An Electron-Nucleon Collider at FAIR

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1 An Electron-Nucleon Collider at FAIR Wolfgang Gradl for the study group Institut für Kernphysik Physics at a High Energy Electron Ion Collider Seattle, 19 th October 009

2 Outline FAIR and PANDA Accelerator considerations Physics studies Gluon helicity g DVCS Using material from A. Jankowiak, A. Lehrach and J. Pretz W. Gradl ENC at FAIR

3 FAIR Facility for Antiproton and Ion Research p Linac SIS 100/300 UNILAC SIS 18 Radioactive Ion Production Target HESR Ring/Device Beam Energie Intensity SIS100 protons 30 GeV 4x10 13 Super FRS Antiproton Production Target 38 U 1 GeV/u 5x10 11 intensity increase factor CR FLAIR 100 m CR/RESR/NESR ion and antiproton storage and experiment rings RESR NESR HESR antiprotons 14 GeV ~10 11 Super-FRS rare-isotope beams 1 GeV/u <10 9 W. Gradl ENC at FAIR 3

4 HESR layout p ring, high-intensity or high-precision modes Momentum range: GeV/c Circumference: 575 m Straight sections: electron cooler, target section W. Gradl ENC at FAIR 4

5 Experimental setup PANDA detector Magnet system Chicane dipole Compensation solenoid PANDA solenoid PANDA dipole Chicane dipole Main quadrupoles W. Gradl ENC at FAIR 5 β x,y *= 1 to 10m

6 An easy idea: ENC at HESR P HESR pring Idea emerged Aug 008 s > 10 GeV 3.3 GeV/c e on 15 GeV/c p polarised e (> 80%) 8MV ecool e -pol. e- -inj. ering PANDA polarised p, d (> 80%) (transversal & longitudinal) use PANDA detector as much as possible Double polarised Electron Nucleon Collider Luminosity: 8 HERA (unpol.) Common effort of German universities (Bonn, Mainz, Dortmund) in collaboration with Research Centres Jülich, DESY, GSI,... W. Gradl ENC at FAIR 6

7 Accelerator considerations W. Gradl ENC at FAIR 7

8 Accelerator Working Group K. Aulenbacher, D. Barber, O. Boldt, R. Heine, W. Hillert, A.Jankowiak, A. Lehrach, Chr. Montag, P. Schnizer, T. Weis W. Gradl ENC at FAIR 8

9 Requirements for Interaction Region Acceptance angles in proton direction: 0 to 5 : detection and momentum resolution of protons in forward direction 5 to 155 : particle detection in target spectrometer 175 to 180 : detection of electrons scattered at small angles Preserve PANDA geometry and PANDA central detector, other than inner tracker (r = 30 cm, l = 1.5 m) β x,y 0.3 m for high luminosity Aperture radii: 6σ p cm for protons, 10σ p cm for electrons W. Gradl ENC at FAIR 9

10 IR design Sufficient separation at s = 1.44 m for 00 bunches β x,y = 0.3 m [Chr. Montag (BNL)] W. Gradl ENC at FAIR 10

11 HESR electron cooler Momentum range (Antiprotons): GeV/c Electron energy: MeV Electron current: 0 1 A Electron radius: 5 mm Temperature of electron beam (t,l): 1eV, 0.5 mev Magnetic field (cooling section): 0. T Field qualtiy (rms): B r /B < 10 5 rad Length of cooling section: L eff = 4 m The Svedberg Laboratory Uppsala University needs upgrade for ENC A. Lehrach W. Gradl ENC at FAIR 11

12 Machine parameters, luminosity Baseline design (protons) ecooler parameters: E = 8 MeV, I = 3 A, B = 0. T, T T = 1 ev, T L = 0.5 mev, B r /B < 10 5, L = 4 m RF parameters: f = 5 MHz, U = 300 kv HESR / 15GeV p L [ring circumference, m] ~ 575 ε norm / ε geo [mm mrad, rms].1 / 0.13 p/p (rms) ~ β IP [m] 0.3 r IP [mm, rms] 0. ering / 3GeV l (bunch length) [m] n (particle / bunch) h (number of bunches) f coll (collision freq) [MHz] ~ 5 l coll (bunch distance) [m] ~ 5.76 Q sc (space charge) 0.05 ξ (beam-beam parameter) L (luminosity) [cm - s -1 ] ~ 10 3 W. Gradl ENC at FAIR 1 A. Lehrach; BetaCool program, JINR Dubna

13 Machine parameters, luminosity Advanced design (protons) ecooler parameters: E = 8 MeV, I = 3 A, B = 0. T, T T = 1 ev, T L = 0.5 mev, B r /B < 10 5, L = 4 m RF parameters: f = 104 MHz, U = 300 kv HESR / 15GeV p L [ring circumference, m] ~ 575 ε norm / ε geo [mm mrad, rms].3 / 0.14 p/p (rms) ~ β IP [m] 0.1 r IP [mm, rms] 0.1 ering / 3GeV l (bunch length) [m] n (particle / bunch) h (number of bunches) f coll (collision freq) [MHz] ~ 104 l coll (bunch distance) [m] ~.88 Q sc (space charge) 0.1 ξ (beam-beam parameter) L (luminosity) [cm - s -1 ] ~ W. Gradl ENC at FAIR 13 A. Lehrach; BetaCool program, JINR Dubna

14 Machine open questions / to do list Upgrade of the electron cooler Lattice for the electron ring Preservation of electron polarisation Modification of interaction region for high luminosity Deuterons: need β IP < 0.1 m to reach 103 cm s 1 IR needs modifying See A. Lehrach s talk at EINN workshop 009 at Milos for complete overview W. Gradl ENC at FAIR 14

15 Physics studies W. Gradl ENC at FAIR 15

16 Physics channels under study Gluon helicity DVCS Transversity Factorisation in fragmentation W. Gradl ENC at FAIR 16

17 Kinematic region covered /GeV 10 Q p = 3.0 GeV, p =15.0 GeV e p W=4GeV x=1,w=m_p x=0.1 x=0.01 ϑ=0.1 4 x=10 6 x=10 E =GeV ϑ=0 ϑ=π/ ϑ=0 muon y E =1GeV E =10GeV E =0.5GeV W=13GeV ϑ=3 Playground in Q y plane (Pol(γ ) y) Blue band: acceptance hole from 5-5 Higher Q min for µ W. Gradl ENC at FAIR 17

18 Gluon helicity g Study by J. Pretz W. Gradl ENC at FAIR 18

19 How to access the gluon distribution? Use hadronic final state in deep inelastic scattering: e + N e + hadrons + X d p u u q q g q hadrons * γ µ hadrons q µ How to tag Photon -Gluon- Fusion sub-process γ g q q? W. Gradl ENC at FAIR 19

20 How to access the gluon distribution? Use hadronic final state in deep inelastic scattering: e + N e + hadrons + X d p u u q q g g q hadrons * γ µ hadrons q µ How to tag Photon -Gluon- Fusion sub-process γ g q q? W. Gradl ENC at FAIR 19

21 How to tag γ g q q? Cleanest way: Look at charmed particles resulting from the fragmentation of the process γ g c c: c 0 D N g (p = x g p ) * g N γ c c 0 D = c u K π + x g x Bj no intrinsic charm, no charm quarks in string fragmentation If both charmed particles are reconstructed, one has access to x g W. Gradl ENC at FAIR 0

22 Results on g from DIS g/g COMPASS, open charm, prel., 0 06 COMPASS, high p, Q >1 (GeV/c), prel., 0 04 T COMPASS, high p, Q <1 (GeV/c), prel., 0 04 T HERMES, high p, all Q T HERMES, single high p hadrons, all Q, prel. T SMC, high p, Q >1 (GeV/c) T GRSV at µ =3 GeV fit with G>0, µ =3(GeV/c) fit with G<0, µ =3(GeV/c) 1 10 G =.5 x g Data show small values of g/g at x g 0.1 confirmed by indirect measurements Scaling violation of g p,n,d 1 structure function p p scattering at RHIC all measurements are concentrated around x g = 0.1, little is known about g(x g ) only COMPASS point is obtained with the (least model dependent) open charm method this result is obtained in 00 days of running W. Gradl ENC at FAIR 1

23 Results on g from DIS g/g COMPASS, open charm, prel., 0 06 COMPASS, high p, Q >1 (GeV/c), prel., 0 04 T COMPASS, high p, Q <1 (GeV/c), prel., 0 04 T HERMES, high p, all Q T HERMES, single high p hadrons, all Q, prel. T SMC, high p, Q >1 (GeV/c) T GRSV at µ =3 GeV fit with G>0, µ =3(GeV/c) fit with G<0, µ =3(GeV/c) 1 10 G =.5 x g Data show small values of g/g at x g 0.1 confirmed by indirect measurements Scaling violation of g p,n,d 1 structure function p p scattering at RHIC all measurements are concentrated around x g = 0.1, little is known about g(x g ) only COMPASS point is obtained with the (least model dependent) open charm method this result is obtained in 00 days of running W. Gradl ENC at FAIR 1

24 QCD analysis on g(x) xf(x) Q =10 GeV u u - 10 g x de Florian, Sassot, Stratmann, Vogelsang largest error in the region x g < 0.1 RHIC covers and will cover 0.01 < x g < 0. on the other hand: all spin effects are observed at large x W. Gradl ENC at FAIR

25 Better Reconstruction of x g At collider, can reconstruct both D using information of one D 0 (5% corr.) hout recontructed x g hout Entries 5347 Mean x Mean y RMS x RMS y both D 0 (70% corr.) hout recontructed x g hout Entries 5347 Mean x Mean y RMS x RMS y true x g true x g W. Gradl ENC at FAIR 3

26 Diluting factors More interesting than L alone: FOM = (diluting factors) L diluting factor ratio COMPASS ENC unpolarised single spin target (P T f ) a) (3 b) ) double spin asymmetries (P T fp B ) a) (3 b) ) reconstruction of hadronic? final state mass resolution displaced vertices target fragmentation a) for 6 LID target b) for NH 3 target Huge potential for polarisation observables! W. Gradl ENC at FAIR 4

27 Summary g(x) Increase of FOM compared to fixed target experiment by two orders of magnitude possible (16 from f P T P B, > 7 from D 0 reconstruction)! Not only increase in FOM but also qualitative improvements (reconstruction of x g ) in parallel measurement of helicity distributions W. Gradl ENC at FAIR 5

28 Deep Virtual Compton Scattering Studies done by D. Kang, M. Fritsch & W. Gradl W. Gradl ENC at FAIR 6

29 Cross Section dσ = DVCS + BH Bethe-Heitler (BH) contributes as background dσ = (dσ BH + dσunpol DVCS + e l a BH Re(A DVCS )) cos(nφ) + (P l dσpol DVCS + e l P l a BH Im(A DVCS )) sin(nφ) e l : lepton charge, P l : lepton polarisation, A 1 H(x,ξ,t) dx 1 x ξ+iɛ, Φ : (l, l plane, γ, p plane) Exploit angular dependence, σ e+ σ e, σ σ,... access to various contributions, handle on GPDs W. Gradl ENC at FAIR 7

30 Deep Virtual Compton Scattering using PANDA setup θ p /degree W. Gradl ENC at FAIR 8

31 Reconstruction efficiency using PANDA setup particle efficiency resolution δp/p resolution δθ/θ e 83% < % < % γ 93% < % < 5% p 64% < 1% < 10% combined efficiency 43% W. Gradl ENC at FAIR 9

32 Kinematic range [D. Kang] W. Gradl ENC at FAIR 30

33 Summary DVCS already with present PANDA setup good acceptance forward tracking to be improved further studies needed (ensure exclusivity, backgrounds,... ) W. Gradl ENC at FAIR 31

34 Summary A polarised electron-nucleon collider with L > 10 3 cm s 1 and s 00 GeV has great potential in helping to understand nucleon structure ENC is interesting extension to FAIR programme Accelerator working group established First designs for machine and interaction zone look promising but a lot of detailed work to be done Spin and beam dynamics in e ring Beam dynamics in HESR, bunch formation Electron cooler... Physics studies gaining momentum W. Gradl ENC at FAIR 3