e+a Experiments at an Electron Ion Collider

Transcription

1 e+a Experiments at an Electron Ion Collider 10 Parton Gas Thomas Ullrich RIKEN/RBRC Workshop on Future Directions in High Energy QCD Q 2 (GeV 2 ) Gold Calcium Proton EIC Coverage Color Glass Condensate October 22, 2011 Λ 2 QCD A x Confinement Regime

2 New Regime of Hadronic Wave Function non-perturbative region Y = ln 1/x BFKL DGLAP ln 2 QCD ln Q 2 2

3 New Regime of Hadronic Wave Function Y = ln 1/x non-perturbative region ln 2 QCD BFKL DGLAP ln Q 2 σ r,nc (x,q 2 ) 2 i x = , i=21 x = , i=20 x = , i=19 x = , i=18 x = , i=17 x = , i=16 x = , i=15 x = , i=14 x = , i=13 x = , i=12 x = 0.005, i=11 x = 0.008, i=10 x = 0.013, i=9 x = 0.02, i=8 x = 0.032, i=7 HERA combined Fixed Target HERAPDF 1.0 x = 0.05, i=6 pqcd and DGLAP & BFKL evolution works with high precision ( HERA) 10 x = 0.08, i=5 x = 0.13, i=4 x = 0.18, i=3 1 x = 0.25, i= x = 0.40, i= x = 0.65, i= Q 2 (GeV 2 ) 2

4 New Regime of Hadronic Wave Function Y = ln 1/x non-perturbative region BFKL DGLAP 7B "!5O!5S!5$ HERA taught us that glue dominates for x < 0.1 '()*+#,'-./' ' :;<4'=:>32;<8:;? '9@A34'=:>32;<8:;? ()*+'G;2=>;=23'/=:>;8@:H'I@2J8:K'E2@=1 L=>45'-M?H5'N'"O"#"O&'0&!!O6'PQRS" '7K'0U"V&!6 'C & 'D'"!'E3F & 7= T 7A T ln 2 QCD ln Q 2!5& '7G'0U"V&!6 pqcd and DGLAP & BFKL evolution works with high precision ( HERA)! "! #$ "! #% "! #& "! #" " 7 2

5 New Regime of Hadronic Wave Function Y = ln 1/x However DGLAP & BFKL evolution have their limits non-perturbative region BFKL DGLAP ln 2 QCD ln Q 2 3

6 New Regime of Hadronic Wave Function Y = ln 1/x non-perturbative region ln 2 QCD BFKL DGLAP ln Q 2 built in high energy catastrophe xg rapid rise violates unitary bound Need to tame/saturate evolution '()'*+ &, However DGLAP & BFKL evolution have their limits Gluon self-interaction has dramatic consequences at small x: &"!-!" - " + &. /.&".012 & + &. / &!" #$!" #%!" #&!" #! ' :.+;<.=>??@?A.1BB@B.) C.=B11,?@?A.1BB@B.) C.=>'1D, EFG@BBA.1BB@B.) C.=>'1D, + &. /.&"".012 & 4567*.HI<.J3*."!&""3 3

7 New Regime of Hadronic Wave Function Y = ln 1/x However DGLAP & BFKL evolution have their limits non-perturbative region BFKL DGLAP ln 2 QCD ln Q 2 3

8 New Regime of Hadronic Wave Function Y = ln 1/x However DGLAP & BFKL evolution have their limits non-perturbative region ln 2 QCD BFKL DGLAP Issue: To what Q 2 is pqcd applicable? ln Q 2 ;F $#! "#!! &! %" ;K)5 )!#!1: )*+,-./0&#1)2234)56789#: )8;6#)<=>87?# )@AB89)<=>87?# )6C7C@8?7DEC?DA=)<=>87?# ) %' &! %( &! ( ( J )G)()H8I ;L)5 )!#!1: %& &! Hints at low-q 2 that things are not in order xg(x,q 2 ) < 0 (OK in NLO) xg(x,q 2 ) < xqsea(x,q 2 )? MC7>N)(!&& ; & 3

9 New Regime of Hadronic Wave Function Y = ln 1/x non-perturbative region ln 2 QCD saturation region BK/JIMWLK BFKL DGLAP Q 2 s (Y) ln Q 2 New Approach: Non-Linear Evolution McLerran-Venugopalan Model: Weak coupling description of wave function Gluon field Aµ~1/g gluon fields are strong classical fields! BK/JIMWLK: non-linear effects saturation characterized by Q s (x) Wave function is Color Glass Condensate in IMF description 4

10 New Regime of Hadronic Wave Function Y = ln 1/x non-perturbative region saturation region BK/JIMWLK BFKL DGLAP Geometric Scaling Q 2 s (Y) *p tot ( b) Appearance of QS at HERA: DIS cross section for x < 0.01 only function of one variable (Stasto, Golec-Biernat, Kwiecinski, 01) Marquet, Schoeffel, Phys.Lett. B639, 471 ln 2 QCD ln Q 2 Geometric scaling predicted by nonlinear JIMWLK/BK evolution equations (Iancu, Itakura, McLerran 02) 10 1 H1 ZEUS ZEUS Low Q 2 E665 NMC x < = Q 2 /Q 2 s(x) 5

11 QS: Matter of Definition and Frame (I) Rest frame of hadron: qq dipole (Mueller dipole) DGLAP: σqq r 2 αs(µ 2 ) xg(x,µ 2 ) explodes with r 2 violates unitarity Saturation: σqq 1-exp(-r 2 αs(µ 2 ) xg(x,µ 2 )) e Q 2 r q q qq 2 saturation non-linear-regime dσ q q Common definition: d 2 b =2N N (x =1/Q S,Y)=1 e 1/4 0 dilute linearregime Q 2 s 1 r 2 Dipole Radius N (x =1/Q S,Y)=1 e 1/2 N (x =1/Q S,Y)=1/2 Important: universality of λ=dlnqs/dy Y = ln 1/x 6

12 QS: Matter of Definition and Frame (II) Infinite Momentum Frame: BFKL (linear QCD): splitting functions gluon density grows BFKL: 7

13 QS: Matter of Definition and Frame (II) Infinite Momentum Frame: BFKL (linear QCD): splitting functions gluon density grows BK (non-linear): recombination of gluons gluon density tamed BFKL: BK adds: 7

14 QS: Matter of Definition and Frame (II) Infinite Momentum Frame: BFKL (linear QCD): splitting functions gluon density grows BK (non-linear): recombination of gluons gluon density tamed BFKL: BK adds: At Qs: gluon emission balanced by recombination k T φ(x, k T 2 ) ~ 1/k T max. density Unintegrated gluon distribution depends on kt and x: the majority of gluons have transverse momentum kt ~ QS (common definition)? know how to do physics here α s 1 Λ QCD Q s α s << 1 kt 7

15 Reaching the Saturation Region HERA (ep): Despite high energy range: F2, Gp(x, Q 2 ) outside the saturation regime Need also Q 2 lever arm! Only way in ep is to increase s Would require an ep collider at s ~ 1-2 TeV 2 ) Q 2 ( G e V ZEUS BPC 1995 ZEUS SVTX 1995 H1 SVTX 1995 HERA 1994 HERA predicted Q 2 s proton (min. bias) x 8

16 Reaching the Saturation Region HERA (ep): Despite high energy range: F2, Gp(x, Q 2 ) outside the saturation regime Need also Q 2 lever arm! Only way in ep is to increase s Would require an ep collider at s ~ 1-2 TeV 2 ) Q 2 ( G e V ZEUS BPC 1995 ZEUS SVTX 1995 H1 SVTX 1995 HERA 1994 HERA predicted Q 2 s proton (min. bias) x 8

17 Reaching the Saturation Region HERA (ep): Despite high energy range: F2, Gp(x, Q 2 ) outside the saturation regime Need also Q 2 lever arm! Only way in ep is to increase s Would require an ep collider at s ~ 1-2 TeV Different approach (ea): (Q A s ) 2 2 A cq 0 x 1/3 L ~ (2m N x) -1 > 2 R A ~ A 1/3 Probe interacts coherently with all nucleons 8

18 Reaching the Saturation Region HERA (ep): Despite high energy range: F2, Gp(x, Q 2 ) outside the saturation regime Need also Q 2 lever arm! Only way in ep is to increase s Would require an ep collider at s ~ 1-2 TeV Different approach (ea): 500 (Q A s ) 2 2 A cq 0 x 1/3 2 (GeV 2 ) Q Kowalski, and Lappi Teaney and Phys.Rev.D68:114005,2003 Venugopalan, PRL 100, (2008)); Armesto et al., PRL 94:022002; Kowalski, Teaney, PRD 68:114005) Q 2 s,g Au (central) Ca (central) protons Enhancement of Q S with A saturation regime reached at significantly lower energy in nuclei A 1/3 ~ 7 1/x 8

19 EIC: The e+a Physics Program Investigate with precision the universal dynamics of gluons Central Topics: Study the Physics of Strong Color Fields Establish the existence of the saturation regime Investigate the dynamics of this regime How do fast probes interact with the gluonic medium? Energy loss, Fragmentation processes Study the nature of color singlet excitations (Pomerons) What s the role in gluons in the nuclear structure? see talks by Abhay & Jianwei 9

20 e+a Physics Program: Science Matrix Result of INT workshop in Seattle in fall 10 (arxiv: ) Deliverables Observables What we learn Phase-I Phase-II integrated gluon distributions F2,L nuclear wave function; saturation, Qs gluons at 10-3 < x < 1 saturation regime kt dependent gluons; gluon correlations di-hadron correlations non-linear QCD evolution / universality onset of saturation measure Qs transport coefficients in cold matter large-x SIDIS; jets parton energy loss, shower evolution; energy loss mechanisms light flavors and charm; jets rare probes and bottom; large-x gluons 10

21 e+a Physics Program: Science Matrix Result of INT workshop in Seattle in fall 10 (arxiv: ) Deliverables Observables What we learn Phase-I Phase-II integrated gluon distributions F2,L nuclear wave function; saturation, Qs gluons at 10-3 < x < 1 saturation regime kt dependent gluons; gluon correlations di-hadron correlations non-linear QCD evolution / universality onset of saturation measure Qs transport coefficients in cold matter large-x SIDIS; jets parton energy loss, shower evolution; energy loss mechanisms light flavors and charm; jets rare probes and bottom; large-x gluons b dependence of gluon distribution and correlations Diffractive VM production and DVCS, coherent and incoherent parts Interplay between small-x evolution and confinement Moderate x with light and heavy nuclei Extend to low-x range (saturation region) 10

22 Example 1: FL Structure Function 11

23 Why is FL Important? FL (x,q 2 ) ~ xg(x,q 2 ) Momentum distribution of glue ratio = F L total leading twist L FL total F e+p e+au J. Bartels, K. Golec-Biernat and L. Motyka, 11 (based on IPSat Model) 12

24 Why is FL Important? FL (x,q 2 ) ~ xg(x,q 2 ) Momentum distribution of glue ratio = F L total leading twist L FL total F e+p e+au J. Bartels, K. Golec-Biernat and L. Motyka, 11 (based on IPSat Model) 12

25 Why is FL Important? FL (x,q 2 ) ~ xg(x,q 2 ) Momentum distribution of glue ratio = F L total leading twist L FL total F e+p e+au Q 2 ~ 2 GeV 2 J. Bartels, K. Golec-Biernat and L. Motyka, 11 (based on IPSat Model) 12

26 Why is FL Important? FL (x,q 2 ) ~ xg(x,q 2 ) Momentum distribution of glue ratio = F L total leading twist L FL total F e+p e+au Q 2 ~ 2 GeV 2 200% J. Bartels, K. Golec-Biernat and L. Motyka, 11 (based on IPSat Model) pqcd: higher twist O(1/Q 2 ) Very different in saturation models! 12

27 First (Last) FL Measurement at HERA HERA in 2007 (last run) run at different energies enabling the first solid measurement of FL in ep Ep = 920, 575, 460 GeV F Q 2 = 2 GeV 2 2,F L Q 2 = 2.5 GeV 2 Q 2 = 3.5 GeV H1 Collaboration Q 2 = 5 GeV 2 Q 2 = 6.5 GeV 2 Q 2 = 8.5 GeV Q2 = 12 GeV 2 Q 2 = 15 GeV 2 Q 2 = 20 GeV Q 2 = 25 GeV Q 2 = 35 GeV Q 2 = 45 GeV 2 F 2 H1 Data F L H1 Data F 2 ACOT F L ACOT x Here H1: 1.5 < Q 2 /GeV < < x < 0.01 Aaron et al., Eur. Phys. J.C

28 First (Last) FL Measurement at HERA HERA in 2007 (last run) run at different energies enabling the first solid measurement of FL in ep Ep = 920, 575, 460 GeV F L 0.4 x H1 Collaboration ZEUS HERAPDF1.0 NLO CT10 NLO NNPDF2.1 NLO H1 MSTW08 NNLO JR09 NNLO ABKM09 NNLO Q 2 / GeV 2 Uncertainties (sys and stat) too large to distinguish unambiguously between models Aaron et al., Eur. Phys. J.C

29 Measuring FL with the EIC (I) d 2 ep ex σ dxdq 2 = 4πα 2 e.m. 1 y + y 2 xq 4 2 F 2 (x,q 2 ) y 2 2 F L (x,q2 ) quark+anti-quark momentum distributions gluon momentum distribution 14

30 Measuring FL with the EIC (I) d 2 ep ex σ dxdq 2 = 4πα 2 e.m. 1 y + y 2 xq 4 2 F 2 (x,q 2 ) y 2 2 F L (x,q2 ) quark+anti-quark momentum distributions gluon momentum distribution In practice use reduced cross-section: σ r = d 2 σ dxdq 2 xq 4 2πα 2 [1 + (1 y) 2 ] = F 2 (x, Q 2 ) y 2 1+(1 y) 2 F L(x, Q 2 ) = F 2 (x, Q 2 ) y2 Y + F L(x, Q 2 ) 14

31 Measuring FL with the EIC (I) d 2 ep ex σ dxdq 2 = 4πα 2 e.m. 1 y + y 2 xq 4 2 F 2 (x,q 2 ) y 2 2 F L (x,q2 ) quark+anti-quark momentum distributions gluon momentum distribution In practice use reduced cross-section: σ r = d 2 σ dxdq 2 xq 4 2πα 2 [1 + (1 y) 2 ] = F 2 (x, Q 2 ) y 2 1+(1 y) 2 F L(x, Q 2 ) = F 2 (x, Q 2 ) y2 Y + F L(x, Q 2 ) How to extract FL Need different values of y 2 /Y + FL slope of σr vs y 2 /Y + F2 intercept of σr vs y 2 /Y + with y-axis σr 0 y 2 /Y + 14

32 Measuring FL with the EIC (II) In order to extract F L one needs at least two measurements of the inclusive cross section with wide span in inelasticity parameter y (Q 2 = sxy) F L runs at various s longer program + Need sufficient lever arm in y 2 /Y +! " #$ % &'* &') &'( &'" Limits on y 2 /Y + : At small y: detector resolution for e At large y: radiative corrections and charge symmetric background & & &'+ &'" &', &'( &'- &') &'. &'* &'/ + E. Aschenauer 11!

33 Measuring FL with the EIC (II) In order to extract F L one needs at least two measurements of the inclusive cross section with wide span in inelasticity parameter y (Q 2 = sxy) F L runs at various s longer program " # $%&'( # ) *+, *+ # *+!!"!#$!"#$%"&'"()*"+!*"!)"#$%,'!"#$%"&'"+!*"!)*"-!"#$%,'!"#$%"&'"!)*"-!*"())"#$%,' ()"#$%"&'"!)*"-!*"())"#$%,' +)"#$%"&'"!)*"-!*"())"#$%,'.)"#$%"&'"!)*"-!*"())"#$%,' Need sufficient lever arm in y 2 /Y + Limits on y 2 /Y + : At small y: detector resolution for e At large y: radiative corrections and charge symmetric background * *+ -. *+ -/ *+ -, *+ -# *+ -* E. Aschenauer 11!

34 Issue for e+a: Radiative corrections Emission of real photons experimentally often not distinguished from non-radiative processes: soft photons, collinear photons Ideal case: True case: Q 2 Q 2 = (l l ) 2, x B = 2P (l l ) Q Q 2 = (l l k) 2 2, x B = 2P (l l k) Distortion of observed structure function: Radiator functions Ri(l, l, k) 16

35 Effect of radiative corrections r c (y) Correction function is fct. of y: ep: 5 GeV + 50 GeV < x < < x < < x < y EPS09 5 GeV GeV 10-3 < x < 10-2 W had > 1.4 GeV y 0.6 Au Fe He p H. Spiesberger 11 17

36 Effect of radiative corrections r c (y) Correction function is fct. of y: ep: 5 GeV + 50 GeV < x < < x < < x < y EPS09 5 GeV GeV 10-3 < x < 10-2 W had > 1.4 GeV How to deal with it? Method 1 simple kinematic cuts in W reduce corrections slightly not very effective Method reconstruct x, Q 2 via hadronic final state (Jacquet-Blondel) Problem in e+a: parton/hadron energy-loss, secondary particle production (typical at low-pt) 0.4 y 0.6 Au Fe He p rc(y) H. Spiesberger 11 ep: 5 GeV + 50 GeV < x < no cut W > 1.4 GeV y

37 First Studies: Extraction of F2 and FL F2,L extracted from pseudo-data generated for 1 month running at 3 EIC (erhic) energies (here ep) GeV GeV GeV 1 F 2,L Q 2 =1.39 GeV GeV GeV 13.9 GeV 2 F GeV GeV 2 Data points added to theoretical expectations from ABKM09 PDF set to indicate stat. errors valid for Q 2 > 2.5 GeV x x F L x 18

38 Example 2: Dihadron Correlations 19

39 h-h Mid-Rapidity Correlation in pa at RHIC beam view Δφ d+au h-h correlations: near and away side are p+p like helped to establish that away side suppression in Au+Au is a final state effect What happens at forward rapidities? x1,2 mt/ s exp(±η) " (! " '&%$ #!" &!" %!" $!"!!" #! )*+,-$""-./0 pp, pa, and AA ep (150 GeV) y= !" #'!" #(!" #&!" #%!" #$!" #!! ) y =

40 h-h Forward Correlation in pa at RHIC p side-view p Low gluon density (pp): pqcd predicts 2 2 process back-to-back di-jet large-x1 (q dominated) low-x2 (g dominated) beam-view π 21

41 h-h Forward Correlation in pa at RHIC p side-view A Low gluon density (pp): pqcd predicts 2 2 process back-to-back di-jet large-x1 (q dominated) low-x2 (g dominated) beam-view π 21

42 h-h Forward Correlation in pa at RHIC side-view p A large-x1 (q dominated) low-x2 (g dominated) beam-view π Low gluon density (pp): pqcd predicts 2 2 process back-to-back di-jet High gluon density (pa): 2 many process expect broadening of away-side Small-x evolution multiple emissions Multiple emissions broadening Back-to-back jets (here leading hadrons) may get broadening in pt with a spread of the order of QS First prediction by: C. Marquet ( 07) Latest review: Stasto, Xiao, Yuan arxiv: (Sep. 11) 21

43 π 0 -π 0 Forward Correlation in pa at RHIC Uncorrected Coincidence Probability (rad -1 ) p+p π 0 π 0 + X, s = 200 GeV d+au π 0 π 0 + X, s = 200 GeV d+au π 0 π 0 + X, s = 200 GeV p T,L > 2 GeV/c, 1 GeV/c < p T,S < p T,L η L =3.2, η S =3.2 p+p STAR Preliminary Peaks Δφ σ ± 0.01 π 0.68 ± p T,L > 2 GeV/c, 1 GeV/c < p T,S < p T,L η L =3.2, η S =3.2 p T,L > 2 GeV/c, 1 GeV/c < p T,S < p T,L η L =3.1, η S =3.2 CGC+offset Peaks Peaks d+au peripheral Δφ σ d+au central Δφ σ ± ± 0.02 STAR Preliminary π 0.99 ± 0.06 STAR Preliminary π 1.63 ± Δφ Δφ Δφ arxiv: v1 Striking broadening in central dau of away-side compared to pp and peripheral dau Robust CGC result - difficult to reproduce in DGLAP x range: x ~

44 Dihadron Correlations: a Theorist s View Excellent saturation signature: e Q 2 q jet-1 "#)#* +,- #)#.#&'( -#)#* +," #)#"#&'(! " #$#%#&'( " q jet-2 A :'#$#.3#&'( */0102#-33#&'( 2456'47#-33#&'(82 "#9#2456'47#-33#&'( Either Jets or use leading hadrons from jets (dihadrons) φ beam view Dominguez, Xiao, Yuan 11 Prediction: factor ~2 suppression at EIC energies At small x, multi-gluon distributions are as important as singlegluon distributions Test of universality: p+a and e+a are sensitive to "dipole" and "quadrupole" operators which (same for both processes) 23

45 Dihadron Correlations: an Experimentalist s View Simulations using DPMJet-III generator: no suppression but leading twist shadowing e+au Ee=30 GeV EAu=100 GeV/n Statistics 7 EIC min Liang Zheng (Wuhan/BNL) e+p 24

46 Dihadron Correlations: an Experimentalist s View Simulations using DPMJet-III generator: no suppression but leading twist shadowing e+au Ee=30 GeV EAu=100 GeV/n Statistics 7 EIC min Liang Zheng (Wuhan/BNL) e+p 0.81±0.03 due to shadowing 24

47 Dihadron Correlations: an Experimentalist s View Simulations using DPMJet-III generator: no suppression but leading twist shadowing Ee=30 GeV EAu=100 GeV/n Statistics 7 EIC min Liang Zheng (Wuhan/BNL) 0.81±0.03 due to shadowing 24

48 Dihadron Correlations: an Experimentalist s View Simulations using DPMJet-III generator: no suppression but leading twist shadowing Ee=30 GeV EAu=100 GeV/n Statistics 7 EIC min Liang Zheng (Wuhan/BNL) 0.81±0.03 due to shadowing What if suppression is small? How sensitive are we? 24

49 Dihadron Correlations: an Experimentalist s View Use realistic detector simulations Assume 30% suppression only Based on statistics equivalent to 7 min EIC running Smeared ea/ep with a 30% suppression away side ea/ep without smear no suppression ea/ep with smear & 30% suppression 0.56 = 0.8 (1-0.3) 0.81±0.03 and 0.56±0.02 Even with small statistics: straight forward measurement that is sensitive to at least 30% suppression True golden measurement 25

50 Example 3: Diffractive Physics 26

51 Seeing Diffraction A DIS event (theoretical view)!"!!"!#$%&' # ) ( (%&$&' $! * #" 27

52 Seeing Diffraction A DIS event (experimental view) 27

53 Seeing Diffraction A DIS event (experimental view) Activity in proton direction 27

54 Seeing Diffraction 27

55 Seeing Diffraction A diffractive event (experimental view)? 27

56 Seeing Diffraction A diffractive event (theoretical view) 27

57 Hard Diffraction in DIS at Small x e W 2 q β γ*(q 2 ) e X (M X ) t = (p-p ) 2 β is the momentum fraction of the struck parton w.r.t. the Pomeron xip = x/β: momentum fraction of the exchanged object (Pomeron) w.r.t. the hadron p, P x IP t P,p Largest rapidity gap in event or breakup of A Y (M Y ) Diffraction in e+p: coherent p intact incoherent breakup of p HERA: 15% of all events are hard diffractive Diffraction in e+a: coherent diffraction (nuclei intact) breakup into nucleons (nucleons intact) incoherent diffraction Predictions: σdiff/σtot in e+a ~25-40% 28

58 Hard Diffraction in DIS at Small x #!! #!!! " e+p #!!! " Diffraction in e+p: coherent p intact incoherent breakup of p HERA: 15% of all events are hard diffractive Diffraction in e+a: coherent diffraction (nuclei intact) breakup into nucleons (nucleons intact) incoherent diffraction Predictions: σdiff/σtot in e+a ~25-40% 28

59 Hard Diffraction in DIS at Small x! " e+p ' %! ) %! +, - &. #!! #!! & * # %! ( %! #!! & %! %!! " Diffraction in e+p: coherent p intact incoherent breakup of p HERA: 15% of all events are hard diffractive!!"!#!"!$!"%&!"%' & * Diffraction in e+a: coherent diffraction (nuclei intact) breakup into nucleons (nucleons intact) incoherent diffraction Predictions: σdiff/σtot in e+a ~25-40% 28

60 Why Is Diffraction So Important? Sensitive to gluon momentum distribution dσ γ p pv dt dσ q q d 2 b r2 α s xg(x, µ 2 )T (b) σ g(x,q 2 ) 2 Ψ V d 2 b Ψe ib dσ q q 2 γ 1 z z r (1 z) r x x p p b V = J/ψ, φ, ρ Sensitive to spatial gluon distribution dσ dt Fourier Transformation of Source Density ρ g (b) Hot topic: Gluonic form factor just Wood-Saxon + nucleon g(b) Incoherent case: measure of fluctuation/ lumpiness in GA(b) & * ' %! ) %! # %! %! ( & %! %! +, - &.!!"!#!"!$!"%&!"%' & * 29

61 Why Is Diffraction So Difficult? Key in identifying diffraction is rapidity gap requires hermetic detector does not allow separation of coherent from incoherent Measuring the scattered nucleus with Forward Spectrometer (Roman Pots) coherent cannot separate from beam incoherent cannot reconstruct all fragments to get p LRG Cannot measure t in ea except in exclusive vector meson production, e.g.: e + A e + J/ψ + A Lack of t not a big issue for measurements of F2 D, FL D and hence G(x,Q 2 ) 30

62 Large Rapidity Gap Method (LRG) Identify Most Forward Going Particle (MFP) Works at HERA but at higher s EIC smaller beam rapidities Diffractive ρ 0 production at EIC: η of MFP η Rapidity Gap η max Other particles (if any) e+p: RAPGAP: MFP in Event GeV - DIS GeV - DIS GeV - DIS GeV - DIS GeV - DIS GeV - Diff GeV - Diff GeV - Diff GeV - Diff GeV - Diff η p/a beam Detector Acceptance p/a direction 0 e direction η e beam Hermeticity requirement: needs just to detector presence does not need momentum or PID simulations: s not a show stopper for EIC (can achieve 1% contamination, 80% efficiency) DIS M. Lamont 10 Diffractive rapidity 31

63 Exclusive Vector Meson Production ' % ) ()*+,-.(/01 $! # 3 $! & $! % $! #!"$ $!!%# ' % ) ()*+,-.(/01 3 $! $! & % $! ' % ) ()*+,-.(/01 #!"# $! 3 $! $! & % $! $! $! $! $ 2$ $! 2% $! 2& $! * * :5*;< $ 2$ $! 2% $! 2& $! $ 2$ $! 2% $! 2& $! 23 $! Sartre 0.1 Event Generator!!"!#!"$!"$#!"%!"%#!"& % =*=+,/01 '!!"!#!"$!"$#!"%!"%#!"& % =*=+,/01 '!!"!#!"$!"$#!"%!"%#!"& % =*=+,/01 ' Golden channel: e + A e + A + VM t = (PA-PA ) 2 = (PVM + Pe - Pe) 2 photoproduction (Q 2 0): t p 2 T,VM moderate Q 2 : need pt of e Issues: transverse spread of the beam (distorts small t) requires beam cooling detect incoherent events detect nuclear breakup 32

64 Detecting Nuclear Breakup Detecting all fragments pa = pn + pp + pd + pα... not possible Focus on n emission Zero-Degree Calorimeter Requires careful design of IR Additional measurements: Fragments via Roman Pots γ via EMC Traditional modeling done in pa: Intra-Nuclear Cascade Particle production Remnant Nucleus (A, Z, E*,...) ISABEL, INCL4 De-Excitation Evaporation Fission Residual Nuclei Gemini++, SMM, ABLA (all no γ) 2 '$!($)*+& :2097;<3.4*79$=75.71* 2!"#$%&?/55/82$' ,-./0*1$23.4*35,67'8970/ ' ' 2 >'74470/82$9*5/13* 1*.7@5 33

65 Experimental Reality Here erhic IR layout: Need ±X mrad opening through triplet for n and room for ZDC Big questions: Excitation energy E*? ep: dσ/my ~ 1/MY m m ea? Assume ep and use E* = MY - mp as lower limit number of n number of neutrons IP m m m m 1.9 cm (p o /2.5) 1.1m m 10 D=120 mm theta distribution of neutrons at E* = 500 MeV SMM =10 mrad =4 mrad =10 mrad beam D=120 mm theta distribution of neutrons at E* = 500 MeV neutrons mrad mrad p c / 2.5 ZDC histotheta500 Entries Mean RMS Gemini++ 16 histotheta500 Entries 2098 Mean RMS h beam e beam E* (MeV) mrad 34

66 Experimental Reality Here erhic IR layout: Need ±X mrad opening through triplet for n and room for ZDC Big questions: Excitation energy E*? ep: dσ/my ~ 1/MY 2 ea? Assume ep and use E* = MY - mp as lower limit IP m 4.50 m 1.95 m m m m 1.9 cm (p o /2.5) m m 10 D=120 mm =10 mrad =4 mrad =10 mrad beam D=120 mm neutrons p c / 2.5 ZDC 16 h beam e beam Simulations using Gemini++ & SMM show it works: For E*tot 10 MeV and 2.5 mrad n acceptance we have rejection power of at least Separating incoherent from coherent diffractive events is possible at a collider with n-detection via ZDCs alone 34

67 Example 4: Properties of Cold Nuclear Matter 35

68 Parton Propagation and Fragmentation? Hadronization not well understood non-perturbative process Nuclei as space-time analyzer EIC can measure: fragmentation time scales to understand dynamic in medium energy loss to characterize medium Observables pt distribution broadening attenuation of hadrons γ* see talk by Jianwei Qiu 36

69 Hadron Attenuation in ndis Energy loss: gluon bremstrahlung? hadronization outside media prehadron absorption? color neutralization inside the medium Energy transfer in lab rest frame HERMES: ν = 2-25 GeV EIC: 10 < ν < 1600 GeV (LHC range) EIC: heavy flavor! Accardi, Dupre 11 EIC Statistics for L = 200 fb -1 37

70 Hadron Attenuation in ndis Energy loss: gluon bremstrahlung? hadronization outside media prehadron absorption? color neutralization inside the medium Energy transfer in lab rest frame HERMES: ν = 2-25 GeV EIC: 10 < ν < 1600 GeV (LHC range) EIC: heavy flavor! Multiplicity Ratio s = 14 GeV Z HERMES data! + K + EIC error bars h (R is arbitrary) A s = 200 GeV^2 20 < " < 30 GeV! + + K D Meson 50 < " < 70 GeV! + + K D Meson Accardi, Dupre 11 EIC Statistics for L = 200 fb -1 37

71 pt Broadening in ndis ΔpT 2 directly linked to saturation scale e.g. BDMPS, Kopeliovich 10 ΔpT 2 of jets as direct measurement of q ^ z, ν dependence to be taken into account 2! P T P T! Vs z h 2 P T 0.08! !P T HERMES data " + " - + K EIC error bars 2 (!P T is arbitrary) D Meson B Meson Accardi, Dupre HERMES data + " - " EIC error bars 2 (!P T is arbitrary) D Meson s = 32 GeV Z A 38

72 pt Broadening in ndis ΔpT 2 directly linked to saturation scale e.g. BDMPS, Kopeliovich 10 ΔpT 2 of jets as direct measurement of q ^ z, ν dependence to be taken into account 2 Ratio Vs Q 2 2 Multiplicity Ratio vs Q 2 ΔpT 2 vs Q 2 Accardi, Dupre # P T 0.08 % Q HERMES data! + EIC error bars A (R is arbitrary) h 2! + (s=200 GeV ) 2! + (s=1000 GeV && 100 < " < 130 GeV) 2 P T 0.04 # HERMES data! + -! EIC error bars 2 (#P T is arbitrary) 2! + (s=200 GeV ) 2! + (s=1000 GeV ) Q EIC: large Q 2 coverage to detect modifications in DGLAP evolution 2 Q

73 Summary The e+a program at an EIC is unprecedented, allowing the study of matter in a new regime where physics is not described by ordinary QCD set of key (aka golden or killer) measurements identified studies underway to establish their feasibility with realistic detectors and machine parameters. The e+a program is also a challenge experimentally new difficulties compared to e+p measurements never conducted in a collider so far found no show-stopper for key measurements most key measurements are energy ( s) hungry but less luminosity demanding 39