Exclusive VM electroproduction

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1 Exclusive VM electroproduction γ * p V p V γ ρ ϕ ψ =,,, J /, ϒ Aharon Levy Tel Aviv University on behalf of the H and collaborations June, 28 A. Levy: Exclusive VM, GPD8, Trento

2 Why are we measuring σ ( W ) W δ IP soft dσ dt e b t g g hard Expect δ to increase from soft (~.2, from soft Pomeron value) to hard (~.8, from xg(x,q 2 ) 2 ) Expect b to decrease from soft (~ GeV -2 ) to hard (~4-5 GeV -2 ) June, 28 A. Levy: Exclusive VM, GPD8, Trento 2

3 Why are we measuring Use QED for photon wave function. Study properties of VM wf and the gluon density in the proton. June, 28 A. Levy: Exclusive VM, GPD8, Trento 3

4 Mass distributions ρ π + π Events/(.3 GeV) 6 4 ρ 2 pb - π DIS + π PHP M ππ (GeV) events (/3.5 MeV) 5 H φ K + K (a) number of events 5 5 J /ψ + µ µ ϒ µ + µ M.5. µµ [GeV] June, 28 m A. Levy: Exclusive VM, GPD8, Trento 4 KK [GeV]

5 Photoproduction σ W δ process becomes hard as scale (mass) becomes larger. real part of amplitude increases with hardness. June, 28 A. Levy: Exclusive VM, GPD8, Trento 5

6 σ(γ*p ρ p) (nb) 3 2 σ(w) ρ δ pb pb W (GeV) Q 2 (GeV 2 ) June, 28 A. Levy: Exclusive VM, GPD8, Trento 6

7 σ(w) ρ, φ H ρ electroproduction (preliminary) H φ electroproduction (preliminary) σ γ p ρp [nb] 3 2 H HERA- prel. H SV Q 2 [GeV 2 ] σ γ p φp [nb] 2 H HERA- prel. Q 2 [GeV 2 ] Fit W δ 2 W [GeV] Fit W δ 2 W [GeV] June, 28 A. Levy: Exclusive VM, GPD8, Trento 7

8 σ(w) - φ, J/ψ, γ p) (nb) p φ * σ (γ Q (GeV ) (a) 98- σ(γp J/ψp) [nb] a) H Q 2 [GeV 2 ] H Fit MRT (CTEQ6M) 5 5 σ DVCS [nb] W (GeV) 2 Q 2 = 8 GeV 2 Q 2 = 5.5 GeV 2 Q 2 = 25 GeV H W γp [GeV] June, 28 A. Levy: Exclusive VM, GPD8, Trento 8 W [GeV]

9 δ (Q 2 +M 2 ) - VM δ ρ 96- (2 pb - ) ρ 94 ρ 95 φ J/ψ DVCS 96- DVCS (prel.) (28 pb - ) J/ψ H DVCS H 96- DVCS H HERAII ρ H HERA- (prel.) Q 2 +M 2 (GeV 2 ) June, 28 A. Levy: Exclusive VM, GPD8, Trento 9

10 Kroll + Goloskokov: δ = ln (Q 2 /4) (close to the CTEQ6M gluon density, if parametrized as xg(x)~x -δ/4 ) δ ρ 96- (2 pb - ) ρ 94 ρ 95 φ J/ψ DVCS 96- DVCS (prel.) (28 pb - ) J/ψ H DVCS H 96- DVCS H HERAII ρ H HERA- (prel.) Q 2 +M 2 (GeV 2 ) June, 28 A. Levy: Exclusive VM, GPD8, Trento

11 σ γ*p ρp (nb) σ ( 2 2 Q M ) + n * γ p ρ σ(q 2 ) Fit to whole Q 2 range gives bad χ 2 /df (~7) p (prel.) (2 pb - ) June, 28 A. Levy: Exclusive VM, GPD8, Trento Q 2 (GeV 2 ) σ(γp J/ψp) [nb] σ / Fit.5.5 VM ρ ϕ J/ψ γ a) b) W γp = 9 GeV H Fit Fit + fit uncertainty MRT (MRST2) MRT (CTEQ6M) MRT (-S) MRT (H QCD Fit) n 2.44± ±.3 ± ±.8 ±.68.54±.9 ±.4 H Q 2 (GeV 2 ) comments Q 2 > GeV 2 Q 2 > GeV 2 All Q Q 2 [GeV 2 2 ] Q 2 >3 GeV 2

12 σ(q 2 ) σ [nb] H ρ electroproduction (preliminary) γ p ρ p H HERA- prel. H SV σ [nb] 2 H φ electroproduction (preliminary) γ p φ p H HERA- prel. H SV γ p ρ Y H HERA- prel. (x.5) γ p φ Y H HERA- prel. (x.5) - W = 75 GeV M Y < 5 GeV σ Q 2 ( ) γ p Q 2 +M 2 [GeV 2 ] * 2 ( Q + M ) 2 2 nq ( ) June, 28 A. Levy: Exclusive VM, GPD8, Trento 2 - W = 75 GeV M Y < 5 GeV Q 2 +M 2 [GeV 2 ] nq ( ) Q 2 2 (for Q 2 > GeV 2 )

13 Proton vertex factorisation IP IP elastic Y p-dissociative - σ γ p ρy / σ γ p ρp H ρ electroproduction (preliminary) H HERA- prel. σ γ p φy / σ γ p φp H φ electroproduction (preliminary) H HERA- prel photoproduction proton vertex factorisation.2 W = 75 GeV M Y < 5 GeV Q 2 [GeV 2 ] June, 28 A. Levy: Exclusive VM, GPD8, Trento 3.2 W = 75 GeV M Y < 5 GeV Q 2 [GeV 2 ] Similar ratio within errors for ρ and φ proton vertex factorisation in DIS

14 Fit dσ dt e b t b(q 2 ) ρ, γ : b (GeV -2 ) pb b [GeV -2 ] 8 6 H H HERA II e - p H HERA I A (-B log(q 2 /(2 GeV 2 ))) Q 2 [GeV 2 ] Q 2 (GeV 2 ) June, 28 A. Levy: Exclusive VM, GPD8, Trento 4

15 b(q 2 +M 2 ) - VM b(gev -2 ) ρ (2 pb - ) ρ 94 ρ 95 ρ H φ 98- φ 94 J/ψ 98- J/ψ J/ψ H 96- g g hard 6 4 < r >= b ( c) DVCS H 96- DVCS H HERAII e - p (prel.) DVCS (prel.) (28 pb - ) Q 2 +M 2 (GeV 2 ) June, 28 A. Levy: Exclusive VM, GPD8, Trento 5

16 Information on σ L and σ T Use ρ decay angular distribution to get r 4 density matrix element f(cos θ ) ( r ) + (3r )cos h θ h Events pb cosθ h R σ L = σt r ε 4 4 r ε - ratio of longitudinal- to transversephoton fluxes ( <ε> =.996) r 4 σ σ L L = = σ L + σt σtot using SCHC - cosθ h June, 28 A. Levy: Exclusive VM, GPD8, Trento 6

17 R=σ L /σ T (Q 2 ) R=σ L /σ T 2 When r 4 close to, error on R large and asymmetric advantageous to use r 4 rather than R. 8 2 pb r 4 = σ L / σ tot pb Q 2 (GeV 2 ) Q 2 (GeV 2 ) June, 28 A. Levy: Exclusive VM, GPD8, Trento 7

18 R=σ L /σ T (Q 2 ) H ρ and φ electroproduction (preliminary) R = σ L / σ T 5 γ p ρ Y H HERA- prel. H γ p φ Y H HERA- prel. H 2 4 Q 2 [GeV 2 ] June, 28 A. Levy: Exclusive VM, GPD8, Trento 8

19 R=σ L /σ T (M ππ ) R=σ L /σ T pb - <Q 2 >=3 GeV 2 <Q 2 >= GeV M ππ (GeV) R = σ L / σ T H ρ electroproduction (preliminary) γ p ρ Y H HERA- prel..6.8 m ππ [GeV] Why?? June, 28 A. Levy: Exclusive VM, GPD8, Trento 9

20 R=σ L /σ T (M ππ ) Possible explanation: R M 2 ππ α (M ππ ) 3 R (GeV 2 ) pb - <Q 2 >=3 GeV 2 <Q 2 >= GeV 2 example for α= M ππ (GeV) June, 28 A. Levy: Exclusive VM, GPD8, Trento 2

21 Photon configuration - sizes small k T large γ T : large size small size large config. k T small config. strong color forces large cross section color screening small cross section γ*: γ* T, γ* L γ* T both sizes, γ* L small size Light VM: transverse size of qq ~ size of proton Heavy VM: qq size small cross section much smaller (color transparency) but due to small size (scale given by mass of VM) see gluons in the proton σ~ (xg) 2 large δ June, 28 A. Levy: Exclusive VM, GPD8, Trento 2

22 σ L /σ tot (W) 4 r = σl / σ tot pb - <Q 2 > = <Q 2 > = <Q 2 > = <Q 2 > = W (GeV) σ L and σ T same W dependence σ L qq in small configuration σ T qq in small and large configurations small configuration steep W dep large configuration slow W dep qq large configuration is suppressed June, 28 A. Levy: Exclusive VM, GPD8, Trento 22

23 σ L /σ tot (t) 4 r = σl / σ tot.8 b b L T.6 size of γ* L γ* T large qq configuration suppressed.4 2 pb - <Q 2 > = 3 GeV 2 <Q 2 > = GeV t (GeV 2 ) June, 28 A. Levy: Exclusive VM, GPD8, Trento 23

24 σ(w) - DVCS γ * p γ p Final state γ is real γ T using SCHC initial γ* is γ* T but W dep of σ steep large γ* T configurations suppressed σ(γ * p γp) (nb) prel. (6 pb - ) 96- (95 pb - ) 2 W (GeV) June, 28 A. Levy: Exclusive VM, GPD8, Trento 24

25 Effective Pomeron trajectory Get effective Pomeron trajectory from dσ/dt(w) at fixed t ρ photoproduction June, 28 A. Levy: Exclusive VM, GPD8, Trento 25

26 Effective Pomeron trajectory α IP (t) α IP (t) ρ electroproduction t (GeV 2 ) 2 pb t (GeV 2 ) α IP (GeV -2 ) α IP () June, 28 A. Levy: Exclusive VM, GPD8, Trento 26

27 Comparison to theory All theories use dipole picture Use QED for photon wave function Use models for VM wave function usually take a Gaussian shape Use gluon density in the proton Some use saturation model, others take sum of nonperturbative + pqcd calculation, and some just start at higher Q 2 Most work in configuration space, MRT works in momentum space. Configuration space puts emphasis on VM wave function. Momentum space on the gluon distribution. W dependence information on the gluon Q 2 and R properties of the wave function June, 28 A. Levy: Exclusive VM, GPD8, Trento 27

28 ρ data () - Comparison to theory Martin-Ryskin-Teubner (MRT) work in momentum space, use parton-hadron duality, put emphasis on gluon density determination. Phys. Rev. D 62, 422 (2). Forshaw-Sandapen-Shaw (FSS) improved understanding of VM wf. Try Gaussian and DGKP (2- dim Gaussian with light-cone variables). Phys. Rev. D 69, 943 (24). Kowalski-Motyka-Watt (KMW) add impact parameter dependence, Q 2 evolution DGLAP. Phys. Rev. D 74, 746 (26). Dosch-Ferreira (DF) focusing on the dipole cross section using Wilson loops. Use soft+hard Pomeron for an effective evolution. Eur. Phys. J. C 5, 83 (27). June, 28 A. Levy: Exclusive VM, GPD8, Trento 28

29 ρ data (H) - Comparison to theory Marquet-Peschanski-Soyez (MPS): Dipole cross section from fit to previous ρ, φ and J/ψ data. Geometric scaling extended to non-forward amplitude. Saturation scale is t-dependent. Ivanov-Nikolaev-Savin (INS): Dipole cross section obtained from BFKL Pomeron. Use kt-unintegrated PDF and off-forward factor. Goloskokov-Kroll (GK): Factorisation of hard process and proton GPD. GPD constructed from standard PDF with skewing profile function. June, 28 A. Levy: Exclusive VM, GPD8, Trento 29

30 Q 2 σ(γ*p ρ p) (nb) pb KMW DF - 2 FSS (Sat-DGKP) FSS (Sat-Gauss) FSS (NoSat-DGKP) FSS (NoSat-Gauss) - 2 Q 2 (GeV 2 ) KMW good for Q 2 >2GeV 2 miss Q 2 = DF miss most Q 2 FSS Gauss better than DGKP June, 28 A. Levy: Exclusive VM, GPD8, Trento 3

31 σ γ*p ρp (nb) Q 2 Data seem to prefer MRST99 and CTEQ6.5M - -2 (prel.) (2 pb - ) MRT (MNRT) MRT (CTEQ65M) MRT (MRST4NLO) MRT (MRST99) -2-2 Q 2 (GeV 2 ) June, 28 A. Levy: Exclusive VM, GPD8, Trento 3

32 σ(γ*p ρ p) (nb) W dependence 2 pb - KMW FSS (Sat-Gauss) FSS (NoSat-Gauss) MRT (CTEQ6.5M) MRT (MRST99) W (GeV) KMW - close FSS: Sat-Gauss right W-dep. MRT: wrong norm. CTEQ6.5M slightly better in W-dep. June, 28 A. Levy: Exclusive VM, GPD8, Trento 32

33 σ L /σ tot (Q 2 ) 4 r = σl /σ tot pb MRT (CTEQ6.5M) MRT (MRST99) FSS (NoSat-Gauss) FSS (Sat-Gauss) Q 2 (GeV 2 ) June, 28 A. Levy: Exclusive VM, GPD8, Trento 33

34 σ L /σ tot (W) 4 r = σl / σ tot pb - 4 r = σl / σ tot pb FSS (Sat-DGKP) FSS (Sat-Gauss) KMW FSS (Sat-DGKP) FSS (Sat-Gauss) KMW MRT (MRST99) MRT (CTEQ6.5M) DF MRT (MRST99) MRT (CTEQ6.5M) DF FSS (Sat-DGKP) FSS (Sat-Gauss) KMW FSS (Sat-DGKP) FSS (Sat-Gauss) KMW.6.5 MRT (MRST99) MRT (CTEQ6.5M) DF MRT (MRST99) MRT (CTEQ6.5M) DF W (GeV) All models have mild W dependence. None describes all kinematic regions W (GeV) June, 28 A. Levy: Exclusive VM, GPD8, Trento 34

35 σ L,σ T (Q 2 +M 2 ) σ L [nb] 3 2 H ρ and φ electroproduction (preliminary) γ L p ρ p H HERA- prel. σ T [nb] 3 2 H ρ and φ electroproduction (preliminary) γ T p ρ p H HERA- prel. GK (GPD) INS (k t fact) MPS (Sat) γ L p φ p γ T p φ p - -2 H HERA- prel. GK (GPD) W = 75 GeV INS (k t fact) MPS (Sat) Q 2 +M 2 [GeV 2 ] - -2 H HERA- prel. W = 75 GeV Q 2 +M 2 [GeV 2 ] Different Q 2 +M 2 dependence of σ L and σ T (σ L at Q 2 =) Best description of σ L by GK; σ T not described. June, 28 A. Levy: Exclusive VM, GPD8, Trento 35

36 Density matrix elements - ρ, φ r 4 Re r 4 r 4 - r r Re r r - Im r Im r 2 - r 5 r Re r r 4 Re r 4 r 4 - r r Re r r - Im r Im r 2 - r 5 r Re r r 5 - Im r 6 Im r Q 2 [GeV 2 ] H ρ electroproduction (preliminary) H HERA- prel. GK (GPD) r 5 - Im r 6 Im r Q 2 [GeV 2 ] H φ electroproduction (preliminary) H HERA- prel. GK (GPD) Fair description by GK r 5 violates SCHC June, 28 A. Levy: Exclusive VM, GPD8, Trento 36

37 Summary and conclusions New high statistics measurements on ρ, φ electroproduction and on DVCS. The Q 2 dependence of σ(γ*p ρp) cannot be described by a simple propagator term. The cross section is rising with W and its logarithmic derivative in W increases with Q 2. The exponential slope of the t distribution decreases with Q 2 and levels off at about b = 5 GeV -2. Proton vertex factorisation observed also in DIS. The ratio of cross sections induced by longitudinally and transversely polarised virtual photons increases with Q 2, but is independent of W and t. The effective Pomeron trajectory has a larger intercept and smaller slope than those extracted from soft interactions. All these features are compatible with expectations of perturbative QCD. None of the models which have been compared to the measurements are able to reproduce all the features of the data. June, 28 A. Levy: Exclusive VM, GPD8, Trento 37

PoS(DIS 2010)071. Diffractive electroproduction of ρ and φ mesons at H1. Xavier Janssen Universiteit Antwerpen

$PoS(DIS 2010)071. Diffractive electroproduction of ρ and φ mesons at H1. Xavier Janssen Universiteit Antwerpen$ Diffractive electroproduction of ρ and φ mesons at Universiteit Antwerpen E-mail: xavier.janssen@ua.ac.be Diffractive electroproduction of ρ and φ mesons is measured at HERA with the detector in the elastic