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Globular clusters (GCs) are established emitters of high-energy (HE, 100MeV<E<100 GeV) \gamma-ray radiation which could originate from the cumulativeemission of the numerous millisecond pulsars (msPSRs) in the clusters' cores orfrom inverse Compton (IC) scattering of relativistic leptons accelerated in theGC environment. GCs could also constitute a new class of sources in thevery-high-energy (VHE, E>100 GeV) \gamma-ray regime, judging from the recentdetection of emission from the direction of Terzan 5 with the H.E.S.S.telescope array.  To search for VHE \gamma-ray sources associated with other GCs, and to putconstraints on leptonic emission models, we systematically analyzed theobservations towards 15 GCs taken with H.E.S.S. We searched for individualsources of VHE \gamma-rays from each GC in our sample and also performed astacking analysis combining the data from all GCs to investigate the hypothesisof a population of faint emitters. Assuming IC emission as the source ofemission from Terzan 5, we calculated the expected \gamma-ray flux for each ofthe 15 GCs, based on their number of millisecond pulsars, their opticalbrightness and the energy density of background photon fields.  We did not detect significant emission from any of the 15 GCs. The obtainedflux upper limits allow to rule out the simple IC/msPSR scaling model for NGC6388 and NGC 7078. The upper limits derived from the stacking analyses arefactors between 2 and 50 below the flux predicted by the simple leptonic model,depending on the assumed source extent and the dominant target photon fields.Therefore, Terzan 5 still remains exceptional among all GCs, as the VHE\gamma-ray emission either arises from extra-ordinarily efficient leptonicprocesses, or from a recent catastrophic event, or is even unrelated to the GCitself.

Search for Very-high-energy gamma-ray emission from Galactic globular clusters with H.E.S.S