XXI Physics in Collision Conference Seoul Korea June 28 - 30 2001

XXI Physics in Collision Conference

Seoul

Korea

June 28 - 30 2001

Christopher M. Cormack

Rutherford Appleton Laboratory

High QHigh Q22 Physics Physics

PIC 2001 - 28th June 2001 High Q2 Physics - C.M. Cormack 2/35

ContentsContents

• 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

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


The Electron-Proton Collider

1994-1997

1998-2000

e+p and e-p

IntroductionIntroduction

Luminosity (pb-1)H1 ZEUS

e-P16 16

e+P100 110

Luminosity Delivered


HERA Deep Inelastic Scattering KinematicsHERA Deep Inelastic Scattering Kinematics

Kinematic Variables

222 )( kkqQ Resolving power

Negative of the four-momentum transfer between lepton and proton

“Momentum fraction of proton carried by the struck quark” qp

Qx

2

2

kp

qpy

Inelasticity

Momentum fraction of the lepton carried by the exchange

22 )( qpW 2)( kps sxM

0,, Z

e+/-

kk

x

,Q2q


HERA KINEMATIC PLANEHERA 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


H1 Detector at HERAH1 Detector at HERA

NC

e+/- p

Fine Grained Liquid Argon Calorimeter (45 000 channels)

EM section %1%12

EE

E

HAD section %1%50

EE

E

Tracking Chambers

ppp 003.0/


ZEUS Detector at HERAZEUS Detector at HERA

Compensating Uranium-Scintillator Calorimeter

EM section EE

E %18

HAD section EE

E %35

Tracking Chambers

TTTT pppp /0014.00065.00058.0/

CC


NCL

2NC3

NC24

2

2

eNC

2 2FyxFYFY

xQdxdQ

d P

L.O. QCD:

Neutral Current DIS Structure FunctionsNeutral Current DIS Structure Functions

Reduced cross section

NCL

NCNCNC

NC FY

yxF

Y

YF

dxdQ

d

Y

xQ

2

322

2

2

4 1

2~

22

2

22 cossin4

1

ZWWZ MQ

Q

Quarks

fNC QxqQxqQAxF )],(),()[( 222

2

Quarks

fNC QxqQxqQBxxF )],(),()[( 222

3

Photon, Z couples to all quark flavours

Parity Violating term - sensitivity to valence quarks

Z exchange


• Standard Model shows good agreement over 6 orders of magnitude

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

Neutral Current DIS -Neutral Current DIS - 2/ dQd


Neutral Current DIS - Effect of ZNeutral Current DIS - Effect of Z00 Exchange Exchange

22 GeV 000 10 Q dx

d

• e - p DATA requires CONSTRUCTIVE - Z interference

• e +P DATA requires DESTRUCTIVE interference


Neutral Current DIS - Reduced Cross SectionNeutral Current DIS - Reduced Cross Section

• SM shows good agreement with data over all Q2 range

2

2

2

4 1

2~

dxdQ

d

Y

xQ NC

NC


Neutral Current DIS - Reduced Cross SectionNeutral Current DIS - Reduced Cross Section

2

2

2

4 1

2~

dxdQ

d

Y

xQ NC

NC

• High Precision at low to medium Q2, x

• First measurements at high Q2 and x

- Z interference seen xF3


Neutral Current DIS - FNeutral Current DIS - Fl l ExtractionExtraction

Bjorken y < 0.75

H1 data extend to small electron

energies

),(),(),(2)( 222

32

24

2

2

2

QxFyQxxFYQxFYxQdxdQ

ped NCL

NCNCNCBorn

y2 FL small at high Q2 Need high y


Neutral Current DIS - xFNeutral Current DIS - xF33

• First extraction of xF3 on PROTON at high Q2, x

Direct Sensitivity to the valence quarks!

820920

1

920

920

820

820

2

4

3

11

2 YYY

Y

Y

YxQxF

),(),(),(2)( 222

32

24

2

2

2

QxFyQxxFYQxFYxQdxdQ

ped NCL

NCNCNCBorn


Charged Current DIS Structure FunctionsCharged Current DIS Structure Functions

Q2

Xpe

))(1(2

2

2

22

22

2

2

sdycuMQ

MG

dxdQ

d

W

WF

Xpe

))(1(2

2

2

22

22

2

2

sdycuMQ

MG

dxdQ

d

W

WF

• Sensitivity to separate parton densities

• Effect of W mass - from propagator

Probe d valence

Probe u valence

Reduced Cross Section

2

2

2

22

2

2~dxdQ

d

M

MQ

G

x

W

W

FCC

W exchange

L.O. CROSS SECTIONS


Charged Current DIS -Charged Current DIS - 2/ dQd

• Effect of different parton densities seen from lower Q2

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


Charged Current DISCharged Current DIS

• Need for more d at high x ?


Charged Current DISCharged Current DIS

sdycux

sdycux

Pe

Pe

2

2

1~

1~

CC

CC

xdyxuPePe 2CCCC 1 versus :

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


Charged Current DIS - Fitting MCharged Current DIS - Fitting MWW

02CC0 Q

PDF Sys.; Stat.; :Errors

GeV 330272481 :Z

GeV 737133980 :H1

for of shape Fit2

....

....

W

W

W

M

M

MdQ

dσ

tZ

W

tZW

mMM

M

mMMMfG

,,

.

,,;

.

...

.

...

H

030060

300310

130160

240250

H

PDF; Sys.; Stat.; :Errors

GeV 5080 :Z

:constraint Model Standard

Consistency check rather than a measurement of MW

August-99 world average:

MW = 80.376 0.039 GeV

2

22

22

2

W

WF

CC

MQ

MG

dQ

d

Q2 dependence of CC cross section includes propagator

term


Searches for New PhysicsSearches 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

Ob

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atio

n o

f E

ven

ts a

t H

igh

PO

bse

rvat

ion

of

Eve

nts

at

Hig

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TT w

ith

Iso

late

d M

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s w

ith

Iso

late

d M

uon

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at

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d L

epto

ns

and

Mis

sin

g P

T

ZE

US

H1


Isolated High PIsolated High PTT Leptons Leptons

A class of Interesting events at HERA

Sensitivity to rare Standard Model Processes

Single - W Production

pbXeWep 0.1) ( e e’

/ Z0

q

q

W

New Physics

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

NLO calculations are underway M. Spira

t~

b~

e

d

l

d

W Stop and Sbottom production

R-Parity Violating Supersymmetery

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

t

b

cu,

l

W


Isolated High PIsolated High PTT Leptons Leptons

W l Kinematics

22YX

CALT PPP

lT

CALT

XT PPP -

hltyAcoplanari

))cos(1(2 M T Tl

T PPMassTransverseCAL

TT PP e,for track

TX

TT PPP

,for

Expect a peak at W mass for W l

Acoplanarity

Neutrino

Jet

Lepton


H1 Isolated High PH1 Isolated High PTT Leptons Leptons

H1 94-00e+p 101.6 pb-1 Electrons Muons E+

combined

PTX> 0 GeV 10 / 7.9 +/- 1.9 8 / 2.6 +/- 0.7

18 / 10.5 +/-2.5(only W 8.2)

PTX> 12GeV 5 / 2.6 +/- 0.7 8 / 2.6 +/- 0.7

13 / 5.1 +/-1.3(only W 4.2)

PTX> 25 GeV 4 / 1.3 +/- 0.3 6 / 1.5 +/- 0.4

10 / 2.8 +/-0.7(only W 2.3)

PTX> 40 GeV 2 / 0.4 +/- 0.1 4 / 0.6 +/- 0.2

6 / 1.0 +/-0.3(only W 0.93)

0 Events found with electron running


ZEUS - Isolated High PZEUS - Isolated High PTT Leptons Leptons

Search for high PT tracks in high PTCAL sample

• PTCAL > 25 GeV

• Pttrack > 10 GeV

22/D Jettrack

ZEUS Preliminary1994-2000

ElectronsObserved/expected

(W)

MuonsObserved/Expected

(W)

e+p 114 pb-1 7 / 9.9 1.6 (2.4) 7 / 4.6 0.6 (1.1)

e-p 16 pb-1 3 / 1.1 0.4 (0.3) 0 / 0.8 0.1 (0.2)

TOTAL 130 pb-1 10 / 11.0 1.6 (2.7) 7 / 5.4 0.7 (1.3)

Check Isolation of high Pt

track wrt to other tracks (Dtrack)

and Jets (Djet)

Event Rate Consistent with SM Prediction


Comparison ZEUS - H1Comparison ZEUS - H1

H1(101 pb-1)

e+p data only18/10.5 (W 8.2)

High Purity/Efficiency

H1(115.2 pb-1)

e p data

18/12.3 (9.4 W)

ZEUS (130 pb-1)e p

data17 / 16.4 (4 W)

Inclusive sampleof lepton events

Selecting the same Phase Space PTX > 25 GeV

H1 (82 pb-1) 9 / 1.8 (1.5 from W)

ZEUS (130 pb-1) 2 / 2.4 (1.5 from W)

• 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


Anomalous Single Top ProductionAnomalous Single Top Production

t

b

cu,

l

W

Single-top production with anomalous FCNC coupling

MissTT P Jet Phigh lepton)( lbWt

ZEUS Leptonic Channel:

Final state with high PT Lepton and large PT

X

• ZEUS Dtrack > 0.5, Djet> 1.0 and PT

X > 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

uAqt

eut

L

Limits for Anomalous FCNC couplings

coupling

LEP e+ e- tc,tu

TEVATRON RARE TOP DECAY


ZEUS and H1 Isolated Lepton Control PlotsZEUS and H1 Isolated Lepton Control Plots

H1

ZEUS

Event rate consistent

with Standard

Model

Observes an excess of

Isolated High PT Events

sample


Search for New particlesSearch for New particles

• This presentation - Leptoquarks (LQ)

• Squarks in SUSY

• Excited Fermions

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

Look for deviations in SM cross section - CONTACT Interactions

PR

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

s

Mq

sJ LQ

22

4)1(

LQ

q

, e

q

e


Resonance Hunting 1Resonance Hunting 1

e e’

/ Z0

q q

e

q

e

q

LQ

NC DIS SCALAR LQ:SUSY R in q~or P

2

1

ydy

d

FLAT

SCALARdy

d

Intriguing HERA events caused

excitement in past years

What About New DATA ?

Me / MCJ


Resonance Hunting 2Resonance 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

y21cos *


Limits from New DataLimits from New Data

Quick look at Contact Interactions

• Large Mass Leptoquarks - See Previous

• Large Extra Dimensions - Kaluza-Klein Gravitons

• Compositness - Quark Radius

scale) (process s whichin expected xsec NC oneffect for Look

...),(),(1)( 2222

2ηη QxBQxAdxdQ

d

dxdQ

d SM

Kaluza-Klein Graviton Exchange - Effective contact interaction

4/ SG M

H1

M-S > 0.93 TeV

M+S > 0.63 TeV

ZEUS

M-S > 0.82 TeV

M+S > 0.81 TeV


Contact InteractionsContact Interactions

Quark form factor:

2

2

22 61 Q

R

dQ

d

dQ

d qSM

Rq - quark radius

ZEUSRq <0.73 x 10-16 cm

The HERA electron

microscope probing scales to 1/1000th the

size of the proton

H1Rq <1.6 x 10-16 cm


The HERA UpgradeThe HERA UpgradeLuminosity 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


- The Structure Function F2 1000 pb-1

1000 pb-1

x = 0.65

Q2 = 4 104

Future PhysicsFuture Physics

Opportunities for a discovery

To complement those at the Tevatron

High precision Structure Function

measurements - high x

constraints important for high energy processes at

Tevatron and LHC


Summary - Summary - HERA High QHERA High Q22 Physics 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


Neutral Current DIS - xF3 Extraction

820920

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4

3

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2 YYY

Y

Y

YxQxF

3820

2820

4

2

2

2 2xFYFY

xQdxdQ

d

3920

2920

4

2

2

2 2xFYFY

xQdxdQ

d

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

• Positron data sample (30 pb-1)

Extraction Method

),(),(),(2)( 222

32

24

2

2

2

QxFyQxxFYQxFYxQdxdQ

ped NCL

NCNCNCBorn

Sign of xF3 term depends on lepton charge y2 FL small at high Q2

XXI Physics in Collision Conference Seoul Korea June 28 - 30 2001

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Transcript of XXI Physics in Collision Conference Seoul Korea June 28 - 30 2001