Results on tau physics from HERA
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Transcript of Results on tau physics from HERA
Results on tau physics from HERA
Junpei Maeda(Tokyo Institute of Technology)
On behalf of
the H1 and ZEUS collaborations
10th Int. Workshop on Tau Lepton Physics (TAU08)September 22–25, 2008
Novosibirsk, Russia
25 Sep 2008 J.Maeda - Results on tau physics from HERA 2
HERA: World’s Only ep Collider
pe+/e–
27.6 GeV 920 GeV
318~s GeV
HERA–I (1992~2000) : L~120 pb–1/exp.
HERA–II (2002~2007) : L~350 pb–1/exp. – luminosity upgraded – longitudinally polarized lepton beam – detector upgrades
0.5 fb–1 data for each experiment!
HERA laid to rest on 30 June 2007.
25 Sep 2008 J.Maeda - Results on tau physics from HERA 3
H1 and ZEUS detector
e+/e–
p
p
e+/e–
Liquid Argon Calorimeter Uranium–scintillator Calorimeterfine granularity, excellent tracking good hadronic energy resolution
EEE /%18/)( EEE /%35/)( for hadrons
for electronsEEE /%12/)( EEE /%50/)( for hadrons
for electrons
25 Sep 2008 J.Maeda - Results on tau physics from HERA 4
Tau Production at HERA
Tau lepton is important in exotic search.
Tau lepton production is a rare process at HERA!
• Isolated lepton with missing transverse momentum(PTmiss) events
• +– pair–production events
• Double charged Higgs Search
• Lepton Flavour Violation
25 Sep 2008 J.Maeda - Results on tau physics from HERA 5
Tau Production at HERA
• Isolated lepton with missing transverse momentum(PTmiss) events
• +– pair–production events
• Double charged Higgs Search
• Lepton Flavour Violation
• Leptonic channel ( )• Semi–leptonic channel ( )• Hadronic channel ( )
e hadhade ,
hadhad
25 Sep 2008 J.Maeda - Results on tau physics from HERA 6
+– pair–production (only leptonic) @ ZEUSZEUS–prel–06–017)(epep
ZEUS e–p 135 pb–1 (prel.)
Data +– +–
3 2.0±0.8 < 0.2
Data agree with SM expectation.
HERA–II e–p data L=135 pb–1
searched for e
electron muon
Ee > 4 GeV
e < 2.6 rad
pT > 2 GeV
0.6 rad ≲ ≲ 2.8 rad(Acceptance of central tracking detector)
elastic requirements – Number of tracks in event : 1~3
– No energy deposit in ”forward” calorimeter region
selection criteria
(leptonic decay)
dominant background)(epep
+
–
PT, (GeV) (rad)
PT,e (GeV) e (rad)
PT,miss (GeV) e, (GeV)
25 Sep 2008 J.Maeda - Results on tau physics from HERA 7
+– pair–production (incl. hadronic) @ ZEUSZEUS–prel–08–009HERA–II e±p data L=364 pb–1)(epep
(BR : ~23%)
(BR : ~42%)
he
hh
To study hadronically–decayed identification, searched for:
more statistics than e channel (~6%)
There are many kinds of large background…
~300 nb (2 jets w/ ET>4 GeV)
~ 10 pb (PT > 5 GeV)
electron jet
pTe > 5 GeV & –2 < e < 2
matched track (pTtrack > 3 GeV)
pTjet > 5 GeV & –2 < jet < 2
at least one associated tracks, electron rejection cut
elastic requirements : No energy deposit in forward calorimeter region, Low track multiplicity
Hadrons from decay is identified by ”jet”.
The most difficult thing : separate a –jet from quark/gluon induced jets
e.g.) diffractive–photoproduction
25 Sep 2008 J.Maeda - Results on tau physics from HERA 8
–jet ID for +– pair–production @ ZEUSZEUS–prel–08–009–ID using PDE Range Searching (discriminant)
had –IDsuggested by T.Carli,
B.Koblitz.
NIMA501(2003)576
x1
x2
test event
background
Signal
• Generalization of one–dimensional PDE approach to n dimensions– Counts number of signal and background events (training sample) in ”vicinity” V of the test event
– Implemented in TMVA
D(ievent,V) =nS(ievent,V) / NS
nS(ievent,V) / NS + nB(ievent,V) / NB
#background events in V#all background events
#all signal events#signal events in VDiscrimination value
– Implemented in TMVA
– 6 variables are inputted to discriminant, then evaluate discrimination value. (next slide)
25 Sep 2008 J.Maeda - Results on tau physics from HERA 9
–jet ID for +– pair–production @ ZEUS
ZEUS–prel–08–009The highest D in event The second highest D
6 variables are prepared for discriminant.
2,
2,
2,
2 )()()()( i
zii
yii
xii
i pppEMass
Mass : invariant mass of clustered CAL cells
Lmean : 1st moment of longitudinal extension
i i
i ii
E
ELLmean
cos
jet axis
Ei
iLi
cell
Nsubj : Number of subjets (ycut=5×10–4)
Rtrk : The sum of distance between the jet axis and the tracks associated with the jet
Ntrk
i iiRtrk )( 22
i i
i ii
E
RERRmean
}{
i i
i ii
E
RRERrms
2)(
Rmean, Rrms : 1st and 2nd moment of radial extension
Outputted discrimination value
had –ID
25 Sep 2008 J.Maeda - Results on tau physics from HERA 10
Results of +– pair–production @ ZEUSZEUS–prel–08–009
Data are in reasonable agreement with SM expectation.
Large uncertainty due to• MC statistics• PHP scale normalization
HERA–II e±p data L=364 pb–1
Discriminant threshold is given for each topology.
)(epep
25 Sep 2008 J.Maeda - Results on tau physics from HERA 11
The highest Mvisible event (M
visible=40 GeV)
25 Sep 2008 J.Maeda - Results on tau physics from HERA 12
+– pair–production @ H1Eur. Phys. J. C48 (2006) 699–714HERA–I e±p data L=106 pb–1)(epep
• To distinguish hadronic 1–prong, 3–prong decays from quark/gluon jets (L1–prong, L3–prong)
• To distinguish hadronic 1–prong decays from misidentified electrons/muons (Lvetoe, Lveto
)
– multiplicities of neutral clusters / invariant mass / number of tracks / 1st moment of energy deposits…
Neural Network based tau–ID
electron muon jet
pTe > 3 GeV pT
> 2 GeVpT
jet > 2 GeV
L1–prong || L3–prong > 0.75
Two isolated e or or jets of opposite charges
elastic requirements : No additional tracks/clusters, No activity in forward regions
NC/di–e/di– rejection : E–Pz < 50 GeV, Lvetoe > 0.75, Lveto
> 0.75
signal efficiency = 50%misideintifed probability = 0.5% (4%)
• leptonic(e), semi–leptonic(e–jet, –jet), hadronic(jet–jet) decay• look at the jets from low PT
• exactly required 1 or 3–tracks in the jet• using neural network to identify –jet
• the first measurement of +– cross section at ep–collider
look for all topologies to be able to identify +– events
had –ID
25 Sep 2008 J.Maeda - Results on tau physics from HERA 13
)(epep
(acceptance ≈ 1%)
Purest final state
Results of +– pair–production @ H1Eur. Phys. J. C48 (2006) 699–714
good agreement with SM expectation!
measured = 13.6±4.4±3.7 pbtheory = 11.2±0.3 pb (GRAPE)
stat. syst.
HERA–I e±p data L=106 pb–1
Phase space definitionelastic events with two leptons of
– pT > 2 GeV
– 20º < < 140º
.
first measurement at HERA !!
25 Sep 2008 J.Maeda - Results on tau physics from HERA 14
+– candidate @ H1Eur. Phys. J. C48 (2006) 699–714
25 Sep 2008 J.Maeda - Results on tau physics from HERA 15
Tau Production at HERA
• Isolated lepton with missing transverse momentum(PTmiss) events
• +– pair–production events
• Double charged Higgs Search
• Lepton Flavour Violation
25 Sep 2008 J.Maeda - Results on tau physics from HERA 16
Isolated tau leptons + PTmiss physics
H1prelim–07–064)(eXWep
PTX
PTmiss
Large PTX
new physics?
pb1.0~BR
Rare process, but sensitive to new physics– SM signal is single W boson production with
subsequent decay W .
– Main background is CC events with narrow jets.
– A complement to isolated e() + PTmiss analysis
(There is a slight excess for e() channel at H1.)> 12 GeV (H1)
Additional high pT jet
An excess at high pTX could be a sign of new physics.
single top production via FCNC etc.
Phys. Lett. B 583 (2004) 41ZEUS :
H1 :
> 20 GeV (ZEUS)
PTX
PTmiss
25 Sep 2008 J.Maeda - Results on tau physics from HERA 17
–ID for Isolated + PTmiss analysis @ ZEUS
Phys. Lett. B 583 (2004) 41
– Same method as analysis. (see above)–ID using PDE Range Searching
HERA–I e±p data L=130 pb–1
– Variable set is different.log(Rtrk) –log(Lrms)
Lrms : 2nd moment of longitudinal extension
jet axis
Ei
iLi
CAL cell
i i
i ii
E
LmeanELrms
2cos
required D > 0.95
Good separation of signal from background!
had –ID
25 Sep 2008 J.Maeda - Results on tau physics from HERA 18
Result of isolated + PTmiss @ ZEUS
Phys. Lett. B 583 (2004) 41Interesting +PT
miss events at large PTX are observed at ZEUS!
ZEUS1994–2000 e±p
L = 130.1 pb–1
ZEUS data SM expectationW
Contribution
Total 3 0.40 –0.13 43%
PThad > 25 GeV 2 0.20±0.05 49%
pThad > 40 GeV 1 0.07±0.01 71%
+0.12
New physics signal
25 Sep 2008 J.Maeda - Results on tau physics from HERA 19
Isolated tau leptons + PTmiss @ H1
H1prelim–07–064)(eXWep
PTjet > 7 GeV, 20º < jet < 120º
• look for jet in LAr calorimeter (cone radius = 1.0)
• Isolation : Distance to other e, , jet in – > 1.0
Radial shower shape (”Jet radius”) < 0.12
h
hjet
jet hjethjetEE
R 22 ),(),(1
(only 1–prong jet)
misidentification probability : < 1%
cut–based tau–ID
• Njettracks = 1
had –ID
• ZEUS HERA–I result has a slight excess for + PTmiss events.
• H1 analyzed all HERA data. 471 pb–1
W
Data in good agreement with SM prediction!
CC events are dominant.
25 Sep 2008 J.Maeda - Results on tau physics from HERA 20
+ PTmiss candidate event
H1prelim–07–064
25 Sep 2008 J.Maeda - Results on tau physics from HERA 21
Tau Production at HERA
• Isolated lepton with missing transverse momentum(PTmiss) events
• +– pair–production events
• Double charged Higgs Search
• Lepton Flavour Violation
25 Sep 2008 J.Maeda - Results on tau physics from HERA 22
Doubly–charged Higgs search @ H1Phys. Lett. B 638 (2006) 432HERA–I e+p data L=88 pb–1
No evidence for H++ e++ decays
SM signal efficiency
e jet
pTe > 10(5) GeV
Isolated
pT > 10(5) GeV
Isolated
pTjet > 10(5) GeV
No other track within
0.15 < R < 1.5
PTmiss > 8 GeV (e–e) / PT
miss > 11 GeV (e–jet)
Charge of Higgs decay product candidates = lepton beam charge
cut–based tau–ID
searched for H++ bosons using
had –ID
–
e+
+H++
hehe
e+
p p (X)
CDF (MH > 114 GeV)(c.f. hep-ex/0808.2161)
25 Sep 2008 J.Maeda - Results on tau physics from HERA 23
Lepton Flavour Violation @ H1/ZEUSEur. Phys. J. C52 (2007) 833–847H1 :
Eur. Phys. J. C44 (2005) 463–479ZEUS : searched for Lepton Flavour Violation
(W±)
()
SM DIS
Leptoquark(LQ)s couple to bothquarks and leptons.
s–channel u–channel
It carries both leptonic(L) andbaryonic (B) numbers.
had –ID
Neural Network based tau–IDlike H1 +– analysis80% signal efficiency
95% quark/gluon induced jet rejection
DNN>0.8 & …
Required :
exactly 1 or 3 tracks in the jet
PTjet1 >25GeV, PT
jet2 >15GeV
–ID using PDE Range Searching
had –ID
same discriminant as in ZEUS +PTmiss search
25 Sep 2008 J.Maeda - Results on tau physics from HERA 24
Limits for LQs in the channel @ H1/ZEUS
No candidate was found. Limits on LQ were set.
HERA–I e±p data L=130 pb–1
Eur. Phys. J. C52 (2007) 833–847 Eur. Phys. J. C44 (2005) 463–479
No evidence for LFV
Data 0
SM 2.3±0.5
sel. eff. 22~30% ( )sM LQ
HERA–I e±p data L=80.2 pb–1
No evidence for LFV
H1 e–p: 13.7 pb–1, e+p: 66.5 pb–1
Data SM MC
ep Xe–p 0 0.75±0.21
e+p 1 4.90±0.85
No significant deviation from SM found.Limits were set on coupling to LQleading to Lepton Flavour Violation.
25 Sep 2008 J.Maeda - Results on tau physics from HERA 25
Summary• Only a few taus have been seen at HERA.
– Detecting taus at HERA is a challenging task.
• They are an important signature for new physics.
• Many tools for the identification of hadronically–decayed taus have been developed by H1 and ZEUS.
• Results for +– pair–production are in agreement with SM prediction (H1/ZEUS).
• New result of isolated + PTmiss from H1 is in agreement with SM expectation.
– ZEUS result using HERA–I data has a slight excess.
• No evidence for H++ e++ decays (H1) and lepton flavour violation (H1/ZEUS)
• HERA data taking ended on June 30 2007 after 15 years successful operation:– Each experiment has collected ~500 pb–1 data.
– Tau analyses have not finalized yet, still more to come for the next years!
backup slides
25 Sep 2008 J.Maeda - Results on tau physics from HERA 27
Background control sample for +– pair–production @ H1
25 Sep 2008 J.Maeda - Results on tau physics from HERA 28
Event selection for isolated tau + PTmiss @ H1
H1prelim–07–064CC selectionPT
miss > 12 GeV
the ratio of the anti–parallel and parallel componentsof the hadronic PT
Tau–jet selection
PTjet > 7 GeV, 20º < jet < 120º
look for jet in LAr calorimeter (cone radius = 1.0)
Isolation : Distance to other e, , jet in – > 1.0
Radial shower shape (”Jet radius”)
h
hjet
jet hjethjetEE
R 22 ),(),(1
(cut–based)
only 1–prong jet (misidentification probability : < 1%)
25 Sep 2008 J.Maeda - Results on tau physics from HERA 29
Isolated tau leptons + PTmiss @ H1
W
H1prelim–07–064
25 Sep 2008 J.Maeda - Results on tau physics from HERA 30
Lepton Flavour Violation @ ZEUS
25 Sep 2008 J.Maeda - Results on tau physics from HERA 31
Limits for LQs in the channel @ H1/ZEUS
No candidate was found.Limits on LQ were set.
HERA–I e±p data L=130 pb–1
e+p data e–p data
Eur. Phys. J. C52 (2007) 833–847
Eur. Phys. J. C44 (2005) 463–479
No evidence for LFV
Data 0
SM 2.3±0.5
sel. eff. 22~30% ( )sM LQ
HERA–I e±p data L=80.2 pb–1
No evidence for LFV
H1 e–p: 13.7 pb–1, e+p: 66.5 pb–1
Data SM MC
ep Xe–p 0 0.75±0.21
e+p 1 4.90±0.85
No significant deviation from SM found.Limits were set on coupling to LQ leading to Lepton Flavour Violation.