LHCspin : a polarized internal target for the LHC - PowerPoint Presentation

Slide1

LHCspin:a polarized internal target for the LHC

PSTP2019Knoxville, Tennessee, September 26th 2019

P. Lenisa – University of Ferrara and INFNfor the LHC-spin study group

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2

A bit of (pre) historyTeflon-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)

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Motivation

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4Kinematics for a fixed target at LHC

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5Advantages of the fixed-target mode (

wrt to collider):Access large-negative xF and large positive xB High luminosities (dense targets)Easy change target typePolarized target – spin physics programPhysics goals:Large-x gluon, antiquark and heavy-quark content in the nucleon and nucleus.Dynamics and spin of gluons in (un)-polarised nucleonsHeavy-ion collisions towards large rapiditiesFixed target mode at LHC: performance

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SMOG2 development at LHCb

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LHCb detector

Forward geometry

Conceived for measurements in collider modeIdeal for

fixed

target

experiments

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SMOG

(System for Measuring Overlap with Gas)Beam-Gas imagingDedicated runs at different energies since 2015

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9Upgrade to SMOG2

installation of a storage cell in 2019 and start data taking in 2021Opened cellClosed cellLHCbVELO Detector

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10

Increase luminosity up to 2 orders of magnitude with the same gas loadInjection of H2, D2, 3,4He, N2, Ne, Ar, Kr, XeWell defined interaction region upstream the IP@13TeV:Possible simultaneous data taking with pp interactions @13 TeVSMOG2 vs SMOG

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11Polarized Gas Target

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Atomic Beam Source

Target Gas AnalyzerSample Beam PolarimeterTarget B12Polarized atomic beam injected from left

Sample beam:QMS to measure molecular fraction.BRP polarimeter to measure atomic polarization.

The HERMES polarized internal gas target @ HERA (1995-2005)

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13Performance for transversely polarized H (2002/03)

HERMES 2002/03 data taking with transverse proton polarizationTop: 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

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PGT at LHC - topology

Z= 0 LHCb - IPPrototype of the new

system:Transverse magnetAdditional tracking system

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15Compatibility with LHC beams

Beam half-life: ≈ 10 hParasitic operation requires small reduction of half-life (< 10%)p beam intensities @ LHCProtons: Ip = 6.8∙1018 p/s @ 7 TeV.1s-radius at IP (full energy): < 0.02 mmNegligible compared with the cell radius (> 5 mm)Safety radius at injection (450 GeV

for p): > 25 mm “Openable” cell required.

Beam tube

Length: 300 mm (L

1

= 150 mm)

Closed: D

1

= 10 mm

.

Opened: D

1

= 50 mm

Cell temperature: T = 100 K

.

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16

Polarized 1H gas target performancespp @ √s = √2MnEp ≈ 100 GeV = 50 mb = 5∙10-26 cm2Max. relative loss rate: (dN/dt)/N = 2∙10-8/s

H, Ctot

= 2 C

1

+ C

2

= 16 l/s, I = 6.5∙10

16

atoms/s (HERMES):

areal density

q

= L

1

∙

r

0

=

1.2∙10

14

atoms/cm

2

Total luminosity:

L

pp

= 8.2∙10

32

/ cm

2

s

About 5% of the collider luminosity

The H target does not affect the life time of the 7

TeV

proton beam

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(A couple of) accelerator issues

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Bunch beam structure and Fourier spectrum at LHC

st= 253 pssn= 0.63 GHzDn= 40.08 MHzTemporal structure of the proton

bunchFourier analysis of the proton

beam

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Beam-induced depolarization (BID)1 - 2

3 - 4

2 - 4

Resonant transitions caused by beam field

Orientation of guide field

B

0

and RF - beam field

B

1

:

p

resonances

for B

1

┴

B

0

D

F = 0, ±1

D

mF

= ± 1

s

resonances

for B

1

||

B

0

D

F = ±1

D

mF

= 0.

Affect nuclear polarization.

s

resonances (

states 2-4

) densely spaced:

high homogeneity of guide field required

p-beam

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Comparison HERA vs LHC

20Machine

NBunch

f

Bunch

(

MHz)

I

beam

(

A)

s

t

(

ps

)

1/e width of Fourier spectrum

HERA-e

210

10.41

0.04

31

5.1 GHz

LHC

2600

40.08

1.0

253

0.63 GHz

BID

at the LHC negligible

wrt

HERA despite the 25x higher beam current

Spin-flip Probability

s

2-4

resonance

,

q

= mixing angle,

t

= crossing time, n index of passage:

B

||

B

1

-RF

field

parallel

to

B

0

(

guide

field

≈ 300mT)

B

1

|| B

0

for

q

= 90°

.

Relative

strength

of

BID

by

ratio

of

the

square

of

B

||

:

s

2-4

transition

at 8.54 GHz

k-th

harmonic

of

Fourier

spectrum

:

LHC: F

213

= 2 ∙ 1.0 A ∙ 1.53 10

-20

HERA: F

820

= 2 ∙ 0.04 A ∙ 7.53 10

-2

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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 actionH recombination and depolarization on C to be studied Option: C with frozen ice layer to preserve H polarization Secondary Electron Yield (SEY) and cell coating

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22

SEY of Water: preliminary studiesOnly few layers required;the cell is short (30 cm);laboratory tests to study dynamical equilibrium

ice layer on a-C; test chamber

first in the SPS?

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Summary

Unique physics opportunities for single-spin physics program at LHCFirst conceptual design developedCell30 cm long-cell (openable at injection)≈ 0.3 T vertical fieldCell surface with a-C coating: To be studiedThin ice layer to suppress recombination and depolarization. Target densities and luminosity depend on the gas load permitted: quite high.Tracker downstream requiredBID estimated: more favorable than at HERMES

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Which dissociator technology with extreme reliability to be used?

No coolant must flow into the vacuum systemSpace 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 regionNICA is also planning a similar polarimeterHow to enable assembly, service and repair within the limited space?Open issues

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Spares

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26Proton-proton collisions: variables

XB: Bjorken-x (0<xB<1)- xB = parton momentum fraction- x1 & x

2 Bjorken-x of beam and target

X

F

:

Feymann

-x (-1<

x

F

<1)

Rapidity (y) and angle with beam axis (

q

)

Collider

Fixed target

y

y

y

y

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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 (→ Bguide vertcal)Arrangement in the tunnel:available space upstream of the VELO vessel