Discovering Heavy New Physics in Boosted $Z$ Channels: $Z \rightarrow l ^+l^- $ vs. $ Z \rightarrow \nu \bar{\nu}$

1.1 MB·English

by  Mihailo Backović

Discovering heavy new physics in boosted Z channels: Z → l+l− vs Z → νν¯
Mihailo Backovi´c,1 Thomas Flacke,2 Jeong Han Kim,2,3 and Seung J. Lee2,4
1Center for Cosmology, Particle Physics and Phenomenology - CP3,
Universite Catholique de Louvain, 2 Chemin du Cyclotron, Louvain-la-Neuve, Belgium
2Department of Physics, Korea Advanced Institute of Science and Technology,
335 Gwahak-ro, Yuseong-gu, Daejeon 305-701, Korea
3IBS Center for Theoretical Physics of the Universe,
70, Yuseong-daero 1689-gil, Yuseong-gu, Daejeon, Korea
4School of Physics, Korea Institute for Advanced Study,
85 Hoegiro, Dongdaemun-gu, Seoul 130-722, Korea
(Dated: August 5, 2015)
WeproposeastrategyfornewphysicssearchesinchannelswhichcontainaboostedZbosonanda
boostedmassivejetinthefinalstate. Ourproposalexploitsthepreviouslyoverlookedadvantagesof
5
boosted Z →νν¯ topologies, where collimated neutrinos result in signals with large missing energy.
1
We illustrate the advantage of this channel in a case study of singly produced TeV scale charge
0
2/3 fermionic top partners (T(cid:48)) which decay to tZ final states. A comparison with the di-leptonic
2
channel reveals that, despite the large tt¯background, signals with missing energy combined with

g jet substructure techniques offer superior probes of new physics at TeV scales. The effect can be
u attributed to a factor of ∼ 3 enhancement in the signal cross section, coming from the branching
A ratioofZ →νν¯. Weexploittheuniqueeventtopologyofsinglyproducedtoppartnerstosuppress
the tt¯background, as well as further improve on the existing proposals to detect T(cid:48) in the boosted
4
di-lepton channel. Our conclusions on advantages of Z → νν¯ can be extended to most resonance

searches which utilize a boosted Z boson in the final state.
]
h
p
- I. INTRODUCTION to E/T (Zinv) accompanied by a boosted massive jet sat-
p isfies this criterion, when the mass scale of new physics
e New physics searches in channels containing a Z bo-
is above 1 TeV.
h son in the final state are an important part of the LHC
[ physics program, with WZ and hZ productions being TheZinv channelwasnotusedinLHCRunIanalyses,
as exploration of the mass scales of O(100) GeV focused
3 some of the important probes of the Standard Model
on Z events with low boost. The large angles between
v (SM). In the context of new physics searches, Z boson
6 the neutrinos hence resulted in missing energy signals
productionaccompaniedbyah, W ortopquarkarealso
5 which were too low to be efficiently used for background
important. Such final states appear (for example) in the
4 discrimination. However, with a large enough boost of
7 decays of charge 2/3 vectorlike top quark partners (T(cid:48)),
the Z, the Z channel becomes relevant for Run II.
0 which emerge as generic features in many models that inv
The utility of missing transverse energy has been dis-
. address the hierarchy problem within the framework of
1 cussed for the VH production in a boosted regime [7] as
0 Naturalness [1–4].
well as the searches for Kaluza-Klein gravitons [8] in the
5 AtthedawnofLHCRunII,anaturalquestiontoaskis
ZZ → E/ l+l channel. Here, we consider the Zt chan-
1 whichoftheZ decaymodeswillbethemostsensitiveto T −
: nel where the top decays hadronically [28] and system-
v newphysicsattheTeVscale. Conventionalwisdomtells
atically compare the leptonic and the invisible Z decay
i us that leptons offer clean signals with low backgrounds.
X modes.
For instance, T decaying into tZ is a primary option
(cid:48)
r The core of our proposal is an observation of several
a for most experimental searches, where Z decaying into
important qualitative changes in the phenomenology of
di-leptons has so far been the most sensitive channel [5].
LHC Run II.
Recently, Ref. [6] also proposed a search strategy for
singly produced T in a boosted di-lepton channel for First, for mass scales (cid:38) 1 TeV, the SM decay prod-
(cid:48)
Run II of the LHC. While leptons are convenient final ucts of heavy new particles become highly boosted. It
states, branching ratios of heavy SM states to leptons follows that boosted Zs expected at Run II will decay
are small, and there is always a lower limit on the signal intocollimatedneutrinosandhencelargemissingenergy
production cross section (and hence an upper limit on signatures (i.e., in resonance searches one could expect
the mass scale) which can be probed by leptons at fixed signatures of E/T ∼Mres/2).
integrated luminosity. Second, standard jet reconstruction techniques and
In the initial stages of LHC Run II, it hence might leptonisolationswillnotbeadequateandtoolsofjetsub-
be desirable to look for alternative search channels with structure and alternative lepton isolation variables will
larger signal cross section and reasonably small back- have to be employed.
grounds, in order to improve the prospects of an early Third,theboostedregimewillbecharacterizedbydif-
discovery. In this paper, we will show that Z decaying ferent efficiencies for reconstruction and tagging of the
2
q¯
q
q
q W b Vtb < 0.92
t
W T λ
b λ
Z
λ
g ¯b l+/ν
l−/ν
FIG. 1: Single production channel for a T(cid:48) decaying into tZ.
FIG.2: SingleproductioncrosssectionforT(cid:48) oritsconjugate
t,Z,W,h decay channels. As a result, experimental sen- decaying into tZ (or t¯Z) in the sample model described by
Eq. (1), for various values of λ with f =780 GeV.
sitivity in different decay modes to new physics searches L
will change compared to Run I. At the same time, SM
backgrounds for signatures of very highly boosted ob-
jects (e.g. very high-p jets, leptons, di-leptons, large
T
E/T, etc.) fall much faster than the signal, implying an L ⊃ T¯˜(cid:0)iD/ −M1(cid:1)T˜+q¯LiD/qL+t¯RiD/tR (1)
alteredbackgroundrejectionpowerforthedifferentchan-
(cid:18) λ fsin(h¯/f) (cid:19)
nels. − λ fcos(h¯/f)t¯ T˜ − L √ t¯ T˜ +H.c. ,
R R L L R
T models are an excellent example of studies where 2
(cid:48)
the boosted Z regime will be relevant in the future LHC
whereh¯ =v+h,f istheHiggscompositenessscale,M is
runs. Past studies of ATLAS [9] and CMS [10] estab- 1
the single mass scale and T˜ denotes the gauge eigenstate
lished bounds on mass of the vectorlike top partners, ex-
of the top partner while T denotes the mass eigenstate.
cluding states with mass lighter than ∼ 700−800 GeV (cid:48)
WeconsideronlyT production,whichdominatesover
(with the precise bound depending on the T branch- (cid:48)
ing fractions). Run II of the LHC will thus p(cid:48)robe the T(cid:48) pair production for high MT(cid:48) due to larger phase
space. For exactly what mass single production be-
TeV mass range, where the boosted regime will become
comesdominantismodeldependent,butinmanymodels
important. For concreteness, here we consider T single
productionwithsubsequentT →tZ decayforwh(cid:48)ichthe this occurs around MT(cid:48) (cid:39) 1 TeV for natural parameter
(cid:48) choices (i.e. only slightly above the scale up to which
processshowninFig.1yieldsthedominantcontribution.
Run I is sensitive).
Inthefollowing,weshowthatconsiderationsofE/ sig-
T The results of our analysis depend on MT(cid:48) and σT(cid:48) ≡
nals greatly extend the ability of Run II of the LHC to σ(pp→T /T¯ +X)×BR(T →tZ),theproductioncross
(cid:48) (cid:48) (cid:48)
discover possible new physics in the boosted Z channel.
sectionoftheT timesthebranchingfractionofT →tZ
(cid:48) (cid:48)
Although we use T searches for the purpose of illustra-
(cid:48) (provided that the width of T is small), while the de-
(cid:48)
tion, our main conclusion that at sufficiently high boost
pendence of the event kinematics on specific model pa-
Z searches will outperform the Z searches is valid in
inv ll rametersissmallenoughtobeneglected. Forillustration
a more general sense and qualitatively applies to many
and completeness, Fig. 2 shows σT(cid:48) in our sample model
physics searches which utilize a boosted Z boson in the
as a function of MT(cid:48) for several values of λL. The two
final state.
points marked by a star are sample points which we use
in our later analysis [29]. The shaded region in Fig. 2 is
excluded by the direct bound |V |>0.92 obtained from
tb
II. SAMPLE MODEL AND EVENT single-topsearches[12].[30]Thislatterboundonthepro-
SIMULATIONS ductioncrosssectionappliestoourspecificsamplemodel
only, while it can be relaxed in composite Higgs models
For the purpose of event simulation, we use the min- with different top partner representations or other vec-
imal composite Higgs model with a partially composite torlikequarkmodelswithtwoormorepartnermultiplets.
top (cf. Ref.[11] for the model Lagrangian, parameter In the following, we present results in terms of MT(cid:48) and
definitions and the detailed derivation of the interac- σT(cid:48) rather than the input parameters M1,λL,f in order
tions.) In the singlet-partner-limit, the model contains to maintain a minimum of model dependence.
only one light vectorlike top partner: an SU(2) singlet We simulate signal and backgrounds with leading or-
L
with charge 2/3. The top-partner sector of the model is der MADGRAPH 5 [13] (using NNPDF2.3LO1 PDFs [14]
described by the effective Lagrangian interfaced with PYTHIA 6 [15] for parton showering and
hadronization,whileweconservativelyassumeak-factor
3
of 2 for all background channels. We match the back- jetwithinthefatjet(∆R <1.0). Weassumeb-tagging
tb
ground samples to extra jets using the 5 flavor so-called efficienciesof75%foreverybjettobetaggedasab,with
MLM [16] matching scheme. afakerateof18%and1%forcandlightjetsrespectively.
We further utilize the fact that the spectator light jet
in thesignal events is typically emitted at low |η|, a very
specialfeatureofsinglyproducedT eventtopology. For
(cid:48)
Onthepartonlevel,wegeneratetheeventswithsimple
the purpose of “forward jet tagging” we recluster the
generationlevelcutsonleptons(p >10GeV,|η|<2.5,
T events with a cone radius r = 0.2 and demand at least
∆R > 0.1 (0.4)) for the Z (Z ) channel and quarks
ll ll inv oneforwardjetwithpfwd >25GeVand2.5<ηfwd <4.5
(p >15GeV,|η|<5,∆R >0.1). Wethenclusterthe T
T jj (see Refs.[11, 25] for a discussion and evaluation of this
showered events using the FASTJET [17] implementation
forward-jet-tagging procedure).
of the anti-kT algorithm [18], where we use R = 1.0 for
In the Z channel, we impose a strong cut of E/ >
“fat jets”, r =0.4 for the light and b-jets and r =0.2 for inv T
400GeV(600GeV)fortheMT(cid:48)=1TeV(1.5TeV)search.
forward jets.
The tt¯background of the invisible Z channel can be fur-
ThemainbackgroundsfortheE/ channelareSMpro-
T ther suppressed by demanding the reconstructed E/ to
cesses containing a Z boson in the final state, as well as T
be isolated from any hard jets by |∆φ |>1.
the SM tt¯production. The “Z-containing” backgrounds E/Tj
includeZ+t,characterizedbyatrueZ andatopquark,
whereweincludeZtt¯andZt/t¯(withuptotwoextrajets)
into our simulation. Similarly, we define Z +X back- IV. RESULTS
ground to be SM events which contain a Z and “fake”
(hadronic) top signal. In this class, we include Z, Zb¯b, Table I shows an example cut flow. The sample signal
cross sections given correspond to the parameter point
Z + Z/W with up to two additional jets. Finally, we
include tt¯background with up to two additional jets. (f = 780 GeV,M1 = 810 GeV,λL = 2.1,λR = 0.67)
for the 1 TeV partner search and (f = 780 GeV,M =
Di-lepton channels are afflicted by similar SM back- 1
grounds, with the exception of tt¯which is effectively ve- 1.3 TeV,λL = 3,λR = 0.7) for the 1.5 TeV partner
search. These parameter points yield a large produc-
toed by requiring two hard leptons which reconstruct a
tion cross section within the model defined by Eq.(1),
Z mass, small missing energy.
representing optimistic scenarios in the searches for T
(cid:48)
channels.
III. T SEARCH STRATEGY FOR LHC RUN Our analysis shows that jet substructure techniques
(cid:48)
II (Ovt) in conjunction with fat jet b-tagging efficiently di-
3
minishtopquarkfreebackgroundchannels(e.g. Z+X).
We choose the cut schemes for the T(cid:48) search in t+j+ For the Zinv search, the E/T cut becomes a crucial dis-
Zinv and the t+j+Zl¯l channels to be identical for cuts criminant,inparticularfortt¯background,withthefactor
focusedonthet+j partoftheeventinordertoallowfor of ∼10 (∼20) improvement in signal to background ra-
a fair comparison. As a part of the “basic cuts”, we de- tio (S/B) in the 1 TeV (1.5 TeV) search. Forward jet
mand at least one fat jet with pfj >400 GeV (600 GeV) tagging provides a significant improvement in both, Z
T inv
fortheMT(cid:48)=1TeV(1.5TeV)searcheswith|ηfj|<2.5as and Zll channels, where we find a factor of ∼4 improve-
well as pjT > 25 GeV for light, b, and forward jets. For ment in S/B. For MT(cid:48) = 1 TeV, the performance of
the Zinv channel, we furthermore require absence of any the Zinv channel√is comparable to Zll, in terms of signal
isolated leptons (mini-ISO >0.7 [19]) with pl >25 GeV significance (S/ B), with the former yielding a larger
T
whilefortheZ channelweinsteadfollowamodifiedpre- signal cross section, but the latter giving a better S/B.
ll
scriptionofRef.[6],requiringatleasttwoisolatedleptons If we go to higher masses, such as MT(cid:48) = 1.5 TeV, Ta-
with pl >25 GeV. The two hardest leptons are then re- ble I already suggests that the Z channel outperforms
T inv
quired to reconstruct a leptonic Z boson candidate. We di-leptons.
demand pz > 225 GeV and |η | < 2.3. Finally, for the Figure3illustratestheresultsinamorecompletefash-
T z
Z -channel, we demand ∆R <1.0 and |m −m |<10 ion. Results for the Z and Z searches are given in
ll ll ll Z inv ll
GeV. the top and bottom panel for MT(cid:48) = 1 TeV (left) and
For top identification we follow a procedure analogous MT(cid:48) = 1√.5 TeV (right). In each plot, the solid contours
to Ref. [11], based on the TEMPLATE TAGGER v.1.0 [20] show S/ B, while the dotted lines show the number of
implementation of the template overlap method [21–24]. signal events after cuts, as a function of luminosity and
For a R=1.0 jet to be tagged as a “top,” we demand a σT√(cid:48). The shaded areas show regions where we expect
3 body top template overlap score of Ovt >0.6. S/ B ≥5 and at least ten signal events. Both the Z
3 inv
We require every fat jet which passes the top selection and the Z channels yield comparable discovery poten-
ll
criteria to also be b-tagged, whereby we define a “fat tial for top partners with masses of ∼ 1 TeV, assuming
jet b-tag” as presence of at least one b-tagged r = 0.4 efficient forward jet tagging from the previous section.
4
Z →νν¯ MT(cid:48) =1.0 TeV search√ MT(cid:48) =1.5 TeV search √
Signal tt¯ Z+X Z+t S/B S/ B(100fb−1) Signal tt¯ Z+X Z+t S/B S/ B(100fb−1)
Basic cuts 3.5 900 6100 11 0.00050 0.42 1.0 140 1200 2.4 0.00074 0.27
Ovt >0.6 2.7 510 840 6.5 0.0020 0.75 0.87 81 230 1.6 0.0028 0.49
3
b-tag 2.0 320 16 4.3 0.0057 1.1 0.54 45 3.2 0.94 0.011 0.77
E/ -cut 1.3 13 5.3 0.89 0.065 2.9 0.41 1.00 0.78 0.14 0.21 3.0
T
N ≥1 0.79 2.6 0.74 0.27 0.22 4.1 0.28 0.20 0.11 0.041 0.80 4.7
fwd
∆φ >1.0 0.66 0.94 0.58 0.22 0.38 5.0 0.22 0.076 0.083 0.033 1.2 5.1
E/T,j
Z →l+l− MT(cid:48) =1.0 TeV sear√ch MT(cid:48) =1.5 TeV sear√ch
Signal Z+X Z+t S/B S/ B(100fb−1) Signal Z+X Z+t S/B S/ B(100fb−1)
Basic cuts 1.1 750 1.3 0.0014 0.39 0.30 170 0.36 0.0018 0.23
Ovt >0.6 0.71 71 0.61 0.010 0.85 0.24 19 0.14 0.012 0.54
3
b-tag 0.52 1.6 0.42 0.25 3.6 0.15 0.36 0.086 0.33 2.2
∆R <1.0 0.52 1.6 0.41 0.26 3.6 0.15 0.36 0.086 0.33 2.2
ll
|m −m |<10 GeV 0.47 1.5 0.37 0.26 3.5 0.13 0.33 0.078 0.32 2.1
ll Z
N ≥1 0.29 0.23 0.11 0.88 5.1 0.088 0.051 0.019 1.3 3.3
fwd
TABLE I: Example-cutflow for signal- and background events in the Z +t+j search (top) and in the Z +t+j channel
√ inv ll √
(bottom) for s = 14TeV. Cross sections after the respective cuts for signal and backgrounds are given in fb. The S/ B
values are given for a luminosity of 100fb−1. The example signals σT(cid:48) ≡σ(pp→T(cid:48)/T¯(cid:48)+X)×BR(T(cid:48) →tZ) displayed here
are 80fb for M(cid:48) =1.0 TeV searches and 24fb for M(cid:48) =1.5 TeV searches. The corresponding parameter points of our sample
T T
model are given in the text.
MT'=1.0 TeV MT'=1.5 TeV
10.0 5.0
102 Nev 102 Nev
−1b) 5.0 100 −1b) 0.5 10 3.0 1.0
L(f 3.0 0.5 L(f 1 1.0
1 1.0
Z → vῡ Z → vῡ
101 MadGraph + Pythia 101 MadGraph + Pythia
No pileup No pileup
10
0 50 100 150 0 5 10 15 20 25
σT×Br(T'→tZ)[fb] σT×Br(T'→tZ)[fb]
MT'=1.0 TeV MT'=1.5 TeV
10
5.0
100
102 Nev 10.0 102 Nev
3.0
−1L(fb) 0.5 3.0 1.0 5.0 −1L(fb) 1 0.5 1.0 1.0
1 1.0
Z → l +l- 10 Z → l +l-
101 MadGraph + Pythia 101 MadGraph + Pythia
No pileup No pileup
0 50 100 150 0 5 10 15 20 25
σT×Br(T'→tZ)[fb] σT×Br(T'→tZ)[fb]
FIG√.3: ReachofRunIIfordiscoveringT(cid:48) statesofMT(cid:48) =1TeV(left)andMT(cid:48) =1.5TeV(right). Shadedregions,signifying
S/ B > 5 and number of signal events N > 10, illustrate the discovery reach of LHC Run II. The reference model points
ev
from Table I are marked with a star. The horizontal dashed line in each plot marks the benchmark integrated luminosity of
100fb−1. The reference production cross sections on the x axis assume a lower cut of pj >15 GeV, for the spectator quarks.
T
√
For a luminosity of 100 fb 1 (dashed horizontal line), S/ B ≥ 5 with N > 10 signal events. A comparison of
−
optimistic cross sections of σT(cid:48) (cid:38)80 fb can be probed at shaded areas in the left panels of Fig. 3 shows that the
5
missing energy channel becomes important at MT(cid:48) ∼ 1 defines the interaction of the heavy resonance with the
TeV, where inclusion of the Z channel in this mass Z can affect the kinematic distributions (i.e. spin cor-
inv
range would greatly complement the di-lepton searches. relations), but these are typically subleading effects. It
Probing masses higher than 1 TeV yields a different hence follows that in a fairly generic scenario of heavy
scenario, as shown in the right panels of Fig. 3 for the resonance decays, there always exists a resonance mass
caseofMT(cid:48) =1.5TeV.ApartnerofmassMT(cid:48) =1.5and range in which Z → νν¯ channel will be more sensitive
a cross section σT(cid:48) =24fb can be discovered in the Zinv than Z →l+l−.
channel with 100fb−1, whereas approximately 200fb−1 Ouranalysissuggeststhatchannelswithlargemissing
would be required in the Zll channel to become sensitive energy will be more sensitive to discovery of vectorlike
to the same cross section. Considerations of lower sig- toppartnersof∼TeVmassscaleatlowintegratedlumi-
nal cross sections yield the same conclusion, as the Zinv nosity. Incaseasignalisobserved,thedi-leptonchannel
channel gives both better sensitivity and a higher num- will still be important for accurate measurements of the
ber of signal events at a fixed luminosity over the entire resonanceproperties,inparticularitsreconstructedmass
space of reasonable signal cross sections. and its spin. Due to the superior ability of ATLAS and
CMS to reconstruct and measure leptons, compared to
missing energy reconstruction, it is likely that the di-
V. CONCLUSIONS
lepton channel will provide better measurements of the
WediscussedtheLHCRunIIpotentialtodiscovernew T(cid:48) mass. However,pastexperiencehasshownthatmeth-
heavy physics in the boosted Z + fat jet channel. As an ods employing kinematic edges, such as mT2 [26], could
illustration, we focused on t+j+E/ and the t+j+ di- result in competitive mass measurements in channels in-
T
lepton search channels for a vectorlike top partner T volving large missing energy. As here we were interested
(cid:48)
decaying into tZ which occurs in a large class of SM mostlyinprospectsfordiscoveryofnewphysics,wechose
extensions. to postpone the comparative analysis of mass measure-
Our main conclusion is that future considerations of ments for future analyses.
the Z channel in searches for new physics in the Effectsofpileupcontaminationshouldbeconsideredin
inv
Z+t,h,W channel will greatly extend the ability of the future analyses, especially considering the high instanta-
earlyLHCRunIItodiscoverpossiblenewparticlesatthe neousluminosityexpectedforRunII.However, worksof
TeV scale. The di-lepton channel maintains competitive Refs. [11, 24] have shown that effects of pileup on E/ ,
T
sensitivityforMT(cid:48) ≈1TeV,withahigherS/B butlower Ov3t, forward jet tagging and b-tagging can be effectively
signalcrosssection. Thesituationchangesrapidlyabove mitigated, even at 50 interactions per bunch crossing,
1 TeV. At MT(cid:48) ≈ 1.5 TeV, we show that the Zinv chan- without requiring exotic pileup subtraction techniques.
nel displays clear superior performance in prospects for Wehenceexpectourconclusionstoberobustevenwhen
discovering the T states, with both larger signal signifi- considering high pileup levels.
(cid:48)
cance and number of events. The di-lepton channel still
remainsimportant,astheeventreconstructioncapability
usingleptonshasanadvantageoverlargemissingenergy.
ACKNOWLEDGMENTS
The discovery reach can be further improved by combin-
ing the two channels. Furthermore, we show that the
discovery potential can be substantially improved by de- The authors would like to thank the Weizmann
manding a high-energy forward-jet tagging in both Z theory group and the organizers of the Naturalness
inv
and Z channels. 2014 workshop for the hospitality during the initial
ll
Our results are a direct consequence of the fact that stages of this project. This work was supported
for M (cid:38) 1 TeV, kinematics of boosted Z decays allow by the National Research Foundation of Korea(NRF)
T(cid:48)
for efficient use of channels with high E/ . A high E/ grant funded by the Korea government(MEST) (No.
T T
cut efficiently removes the tt¯background in the t+E/ 2012R1A2A2A01045722), and Basic Science Research
T
channel, while forward jet tagging greatly improves the Program through the National Research Foundation of
performance in both channels. Korea(NRF) funded by the ministry of Education, Sci-
We base our conclusions on an example study of ence and Technology (No. 2013R1A1A1062597). This
searchesforcharge2/3vectorlikequarks,butthequalita- work is also supported by HTCaaS group of KISTI (Ko-
tiveargumentappliesmorebroadlytosearchesforheavy rea Institute of Science and Technology Information). S.
resonances in channels containing a boosted Z boson in L.andT.F.arealsosupportedbyKorea-ERCresearcher
the final state. The kinematics of heavy resonance de- visiting program through the National Research Foun-
caysingeneralaremainlydeterminedbythemassofthe dation of Korea(NRF) (No. 2014K2a7B044399 and No.
resonance,whilethemodeldependentdetailsofcoupling 2014K2a7A1044408). M. B. is in part supported by the
strength and spin of the resonance only affect the over- Belgian Federal Science Policy Office through the Inter-
all production rate. The structure of the vertex which university Attraction Pole P7/37.
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