zeus highlights for ichep02 a personal selection
TRANSCRIPT
ZEUS Highlights for ICHEP02... a personal selection
• What is the structure of the proton ? • Is DGLAP working at low-x ?• How are heavy quarks produced ?
• Is the SM valid at high energies ?
• How can we understand soft processes ?• More complex proton description : GPD ?• What drives colour singlet proton component ?
Main Questions at HERA:
Incl. DIS & PDF Fits
strange, charm, beauty
Tau
High Et: electrons&jets
DVCS/J/Ψ & F2D3
ZEUS
0
1
2
3
4
5
1 10 102
103
104
105
F2 em
-log 10
(x)
Q2(GeV2)
ZEUS NLO QCD fit
tot. error
ZEUS 96/97
BCDMS
E665
NMC
x=6.32E-5x=0.000102x=0.000161
x=0.000253
x=0.0004x=0.0005
x=0.000632x=0.0008
x=0.0013
x=0.0021
x=0.0032
x=0.005
x=0.008
x=0.013
x=0.021
x=0.032
x=0.05
x=0.08
x=0.13
x=0.18
x=0.25
x=0.4
x=0.65
Final incl. DIS PDF-Fits
Not always Gaussian
Proton structure function F2: impressive precision over wide x, Q2 range
•Needs precise data and careful evaluation of exp. uncertainties•much improved fit technique
Final PDF-fits:
ZEUS
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
10-3
10-2
10-1
1
ZEUS NLO QCD fit
αs(MZ2) = 0.118
tot. error
CTEQ 6M
MRST2001
Q2=10 GeV2
xuv
xdv
xg(× 0.05)
xS(× 0.05)
x
xfExtraction ofparton densitiesandexp. uncertainties
•impressive precision•agreement with global fits• simultaneous fit: PDF & αs:
( ) (model) 0.0018 (norm) 0.0036
(corr) 0.0032 (uncorr) 0.0008 0.1166 MZ
±±
±±=sα
scale ren.from 0.004
additional plus±
ZEUS
10-2
10-1
1
0 0.2 0.4 0.6 0.8 1
xqV
Q2=1 GeV2
0 0.2 0.4 0.6 0.8 1
20 GeV2
ZEUS ONLY fit (prel.)
(94-00 data)
200 GeV2 2000 GeV2
ZEUS + fixed targetZEUS only, i.e. F2HERA-I: high-Q2 NC/CC ZEUS
1 0 0.2 0.4 0.6 0.8 1
20 GeV2
ZEUS NLO QCD fit
2000 GeV2
uncorr. error
u better known than d, d can be fixed by high-Q2 CC, no need to discuss deuterium binding corrections in fixed target data... hardly need fixed target data
x x
Valence Quarks from One Experiment:
-0.2
0
0.2
0.4
xF3
Q2 = 1500 GeV2 Q2 = 3000 GeV2 Q2 = 5000 GeV2
0
0.2
0.4
10-1
1
Q2 = 8000 GeV2
10-1
1
Q2 = 12000 GeV2
10-1
1x
Q2 = 30000 GeV2
ZEUS e±p 96−99ZEUS-S
a)ZEUS
Parity Violating Part of the Proton Structure Function
( ) quark valence to sensitive (x)q x q(x) x ~F x RL,3 −
[ ] 2RL,3-
RL,24
22
y)-(1 1 Y with F x YF Y Q x
2 d
±== ±+
±
mπα
2
NCe
dQdx
σRL,
Comparing e+p/e-p
First measurement Need more luminosity with e-p
ZEUS
-2
0
2
4
6 Q2=1 GeV2
ZEUS ONLY fit
xg
xS
2.5 GeV2
xS
xg
0
10
207 GeV2
tot. error
uncorr. error
xS
xgxf
20 GeV2
xS
xg
0
10
20
30
10-4
10-3
10-2
10-1
1
200 GeV2
xS
xg
10-4
10-3
10-2
10-1
1
2000 GeV2
x
xS
xg
Gluon Density
• Gluon known within 20% for Q2>20 GeV2 and 10-4<x< 10-1
by ZEUS only considerable uncertainty for x>0.1 -> include jets !
•Gluon valence-like or even negative for Q2->0: end of applicability of DGLAP ? Fitted FL also negative direct determination of FL
would provide additional independent information -> lower HERA Ep or use ISR
Greatly improved precision !
ZEUSQ2 = 0.3 GeV2
F2 Q2 = 0.65 GeV2
Q2 = 1.3 GeV2 Q2 = 2.5 GeV2
Q2 = 4.5 GeV2 Q2 = 10 GeV2
Q2 = 22 GeV2
x
ZEUS 96/97
ZEUS SVX 95
ZEUS (prel.) ISR 96
ZEUS BPC 96/97 ZEUS NLO-QCD Fit
ALLM97
0
0.2
0.4
0.6
0
0.5
1
00.5
11.5
2
10-5
10-4
10-3
10-2
0
1
2
3
10-5
10-4
10-3
10-2
New F2 Points at low Q2: ISR Analysis
x
Q2 (
GeV
2 )
Kinem
atic
limit
y=1
y=0.
004
ZEUS 1996-97
ZEUS 1998-99 (Prel.)
ZEUS BPT 1997
ZEUS SVX 1995
ZEUS ISR 1996 (Prel.)
NMC
BCDMS
CCFR
E665
10-1
1
10
10 2
10 3
10 4
10-6
10-5
10-4
10-3
10-2
10-1
1
ISR lowers electron energydifficult analysis: needprecise knowledge ofBethe-Heitler overlays
previously unexplored !
Consistency in overlap region:prove of method -> direct FL in reach ?
So far only small data setanalysed
ZEUS
0
0.2
0.4
0.6
0.5 0.6 0.7 0.8 0.9 1 1.1
ZEUS (prel.) 1995-97Monte Carlo models (CTEQ5)
LEPTO,ARIADNE (0.2 < λs < 0.3):
with γ*s → s+X
without γ*s → s+X
HERWIG with γ*s → s+X
HERWIG without γ*s → s+X
xp (φ)
dσ /
d x p
(φ)
(nb)
0
10
20
30
40
1 1.02 1.04 1.06
0.8 < xp < 1.1
M (GeV)
entr
ies/
(2.5
MeV
)
Φ−meson: Access to Strange Sea ?
s
s
Lab:
Breit: current quarkhemisphere
Φ
Φ
particle leading :1 Qp 2xp Φ→=
xp -> 1: need strange sea as expected from PDF-fitslow xp : better understanding of Φ formation needed !
s
Charm: D* Cross Sections in γp CollisionsZEUS
10-3
10-2
10-1
1
10
5 10 15 20
pT(D*) (GeV)
dσ/d
p T (
nb/G
eV)
ZEUS (prel.) 98-00 a)
NLO QCD
FONLL
0
2
4
6
8
10
12
14
-1 0 1
η(D*)
dσ/d
η (n
b) b)
0
0.05
0.1
0.15
0.2
0.25
0.3
150 200 250
W (GeV)
dσ/d
W (
nb/G
eV)
c)
10
10 2
0 0.2 0.4 0.6 0.8 1
z(D*)
dσ/d
z (n
b) d)FONLL:massive NLO QCDplus resummationof NLO logs not better
central NLOsignificantly below datalargest disagreement:• medium pT,D• forward η• low z=(E-Pz)D/(E-Pz)all
major exp. progress:data errors smallerthan theory errors !
Need better theory
ZEUS
0
2
4
6
8
10
12
14
-1 0 1
η(D*)
dσ/d
η (n
b)
ZEUS (prel.) 98-001.9 < pT(D*) < 3.25 GeV
a)
0
0.5
1
1.5
2
2.5
3
3.5
-1 0 1
η(D*)dσ
/dη
(nb)
3.25 < pT(D*) < 5 GeVb)
0
0.2
0.4
0.6
0.8
1
-1 0 1
η(D*)
dσ/d
η (n
b)
5 < pT(D*) < 8 GeV c)
NLO QCD
0
0.05
0.1
0.15
0.2
0.25
0.3
-1 0 1
η(D*)
dσ/d
η (n
b)
8 < pT(D*) < 20 GeV d)
FONLL
Central NLOsignificantly below datalargest disagreement:• medium pT,D• forward η• low z=(E-Pz)D/(E-Pz)all
major exp. progress:data errors smallerthan theory errors !
FONLL:massive NLO QCDplus resummationof NLO logsnot better
Beauty in γp Collisions - semi-leptonic µ−decay
ZEUS
1
10
3 4 5 6 7 8 9 10pT
µ (GeV)
dσ/
dp
Tµ (p
b/G
eV)
dσdpTµ (ep→bb
–→e jj µ X)
Q2<1 GeV2 0.2<y<0.8pj1,j2>7,6 GeV |ηj|<2.5pT-1.6<ηµ<2.3
ZEUS (prel.) 96-00NLO QCD x hadr.NLO QCD
ZEUS
0
5
10
15
20
25
30
35
40
-1.5 -1 -0.5 0 0.5 1 1.5 2ηµ
dσ/
dηµ (
pb
)
dσdηµ (ep→bb
–→e jj µ X)
Q2<1 GeV2 0.2<y<0.8pj1,j2>7,6 GeV |ηj|<2.5pT
pTµ>2.5 GeV
ZEUS (prel.) 96-00NLO QCD x hadr.NLO QCD
Full HERA-I data set -> data error ~ theory errors
Visible beauty cross-section: ep -> e + jet + jet + µ+X
data/theory ~ 1.4, but compatible within exp/theo uncertainty !
Kπ
π
K
secondaryvertex
primary vertex
jet
jet
D
D
e
µ
µ
B
B
D*
ZEUS
ZEUS (prel.) 96-00beautycharm (prompt µ)charm (fake µ)
∆R (µ-D*)
can
did
ates
0
5
10
15
20
25
30
35
40
0 0.5 1 1.5 2 2.5 3 3.5 4
Beauty in γp Collisions - via µ and D*-decayFull HERA-I data set:
Almost backgroundfree sample !
Gives access to low pTstudy b close to kin limit
( ) pb 65(syst)(stat) 41 159XDXbbpσ * ±±=→→ µγ
10-3
10-2
10-1
1
10 102
103
ZEUS
Q2 (GeV2)
dσ/
dQ
2 (p
b/G
eV2 )
ZEUS (prel.) 99-00
NLO QCD (HVQDIS)
4.5 < mb < 5.0 GeV
1/4(Q2+4mb2) < µ2 < 4(Q2+4mb
2)
σ(e+p → e+ bb- X → e+ µ± Jet X)
0.05 < y < 0.7
Pµ > 2 GeV, 30o < θµ < 160o
Et,Jet
Breit > 6 GeV, -2 < ηJet
Lab < 2.5
10-3
10-2
10-1
1
10 102
103
ZEUS
Q2 (GeV2)
dσ/
dQ
2 (p
b/G
eV2 )
ZEUS (prel.) 99-00
O(αs) QCD⊗ CCFM (CASCADE)
O(αs) QCD⊗ DGLAP (RAPGAP)
σ(e+p → e+ bb- X → e+ µ± Jet X)
0.05 < y < 0.7
Pµ > 2 GeV, 30o < θµ < 160o
Et,Jet
Breit > 6 GeV, -2 < ηJet
Lab < 2.5
Beauty in DIS - semi-leptonic µ-decayFirst time differential distributions (L~ 60 pb-1)In Breit frame: Visible beauty cross-section: ep -> e + jet + µ+X
NLO agrees within uncertainties, LO+CCFM perfect B-puzzle solved !?
D0 0.2 0.4 0.6 0.8 1
dDdn
N1
10-3
10-2
10-1
p+
ZEUS (prel.) 99-00 eSM CC DIS
(hadr.)τν →SM W
ZEUS
Tau-Identification:consider hadronic tau -decaybased on internal jet structure: collimated (pencil-like) jets, mostly only 1 track
Multi-variate Discriminant (hep-ph/0011224)based on range searchingoptimised on CC-DIS and W->ντ sample:
QCD jets Tau jets
Good separationtau efficiency ~25%bg rejection ~550
Search for Isolated Tau-Leptons and Missing Pt
(GeV) XTP
0 20 40 60 80 100
even
ts
10-3
10-2
10-1
1
10ZEUS (prel.) 94-00SMW onlySingle Top MC
(GeV) XTP
0 20 40 60 80 100
even
ts
10-3
10-2
10-1
1
10ZEUS
acoplanar not -muon or electron not -
1.8)D 0.5,(D GeV 5p with track isolated -
GeV 20p -
jettrack,tracktrack,
T
missT
>>
>
>
Event selection:
4 events found !3 are compatible with tau hypothesis, i.e. Discriminant D > 0.95
0.02 0.12 :SM 2 :data:GeV 25P
0.06 0.23 :SM 3 :data :0.95D
XT
±
>
±
>
Tau-1 Candidate
GeV 32MGeV 48 PGeV 37 P TX
TCAL
T ===
Tau-2 Candidate
GeV 68MGeV 37 PGeV 39P TX
TCAL
T ===
Status: Isolated Lepton Events at HERA I
H1 (e and µ events) (τ events)
Multi-Electron EventsZEUS
10-2
10-1
1
10
10 2
0 20 40 60 80 100 120 140M12 (GeV)
even
ts
ZEUS (prel.) 94-00
GRAPE+NC+QEDC
NC+QEDC
QEDC(a) Bethe-Heitler type diagrams
e
e
e el
l-+
l+
lγ
γp pN N
-
l-
+
l
ee
p N
lγ
γe e
p N
γ
γl
l-
+
l
/Ζ0 /Ζ0
γγ
(b) QED-Compton type diagrams
Grape:
+ electroweak diagrams
Overall good agreementno excess at high massin µ−channel no event M>100 GeV 0.11.4 0.11.4 2
GRAPE SM Data GeV 30 E :electrons Three0.1 0.5 0.10.8 2 GRAPE SM Data
:GeV 100 M :electrons Two
T,1
1,2
±±
>
±±
>
GeV 134 MGeV 53 EGeV 56 E T2T1 ===
rad 0.58 GeV 36 Erad 0.76 GeV 47 E
rad 1.0 GeV 52 E
3T3
2T2
1T1
==
==
==
θθθ
GeV 94 M2 =
Inclusive Jet-Cross Sections in γp ZEUS
10-3
10-2
10-1
1
10
10 2
ZEUS (prel.) 98-00 (82.2 pb-1)•NLO QCDLO QCD
dσ/
dET jet (
pb/G
eV)
-1
-0.5
0
0.5
20 30 40 50 60 70 80 90
jet energy scale uncertainty
NLO uncertainty
ET jet (GeV)
(Dat
a-N
LO Q
CD
)/N
LO Q
CD High precision data
Excellent agreement over4 orders of magnitudeno excess at high ET
ZEUS
0.8
1
1.2
1.4
0.2 0.3 0.4
jet energy scale uncertainty
NLO uncertainty
ZEUS (prel.) 98-00 (82.2 pb-1)•NLO QCD
scaling
Wγp= 180 GeV/Wγp= 255 GeV
-2 < ηjet
γp < 0
xT = 2 ET jet /Wγp
Rat
io o
f sca
led
cros
s se
ctio
ns ZEUS
10-6
10-5
10-4 ZEUS (prel.) 98-00 (82.2 pb-1)•
NLO QCDLO QCD
-2 < ηjet
γp < 0 and Wγp = 255 GeV
(E
T jet )4 E
jet d
3 σ/d(
pjet )3
-1
-0.5
0
0.5
0.2 0.3 0.4 0.5 0.6
jet energy scale uncertainty
NLO uncertainty
xT = 2 ET jet /Wγp
(Dat
a-N
LO Q
CD
)/N
LO Q
CD
Invariant Inclusive Jet-Cross Sections
Evidence for scaling violationsin γp collisions
Inclusive Jet Production in DIS
ZEUS
10-3
10-2
10-1
1
10
10 2
10 3
10 4
10 5
10 6
5 10 15 20 25 30 35 40 45
dσ/
dE
B
T,je
t (p
b/G
eV)
EB T,jet (GeV)
125 < Q2 < 250 GeV 2
250 < Q2 < 500 GeV 2
500 < Q2 < 1000 GeV 2
1000 < Q2 < 2000 GeV 2
2000 < Q2 < 5000 GeV 2
Q2 > 5000 GeV 2
(×105)
(×104)
(×103)
(×100)
(×10)
(×1)
ZEUS 96-97
Jet energy scale uncertainty
NLO QCD: (corrected to hadron level)
αs (MZ)= 0.1175
DISENT MRST99 (µR=EB T,jet )
DISENT MRST99 (µR=Q)
ZEUS
0.12
0.14
0.16
0.18
0.2
0.22
0.24
10 20 30 40 50
ZEUS 96-97
Theoretical uncertainty
from αs (MZ)= 0.1212 +0.0040 -0.0044
α s (E
B
T,je
t )
EB T,jet (GeV)
(theo)0.00270.0028
(syst)0.00310.0023
(stat)0.0017 0.1212)M(:GeV 500 Q for
Z
22
−+
−+
±=
>
sα
Impressive description of NLO QCDof these precise data:
Very precise measurement !
ZEUS
10-2
10-1
1
10
10 20 30 40 50 60 70 80 90 100Q2 (GeV2)
σ(γ* p
→ γ
p)
(nb
)
ZEUS (prel.) 96-97,99-00 e+p
FFS
DD
40 < W < 140 GeV
W = 89 GeV
Deeply Virtual Compton Scattering
1 x
p’p
2γ
e’γ∗e
2x
Q2Q
γ*
x1
p
γee’
x 2
p’
High-x (HERMES) Low-x (ZEUS)
GPD-based Model (FFS)
∫ )Q,H(x, )Q/x,C( x
dx ~ A 22 ξξ
0.071.47n ,Q n 2 -DVCS ±=∝σ
b
R
1−z
zγ* γ
21 xx ≠
Colour Dipole Model (DD)
γγ ΨσΨ outzR,
dipoleini ~ A*
∫
Data getting preciseQ2 spectrum seems harder than predicted by FFSHERA-II: e+/e- and polarisation !
H: Off-diagonal PDF
pp’
γ∗
e e’
V
p(P)
e(k)
e(k')
p(P')
γ*
Q2 γ
ZEUS
0
2
4
6
8
10
12
14
40 60 80 100 120 140W (GeV)
σ(γ* p
→ γ
p)
(nb
)
ZEUS (prel.) 96-97,99-00 e+p
FFS
DD
5 < Q2 < 100 GeV2
Q2 = 9.6 GeV2
ZEUS
ZEUS 96-97 J/ψ → µ+µ-
ZEUS 99-00 J/ψ → e+e-
H1E401E516
W (GeV)
σ γp →
J/ψ
p (n
b)
Wδ fit to ZEUS dataδ = 0.69 ± 0.02 (stat.) ± 0.03 (syst.)
0
25
50
75
100
125
150
175
200
225
0 50 100 150 200 250 300
W-dependence points to hard process as e.g. in J/Ψ production
0.10.78 ,W DVCS ±=∝ δσ δ
MX < 2
ZEUS ZEUS (prel.) 98/99
<β>=0.63
2 - 4<β>=0.23
4 - 8<β>=0.072
8 - 15<β>=0.019
15 - 25<β>=0.0064
25 - 35 GeV<β>=0.0028
Q2 =
2.2
- 3
GeV
2
<β>=0.7 <β>=0.31 <β>=0.1 <β>=0.029 <β>=0.0094 <β>=0.0043
Q2 =
3 -
5
<β>=0.77 <β>=0.4 <β>=0.15 <β>=0.043 <β>=0.014 <β>=0.0066
Q2 =
5 -
7
<β>=0.82 <β>=0.48 <β>=0.2 <β>=0.06 <β>=0.02 <β>=0.0092
Q2 =
7 -
10
<β>=0.87 <β>=0.59 <β>=0.29 <β>=0.097 <β>=0.033 <β>=0.015
Q2 =
10
- 20
<β>=0.93 <β>=0.73 <β>=0.43 <β>=0.17 <β>=0.064 <β>=0.03
Q2 =
20
- 40
<β>=0.82 <β>=0.84 <β>=0.58 <β>=0.29 <β>=0.12 <β>=0.058
Q2 =
40
- 80
γ*
e
p
MN
gap
Mx
New: F2D3 Data
Analysis using FPC (L=4 pb-1):• coverage 4.0 < η < 5.0• increased MX range• reduced bias from nucleon dissociation
! component hard has ndiffractio:data from
1) ( soft is ndiffractio if
const, ~ F x expect x1 ~F if D3
2P|P|
D32
≈
λ
λ
p
22XP|
xx
)Q/M(1 xx
=
+=
β
+extension
to lower Q2
W
ZEUSZEUS (prel.) 98/99
MX = 0 - 2 GeV MX = 8 - 15 GeV
MX = 2 - 4 GeV MX = 15 - 25 GeV
MX = 4 - 8 GeV MX = 25 - 35 GeV
Naive expectation:
λεσ
σ
σ
ε
λ
λ
<<= 0.08 ,x ~ :Softx~)Qg(x, ~ :Hardx~ )Qg(x, ~
-diff
2-22diff
-2tot
Diffraction contains soft and hardpieces even at large Q2
What happens here ?
Same energy dependencein inclusive and diffractivescattering !
Much improved precision !
Recently models (like CDM) tried to explain this -> new challenge by more precise data !
Conclusions• New level of extraction of parton density and αs and their experimental uncertainties reached ...hardly need fixed target data HERA-II: e+/ e- program ahead of us ! (also for xF3 !) • Direct FL measurement seems in reach via ISR analysis HERA-II: dedicated run with lower beam energy ?• Analysis of hadronic final state enters new stage: many interesting results from jets -> combine with incl. DIS particle ID: strange, charm, bottom, ...tau HERA holds the key for production mechanism of heavy quarks• Isolated Lepton story continues: wait for answer at HERA-II Can the SM hold the strength ?• DVCS: towards determination of off-diagonal PDF HERA-II: e+/ e- and polarisation• new precise F2
D3 new challenge for models
Internal Jet structure
ZEUS
11.11.21.31.41.51.61.71.81.9
2
20 30 40 50 60 70 80 90100
ycut = 10 - 2 ZEUS (prel.) 95-97 e+p CC - DIS
Q2 > 200 GeV 2
EjetT > 14 GeV
-1 < ηjet < 2
MEPJET (NLO)
CDM (LO)
Ejet
T [ GeV ]
< n
sbj >
Internal jet structure well described by NLO and MC
-log(1-D) 0 1 2 3
even
ts
10-4
10-3
10-2
10-1
1
10
102
ZEUS (prel.) 94-00SMW onlySingle Top MC
-log(1-D) 0 1 2 3
even
ts
10-4
10-3
10-2
10-1
1
10
102
D>0.95
ZEUS
Isolated high-pt lepton selection:
acoplanar not muon, or electron not1.8)D 0.5,(DGeV 5p with track isolated
GeV 20p
jettrack,tracktrack,
T
missT
>>
>
>
4 events found3 are compatible with tau hypothesis