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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

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Xxi physics in collision conference seoul korea june 28 30 2001

XXI Physics in Collision Conference

Seoul

Korea

June 28 - 30 2001

High Q2 Physics

Christopher M. Cormack

Rutherford Appleton Laboratory


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

Introduction

The Electron-Proton Collider

1998-2000

e+p and e-p

1994-1997

Luminosity Delivered

High Q2 Physics - C.M. Cormack


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

CC

ZEUS Detector at HERA

Compensating Uranium-Scintillator Calorimeter

EM section

HAD section

Tracking Chambers

High Q2 Physics - C.M. Cormack


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

Neutral Current DIS - Effect of Z0 Exchange

  • e - pDATA requiresCONSTRUCTIVE - Z interference

  • e +P DATA requires DESTRUCTIVE interference

High Q2 Physics - C.M. Cormack


Xxi physics in collision conference seoul korea june 28 30 2001

Neutral Current DIS - Reduced Cross Section

  • SM shows good agreement with data over all Q2 range

High Q2 Physics - C.M. Cormack


Xxi physics in collision conference seoul korea june 28 30 2001

  • 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


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

Charged Current DIS

  • Need for more d at high x ?

High Q2 Physics - C.M. Cormack


Xxi physics in collision conference seoul korea june 28 30 2001

Charged Current DIS

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

High Q2 Physics - C.M. Cormack


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

H1 Isolated High PT Leptons

0 Events found with electron running

High Q2 Physics - C.M. Cormack


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

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


Xxi physics in collision conference seoul korea june 28 30 2001

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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