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Polarization at HERA , F. Metlica 1
Polarization at HERA
Fabio Metlica
(Penn State University)
ZEUS Students Seminar
06/06/03
Polarization at HERA , F. Metlica 2
• Physics with Polarized Lepton Beams
• The HERA Upgrade => HERA II
• Polarization at HERA
• HERA Polarimeters: TPOL and LPOL
• Summary
Polarization at HERA
Polarization at HERA , F. Metlica 3
HERA II: Physics with Polarized Lepton Beams The study of polarized lepton (e+/e-) proton deep inelastic scattering at high will be
one of the main physics topics at HERAII. Accurate polarization (P0.7) measurement together with high luminosity opens a new field for HERA physics at high . Possibility to study the chiral structure of the SM:
-Charged currents: only LH particles interact
-Neutral currents: LH, RH particles interact with Z unequally
• Electroweak physics: study EW interactions using the 4 possible combinations: e-, e+ with P<0 and P>0. (Future Physics at HERA workshop).
-Polarized NC,CC cross section measurements;
-Light quark couplings to the Z-boson;
-Precise measurements of EW parameters.
• QCD: G2 structure function
• Search for new physics: physics beyond SM -Right handed charged currents
-Leptoquarks
2Q
2Q
Polarization at HERA , F. Metlica 4
Polarized NC, CC Cross Sections Investigate EW physics: NC and CC cross section measurements at high with P>0, P<0.
Cross sections for NC and CC
pol,NCunpol,NCNC P
unpol,CCCC )P1(
}X(p`) }X(p`)
2Q
Polarization at HERA , F. Metlica 5
Light Quark Couplings to the Z Boson
• Polarization effect is large on cross sections
for .
• Different behavior at high due to Z exchange.
• Split up to factor 2, at .
• Exploit difference to extract the light
quark(u,d) couplings to the Z-boson.
2Q
x
Neutral Current
242 GeV10Q
242 GeV10Q
Polarization at HERA , F. Metlica 6
Light Quark Couplings to the Z Boson• Measurement of polarized NC,CC disentangle the light quark(u,d) couplings to Z.
Done by using all four charge/polarization combinations.
• Unpolarized DIS with e-/e+ beams axial couplings.
• Polarized DIS with the 4 charge/ polarization combinations vector couplings.1 Contours for NC Couplings for Different Polarizations
d coupling fixed u coupling fixed
Polarization at HERA , F. Metlica 7
Light Quark Couplings to the Z Boson• With of data equally divided between e+/e- and
P=±0.7:
• Based on full MC simulation; detector improvements would improve precision.
• Complementary to LEP measurements with heavy quarks and similar to LEP precision for heavy quarks.
1fb1
%17%;17
%6%;13
ud
uu
av
av
u,d couplings to Z-boson
Polarization at HERA , F. Metlica 8
Measurements of EW Parameters: •Free parameters in SM
•Measure constrain
• data from NC/CC cross sections with beam polarization
•Test of EW universality.
•LH gives highest precision: cross section largest.
•High Pol. is worth a factor 4 in Lumi for NC.
)M,M,M,M,( tHWZ
CC
e
NC
e,
1fb1
e
WM
GeV5M Tevatron From t
MeV55MW
7.0Pe
)M,M( tW
Polarization at HERA , F. Metlica 9
Measure G2 Structure Function• structure function arising from Z interference.
• G2 can be measured from the neutral current parity violating asymmetry
= degree of polarization (P) = axial charge of electron
• Simulation for P=50% with for each polarization setting: G2 can be well measured at high x (M. Klein DIS2001 Bologna).
)qq(vex2FG qqZ
2
x1
A
ea
1pb200
Polarization at HERA , F. Metlica 10
Search for Right Handed CC
CCR
CCL
CC
Xpe)P1()P1(
•Standard model: only LH CC exists
•Cross section vanishes for purely RH electron (for P=+1):
RHCCLHCC
For e+ reverse sign
Polarization at HERA , F. Metlica 11
Search for Right Handed CC
RW•Set a limit on the mass of the hypothetical boson (model dependent) (~250 data).
•Direct search.
•Need high polarization 50%, and precise polarization measurement.
GeV400M RW
e-p SM MC
e+p SM MC
1pb
Polarization at HERA , F. Metlica 12
•Polarization is a useful tool for searching new physics signals.
•SM backgrounds can be reduced (turned off) by varying the degree of polarization. If new physics have different couplings, the S/B will be increased.
•Helps determine properties of newly discovered particles. Study chirality of new particles e.g. leptoquarks.
New Physics: Beyond SM
Polarization at HERA , F. Metlica 13
HERA II• HERA UPGRADE: increase luminosity and provide longitudinal
lepton beam polarization to the colliding experiments. Long shutdown 2000-2001, to modify IP and install spin rotators.
LUMINOSITY UPGRADE
• Strong focusing at IP: major changes of machine lattice near IP. Sets of superconducting quadrupoles installed close to the H1/ZEUS IP, inside the detectors.
• Design luminosity HERA I (achieved):
• Delivered by HERA I:
(during 1992-2000)
• Design luminosity HERA II :
• To be delivered by HERA II by end 2006:
(original plan, now?)
Likely startup value for lumi:
1231105.1 scmL
1231105.7 scmL
1INT pb180L
1INT fb1L
1231 scm108.3L
IP AREA
Polarization at HERA , F. Metlica 14
POL2000 Group: Polarization Upgrade
• ZEUS: TPOL position sensitive detector (silicon microstrip + fiber detector) IC-London and Tokyo Metropolitan University
• H1: LPOL cavity and fast DAQ for TPOL
• HERMES: LPOL operation
• HERA: polarized lepton beam studies and operation
Polarization at HERA , F. Metlica 15
HERA II: Polarization • In HERA leptons become transversely polarized through the emission of synchrotron
radiation (spin flips): Sokolov-Ternov effect.
• The transverse polarization is converted into longitudinal polarization near the interaction points by Spin Rotators (HERA I: HERMES; HERA II also H1/ZEUS) .
• The lepton beam transverse
polarization is measured by the
TPOL polarimeter, and the
longitudinal polarization is
measured at the LPOL
polarimeter, independently.
Polarization at HERA , F. Metlica 16
Polarization• Polarization is defined as:
• Polarization has to be known at the same level of precision as Total Luminosity, because it enters linearly in the cross section for many processes e.g.:
• Polarization precision goal for HERA II: 0.01 ( 0.02-0.04 for HERA I),
needed for polarization physics.
• The absolute value of the degree of lepton polarization is the same along the whole ring. The actual location of the polarization measurement is not confined to the experiment IP.
• Precise measurement from the TPOL/LPOL polarimeters together with machine lattice simulations, will provide confidence of having an accurate P measurement at IP.
pol,NCunpol,NCNC P
unpol,CCCC )P1(
TransLong PP
DOWNUP
DOWNUP
NN
NNP
P/P
Polarization at HERA , F. Metlica 17
Polarization • Polarization builds up and settles asymptotically to an equilibrium value.
55%)~P (for 20mintime buildup onpolarizatistic characteri
ttime given a atvalue onpolarizati
value mequilibriu onpolarizati asymptotic
-
-P(t)
-P
)exp1(P)t(P
eq
/teq
•Theoretical max polarization 92%, but reduced by counteracting depolarizing effects (dependence on ring parameters),each spin rotator pair reduces polariz ~3%.
•HERA I: 55%-65% polarization
•HERA II : startup 50% polarization (aim for more 60%). Spin rotators and different lattice setups reduces polarization.
HERA I
HERA I
Polarization at HERA , F. Metlica 18
Polarization Measurement• The polarimeters make use of the spin-dependent cross section for Compton scattering of polarized photons on polarized leptons(e+/-) :
• Alternatively L/R (~100Hz) circularly polarized laser light is scattered off leptons . The produced Compton photons are backscattered (in lab frame) into a narrow cone centered around the initial lepton direction and are detected by the polarimeter (LPOL or TPOL).
• The Compton beam size at the TPOL is:
angles scatteringthe of function as photon scatteredthe of onsdistributithe describe -functions
onpolarizati circular light laser3S
onpolarizati linear light laser1S
onpolarizati allongitudin and transverseZP,YPonspolarizati lepton and photon initialP,S
]Z2ZPY2YP[3S11S0)P,S(d
Cd
mm5.0,mm4.3 yx
Polarization at HERA , F. Metlica 19
Polarization MeasurementThe polarization at HERA is determined by measuring asymmetries.
asymmetry energy asymmetry spatial onpolarizati allongitudin onpolarizati transverse
K)YY(PRLT
TPOLLPOL
Z3L S/)E(AP
Polarization at HERA , F. Metlica 20
Polarization Measurement
• The polarization of lepton colliding and non-colliding bunches differs (measured by LPOL at HERA I). Depends on the machine polarization tuning and varies in time (beam-beam effects).
HERA ILPOL
• Need accurate per bunch per minute polarization measurement LPOL and TPOL upgrade for HERA2.
Polarization at HERA , F. Metlica 21
Polarization: TPOL TPOL upgrade completed
• Fast DAQ to measure the polarization of individual bunches per minute.
• Radhard silicon position sensitive detector to allow in-situ eta-y calibration.
• TPOL ready for polarization measurement.
HERA Tunnel
Laser room 9th floor HERA B
TPOL
TPOL Setup(similar setup for LPOL)
HERA BLepton direction
Polarization at HERA , F. Metlica 22
TPOL-Spatial Asymmetry• Spatial asymmetry:
• The typical total average vertical shift is about 0.15 mm.
• In practice is obtained by measuring the up-down calorimeter energy asymmetry of the Compton photons:
• determined by the calibration MC + test beam data.
• transformation is of primary importance (main source of systematic error).
power analyzing)(E
onpolarizati transverseP
onpolarizati circular light laser S,S2
SSS
light) laser polarized circularly R(L, photons Compton ofsample large a forface rcalorimetethe on position y meanY
Y
Y
R3L3R3L3
3
R,L
)E(Y3SYP2RYLY
)E(Y
power analyzingffective e)E(
DOWNEUPE
DOWNEUPE
)E(3SYP2
RL)E(
)E(
y
test beam data
YP
Polarization at HERA , F. Metlica 23
TPOL: HERA I• TPOL: Tungsten scintillator sampling calorimeter, 10W CW laser
alternating LCP, RCP at 90Hz .
• Operated in Single -photon mode: 1 photon per 200 bunch crossings;
Compton energy spectrum of TPOL (HERA1)
Compton spatial distribution at TPOL (HERA1)
)(mm
Polarization at HERA , F. Metlica 24
Upgraded TPOL• TPOL calo measures: total energy
. ,vertical position Y of the
Compton by the transformation.
• Silicon detector: improve position resolution from ~1 mm (calo) to better than 50 m (silicon); intrinsic silicon resol. is 24m.
• Transformation: determine accurately in-situ in real time, do not have to rely on test beam data.
• Silicon position sensitive detector: prototype (1cm*1cm), final setup (6.3cm*6.3cm) (IC-London).
• A single scintillating fiber detector for position calibration (5m) and monitoring of the Si-detector (Tokyo Metro. Uni).
y
y
DOWNEUPE
DOWNEUPE
DOWNUPTOT EEE
TPOL calo: Tungsten scintillator sampling calorimeter.Laser: 10W CW laser alternating LCP,RCP 90Hz .
Polarization at HERA , F. Metlica 25
Prototype Silicon Detector for TPOL
• Prototype silicon detector:1cm*1cm,
APV25 readout chip.
• Tested with DESY T22 test beam
(6 GeV electrons).
•Results in ZEUS Note: ZEUS-01-019 Strips S/N 20, Efficiency 97% Position resolution < 50 m (beam telescope). Good Eta-Y measurement
Landaudistr.
Polarization at HERA , F. Metlica 26
Silicon Detector for TPOL•CERN test beam: 6-50 GeV •Si detector(6.3cm*6.3cm),readout by 6 APV25, 80m pitch •Spare TPOL calo. (tungsten-scintillator sampling)•Scintillating fiber Detector: (7cm,1mm) precision stage motor (reso. ~1 m).
CERN test beam results and upgraded TPOL setup in ZEUS Note: ZEUS-02-019
Polarization at HERA , F. Metlica 27
CERN Test Beam Results
Non-Linearity:<1%
Resolution:~ 25%/sqrt(E)
Fiber calib. Precis:~50m
Good eta-y
Polarization at HERA , F. Metlica 28
TPOL: HERAII Data
Silicon Raw dataSilicon event
signal
y ationparametriz y
Polarization at HERA , F. Metlica 29
Silicon Detector for TPOL
APV25 44m
Silicon 80m
Pitch Adaptor 44m->80m
Silicon
Polarization at HERA , F. Metlica 30
TPOL in HERA Tunnel
TPOL BOX Open TPOL( Calo+Silicon+Fiber)
Polarization at HERA , F. Metlica 31
LPOL No major change: Original LPOL operational
• Two calorimeters (Crystal and Sampling ) which may be used alternatively (movable support tables). Change to sampling: better energy linearity.
• Pulsed laser: operates in Multi-photon mode: approx. 600 to1000 Compton photons produced per laser pulse (~100 Hz) shot on a lepton bunch.
• Measure shifts of energy spectra for the two light polarizations.
• Large difference in the spectra close to the Compton edge.
• LPOL ready for polarization measurements.
RCP
LCP
Z3L S/)E(AP
power analyzing
states laser twothe of onpolarizati
circular of difference to relatedS
onpolarizati allongitudinP
asymmetry energy)E(A
Z
3
Z
Polarization at HERA , F. Metlica 32
LPOL Cavity Upgrade in Progress LPOL upgrade: New more powerful laser system ( Fabry-Perot cavity + new laser)
to operate in single photon mode (~1-2 photons per bunch crossing). Large laser photon flux: increase probability of Compton scattering. 1) direct calibration with Compton edge (define energy scale of calo) 2) improve statistical error by having a high average laser power ~10kW (not
commercially available).
CW laser
Linear polarized laser light
Circular polarized laser light
HERMES
Lepton direction
LPOLIP
OriginalLPOL IP
LPOL Cavity IP
Polarization at HERA , F. Metlica 33
LPOL Cavity
•The cavity has been successfully installed during shutdown in HERA tunnel (near HERMES).
•Cavity is locked and stable (gain factor ), should be ready by end of shutdown.
•Startup plan: start with original LPOL setup, then move to laser cavity setup.
(Orsay)
4105~
Polarization at HERA , F. Metlica 34
LPOL Cavity Installation in HERA Tunnel, 2003
Polarization at HERA , F. Metlica 35
HERA Polarization Tuning 2003
•High polarization , P~50%, with all 3spin rotators on and colliding beams.
•Both LPOL and TPOL working, and in reasonable agreement. TPOL minor technical problems: low TPOL luminosity.
Polarization at HERA , F. Metlica 36
Polarimeter Online Java Display
Displays various polarization info
Polarization at HERA , F. Metlica 37
Polarization Data for ZEUS • All polarimeter info is stored into the
ORACLE database. Accessible to all HERA experiments.
• Software developed (Arafat Gabareen) to read polarization data from ORACLE and integrate it with the rest of the ZEUS data.
• Polarization data integration: during ZEUS event reconstruction, typically a few days or a week after the data is taken.
• Two ADAMO tables: 1)TPOL and LPOL values P,P for all 220
bunches. 2)TPOL and LPOL values P,P average for
colliding and non-colliding bunches.
Polarization at HERA , F. Metlica 38
• e+e- 4-6 weeks. Orbits differ, magnets need to be moved by ~6mm.
• Longitudinal Polarization flip: ~1-2 days. HERA1 (LPOL) done once a month during access day (mechanical movement of magnets) plus time for beam polarization tuning.
• Longitudinal Polarization direction (P<0 or P>0): each experiment can choose independently.
• Polarimeters: no background problem seen. No lattice modification carried out at polarimeter locations, backgrounds similar to HERA1.
• Lepton transverse polarization did not affect the measurements at HERAI
(H1/ZEUS). suppressed to order compared to . (Does Transverse Electron Polarization Affect Measurements at HERA? M. Kraemer et. al.)
Extra Info
ee E/mTPunpolP
Polarization at HERA , F. Metlica 39
Summary
• HERA has been upgradedHERAII:
- luminosity increase
- lepton beam polarization P50% with P/P ~1% (upgraded polarimeters).
• New field of HERA physics is opened with polarized lepton beams.
• Two polarimeters LPOL(cavity upgrade to be completed) and TPOL to provide accurate polarization measurements to the HERAII experiments.
• Polarimeters will operate independently and cross check one another; together with HERAII machine lattice simulations will provide confidence in the IP polarization value.
• TPOL/LPOL working, measured 50% polarization before start of shutdown.
• Discussion between experiments and DESY to organize running and maintenance of the polarimeters.