Post on 10-Feb-2022
Brian Foster - DIS01 - Bologna
1
HERA II PhysicsBoth ZEUS & H1 have made major upgrades in order toutilise the increase in HERA luminosity to the full.
Brian Foster - DIS01 - Bologna
2
HERA II PhysicsThe upgrades concentrate mainly on the following areas:
- Vertex region (MVD) - Studies of heavy quarks, exotics, etc.
- Forward region (STT) - Improved kinematic reconstruction of both jets and scattered electron.
- Luminosity monitor - Cope with greatly increased synchrotronbackground + likelihood of multipleoverlapping Brems. Photons + physics payoff for improved lumi. precision ~ 1%
- Trigger & electronics - Important for all physics. On ZEUS,triggering stage between Levels 1 & 2 -“Fast Clear” that has been available but never needed to be used; and including MVD in Level 2.
- Polarimeter - ZEUS involved with TPOL positionmeasurement.
Brian Foster - DIS01 - Bologna
3
Vertex RegionThe ZEUS MVD is a silicon strip detector constructed from n-typesilicon with p+type implants and 20µ pitch strips, readout with 120µ pitch. There are 712 sensors and > 200K readout channels.
Brian Foster - DIS01 - Bologna
4
Vertex PhysicsThe major physics topic will be the flavour composition breakdown of the proton (and indeed the photon). We already have quite precise measurements of the charm-quark structurefrom HERA I.
Very precise measurements will be possible for HERA II;also gives accurategluon determination.
Accurate b contributionto F2 will becomepossible
500 pb-1500 pb-1
Brian Foster - DIS01 - Bologna
5
Vertex PhysicsA high-precision, high-acceptance vertex detector willallow both collaborations to make a full flavourdecomposition of the inclusive F2 structure function.
For example, charmsignal in charged currents in principal measures thes-quark density (+ leadingparticles in NC etc.; but alsocompeting non-s digrams in CC)At HERA II, both singlet & non-singlet pdfsu, d, s (CC DIS)c, b, g (NC DIS)can be determined with good accuracy.
Brian Foster - DIS01 - Bologna
6
Forward PhysicsZEUS major upgrade in forward direction replacement of TRD’swith two stations of straw-tube chambers, each with 3 stereolayers.
The forward wheelsin the MVD also give improved resolution inforward direction.
Brian Foster - DIS01 - Bologna
7
Forward PhysicsMajor payoff in increased accuracy for high-Q2 NC
The improvedaccuracy inforward directionwill also greatly improve resolutionon forward jets etc.and therefore“BFKL” non-DGLAPevolution studies.
1000 pb-1
x = 0.65
Q2 = 4 ×× 104
[ ]%3
003.0S
≈∆
≤∆
xg
xg
α
1000 pb-1
Q2 = 2 GeV2
Q2 = 20 GeV2
Q2 = 200 GeV2
Q2 = 2000 GeV2
Brian Foster - DIS01 - Bologna
8
Active
FilterCalorimeter
ZEUS
6m Tagger
Spectrometer
e detector
Thin window
5.3 m
92 m
105 m
105.5 m
Spectrometer
dipole
95.2 m
ZEUSI.P.
γe
Lumi MonitorZEUS went for “belt & braces” approach: two devices withvery different systematics plus precision electron tagger.
“Standard” Pb/scintillatorcalorimeter plus “activefilter” of aerogel.
Dipole spectrometer tomeasure converting e+e- pairs.
“6m tagger” W/fibre tomeasure the energyafter the bremms.
Aim is to get to around 1% error in luminosity.
Brian Foster - DIS01 - Bologna
9
PolarisationHERA II will give us access to a qualitatively new regionof physics via longitudinal polarisation.
Spin rotators will be commissionedaround H1 & ZEUS IRs.
Although thetheoreticalattainablepolarisation will fall somewhat because of the new lattice, we expect similar performance to that enjoyed until now by HERMES.
Laser
Laser
LPOL
TPOL
HERA ring
Spin rotator (new)
Spin rotator (new)
electrons
HERMES
ZEUSH1
HERA-B0 0.5 1 1.5 2
Brian Foster - DIS01 - Bologna
10
PolarisationAccurate measurement of both transverse (TPOL) and longitudinal (LPOL) polarisation plus machine lattice simulationwill give us confidence in an accurate measurement at IP.
To do this we need accurate, short-time scale, determinationof the polarisation, ideally bunch-by-bunch. This is a challenge in high synchrotron radiation environment.
Key is to use back-scattered laser light and precisiondetectors and DAQ.
Brian Foster - DIS01 - Bologna
11
PolarisationFor longitudinalpolarisation, consider situation in thephoton-electron CM frame
21=ZL
23−=ZL
Measure ENERGY asymmetry of back-scattered Compton photons:
Angular dependence ofscattering in CM systemdepends on degree ofpol. Boosting back tolab converts this angular asym. toan energy asymmetry.Measure with accurate calorimetry, preferably bunch-by-bunch.
Brian Foster - DIS01 - Bologna
12
PolarisationFor transverse polarisation, the spin direction already definesa spatial axis wrt the beam direction, so that it is clear thatthere will be asymmetries in this axis depending on the relativefraction of up- and down-polarised electrons.
( ) ηΚ−= RL yyP
Requires high-precision radhard position detector to detect theup-down asymmetry.
Brian Foster - DIS01 - Bologna
13
Polarisation
LPOL implementation (and overall DAQ) responsibility of French groups in H1; uses Fabry-Perot cavity to increase continuous laser power to allow operation in single-photon mode.
Advantages are in-situ calibration using Compton edge, high rateand thereby bunch-by-bunch measurement.
TPOL implementation - position-sensitive detector responsibility of IC London & Tokyo ZEUS groups.
Brian Foster - DIS01 - Bologna
14
Polarisation physicsThe accurate measurement of polarisation opens up a completelynew domain of HERA physics at high Q2.
( )
onpolarisati
1CCpe
=
±∝±
P
Pσ
Resolution on MW
80 MeV
Exclusion limit
MW(R) > 400 GeV
Brian Foster - DIS01 - Bologna
15
Polarisation physicsPolarisation dependence of cross-sections is a LARGE effect
For example,@ Q2 = 104 GeV2,
x = 0.2, σ(eL
-) / σ(eR-)
is almosta factor 2, andcan bemeasured toabout 10%tot. uncertainty
Brian Foster - DIS01 - Bologna
16
Polarisation physicsQuark coupings can be accurately measured, e.g. light quarkcouplings by looking at differences between σ(L,R).
Great improvementover unpolarisedcase.
%17%17
%6%13
d
u
av
beamper pb 250
%70 ,
1-
RL, ±=± Pe
Brian Foster - DIS01 - Bologna
17
Beyond SM & Pol.Beyond SM - maybe one will see new right-handedparticles!
For any new physics signal, polarisation is a very preciseand flexible tool - one can ~ “turn off” SM backgroundsby varying polarisation - if the new physics hasdifferent couplings to SM - which seems verylikely - that the S/B will be enhanced.
HERA is a unique facility for probing some aspectsbeyond the SM - it is our duty to ensure that we exhaust thephase-space it can reach - e.g. in CM energy, inpol. and charged lepton states - to maximise discovery potential.