XXI Physics in Collision Conference
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XXI Physics in Collision Conference Seoul Korea June 28 - 30 2001. High Q 2 Physics. Christopher M. Cormack Rutherford Appleton Laboratory. Contents.

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XXI Physics in Collision Conference

Seoul

Korea

June 28 - 30 2001

High Q2 Physics

Christopher M. Cormack

Rutherford Appleton Laboratory


Contents

A very broad range of subjects for High Q2 and High PT - Results include Structure Functions from H1 + ZEUS Exotics Phenomena - overlap with HERA, LEP, TEVATRON

  • Introduction

    • HERA

    • DATA

    • H1 / ZEUS Detectors

  • Neutral Current

    • Z Exchange

  • Charged Current

    • W Exchange

  • New Physics ?

    • LQ Resonances

    • Isolated Leptons

    • Top Searches

  • The Future

  • Summary + Outlook

High Q2 Physics - C.M. Cormack


Introduction

The Electron-Proton Collider

1998-2000

e+p and e-p

1994-1997

Luminosity Delivered

High Q2 Physics - C.M. Cormack


e+/-

,Q2

HERA Deep Inelastic Scattering Kinematics

Kinematic Variables

Resolving power

Negative of the four-momentum transfer between lepton and proton

“Momentum fraction of proton carried by the struck quark”

Inelasticity

Momentum fraction of the lepton carried by the exchange

High Q2 Physics - C.M. Cormack


HERA KINEMATIC PLANE

  • Accessible Kinematic Plane now almost completely covered

  • Measurements extend to cover high y, high x and very high Q2

  • Probe distances to ~ 1/1000th of proton size

High Q2 Physics - C.M. Cormack


e+/-

p

NC

H1 Detector at HERA

Fine Grained Liquid Argon Calorimeter (45 000 channels)

EM section

HAD section

Tracking Chambers

High Q2 Physics - C.M. Cormack


CC

ZEUS Detector at HERA

Compensating Uranium-Scintillator Calorimeter

EM section

HAD section

Tracking Chambers

High Q2 Physics - C.M. Cormack


Photon, Z couples to all quark flavours

Z exchange

Parity Violating term - sensitivity to valence quarks

Neutral Current DIS Structure Functions

Longitudinal structure function

L.O. QCD:

Reduced cross section

High Q2 Physics - C.M. Cormack


Neutral Current DIS -

  • Standard Model shows good agreement over 6 orders of magnitude

  • Effect of the Z0 contribution fron xF3 clearly seen at high Q2

High Q2 Physics - C.M. Cormack


Neutral Current DIS - Effect of Z0 Exchange

  • e - pDATA requiresCONSTRUCTIVE - Z interference

  • e +P DATA requires DESTRUCTIVE interference

High Q2 Physics - C.M. Cormack


Neutral Current DIS - Reduced Cross Section

  • SM shows good agreement with data over all Q2 range

High Q2 Physics - C.M. Cormack


  • High Precision at low to medium Q2, x

  • First measurements at high Q2 and x

  •  - Z interference seen xF3

Neutral Current DIS - Reduced Cross Section

High Q2 Physics - C.M. Cormack


y2 FL small at high Q2

Need high y

Neutral Current DIS - Fl Extraction

H1 data extend to small electron energies

 Bjorken y < 0.75

Sign of xF3 term depends on lepton charge

First Measurement of Longitudinal Structure Function FL at High Q2

High Q2 Physics - C.M. Cormack


Neutral Current DIS - xF3

y2 FL small at high Q2

  • First extraction of xF3 on PROTONat high Q2, x

Direct Sensitivity to the valence quarks!

High Q2 Physics - C.M. Cormack


e+p:d, s and u, c

e-p:u, c and d, s

Charged Current DIS Structure Functions

`invisible`Missing PT

Q2

W exchange

L.O. CROSS SECTIONS

Probed valence

Probeu valence

  • Sensitivity to separate parton densities

  • Effect of W mass - from propagator

Reduced Cross Section

High Q2 Physics - C.M. Cormack


Charged Current DIS -

  • Effect of different parton densities seen from lower Q2

  • Factor of 10 difference in e+/e- cross section at high Q2

High Q2 Physics - C.M. Cormack


Charged Current DIS

  • Need for more d at high x ?

High Q2 Physics - C.M. Cormack


Charged Current DIS

  • Possibility to extract d/u using proton as target - Higher Statistics

High Q2 Physics - C.M. Cormack


Charged Current DIS - Fitting MW

Q2 dependence of CC cross section includes propagator term

Consistency check rather than a measurement of MW

August-99 world average:

MW = 80.376  0.039 GeV

High Q2 Physics - C.M. Cormack


Searches for New Physics

The High Q2 / PT Range Accessible at HERA allows the competitive searches in many areas for New Physics.

  • Some of the Topics Covered

  • W/Z production - High PT Leptons

  • Single Top Production

  • New Lepton-Quark Interactions

  • Excited Fermions / Quark Substructure

  • SuperSymmetry - Talks from U. Heintz & M. Chertok

High Q2 Physics - C.M. Cormack


H1

Since 1994 Both Experiments Have observed a strange type of Event

Produced at High PT With Isolated Leptons and Missing PT

Observation of Events at High PT with Isolated Muons

ZEUS


e

e’

 / Z0

q

e

e’

W

q

 / Z0

q

W

q

Isolated High PT Leptons

  • A class of Interesting events at HERA

  • Sensitivity to rare Standard Model Processes

Single - W Production

Leptonic decay of W  events with a high energy lepton and missing transverse momentum

NLO calculations are underway M. Spira

New Physics

Stop and Sbottom production

R-Parity Violating Supersymmetery

Single Top production through anomalous flavour changing Neutral Current Coupling (FCNC)

High Q2 Physics - C.M. Cormack


Neutrino

Jet

Acoplanarity

Lepton

Isolated High PT Leptons

W l  Kinematics

Expect a peak at W mass for W l 

High Q2 Physics - C.M. Cormack


H1 Isolated High PT Leptons

0 Events found with electron running

High Q2 Physics - C.M. Cormack


ZEUS - Isolated High PT Leptons

  • Search for high PT tracks in high PTCAL sample

  • PTCAL > 25 GeV

  • Pttrack > 10 GeV

Check Isolation of high Pttrack wrt to other tracks (Dtrack) and Jets (Djet)

Event Rate Consistent with SM Prediction

High Q2 Physics - C.M. Cormack


Comparison ZEUS - H1

Selecting the same Phase Space PTX > 25 GeV

  • SM expectations are in agreement

  • H1 sees more events at high PTX

  • ZEUS has the acceptance to detect events

  • Statistical fluctuation from the SM or an indication of Physics BSM? More Data Soon

High Q2 Physics - C.M. Cormack


Anomalous Single Top Production

Single-top production with anomalous FCNC coupling

  • ZEUS Leptonic Channel:

  • Final state with high PT Lepton and large PTX

  • ZEUS Dtrack > 0.5, Djet> 1.0 and PTX > 40 GeV

  • ZEUS sees no events

  • H1 Leptonic Channel:

  • Final state with high PT (Jet) > 35 (25)Lepton and (jet) < (>) 35o

  • MTlv > 10 GeV (Reject -ve leptons)

  • H1 sees 5 events(3e+2) for 1.4  0.5 expected

Limits for Anomalous FCNC couplings

 coupling

LEP e+ e- tc,tu

TEVATRON RARE TOP DECAY

High Q2 Physics - C.M. Cormack


ZEUS and H1 Isolated Lepton Control Plots

H1

Observes an excess of Isolated High PT Events

ZEUS

 sample

Event rate consistent with Standard Model

High Q2 Physics - C.M. Cormack


Search for New particles

Look for the direct production of resonances with Mass M < s

Look for deviations in SM cross section - CONTACT Interactions

  • This presentation - Leptoquarks (LQ)

  • Squarks in SUSY

  • Excited Fermions

  • Leptoquarks (LQ)

  • Scalar and Vector, colour triplet bosons

  • Carry Fermion number F=3B+L=0,2

  • Decays - Look for Resonances in e q system

  • Generic Models LQ  l q

  • LQ   q

High Q2 Physics - C.M. Cormack


e

SCALAR LQ:

e’

 / Z0

q

q

e

e

LQ

q

q

Resonance Hunting 1

Mass plots H1 and ZEUS + limits

NC DIS

Me / MCJ

W

Intriguing HERA events caused excitement in past years

What About New DATA ?

High Q2 Physics - C.M. Cormack


Resonance Hunting 2

Analysis of Latest 1999 -2000 Data

Excess in old data not confirmed by New DATA H1 / ZEUS  Derive Limits on LQ couplings  and Masses MLQ (In BRW Model)

LEP -Virtual effects to hadronic xsec

Tevatron - LQ produced via strong coupling

HERA - Stringent limits for intermediate mass range

High Q2 Physics - C.M. Cormack


Limits from New Data

  • Quick look at Contact Interactions

  • Large Mass Leptoquarks - See Previous

  • Large Extra Dimensions - Kaluza-Klein Gravitons

  • Compositness - Quark Radius

Kaluza-Klein Graviton Exchange - Effective contact interaction

H1

M-S > 0.93 TeV

M+S > 0.63 TeV

ZEUS

M-S > 0.82 TeV

M+S > 0.81 TeV

High Q2 Physics - C.M. Cormack


Contact Interactions

Quark form factor:

Rq - quark radius

ZEUS

Rq <0.73 x 10-16 cm

H1

Rq <1.6 x 10-16 cm

The HERA electron microscope probing scales to 1/1000th the size of the proton

High Q2 Physics - C.M. Cormack


The HERA Upgrade

  • Luminosity Upgrade:

  • Large increase on present luminosity

    • Running Programme:

    • Five years of running

    • starting in September 2001

    •  1000 pb-1 for both H1 / ZEUS

  • Polarisation for Collider Experiments:

    • Longitudinally Polarised electron/positron beams

    •  60% (design goal)

  • Measurements of NC and CC DIS using high luminosity and

  • upgraded detectors will constrain:

  • Singlet, non-singlet quark densities

  • u, d, s (CC DIS)

  • c, b, g (NC DIS)

  • i.e. COMPLETE study of proton structure

Measurements of NC and CC DIS using high luminosity and upgraded detectors will constrain:

Singlet, non-singlet quark densities

u, d, s (CC DIS)

c, b, g (NC DIS)

i.e. COMPLETE study of proton structure

High Q2 Physics - C.M. Cormack


x = 0.65

Q2 = 4  104

1000 pb-1

Future Physics

- The Structure Function F2

1000 pb-1

High precision Structure Function measurements - high x constraints important for high energy processes at Tevatron and LHC

Opportunities for a discovery To complement those at the Tevatron

High Q2 Physics - C.M. Cormack


Outlook for HERA

Summary - HERA High Q2 Physics

  • Results shown of High Q2 NC + CC cross sections - with high statistics data sets (e- & e+)

  • Wealth of Data + measurements allowing tests of QCD and Electroweak parameters

  • The recent 16 pb-1 electron data has allowed the first extraction of xF3 the last unmeasured proton structure function - Effect of - Z interference observed

  • High Q2 cross sections are well described by the Standard model - a triumph for QCD

  • Opportunity to constrain pdfs (d/u ratio) at high x possible with clean proton target

  • Need for forth coming higher statistics to improve Charged Current xsec and better constraint on the high x valence pdfs - xF3

  • Oportunity for discovery (LQ)

  • More Isolated Leptons ?

The HERA Upgrade

High Q2 Physics - C.M. Cormack


Sign of xF3 term depends on lepton charge

y2 FL small at high Q2

Neutral Current DIS - xF3 Extraction

Extraction Method

  • Error limited by electron sample (16 pb-1)

  • Positron data sample (30 pb-1)

High Q2 Physics - C.M. Cormack


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