{"id":31099,"date":"2025-07-01T23:29:14","date_gmt":"2025-07-01T23:29:14","guid":{"rendered":"https:\/\/www.europesays.com\/us\/31099\/"},"modified":"2025-07-01T23:29:14","modified_gmt":"2025-07-01T23:29:14","slug":"atlas-takes-a-breath-of-oxygen","status":"publish","type":"post","link":"https:\/\/www.europesays.com\/us\/31099\/","title":{"rendered":"ATLAS takes a breath of oxygen"},"content":{"rendered":"

The ATLAS Experiment at CERN dives into uncharted waters, recording its first-ever collisions of oxygen and neon ions. These are not your typical heavy-ion collisions. Oxygen and neon nuclei are far smaller than lead \u2013 the LHC\u2019s usual candidate for ion runs \u2013 and offer physicists exciting new opportunities to study the strong force.<\/strong><\/p>\n

Though best known for its high-energy proton\u2013proton collisions, the Large Hadron Collider (LHC) also collides heavy ions. These ions smash together to create quark-gluon plasma (QGP), a unique state of matter that existed shortly after the Big Bang. In the hot, dense state of the QGP, the strong force \u2013 which, in \u201ccold\u201d conditions, holds protons and neutrons together \u2013 begins to behave differently.<\/p>\n

Lead ions, with 82 protons and 126 neutrons, have long served as the LHC\u2019s go-to tool for generating QGP. Oxygen and neon ions, with just 8 and 10 protons and neutrons respectively, are expected to form smaller droplets of QGP when they collide, compared to those in lead collisions \u2013 offering a new pool of data for physicists to dive into.<\/p>\n

\u201cThese collision systems will let us investigate how the properties of the QGP emerge in relation to the system size,\u201d says Riccardo Longo, a physicist with the ATLAS heavy-ion group. \u201cWhile we understand the strong force well in \u2018cold\u2019 conditions, thanks to studies of proton\u2013proton collisions, and in extremely hot and dense environments like lead\u2013lead collisions, the question remains: what happens in between? We hope these lighter systems will let us connect the dots between the two.\u201d<\/p>\n

Oxygen and neon ions, with just 8 and 10 protons and neutrons respectively, are expected to form smaller droplets of QGP compared to lead-ion collisions \u2013 offering a new pool of data for physicists to dive into.<\/p>\n

\"Physics,ATLAS\"<\/a>Figure 1: Comparison of lead-lead (Pb+Pb), xenon-xenon (Xe+Xe), proton-lead (p+Pb) and oxygen-oxygen (O+O) collision system sizes. The ions or particles, represented by light blue and red circles, travel in opposite directions and collide to form systems of varying sizes, shown as solid blue and red circles. (Image: ATLAS Collaboration\/CERN)<\/p>\n

Not too big, not too small<\/p>\n

One of the first phenomena ATLAS physicists will be looking for is jet quenching, where high-energy particle jets lose energy as they traverse the QGP. The jets that emerge are some of the most powerful tools for studying the medium and the ATLAS experiment \u2013 purpose-built to measure high-energy jets \u2013 is uniquely suited to wield these tools.<\/p>\n

Jet quenching was one of the ATLAS Collaboration\u2019s first major observations<\/a> in the heavy-ion domain. It was later observed<\/a> in xenon\u2013xenon collisions but \u2013 critically \u2013 not in proton\u2013lead collisions, which form a much smaller QGP system (see Figure 1). So what\u2019s the tipping point?<\/p>\n

\u201cTheory predicts we should see the onset of jet quenching in oxygen\u2013oxygen collisions,\u201d explains Longo. \u201cIf we observe even modest suppression, it could pin down the critical system size at which jet quenching begins.\u201d<\/p>\n

Interestingly, physicists have observed strong collective flow \u2013 a collective motion of particles emerging from the QGP \u2013 in collision systems of many different sizes. Even in smaller systems, where signs of energy loss by quarks and gluons have faded, evidence of QCD\u2019s long-range, collective behaviour remains. By colliding light ions like oxygen, physicists can vary the initial conditions of the QGP\u2019s formation, providing insight into how collective behaviour develops over space and time. The degree of collectivity may also help uncover the complex geometrical structure of oxygen nuclei, which are thought to be a composition of four alpha particles.<\/p>\n

Neons bring a twist<\/p>\n

Though close in size to oxygen, theorists suggest<\/a> that neon ions have a bowling pin shape rather than the usual sphere (see Figure 2). This shape may impact the initial configurations of the ion collisions, providing new insights into the role of geometry in QGP formation.<\/p>\n

\u201cWhat\u2019s even better is that the oxygen and neon runs will be right after one another,\u201d says Qipeng Hu, ATLAS Heavy Ion Physics Group convenor. \u201cThis adds incredible value to the datasets when we do our comparison, as they\u2019ll have exactly the same experimental conditions.\u201d<\/p>\n

\"Physics,ATLAS\"<\/a>Figure 2: Comparison between an oxygen ion and a neon ion, showcasing the distinct \u201cbowling pin\u201d shape of the neon ion. (Image: Giacalone et al., arXiv:2402.05995)<\/p>\n

Aiming high<\/p>\n

The LHC will also collide oxygen ions with protons, providing an unexpected link between collider physics and cosmic rays. As high-energy particles from space hit the oxygen and nitrogen Earth\u2019s atmosphere, they produce \u201ccosmic ray\u201d showers of particles that are still not fully understood. By reproducing such interactions in laboratory conditions, scientists can better understand the composition of these showers. The LHCf experiment<\/a>, just downstream of the ATLAS interaction point, will use the particles produced in proton\u2013oxygen collisions in the proton-going direction for this purpose \u2013 providing valuable input for cosmic-ray experiments like AMS<\/a>, located on the International Space Station. LHCf will be aided by the ATLAS Zero Degree Calorimeter (ZDC) \u2013 also located downstream of the interaction point \u2013 which will greatly enhance detector precision when measuring near-beam neutrons.<\/p>\n

Proton\u2013oxygen collisions recorded by ATLAS will also provide crucial data for refining nuclear parton distribution functions (nPDFs) \u2014 theoretical inputs that describe how quarks and gluons are distributed inside a nucleus. Until now, the nPDFs for oxygen were based only on simulated data.<\/p>\n

Studies of these collisions will advance our understanding of the strong force and help shape the future of the LHC heavy-ion programme.<\/p>\n

All this, in just a few days<\/p>\n

The new ion run kicks off today, 1 July 2025, and concludes just over a week later, on 9 July 2025. To make the most of this rare opportunity, the ATLAS experiment has carefully adapted its data-taking strategy to match the fast-paced schedule.<\/p>\n

\u201cOne of our biggest challenges was working out how we could maximise our recorded data,\u201d says Tomasz Bold, ATLAS Heavy Ion Physics Group convenor. \u201cWorking together with trigger, data acquisition and data preparation experts, we\u2019ve managed to increase the experiment\u2019s data bandwidth by nearly 50%. Instead of sending the collision data to the CERN Computing Centre immediately, we temporarily store it locally at the experiment during each fill, and only transfer it afterward.\u201d To support this, they also developed new event-selection protocols (\u201ctriggers\u201d) that carefully balance the search for rare physics signals with the need to keep an unbiased sample of events.<\/p>\n

Another key preparation for this run was the installation of the ZDC. The ZDC measures neutral particles that emerge close to the beamline, particularly \u201cspectator neutrons\u201d originating from the evaporation of the non-overlapping regions of the colliding nuclei. For proton\u2013oxygen and oxygen\u2013oxygen data-taking, the ZDC will play a particularly important role in monitoring the beam composition in real time. By analysing the evolution of newly implemented ZDC triggers corresponding to different neutron topologies, experts will be able to estimate any beam contamination due to transmutation<\/a> and adjust data-taking on the fly.<\/p>\n

Getting it right matters. The data gathered during this brief run has the potential to impact the heavy-ion community for years to come. \u201cThis special run is a great example of how different physics communities can benefit from the unique flexibility of the LHC,\u201d concludes Longo. \u201cFrom heavy-ion to cosmic-ray physicists, there is deep and diverse physics potential in these data. Studies of these collisions will advance our understanding of the strong force and help shape the future of the LHC heavy-ion programme.\u201d<\/p>\n

About the image banner: First proton\u2013oxygen collisions Event display of a proton\u2013oxygen collision event recorded in ATLAS on 1 July 2025. (Image: ATLAS Collaboration\/CERN)<\/p>\n

Learn more<\/p>\n","protected":false},"excerpt":{"rendered":"The ATLAS Experiment at CERN dives into uncharted waters, recording its first-ever collisions of oxygen and neon ions.…\n","protected":false},"author":3,"featured_media":31100,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[25],"tags":[26353,26371,6753,26351,18187,3213,807,10019,9416,21744,26369,4060,26362,26367,26366,26364,26363,26359,810,26355,26370,808,809,26354,26357,813,26368,492,159,26358,26356,26365,26361,26360,16997,26352,67,132,6747,68],"class_list":{"0":"post-31099","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-physics","8":"tag-alice","9":"tag-andreas-hoecker","10":"tag-atlas","11":"tag-atlas-experiment","12":"tag-big-bang","13":"tag-black-hole","14":"tag-cern","15":"tag-cms","16":"tag-collaboration","17":"tag-dark-matter","18":"tag-david-charlton","19":"tag-experiment","20":"tag-extra-dimensions","21":"tag-fabiola-gianotti","22":"tag-geneva","23":"tag-hadron","24":"tag-heavy-ion","25":"tag-higgs","26":"tag-high-energy-physics","27":"tag-international-collaboration","28":"tag-karl-jakobs","29":"tag-large-hadron-collider","30":"tag-lhc","31":"tag-lhcb","32":"tag-particle","33":"tag-particle-physics","34":"tag-peter-jenni","35":"tag-physics","36":"tag-science","37":"tag-science-education","38":"tag-scientific-collaboration","39":"tag-stem","40":"tag-supersymmetry","41":"tag-susy","42":"tag-switzerland","43":"tag-the-atlas-experiment","44":"tag-united-states","45":"tag-unitedstates","46":"tag-universe","47":"tag-us"},"share_on_mastodon":{"url":"","error":"Validation failed: Text character limit of 500 exceeded"},"_links":{"self":[{"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/posts\/31099","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/comments?post=31099"}],"version-history":[{"count":0,"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/posts\/31099\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/media\/31100"}],"wp:attachment":[{"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/media?parent=31099"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/categories?post=31099"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.europesays.com\/us\/wp-json\/wp\/v2\/tags?post=31099"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}