THERA Ulrich F. Katz, ZEUS · Detector and Infrastructure L Bauerdick (DESY HH) J Crittenden (U...
Transcript of 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
-
U. Katz ECFA/DESY LC Workshop, Padova, 05.05.00 3
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
-
U. Katz ECFA/DESY LC Workshop, Padova, 05.05.00 4
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
-
U. Katz ECFA/DESY LC Workshop, Padova, 05.05.00 5
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, : : :
-
U. Katz ECFA/DESY LC Workshop, Padova, 05.05.00 6
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
-
U. Katz ECFA/DESY LC Workshop, Padova, 05.05.00 7
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
-
U. Katz ECFA/DESY LC Workshop, Padova, 05.05.00 8
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?
-
U. Katz ECFA/DESY LC Workshop, Padova, 05.05.00 9
THERA interaction region
0z (m) 10 -10
p
e
proton focusingmagnets
e dipole
synchrotronradiation fan
x
y
0
0
-10cm
20µm
x
-
U. Katz ECFA/DESY LC Workshop, Padova, 05.05.00 10
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
-
U. Katz ECFA/DESY LC Workshop, Padova, 05.05.00 11
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)
-
U. Katz ECFA/DESY LC Workshop, Padova, 05.05.00 12
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?
-
U. Katz ECFA/DESY LC Workshop, Padova, 05.05.00 13
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 179:5� 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
-
U. Katz ECFA/DESY LC Workshop, Padova, 05.05.00 14
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, : : :
-
U. Katz ECFA/DESY LC Workshop, Padova, 05.05.00 15
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
-
U. Katz ECFA/DESY LC Workshop, Padova, 05.05.00 16
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
)
-
U. Katz ECFA/DESY LC Workshop, Padova, 05.05.00 17
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
-
U. Katz ECFA/DESY LC Workshop, Padova, 05.05.00 18
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
-
U. Katz ECFA/DESY LC Workshop, Padova, 05.05.00 19
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
-
U. Katz ECFA/DESY LC Workshop, Padova, 05.05.00 20
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
-
U. Katz ECFA/DESY LC Workshop, Padova, 05.05.00 21
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)
-
U. Katz ECFA/DESY LC Workshop, Padova, 05.05.00 22
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!
-
U. Katz ECFA/DESY LC Workshop, Padova, 05.05.00 23
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
-
U. Katz ECFA/DESY LC Workshop, Padova, 05.05.00 24
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)
-
U. Katz ECFA/DESY LC Workshop, Padova, 05.05.00 25
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.