1. XI International workshop on high energy spin physics
Spin physics program in the U70 polarized proton beam A.N.Vasiliev (IHEP-Protvino) on behalf of the polar70 group
XI International workshop on high energy spin physics
(DUBNA-SPIN-05)
September 27 – October 1, 2005

2. V.V.Abramov, S.I.Alekhin, A.S.Belov, V.I.Garkusha,
A.V.Efremov, P.F.Ermolov, S.V.Ivanov, V.I.Kravtsov, V.I.Kryshkin, A.V.Kubarovsky, A.K.Likhoded, V.V.Mochalov, S.B.Nurushev, A.F.Prudkoglyad, V.N.Ryadovikov, I.A.Savin, Y.M.Shatunov, S.R.Slabospitsky, L.A.Tikhonova,D.K.Toporkov,
S.M.Troshin, E.F.Troyanov, M.N.Ukhanov, A.N.Vasiliev
BINR-Novosibirsk, JINR-Dubna, IHEP-Protvino,
INR-Troitsk, MSU-Moscow

3. Contents Introduction Acceleration of polarized protons at U70
Polarization in elastic scattering
Single-spin asymmetries in inclusive processes
Spin effects in strange hadron production
Measurement of quark transversity distributions in a polarized proton
Double-spin asymmetry in Charmonium production
Conclusion

4. Introduction
A possibility to accelerate high-intensive polarized proton beam up to 70 GeV at the IHEP U70 accelerator, extract it from the main ring and deliver to several experimental setups is being studied now in Protvino.
We propose to study a wealth of single- and double-spin observables in various reactions using longitudinally and transversely polarized proton beams at U70.
March 1-2, 2005 – Workshop on polar70 at IHEP.
Over120 people participated. The IHEP management charged the
polar70 working group to prepare the report for SPIN-2005
workshop in Dubna.

5. Accelerated polarized proton beam at U70
For extracted beams :
Intensity up to 5x1012/spill
Energy up to 70 GeV
Polarization up to 70%
Polarized proton source up to 20 mA
Fight depolarization :
One partial snake in Booster
Three partial snakes in U70 (snake
strength W=/2= , more ?)
Snakes : 12 superconducting helicoidal magnets , length m, magnetic field 5-6 Tl (straight sections in U m) – [Shatunov’s report]
Polarimetry – elastic scattering in CNI region (polarized jet target) –[Nurushev’s report]
Collaboration of the three institutes :
Institute for High Energy Physics, Protvino
Institute of Nuclear Research, Troitsk
Budker Institute of Nuclear Physics, Novosibirsk

6. Polarized Proton in RHIC
Absolute Polarimeter (H jet)
RHIC pC Polarimeters
BRAHMS & PP2PP
PHENIX
STAR
Siberian Snakes
Spin Rotators
Partial Siberian Snake
Pol. Proton Source
500 mA, 300 ms
Strong AGS Snake
2  1011 Pol. Protons / Bunch
e = 20 p mm mrad
LINAC
BOOSTER
AGS
200 MeV Polarimeter
AGS Internal Polarimeter
Rf Dipoles
AGS pC Polarimeters

7. Spin physics program in the U70 polarized proton beam:
AN and ANN in elastic scattering [high pT2]
Precision measurement of single-spin asymmetry in inclusive charged hadron production in pp and pA collisions at different production angles
Miscellaneous spin parameters (A,DNN,ALL) in
hyperon production
Transversity in Drell-Yan muon pairs
Double-spin asymmetry ALL in Charmonium production (∆G/G gluon polarization through 2 if gluon-gluon fusion is significant)

8. Elastic scattering ½ ½ -> ½ ½ - physics observables and amplitudes
non–flip
double flip
single flip

9. AN and ANN in elastic scattering Big effects in the previous experiments

10. Experimental setup SPIN@U70 at IHEP (channel 8 at U70)

11. Measurements of Polarization in pp-elastic scattering at SPIN@U70
Both particles, forward and recoil protons will be detected by scintillation hodoscopes (forward arm) and drift chambers (recoil arm).
Beam intensity up to 1012 protons/spill.
Particle identification will be performed by Cherenkov counters and additionally by a time-of-flight technique in the recoil arm.
Accuracies to be achieved in the AN measurements :
- less than 1% for pT2 up to 6 (GeV/c2) for 200 hours at beam ;
- 3% for 10 (GeV/c2) and 6% for 12 (GeV/c2) for 600 hours at beam.

12. Single spin asymmetry in inclusive pion production
E704 result at 200 GeV
There are several recent results of
such a big asymmtery –
1) E925 at BNL at 22 GeV
2) PROZA in Protvino at 40/70 GeV
3) STAR at RHIC at s=200 GeV

13. Theoretical approaches to explain big single-spin asymmetry in inclusive hadron production
Sivers: spin and k correlation in initial state (related to orbital angular momentum?)
Collins: Transversity distribution function & spin-dependent fragmentation function
Qiu and Sterman (initial-state) / Koike (final-state) twist-3 pQCD calculations
Usually we have combinations of these three effects in a particular experiment and special technics are required to separate them from observed asymmetries.

14. FODS – Focusing double arm spectrometer (channel 22 at U70)
The channel shielding allows to get a beam intensity
up to proton/spill, FODS setup up to ~109 proton/spill.

15. Particle ID at FODS Hodoscope photomultipliers
are used to detect the Cherenkov
light rings.
Charged hadron identification
in the momentum range of
6 GeV/c ≤ р ≤ 30 GeV/c

16. Single spin measurements which can be done at FODS
* Precise measurements of AN in inclusive production of charged pions, kaons, protons and antiprotons at hydrogen and nuclear targets – big xT, to separate PT and XF asymmetry dependence, the measurements at several angles are needed (might be done in the range of in c.m.)
* AN in symmetric hadron pair production
symmetric pairs (+ -,etc. )– hadrons produced in the c.m. with about the same momenta and moving in the opposite sides;
for these processes kT 0 and there is no Sivers effect;
if АN ≠0 – possible explanation might be an orbital moment ?
* Polarization in elastic pp-scattering.
* AN in Drell-Yan muon pairs
no fragmentation (q+q →l+l ) – no Collins effect,
AN in р↑р might be significant if valence quark angular momentum contributes, to suppress hadrons, additional absorbers in each arm will be installed)

17. Spin parameters in hyperon production
* Miscellaneous spin parameters (A,DNN,ALL) in -hyperon production can be detected at the experimental setup SVD (channel 22 at U70).
* The mass spectra of -hyperons at SVD 
* More than 200,000 -hyperons were
detected over one month of data taking
with a beam intensity of 0.5*106 protons/sec.
* -hyperons are very well detected in the beam
fragmentation region where big spin effects
are expected.
* Asymmetry in -meson production
* Spin effects in strange hadron production -
role of strange quarks in the spin structure
of nucleon ?

18. Experimental setup SVD
C1,C2-beam scintillation and Si hohoscopes; C3,C4 – target station and vertex Si detector; 1,2,3 – drift tubes (tracking detector) ; 4 – proportional chambers (magnet spectrometer);
5 – threshold Cherenkov counter; 6- scintillation hodoscope; 7 -  -detector

19. Structure functions + f1(x) - g1(x) h1(x) - q(x) Dq(x) Parton model
proton
proton’
quark
quark’
1/2 R
1/2 L
f1(x) +
q(x)
1/2 R
1/2 L
g1(x) -
Dq(x)
Parton model
h1(x) -  
u = 1/2(uR + uL)
u = 1/2(uR - uL)
dq(x)

20. Transverse double-spin asymmetry in Drell-Yan pairs – transversity distribution
One of the first measurements of the transversity distribution hq1(x,Q2) of the valence quarks and sea anti-quarks in the transversely polarized proton ;
Measure the transverse double spin asymmetry ATT in the Drell-Yan production of muon pairs ;
Luminosity of p↑p↑ - interactions is about 1035 cm-2s-1
( compare to cm-2s-1 for PAX at GSI or for RHIC) ;
Existing “Neutrino Detector (ND)” setup at U70 – make absorber
smaller (5 m instead of 70m), put polarized target in front of the absorber and use the muon detector of the ND setup ;
* Acceptance for the Drell-Yan muon pairs is close to 100% .

21. Transversity distribution in the proton
* In proton-proton interactions one measures the product of two transversity distributions, one for a quark and one for antiquark (both in a proton). At U70 energies GeV one expects measurements at x1x2 = M2/s =>
for 50 GeV, M=1.5-3 GeV/c2, x1x2 = ;
for 70 GeV, M=1.5-3 GeV/c2, x1x2 = =>
this leads to the constraint on the quark and antiquark proton content .
* The region 1.5 < M < 3 GeV/c2 is free from resonances and can be exploited to access hq1(x,Q2) via Drell-Yan processes.

22. Estimated number of Drell-Yan events
For a beam intensity of p/spill at a polarized target and
30 days at beam, the estimated number of the Drell-Yan muon
pairs to be detected by the ND setup is as follows :
Mass of -pair, MeV/c number of DY events
,000
,000
,000
For Polbeam = 0.7 and Poltarget = 0.8 with Dilution Factor =4, the ATT errors in these bins are expected to be in the range of (2-4)%.

23. Transversity – experimental difficulties
The scheme of the experiment is as follows –> polarized beam
interacts with polarized target , then absorber and finally muon detector to detect Drell-Yan muon pairs (beam-dump experiment).
The hadronic background can originate from decays of charged pions and kaons before reaching the absorber and from hadrons penetrating the material (punch-through).
The polarized target will be a major effort; with a 20cm long target, at 5T the requirement's on a magnet are severe. Also the energy generated by the beam at 10^11 p cm^-2 is > 1 joule/spill. The microwave power required is also substantial ~40 mW/gm, again assuming 140 GHz -> 5 T. So we will need a very substantial pumping system for the highest intensity beams.  

24. Transversity – conclusion
Kinematics in three Transversity projects (for Drell-Yan pair masses from 1.5 to 3 GeV/c2 ):
1) RHIC(BNL) – > τ = x1 x2 = ;
2) U – > τ = x1 x2 =
3) PAX at FAIR(GSI) – > τ = x1 x2 = ;
4) First results on transversity from hydrogen and deuterium are published by HERMES and COMPASS.
The different kinematics makes FAIR, RHIC and U70
really complementary in the transversity measurements

25. Longitudinal double-spin asymmetry in Charmonium production
We propose to simultaneously measure the double-spin asymmetry
ALL for inclusive 2 , 1 and J/ by utilizing the 70 GeV/c longitudinally polarized-proton beam on a longitudinally polarized target.
Our goal is to obtain besides the quark-spin information also the gluon-spin information from these three processes in order to determine what portion of the proton spin is carried by gluons.
Gluon contribution into the proton spin as well as strange quarks and orbital momentum contributions - worldwide studies at HERMES, COMPASS, RHIC, JLAB, SLAC.
We propose a new experiment in this field – should be complimentary to the existing experiments.

26. (DS)  G + L Physics Motivation Proton Spin:
Quark spin Gluon Spin Angular momentum
It has been determined, through polarized deep inelastic scattering
experiments, that the quarks alone can not account for the spin of
the proton (i.e. DS is less than 0.3 )
To account for the spin of the proton, either the gluons are polarized
and/or there are significant contributions to the protons spin from
the orbital motion of its constituents.

27. Requirements on beam intensity
Information about gluon polarization might be obtained through simultaneous measurements of ALL in inclusive production of 2 and J/ . This experiment was proposed at Fermilab (P838) at 200 GeV as a continuation of E704. The Fermilab’s PAC pointed out that physics is extremely interesting , but an intensity of the polarized proton beam from -hyperon decays was small – the statistics would not be enough. The experiment was rejected.
In our new proposal for U70 we expect instead of 2.7*107/min (P838) to have up to 4 · 108 /min (factor 15!).
In this report we use some estimates for 70 GeV on the base of the estimates which were done for P838 at 200 GeV.

28. Charmonium production mechanisms in hadronic interactions
The hadronic production of the  states involves three parton fusion diagrams : (c)
- gluon fusion (a);
- light quark annihilation (b);
- color evaporation (c).
(a) (b)

29. Parton distributions in proton
Parton distributions (at =3.5 GeV,
close to the masses of -states)
in the 70 GeV proton  see Figure
(Alekhin-2005)
- valence u-quarks (blue) ;
- valence d-quarks(green);
- sea quark/antiquarks (red) ;
- gluons (black)
Estimate shows that at 70 GeV
the contributions of gluon-gluon
fusion and quark-antiquark
annihilation to produce
charmonium with a mass of
3.5 GeV in pp-interactions are
comparable.

30. Goals of the experiment
The goal is to measure double-spin asymmetry ALL with the use of longitudinally polarized beam and target in the following processes :
p  + p  -> 2 + X и p  + p  -> J/ + X
J/ +   e+ e- 
e+ e- 
J/ (3096) JPC = 1--
 (3510) JPC = 1++
 (3555) JPC = 2++

31. Double spin asymmetry ALL
The measured experimental asymmetry is given by
ALL = [ 1/(PB * PTeff)] * [ I(++) – I(+ –)] / [ I(++) + I(+ –)],
where PB is the beam polarization,
PTeff – effective target polarization ,
I(++) ,I(+–) are the number of events normalized to the incident beam.
The helicity states (++) and (+–) correspond to () and
() respectively , where arrows indicate the beam and
target spin direction in the laboratory system.
Theoretical predictions of ALL mainly depend on two assumptions :
1. gluon polarization ∆G/G and
2. charmonium production mechanism which defines ÂLL
at the parton level (in parton-parton interaction)

32. Gluon polarization in different models
In the proposed experiment х ~0.3, where ∆G/G in different theoretical models is in the range between and 1.
In Gluon fusion model :
ALL (xF) = ÂLL * [ ∆G / G (x1) * ∆G / G (x2) ], where ÂLL = -1.
[Doncheski, Robinet] : ALL is negative for 2 and J/
In Colour evaporation model [Contogouris] ALL is positive for 2 and J/

33. Experimental setup might be assembled at channel 24(former channel 7) at U70
Open geometry experiment. Main parts : electromagnetic calorimeter, proportional chambers, trigger hodoscope

34. Geometrical acceptance to detect  at 70 GeV
Simulations were
made for 70 GeV :
must be in the
lead tungstate array
and e+e- from the
J/ -decay are at
any place in the
combined calori-
meter

35. Electromagnetic calorimeter
To separate 1 (3510 МэВ) and 2(3555 МэВ) the energy resolution of the calorimeter is critical, especially for decaying .
According to the decay kinematics of 2 , the ’s are effectively detected at very forward angle (<100 мрад).
If the calorimeter is placed at ~4.5м from the target, the central part of the calorimeter (from ~10 up to ~100 mrad) has to consist of lead tungstate crystals (2,8×2,8 × 22 cm3) – an array of 34х34 with a hole of 2x2 in the middle for non-interacted beam.
To cover a big angle region from ~100 up to ~200 mrad, we need to add 1875 Pb-glass counters with a cross section of 3,81 × 3,81 cm2 -an array of 50х50 with a hole in the middle of 25х25 to place PWO-crystals.
Such combined calorimeter will cover the region of 2 production
хF from 0 up to 0.4 (see the next slide).

36. The xF-distribution of the accepted 2-events.

37. 1 / 2 separation
Monte-Carlo for 200 GeV. The J/ mass is reconstructed – the e+,e-
energies are measured by Pb-glass calorimeter, the angles are measured by the proportional chambers. Resolution is 75 MeV/c2. The momenta of e+ and e- are constrained to give exact J/(3096 MeV) mass by scaling the energies of e+ and e-, while keeping the e+ e- angles unchanged. The e+e- momenta thus constrained are combined with the momentum of the  on the PWO to calculate the 2 mass. Resolution () is less than 10 MeV/c2. -

38. Proportional chambers and the trigger
The proportional chambers placed between the target and the calorimeter serve to track e+ and e- particles and assure that there are no charged tracks in the  direction.
Trigger on J/ with the pT signals of e+ and e- . Super-blocks in calorimeter – pT for super-block. The scintillator-pad hodoscope containing 100 pads is placed 3.3 m from the target ( 1 m in front of the EM calorimeter ) to tag the charged particles. The size and position of each scintillator pad corresponds to each calorimeter super-block.
The trigger requirements :
- 2 or more electron candidates which have pT (super-block) > 0.6 GeV
and have hits on the corresponding separate scintillator pads;
-  рT (super-block) of the electron candidates being greater than 2.5 GeV.
88% of J/’s detected in Pb-glass and PWO calorimeters satisfy these requirements (see next slide).

39. The pT correlation between e+ and e- from 2 decays

40. Trigger rate and background
* The trigger rate estimated by Monte-Carlo simulations is
~ 200 events/spill for 6*107 protons/spill (spill beam duriation is 2 sec).
~ 35% by electrons from -conversion;
~ 65% from charged hadrons overlapped with ’s within the
super-block.
* Background for J/- charged hadrons.
(hadron pairs – low masses; rejection by lateral
shower profile )
For J/ background is ~10%
(hadrons and conversion electrons)
For 2 background is ~10%
( J/ +  from 0 )  see Figure

41. Expected sensitivity in ALL for charmonium
The Р838 estimate was1640 2/month and 9200 J/ month for a beam intensity of 2,7*107 protons/min.
Assuming factor 1/3 in cross section decrease (from 200 GeV down to 70 GeV) and factor 15 in intensity rise, the overall merit factor is 5. We expect 8200 2/month and J/ /month .
We expect to get a precision of  (ALL) = for 2 and for J/ for one month of data taking.

42. Conclusions
To accelerate the polarized proton beam in the existing U70 up to 70 GeV with intensity up to 5*1012 protons/spill and polarization up to 70%, the following main tasks need to be completed :
- polarized proton source up to 20 mA ;
- one snake to be installed in the 1.5 GeV booster ;
- equipment from three straight sections (4.6 m each) to be removed;
- three partial snakes to be installed in the U70 main ring ;
- correction of the U70 vertical orbit down to ±1 mm;
- absolute (polarized jet target) and relative polarimetry.
Acceleration of the p beam at U70 gives a brand new opportunity for high energy spin physics in the new kinematic region. The presented spin program includes five miscellaneous sets of measurements :
- polarization in elastic scattering ;
- single spin asymmetry in inclusive charged hadron production ;
- miscellaneous spin parameters in hyperon production ;
- transversity in Drell-Yan muon pairs ;
- double-spin asymmetry in charmonium.
The results will be complementary to those which might be obtained at COMPASS, HERMES, RHIC, JLaB, GSI and JPARC.