THERA Ulrich F. Katz, ZEUS · Detector and Infrastructure L Bauerdick (DESY HH) J Crittenden (U...

Physics with THERA

(TESLA on HERA)

Ulrich F. Katz, ZEUS

University of Bonn

ECFA/DESY LC Workshop

Padova, 05. May 2000

� Introduction{ Studying the THERA option

{ Kinematics outreach

� Machine and detector visions{ THERA layout and parameters

{ Detector requirements

� Some selected physics topics{ QCD at low x and Q2

{ Heavy quarks

{ High-Q2 cross sections, �s{ New phenomena

� Conclusions and plans

The following report is based on

work of the THERA study group

and on discussions withthe DESY accelerator experts.

U. Katz ECFA/DESY LC Workshop, Padova, 05.05.00 2

The THERA study group

Meetings:Previous: 08{09.02 and 14{15.04.2000

Future: 18{20.10.2000 (tentative date)

Please join if you are interested!

WorkingGroups Convenors

Low x P Newman (U Birmingham)E Levin (Tel Aviv) A Levy (Tel Aviv)

Heavy Flavours K Daum (Wuppertal)L Gladilin (U Hamburg,Moscow)

Photon structure J Butterworth (UC London)S Söldner-Rembold (CERN/U Freiburg)M Krawczyk (Warsawa)

High Q2 E Perez (Saclay)K Long (IC London)M Kuze (KEK Tanashi)

QCD and MC simulation L Lönnblad (U Lund)H Spiesberger (U Mainz)H Jung(U Lund)

Detector and Infrastructure

L Bauerdick (DESY HH)J Crittenden (U Bonn)U Katz (U Bonn)M Klein (DESY Z)D Pitzl (DESY HH)

Machine S Schlenstedt(DESY Z) U Schneekloth(DESY)

Polarization E Rondio (Warsawa)A Deshpande (Yale U)

Nuclei M Strikman (Penn State)

Gamma S Sultansoy (Ankara)

More information inhttp://www.ifh.de/thera


Questions and objectives

Questions:

Feasibility:

can the THERA project

be realized without negative

interference with TESLA?

Physics potential:

what can be learned from THERA?

Objectives:

Answer the above questions.

Document the results.

Section in TESLA TDR:

physics potential of a

TESLA{HERA ep option

(draft 10/2000, �nal by spring 2001)

Year

Res

olve

d di

men

sion

[fm

]

10

1

0.1

0.01

1900 1950 2000

0.001

0.0001

Rutherford

Hofstadter

SLAC ep

CERN µ,ν N

HERA

THERA

partons10-16

10-19

[m]

THERA is the

canonical

successorof a series of

very successful

DIS

experiments


Kinematics of ep scattering

p(P)p remnant

q

; Z

e(k)e(k0)

q

p(P)p remnant

q

W

e�(k)

, -� (k0)

q0

Neutral Current (NC) Charged Current (CC)

ep center-of-mass energy squared:

s = (k+ P )2 = 4EeEp

four-momentum transfer:

Q2 = �(k � k0)2 = 2EeE0(1 + cos �e)

�e = e scattering angle w.r.t. proton direction

momentum fraction of struck quark:

x =Q2

2 (k � k0) � P

inelasticity:

y =(k � k0) � P

k � P=

Q2

xs


The THERA outreach

10-1

1

10

10 2

10 3

10 4

10 5

10-6

10-5

10-4

10-3

10-2

10-1

x

Q2

(GeV

2 )

THER

A kin

emati

c lim

it (25

0GeV

*920

GeV)

HERA

kine

matic

limit (

27.5G

eV*8

20Ge

V)

179.5°179.5°

179°179°

178°178°

175°175°

θe

HERA 1993

HERA 1994

HERA 1994-1997

HERA SVTX

ZEUS BPC 1995

E665

BCDMS

CCFR

SLAC

NMC

THERA domain

Extend HERA range by

� 1 order of magnitudeto higher x and Q2

+ \electroweak region"+ new phenomena?{ small cross sections

Reach x = a few� 10�6at Q2 & 1GeV2

+ high parton densities+ new QCD e�ects+ large cross section{ diÆcult to measure

Cover one decade of Q2

in perturbative regime

for x � 10�4+ onset of pQCD+ gluon density, �s, : : :+ forward jets, : : :


The THERA complex

e±

e±

TE

SLA

HERA

p

injectionfrom TESLA

e beam dump

connection line

N

Hall West

PETRA

THERA

p

THERA: pHERA: e

HERA: p

HERA p-ring and

tunnel modi�cations

� Reverse proton direction{ New magnets for p

injection to HERA(7T or new tunnel)

{ Move p dump orbeam kickers

� ep beam separation,new p focusing

� Option: Additional RFto reduce p emittance

� Transfer e beam intoand out of HERA tunnel

New components

� Transfer line fromTESLA to HERA

{ civil engineering,not on DESY area

{ no active beam lineelements

{ \thin" tube mightbe suÆcient

� e beam dump{ 1� 1� 8m3 H2O in

4m concrete walls

{ tunnel HERA!dump{ not clear whether

suÆcient spaceon DESY area


THERA running modes

e-

TE

SLA

HERA

Dedicated mode

+ Use full length of TESLA,get maximal energy and beam power

+ No modi�cation of TESLA necessary

{ TESLA (e+e�) and THERA (ep)operation mutually exclusive

{ Only e� available, e+ productionneeds high-energy e� beam at\far end" of TESLA (reducesluminosity by factor 2)

{ Full TESLA energy probably notusable (beam separation)

e+

e- e+

HERA

TE

SLA

Symbiotic mode

+ Simultaneous operation of,TESLA and THERA, no eÆciencyor luminosity loss for TESLA

+ Relaxes time constraints for THERA

{ Requires extra beam line in oneTESLA arm (moderate e�ort)

{ Only e+ available

{ Maximal e energy and beam power50% lower than for dedicated mode

{ Transport of e+ beam throughe+e� interaction region diÆcult,

induces radiation and energy spread


THERA parameters

bunch

structure

TESLA: trains of 2800 bunches,�t=337ns, 950�s/train,repetition rate 5Hz;

HERA: time structure enforced byDESY3: �t=96ns� (11=n)(�t=352ns for n=3);

HERA and TESLA can be matched

e beam

energy

Symbiotic: limited to � 400GeVDedicated: TESLA allows � 800GeV

But: Ee . 500GeVrequired for beam separation

luminosity

Standard: 1030 cm�2 s�1 (10pb�1=y)

Possible: enhancement by factor 2�4by reducing p emittance;

substantial e�ort (RF, : : : )

Further increase:

R&D beyond current

concepts (proton cooling)

Warning: L� Ee � const.

polarization

Electrons: no obvious problems

to transfer polarization

from TESLA to THERA

Protons: studied as future HERA

option; active R&D

program at DESY;

slightly easier for THERA

since no vertical bends?


THERA interaction region

0z (m) 10 -10

p

e

proton focusingmagnets

e dipole

synchrotronradiation fan

x

y

0

0

-10cm

20µm

x


Kinematics at low x and Q2

THERA: 250GeV (e) � 920GeV (p)

10-1

1

10

10 2

10 3

10 4

10-7

10-6

10-5

10-4

10-3

hadrons

10-1

1

10

10 2

10 3

10 4

10-7

10-6

10-5

10-4

10-3

electrons

electrons:

in narrow

backward cone(Q2 . 100GeV2)

high energy:

E0 � (1� y)Ee

hadrons:

also very backward

typical energy:

Eh � yEe


Kinematics at high Q2

THERA: 250GeV (e) � 920GeV (p)

10 3

10 4

10 5

10 6

10-3

10-2

10-1

1

hadrons

10 3

10 4

10 5

10 6

10-3

10-2

10-1

1

electronselectrons:

central/forward

energy:

up to Ep(like at HERA)

kinematic peak:x0 = Ee=Ep

hadrons:

central/forward

Eh up to Ep

Q2 = (2xEp tan

�h

2)2

) cover small �hto reach low y

() Q2 lever arm)


A high-Q2 event at THERA

THERA NC DIS event

simulated in H1 detector

(250GeV (e) � 920GeV (p))

Q2 = 3� 106GeV2

x = 0:6

e p

Such events are contained in central detector

Can ZEUS/H1 detectors cover central region?


Detector requirements

high

x and Q2:

Requires central detector

� ZEUS or H1 detector usable?� Problems: age, calorimeter linearity,

tracking resolution (RB dl)

\Simple" solution possible?

low

x and Q2:

Electron and hadronic system

are very backward:

� acceptance at least to 179:5Æ� 2� azimuthal coverage for

background rejection & trigger

� e=h separation (also in jets)� good e energy resolution

crucial for kinematic reconstruction

� good angular resolution (tracking)� jet measurements at Eh � EeHighly demanding requirements

for backward detector

forward:

Jets, heavy quarks:

� require maximal rapidity coverageForward detector design?

taggers:

We want more than DIS:

� photoproduction: backward e tagger� luminosity, ISR: backward tagger� di�raction: forward p tagger

No prohibiting constraints


QCD at low x and Q2

goals:

� Assess proton structure at low x� Understand QCD vacuum in

perturbative non-DGLAP domain

(large ln(1=x) and Q2 & O(1GeV2))� What happens as cross sections

approach unitarity limit?

When does saturation set in?

� � � �

� : mentioned in the following

answers

expected

from

THERA:

� scaling violations, FL and g(x)� vector meson cross sections� di�raction at large mass MX

) jet production, parton dynamics� forward jet production at x . 10�4

) BFKL, : : :

additional

options:

� Polarized protons in HERA) spin structure functions

� Light/heavy nuclei in HERA) �(A)=�(d)

� p collisions byusing back-scattered laser light

) photon structure, : : :


Saturation

Virtual photon-proton interactions at low x

� are characterized by two transverse scales:1=Q =transverse size of virtual qq pair

R0 � (x=x0)�=2 = color dipole size(typical distance between quarks)

� Saturation expected for R0 � 1=Qat HERA: at Q2 � 1GeV2, non-perturbativeat THERA: at Q2 � 2� 3GeV2, perturbative

� THERA reaches lower x at higher Q2) new insights expected.

W2 � Q2=x


The gluon density at low x

At low x: (@F2=@ lnQ2) � �sxg(x)

need suÆcient Q2 range to disentangle:

� pQCD evolution� higher-twist e�ects� saturation� non-pQCD e�ects� � � �

need THERA to reach

suÆciently large Q2 at

x � 10�4

extrapolation of

g(x) from H1unitarity

limit

R0 = 1=Q

)saturation

H1 96-97

0

2.5

5

7.5

10

12.5

15

17.5

20

22.5

10-4

10-3

10-2

10-1

x

xg(x

,Q2 )

Q2=5 GeV2

Q2=20 GeV2

Q2=200 GeV2

H1 prel.

exp thy ⊕

30

20

10

0-6

10-5

10-4

10-3

10-2

10-1

10 x

xg(x

)


Heavy avor physics

Heavy quark production and what we learn from it

process information

DIS �c=b! c=b heavy avor QCD, PDFs

�

g ! cc; bb QCD, g(x) in protonW

�

s ! c,W

�

g ! sc s(x) and g(x) in protonPHP g ! cc; bb gluon distribution in proton

g ! c=c+ Rest,

g ! b=b+Rest

heavy quark content of

(resolved processes)

� Cross sections 3-20 times larger than at HERA� backward coverage essential

0

50

100

150

200

-6 -4 -2 0

log(xg)

dσ

ep →

cX/d

log(x

g)

(nb)

THERA

HERA

0

20

40

60

-4 -2 0 2 4

ηc

dσ

ep →

cX/d

ηc

(nb

)

THERA

HERA

c

pt(c) > 2GeV

0

1

2

-6 -4 -2 0log(xg)

dσ

ep →

bX/d

log(x

g)

(nb)

THERA

HERA

0

1

-4 -2 0 2 4ηb

dσ

ep

→ b

X/d

ηb (n

b)

THERA

HERA

b

pt(b) > 2GeV


DIS at high Q2

Reduced NC cross section:

~�NC =xQ

4

2��2(1 + (1� y)2) �d2�NC

dx dQ2

� THERA high-Q2 domain: large Z contributions� Reasonable measurement accuracy up to

Q2 � 106GeV2, also at high x (200pb�1 assumed)

� Large Q2 range of combined dataallows precision measurement of �s and PDFs


Precision measurement of �s

�s determination at THERA:

� Expected theoretical uncertainty:�the�s = 0:001 (3-loop calculation)

� Experimental determination from scaling violationsusing THERA, HERA and �xed-target data

in high-Q2 region of pQCD:

�exp�s = 0:0005 (preliminary result)

� free of �nal{state e�ects!Highly relevant for

� precision measurements of �, GF , sin2 �w, g � 2,� LHC analyses,� � � �

21/6π

23/6π

25/6π

27/6π

2mt

2mt’

2mc

2mb

“log(E)”MU

1/α U

“1/α

s”

❊

1

�s(Q2)=

1

�u

+33� 2Nf

6�� ln Q

Mu

Note: New colored particles would

increase Nf above a threshold Q2 �M2x


Exploiting the e polarization

The e polarization can help:

� in electroweak analyses of DIS cross sections� in searches for new phenomena� for spin-dependent PDF and QCD studies

if polarized protons and/or nuclei are available

Example:

search for right-handed charged currents

~�CC =2�x

G2F

Q2+M2

W

M2W

� d2�NC

dx dQ2/ P

� TESLA o�ers large jP j) large lever arm for testing ~�CC / P

� Increase of Q2 by an order of magnitudew.r.t to HERA ) increased sensitivity range

HERA THERA


Leptoquarks and squarks

Leptoquarks and RP -violating squarks:

� couple to eq with Yukawa coupling �� can be resonantly produced in ep scattering

�LQ / �2 � q(x =M2LQ=s)� THERA increases current sensitivity : : :

10-2

10-1

1

103

MLQ [GeV]

λ LQ

HERA 2 x 400 pb-1

THERA e-p 100 pb-1

TESLA eγ 10 fb-1

TESLA e+e- 10 fb-1

Ee = 500 GeV

Current limits

APV signal

S1e e

q q

LQ

� �

Note: Experimental hints for LQs exist

(>3�, mostly from APV data

A.F. _Zarnecki, hep-ph/0003271)

� If real: THERA=\LQ factory" for MLQ . 0:8TeV� e charge and pol. allow to determine LQ properties

(P. Taxil, E. Tugcu, J.M. Virey, hep-ph/9912272)


Competing with LHC

LQ production at LHC & Tevatron:

�(pp! LQLQ X) /��

g

gg

LQ

LQ

+

q

qg

LQ

LQ

+ : : :

��

2

�(pp! LQLQ X ! eeqq X) / BR(LQ! eq)2

250 GeV e+ x 820 GeV p

0

0.2

0.4

0.6

0.8

1

300 400 500 600 700 800 900

LHC limit, 100 fb

-1

LHC lim

it

L = 10

fb-1

For L = 10 pb-1 :excluded forλ = 0.1

LQ coupling to e+ u

MLQ (GeV)

β (L

Q →

eq

)

0

0.2

0.4

0.6

0.8

1

300 400 500 600 700 800 900

LHC limit, 100 fb

-1

LHC lim

it

L = 10

fb-1

For L = 60 pb-1 :λ = 0.1λ = 0.03

LQ coupling to e+ u

MLQ (GeV)

β (L

Q →

eq

)

THERA

limits

The discovery potential of LHC is larger, but

complementary data from THERA if LQ is in reach!


Excited fermions

If fermions are composite : : :

� e�, �� and q� can be directly produced at THERA� competition:

e+e� ! ff� at TESLA,

qq ! f�f� (Drell-Yan) at LHC� But: cross section at LHC is suppressed

by factor O(�=�s) w.r.t. LQ channel

ZEUS 98+99

LE

P 18

9 G

eV

THERA 250GeV e x 920 GeV p, 30 pb -1

THER

A

e

pp;X

; Z;W

e�; ��

e; �

; Z;W


A �� event at THERA

�� production at THERA

simulated in ZEUS detector

(250GeV (e) � 920GeV (p))

ep! ��+ j+X ! e+3j +X(�� ! eW ! eqq)M�� = 400GeV

e p

Event is almost completely

contained (E � pz = 482GeV)


Conclusions and Plans

The TESLA�HERA (THERA) ep mode isbeing studied. The goal is to assess and

document the physics potential and technicalfeasibility and to contribute achapter to the TESLA TDR.

No obvious show-stoppers so far.It seems possible that

THERA could run in parallel with TESLA.

THERA seems to o�er many attractivepossibilities, in particular for investigating

the dynamics of strong interactions.

The success of THERA depends criticallyon the detector design.

Let's establish a list of fundamental questionsto a future ep machine at

ps = 1TeV!

You are invited to join the e�ort!

Thanks to all who have contributed or will

contribute.

THERA Ulrich F. Katz, ZEUS · Detector and Infrastructure L Bauerdick (DESY HH) J Crittenden (U...

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Transcript of THERA Ulrich F. Katz, ZEUS · Detector and Infrastructure L Bauerdick (DESY HH) J Crittenden (U...