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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 26 th 2019. A bit of (pre) history. Teflon-coated storage cell filled with polarized H proposed by Prof. W. Haeberli
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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
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)
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
LHCb detector Forwardgeometry Conceived for measurements in collider mode Ideal for fixed target experiments
SMOG(System for MeasuringOverlap with Gas) • Beam-Gas imaging • Dedicatedrunsatdifferentenergiessince 2015
Upgrade to SMOG2 installation of a storage cell in 2019 and start data taking in 2021 LHCb VELO Detector Opened cell Closed cell
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
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.
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
PGT at LHC - topology Z= 0 LHCb - IP Prototype of the new system: • Transversemagnet • Additionaltrackingsystem
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.
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
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
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
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
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
SEY of Water: preliminary studies • Onlyfewlayersrequired; • the cellis short (30 cm); • laboratorytests to studydynamicalequilibriumicelayer on a-C; • test chamber first in the SPS?
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
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?
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
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)