Polarized Target Options for Deuteron Tensor Structure Function Studies

Transcription

1 Polarized Target Options for Deuteron Tensor Structure Function Studies Oscar A. Rondón University of Virginia Tensor Polarized Solid Target Workshop JLab March 12, 2012

2 Inclusive Spin Dependent Observables: Single Spin Target Asymmetries vs Beam-Target Asymmetries 3/12/14 2

3 Spin Dependent Physics General expression for spin dependent cross-section [1] σ=σ U (1+h A h +P V A V +P T A T +h( P v A hv + P T A ht )) h = beam helicity P V, P T = Vector, Tensor target polarizations No out-of-plane A h in inclusive scattering A T, A ht = 0 for spin <1 ħ Target asymmetries depend on opposite target polarizations Target polarizations hard to flip, unlike beam helicity Two options to flip P t(arget ) - single target cell, periods of alternating P t - multiple targets cell each with independent P t [1] Z. Phys. A 331,123 (1998); Phys.Rev. C 43,1022, (1991) 3/12/14 3

4 Example: Deuteron Tensor b 1 Cross section for unpolarized electron scattering on longitudinally polarized deuterons [1] σ ( x, Q 2 ) = Kx (F d 1 ( x,q 2 ) P T 3 b d 1 ( x,q 2 )) K ( y, E,Q 2 ): kinematic factor; unpolarized σ U =KxF 1 d. Cross section difference σ U σ =Kx P T 3 b 1 Get b 1 by taking data simultaneously on two (or more) unpolarized and polarized in-line cells: - yields from cells share beam charge, detector efficiency; - can form both beam upstream-downstream differences and same cell differences for different polarization periods. [1] Nucl.Phys. B312(1989)571 3/12/14 4 d

5 Multiple Cell Targets 3/12/14 5

6 Multiple cell Polarized Targets Not a novel concept: introduced by the EMC (CERN NA2') to deal with single polarization of the muon beam (always negative) Upstream and downstream cells with separate microwave feeds Used in subsequent SMC and COMPASS targets EMC dual cell target [1] SMC dual cell target [2] [1] EMCtarget R. Piegaia's thesis 3/12/14 [2] SMCtarget NIM A 437 (1999) 23 COMPASS J. Koivuniemi

7 Multiple cell Polarized Targets Not a novel concept: introduced by the EMC (CERN NA2') to deal with single polarization of the muon beam (always negative) Upstream and downstream cells with separate microwave feeds Used in subsequent SMC and COMPASS targets COMPASS triple cell target [1] 3/12/14 COMPASS J. Koivuniemi [1] /Drawings/NH3target07v01.png Up Center Down

8 Multiple cell Polarized Targets Not a novel concept: introduced by the EMC (CERN NA2') to deal with single polarization of the muon beam (always negative) Upstream and downstream cells with separate microwave feeds Used in subsequent SMC and COMPASS targets Triple cell insert Ø 40 mm Dual cell insert Ø 30 mm s/detector/target/na58ptphoto/na 58PTphotos.html 3/12/14 8

9 Pros and Cons of Multi-cell Targets Pros compensate for few/no polarization reversals by taking simultaneous data on two or more polarization states use favorable cylindrical symmetry for simple, more intense solenoidal magnetic field 6.5 T increased data rate: lower beam current; fewer anneals, insert swaps reduced or removed time dependent systematics Cons more complicated: refrigeration, microwaves feeding and isolation increased radiation thickness increases external radiative corrections event loss from acceptance matching cuts 3/12/14 9 cell dependent packing fractions

10 A more detailed look 3/12/14 10

11 Multiple cell Target Solenoid Magnet COMPASS target[1] Magnets: (Oxford) 2.7 T solenoid plus 0.5 Tdipole solenoid aspect L/R = 20/3.3 <10-4 uniformity old cells: cm with 5 cm spacing new 40 mm cells: Upstream +downstream cm Center = 60 cm ±14 acceptance (Oxford) 3/12/14 [1] 11 /target/talks/tis_meet_oct_00.pdf

12 Multiple cell Target Solenoid Magnet COMPASS target[2] Magnets: (Oxford) 2.7 T solenoid plus 0.5 Tdipole solenoid aspect L/R = 20/3.3 <10-4 uniformity old cells: cm with 5 cm spacing new 40 mm cells: Upstream +downstream cm Center = 60 cm ±75 mr acceptance (Saclay) [2]Saclay magnet with triple cell 3/12/14 /target/drawings/nh3target07v01.png 12

13 Magnet Design for Multi-cell Target Solenoid for longitudinal field trim, compensation coils For JLab: 1/5 scale Oxford COMPASS magnet, almost same aspect L/R = 200/33 40/6 (Saclay magnet) COMPASS N. Takabayashi thesis fig. 5.1 uniform region Optional: COMPASS = ±65 cm JLab ± 6.5 cm dipole for transverse field Slow raster envelope Simple solenoid 3/12/14 L R=40 6 cm

14 Magnet Design for Multi-cell Target Solenoid for longitudinal field trim, compensation coils For JLab: 1/5 scale Oxford COMPASS magnet, almost same aspect L/R = 200/33 40/6 (Saclay magnet) COMPASS N. Takabayashi thesis fig. 5.1 uniform region Optional: COMPASS = ±65 cm JLab ± 6.5 cm 1.0E+0 1.0E z [cm] dipole for transverse field Simple solenoid 3/12/14 L R=40 6 cm B/B(0) B/B(+/- 4 cm) E-1 1.0E-2 1.0E-3 1.0E

15 Magnet Design for Multi-cell Target Solenoid for longitudinal field trim, compensation coils For JLab: 1/5 scale Oxford COMPASS magnet, almost same aspect L/R = 200/33 40/6 (Saclay magnet) COMPASS N. Takabayashi thesis fig. 5.1 uniform region Optional: COMPASS = ±65 cm JLab ± 6.5 cm dipole for transverse field Raster [cm] 1 Cup length [cm] Cup spacing [cm] Min. theta Acceptance (target centered along coil) Simple solenoid 3/12/14 L R=40 6 cm 15

16 Using Multicell Targets 3/12/14 16

17 Data Analysis with Multiple Cells Vertex reconstruction allows identifying data from individual cells Clean separation with small loss of events from ends of cells Cell regions (old) All events Events after cuts (new cells) COMPASS NIM 577 (2007) 455 3/12/14 COMPASS A. Richter thesis fig

18 Data Analysis with Multiple Cells Vertex reconstruction allows identifying data from individual cells Clean separation with small loss of events from ends of cells Example: simulated HMS[1] cm upstream + downstream cells 5 cm LHe between cells 0.5 cm at ends Example: simulated SHMS[1] 0.5 cm LHe outside cells (at all ends) 3/12/14 [1] ntuples by N. Kalantarians 18

19 Data Analysis with Multiple Cells Vertex reconstruction allows identifying data from individual cells Clean separation with small loss of events from ends of cells Example: simulated HMS[1] cm upstream + downstream cells 5 cm LHe between cells 0.5 cm at ends Example: simulated SHMS[1] 0.5 cm LHe outside cells (at all ends) 3/12/14 [1] ntuples by N. Kalantarians 19

20 Data Analysis with Multiple Cells Vertex reconstruction allows identifying data from individual cells Clean separation with small loss of events from ends of cells Example: simulated HMS[1] cm upstream + downstream cells 5 cm LHe between cells 0.5 cm at ends Example: simulated SHMS[1] 0.5 cm C disks at cell ends as optics target 3/12/14 [1] histogram by N. Kalantarians 20

21 Yield Differences for Multi-cell Targets Many types of yield differences can be formed with multi-cell target configurations not possible with single cells different systematics: time dependent (beam charge Q, detector efficiency e, packing fraction) vs cell dependent (acceptance A= E' W, packing fraction) optimize length vs radiative corrections: balance faster counting vs systematic error for cm cells with 60% pf, each is 4.6%X 0, but Born rate is 2 greater than SANE/RSS/GEn cups. 3/12/14 21

22 Yield Differences for Multi-cell Targets Many types of differences can be formed with multi-cell target configurations Example: dual cell target Cell Differences Changes Period U D Different cells Same cell 1 U 0 D p D 1 d = U 01 D p1 A U,D, pf U,D 2 U p D 0 D 2 d = U p2 D 02 D Us = U 01 U p2, D D s = D p1 D 02 Q 1-2, e 1-2, pf 1,2 (U),pf 1,2 (D) 3 U p D 0 4 U 0 D p D 4 U = U 01 + U 04 - (U p2 + U p3 ), 3/12/14 D 4 D = D p1 + D p4 - (D 02 + D 03 ) 22

23 Differences for Multiple Cell Targets Many types of differences can be formed with multi-cell target configurations Examples Left: COMPASS triple cell labeling scheme [1] Right: Polarization sequence for E , but if +P zz and -P zz are both available then one can cancel F 1 by taking the difference for one cell with +P zz and the other with -P zz [1] COMPASS S. Levorato thesis fig /12/14 23

24 A brief look at Systematic Errors Systematic errors (other than scale factors) for a single difference of yields depend on the relative differences in acceptances A and packing fractions p f Controlling those errors depends on the uncertainties in those differences better ways of measuring p f understanding of relative acceptances: extensive simulations, optics target Difference of yields from unpolarized (U) and longitudinally polarized ( ) cells depends on acceptances A, lengths l and cross sections σ Δ Y =A U l U σ U A l σ For each cell we have l U σ U =N 0 z ( D ND3 (σ N +3σ D ) p f U +D He σ He (1 p f U )) l σ = N 0 z (D ND3 (σ N +3σ D K xp zz b 1 ) p f +D He σ He (1 p f )) Replacing p f = p f U Δ p f, A =A U Δ A the differences are Δ Y s A f Δ p f U U p f ( f + D He σ He D ND3 p )Δ A U f A = U where s=n 0 z p f U D ND3 and f =σ N +3σ D D He D ND3 σ He K x P zz b 1 (1 Δ p f p f U Δ A A U ) 3/12/14 24

25 A brief look at Systematic Errors Systematic errors (other than scale factors) for a single difference of yields depend on the relative differences in acceptances A and packing fractions p f Controlling those errors depends on the uncertainties in those differences Packing fraction difference better ways of measuring p f Ammonia mass ~ 9 g in 3 cm long cell at 0.6 p f Careful weighing of loads could resolve 1 mg in ~ 10g understanding of relative Material preparation in known shapes and dimensions acceptances: extensive might do better in both p f and its error 3/12/14 25 simulations, optics target Some rough estimates For solid angle difference at angular resolution limits Δ θ= (θ 1 θ 2 )= 2δθ ; Δ ϕ= 2 δ ϕ so the relative difference = relative solid angle error Using the HMS angle resolutions Δ A A = ΔΩ Δ Ω = 2δθδ ϕ mr 0.8 mr Δ Ω = = msr effective solid angle 2.5 msr has acceptance matching cuts Approximating σ N 7σ D, σ He 2 σ D so f 8.5 σ D the relative difference can be compared to the r.h.s Δ A A =K x P b 1 b U zz σ P 1 zz D d F = with P zz =20 %, D He / D ND3 =0.8, p f =0.5

26 Summary Multiple cell polarized targets are being used and have been used very effectively for controlling systematics when it's hard or impossible to flip helicities quickly and frequently, e.g. for LiD The in-line configuration favors using a simple solenoidal field for longitudinal spin observables but transverse observables still accessible at a price Could be a good option for a longitudinal vector and tensor spin observables program at JLab New observables 10 to 100 times smaller than traditional spin ones require advanced methods Interesting target physics R&D in addition to compelling physics 3/12/14 26

27 3/12/14 27

28 Polarized Target Ammonia + LHe Dynamic Nuclear Polarized ammonia (NH 3, <P> ~ 70% in beam) and deuterated ammonia (ND 3, <P> 20-30%) Wide range of field orientations Target used in six experiments before SANE: SLAC E143, E155, E155x (g 2 ) JLab GEn98, GEn01, RSS Damaged coils successfully repaired in Nov. '08 by JLab staff with Oxford Inst. help 3/12/14 28

29 SANE Layout BETA (40 ) HMS (15-42 ) calibrations, backgd. BigCal Lucite Hodoscope Gas Cherenkov Forward Hodoscope B at 80 or 180 Polarized Target Beam Line 3/12/14 29

30 Spin Dependent Structure Functions g 1 measured in all halls NH 3, ND 3 in all Halls 3 He in Hall A g 2 in C and A Duality in g 1 Transverse structures A 2 and g T Moments and twist-3 Sum Rules: GDH, B-C, Bjorken n SSF's from 3 He and from d - p Inclusive Program at 6 GeV Experiment Hall Target Measured quantity A Kinematics Q 2 GeV 2 3 He A, A Resonances CLAS eg1a-b B p, d A DIS, Resonances A A A 3 He A DIS He A, A Elastic, Resonances He A, A DIS 2.7, 3.5, (RSS) C p, d A, A Resonances A 3 He A, A Resonances 1 4 CLAS eg4 B p A Elastic, Resonances (SANE) C p A, A DIS, Resonances A 3 He A, A DIS <3> (g2p) A p A, A Resonances /12/14 30