$\frac{dE}{dx }$ searches for long-lived charged particles

by Daniele Teresi (CERN), Leonardo Rossi (INFN e Universita Genova (IT)), Ismet Siral (CERN)

Thursday 1 Sept 2022, 11:00 → 12:00 Europe/Zurich

4/3-006 - TH Conference Room (CERN)

In the first part of the talk the results presented in the recent ATLAS paper "Search for heavy, long-lived, charged particles with large ionisation energy loss in pp collisions at $\sqrt{S}$ =13 TeV using the ATLAS experiment and the full Run 2 dataset"  (arXiv:2205.06013) will be discussed by Ismet Siral and Leonardo Rossi.

The analysis presented in this article is focused on the search for particles that are expected to move significantly slower than the speed of light and should be identifiable by their high transverse momenta and anomalously large specific ionisation losses. The discussion will be aimed at discussing and understanding the excess that has been reported in this paper. 

Then, in the second part of the talk, Daniele Teresi will show how this excess can be explained without conflicting with the determination of β from ionisation and time-of-flight measurements. In this interpretation, the large ionisation signal is due to boosted charge-two long-lived particles. This scenario provides, in addition, complementary signals that will be probed in the near future at the LHC.

Daniele -- bio

Daniele Teresi is a theoretical physicist working at CERN. After his PhD at the University of Manchester he worked at the Université Libre de Bruxelles and at the University of Pisa, before joining CERN in 2020. His research interests span several aspects of BSM physics, as well as particle cosmology and astroparticle physics.

Ismet -- bio

Ismet Siral is a particle physicist working for the ATLAS experiment as a CERN fellow. I have been part of the ATLAS collaboration since 2011. He did his Ph.D. at University of Michigan and prior to that he did his masters at Bogazici University. Between 2019-2022 he worked as a Post-Doc at University of Oregon. His research interests lies in long-lived particles and Standard Model electroweak physics. He is also an active contributor to the ATLAS ITk project (upgrade to ATLAS inner tracker and BCM detectors).

Leonardo -- bio

My career as a physicist is “detector driven”. As soon as I have been able to decide myself which experiments to do I have been involved in (or I have directed) experiments using precision silicon detectors trying to get the maximum physics out of them, sometimes also with non conventional approaches.

At the infancy of the microstrip detectors I have directed two experiments WA82 and WA92. Both had a “large” (for the standards of the 80’s) silicon microstrip telescopes. WA82 was characterized by a specially designed secondary vertex triggering capability. WA92 was characterized by a kind of “silicon bubble chamber” conceived to disentangle the complex b- hadron decay topologies. I was the proponent of both ideas which were at the heart of the two experiments and I have myself taken active part in the design and operation of the trigger telescopes and of the “silicon bubble chamber”. With these experiments hadroproduction of charm and beauty hadrons has been studied in an energy regime where this was difficult (especially for beauty).

I have also taken part in the infancy of the Pixel detectors working in the RD19 collaboration first and in the WA97 experiment later. In WA97 the first “large” (again for the standards of the 90’s) Pixel detector has been used to measure the strangeness content in interactions to search for quark- gluon plasma formation.

I’m in the ATLAS experiment since the early 90’s and, again, I have taken an active part in the design, construction, integration and commissioning of the tracker. I have joined the ATLAS Pixel project in 1993 and I have contributed to enlarge and shape the collaboration behind this project. I have been elected Project Leader of the Pixel Detector from 1997 to 2005, and of the whole Inner Detector from 2005 to 2009. From 2009 to 2013 I have been ATLAS National Contact Physicist for Italy.

In the last years I have shared my research time between the ATLAS Upgrade program for the High-Luminosity LHC and two physics analyses. Both these analyses (R-hadron search through Pixel specific ionization and Higgs in b-bbar in Vector Boson Fusion processes) use the tracker information as main ingredient. Limits on the R-hadron mass and on the cross-section for H→bbar have been published. Among the ATLAS Upgrade projects I have dedicated my time to the new tracker (ITk), with emphasis on the innermost pixel detector.

From 2014 to 2017 I have been elected Chair of the ITk Collaboration board and I have contributed to shape the collaboration, now of more than 100 labs, and bring the project to the presentation of the first TDR for the ATLAS Upgrade.

I’m currently sharing my working activity between the ITk Upgrade (I’m chair of the ITk referee group of the ATLAS Project Office) and the search for long lived heavy charged particles predicted by several SUSY models. I have proposed the search strategy based on the measurement of the pixel specific ionization as indicator of heavy charged particles. This search started ~10 years ago with a small Genoa group and has now grown to a sizeable international collaboration providing state of the art results in the field.

I have been in the IAC of the conference series “Heavy quarks at fixed target” from 1993 to 2000.  I have started the series of workshop on Pixel detectors in 2000 and I’m in the IAC of these workshops since then.

I’m the author of the book “Pixel Detectors from Fundamentals to Applications” Springer, 2006, together with P. Fischer, T. Rohe and N. Wermes.

I’m referee of several scientific journals, and of European and National and International (ERC, SNSF) projects in High Energy Physics or in detector related studies.

have been member of international scientific committees (PSSC and DRDC of CERN and the BaBar technical committee of SLAC) I have made my career in INFN (with several leaves of absence at CERN) and as Research Director since 1998.