LHCspin : a polarized internal target for the LHC

1. LHCspin:a polarized internal target for the LHC P. Lenisa – University of Ferrara and INFN for the LHC-spin study group PSTP2019 Knoxville, Tennessee, September 26th 2019

2. A bit of (pre) history • Teflon-coated storage cell filled with polarized H proposed by Prof. W. Haeberli • 2nd Polarization Symposium (Karlsruhe 1965) • First test in Madison (Wisconsin): • 5th Int. Symp. on Pol. Phenomena in Nuclear Physics (Santa Fe 1980)

3. Motivation

4. Kinematics for a fixed target at LHC

5. Fixed target mode at LHC: performance • Advantages of the fixed-target mode (wrt to collider): • Access large-negative xF and large positive xB • High luminosities (dense targets) • Easy change target type • Polarized target – spin physics program • Physics goals: • Large-x gluon, antiquark and heavy-quark content in the nucleon and nucleus. • Dynamics and spin of gluons in (un)-polarised nucleons • Heavy-ion collisions towards large rapidities

6. SMOG2 development at LHCb

7. LHCb detector Forwardgeometry Conceived for measurements in collider mode Ideal for fixed target experiments

8. SMOG(System for MeasuringOverlap with Gas) • Beam-Gas imaging • Dedicatedrunsatdifferentenergiessince 2015

9. Upgrade to SMOG2 installation of a storage cell in 2019 and start data taking in 2021 LHCb VELO Detector Opened cell Closed cell

10. SMOG2 vs SMOG • Increase luminosity up to 2 orders of magnitude with the same gas load • Injection of H2, D2, 3,4He, N2, Ne, Ar, Kr, Xe • Well defined interaction region upstream the IP@13TeV: • Possible simultaneous data taking with pp interactions @13 TeV

11. Polarized Gas Target

12. The HERMES polarized internal gas target @ HERA (1995-2005) Target Gas Analyzer Sample Beam Polarimeter Target B Atomic Beam Source • Polarized atomic beam injected from left • Sample beam: • QMS to measure molecular fraction. • BRP polarimeter to measure atomic polarization.

13. Performance for transversely polarized H (2002/03) HERMES 2002/03 data taking with transverse proton polarization Top: Degree of dissociation measured by the TGA (a = 1: no molecules); Bottom: Vector polarization Pz measured by Breit-Rabi-Polarimeter. Coating: ice layer on Drifilm surface

14. PGT at LHC - topology Z= 0 LHCb - IP Prototype of the new system: • Transversemagnet • Additionaltrackingsystem

15. Compatibility with LHC beams • p beam intensities @ LHC • Protons: Ip = 6.8∙1018 p/s @ 7 TeV. • Beam tube • Length: 300 mm (L1 = 150 mm) • Closed: D1 = 10 mm. • Opened: D1 = 50 mm • Cell temperature: T = 100 K. • Beam half-life: ≈ 10 h • Parasitic operation requires small reduction of half-life (< 10%) • 1s-radius at IP (full energy): < 0.02 mm • Negligible compared with the cell radius (> 5 mm) • Safety radius at injection (450 GeV for p): > 25 mm • “Openable” cell required.

16. Polarized 1H gas target performance H, Ctot= 2 C1 + C2 = 16 l/s, I = 6.5∙1016 atoms/s (HERMES): areal density q = L1∙ r0 = 1.2∙1014 atoms/cm2 • Total luminosity: Lpp = 8.2∙1032/ cm2 s • About 5% of the collider luminosity • spp @ √s = √2MnEp ≈ 100 GeV = 50 mb = 5∙10-26 cm2 • Max. relative loss rate: (dN/dt)/N = 2∙10-8/s The H target does not affect the life time of the 7 TeV proton beam

17. (A couple of) accelerator issues

18. Bunch beam structure and Fourier spectrum at LHC Temporalstructure of the protonbunch st= 253 ps Fourier analysis of the protonbeam sn= 0.63 GHz Dn= 40.08 MHz

19. Beam-induced depolarization (BID) 1 - 2 2 - 4 p-beam 3 - 4 • Resonant transitions caused by beam field • Orientation of guide field B0 and RF - beam field B1: • p resonances for B1 ┴B0 DF = 0, ±1 DmF = ± 1 • s resonances for B1 ||B0DF = ±1 DmF = 0. • Affect nuclear polarization. • s resonances (states 2-4) densely spaced: • high homogeneity of guide field required

20. Comparison HERA vs LHC • Spin-flip Probabilitys2-4 resonance, q = mixing angle, t = crossing time, n index of passage: • B|| B1-RF field parallel to B0 (guidefield ≈ 300mT) • B1 || B0forq = 90°. • Relative strengthof BID byratioofthesquareof B||: • s2-4transition at 8.54 GHz • k-thharmonicof Fourier spectrum: • LHC: F213 = 2 ∙ 1.0 A ∙ 1.53 10-20 • HERA: F820 = 2 ∙ 0.04 A ∙ 7.53 10-2 BID at the LHC negligible wrt HERA despite the 25x higher beam current

21. Secondary Electron Yield (SEY) and cell coating • Coatings for surfaces close to the LHC beam: materials with SEY ≤ 1.4 allowed • Non-Evaporable Getter (NEG) (standard) • Amorphous Carbon (a-C) (tested and applied more frequently) • NEG coating for the tube’s inner surface excluded because of its pumping action • H recombination and depolarization on C to be studied • Option: C with frozen ice layer to preserve H polarization

22. SEY of Water: preliminary studies • Onlyfewlayersrequired; • the cellis short (30 cm); • laboratorytests to studydynamicalequilibriumicelayer on a-C; • test chamber first in the SPS?

23. Summary • Unique physics opportunities for single-spin physics program at LHC • First conceptual design developed • Cell • 30 cm long-cell (openable at injection) • ≈ 0.3 T vertical field • Cell surface with a-C coating: • To be studied • Thin ice layer to suppress recombination and depolarization. • Target densities and luminosity depend on the gas load permitted: quite high. • Tracker downstream required • BID estimated: more favorable than at HERMES

24. Open issues • Which dissociator technology with extreme reliability to be used? • No coolant must flow into the vacuum system • Space is tight on the side of the beam foreseen for diagnostics. • How would a minimal BRP and TGA look like? • Is there a p-p channel we could use for polarimetry? • see RHIC jet polarimeter detecting recoil p’s from CNI region • NICA is also planning a similar polarimeter • How to enable assembly, service and repair within the limited space?

25. Spares

26. Proton-proton collisions: variables XF: Feymann-x (-1<xF<1) y Collider y XB: Bjorken-x (0<xB<1) - xB = parton momentum fraction - x1 & x2Bjorken-x of beam and target Fixed target y Rapidity (y) and angle with beam axis (q) y

27. Arrangement in the tunnel: available space upstream of the VELO vessel • Along the beam: • About 1m, limited by shielding wall. • Could be moved, but important for the PGT to stay as close to the VELO as possible! • In transverse direction: • Enough to place ABS and diagnostics in the horizontal plane (→ Bguidevertcal)