: O(1%) Ion Polarimetry!!! Holy Grail: excellent determination of  s (Q 2 )

Flavor Decomposition through semi-inclusive DIS Solution: Detect a final state hadron in addition to scattered electron  Can ‘tag’ the flavor of the struck quark by measuring the hadrons produced: ‘flavor tagging’ DIS probes only the sum of quarks and anti-quarks  requires assumptions on the role of sea quarks }  quark Fragmentation Function

Flavor Decomposition HERMES EIC White Paper 2002 @10 33 luminosity (Stoesslein, Kinney)

New Spin Structure Function: Transversity Nucleon’s transverse spin content  “tensor charge” No transversity of Gluons in Nucleon  “all-valence object” Chiral Odd  only measurable in semi-inclusive DIS  first glimpses exist in data (HERMES, JLab-6)  Later work: more complicated  COMPASS 1 st results: ~0 @ low x  Future: Flavor decomposition - (in transverse basis)  q(x) ~ EIC Monte Carlo work by Naomi Makins Need (high) transverse ion polarization

k k'k' ** q q'q'  pp'p' e Model calculation of u-quark distributions in protons at different momentum fractions. Generalized Parton Distributions and Nucleon Tomography A Major new direction in Hadron Physics aimed at the 3-D mapping of the quark structure of the nucleon. Simplest process: Deep-Virtual Compton Scattering Accessible through (Deep) Exclusive Reactions

Tomography of the Nucleon  A framework to extract 3-D spatial information of quarks in a nucleon at rest  Generate Wigner (quantum phase-space) distributions  Obtain proton images at fixed x  Direct connection to GPDs through Fourier Transforms Ji Ultimate strategy: Data on various hard exclusive processes Deconvolution and global fits to obtain GPDs Further constraints from Lattice QCD Obtain tomographic 3-D pictures of the nucleon Understand origins of mass and spin structure Generalized Parton Distributions

(so, the accounting must be fine!) “The numbers don’t add up” Understand origins of mass and spin structure… “People expected most of a proton’s properties to come from the three quarks” But no. The three not only fail to bring enough mass to the party, but they also fall short on spin. So far, the answer [to the gluon contribution to the proton spin] seems to be no more than 40%, and perhaps zero. “If the answer turns out to be at the low end of this range, we’re going to have spin crisis No. 2” “Can we say we understand the proton if we can’t answer these basic questions?” We learned that protons are balls of energy (gluons!). Need to understand the role of orbital momentum!

GPDs & Deeply Virtual Exclusive Processes x Deeply Virtual Compton Scattering (DVCS) t x+  x-  H(x, , t ), E(x, , t ),.. hard vertices  – longitudinal momentum transfer x – quark momentum fraction – t – Fourier conjugate to transverse impact parameter  “handbag” mechanism “Generalized Parton Distributions”     J G =  1 1 )0,,()0,,( 2 1 2 1 xE x HxdxJ qqq Quark angular momentum (Ji’s sum rule) X. Ji, Phy.Rev.Lett.78,610(1997)

Orbital Angular Momentum Analysis of hard exclusive processes leads to a new class of generalized parton distributions Four new distributions: helicity conserving  H(x, ,t), E(x, ,t) helicity-flip  H(x, ,t), E(x, ,t) ~ ~ “skewedness parameter”   mismatch between quark momenta  sensitive to partonic correlations 3-dimensional GPDs give spatial distribution of partons and spin  Angular Momentum J q = ½  + L q ! New Roads:  Deeply Virtual Meson Production @ Q 2 > 10 GeV 2  disentangles flavor and spin!   and  Production give access to gluon GPD’s at small x (<0.2) Can we achieve same level of understanding as with F 2 ?

Generalized Parton Distributions and Pion Electroproduction

What E cm and Luminosity are needed for Deep Exclusive Processes? New Roads:   and  Production give access to gluon GPD’s at small x (<0.2)  Deeply Virtual Meson Production @ Q 2 > 10 GeV 2  disentangles flavor and spin! Well suited processes for the EIC  transverse spatial distribution of gluons in the nucleon Can we do such measurements at fixed x in the valence quark region? This IS important if we really want a full picture of orbital motion… Original motivation for EIC: HERMES at higher L (+ E cm ) HERMES : s 1/2 = 7, L ~ 10 31  FOM = 1.0 EIC low :s 1/2 = 20, L ~ 10 33  FOM = 1.5 EIC high : s 1/2 = 100, L ~ 10 33  FOM = 0.0024 fixed x:  ~ s/Q 2 (Mott) x 1/Q 4 (hard gluon exchange) 2 (o.k, remember  L ~ 1/Q 6 )  Use for back-of-envelope count rate estimates ~ 1/s 2 x L Initial Conclusion: Needs High L at lower E cm range

Projected A(W - ) Assuming xF 3 will be known Parity-Violating g 5 Structure Function To date unmeasured due to lack of high Q 2 polarized e-p possibility. From EIC White Paper (Contreras et al). Assumptions: 1)Q 2 > 225 GeV 2 2)One month at luminosity of 10 33 Requires positron beam

Access GPDs through DVCS,  and A (symmetries) Accessed by cross sections Accessed by beam/target spin asymmetry t=0 Quark distribution q(x) -q(-x) DIS measures at  =0 Difference of  for e - and e + constrains real part  Positrons important, but can be at lower Luminosity

Physics Driven Machine Requirements for the Electron Ion Collider (EIC) - What are the Energy Requirements? - What Kind of Nuclei are Essential? - What are the Polarization Requirements? - Does one need Positrons? - What are the Implications for the Interaction Region? - What are the Implications for the Detector? - Are there any constraints on the Bunch Spacing??? Yield to Discussion Session with C. Montag. Realistic designs exist, need to worry about synchrotron radiation, want +/- 3 meters of free space for detector!

Open Charm Production (Glue, Glue, Glue!): 1)Dominant reaction mechanism through glue at small x  e/ion momentum mismatch not so relevant and created nearly at rest  Decay products at large angles. 2)Background reduction critical issue  requires <100  vertex resolution  drives vertex detector 3)Decay products have typical momenta between 0-2 GeV  Need good particle id in this region and good track capability in large rate region  for the former, use dE/dx plus TOF of hodoscope? (with 100 ps timing resolution, 3.2 meters gives 3  /K separation) 4)HERA typical momentum cutoff of 5 GeV, studies show can push down to ~Field (in Tesla) of Solenoid. STAR has only 0.5 T field and lower cut-off of 0.4 GeV  Need low T (about 0.5) magnetic field in central region. Detector Considerations @EIC

Open Charm Production @EIC (Antje Bruell, EIC MC Group Meeting @ Boulder, Nov. 04) Black curve: divided by p D to cross check life time  ok Large rate at small vertex separation  good vertex separation enhances rate vs. background Example of vertex displacement for charm (D 0 ) events 100  m

Open Charm Production @EIC - II PYTHIA – hadronic D 0 decays (Antje Bruell, EIC MC Group Meeting @ Boulder, Nov. 04) Need both Particle Id. and vertex detection (preliminary) Charm counts from AROMA ~ Charm counts from PYTHIA (as cross check)

1)Can one get away with a small length inner vertex detector to only cover the bunch crossing? 2)Does one need a composite field structure (~0.5T in inner region, step function more radially out? ~PHENIX). 3)Is PbWO4 and a 0.5 T solenoid field sufficient for electron resolutions? Could we use a toroidal field? 4)What momentum resolutions are required for few-GeV/c pions/kaons? What field would be needed for this? 5)Is a gap in  /K identification acceptable for the intermediate hadron momenta (2-5? GeV/c)? 6)Are EM calorimeters all around the ring sufficient for very-small angle electron detection? 7)What are the implications of a 100 mr crossing angle? (relevant for ELIC only) Detector Considerations @EIC - Questions

Multiplicity for High-Energy Hadron Interactions F. Braccella and L. Popova, J. Phys. G 21 (1995) 1379 My Simple Estimate: Total Multiplicity ~ s 1/4 s 1/2 (GeV) n (article) 2s 1/4 20 (ISR/FNAL) 9 9 540 (SPS) 45 46 1800 82 86 CLAS(L = 2 x 10 34 )n = 3.7 CLAS12(L = 1 x 10 35 )n = 4.2 EICE cm = 65 (ELIC) 16 100 (eRHIC) 20 } Factor of 4-5 (close to empirical observation in CLAS)

7 GeV electron 150 GeV proton Typical one-event display from EIC Monte Carlo Count the hadrons  19 here Corresponds well to simple estimate (16) of before

Numerical Example at High Luminosity At a luminosity of 10 35 cm -2 s -1, the total hadronic production rate is about 1 x 10 7 s -1 Assume a data-acquisition capability of 5,000 s -1 [CLAS @ Moment, at dead times of 15%, has achieved an event rate of up to 8,000 s -1, a data rate of 30+ MB/s, using pipeline TDCs, dual-CPU ROCs, and multiprocessing in Event Builder]  Trigger would need to provide a factor of 2,000 rejection of hadronic events: seems challenging but near reality (CLAS12 assumes >2,000).

Bunch Spacing from Detector Point of View CLAS operates at a 500 MHz bunch frequency. The e - can be traced back to the specific bunch, which is then used as “RF time tag” to calibrate the detectors for the hadrons. Question: What are the implications in collider mode? 1. For the specific e-ion process, you still have the e - tag 2. Collection times for (fast) detection devices is 10-20 ns (e.g., silicon, scintillator, and PMT’s, but not for e.g. Ar calorimetry) 3. Ultrafast digitization allows determinination of time less than the resolving time of the specific detector (now, calibration becomes the main issue, cf. CLAS) 4. The multiplicity w.r.t. CLAS increases by a factor of 4-5 5. Hence, can one untangle the interactions separated in time by less than the resolving time of the detector in the face of pileup? 6. GHz digitizers with 8-bit accuracy already on the market (250 MHz flash ADCs (10/12 bit) being developed at JLab) Issue was/is also relevant for VLHC(<1.8 ns?), SLHC (12.5 ns?)

“Proof of Principle” “Easy” at a fixed-target facility with a 500 MHz beam structure 2 ns may well be doable 2/3 ns looks difficult

EIC Physics Specifications  Various Drivers: High L at HERMES+ Energies (E cm = 20+?): H, D, 3 He Large Reach in x (down to 10 -4 ?) for large range in A  Energy Asymmetry of ~ 10-20?  Needs Flexible Center-of-mass energy for L/T Separation  CW Luminosity of over 1x10 33 cm -2 sec -1 per Interaction Point More seems very useful at lower E cm range  Many Ion species of interest (Many of us Nuclear Physics Funded!)  Proton and neutron: H and D for sure, 3 He good  Light-medium ions not necessarily polarized  Up to Calcium for “EMC Effect”  Up to A = 200+ for Saturation/CGC  Longitudinal polarization of both beams in the interaction region (+Transverse polarization of ions +Spin-flip of both beams) all polarizations 70+% desirable, need good ion polarimetry  Positron Beams desirable, but lower luminosity seems o.k.

In Proton Rest Frame d 2  /dW dQ 2 =  (  T +   L ) =  T (1 +  R)  is flux of photons  T,L are cross sections for transversely, and longitudinally polarized photons to scatter from proton, with R their ratio.  is the relative flux F 2 = Q 2 /4  2  (  T +   L ) In Infinite Momentum Frame (Bjorken Limit: Q 2,  infinity, with x = Q 2 /2M fixed) d 2  /dxdQ 2 = 2  2 /xQ 4 [(1+(1-y) 2 )F 2 - y 2 F L ] F 2 =  f e 2 f x {q(x,Q 2 ) + q(x,Q 2 ) }, where e f is the parton charge and q(x,Q 2 ) the parton distribution F L = 0 in Leading Order (LO) in the Parton Model, but can be non-zero after gluon radiation. _

Physics Driven Machine Requirements for the Electron Ion Collider (EIC) Rolf Ent, QCDFP BNL, 07/17/06 Will step-by-step go over (some) machine.

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Physics Driven Machine Requirements for the Electron Ion Collider (EIC) Rolf Ent, QCDFP BNL, 07/17/06 Will step-by-step go over (some) machine.

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Presentation on theme: "Physics Driven Machine Requirements for the Electron Ion Collider (EIC) Rolf Ent, QCDFP BNL, 07/17/06 Will step-by-step go over (some) machine."— Presentation transcript:

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