Neutron DVCS. Carlos Muñoz Camacho. IPN-Orsay, CNRS/IN2P3 (France)

Transcription

1 Neutron DVCS Carlos Muñoz Camacho IPN-Orsay, CNRS/IN2P3 (France) Next generation of nuclear physics with JLab12 and EIC Florida International University February 10 13, 2016 Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

2 Outline Introduction Motivation of DVCS off the neutron and experimental challenges Experimental program at Jefferson Lab Recent (preliminary) results from Hall A Outlook at JLab12 Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

3 Introduction Motivation Deeply Virtual Compton Scattering (DVCS): γ p γ p High Q 2 Perturbative QCD Non-perturbative GPDs Handbag diagram Bjorken limit: Q 2 = q 2 ν } x B = Q2 2Mν fixed Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

4 Introduction Experiments DVCS experimentally: interference with Bethe-Heitler (BH) At leading twist: d 5 σ d 5 σ = Im (T BH T DV CS ) d 5 σ +d 5 σ = BH 2 + Re (T BH T DV CS ) + DV CS 2 +1 T DV CS = +1 1 H(x, ξ, t) P dx 1 x ξ }{{} Access in helicity-independent cross section H(x, ξ, t) dx x ξ + iɛ + = iπ H(x = ξ, ξ, t) +... }{{} Access in helicity-dependent cross-section Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

5 Accessing different GDPs Introduction Experiments Polarized beam, unpolarized target (BSA) dσ LU = sin φ Im{F 1 H + x B (F 1 + F 2 ) H kf 2 E}dφ Unpolarized beam, longitudinal target (ltsa) dσ UL = sin φ Im{F 1 H + xb (F 1 + F 2 )( H + x B /2E) x B kf 2 Ẽ... }dφ Polarized beam, longitudinal target (BlTSA) dσ LL = (A + B cos φ) Re{F 1 H + xb (F 1 + F 2 )( H + x B /2E)... }dφ Unpolarized beam, transverse target (ttsa) dσ UT = cos φ Im{k(F 2 H F 1 E) +... }dφ Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

6 Neutron DVCS Introduction n-dvcs 1 Flavor sensitivity of GPDs (when combined with proton DVCS) ImH = ImH = ( 4 π 9 Hu + 1 ) 9 Hd ( 1 π 9 Hu + 4 ) 9 Hd (Proton) (Neutron) 2 Enhanced sensitivity to GPD E (eg. with long. e off unpol. target) LD 2 target (F n 2 (t) F n 1 (t)!) A = F 1 (t)h + x B [F 1 (t) + F 2 (t)] 2 x H t B 4M 2 F 2(t) E }{{} Main contribution for neutron H is expected small by compensation of u and d distributions in n Contribution of the angular momentum of quarks to proton spin: J = dx x[h(x, ξ, 0) + E(x, ξ, 0)] 1 Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

7 Experimental results The n-dvcs program at Jefferson Lab Hall A: E03-106: Beam helicity-dependent DVCS cross section E08-025: Beam helicity-independent DVCS at 2 beam energies Hall B: E : Beam spin asymmetries with CLAS12 Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

8 Experimental results E Hall A DVCS experimental setup High Resolution Spectrometer 100-channel scintillator array 132-block PbF2 electromagnetic calorimeter Carlos Mun oz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

9 Experimental results E Neutron detection (proton veto) Charged particle veto in front of scintillator array: Proton: signal in both detectors Neutron: signal only in thick scintillator Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

10 Impulse approximation Experimental results E D( e, e γ)x = d( e, e γ)d + n( e, e γ)n + p( e, e γ)p +... N(P) dp Spectator nucleon Recoil nucleon P (GeV) FSI between the np pair should be small Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

11 Experimental results E Neutron and coherent deuteron ( MX 2 = (n + q q ) 2 = Mn M ) n t Mn 2 + t M d 2 Coherent d separated using kinematical separation in the M 2 X spectrum Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

12 Missing mass & exclusivity Experimental results E Exclusivity ensured by a cut at the π-production threshold Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

13 Helicity signal Experimental results E S h = π 0 (N + N ) dφ 2π π (N + N ) dφ, S h 3500 D 2 data M X cut H 2 data 2500 p-dvcs simulation S h n-dvcs 2 2 d-dvcs simulation M X (GeV ) d-dvcs 1000 n-dvcs simulation n-dvcs + d-dvcs M (GeV ) No significant signal after LD 2 LH 2 subtraction Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

14 E results Experimental results E I exp ) d Im(C This experiment Cano & Pire calculation [29] Model-dependent sensitivity to J u, J d J d JLab Hall A n-dvcs exp I ) n Im(C This experiment 2 2 t (GeV ) J u = J d = J u J =0.3 d= AHLT calculation [32] VGG calculation [30] J u =0.6 J d = t (GeV ) J u J d = ± 0.14 Lattice QCDSF HERMES Preliminary p-dvcs J u Helicity-dependent ndvcs cross-section compatible with zero, BUT still sets constraints to GPD combinations (and J u, J d models... ) Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

15 E03-106: lessons learnt Experimental results E LD 2 LH 2 subtraction very sensitive to calorimeter calibration (drifts) LD 2 and LH 2 running should be interleaved Significant contamination from π 0 s that was hard to subtract high γ threshold reduced with improved trigger+electronics Recoil particle detection/tagging extremely difficult at high luminosity ARS channels Large background + low recoil momentum Charge exchange reaction difficult to measure/estimate t (ns) No recoil detector anymore less deadtime and higher statistics Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

16 Experimental results E E08-25 ndvcs experiment Ran in 2010 No recoil detection higher luminosity Improved trigger and DAQ reduced deadtime Interleaved LD 2 and LH 2 running Q 2 = 1.75 GeV 2, x B = 0.36 at E b = 4.45 and E b = 5.55 GeV C. Desnault s PhD thesis Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

17 Analysis method Experimental results E σ = BH 2 + Γ 0 (x B, Q 2, t, ϕ)1c 0 (ξ, t) + Γ 1 (x B, Q 2, t, ϕ) C 1 (ξ, t) cos ϕ+ Γ 2 (x B, Q 2, t, ϕ) C 2 (ξ, t) cos 2ϕ ξ x B 2 x B C i (ξ, t): combinations of GPDs N Exp (i e ) = N ie Ni BH [ e ] N MC (i e ) = L C i Γ i cos (iϕ) Acc. i x i } e {{} MC sampling MC includes real radiative corrections (both external and internal). χ 2 = i e [ N Exp (i e ) N MC (i e ) ] 2 [σ Exp (i e )] 2 { C0 C 1,... Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

18 Experimental results E Rosenbluth-like separation of the DVCS cross section σ(ep epγ) = BH 2 + I(BH DV CS) + DV CS 2 }{{}}{{}}{{} Known to 1% Linear combination of GPDs Bilinear combination of GPDs I 1/y 3 = (k/ν) 3, T DV CS 2 1/y 2 = (k/ν) 2 BKM-2010 at leading twist 7 independent GPD terms: { Re, Im [ C I, C I,V, C I,A] (F) }, and C DV CS (F, F ). ϕ-dependence provides 5 independent observables: 1, cos ϕ, sin ϕ, cos(2ϕ), sin(2ϕ) The measurement of the cross section at two or more beam energies for exactly the same Q 2, x B, t kinematics, provides the additional information in order to extract all leading twist observables independently. Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

19 Outlook Hall B E E : DVCS sur le neutron avec CLAS12 Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

20 E : projections Outlook Hall B E Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

21 Polarized 3 He target Outlook Future possibilities n lum. of /cm 2 /s (14 atm 40 cm) Background luminosity: p in 3 He + entrance/exit windows /cm 2 total luminosity Polarization: 50% Nuclear physics dilution factor 0.86 (d-state) -2.8% p polarization Long. & Trans. Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

22 3 He target upgrade Outlook Future possibilities Separate polarization and tgt volumes Increase throughput by factor Cool and/or compress 3 He in target area by a factor of 10 (10K at 10 atm 20 cm) Rapid cycling of 3 He through target Reduce depolarization effect of tgt density, beam current, tgt walls Replace thick glass with thin metallic walls Neutron luminosity of /cm 2 /s Proton luminosity /cm 2 /s Endcaps /cm 2 /s Target polarization: 0.5 (0.86n 0.028p) Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

23 Outlook DVCS on polarized neutron Future possibilities n( e, e γ) via 3 He( e, e)x Long or Trans normal polarization Target single spin cross sections dσ sin φ (twist-2): Im[BH DVCS] Unpolarized protons in 3 He cancel Target double spin dσ c 0 + c 1 cos φ: Re[BH 2 +(BH DVCS)+DVCS 2 ] Unpolarized protons cancel Transverse sideways: sin φ cos φ All other neutron observables (total σ, beam-spin) have large incoherent proton contributions Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

24 Outlook Future possibilities Cross section projections (at cm 2 s 1 ) C. Hyde Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

25 Summary Conclusion Neutron DVCS is a required complement to the proton program: Flavor separation of GPDs Access to different combinations of GPDs Very challenging experimentally: Difficult to detect at high luminosities Efficiencies, charge exchange, etc hard to estimate Hall A program in Hall A provided some initial results and contraints Approved program with CLAS12 off unpolarized neutrons Possibilites of polarized ndvcs with high luminosity 3 He target Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26

26 Acknowledgements This work was supported by: IN2P3/CNRS Office for Science & Technology at the Embassy of France (U.S.A.) Carlos Muñoz Camacho (IPN-Orsay) Neutron DVCS FIU, Feb / 26