Polarization at HERA Fabio Metlica ( Penn State University) ZEUS Students Seminar 06/06/03

Polarization at HERA , F. Metlica 1

Polarization at HERA

Fabio Metlica

(Penn State University)

ZEUS Students Seminar

06/06/03


• Physics with Polarized Lepton Beams

• The HERA Upgrade => HERA II

• Polarization at HERA

• HERA Polarimeters: TPOL and LPOL

• Summary

Polarization at HERA


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


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


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


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


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


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


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


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


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 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


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


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


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• 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 • 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 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 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 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: 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


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


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


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 .


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.


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


CERN Test Beam Results

Non-Linearity:<1%

Resolution:~ 25%/sqrt(E)

Fiber calib. Precis:~50m

Good eta-y


TPOL: HERAII Data

Silicon Raw dataSilicon event

signal

y ationparametriz y


Silicon Detector for TPOL

APV25 44m

Silicon 80m

Pitch Adaptor 44m->80m

Silicon


TPOL in HERA Tunnel

TPOL BOX Open TPOL( Calo+Silicon+Fiber)


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


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


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~


LPOL Cavity Installation in HERA Tunnel, 2003


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.


Polarimeter Online Java Display

Displays various polarization info


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.


• 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


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.

Documents

Polarization at HERA Fabio Metlica ( Penn State University) ZEUS Students Seminar 06/06/03