Recent results from the H1 experiment

1
14th International Workshop on Deep Inelastic
Scattering
Recent Results from the H1 Experiment
Emmanuelle PEREZ DESY CEA-Saclay

• High Q2 DIS inclusive measurements
• searches for new physics, jets
• Hadronic Final State in low Q2 NC DIS
• Diffraction vector mesons
• inclusive diffraction
• final states
• Rare processes

20 April 2006
DIS 06, Tsukuba
2
H1 datasets
HERA I 130 pb-1 - mainly e p data -
several analyses getting finalised on HERA I
data
HERA II (since 2003) - 50 pb-1 of ep - 100
pb-1 of e-p - polarised leptons, P typically 30
-40 - analysed so far what benefits from
polar, stat, and new capabilities of the H1
detector
Analyses presented here up to 280 pb-1
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Charged Current DIS
?CC(e?,SM) (1 ? Pe)

• e p first publication
• on HERA II data
• (PLB 634 (2006) 173)

e- p

• e- p prelim. measurements with the
• full available 05 stat.

69 pb-1
HERA I
?(syst.) typically 4, ?(stat.) from 2 to 8
30 pb-1
27 pb-1
21 pb-1
e p
Extrapolations to Pe ? 1 consistent with no WR
First H1 diff. CC x-section measurements on HERA
II data agreement with H1PDF2000
4
Polarised Neutral Current DIS
d?/dQ2 measured for NC DIS in HERA II polarised
data.
At high Q2 ( ?Z interference ) RH / LH gt 1
for e p, RH / LH lt 1 for e- p
e p RH / LH
Expected polarisation dependence confirmed
although with limited precision.
e- p RH / LH
5
Measurement of xF3


Correct for polar. effect
?(e-) - ?(e) gives access to the non-singlet SF
xF3 x ( q q )
-
Combine HERA I (15 pb-1 e-, 100 pb-1 e) with
HERA II (120 pb-1 e-, 50 pb-1 e)

• stat. errors reduced
• by 20-30

• Neglect pure Z contribution
• (small) and correct for
• propagator terms ? little
• dependence on Q2
• Test the x dependence
• of valence quarks.

2uv dv
-
(if s s )
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Jets in high Q2 NC DIS constraints on ?

• Excited fermions signature of a new scale of
  matter
• Can be singly produced in DIS
• Excited neutrinos would be produced much more
• copiously in e- p than in e p

f/?

• Analysis of 2005 e- data (114 pb-1)

decay ?? ?Z eW
SM background Radiative CC CC multijets NC multijets
All decays analysed (with W/Z ? jets) For large
M(?) ? ? eW dominates
No resonance in any of the 3 channels
Most stringent constraints so far !
For f/? 1 /M M gt 188 GeV
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Jets in High Q2 NC DIS ?S measurements
Inclusive jets in Breit frame
61 pb-1
Large statistics !
Q2 gt 150 GeV2
Fit ?S(MZ) in each (Q2, ET) bin using NLO
calculations.
Combined fit leads to
Exp. error 1.3 Reduced by a factor of 2
w.r.t. 2001 analysis (reduced had. scale
uncertainty)
but large theo. error (scale uncertainties)
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HFS in high Q2 DIS fragmentation
For tracks in the current region of the Breit
frame
Norm. charged particle momentum distrib.
xp p / (Q/2)
45 pb-1 (2000)
Increased stat. (60k evts) High Q2, ltQgt up to
ELEP Full xp range
1/Nevents dn/dxp
Clear scaling violations observed
Q increasing
xp
Well described by RAPGAP (frag. model tuned to ee
data)
Good agreement with ee data (a bit softer ?) ?
quark fragmentation universality
Comparison with NLO calculations show sensitivity
to ? frag. functions.
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?0 / ? separation in low Q2 DIS
e ? ? e ? and q ? ? q ?
Measurement of prompt photon in DIS
Q2 gt 4 GeV2, ET? gt 3 GeV, -1.2 lt ?? lt 1.8
Extended range (? x 10) w.r.t. previous HERA meas.
isolated ? with z E? / Ejet gt 0.9
Variables based on the shower shape combined
into a likelihood discriminator
HERA I data, 71 pb-1
MC describes the rate of isolated ?0 in the HFS !
e ? ? e ? dominates
q ? ? q ? dominates
-1.2 lt ?? lt -0.6
0.2 lt ?? lt 0.9
Cross sections well described by recent O(?3) QED
calculation
First H1 measurement of prompt ? in DIS
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Jets in low Q2 DIS QCD at low x
Study jets in low x DIS, where DGLAP might be
unsufficient to describe g radiation

• forward jets theory models
• too low at low xBj

hep-ex/0508055

• search for gluon radiation
• unordered in kT in 3-jet events

99-00 data, 44 pb-1

• 3 jets with PT gt 4 GeV

10-4 lt x lt 10-2, 5 lt Q2 lt 80 GeV2
40 000 events
Comparison with MC programs - DGLAP based MC
normalisation too low (60) shapes are not
described - Color Dipole Model (unordered kT)
OK
Only MC with kT-unordered gluon
radiation describes the data.
11
3-Jets in low Q2 DIS QCD at low x
Comparison with NLO O(?S3) NLO lt data at
lowest x, largest ?

• Look separately in 2 subsamples
• - 1 forward 2 central jets
• - 2 forward 1 central jets

Discrepancy mainly in the 2 forward jets
sample.
Huge improvement LO ? NLO O(?S3) includes the
first kT-unordered radiation
Strong hints that, in this region of phase
space, the effect of kT-unordered gluon
radiations is important.
12
Further BFKL insights VM at large t
At large t photoproduction of VM described in
pQCD by - LO exchange of two gluons -
beyond LO exchange of a gluon ladder
Different predictions for the t-dependence
and for the helicity structure of the interaction.
Probability for ?T ? ?L
t
2g
Analysis of ? ? ??, 20 pb-1 (2000)
e detected in low-angle electron tagger (trigger)
BFKL

• t-dependence
• spin density matrix elements

hep-ex/0603038
better described by gluon ladder exchange.
BFKL
interference
2g
But no model describes all the features of the
data.
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? photoproduction at low t
VM production with no hard scale expected to be
described by Regge phenom.
Old H1 meas. (1994 data) 300 events (tagged ?p)
H1 2005
HERA II Fast Track Trigger ? trigger on tracks
down to PT of 100 MeV
300 K events !
? New measurement on 2005 data
d?/dt (W) for elastic and p-dissociation
- Extraction within a single experiment - No use
of low W data (exchange of other trajectories)
Assuming ?(t) ?0 ? t
OK with DL
???
? much lower than the slope of the soft Pom !!!
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The Pomeron Trajectory in diffractive DIS
Select diffractive DIS events by tagging the
leading proton (carrying a fraction 1-xPom of
incoming p momentum) in our Forward Proton
Spectrometer (FPS)
xPom

• Allows t measurement
• Study d?/dt eBt in bins of xPom

p
Regge approach B B0 2 ? ln(xPom)
Low xPom B 6 GeV-2
3000 events
28 pb-1 (99-00)
Small shrinkage favoured
Final results
? 0.06 0.19 -0.06 GeV-2
Factorisation of the t-dependence from (Q2, x)
?P(0) also extracted from the xPom dependence
Increased Reggeon contrib.
( x / xPom)
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Diffractive DIS with Large Rapidity Gaps
Our final results
LRG (?max method)
xPom 0.003
Q2 range Luminosity
3 lt Q2 lt 13.5 GeV2 2 pb-1 (1997 minimum bias)
13.5 lt Q2 lt 105 GeV2 11 pb-1 (1997)
133 lt Q2 lt 1600 GeV2 62 pb-1 (1999-2000)
?0.017 (x 5 10-5 )
H1 LRG

• Large kinematic domain covered
• Precise measurements syst. typically 5,
• normalisation 6, stat. 5 20

Comparison with FPS data
Amount of p-diss in LRG meas. shows no kinem.
dependence on Q2, xPom, ?
?0.67 (x 0.002)
LRG/FPS 1.23 ? 0.16
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Diffractive DIS with Large Rapidity Gaps
? dependence driven by quark diff. PDFs
xPom 0.003
Diffractive cross-section remains sizeable up to
largest ? values.
xPom 0.03
Reggeon contribution important at high xPom and
low ?
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QCD analysis of LRG ? DPDFs
(Proton vertex factorisation assumed)
No kinem. dependence of ?P(0) observed.
IP Reggeon contributions
?2 / ndf 158 / 183
MRS ansatz A zB (1-z)C
A,B and C necessary for ?(z) Gluon poorly
constrained
Similarly good fits obtained with Ag and Cg, and
with Ag only (Fit B)
Fitted Reggeon normalisation in very good
agreement with that obtained in the FPS data.
Gluon carries 70 of the momentum of the
colorless exchange
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Factorisation in diff. DIS jets
Dijet events with a LRG ? 2700 evts ( x 6 w.r.t.
previous H1 analysis 50 pb-1 (99-00 data),
extended kinematic range )
Overall good agreement with NLO predictions.
Fit
Fit B
Confirmation that factorisation holds.
Log10(xPom)
Preference for Fit B
Previous analysis
Fit B
Differences show up in variables most
sensitive to the gluon density at high z
xPom
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Using jets to better constrain DPDFs
Combined fit of F2D and dijet data
?2/ndf (total) 196 / 217 ?2/ndf (dijets) 27 /
36 ?2/ndf (F2D) 169 / 190
Both datasets well described by the combined fit.
Combined fit close to Fit B dijets
provide important constraints on high z gluon !
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Factorisation in diff. DIS charm

• Use D to identify c quarks ? prel. meas.

50 pb-1 (99-00)

• New measurement exploit the long lifetime of
• charmed hadrons
• Use track impact parameters meas. with the
  SiDet
• inclusive method ? no large extrapolations

S ? / ?(?)
? measurement of F2Dcc in bins in (xPom, Q2, ?)
Cf H1, EPJ. C45 (2006) 23
Good agreement with the D x-sections (extrapolati
on factor 2.5)
Q2 35 GeV2 xPom 0.018
Good agreement with NLO QCD using the DPDFs
obtained from F2D (complementary to jets since
lower PT ? lower z)
Charm production accounts to 20 of the diff.
x-section (cf. inclusive case)
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F2D on 99-04 data
Medium Q2 12 lt Q2 lt 90 GeV2

• 97 10 pb-1
• 99-00 35 pb-1
• 2004 35 pb-1 (fwd det. a bit ? )

99-04 Low Q2 large ? not yet
Measurements confirm 97 data with reduced stat.
errors
Q2
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Extraction of the diff. component ?max vs MX
Non-diff exp. fall-off
Comparison H1 / ZEUS ? methods used ? Try the
MX method on 99-00 data
Result of subtraction
Limited lever-arm due to acceptance MX recoed
with LAr calorimeter (? lt 3.4)

• ZEUS good E meas. up to ? 5
• in contrast, H1 has good taggers
• up to ? ? 7.5

No bias found with the MX method in the (limited)
range where H1 can apply it.
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Rare processes at HERA ??- production
Final states e?, e?jet, ??jet, ?jet?jet
Maximal S/B when restricting to elastic
production i.e. DIS ?p backgrounds mainly from
diffractive processes
Use of neural networks to separate ?-jets from
hadronic jets
Bckgd from diff. dijets at zpom ? 1
signal
108 pb-1 (HERA I data)
Nobs 30 (7 e?, 2 e?jet, 10 ??jet, 11 ?jet?jet )
Nexp 27.1 ? 4.1 (60 from ??)
hep-ex/0604022
In kinem. range 20o lt ?? lt 160o, PT? gt 2 GeV
? 13.6 ? 4.4 ? 3.7 pb
First observation of ? pair production at HERA
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Search for W ? ??
hep-ex/0604022
Search for W ? ? in HERA-I data completed
Isolated ? PT,miss
PTX

• Effi. x Acc. 8
• 1-prong had. decays
• only ( 49)
• limited ? range

• (W prod)
• ? 1 pb

Combining with prelim. results on HERA-II data
H1 prelim., 278 pb-1
H1 prelim 94-05 Observed SM expectation Signal
All PTX 25 24.3 ? 4.6 2.0 ? 0.4
PTX gt 25 GeV 3 0.74 ? 0.15 0.43 ? 0.09
A few events observed at PTX gt 25 GeV in HERA II
data but limited statistics
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W Production (e ?)
W ? e, ? isolated e, ? PT,miss had. System
(PTX)
Positrons
Electrons
Effi. x Acc. 30 Wide ? range High W
purity (87 at high PTX)
PTX gt 25 GeV e channel ? channel Combined e ?
Electrons, 98-05 121 pb-1 2 / 2.4 ? 0.5 0 / 2.0 ? 0.3 2 / 4.4 ? 0.7
Positrons, 94-04 158 pb-1 9 / 2.3 ? 0.4 6 / 2.3 ? 0.4 15 / 4.6 ? 0.8
excess not seen in e- p !
In e p 3.4 ? effect Our best chance for
a discovery !
26
Multilepton events at HERA
Events with ? 2 leptons in final state. Mainly
produced via ??
Cross-section when both leptons are central, PT1
gt 10 GeV, PT2 gt 5 GeV ? lt 1 pb
H1 data 94-00 excess of 2e3e events at high
M12 mass of two highest PT e
The H1 evts are not consistent with e? ? H (e)
? ee(e)
hep-ex/0604027
Significant constraints set on H coupling to
e-? and to e-?
Analysis extended to include 03-05 data
Extended to other 2l 3l topologies Now ee,
??, e?, eee, e?? are considered

• no new 2e / 3e evt at M12 gt 100 GeV
• (but one high mass 3e event )
• one e?? evt at M?? gt 100 GeV, one at Me? gt 100
  GeV

Altogether, at ? PT gt 100 GeV Nobs 4, Nexp
1.1 ? 0.2
All high mass evts in ep
E. Perez
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Concluding remarks

• Finalisation of analyses on HERA I data

Diffraction finalisation of analysis using
the Forward Proton Spectrometer and of
inclusive Large Rapidity Gap analysis
Combined fit F2D dijet data
Further tests of factorisation (also D in
photoproduction)
Also on hadronic final states and heavy flavor
physics

• New preliminary results on HERA II data
• ?, F2D, ? with Fast Track Trigger,
  also DVCS measurement

• First combinations of HERA I HERA II xF3
  measurement, searches

We are entering a new phase of analyses aiming to
the highest precision.
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H1 talks at DIS06
Andrei Nikiforov   Neutral current studies at
HERA II   Jacek Turnau   Measurement of Event
Shape Variables in DIS at HERA   Katja Krueger
  Photoproduction of di-jets with High Transverse
Momenta at HERA   Steve Maxfield   Inclusive Jet
Production in DIS at high Q2 at HERA   Dima
Ozerov Search for a Narrow Baryonic Resonance
Decaying to K0_s p(pbar)   Carsten Schmitz  
Prompt Photons in DIS   Christoph Werner  
Parton Dynamics in DIS multi jet events at small
x   Magnus Hansson   Di-jets at low x and low
Q2   Dan Traynor   Scaled Charged Particles
Momentum Distributions at high Q2   Lars Finke
  Production of charm and beauty dijets at HERA  
Ying-Chun Zhu   Elastic J/Psi production at
HERA   Biljana Antunovic   Charged current
studies at HERA II   Paul Laycock   F2bb/F2cc
at HERA   Benoit Roland   DVCS at HERA   Jan
Olsson   Rho Photoproduction at HERA   Carl
Gwilliam   Rho production at large t at HERA  
Paul Newman   F2D3 and F2D4 measurements  
Emmanuel Sauvan   F2D3 new analysis at medium
Q2   Olaf Behnke   Diffractive D and F2D(cc)  
Matthias Mozer   Diffractive di-jets and
combined fits   Max Klein   FL measurements and
low energy running   Dave South   New H1
results on Isolated leptons and Missing PT at
HERA   Claude Vallee   Multi-lepton events and
search for H at HERA   Christian Helebrant
Leptoquark searches at HERA   Stefania Xella  
Tau lepton production at HERA   Cristinel
Diaconu   Search for excited neutrinos at HERA
  Christiane Risler   Forward Jet Production
in Deep Inelastic Scattering at HERA  
29
Backup Divers
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Azimuthal correlations in dijet low Q2 events
Alternative test of DGLAP in low x DIS Study the
?? between the two jets closest in ? to the
e. Large kT of gluon ? broadening of ??
64 pb-1 (99-00) W.r.t. previous analysis much
larger stat, improved resolution on the HFS
measurement.
- O(?S2) unsufficient to describe the data.

• O(?S3) much better, still low at small ??
• (but large scale errors on the prediction)

• Normalising to the x-section integrated
• over ?? lt 170 deg. amplifies the differences
• (cf H1, Eur. Phys. J. C33 (2004) 477)

i.e. hints that O(?S3) not enough
31
QCD analysis of LRG ?
No kinem. dependence of ?P(0) observed.
Scaling violations at large ? are driven by q ?
qg and not g splittings.
i.e. inclusive diff. DIS not much sensitive to
the Dgluon at large Fractional momentum !
32
Factorisation in diff. ?p D
Diffractive photoproduction of jets breaking of
factorisation both for the resolved ? (
expected) and direct ? (unexpected ?) processes.
? Investigate diff. ?p of D (direct process
largely dominates)
?p events e detected in low angle electron
tagger (trigger..) ? limited statistics
50 pb-1
D ? D0 ?slow ? K- ? ?slow (c.c.)
Comparison with NLO calculation (FMNR) Good
agreement within the (large) errors.
No evidence for a breaking of factorisation in
diff. ?p of D mesons.