{"id":9603,"date":"2021-11-15T11:16:05","date_gmt":"2021-11-15T10:16:05","guid":{"rendered":"https:\/\/www.pi.infn.it\/?p=9603"},"modified":"2021-11-15T11:16:05","modified_gmt":"2021-11-15T10:16:05","slug":"ultra-low-mass-drift-chambers-the-experience-of-the-meg-ii-positron-tracker-marco-chiappini-infn-pisa","status":"publish","type":"post","link":"https:\/\/www.pi.infn.it\/?p=9603","title":{"rendered":"Ultra-low mass drift chambers: the experience of the MEG II positron tracker (Marco Chiappini – INFN Pisa)"},"content":{"rendered":"\n

Abstract<\/span>
In<\/span> the<\/span> quest<\/span> for<\/span> the<\/span> Lepton<\/span> Flavour<\/span> Violation<\/span> (LFV)<\/span> the<\/span> MEG<\/span> experiment<\/span> at<\/span> the<\/span> Paul<\/span> Scherrer <\/span>Institut (PSI) represents the state of the art in the search for the charged LFV<\/span> \u03bc<\/span>+<\/span> \u2192<\/span>e<\/span>+<\/span>\u03b3<\/span> decay.<\/span>
MEG<\/span> set<\/span> the<\/span> most<\/span> stringent<\/span> upper<\/span> limit<\/span> on<\/span> the<\/span> BR(<\/span>\u03bc<\/span>+<\/span> \u2192<\/span> e<\/span>+<\/span>\u03b3<\/span>)<\/span> \u2264<\/span> 4<\/span>.<\/span>2<\/span> \u00d7<\/span> 10<\/span>\u2212<\/span>13<\/span> (90%<\/span> C.L.), <\/span>imposing<\/span> one<\/span> of<\/span> the<\/span> tightest<\/span> constraints<\/span> on<\/span> models<\/span> predicting<\/span> LFV-enhancements<\/span> through<\/span> new <\/span>physics beyond the Standard Model.<\/span> An upgrade of MEG, MEG II, was designed and it recently <\/span>started the first physics data taking,<\/span> aiming at reaching a sensitivity level of 6<\/span> \u00d7<\/span>10<\/span>\u2212<\/span>14<\/span>.<\/span> In order <\/span>to<\/span> reconstruct<\/span> the<\/span> positron<\/span> momentum<\/span> vector<\/span> a<\/span> Cylindrical<\/span> Drift<\/span> CHamber<\/span> (CDCH)<\/span> was<\/span> built, <\/span>featuring angular and momentum resolutions at 6.5 mrad and 100 keV\/c level.<\/span> Despite this kind of <\/span>gas detectors was used since late \u201960s, the MEG II drift chamber presents a series of unprecedented <\/span>peculiarities.<\/span> CDCH is a 2-meter long, 60 cm in diameter, low-mass, single volume detector with <\/span>high<\/span> granularity:<\/span> 9<\/span> layers<\/span> of<\/span> 192<\/span> drift<\/span> cells,<\/span> few<\/span> mm<\/span> wide,<\/span> defined<\/span> by<\/span> 12000<\/span> wires<\/span> in<\/span> a<\/span> stereo <\/span>configuration<\/span> for<\/span> longitudinal<\/span> hit<\/span> localization.<\/span> The<\/span> single<\/span> drift<\/span> cell<\/span> is<\/span> quasi-square<\/span> with<\/span> a<\/span> 20<\/span> \u03bc<\/span>m <\/span>Gold-plated<\/span> Tungsten<\/span> sense<\/span> wire<\/span> surrounded<\/span> by<\/span> 40\/50<\/span> \u03bc<\/span>m<\/span> Silver-plated<\/span> Aluminum<\/span> field<\/span> wires.<\/span>
Given<\/span> the<\/span> high<\/span> wire<\/span> density<\/span> (12<\/span> wires\/cm<\/span>2<\/span>),<\/span> CDCH<\/span> is<\/span> the<\/span> first<\/span> drift<\/span> chamber<\/span> ever<\/span> designed<\/span> and <\/span>built<\/span> in<\/span> a<\/span> modular<\/span> way.<\/span> The<\/span> filling<\/span> gas<\/span> mixture<\/span> is<\/span> Helium:Isobutane<\/span> 90:10.<\/span> The<\/span> total<\/span> radiation <\/span>length<\/span> is<\/span> 1<\/span>.<\/span>5<\/span> \u00d7<\/span> 10<\/span>\u2212<\/span>3<\/span> X<\/span>0<\/span>,<\/span> thus<\/span> minimizing<\/span> the<\/span> Multiple<\/span> Coulomb<\/span> Scattering<\/span> and<\/span> allowing<\/span> for<\/span> a <\/span>single-hit<\/span> resolution<\/span> <<\/span> 120<\/span> \u03bc<\/span>m.<\/span> After the<\/span> assembly<\/span> phase<\/span> at INFN<\/span> Pisa,<\/span> CDCH was<\/span> transported<\/span> to PSI and it has been integrated into the MEG II experimental apparatus since 2018.<\/span> Aluminum<\/span>
wire breaking problems arose during the assembly and commissioning.<\/span> Deep analyses showed that <\/span>the<\/span> origin<\/span> of<\/span> the<\/span> breaking<\/span> phenomenon<\/span> is<\/span> the<\/span> chemical<\/span> corrosion<\/span> of<\/span> the<\/span> Al<\/span> core<\/span> in<\/span> presence<\/span> of<\/span> water<\/span> condensation<\/span> on<\/span> wires<\/span> from<\/span> ambient<\/span> humidity.<\/span> Keeping<\/span> the<\/span> wires<\/span> volume<\/span> in<\/span> an<\/span> absolutely <\/span>dry<\/span> atmosphere<\/span> proved<\/span> to<\/span> be<\/span> effective<\/span> to<\/span> stop<\/span> the<\/span> development<\/span> of<\/span> corrosion.<\/span> Anomalous<\/span> high <\/span>currents (up to 300<\/span> \u03bc<\/span>A) were observed in some sectors during the conditioning period.<\/span> These were <\/span>cured through a gas mixture optimization with the addition of up to 2% Oxygen, which was then <\/span>gradually reduced to a lower content.<\/span> The commissioning phase lasted for the past three years with <\/span>continuous improvements both on the hardware and software side.<\/span> The final lengthening was set <\/span>and the<\/span> operational stability<\/span> was<\/span> reached<\/span> in 2020.<\/span> The<\/span> complete read<\/span> out electronics<\/span> is<\/span> available <\/span>for the first time in 2021, allowing a full noise and signal check and the tuning of the reconstruction <\/span>algorithms.<\/span> The physics data taking period will take the upcoming three years<\/span><\/p>\n

\n

Abstract e slide disponibili su: https:\/\/agenda.infn.it\/event\/28894\/<\/a><\/p>\n

Il seminario si terr\u00e0 in presenza nella Sala Galilei (stanza 131) per un numero limitato di persone (32) e via Zoom al seguente indirizzo:<\/p>\n

https:\/\/infn-it.zoom.us\/j\/84261721878?pwd=MDZNaGdBUlcvUUJXa2phSHZVZk5sdz09<\/a>

ID riunione: 842 6172 1878
Passcode: 611379<\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"

AbstractIn the quest for the Lepton Flavour Violation (LFV) the MEG experiment at the Paul Scherrer Institut (PSI) represents the state of the art in the search for the charged LFV \u03bc+ \u2192e+\u03b3 decay.MEG set the most stringent upper limit on the BR(\u03bc+ \u2192 e+\u03b3) \u2264 4.2 \u00d7 10\u221213 (90% C.L.), imposing one of the […]<\/p>\n","protected":false},"author":26,"featured_media":9605,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_links_to":"","_links_to_target":""},"categories":[8],"tags":[],"publishpress_future_action":{"enabled":false,"date":"2026-05-14 01:03:33","action":"change-status","newStatus":"draft","terms":[],"taxonomy":"category"},"_links":{"self":[{"href":"https:\/\/www.pi.infn.it\/index.php?rest_route=\/wp\/v2\/posts\/9603"}],"collection":[{"href":"https:\/\/www.pi.infn.it\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.pi.infn.it\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.pi.infn.it\/index.php?rest_route=\/wp\/v2\/users\/26"}],"replies":[{"embeddable":true,"href":"https:\/\/www.pi.infn.it\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=9603"}],"version-history":[{"count":4,"href":"https:\/\/www.pi.infn.it\/index.php?rest_route=\/wp\/v2\/posts\/9603\/revisions"}],"predecessor-version":[{"id":9623,"href":"https:\/\/www.pi.infn.it\/index.php?rest_route=\/wp\/v2\/posts\/9603\/revisions\/9623"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.pi.infn.it\/index.php?rest_route=\/wp\/v2\/media\/9605"}],"wp:attachment":[{"href":"https:\/\/www.pi.infn.it\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=9603"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.pi.infn.it\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=9603"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.pi.infn.it\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=9603"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}