The Legacy of HERAlevonian/papers/Prague_2013.pdf · Sergey Levonian DESY, Hamburg The Legacy of...

Sergey Levonian

DESY, Hamburg

The Legacy of HERA

Seminar of the Physics Institute of the Czech Academy of Sciencies Prague, 12-Feb-2013

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Looking deeper inside matter

λ = h/p ∼ 1E

Illustration of improved understandingof the structure of matter with time(and with increasing resolution power)

High energy scattering processhas been the basic tool during last 100 years

λ = h/p ∼ 1E

Rutherford (1911)

– elastic (Coulomb) scattering of 7 MeV α on Au

– planetary model of atom ⇒ QM

; N(θ)∼ 1sin4(θ/2)

λ = h/p ∼ 1E

Rutherford (1911)

Hofstadter (1953)

– (in)elastic eN scattering of 400 MeV electrons

– Nucleus structure; size of A,p

λ = h/p ∼ 1E

Rutherford (1911)

Hofstadter (1953)

SLAC (1968)– Fixed target DIS with 20 GeV electron beam

– internal structure of hadrons

– experimental evidence for quarks

λ = h/p ∼ 1E

Rutherford (1911)

Hofstadter (1953)

HERA (1992 − 2007)

– first (and so far the only) ep collider

– energy frontier:√s = 319 GeV

– resolution power down to 10−18m

– QCD in low x regime (x > 10−5)

λ = h/p ∼ 1E

Rutherford (1911)

Hofstadter (1953)

HERA (1992 − 2007)

– first (and so far the only) ep collider

– energy frontier:√s = 319 GeV

– resolution power down to 10−18m

– QCD in low x regime (x > 10−5)

By increasing E we are not only looking deeper into matter,but also perform ‘backward evolution’ of the Universe in attemptto understand better fundamental forces of nature

Looking deeper inside matter Restoring Universe Evolution

→ 1µsec

HERATevatronLHC

λ = h/p ∼ 1E

E ∼ T

In the beginning the was the Idea...

...then a lot of Hard Work...

1984-1991

1984-19911986-1992

Days of running

Status: 1-July-2007

0 500 1000 15000

400electronspositronslow E

HERA-1

HERA-2

1984-19911986-1992

1992-2007

...and finally...

]2 [GeV2Q310 410

p CC (prel.)+H1 e

p CC (prel.)-H1 e

p CC 06-07 +ZEUS e

p CC 04-06-ZEUS e

p CC (HERAPDF 1.0)+SM e

p CC (HERAPDF 1.0)-SM e

p NC (prel.)+H1 ep NC (prel.)-H1 e

p NC 06-07 (prel.)+ZEUS ep NC 05-06-ZEUS e

p NC (HERAPDF 1.0)+SM ep NC (HERAPDF 1.0)-SM e

y < 0.9 = 0eP

-410 -310 -210 -110 1

HERAPDF1.5 (prel.)

exp. uncert.

model uncert.

parametrization uncert.

xxf 2 = 10 GeV2Q

0.05)×xS (

0.05)×xg (

H1 and ZEUS HERA I+II Combined PDF Fit

(Msα0.11 0.12 0.13

uncertainty

World averageS. Bethke, Eur. Phys. J. C64, 689 (2009)

D0 incl. midpoint cone jetsPhys. Rev. D80, 111107 (2009)

Aleph Event Shapes, NNLO+NLLAJHEP 08, 036 (2009)

Aleph 3−jet rate, NNLOPhys. Rev. Lett. 104, 072002 (2010)

jets, NLOTZEUS incl. anti−kPhys. Lett. B691, 127 (2010)

jets, NLOTZEUS incl. kPhys. Lett. B 649, 12 (2007)

multijets, NLOT k2H1 low QEur. Phys. J. C67, 1 (2010)

multijets, NLOT norm. k2H1 high QEur. Phys. J. C65, 363 (2010)

H1+ZEUS NC, CC and jet QCD fits, NLOH1−prelim−11−034

trijet, NLO2H1 high QH1−prelim−11−032

dijet, NLO2H1 high QH1−prelim−11−032

inclusive jet, NLO2H1 high QH1−prelim−11−032

[GeV]LQM200 400 600 800 1000

λH1 Search for First Generation Scalar Leptoquarks

H1d)+ (eL

H1 limitH1 94-00 limitH1 CI analysis limitCMS pair productionATLAS pair productionDØ pair productionOPAL indirect limit

Lots of Textbook results

2 10 50

HERAPDF1.0 NLOCT10 NLO JR09 NNLO

ABKM09 NNLONNPDF2.1 NLO

MSTW08 NNLO

H1 Collaboration

Q2 / GeV2

HERAρ ZEUS 96-00ρ ZEUS 94

ρ ZEUS LPS 94ρ ZEUS 95ρ H1 95-96φ ZEUS 98-00φ ZEUS 94J/ψ ZEUS 98-00J/ψ ZEUS 96-97J/ψ H1 96-00

DVCS H1 HERA IDVCS H1 HERA II e-p

DVCS ZEUS LPS (31 pb -1)

Q2+M2(GeV2)

0 10 20 30 40 50

0 5 10 15 20 25 30

H1 99-00 b jetH1 99-00 b→µ jetZEUS 96-00 b→µ jetZEUS 05 b→µ jetH1 (prel) 06/07 b →µ jetZEUS 96-97 b→eZEUS 120 pb -1 b→eH1 97-00 b→D*µZEUS 96-00 b→D*µZEUS 114 pb -1 bb→µµZEUS (prel) 128 pb -1 b jet

NLO QCD (FMNR)µ2 = 1/4 (m2 + pT

µ2 = m2 + pT2

<pTb> (GeV)

dσ/dpT(ep→ebX)dσ/dpb

Q2<1GeV2, 0.2<y<0.8, |ηb|< 2

4 HERA: The World’s Only ep Collider

Days of running

Status: 1-July-2007

0 500 1000 15000

400electronspositronslow E

HERA-1

HERA-2

• 1998 Ep upgrade: 820 ⇒ 920 GeV(√s : 301 ⇒ 319 GeV)

• 2001 HERA-2 upgrade: L × 3, Polarised e+/e−

(〈P 〉 = 40%)

HERA-1 (1993-2000) ≃ 120 pb−1

HERA-2 (2003-2007) ≃ 380 pb−1

Final Data samples

H1+ZEUS: 2 × 0.5 fb−1

5 Deep-Inelastic Scattering at HERA

Neutral Current DIS: ep → e′X

Charged Current DIS: ep → νX

Kinematics: (Momentum transfer)2: Q2 = −q2

Bjorken x: x = Q2/(2p · q)

Inelasticity: y = (p · q)/(p · l)

(Total hadronic energy)2: W 2 = (p + q)2

W 2 ≃ Q2/x

6 Physics landscape at HERA

• HERA as Super-microscope

⊲ Proton structure at high resolution

⊲ Impact for LHC

• HERA as Energy frontier machine

⊲ Electroweak unification at work

⊲ Anything beyond the Standard Model?

• HERA as QCD laboratory

⊲ Putting QCD in stringent tests with:◦ Jets (parton evolution schemes, NLO QCD, αs)◦ Heavy flavor sector (multiscale problem: Q2,MQ, Et)◦ Diffraction (interplay of soft and hard physics)

⊲ HERA specifics: lox x physics

⊲ Impact for LHC

⇒⇓

TEVATRON

⊲ Impact for LHC

⇒⇓

TEVATRON

x0, k ⊥ 0

x i, k ⊥ i

x i+1 , k ⊥ i+1

⊲ Impact for LHC

⇒⇓

TEVATRON

x0, k ⊥ 0

x i, k ⊥ i

x i+1 , k ⊥ i+1

Search for Novel PhenomenaPrecision Measurements

HERA as Energy Frontier Machine

7 HERA at Energy Frontier

Unpolarized DIS cross sections σCCpol (e

±p) = (1 ± Pe) · σCCunpol(e

]2 [GeV2Q310 410

p CC (prel.)+H1 e

p CC (prel.)-H1 e

p CC 06-07 +ZEUS e

p CC 04-06-ZEUS e

y < 0.9 = 0eP

Electro-Weak Unification

7 HERA at Energy Frontier

Unpolarized DIS cross sections σCCpol (e

±p) = (1 ± Pe) · σCCunpol(e

]2 [GeV2Q310 410

p CC (prel.)+H1 e

p CC (prel.)-H1 e

p CC 06-07 +ZEUS e

p CC 04-06-ZEUS e

y < 0.9 = 0eP

eP-1 -0.5 0 0.5 1

120p Scattering±HERA Charged Current e

2 > 400 GeV2Q

y < 0.9

Xν →p +e

Xν →p -e

HERAPDF 1.0

H1 HERA IH1 HERA II (prel.)ZEUS 98-06

H1 HERA IH1 HERA II (prel.)ZEUS 06-07ZEUS HERA I

eP-1 -0.5 0 0.5 1

Electro-Weak UnificationNo W coupling

to e−R and e+L

8 Anything beyond the SM ?

⇒⇓

TEVATRON

√s = 319 GeV

So far all NC and CC HERA data were in good agreement with the SM.Try to look more carefully at the tails, using two strategies:

1. Specific BSM signals search (LQ, LFV, SUSY, ...) – guided by theory

2. Model independent generic search (data vs SM) – guided by data

9 Leptoquarks ?

Proton(P)

γ,Z (W+)

e+ (ν)

q (q ,)

λ n kλ 1 i

e+ l+n

q k– q i

–λ n k

λ 1 i

Q2e (GeV2)

/ SM H1 (b)

5000 10000 15000 20000 25000 30000

Q2 = 16950 GeV2; y = 0:44; M = 196 GeVe+ jet� �

Et/GeV1994-97: High Q2 events.Rate in excess of Standard Model!

9 Leptoquarks ?

Proton(P)

γ,Z (W+)

e+ (ν)

q (q ,)

λ n kλ 1 i

e+ l+n

q k– q i

–λ n k

λ 1 i

Q2e (GeV2)

/ SM H1 (b)

5000 10000 15000 20000 25000 30000

Q2 = 16950 GeV2; y = 0:44; M = 196 GeVe+ jet� �

Et/GeV1994-97: High Q2 events.Rate in excess of Standard Model!

2011: Final status

100 200 300

310NC data

CC data

H1 p-e-1= 164 pb

[GeV]LQM100 200 300

310NC data

CC data

H1 p+e-1= 282 pb

[GeV]LQM

H1 Search for First Generation Leptoquarks

[GeV]LQM200 400 600 800 1000

λH1 Search for First Generation Scalar Leptoquarks

H1d)+ (eL

H1 limitH1 94-00 limitH1 CI analysis limitCMS pair productionATLAS pair productionDØ pair productionOPAL indirect limit

10 Model independent search for New Phenomena

j-je-j

-jµ-jννe-

e-eµe-µ-µ-jγ

-eγµ-γν-γγ-γ

j-j-je-j-j

-j-jµ-j-jν

e-e-jνe-e-

e-e-e-jµ-µµ-µe-ν-µ-µ-jµe--jνe--jν-µν-µe-

-j-jγ-e-jγ

-jν-γe-j-j-j

-j-j-jν-j-jν-γ-j-jνe--j-j-eγ

-jνe-e--jν-µe-

j-j-j-je-j-j-j-j

-j-j-j-jνj-j-j-j-j

j-je-j

-jµ-jννe-

e-eµe-µ-µ-jγ

-eγµ-γν-γγ-γ

j-j-je-j-j

-j-jµ-j-jν

e-e-jνe-e-

-j-jγ-e-jγ

-jν-γe-j-j-j

-jνe-e--jν-µe-

j-j-j-je-j-j-j-j

-j-j-j-jνj-j-j-j-j

j-je-j

-jµ-jννe-

e-eµe-µ-µ-jγ

-eγµ-γν-γγ-γ

j-j-je-j-j

-j-jµ-j-jν

e-e-jνe-e-

-j-jγ-e-jγ

-jν-γe-j-j-j

-jνe-e--jν-µe-

j-j-j-je-j-j-j-j

-j-j-j-jνj-j-j-j-j

H1 Data

-210 -110 1 10 210 310 410 510

)-1p, 285 pb+H1 General Search at HERA (e

Events

• Identify isolated objects:e, µ, γ, j, ν

• Select events, having at least twoobjects with high PT>20GeV

• Classify into exclusive channelscontaining from 2 to 5 objects

• Compare with SM predictions⇒ good overall agreement

• Find interesting regionswith greatest deviations from SMin kin. distributions (Mall, ΣPT )

⇒ Combine H1 and ZEUS data

10 Model independent search for New Phenomena

j-je-j

-jµ-jννe-

e-eµe-µ-µ-jγ

-eγµ-γν-γγ-γ

j-j-je-j-j

-j-jµ-j-jν

e-e-jνe-e-

-j-jγ-e-jγ

-jν-γe-j-j-j

-jνe-e--jν-µe-

j-j-j-je-j-j-j-j

-j-j-j-jνj-j-j-j-j

j-je-j

-jµ-jννe-

e-eµe-µ-µ-jγ

-eγµ-γν-γγ-γ

j-j-je-j-j

-j-jµ-j-jν

e-e-jνe-e-

-j-jγ-e-jγ

-jν-γe-j-j-j

-jνe-e--jν-µe-

j-j-j-je-j-j-j-j

-j-j-j-jνj-j-j-j-j

j-je-j

-jµ-jννe-

e-eµe-µ-µ-jγ

-eγµ-γν-γγ-γ

j-j-je-j-j

-j-jµ-j-jν

e-e-jνe-e-

-j-jγ-e-jγ

-jν-γe-j-j-j

-jνe-e--jν-µe-

j-j-j-je-j-j-j-j

-j-j-j-jνj-j-j-j-j

H1 Data

-210 -110 1 10 210 310 410 510

)-1p, 285 pb+H1 General Search at HERA (e

Events

[GeV]T PΣ0 20 40 60 80 100 120 140 160 180

SM Pair Prod.

)-1H1+ZEUS (0.56 fbp+e

Multi-Leptons at HERA

[GeV]XTP

0 10 20 30 40 50 60 70 80 90 100

[GeV]XTP

0 10 20 30 40 50 60 70 80 90 100

210SMSM Signal

)-1H1+ZEUS (0.59 fb

[GeV]XTP

0 10 20 30 40 50 60 70 80 90 100

H1+ZEUS,0.59 fb−1

Largest observed deviationsfrom the SM at HERA

JHEP 0910:013 (2009)JHEP 1003:035 (2010)

• Identify isolated objects:e, µ, γ, j, ν

• Select events, having at least twoobjects with high PT>20GeV

• Classify into exclusive channelscontaining from 2 to 5 objects

• Compare with SM predictions⇒ good overall agreement

• Find interesting regionswith greatest deviations from SMin kin. distributions (Mall, ΣPT )

⇒ Combine H1 and ZEUS data

HERA at Energy Frontier:

Standard Model is still in excellent shape!

HERA as Super−microscope

11 DIS: Cross sections and Structure Functions

Dominant contribution

Only sensitive at high Q2 ∼ M2Z

Only sensitive at high y

(similarly for pure weak CC analogues: W±2 , xW3 and W±

12 Structure of the proton

dotted lines show the spread in predictionsprior to HERA startup (1992)

H1 and ZEUS

x = 0.00005, i=21x = 0.00008, i=20

x = 0.00013, i=19x = 0.00020, i=18

x = 0.00032, i=17x = 0.0005, i=16

x = 0.0008, i=15x = 0.0013, i=14

x = 0.0020, i=13

x = 0.0032, i=12

x = 0.005, i=11

x = 0.008, i=10

x = 0.013, i=9

x = 0.02, i=8

x = 0.032, i=7

x = 0.05, i=6

x = 0.08, i=5

x = 0.13, i=4

x = 0.18, i=3

x = 0.25, i=2

x = 0.40, i=1

x = 0.65, i=0

Q2/ GeV2

σ r,N

HERA I+II NC e +p (prel.)Fixed TargetHERAPDF1.5

1 10 102

Combined HERA e+p data(L = 2 × 250 pb−1)

Bjorken scaling regime at x > 0.05

Large scaling violation at x < 0.01

F2H1 and ZEUS

x = 0.00005, i=21x = 0.00008, i=20

x = 0.00013, i=19x = 0.00020, i=18

x = 0.00032, i=17x = 0.0005, i=16

x = 0.0008, i=15x = 0.0013, i=14

x = 0.0020, i=13

x = 0.0032, i=12

x = 0.005, i=11

x = 0.008, i=10

x = 0.013, i=9

x = 0.02, i=8

x = 0.032, i=7

x = 0.05, i=6

x = 0.08, i=5

x = 0.13, i=4

x = 0.18, i=3

x = 0.25, i=2

x = 0.40, i=1

x = 0.65, i=0

Q2/ GeV2

σ r,N

1 10 102

-410 -310 -210 -110 1

HERAPDF1.5 (prel.)

exp. uncert.

model uncert.

xf 2 = 10 GeV2Q

0.05)×xS (

0.05)×xg (

• Precision of (1 − 2)% in the bulk region

• Perfect desciption of the data by NLO QCDover many orders in x and Q2

• using QCD factorisation: σDIS ∼∑

aCa ⊗ fa/puniversal PDFs, fa/p, determined with error bands

Any substructures at 10−18m ?

F2H1 and ZEUS

x = 0.00005, i=21x = 0.00008, i=20

x = 0.00013, i=19x = 0.00020, i=18

x = 0.00032, i=17x = 0.0005, i=16

x = 0.0008, i=15x = 0.0013, i=14

x = 0.0020, i=13

x = 0.0032, i=12

x = 0.005, i=11

x = 0.008, i=10

x = 0.013, i=9

x = 0.02, i=8

x = 0.032, i=7

x = 0.05, i=6

x = 0.08, i=5

x = 0.13, i=4

x = 0.18, i=3

x = 0.25, i=2

x = 0.40, i=1

x = 0.65, i=0

Q2/ GeV2

σ r,N

1 10 102

-410 -310 -210 -110 1

HERAPDF1.5 (prel.)

exp. uncert.

model uncert.

xf 2 = 10 GeV2Q

0.05)×xS (

0.05)×xg (

• Precision of (1 − 2)% in the bulk region

• Perfect desciption of the data by NLO QCDover many orders in x and Q2

• using QCD factorisation: σDIS ∼∑

aCa ⊗ fa/puniversal PDFs, fa/p, determined with error bands

Any substructures at 10−18m ?

No. Quarks are still pointlike

]2 [GeV2Q310 410

1−p NC 0.16 fb−H1 e

m18−

10⋅ = 0.65 qR

1−p NC 0.28 fb+H1 e

m18−

10⋅ = 0.65 qR

Quark Radius

Upper limit: Rq < 0.65 · 10−3 fm

13 HERAPDF for LHC

W+ cross-section

��

Tevatron Jet Cross Sections

1.6 < |yjet| < 2.1 (x 10-6)

1.1 < |yjet| < 1.6 (x 10-3)

0.7 < |yjet| < 1.1

0.1 < |yjet| < 0.7 (x 103)

|yjet| < 0.1 (x 106)

KT D=0.7 - fastNLO

HERAPDF1.0(corrected to hadron level)

CDF Data (RunII)(Stat. unc. only)

PT jet [Gev/c]

d2 σ/dy

jet dp

t [nb/

0 100 200 300 400 500 600 700

CDF Data

(Run II)

LHC Data

HERA as a Super-microscope:

• best ever measurement of the proton structure down to 0.001 fm (F2, FL, xF3)

• lots of glue at low x ⇒ in high enery limit QCD processes are gluon-driven

HERA as QCD factory

14 HERA as QCD factory

leadLx

0.1 0.3 0.5 0.7

H1 DataSIBYLL 2.1EPOS 1.99QGSJET II-03QGSJET 01

H1Forward Photons

)η∆

H1 FPS Data (Prel.)RapGap / 1.23NLO DPDF Fit B / 1.23

H1 Preliminary

1 central jet + 1 forward jet

*|η∆|0 1 2 3

ZEUS 82 pb-1

NLO hadr Z0⊗ ⊗

Q2 > 125 GeV2

-2 < ηB jet < 1.5

|cos γh| < 0.65

jet energy scale uncertainty

kT (x 100)

anti-kT(x 10)

SIScone

5 10 15 20 25 30 35 40 45 50 55

kT (+0.05)

anti-kT

SIScone

hadronisation uncertainty

EjetT,B (GeV)

(x) 10

log-4 -3.5 -3

(x) 10

log-4 -3.5 -3

H1 Data (Prel.)

NLO DPDF Jets 2007 (x 0.83)

VFPS DIS Dijets

H1 Preliminary

ep →

σ ep →

ZEUS 40 pb -1 pT2 < 0.476 xL

2 GeV2

ep → ejjXnQ2 < 1 GeV2

ZEUS 40 pb -1

ep → eXnQ2 > 2 GeV2

ZEUS 6 pb -1

ep → eXnQ2 < 0.02 GeV2

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

H1 and ZEUS

F2 cc_

Q2= 2 GeV2 Q2= 4 GeV2

Q2= 6.5GeV2

0.5 Q2= 12GeV2 Q2= 20GeV2

Q2= 35GeV2

0.5 Q2= 60GeV2 Q2=120GeV2

Q2=200GeV2

Q2=400GeV2

Q2=1000GeV2

HERA (prel.)

MSTW08 NNLOMSTW08 NLOCTEQ 6.6ABKM BMSN

H1 data

data correlated uncertainty

)hadrδ (1+×NLO H1 2006 Fit B

Rapgap

H1 data

Rapgap

H1 data

Rapgap

H1 data

Rapgap

H1 data

Rapgap

H1 data

Rapgap

H1 data

Rapgap

H1 data

Rapgap

H1 data

Rapgap

γjetsx

0.2 0.4 0.6 0.8 1

γjetsx

0.2 0.4 0.6 0.8 1

γjetsx

0.2 0.4 0.6 0.8 1

1(a)H1

[GeV]jet1TE

6 8 10 12 14

[GeV]jet1TE

6 8 10 12 14

[GeV]jet1TE

6 8 10 12 14

IPjetsz

0.2 0.4 0.6 0.8

IPjetsz

0.2 0.4 0.6 0.8

IPjetsz

0.2 0.4 0.6 0.8

H1 data / theory

)hadrδ (1+×NLO H1 2007 Fit Jets

)hadrδ (1+× 1.23 ×NLO ZEUS SJ

H1 data / theory

-0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

(a)γprompt + jet7 < ET γ < 16 GeV

6 < ET jet < 17 GeV

ηγ (pb

6 8 10 12 14 16

ZEUS (77 pb-1)NLO+had. (KZ) 0.5< µR< 2

NLO+had. (FGH) µR=1kT -fact.+had. (LZ) 0.5< µR < 2

PYTHIA 6.3

HERWIG 6.5

ET jet (GeV)

T jet (

-1.5 -1 -0.5 0 0.5 1 1.5 2

η jet

ηjet (

0 5 10 15 20 25 30Q2 [GeV2]

H1 HERA IH1 HERA II

ZEUS HERA I

Dipole modelGPD model

W = 82 GeV

| [degrees]φ|0 20 40 60 80 100 120 140 160 180

0.6H1 H1 HERA II

φ0.16 cos GPD model

*η0 1 2 3 4 5 6

*ηd dn

0.4 H1 Preliminary

* > 1 GeV T

° < 155θ < ° 10 lab

H1 data (prelim.)DJANGOHRAPGAP (ALEPH tuning)RAPGAP (default PYTHIA hadronisation)CASCADE

15 Jets at HERA

Precision QCD

from Jet Cross Sections in DISsα

/ GeV r

µ10 210

/ GeV r

µ10 210

2 < 100 GeV2H1 data for 5 < Q2 > 150 GeV2H1 data for Q

Central value and exp. unc.

PDF unc.⊕Theory

(th.) ± 0.0016 (PDF)−0.0030+0.0046± 0.0007 (exp.) = 0.1168 sα

[arXiv:0904.3870]2 > 150 GeV2Fit from Q

Running αs in a single experiment!

15 Jets at HERA

Precision QCD

/ GeV r

µ10 210

/ GeV r

µ10 210

PDF unc.⊕Theory

(th.) ± 0.0016 (PDF)−0.0030+0.0046± 0.0007 (exp.) = 0.1168 sα

(Msα0.11 0.12 0.13

uncertainty

inclusive jet, NLO2H1 high QH1−prelim−11−032 Running αs in a single experiment!

HERA results are comparable (and competetive)with the world average

Errors are dominated by theoretical uncertainties(calculations are lacking HO (NNLO) terms)

15 Jets at HERA

Precision QCD

/ GeV r

µ10 210

/ GeV r

µ10 210

PDF unc.⊕Theory

(th.) ± 0.0016 (PDF)−0.0030+0.0046± 0.0007 (exp.) = 0.1168 sα

(Msα0.11 0.12 0.13

uncertainty

inclusive jet, NLO2H1 high QH1−prelim−11−032

Grand Unification?

Precision does matter!

16 QCD at low x

x0, k ⊥ 0

x i, k ⊥ i

x i+1 , k ⊥ i+1

Lots of glue in the proton ⇒ long gluon cascade at low x. Perturbative expansion

of evolution equations ∼ ∑mnAmn ln(Q2)m ln(1/x)n hard to calculate explicitely

⇒ approximations needed

DGLAP: resums ln(Q2)n terms, neglecting ln(1/x)n terms

strong kT ordering in partonic cascade

BFKL: resums ln(1/x)n terms

no kT ordering in partonic cascade ⇒ more hard gluons

are radiated far from the hard interaction vertex

CCFM: angular ordered parton emission ⇒reproduces DGLAP at large x and BFKL at x → 0

• How long is partonic cascade at HERA, at small x?

• Do the ln(1/x)n terms play a major role in parton dynamics as suggested by BFKL?

⇒ Look at (multi)jet final states at low x in different configurations

17 Jets at HERA: New dynamics?

x0, k ⊥ 0

x i, k ⊥ i

x i+1 , k ⊥ i+1

look at different topologies

especially with forward jets

jet, Et>4 GeV

x0, k ⊥ 0

x i, k ⊥ i

x i+1 , k ⊥ i+1

jet, Et>4 GeV

1 forward jet + 2 central jets

10−4

10−3

Datacorr. errorO(αs

3)O(αs

NLO DGLAP is OK

x0, k ⊥ 0

x i, k ⊥ i

x i+1 , k ⊥ i+1

jet, Et>4 GeV

1 forward jet + 2 central jets

10−4

10−3

3)O(αs

NLO DGLAP is OK

2 forward jets + 1 central jet

10−4

10−3

3)O(αs

[pb] H1

NLO DGLAP fails at low x

NLO DGLAP insufficientat low x ⇒ Room fornon-DGLAP dynamics!

Diffraction

π,η,...

Diffraction

π,η,...

D i f f r a c t i o n

Diffraction in HEP =

Colorless exchange carrying vacuum quantum numbers

18 Two approaches to Strong Interactions

1. Regge Pole Model ⇒ RFT 2. Quark-Parton Model ⇒ QCD

A(s, t) =

g1(m1,M1, t)g2(m2,M2, t)sα(t)±(−s)α(t)

sin(πα(t))

σab =∫fi/a(xi, µ

2) · fj/b(xj, µ2) · σ̂ij(xi, xj, µ2)

hadronic language sub-hadronic language

Ultimate goal: derive (1) from (2)

19 RFT: soft hh scattering vs QCD: deep inelastic ep scattering

• Hadronic degrees of freedom • Partonic degrees of freedom

• Validity: large s ≫ t • Low x: W 2 ≫ Q2, t (Q2/W 2 ≃ x ≪ 1)

• IP dominates: αIP (0) > αIR(0) • gluons dominate: xg(x) ≫ xqval(x)

→ σtot ∝ sαIP (0)−1 F2(x, Q2) ∝ xg(x) ∼ x−λ

• Unitarity corrections unavoidable • Saturation of the xg(x)

(σtot ≤ ln2(s/s0) at s → ∞) (non-linear effects, shadowing, ...)

• When? ssat =? • xsat(Qsat) =?

• First to be seen in diffraction: σD ∝ s2(α−1) • First to be seen in diffraction: σD ∝ |xg(x)|2

⇒ Diffraction ≡ Physics of the Pomeron, ⇒ Diffraction ≡ Gluodynamics,the essence of strong interactions the essence of QCD

(in high energy limit) .

20 Diffraction at HERA

� Fundamental aim: understand high energy limit of QCD (gluodynamics; CGC ?)

� Novelty: for the first time probe partonic structure of diffractive exchange

� Practical motivations: study factorisation properties of diffraction; try to transport tohh scattering (e.g. predict diffractive Higgs production at LHC)

′(MY )

xIP = ξ =Q2+M2

XQ2+W 2

(momentum fraction of colour singlet exchange)

β = Q2

Q2+M2X

= xq/IP = xxIP

(fraction of exchange momentum, coupling to γ∗)

t = (p− p′)2

(4-momentum transfer squared)

Experimental methods:

1) selecting LRG events

2) detecting p in Roman Pots(60 − 220 m from IP) FPS, VFPS

21 Inclusive Diffraction in DIS

ZEUS-1993

First observation

of diffraction in DIS

1992 data, 24.7 nb−1

21 Inclusive Diffraction in DIS

ZEUS-1993

First observation

of diffraction in DIS

1992 data, 24.7 nb−1

Current H1 status H1 VFPS PreliminaryH1 FPS PreliminaryH1 LRG Preliminary x 0.81

H1 LRG Published x 0.81H1 2006 DPDF Fit B x 0.81H1 2006 DPDF Fit B x 0.81 (extrapol.)

210 10 210 10 210 10 210 10 210 10 210 10]2 [GeV2Q

0.020.040.06 =0.017β

=0.0003IPx

0.020.040.06 =0.027β

0.020.040.06 =0.043β

0.020.040.06 =0.067β

0.020.040.06 =0.110β

0.020.040.06 =0.170β

0.020.040.06 =0.270β

0.020.040.06 =0.430β

0.020.040.06 =0.670β

0.020.040.06 =0.0010IPx

0.020.040.06

0.020.040.06 =0.0030IPx

0.020.040.06

10 210

0.06 =0.011β

10 210

0.06 =0.022β

10 210

0.06 =0.045β

10 210

0.06 =0.089β

10 210

0.06 =0.178β

10 210

0.06 =0.355β

10 210

0.06 =0.708β

0.020.040.06 =0.002β

=0.035IPx

0.020.040.06 =0.006β

0.020.040.06 =0.018β

0.020.040.06 =0.056β

0.020.040.06 =0.178β

0.020.040.06 =0.562β

0.020.040.06 =0.050IPx

0.020.040.06

0.020.040.06 =0.075IPx

0.020.040.06

10 210

0.020.040.06 =0.002β

=0.010IPx

10 210

0.020.040.06 =0.004β

10 210

0.020.040.06 =0.007β

0.020.040.06 =0.013IPx

0.020.040.06

0.020.040.06 =0.017IPx

0.020.040.06

0.020.040.06 =0.022IPx

0.020.040.06

scaling violation up to

very large β (= x of IP )

• Compelling confirmation of the NLO QCD picture of diffractionover a wide kinematic range. Clear candidate for the textbook!

• Diffractive PDFs are determined from these data. Are they universal?

22 Factorisation properties in diffraction

X (M )X

QCD collinearfactorisation at

fixed x , t

(x )IP

(Q )2g*

ppIP= x

QCD versus Regge factorisation

QCD factorisation(rigorously proven for

DDIS by Collins et al.):

Regge factorisation(conjecture, e.g. RPM

by Ingelman,Schlein):

σD(4)r ∝ ∑

i σ̂γ∗i(x,Q2) ⊗ fDi (x,Q2;xIP , t)

• σ̂γ∗i – hard scattering part, same as in inclusive DIS

• fDi

– diffractive PDF’s, valid at fixed xIP , t which obey (NLO) DGLAP

FD(4)2 (xIP , t, β,Q

2) = Φ(xIP , t) · F IP2 (β,Q2)

• In this case shape of diffractive PDF’s is independent of xIP , t

while normalization is controlled by Regge flux Φ(xIP , t)

23 QCD Factorisation Tests in Diffraction at HERA

QCD Factorisation holds in DIS regime, e.g.:

(x) 10

log-4 -3.5 -3

(x) 10

log-4 -3.5 -3

H1 Data (Prel.)

VFPS DIS Dijets

H1 Preliminary

800H1 FPS Data (Prel.)RapGap / 1.23NLO DPDF Fit B / 1.23

H1 Preliminary

2 central jets

IPz0 0.5 1

(x) 10

log-4 -3.5 -3

(x) 10

log-4 -3.5 -3

H1 Data (Prel.)

VFPS DIS Dijets

H1 Preliminary

2 central jets

IPz0 0.5 1

However, it breaks down at Tevatron ...

H1 2002 σrD QCD Fit (prel.)

QCD fit to ZEUS 97 data

CDF IP+RR

FJJD (

Tevatron vs HERA

(x) 10

log-4 -3.5 -3

(x) 10

log-4 -3.5 -3

H1 Data (Prel.)

VFPS DIS Dijets

H1 Preliminary

2 central jets

IPz0 0.5 1

However, it breaks down at Tevatron ......due to soft remnant rescattering (S ∼ 0.15)

CDF IP+RR

FJJD (

Tevatron vs HERA

(x) 10

log-4 -3.5 -3

(x) 10

log-4 -3.5 -3

H1 Data (Prel.)

VFPS DIS Dijets

H1 Preliminary

2 central jets

IPz0 0.5 1

CDF IP+RR

FJJD (

Tevatron vs HERA

⇒ Test it in photoproduction:

p(P) )Y

IPz (v)

* (q)γ (u)

e(k) e(k’)

remnant

e(k) e(k’)

* (q)γ

jet 12M )X

(v)IPz

remnant

p(P) )Y

remnant

(a) (b)

direct, xγ=1 (DIS-like) resolved, xγ<1 (hadron-like)

(x) 10

log-4 -3.5 -3

(x) 10

log-4 -3.5 -3

H1 Data (Prel.)

VFPS DIS Dijets

H1 Preliminary

2 central jets

IPz0 0.5 1

CDF IP+RR

FJJD (

Tevatron vs HERA

⇒ Test it in photoproduction:

p(P) )Y

IPz (v)

* (q)γ (u)

e(k) e(k’)

remnant

e(k) e(k’)

* (q)γ

jet 12M )X

(v)IPz

remnant

p(P) )Y

remnant

(a) (b)

direct, xγ=1 (DIS-like) resolved, xγ<1 (hadron-like)

S = 0.58 ± 0.21

• Global, xγ-independent suppresion factor is observed – somewhat unexpected

⇒ Details of factorisation breaking mechanism in γp at HERA are not fully understood yet

24 Vector Mesons at HERA

αIP(t)=α(0)+α′t

soft IPomeron exchange hard IPomeron diagrams

Exclusive VM production at HERA – a nice tool to study ‘soft’ vs ‘hard’ Pomeron regimes

soft IPomeron exchange hard IPomeron diagramsHard scales: Q2,MV , t

Predictions

αIP (0) ≃ 1.08 / 1.20

α′IP ≃ 0.25 / 0.0

Universal scale µ2 = (Q2+M2V )/4

Exclusive VM production at HERA – a nice tool to study ‘soft’ vs ‘hard’ Pomeron regimes

soft IPomeron exchange hard IPomeron diagramsHard scales: Q2,MV , t

Predictions

αIP (0) ≃ 1.08 / 1.20

α′IP ≃ 0.25 / 0.0

Universal scale µ2 = (Q2+M2V )/4

transition from soft to hard regime at µ2 ≃ 4÷5 GeV2

25 Vector Mesons at HERA:t−dependence

dσ/dt ∼ e−b|t| → diffractive peak (approximated from Bessel function)

b = (R/2)2 → transverse size of the target (geometric picture)

Predictions: b = b0 + 4α′IP ln(W/W0);

soft IP : shrinkage of diffractive peak (α′IP =0.25); large b0 ≈ 10 GeV−2

hard IP : no (or small) shrinkage (α′IP <0.1); small b0 ≈ 5 GeV−2

⟨Q2⟩ = 0.05 GeV2H1a)

Wγp [GeV]

50 100 200

H1ZEUS2D-Fit

⟨Q2⟩ = 8.9 GeV2H1b)

Example: shrinkage in γ∗p → J/ψp

Q2 < 1 GeV2:

α′IP = 0.164 ± 0.028 ± 0.030

Q2 = 2 − 80 GeV2:

α′IP = 0.019 ± 0.139 ± 0.076

Dipole picture interpretation:

b = bVM + bp

bVM ∼ 1/(Q2 +M2VM)

bp → size of the gluons area:

〈r2〉 = 2bp·(~c)2 ≃ 0.6 fm

Gluons confinement area (0.6 fm) is smaller than the proton size (0.8 fm)

26 Summary

� Standard Model survived 1 fb−1 of HERA data and is still in a good shape.Next challenge is now coming from the LHC - stay tuned!

� Combining H1 and ZEUS data allowed proton structure to be measuredwith unprecedental precision

� NLO DGLAP is surprisingly successful down to lowQ2 and low x in describ-ing bulk of HERA data. However, some room for parton evolution beyondDGLAP is found at specific phase space corners ⇒ important message forLHC

� Gained new insights into high energy diffraction: Pomeron under the HERAmicroscope shows complicated interplay of soft and hard phenomena.Understanding colour singlet exchange remains a major challenge in QCD

� Is this the end of DIS experiments? Or what’s next at the horizon?

27This is dummy text in order to force correct page orientation (landscape). Attempt to cure autorotation by pdf conversion

e±p(60 − 140)GeV × 7000 GeV

Project under discussion For late LHC period:

∼ 2022−2032

√s ≈ (4 − 6)×HERA L ≈ (50 − 100)×HERA

28 100 years of studying the structure of matter

� Fixed target experiments

⊲ Rutherford – 1911 (7 MeV, αAu)structure of atoms ⇒ planetary model ⇒ quantum mechanics

⊲ Hofstadter – 1953 (400 MeV, eA)structure of the nucleus; determination of the size of A and p

⊲ SLAC – 1968 (20 GeV, ep)structure of the proton ⇒ quarks ⇒ QPM

⊲ SPS@CERN – 1976 (EMC, NA4, etc. studying DIS with µ beam)

� Collider experiments

⊲ HERA – 1992 (27.5 × 920 GeV ep)gluon dominated proton (and Pomeron); low x QCD; EW sector of SM

⊲ LHeC – 2022 (60 × 7000 GeV, ep/eA) – not approved yet

non-linear QCD? Strong parton saturation? BSM phenomena?

The Legacy of HERAlevonian/papers/Prague_2013.pdf · Sergey Levonian DESY, Hamburg The Legacy of...

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